WFDASH-WEBAPP/src/lib/server/delivery-notes-service.ts

/**
 * Server-side delivery-notes service.
 *
 * Admin-scoped writes for the three actions that drive the
 * delivery_note → quote → invoice lifecycle:
 *
 *   1. createQuoteFromDeliveryNote
 *        Draft  →  Sent
 *      Reads the delivery note + its order_items, creates a new
 *      Quote with status="delivery_note", copies each order_item
 *      into a new quote_item, links the new quote back to the
 *      delivery note, and flips the delivery note's status to
 *      "sent" (we now have a quote ready to send with the DN).
 *
 *   2. setDeliveryNoteCustomerPo
 *        Sent  →  po_received
 *      Stamps the customer's PO on the delivery note and flips
 *      the status. The operator types the PO after the customer
 *      sends it back with their PO number.
 *
 *   3. markDeliveryNoteInvoiced
 *        po_received  →  invoiced
 *      Flips the order_items from item_status="delivery_note" to
 *      item_status="ready_invoice" so they show up in the
 *      Invoicing page ready to invoice. Updates the delivery
 *      note's status to "invoiced". The actual invoice creation
 *      happens through the normal Invoicing flow.
 *
 * Why a service module instead of inlining in the routes:
 *   - The "create quote + items + flip status" sequence is 3+ PB
 *     writes; the route stays small + the logic is testable.
 *   - Other callers (cron, future bulk tools) can reuse these.
 */

import { getAdminPocketBase } from "./pocketbase-admin";
import { generateQuoteNumberServer } from "./quotes-service";
import { renderDeliveryNotePdf } from "@/lib/pdf/render";
import { resolveDeliveryNoteLineQty } from "@/lib/pdf/delivery-note-document";
import {
  fetchLetterhead,
  loadLetterheadLogoDataUri,
} from "@/lib/letterhead";
import type {
  DeliveryNote,
  DeliveryNoteStatus,
  OrderItem,
  Quote,
  QuoteItem,
} from "@/lib/types";

const DELIVERY_NOTES = "delivery_notes";
const ORDER_ITEMS = "order_items";
const QUOTES = "quotes";
const QUOTE_ITEMS = "quote_items";
const QUOTE_ATTACHMENTS = "quote_attachments";
const CUSTOMERS = "customers";
const COMPANIES = "companies";
const SUPPLIERS = "suppliers";
const ORDERS = "orders";

/**
 * The letterhead every delivery-note PDF renders under.
 *
 * Hardcoded by business decision: the Westcott group owns
 * multiple subsidiaries (CNL, ISHERWOOD, Test Engineering,
 * etc.) but the printed DN is a Westcott-Group-branded
 * document regardless of which subsidiary the customer
 * belongs to. The actual letterhead content (logo, address,
 * banking, accent colour) lives in `letterhead_settings` —
 * this constant is the *lookup* into that table, not the
 * content itself.
 *
 * `fetchLetterhead` runs a case-insensitive substring match
 * on `letterhead_settings.display_name` against this value,
 * so the matching row in PB must have a display_name that
 * contains this string (verbatim or as a substring). The row
 * the user added in PB (id `5wezvypn6fy47p9`) has
 * display_name `WESTSCOTT GROUP OF COMPANIES` which matches
 * cleanly.
 *
 * If you want to swap the brand (e.g. rebrand to a new parent
 * company), update the PB row and change this string in
 * lockstep. The PDF will pick up the new content from PB
 * automatically without any code change beyond the constant.
 */
const DELIVERY_NOTE_LETTERHEAD_CODE = "WESTSCOTT GROUP OF COMPANIES";

/**
 * Lifecycle transitions for the delivery_notes.status field. The
 * service methods enforce these — they reject any transition that
 * isn't on the list, so the route layer can pass the requested
 * status and trust that the service won't silently corrupt state.
 */
const ALLOWED_TRANSITIONS: Record<DeliveryNoteStatus, DeliveryNoteStatus[]> = {
  draft: ["sent", "cancelled"],
  sent: ["po_received", "cancelled", "draft"],
  po_received: ["invoiced", "cancelled"],
  invoiced: ["completed", "cancelled"],
  completed: [],
  cancelled: ["draft"],
};

/** Throws a typed error the route can surface verbatim to the user. */
function rejectTransition(
  from: DeliveryNoteStatus,
  to: DeliveryNoteStatus,
): never {
  const allowed = ALLOWED_TRANSITIONS[from] ?? [];
  const list = allowed.length > 0 ? allowed.join(", ") : "none";
  throw new Error(
    `Cannot transition delivery note from "${from}" to "${to}" (allowed: ${list}).`,
  );
}

function assertTransition(
  from: DeliveryNoteStatus,
  to: DeliveryNoteStatus,
): void {
  const allowed = ALLOWED_TRANSITIONS[from] ?? [];
  if (!allowed.includes(to)) rejectTransition(from, to);
}

/**
 * The result of a Create-Quote action. The route hands this back
 * to the client so the UI can navigate to the new quote.
 */
export interface CreateQuoteFromDeliveryNoteResult {
  id: string;
  quote_number: string;
}

/**
 * Create a Quote that prices the items in this delivery note.
 *
 * Reads:
 *   - delivery_notes[id] — the header (customer, company)
 *   - order_items where delivery_note_number = dn.delivery_note_number
 *
 * Writes:
 *   - quotes.create  (status="delivery_note", delivery_note=dn.id)
 *   - quote_items.create  (one per order_item, description / qty /
 *     supplier / cost_price / selling_price copied)
 *   - delivery_notes.update  (status: "draft" → "sent")
 *
 * Pricing rule (per the user's brief):
 *   - If order_item.selling_price is set, copy it to the quote_item.
 *     The operator confirms on the quote detail page.
 *   - If order_item.selling_price is null, copy cost_price so the
 *     operator can see what they paid and decide a margin. The
 *     quote_item.pricing_source is set to "manual" so the UI shows
 *     a "needs pricing" badge.
 *
 * Idempotency: a delivery note should only have ONE quote linked
 * (status="delivery_note" and delivery_note=dn.id). If one already
 * exists, the route surfaces a 409 — the operator can re-open the
 * existing quote instead of creating a duplicate.
 */
export async function createQuoteFromDeliveryNote(
  deliveryNoteId: string,
): Promise<CreateQuoteFromDeliveryNoteResult> {
  const pb = await getAdminPocketBase();

  const dn = await pb.collection(DELIVERY_NOTES).getOne<DeliveryNote>(deliveryNoteId, {
    expand: "customer,company,order",
  });

  if (dn.status !== "draft") {
    throw new Error(
      `Delivery note must be in "draft" status to create a quote (current: "${dn.status}").`,
    );
  }

  // Reject if a quote already exists for this delivery note. The
  // status filter is a belt-and-braces check — the operator could
  // in theory have transitioned the previous quote to "sent" or
  // beyond, in which case the relationship is no longer "active".
  // We look for the *primary* quote (status="delivery_note" with
  // delivery_note=dn.id) — a quote that has been sent and is now
  // in flight doesn't count.
  const existing = await pb.collection(QUOTES).getList<Quote>(1, 1, {
    filter: `delivery_note = "${deliveryNoteId}" && status = "delivery_note"`,
  });
  if (existing.items.length > 0) {
    const q = existing.items[0];
    throw new Error(
      `A delivery-note quote already exists for this delivery note (${q.quote_number}). Open it instead of creating a duplicate.`,
    );
  }

