/**
 * order-quote-link-service — server-side order ↔ quote matching.
 *
 * The PocketBase half of the matcher. Its predecessor lives in
 * `src/lib/pb-helpers.ts` and runs on the browser's PB singleton,
 * which is why matching could only ever happen when an operator
 * clicked a button. This version runs on `getAdminPocketBase()` so it
 * can be called from `createOrder`, from the backlog sweep, and from
 * route handlers.
 *
 * The pure scoring (`scoreOrderVsQuote`, `pairQuoteLines`,
 * `quoteWindowForOrder`) lives in `order-quote-match.ts` and is reused
 * untouched — DO NOT reimplement any of it here.
 *
 * Policy: this module NEVER writes `orders.quote`. It only ever writes
 * the soft suggestion (`potential_quote`). Promoting a suggestion to a
 * hard link is a deliberate human action that goes through
 * `setOrderQuote` in `orders-service.ts`.
 */

import { ClientResponseError } from "pocketbase";
import { getAdminPocketBase } from "@/lib/server/pocketbase-admin";
import { fetchQuoteItemsForQuotesAdmin } from "@/lib/server/quotes-service";
import type { QuoteItem } from "@/lib/types";
import {
  scoreOrderVsQuote,
  pairQuoteLines,
  quoteWindowForOrder,
  quoteToOrderAgeDays,
  MATCH_CONFIDENCE_THRESHOLD,
  FUZZY_CANDIDATE_CAP,
  FUZZY_WINDOW_DAYS,
  FUZZY_WINDOW_WIDEN_DAYS,
  type ScoreBreakdown,
} from "@/lib/server/order-quote-match";

export type QuoteMatchMethod =
  | "exact_quote_number"
  | "exact_quote_reference"
  | "exact_rfq_number"
  | "exact_external_number"
  | "company_customer_desc_price"
  | "no_match";

export interface QuoteMatchCandidate {
  quoteId: string;
  quoteNumber: string;
  quoteCreated: string;
  confidence: number;
  breakdown?: ScoreBreakdown;
  method: Exclude<QuoteMatchMethod, "no_match">;
}

export interface SuggestQuoteResult {
  orderId: string;
  best: QuoteMatchCandidate | null;
  alternatives: QuoteMatchCandidate[];
  method: QuoteMatchMethod;
  /** Which pass produced the result — for the sweep's reporting.
   *  "initial" is the FUZZY_WINDOW_DAYS pass, not a fixed "90d" label
   *  — retuning that constant must not make this label lie. */
  window: "exact" | "initial" | "widened" | "none";
  /** Days from the matched quote's creation to the order's. null when unmatched. */
  ageGapDays: number | null;
  /** Set when the order was deliberately not processed. */
  skipped?: "already_linked";
}

interface OrderRow {
  id: string;
  created: string;
  company?: string;
  customer?: string;
  quote?: string;
  quote_reference_text?: string;
  rfq_number?: string;
}

interface QuoteRow {
  id: string;
  quote_number?: string;
  company?: string;
  customer?: string;
  created: string;
}

interface LineRow {
  id: string;
  description?: string;
  selling_price?: number;
  quantity?: number;
}

const ORDER_COLLECTION = "orders";
const QUOTE_COLLECTION = "quotes";
const ORDER_ITEMS_COLLECTION = "order_items";

/** The scalars `fuzzyPass` reads off each candidate quote. Explicit
 *  `fields` on the query — `quotes` also carries `email_body`,
 *  `ai_insights`, `migration_meta`, etc., and pulling those for up to
 *  FUZZY_CANDIDATE_CAP (200) candidates (twice, if the window widens)
 *  to read five scalars would dominate the whole operation's cost at
 *  intake volume. */
const CANDIDATE_QUOTE_FIELDS = "id,quote_number,company,customer,created";