  // Fetch the order_items that this delivery note groups together.
  // No expand here — we only need the fields listed below.
  const items = await pb.collection(ORDER_ITEMS).getFullList<OrderItem>({
    filter: `delivery_note_number = "${dn.delivery_note_number}"`,
  });

  if (items.length === 0) {
    throw new Error(
      `No order items found with delivery_note_number = "${dn.delivery_note_number}". Cannot create an empty quote.`,
    );
  }

  const quoteNumber = await generateQuoteNumberServer();
  const now = new Date().toISOString();

  // Create the quote header.
  const quoteCreate: Record<string, unknown> = {
    quote_number: quoteNumber,
    status: "delivery_note",
    delivery_note: dn.id,
    // customer/company are required on the Quote collection schema.
    // The delivery note has both, so we just copy through.
    customer: dn.customer ?? "",
    company: dn.company ?? "",
    quote_date: now,
    validity_days: 30,
    // Stamp the delivery note number on the quote as the RFQ
    // reference. The DN IS the request for pricing here — it's
    // the document that the office is responding to with the
    // quote. Operators see the DN number on the quote's RFQ line
    // and know instantly "this came from a delivery note, not
    // from a customer email".
    rfq_number: dn.delivery_note_number,
    description:
      // `??` only falls back on null/undefined, so an empty
      // `dn.notes` would pass through as an empty description.
      // `||` also catches empty strings, which is what we want —
      // an empty notes value should trigger the default.
      dn.notes || `Delivery note ${dn.delivery_note_number} pricing`,
  };
  const quote = await pb.collection(QUOTES).create<Quote>(quoteCreate);

  // Create one quote_item per order_item. We deliberately DON'T
  // touch order_item status here — the items stay at
  // item_status="delivery_note" until the operator clicks
  // "Mark Invoiced". The quote and the order_items are two views
  // of the same physical goods; flipping order_items here would
  // break the Invoiced-tab count before any invoice exists.
  for (const it of items) {
    const itemCreate: Record<string, unknown> = {
      quote: quote.id,
      quote_number: quoteNumber,
      description: it.description ?? "",
      quantity: Number(it.quantity ?? 1),
      // Copy the supplier so the operator can see the original
      // supplier on the quote detail page even if the order
      // item's supplier is later reassigned.
      supplier: it.supplier ?? null,
      // Costs always carry over — the operator needs to see what
      // the office paid to set a margin.
      cost_price: Number(it.cost_price ?? 0),
      // Selling price is best-effort: copy if set, otherwise 0
      // and pricing_source="manual" so the UI flags it.
      selling_price: Number(it.selling_price ?? 0),
      notes: it.notes ?? "",
      sku: it.sku ?? "",
      pricing_source: it.selling_price ? it.pricing_source ?? "" : "manual",
    };
    await pb.collection(QUOTE_ITEMS).create<QuoteItem>(itemCreate);
  }

  // v3-C: also attach the delivery note to the new quote so
  // the email-send modal can include it. The email-send
  // modal already lets the operator check which
  // quote_attachments to include in the outbound email, so
  // by uploading the DN as kind="delivery_note" the operator
  // can include "the delivery note" alongside "the quote PDF"
  // in one click.
  //
  // v3-E.2 — signed-copy preference: if the operator has
  // uploaded a signed copy to `delivery_notes.signed_copy`,
  // we attach THAT (it's what the customer actually signed).
  // Otherwise we re-render the unsigned PDF from the order
  // items. Both versions are useful; signed is the right
  // default when present.
  //
  // Best-effort: a failure here doesn't roll back the quote.
  // The quote + items are the source of truth; the attachment
  // is a convenience for the email-send step. If it fails, the
  // operator can re-run the attach from the detail page.
  try {
    await attachDeliveryNoteToQuote(
      quote.id,
      quote.quote_number,
      dn,
      items,
    );
  } catch (attachErr) {
    // Surface to the operator via console; the route layer
    // doesn't need to fail the whole create-quote flow over a
    // PDF render hiccup. The detail page can detect the
    // missing attachment and offer to re-run.
    console.error(
      "[delivery-notes-service] delivery-note attach failed:",
      attachErr,
    );
  }

  // Flip the delivery note status: draft → sent (we now have a
  // quote ready to send with the DN). Use the assert helper so a
  // future schema-driven status rename can't silently no-op.
  assertTransition("draft", "sent");
  await pb.collection(DELIVERY_NOTES).update(dn.id, { status: "sent" });

  return { id: quote.id, quote_number: quote.quote_number };
}

/**
 * Attach the delivery note PDF (or signed copy if uploaded) to
 * the new quote as a `quote_attachments` row of
 * kind="delivery_note".
 *
 * The signed-copy preference:
 *   - If `dn.signed_copy` is set (operator uploaded a signed
 *     PDF / scan), we attach THAT. It's what the customer
 *     actually signed — the right thing to email back to them.
 *   - Otherwise we re-render the unsigned PDF from the order
 *     items (same render path the legacy delivery-note route
 *     uses, just inlined here so we don't need a network hop).
 *
 * What this gives the operator:
 *   - The email-send modal already shows quote_attachments
 *     with checkboxes. With this attachment on the quote, the
 *     operator can include both "the delivery note" and
 *     "the quote PDF" in the customer email in one send.
 *   - The quote detail page can also show the DN as a
 *     downloadable file alongside the quote's own PDF.
 *
 * Why this is one function: both code paths share the same
 * downstream "upload to quote_attachments as kind=delivery_note"
 * step. Splitting them would duplicate the upload + DB write
 * for no real benefit — the only thing that differs is where
 * the bytes come from (signed copy vs re-rendered).
 */
async function attachDeliveryNoteToQuote(
  quoteId: string,
  quoteNumber: string,
  dn: DeliveryNote,
  items: OrderItem[],
): Promise<void> {
  const pb = await getAdminPocketBase();

  // Path 1: signed copy already on the record. Download the
  // bytes from PB's file endpoint and re-upload to the quote
  // attachment (PB file fields are record-scoped, can't be
  // shared by reference).
  const signedCopyName = Array.isArray(dn.signed_copy)
    ? dn.signed_copy[0]
    : null;

  let filename: string;
  let blob: Blob;
  let contentType: string;
  let sizeBytes: number;

  if (signedCopyName) {
    // Fetch the bytes from PB. The URL is the public file
    // endpoint; we use the admin client to bypass the
    // per-user auth header.
    const fileUrl = pb.files.getURL(dn, signedCopyName);
    const res = await fetch(fileUrl);
    if (!res.ok) {
      throw new Error(
        `Failed to fetch signed copy from PB (HTTP ${res.status})`,
      );
    }
    const arrayBuffer = await res.arrayBuffer();
    filename = signedCopyName;
    contentType = res.headers.get("content-type") || "application/pdf";
    sizeBytes = arrayBuffer.byteLength;
    blob = new Blob([new Uint8Array(arrayBuffer)], { type: contentType });
  } else {
    // Path 2: re-render the unsigned PDF from the order items.
    const companyName = dn.expand?.company?.company ?? "";
    // All delivery-note PDFs render under the Westcott
    // Group letterhead, regardless of which subsidiary the
    // customer belongs to — see DELIVERY_NOTE_LETTERHEAD_CODE.
    // The `companyName` above still goes into the PDF meta
    // block so the printed document tells the driver which
    // subsidiary the delivery is for.
    const letterheadCode = DELIVERY_NOTE_LETTERHEAD_CODE;
    const letterhead = await fetchLetterhead(letterheadCode);
    const logoDataUri = await loadLetterheadLogoDataUri(letterheadCode);
    const customerName = dn.expand?.customer?.customer ?? "";
    const orderNumber = dn.expand?.order?.order_number ?? "";

    const pdfBuffer = await renderDeliveryNotePdf({
      header: {
        deliveryNoteNumber: dn.delivery_note_number,
        dateIso:
          dn.delivery_date ||
          new Date(dn.created || Date.now()).toISOString().slice(0, 10),
        orderNumber,
        companyName,
        customerName,
      },
      lines: items.map((it) => ({
        id: it.id,
        description: (it.description ?? "").trim() || "(no description)",
        qty: Number(it.quantity ?? it.order_qty ?? 1) || 1,
      })),
      letterhead,
      logoDataUri,
    });
    filename = `${dn.delivery_note_number}.pdf`;
    contentType = "application/pdf";
    sizeBytes = pdfBuffer.byteLength;
    blob = new Blob([new Uint8Array(pdfBuffer)], { type: contentType });
  }

  const form = new FormData();
  form.append("file", blob, filename);
  form.append("quote", quoteId);
  form.append("filename", filename);
  form.append("content_type", contentType);
  form.append("size_bytes", String(sizeBytes));
  form.append("kind", "delivery_note");
  // Mark as outbound: the email-send UI distinguishes
  // operator-uploaded attachments from inbound RFQ attachments.
  form.append("direction", "outbound");

  await pb.collection(QUOTE_ATTACHMENTS).create(form);
  // `quoteNumber` is useful for log context if this ever
  // needs to surface an error; reference it so the no-
  // unused-vars lint is happy.
  void quoteNumber;
}

/**
 * Stamp the customer's PO on the delivery note and flip status
 * from "sent" to "po_received". The operator triggers this after
 * the customer sends their PO back with the quote.
 *
 * Idempotency: setting the same PO twice is a no-op (PB returns
 * the same record). Setting a *different* PO on an already-
 * po_received record is allowed — customers sometimes correct
 * their PO mid-flight.
 */
export async function setDeliveryNoteCustomerPo(
  deliveryNoteId: string,
  customerPo: string,
): Promise<DeliveryNote> {
  const pb = await getAdminPocketBase();

  const trimmed = (customerPo ?? "").trim();
  if (!trimmed) {
    throw new Error("Customer PO cannot be empty.");
  }

  const dn = await pb.collection(DELIVERY_NOTES).getOne<DeliveryNote>(deliveryNoteId);

  // Allow the operator to set the PO again on a po_received /
  // invoiced / completed record (customer may have sent a
  // correction). Only "sent" → "po_received" is an automatic
  // status flip; later transitions are explicit operator actions.
  if (dn.status === "sent") {
    assertTransition("sent", "po_received");
    return pb.collection(DELIVERY_NOTES).update<DeliveryNote>(dn.id, {
      customer_po: trimmed,
      status: "po_received",
    });
  }
  if (dn.status === "po_received" || dn.status === "invoiced" || dn.status === "completed") {
    return pb.collection(DELIVERY_NOTES).update<DeliveryNote>(dn.id, {
      customer_po: trimmed,
    });
  }
  // draft → would skip the "sent" step (we never sent a quote)
  // cancelled → pointless
  throw new Error(
    `Cannot set customer PO on a delivery note in status "${dn.status}". The note must be sent first.`,
  );
}

/**
 * Mark the delivery note as "invoiced". This is the operator's
 * signal that the invoice has been created (through the normal
 * Invoicing page). It does NOT create the invoice itself — that
 * happens through the existing Invoicing flow against the items
 * with item_status="ready_invoice".
 *
 * What it does:
 *   1. Flip every order_item with this delivery_note_number from
 *      item_status="delivery_note" → item_status="ready_invoice".
 *      After this, the items appear in the Invoicing page ready
 *      to be invoiced.
 *   2. Flip delivery_notes.status from "po_received" → "invoiced".
 *
 * The "completed" transition (invoiced → completed) is left to
 * the operator to do manually, since "completed" depends on
 * whether the invoice has been *paid* — that's an external
 * signal, not something the office tracks inside WFDASH.
 */
export async function markDeliveryNoteInvoiced(
  deliveryNoteId: string,
): Promise<DeliveryNote> {
  const pb = await getAdminPocketBase();

  const dn = await pb.collection(DELIVERY_NOTES).getOne<DeliveryNote>(deliveryNoteId);

  if (dn.status !== "po_received") {
    throw new Error(
      `Delivery note must be in "po_received" status to mark invoiced (current: "${dn.status}").`,
    );
  }
  // Belt-and-braces: PB should reject "invoiced" if it isn't in
  // the enum, but the explicit assert surfaces a clearer error if
  // a future migration drops the value.
  assertTransition("po_received", "invoiced");

  // Flip the order_items to "ready_invoice" so they show up in
  // the Invoicing page. Done as a parallel fan-out for the
  // common case of a small batch. For very large batches the
  // existing Invoicing flow batches PATCHes the same way.
  const items = await pb.collection(ORDER_ITEMS).getFullList<OrderItem>({
    filter: `delivery_note_number = "${dn.delivery_note_number}"`,
  });
  if (items.length === 0) {
    throw new Error(
      `No order items found with delivery_note_number = "${dn.delivery_note_number}". Cannot mark as invoiced.`,
    );
  }
  await Promise.all(
    items.map((it) =>
      pb.collection(ORDER_ITEMS).update(it.id, {
        item_status: "ready_invoice",
      }),
    ),
  );

  return pb.collection(DELIVERY_NOTES).update<DeliveryNote>(dn.id, {
    status: "invoiced",
  });
}

/**
 * Mark the delivery note as "completed". Operator signal that
 * the work has wrapped up and the items are no longer in flight.
 * Allowed from "invoiced" only — once cancelled you have to
 * revert to draft first.
 *
 * Side effects:
 *   - delivery_notes.status flips "invoiced" → "completed".
 */
export async function markDeliveryNoteComplete(deliveryNoteId: string): Promise<DeliveryNote> {
  const pb = await getAdminPocketBase();

  const dn = await pb.collection(DELIVERY_NOTES).getOne<DeliveryNote>(deliveryNoteId);
  if (dn.status !== "invoiced") {
    throw new Error(
      `Delivery note must be in "invoiced" status to mark complete (current: "${dn.status}").`,
    );
  }
  assertTransition("invoiced", "completed");

  return pb.collection(DELIVERY_NOTES).update<DeliveryNote>(dn.id, {
    status: "completed",
  });
}

export interface MarkDeliveryNoteCompletedByInvoiceInput {
  /**
   * The QuickBooks invoice number / id returned by the n8n
   * `wfdash-quickbooks-invoice-creator` webhook. Stamped on the
   * DN's `notes` field so an auditor can find the DN from the
   * invoice (and vice-versa) later.
   */
  invoiceNumber: string;
  /**
   * Operator display name (the one who clicked "Invoice via
   * QuickBooks"). Stamped alongside the invoice number for
   * accountability.
   */
  sentByName?: string | null;
  /**
   * Optional ISO timestamp. Defaults to `new Date().toISOString()`
   * server-side. Useful in tests for deterministic assertions.
   */
  sentAtIso?: string;
}