/** What `scoreOrderVsQuote` needs off each quote line. Passed
 *  explicitly to `fetchQuoteItemsForQuotesAdmin` — its default
 *  projection belongs to the duplicate-quote scan, a different
 *  stakeholder with different needs. If that default is ever trimmed,
 *  this call must not silently lose `description` or `selling_price`
 *  and start scoring every candidate near zero. */
const MATCHER_QUOTE_ITEM_FIELDS = "id,quote,description,selling_price,quantity";

/** What `pairOrderLines` needs off each order line: enough to pair by
 *  description, plus the existing `quote_item` so the write loop can
 *  detect an already-set link and never clobber it. If this ever
 *  drops `quote_item`, that guard goes silently blind — every line
 *  reads as unlinked and a human-confirmed pairing can be
 *  overwritten. */
const PAIR_ORDER_ITEM_FIELDS = "id,description,quote_item";

/** What `pairOrderLines` needs off each quote line — just enough to
 *  pair by description. Passed explicitly to
 *  `fetchQuoteItemsForQuotesAdmin` for the same reason as
 *  `MATCHER_QUOTE_ITEM_FIELDS` above: its default projection belongs
 *  to the duplicate-quote scan, a different caller with different
 *  needs, and must not silently drift under this one. */
const PAIR_QUOTE_ITEM_FIELDS = "id,quote,description";

function esc(s: string): string {
  return (s || "").replace(/"/g, '\\"');
}

function project(rows: ReadonlyArray<LineRow>) {
  return rows.map((r) => ({
    description: r.description || "",
    selling_price: Number(r.selling_price) || 0,
    quantity: Number(r.quantity) || 1,
  }));
}

/**
 * Try the four exact-identifier fields, in priority order. Never date
 * limited — a citation is evidence regardless of age.
 *
 * Scoped to the order's own company when known: `quote_reference_text`
 * and `rfq_number` are customer-supplied free text, and without this
 * clause a reference-number collision across two customers would
 * return a confidence-1.0 suggestion pointing at a different
 * company's quote.
 */
async function findExactMatch(
  pb: Awaited<ReturnType<typeof getAdminPocketBase>>,
  ref: string,
  companyId?: string,
): Promise<{ quote: QuoteRow; method: QuoteMatchCandidate["method"] } | null> {
  const trimmed = (ref || "").trim();
  if (!trimmed) return null;
  const fields = [
    ["quote_number", "exact_quote_number"],
    ["quote_reference", "exact_quote_reference"],
    ["rfq_number", "exact_rfq_number"],
    ["external_number", "exact_external_number"],
  ] as const;
  for (const [field, method] of fields) {
    const clauses = [`${field} = "${esc(trimmed)}"`];
    if (companyId) clauses.push(`company = "${esc(companyId)}"`);
    try {
      const list = await pb
        .collection(QUOTE_COLLECTION)
        .getList<QuoteRow>(1, 5, { filter: clauses.join(" && ") });
      if (list.items.length > 0) return { quote: list.items[0], method };
    } catch (err) {
      // A field this deploy's PB schema doesn't have 400s — try the
      // next one; all four fields exist per pb-exports/pb_schema-2.json
      // so this is a defensive fallback, not the expected path.
      // Anything else (expired admin token, connection reset, PB
      // restart mid-sweep) is a real failure and must propagate:
      // swallowing it here would let the fuzzy path silently run
      // instead, and writeSuggestion would then persist
      // `quote_matching_attempted: true` / `quote_match_method:
      // "no_match"` for an order that actually had a valid citation —
      // permanently hiding it from the sweep's "haven't tried yet"
      // filter, since nothing revisits an order once that flag is set.
      if (err instanceof ClientResponseError && err.status === 400) continue;
      throw err;
    }
  }
  return null;
}