/**
 * Auto-close a delivery note after a successful QuickBooks invoice
 * creation. Used by the `/api/v1/delivery-notes/[id]/invoice`
 * endpoint — the page-level "Invoice via QuickBooks" button calls
 * this after the n8n webhook returns 2xx, so the operator doesn't
 * have to click "Mark complete" as a second step.
 *
 * Same eligibility as `markDeliveryNoteComplete`:
 *   - DN must currently be in "invoiced" status.
 *   - Allowed transition: invoiced → completed.
 *
 * Audit trail: a single banner is appended to `delivery_notes.notes`
 * (with a leading newline separator if notes was non-empty) of the
 * form:
 *
 *   Auto-closed via QuickBooks invoice <num> by <name> on <iso>
 *
 * The banner mirrors the convention used by `cancelDeliveryNote`
 * (single-line, leading newline separator, no leading/trailing
 * whitespace). Operators can grep notes for "QuickBooks" to find
 * every DN that was auto-closed by this flow.
 *
 * Why we don't reuse `markDeliveryNoteComplete` then PATCH notes
 * separately: a half-applied state (status=completed, no banner)
 * would still pass existing tests and look correct in the UI but
 * lose the audit trail. Doing both fields in a single update keeps
 * the audit trail atomic with the status flip.
 */
export async function markDeliveryNoteCompletedByInvoice(
  deliveryNoteId: string,
  input: MarkDeliveryNoteCompletedByInvoiceInput,
): Promise<DeliveryNote> {
  const pb = await getAdminPocketBase();

  const dn = await pb.collection(DELIVERY_NOTES).getOne<DeliveryNote>(deliveryNoteId);
  // Operator signal: invoice and close from ANY non-terminal stage.
  // The "Invoice via QuickBooks" button on the detail page is shown
  // on every active DN (draft / sent / po_received / invoiced). The
  // only statuses we refuse are the terminal ones — `completed`
  // (already done) and `cancelled` (don't resurrect a cancelled DN).
  if (dn.status === "completed" || dn.status === "cancelled") {
    throw new Error(
      `Delivery note in "${dn.status}" status cannot be auto-closed via invoice.`,
    );
  }
  // Bypass the standard `ALLOWED_TRANSITIONS` graph (which only
  // allows `invoiced → completed`). The QB flow is the operator's
  // explicit "fast-forward" — they picked the customer, they
  // confirmed the order number, they hit Send. The webhook's
  // writeback is what flips the items to `invoiced`; the DN can
  // skip straight to `completed` because the audit banner on
  // `notes` records the invoice number that was created.
  // We intentionally do NOT touch `ALLOWED_TRANSITIONS` itself —
  // the manual "Mark complete" button still uses the standard
  // transition. The fast-forward only applies to this entrypoint.

  const invoiceNumber = input.invoiceNumber.trim();
  if (!invoiceNumber) {
    throw new Error("invoiceNumber is required to auto-close the delivery note.");
  }

  const sentByName = (input.sentByName ?? "").trim();
  const sentAt = input.sentAtIso ?? new Date().toISOString();
  const banner = sentByName
    ? `Auto-closed via QuickBooks invoice ${invoiceNumber} by ${sentByName} on ${sentAt}`
    : `Auto-closed via QuickBooks invoice ${invoiceNumber} on ${sentAt}`;

  const existingNotes = (dn.notes ?? "").trimEnd();
  const mergedNotes = existingNotes
    ? `${existingNotes}\n${banner}`
    : banner;

  return pb.collection(DELIVERY_NOTES).update<DeliveryNote>(dn.id, {
    status: "completed",
    notes: mergedNotes,
  });
}

export interface CancelDeliveryNoteInput {
  setById?: string | null;
  setByName?: string | null;
  note?: string | null;
}

/**
 * Cancel a delivery note. Items are flipped to "cancelled"
 * (no longer "delivery_note") so they fall off the Invoicing
 * "ready for delivery note" list, with a note stamping who
 * cancelled it, when, and why. The DN header itself also goes
 * to "cancelled" — both ends match.
 *
 * Why "cancelled" on the order_items, not "completed": the
 * `order_items.item_status` select field on PB does not include
 * "completed" (only the `delivery_notes.status` field does — the
 * mark-invoiced flow on the DN uses it as the terminal state).
 * We mirror the DN's own "cancelled" status on the items so the
 * order_items enum is satisfied without needing a PB admin
 * schema change, and so the audit trail reads consistently
 * (cancelled DN → cancelled items).
 *
 * Allowed from draft / sent / po_received / invoiced. From
 * "completed" you must not cancel — terminal. From "cancelled"
 * it's a no-op.
 */
export async function cancelDeliveryNote(
  deliveryNoteId: string,
  input: CancelDeliveryNoteInput = {},
): Promise<DeliveryNote> {
  const pb = await getAdminPocketBase();

  const dn = await pb.collection(DELIVERY_NOTES).getOne<DeliveryNote>(deliveryNoteId);
  const from = dn.status;
  if (from === "cancelled") {
    return dn;
  }
  if (from === "completed") {
    throw new Error(
      `Cannot cancel a delivery note in "completed" status.`,
    );
  }
  assertTransition(from, "cancelled");

  const trimmedNote = (input.note ?? "").trim();
  const setById = input.setById ?? "";
  const setByName = input.setByName ?? "";
  const setAt = new Date().toISOString();
  const banner = `Delivery note CANCELLED by ${setByName || setById || "unknown"} on ${setAt}${trimmedNote ? ` — ${trimmedNote}` : ""}`;

  const items = await pb.collection(ORDER_ITEMS).getFullList<OrderItem>({
    filter: `delivery_note_number = "${dn.delivery_note_number}"`,
  });
  await Promise.all(
    items.map((it) =>
      pb.collection(ORDER_ITEMS).update(it.id, {
        item_status: "cancelled",
        notes: it.notes ? `${it.notes}\n${banner}` : banner,
      }),
    ),
  );

  return pb.collection(DELIVERY_NOTES).update<DeliveryNote>(dn.id, {
    status: "cancelled",
  });
}

// ─────────────────────────────────────────────────────────────────
// Ad-hoc (Path B) creation
// ─────────────────────────────────────────────────────────────────

/**
 * Generate the next delivery note number for `now`. Format
 * `DN{YY}{MM}{DD}{NN}` with a 2-digit per-day sequence. Counts the
 * most-recent matching record (queries `order_items` because
 * that's where the DN number is stamped on every line — querying
 * the `delivery_notes` header would miss records where the header
 * create failed and only the order_items stamps landed) and
 * increments; concurrent requests may collide — accepted as a
 * known limitation for v1.
 *
 * The mirror of this function lives in
 * `src/app/api/invoicing/delivery-note/route.ts` (the legacy
 * "mark as delivery note" route). Any change to the format here
 * must be mirrored there too, or the two code paths will produce
 * different numbers for the same day.
 */
export async function generateDeliveryNoteNumberServer(
  now: Date = new Date(),
): Promise<string> {
  const pb = await getAdminPocketBase();
  const yy = String(now.getFullYear()).slice(-2);
  const mm = String(now.getMonth() + 1).padStart(2, "0");
  const dd = String(now.getDate()).padStart(2, "0");
  const prefix = `DN${yy}${mm}${dd}`;
  try {
    const existing = await pb
      .collection(ORDER_ITEMS)
      .getList<OrderItem>(1, 1, {
        filter: `delivery_note_number ~ "${prefix}"`,
        sort: "-delivery_note_number",
      });
    let seq = 1;
    if (existing.items.length > 0) {
      const last = existing.items[0].delivery_note_number ?? "";
      const lastSeq = parseInt(last.slice(prefix.length), 10);
      if (Number.isFinite(lastSeq) && lastSeq > 0) {
        seq = lastSeq + 1;
      }
    }
    return `${prefix}${String(seq).padStart(2, "0")}`;
  } catch {
    // If the `delivery_note_number` field doesn't exist on
    // order_items yet, fall back to a random suffix so the
    // operation still completes. The operator can rename in PB
    // admin if needed.
    const fallback = Math.floor(Math.random() * 90 + 10);
    return `${prefix}${fallback}`;
  }
}

/**
 * The shape of one line in the ad-hoc "create delivery note"
 * form. The customer + qty are required; supplier + prices are
 * optional (operator fills them in on the quote detail page if
 * they're known at counter time, or leaves them for the
 * catalogue-match step).
 */
export interface AdHocDeliveryNoteItemInput {
  description: string;
  quantity: number;
  supplier?: string | null;
  cost_price?: number | null;
  selling_price?: number | null;
  sku?: string | null;
  notes?: string | null;
}