/** Score every candidate quote inside one date window. */
async function fuzzyPass(
  pb: Awaited<ReturnType<typeof getAdminPocketBase>>,
  order: OrderRow,
  orderItems: LineRow[],
  windowDays: number,
): Promise<QuoteMatchCandidate[]> {
  if (orderItems.length === 0) return [];

  const win = quoteWindowForOrder(order.created, windowDays);
  const filters: string[] = [
    `created >= "${win.from}"`,
    `created <= "${win.to}"`,
    "is_template != true",
  ];
  if (order.company) filters.push(`company = "${esc(order.company)}"`);
  if (order.customer) {
    filters.push(`(customer = "${esc(order.customer)}" || customer = "")`);
  }

  const candidates = await pb
    .collection(QUOTE_COLLECTION)
    .getList<QuoteRow>(1, FUZZY_CANDIDATE_CAP, {
      filter: filters.join(" && "),
      sort: "-created",
      fields: CANDIDATE_QUOTE_FIELDS,
    });
  if (candidates.items.length === 0) return [];

  // A naive `quote = "x" || quote = "y" || ...` OR-chain over
  // FUZZY_CANDIDATE_CAP (200) ids blows PB's filter length limit
  // (HTTP 400) well before hitting the cap — `fetchQuoteItemsForQuotesAdmin`
  // tries PB's `IN (...)` syntax first and falls back to chunked
  // OR-chains, so a company with a large quote history doesn't break
  // the matcher outright. Reused (not reimplemented) from
  // `quotes-service.ts`, which already has this exact chunking logic
  // for its duplicate-quote scan.
  const quoteIds = candidates.items.map((q) => q.id);
  const quoteItems = await fetchQuoteItemsForQuotesAdmin(pb, quoteIds, MATCHER_QUOTE_ITEM_FIELDS);

  const byQuote = new Map<string, QuoteItem[]>();
  for (const it of quoteItems) {
    if (!it.quote) continue;
    const bucket = byQuote.get(it.quote);
    if (bucket) bucket.push(it);
    else byQuote.set(it.quote, [it]);
  }

  const projectedOrder = project(orderItems);
  const scored: QuoteMatchCandidate[] = [];
  for (const q of candidates.items) {
    const breakdown = scoreOrderVsQuote(
      { companyId: order.company, customerId: order.customer, items: projectedOrder },
      { company: q.company, customer: q.customer, items: project(byQuote.get(q.id) ?? []) },
    );
    if (breakdown.confidence >= MATCH_CONFIDENCE_THRESHOLD) {
      scored.push({
        quoteId: q.id,
        quoteNumber: q.quote_number || "",
        quoteCreated: q.created,
        confidence: breakdown.confidence,
        breakdown,
        method: "company_customer_desc_price",
      });
    }
  }
  scored.sort((a, b) =>
    b.confidence !== a.confidence
      ? b.confidence - a.confidence
      : (b.quoteCreated || "").localeCompare(a.quoteCreated || ""),
  );
  return scored;
}

/**
 * Find the best candidate quote for an order and write it as a soft
 * suggestion. Idempotent and safe to re-run.
 */
export async function suggestQuoteForOrder(
  orderId: string,
): Promise<SuggestQuoteResult> {
  const pb = await getAdminPocketBase();
  pb.autoCancellation(false);

  const order = await pb.collection(ORDER_COLLECTION).getOne<OrderRow>(orderId);

  // An order with a confirmed hard link is settled. Never second-guess it.
  if (order.quote) {
    return {
      orderId,
      best: null,
      alternatives: [],
      method: "no_match",
      window: "none",
      ageGapDays: null,
      skipped: "already_linked",
    };
  }

  // 1. Exact identifier citation, if the order carries reference text.
  const ref = (order.quote_reference_text || order.rfq_number || "").trim();
  const exact = await findExactMatch(pb, ref, order.company);
  if (exact) {
    const best: QuoteMatchCandidate = {
      quoteId: exact.quote.id,
      quoteNumber: exact.quote.quote_number || "",
      quoteCreated: exact.quote.created,
      confidence: 1,
      method: exact.method,
    };
    await writeSuggestion(pb, orderId, best);
    return {
      orderId,
      best,
      alternatives: [],
      method: exact.method,
      window: "exact",
      ageGapDays: quoteToOrderAgeDays(exact.quote.created, order.created),
    };
  }