/**
 * The full ad-hoc creation payload. The customer is required
 * (we need somewhere to ship the items to); company is optional
 * (we can derive from customer, or leave blank for unknown
 * billing); the items list must have at least one entry.
 */
export interface AdHocDeliveryNoteInput {
  customer: string;
  company?: string | null;
  notes?: string | null;
  items: AdHocDeliveryNoteItemInput[];
  /**
   * PB user id of the operator who triggered the create. Used
   * to stamp `created_by` on the delivery_notes header so the
   * detail page can show "Created by X" in the audit panel.
   */
  createdBy?: string | null;
}

export interface AdHocDeliveryNoteResult {
  id: string;
  delivery_note_number: string;
}

/**
 * Create a delivery note from scratch — Path B (counter pickup).
 * No supplier order, no previous quote, no prior history. The
 * operator types in what the customer took off the shelf and
 * the system creates:
 *
 *   - one `delivery_notes` header (status="draft")
 *   - one `order_items` row per input item, stamped with the
 *     new DN number and `order: null` (no parent order — ad-hoc)
 *   - the DN PDF rendered + uploaded to every item's
 *     `order_item_attachements` field, so the operator can hit
 *     "Print" / "Download" immediately and `/api/invoicing/delivery-note-pdf`
 *     finds it. This mirrors what Path A (`/api/invoicing/delivery-note`)
 *     does after the status flip.
 *
 * The items are stamped with `item_status: "delivery_note"`
 * immediately (the delivery-note lifecycle for ad-hoc items
 * starts here; the operator doesn't need a separate "mark as
 * delivery note" step like Path A does).
 *
 * Errors:
 *   - missing customer
 *   - empty items list
 *   - item with no description
 *   - item with quantity <= 0
 */
export async function createAdHocDeliveryNote(
  input: AdHocDeliveryNoteInput,
): Promise<AdHocDeliveryNoteResult> {
  const pb = await getAdminPocketBase();

  // ── 1. Validate input ────────────────────────────────────────
  if (!input.customer) {
    throw new Error("Customer is required for an ad-hoc delivery note.");
  }
  if (!Array.isArray(input.items) || input.items.length === 0) {
    throw new Error(
      "At least one item is required for an ad-hoc delivery note.",
    );
  }
  for (let i = 0; i < input.items.length; i++) {
    const it = input.items[i];
    if (!it.description || !it.description.trim()) {
      throw new Error(`Item #${i + 1} is missing a description.`);
    }
    const qty = Number(it.quantity);
    if (!Number.isFinite(qty) || qty <= 0) {
      throw new Error(`Item #${i + 1} ("${it.description}") has invalid quantity: ${it.quantity}.`);
    }
  }

  // ── 2. Generate the DN number ─────────────────────────────────
  const deliveryNoteNumber = await generateDeliveryNoteNumberServer();

  // ── 3. Create the delivery_notes header ──────────────────────
  // The route layer is responsible for knowing the auth'd
  // user; the service just trusts `createdBy` (which is null
  // in tests / cron scenarios).
  const header = await pb.collection(DELIVERY_NOTES).create<DeliveryNote>({
    delivery_note_number: deliveryNoteNumber,
    customer: input.customer,
    company: input.company ?? null,
    order: null, // ad-hoc — no parent order
    status: "draft",
    notes: input.notes ?? "",
    created_by: input.createdBy ?? null,
  });

  // ── 4. Create the order_items rows ────────────────────────────
  // Each item is ad-hoc (no parent order) and stamped with the
  // DN number + the delivery-note status. We do this in parallel
  // since the items are independent writes. The created rows are
  // captured so step 5 can attach the PDF to each one.
  const createdItems = await Promise.all(
    input.items.map((it) =>
      pb.collection(ORDER_ITEMS).create<OrderItem>({
        order: null,
        delivery_note_number: deliveryNoteNumber,
        description: it.description.trim(),
        quantity: Number(it.quantity),
        supplier: it.supplier ?? null,
        cost_price: Number(it.cost_price ?? 0),
        selling_price:
          it.selling_price != null ? Number(it.selling_price) : null,
        sku: it.sku ?? "",
        notes: it.notes ?? "",
        // Ad-hoc items start the DN lifecycle here. The Path A
        // flow does a separate "mark as delivery note" step in
        // Invoicing; for Path B that step is implicit.
        item_status: "delivery_note",
        // The other workflow fields are not relevant for an
        // ad-hoc DN — leave them at PB defaults.
      }),
    ),
  );

  // ── 5. Render + upload the DN PDF ─────────────────────────────
  // Mirrors `/api/invoicing/delivery-note` step 2: render the PDF
  // and attach it to every item's `order_item_attachements` field
  // so the print / download buttons on the detail page can find it.
  // Without this step, the user lands on the detail page, clicks
  // Download, and gets "No saved PDF for this delivery note" because
  // no item has anything in the attachments field.
  //
  // The PDF needs a company name (for the letterhead) and a customer
  // name (for the meta block). For ad-hoc DNs there's no parent
  // order to derive either from, so we resolve them via the
  // relations on the header. Failures here are non-fatal — the
  // header + items are already saved; the operator can hit the
  // print route which falls back to regenerating on the fly.
  try {
    const [customerRow, companyRow] = await Promise.all([
      pb.collection(CUSTOMERS).getOne(input.customer).catch(() => null),
      input.company
        ? pb.collection(COMPANIES).getOne(input.company).catch(() => null)
        : Promise.resolve(null),
    ]);
    const customerName =
      typeof (customerRow as { customer?: unknown } | null)?.customer === "string"
        ? (customerRow as unknown as { customer: string }).customer
        : "";
    const companyName =
      typeof (companyRow as { company?: unknown } | null)?.company === "string"
        ? (companyRow as unknown as { company: string }).company
        : "";

    const letterheadCode = DELIVERY_NOTE_LETTERHEAD_CODE;
    const letterhead = await fetchLetterhead(letterheadCode);
    const logoDataUri = await loadLetterheadLogoDataUri(letterheadCode);

    const pdfBuffer = await renderDeliveryNotePdf({
      header: {
        deliveryNoteNumber,
        dateIso: new Date().toISOString().slice(0, 10),
        orderNumber: "", // ad-hoc — no parent order
        companyName,
        customerName,
      },
      lines: createdItems.map((it) => ({
        id: it.id,
        description: (it.description ?? "").trim() || "(no description)",
        qty: resolveDeliveryNoteLineQty({
          quantity: it.quantity,
          orderQty: it.order_qty,
          qtyCollected: it.qty_collected,
        }),
      })),
      letterhead,
      logoDataUri,
    });

    const filename = `${deliveryNoteNumber}.pdf`;
    const blob = new Blob([new Uint8Array(pdfBuffer)], {
      type: "application/pdf",
    });
    await Promise.all(
      createdItems.map(async (it) => {
        const form = new FormData();
        form.append("order_item_attachements", blob, filename);
        await pb.collection(ORDER_ITEMS).update(it.id, form);
      }),
    );
  } catch (pdfErr) {
    // Non-fatal — surface in the server log so the operator can
    // regenerate the PDF via the print route's fallback (which
    // re-renders from the order_items rows when no saved copy is
    // present), but don't fail the whole create.
    console.error(
      "[createAdHocDeliveryNote] PDF save failed (non-fatal):",
      pdfErr,
    );
  }

  return {
    id: header.id,
    delivery_note_number: deliveryNoteNumber,
  };
}

/**
 * Regenerate (and re-save) the DN PDF for an existing delivery note.
 *
 * Re-renders the PDF from the current `order_items` rows + the
 * header relations, then uploads the bytes to each item's
 * `order_item_attachements` field so the print / download /
 * preview-PDF endpoints can serve it.
 *
 * Why this exists: the older `createAdHocDeliveryNote` flow
 * created header + items but never saved a PDF, so any DN
 * created before the save-on-create fix landed (e.g. `DN26081307`
 * from the 2026-08-13 morning session) gets a `404 No saved PDF`
 * from `/api/invoicing/delivery-note-pdf`. The button on the
 * detail page that calls this lets the operator regenerate the
 * PDF on demand. After it succeeds, the saved copy takes over
 * and the regular endpoints serve it.
 *
 * Works for any DN — old or new. If the operator has edited
 * items (e.g. re-priced a line) since the original PDF was
 * saved, this picks up the latest state.
 *
 * Errors:
 *   - 404 (route layer) — DN id not found
 *   - 500 — render or upload failure
 */
export async function regenerateDeliveryNotePdf(
  deliveryNoteId: string,
): Promise<{ pdfSaved: true; filename: string }> {
  const pb = await getAdminPocketBase();

  const dn = await pb
    .collection(DELIVERY_NOTES)
    .getOne<DeliveryNote>(deliveryNoteId);
  const deliveryNoteNumber = dn.delivery_note_number;

  // Pull the items for this DN. Same expand pattern as the print
  // route's fallback render — we need order.customer / company
  // for the PDF meta block, and the items themselves for the
  // line rows. Ad-hoc DNs (no parent order) work fine here:
  // `expand.order` will be undefined and we fall back to the
  // header's customer / company relations.
  const items = await pb
    .collection(ORDER_ITEMS)
    .getFullList<OrderItem>({
      filter: `delivery_note_number = "${deliveryNoteNumber}"`,
      expand: "purchase_order.supplier,order.company,order.customer",
    });
  if (items.length === 0) {
    throw new Error(
      `No order items found for delivery note ${deliveryNoteNumber}.`,
    );
  }

  // Resolve customer / company names. Prefer the order's expand
  // (Path A — items have a parent order), fall back to the
  // header's customer / company relations (Path B — ad-hoc).
  const firstOrder = items[0].expand?.order;
  const customerName =
    firstOrder?.expand?.customer?.customer ??
    (await resolveRelationName(pb, dn.customer, CUSTOMERS, "customer")) ??
    "";
  const companyName =
    firstOrder?.expand?.company?.company ??
    (await resolveRelationName(pb, dn.company, COMPANIES, "company")) ??
    "";

  // All delivery-note PDFs render under the Westcott
  // Group letterhead, regardless of which subsidiary the
  // customer belongs to — see DELIVERY_NOTE_LETTERHEAD_CODE.
  // The `companyName` above still goes into the PDF meta
  // block so the printed document tells the driver which
  // subsidiary the delivery is for.
  const letterheadCode = DELIVERY_NOTE_LETTERHEAD_CODE;
  const [letterhead, logoDataUri] = await Promise.all([
    fetchLetterhead(letterheadCode),
    loadLetterheadLogoDataUri(letterheadCode),
  ]);

  const pdfBuffer = await renderDeliveryNotePdf({
    header: {
      deliveryNoteNumber,
      dateIso:
        dn.delivery_date ||
        new Date(dn.created || Date.now()).toISOString().slice(0, 10),
      orderNumber: firstOrder?.order_number ?? "",
      companyName,
      customerName,
    },
    lines: items.map((it) => ({
      id: it.id,
      description: (it.description ?? "").trim() || "(no description)",
      qty: resolveDeliveryNoteLineQty({
        quantity: it.quantity,
        orderQty: it.order_qty,
        qtyCollected: it.qty_collected,
      }),
    })),
    letterhead,
    logoDataUri,
  });

  // Same upload pattern as `/api/invoicing/delivery-note` step 2:
  // PB's file field PATCH REPLACES the existing list with whatever
  // we send, so a re-regenerate cleanly overwrites the previous
  // copy. Same filename → the retrieval endpoint (which looks for
  // a file named `{deliveryNoteNumber}.pdf` on the first item)
  // just picks up the new bytes.
  const filename = `${deliveryNoteNumber}.pdf`;
  const blob = new Blob([new Uint8Array(pdfBuffer)], {
    type: "application/pdf",
  });
  await Promise.all(
    items.map(async (it) => {
      const form = new FormData();
      form.append("order_item_attachements", blob, filename);
      await pb.collection(ORDER_ITEMS).update(it.id, form);
    }),
  );

  return { pdfSaved: true, filename };
}

/**
 * Look up a single relation's display field. Used by
 * `regenerateDeliveryNotePdf` to fall back to the header's
 * customer / company relations when the items don't have a
 * parent order (ad-hoc / Path B delivery notes).
 *
 * Returns null when the relation is unset, the id is missing,
 * or the lookup fails. The caller treats null as "blank" and
 * the PDF meta block renders an empty cell.
 */
async function resolveRelationName(
  pb: Awaited<ReturnType<typeof getAdminPocketBase>>,
  relationId: string | null | undefined,
  collection: string,
  field: string,
): Promise<string | null> {
  if (!relationId) return null;
  try {
    const row = (await pb.collection(collection).getOne(relationId)) as {
      [k: string]: unknown;
    };
    const value = row[field];
    return typeof value === "string" && value.length > 0 ? value : null;
  } catch {
    return null;
  }
}

/**
 * Input for `combineDeliveryNotes`. The operator picks 2+ DNs
 * from the list page; the service picks the oldest as the
 * survivor (so the printed number the customer has already
 * seen stays stable), moves every other DN's items onto the
 * survivor, and cancels the others.
 *
 * Attaching the merged result to an order is optional. Two
 * ways to do it (mutually exclusive):
 *   - `orderNumber` (string) — looked up against `orders.order_number`.
 *     Used by the operator typing the number they know. If the
 *     PB schema's `order_number` is non-unique (currently the
 *     case on this collection — see OrderCandidatesError below),
 *     the lookup can match multiple orders and the operator
 *     has to disambiguate via the second step.
 *   - `orderId` (PB id) — used after disambiguation, or when the
 *     picker UI provides the id directly. Bypasses the
 *     string lookup entirely; the service fetches the exact
 *     order row by id.
 *
 * `note` is appended to the survivor's notes ("Merged from
 * DN…") and to each cancelled DN's notes for the audit trail.
 */
export interface CombineDeliveryNotesInput {
  deliveryNoteIds: string[];
  orderNumber?: string | null;
  orderId?: string | null;
  note?: string | null;
}

export interface CombineDeliveryNotesResult {
  survivor: { id: string; delivery_note_number: string };
  cancelled: Array<{ id: string; delivery_note_number: string }>;
  itemsMoved: number;
  pdfRegenerated: boolean;
}

/**
 * One row in the "pick which order to attach" picker that
 * surfaces when the operator's typed `orderNumber` matched
 * more than one order. Carries just enough info for the
 * operator to make a confident choice: PB id (used as the
 * retry body's `orderId`), customer / company display
 * names, and the order's created timestamp.
 */
export interface OrderCandidate {
  id: string;
  order_number: string;
  customer_name: string | null;
  company_name: string | null;
  created: string;
}

/**
 * Thrown by `combineDeliveryNotes` when the operator's typed
 * `orderNumber` matched 2+ orders. The `orders` collection
 * does NOT have a unique index on `order_number` (verified
 * 2026-08-13 against live PB) — the same string can legitimately
 * appear on multiple orders because the field is the customer's
 * own PO / quote reference, not a unique system identifier.
 *
 * The route layer catches this and returns a 409 with the
 * candidates attached, so the page modal can render a picker
 * that lets the operator disambiguate by customer / company /
 * created date. The retry path uses the picked candidate's id
 * via `CombineDeliveryNotesInput.orderId` (no second string
 * lookup — the operator's typed value is replaced by the
 * specific id they picked).
 */
export class OrderCandidatesError extends Error {
  public readonly candidates: OrderCandidate[];
  public readonly orderNumber: string;
  constructor(orderNumber: string, candidates: OrderCandidate[]) {
    super(
      `Order number "${orderNumber}" matched ${candidates.length} orders — pick the right one.`,
    );
    this.name = "OrderCandidatesError";
    this.candidates = candidates;
    this.orderNumber = orderNumber;
  }
}

const COMBINABLE_STATUSES: DeliveryNoteStatus[] = ["draft", "sent"];

/**
 * Combine N delivery notes into the oldest of the bunch.
 *
 * Workflow:
 *   1. Fetch every selected DN header.
 *   2. Reject if any is not in `draft` or `sent` (the user
 *      asked to gate combine on those — once a DN has a
 *      customer PO on it or an invoice was generated, the
 *      merge would invalidate the audit trail).
 *   3. Sort by `created` ascending; the first one survives.
 *   4. If the operator supplied `orderNumber`, re-fetch that
 *      order and stamp its id on the survivor header (+ the
 *      customer / company relations for completeness).
 *   5. For each non-survivor DN:
 *      - re-stamp every item's `delivery_note_number` to the
 *        survivor's number (and its `order` to the new order
 *        id when `orderNumber` was supplied);
 *      - flip the DN header to status="cancelled" with a
 *        "Merged into <survivor number>" note appended to the
 *        existing notes field.
 *   6. Regenerate the survivor's PDF so it lists every line
 *      (including the just-moved ones). Returns `pdfRegenerated:
 *      false` on render failure — the merge still committed,
 *      the operator can hit Regenerate on the detail page.
 *
 * The merge is *not* transactional: a failure midway leaves
 * the data in a partially-merged state. We log every step so
 * the operator (or an admin) can see where it stopped. Each
 * item update and each header update is wrapped in its own
 * try/catch so one bad row doesn't abort the rest of the
 * batch.
 */
export async function combineDeliveryNotes(
  input: CombineDeliveryNotesInput,
): Promise<CombineDeliveryNotesResult> {
  const pb = await getAdminPocketBase();
  const ids = Array.from(
    new Set(
      (input.deliveryNoteIds ?? [])
        .filter((id): id is string => typeof id === "string" && id.length > 0),
    ),
  );
  if (ids.length < 2) {
    throw new Error("Combine needs at least 2 distinct delivery notes.");
  }

  // 1. Fetch every header (one round trip).
  const headers = await pb.collection(DELIVERY_NOTES).getFullList<DeliveryNote>({
    filter: ids.map((id) => `id = "${id}"`).join(" || "),
  });
  if (headers.length !== ids.length) {
    const found = new Set(headers.map((h) => h.id));
    const missing = ids.filter((id) => !found.has(id));
    throw new Error(`Delivery note(s) not found: ${missing.join(", ")}`);
  }

  // 2. Status guard.
  for (const h of headers) {
    if (!COMBINABLE_STATUSES.includes(h.status)) {
      throw new Error(
        `Delivery note ${h.delivery_note_number} is "${h.status}" — only draft or sent DNs can be combined.`,
      );
    }
  }

  // 3. Oldest survives.
  headers.sort(
    (a, b) =>
      new Date(a.created || 0).getTime() -
      new Date(b.created || 0).getTime(),
  );
  const survivor = headers[0];
  const cancelled = headers.slice(1);

  // 4. Resolve the order to attach. Two input paths:
  //    a) `orderId` (PB id) — operator already disambiguated,
  //       fetched straight by id, no string lookup. Used after
  //       the picker from the duplicate-match flow.
  //    b) `orderNumber` (string) — looked up against
  //       `orders.order_number`. If exactly one match, use it.
  //       If 0, throw "not found". If 2+, throw
  //       OrderCandidatesError with the candidate list so the
  //       modal can show a picker.
  //    c) Neither — leave the survivor's order unset (ad-hoc
  //       combined DN, no parent order).
  let orderId: string | null = null;
  let orderCustomerId: string | null = null;
  let orderCompanyId: string | null = null;

  if (input.orderId && input.orderId.trim().length > 0) {
    try {
      const order = await pb.collection(ORDERS).getOne<{
        id: string;
        order_number: string;
        customer?: string;
        company?: string;
      }>(input.orderId.trim());
      orderId = order.id;
      orderCustomerId = order.customer ?? null;
      orderCompanyId = order.company ?? null;
    } catch (err) {
      // The orderId we got from the picker was stale (deleted
      // between the picker fetch and the retry). Surface a
      // clear message — the operator just needs to redo the
      // picker.
      if (err instanceof Error) throw err;
      throw new Error(String(err));
    }
  } else if (input.orderNumber && input.orderNumber.trim().length > 0) {
    const orderNumber = input.orderNumber.trim();
    try {
      const orderRows = await pb.collection(ORDERS).getFullList<{
        id: string;
        order_number: string;
        customer?: string;
        company?: string;
        created?: string;
      }>({
        filter: `order_number = "${orderNumber.replace(/"/g, '\\"')}"`,
      });
      if (orderRows.length === 0) {
        throw new Error(
          `Order "${orderNumber}" not found — leave the field blank to combine without linking an order.`,
        );
      }
      if (orderRows.length > 1) {
        // Non-unique match — surface the candidates so the
        // operator can disambiguate via the picker on the
        // modal. We batch one fetch of customer + company
        // names so the picker rows show the right label
        // instead of just the relation id.
        const customerIds = Array.from(
          new Set(
            orderRows
              .map((o) => o.customer)
              .filter((c): c is string => typeof c === "string" && c.length > 0),
          ),
        );
        const companyIds = Array.from(
          new Set(
            orderRows
              .map((o) => o.company)
              .filter((c): c is string => typeof c === "string" && c.length > 0),
          ),
        );
        const [customerRows, companyRows] = await Promise.all([
          customerIds.length > 0
            ? pb.collection("customers").getFullList<{
                id: string;
                customer?: string;
              }>({
                filter:
                  customerIds.map((id) => `id = "${id}"`).join(" || ") ||
                  "id = \"\"",
              })
            : Promise.resolve([] as Array<{ id: string; customer?: string }>),
          companyIds.length > 0
            ? pb.collection("companies").getFullList<{
                id: string;
                company?: string;
              }>({
                filter:
                  companyIds.map((id) => `id = "${id}"`).join(" || ") ||
                  "id = \"\"",
              })
            : Promise.resolve([] as Array<{ id: string; company?: string }>),
        ]);
        const customerById = new Map(
          customerRows.map((c) => [c.id, c.customer ?? null]),
        );
        const companyById = new Map(
          companyRows.map((c) => [c.id, c.company ?? null]),
        );
        const candidates: OrderCandidate[] = orderRows.map((o) => ({
          id: o.id,
          order_number: o.order_number,
          customer_name: o.customer
            ? customerById.get(o.customer) ?? null
            : null,
          company_name: o.company
            ? companyById.get(o.company) ?? null
            : null,
          created: o.created ?? "",
        }));
        throw new OrderCandidatesError(orderNumber, candidates);
      }
      const order = orderRows[0];
      orderId = order.id;
      orderCustomerId = order.customer ?? null;
      orderCompanyId = order.company ?? null;
    } catch (err) {
      // OrderCandidatesError is intentional — re-throw so the
      // route layer can map it to a structured 409. Other
      // errors bubble up as plain 500s.
      if (err instanceof OrderCandidatesError) throw err;
      if (err instanceof Error) throw err;
      throw new Error(String(err));
    }
  }

  // 5a. Patch the survivor header. When the operator linked
  //     an order, we override the customer / company to the
  //     order's relations so the merged DN points at exactly
  //     one customer + company record (the assumption being
  //     that all the items being merged were for the same
  //     physical order).
  try {
    const survivorPatch: Record<string, unknown> = {};
    if (orderId) {
      survivorPatch.order = orderId;
      if (orderCustomerId) survivorPatch.customer = orderCustomerId;
      if (orderCompanyId) survivorPatch.company = orderCompanyId;
    }
    const mergedFromNumbers = cancelled.map((h) => h.delivery_note_number);
    const existing = survivor.notes ?? "";
    const appendNote =
      mergedFromNumbers.length > 0
        ? `${existing ? `${existing}\n` : ""}Merged from ${mergedFromNumbers.join(", ")}${input.note ? ` — ${input.note}` : ""}`
        : `${existing ? `${existing}\n` : ""}${input.note ?? ""}`;
    survivorPatch.notes = appendNote;
    await pb.collection(DELIVERY_NOTES).update(survivor.id, survivorPatch);
  } catch (err) {
    throw new Error(
      `Failed to update survivor DN ${survivor.delivery_note_number}: ${
        err instanceof Error ? err.message : String(err)
      }`,
    );
  }

  // 5b. Move items from each cancelled DN onto the survivor.
  //     One fetch per cancelled DN (their items are filtered
  //     by their own DN number), then a per-item update with
  //     the survivor's DN number + the optional new order id.
  let itemsMoved = 0;
  for (const dead of cancelled) {
    let deadItems: OrderItem[] = [];
    try {
      deadItems = await pb.collection(ORDER_ITEMS).getFullList<OrderItem>({
        filter: `delivery_note_number = "${dead.delivery_note_number}"`,
      });
    } catch (err) {
      console.error(
        `[combineDeliveryNotes] failed to fetch items for ${dead.delivery_note_number}:`,
        err,
      );
      // Continue — the operator can move the items by hand if
      // this fetch blew up. We don't abort the whole merge.
      continue;
    }
    for (const it of deadItems) {
      try {
        const patch: Record<string, unknown> = {
          delivery_note_number: survivor.delivery_note_number,
        };
        if (orderId) patch.order = orderId;
        await pb.collection(ORDER_ITEMS).update(it.id, patch);
        itemsMoved += 1;
      } catch (err) {
        console.error(
          `[combineDeliveryNotes] failed to move item ${it.id} from ${dead.delivery_note_number} → ${survivor.delivery_note_number}:`,
          err,
        );
      }
    }

    // Cancel the source header.
    try {
      const existingDeadNote = dead.notes ?? "";
      const mergedIntoNote = `${existingDeadNote ? `${existingDeadNote}\n` : ""}Merged into ${survivor.delivery_note_number}${input.note ? ` — ${input.note}` : ""}`;
      await pb.collection(DELIVERY_NOTES).update(dead.id, {
        status: "cancelled",
        notes: mergedIntoNote,
      });
    } catch (err) {
      console.error(
        `[combineDeliveryNotes] failed to cancel ${dead.delivery_note_number}:`,
        err,
      );
    }
  }

  // 6. Regenerate the survivor's PDF so the merged line list
  //    is reflected in the saved copy. Same pattern as the
  //    regenerate-PDF button — best-effort, log on failure.
  let pdfRegenerated = false;
  try {
    await regenerateDeliveryNotePdf(survivor.id);
    pdfRegenerated = true;
  } catch (err) {
    console.error(
      `[combineDeliveryNotes] PDF regen failed for ${survivor.delivery_note_number}:`,
      err,
    );
  }

  return {
    survivor: {
      id: survivor.id,
      delivery_note_number: survivor.delivery_note_number,
    },
    cancelled: cancelled.map((h) => ({
      id: h.id,
      delivery_note_number: h.delivery_note_number,
    })),
    itemsMoved,
    pdfRegenerated,
  };
}

/**
 * Update the `quantity` field on a single order_item that
 * belongs to a delivery note.
 *
 * Two validations before the write:
 *   1. The item resolves and has a `delivery_note_number`.
 *      Items without a DN aren't editable through this path —
 *      they're plain order items and the operator should
 *      edit them via the order page instead.
 *   2. The parent DN's status is `draft` or `sent`. Once a DN
 *      has a customer PO or an invoice, editing a qty changes
 *      what's actually being delivered under a number the
 *      customer already has on file. Block + point the
 *      operator at the right flow.
 *
 * Bounds: `quantity > 0` only. No upper bound — top-ups
 * (qty > order_qty) are allowed because the operator might
 * have under-ordered and is now handing the customer the
 * full remaining stock. The detail page shows order_qty
 * alongside the editable qty so the operator can see the
 * original order size at a glance.
 *
 * On success, triggers a PDF regeneration for the parent DN
 * so the printed copy matches the new qty. Auto-regen is the
 * user's chosen UX (every save re-renders).
 */
export async function updateDeliveryNoteItemQuantity(input: {
  itemId: string;
  quantity: number;
}): Promise<{
  item: { id: string; quantity: number; delivery_note_number: string };
  pdfRegenerated: boolean;
}> {
  const pb = await getAdminPocketBase();
  const qty = Number(input.quantity);
  if (!Number.isFinite(qty) || qty <= 0) {
    throw new Error(`Quantity must be a positive number (got ${input.quantity}).`);
  }

  // Fetch + guard 1: must belong to a DN.
  const item = await pb
    .collection(ORDER_ITEMS)
    .getOne<OrderItem>(input.itemId);
  if (!item.delivery_note_number) {
    throw new Error(
      `Item ${input.itemId} isn't on a delivery note — edit it from the order page.`,
    );
  }

  // Fetch + guard 2: parent DN must be draft or sent.
  const dnRows = await pb
    .collection(DELIVERY_NOTES)
    .getFullList<DeliveryNote>({
      filter: `delivery_note_number = "${item.delivery_note_number}"`,
    });
  if (dnRows.length === 0) {
    throw new Error(
      `Delivery note ${item.delivery_note_number} not found for item ${input.itemId}.`,
    );
  }
  // If the same DN number is somehow on multiple headers
  // (shouldn't happen — it's unique-indexed), refuse rather
  // than pick.
  if (dnRows.length > 1) {
    throw new Error(
      `Multiple delivery_notes rows match "${item.delivery_note_number}" — fix in PB admin before editing qtys.`,
    );
  }
  const dn = dnRows[0];
  if (!COMBINABLE_STATUSES.includes(dn.status)) {
    throw new Error(
      `Cannot edit qty on a "${dn.status}" delivery note — only draft or sent DNs are editable.`,
    );
  }

  // Apply the update.
  await pb.collection(ORDER_ITEMS).update(input.itemId, { quantity: qty });

  // Auto-regenerate the parent DN's PDF per UX decision. Same
  // best-effort pattern as the merge — log on failure but
  // don't surface to the caller (the qty edit succeeded, the
  // operator can hit Regenerate to retry the PDF).
  let pdfRegenerated = false;
  try {
    await regenerateDeliveryNotePdf(dn.id);
    pdfRegenerated = true;
  } catch (err) {
    console.error(
      `[updateDeliveryNoteItemQuantity] PDF regen failed for ${dn.delivery_note_number}:`,
      err,
    );
  }

  return {
    item: {
      id: item.id,
      quantity: qty,
      delivery_note_number: item.delivery_note_number,
    },
    pdfRegenerated,
  };
}