  // 2. Fuzzy — 90-day window first, widening only if it comes up empty.
  const orderItems = await pb
    .collection(ORDER_ITEMS_COLLECTION)
    .getFullList<LineRow>({
      filter: `order = "${esc(orderId)}"`,
      fields: "id,description,selling_price,quantity",
      batch: 1000,
    });

  let scored = await fuzzyPass(pb, order, orderItems, FUZZY_WINDOW_DAYS);
  let window: SuggestQuoteResult["window"] = "initial";
  if (scored.length === 0) {
    scored = await fuzzyPass(pb, order, orderItems, FUZZY_WINDOW_WIDEN_DAYS);
    window = "widened";
  }

  const best = scored[0] ?? null;
  await writeSuggestion(pb, orderId, best);

  return {
    orderId,
    best,
    alternatives: scored.slice(1, 6),
    method: best ? "company_customer_desc_price" : "no_match",
    window: best ? window : "none",
    ageGapDays: best ? quoteToOrderAgeDays(best.quoteCreated, order.created) : null,
  };
}

/** Persist (or clear) the soft suggestion. Never touches `quote`. */
async function writeSuggestion(
  pb: Awaited<ReturnType<typeof getAdminPocketBase>>,
  orderId: string,
  best: QuoteMatchCandidate | null,
): Promise<void> {
  await pb.collection(ORDER_COLLECTION).update(orderId, {
    quote_matching_attempted: true,
    quote_match_method: best ? best.method : "no_match",
    potential_quote: best ? best.quoteId : null,
    potential_quote_confidence: best ? best.confidence : 0,
  });
}

/* ============================================================================
 * Per-line pairing
 *
 * `order_items.quote_item` has existed all along but was only ever
 * written by `createOrderFromQuote`. When a quote is linked to an
 * order after the fact, nothing paired the lines — so the process page
 * re-guessed the pairing on every render with an exact/substring
 * match, and any wording difference silently hid the buyer's note.
 *
 * Confident pairs are persisted here so the guess happens once.
 * Possible pairs are returned but NOT written: the operator confirms
 * them, so a buyer is never shown a note from the wrong line without
 * being told it is a guess.
 * ========================================================================== */

export interface PairedLine {
  orderItemId: string;
  quoteItemId: string;
  /** Jaccard overlap of the two descriptions, 0..1. */
  confidence: number;
}

export interface PairOrderLinesResult {
  confident: PairedLine[];
  possible: PairedLine[];
  unmatchedOrderItemIds: string[];
}

/**
 * Pair an order's lines against a quote's lines, persisting only the
 * confident ones. Safe to re-run: a line whose `quote_item` is already
 * set is never overwritten.
 */
export async function pairOrderLines(
  orderId: string,
  quoteId: string,
): Promise<PairOrderLinesResult> {
  const pb = await getAdminPocketBase();
  pb.autoCancellation(false);

  const [orderItems, quoteItems] = await Promise.all([
    pb
      .collection(ORDER_ITEMS_COLLECTION)
      .getFullList<LineRow & { quote_item?: string }>({
        filter: `order = "${esc(orderId)}"`,
        fields: PAIR_ORDER_ITEM_FIELDS,
        batch: 1000,
      }),
    // Reuses the same helper the fuzzy pass uses for quote_items — it
    // already handles PB's IN(...) filter and the chunked-OR-chain
    // fallback, so there is one code path in this file that knows how
    // to fetch quote_items rather than two.
    fetchQuoteItemsForQuotesAdmin(pb, [quoteId], PAIR_QUOTE_ITEM_FIELDS),
  ]);

  // `pairQuoteLines` returns indices into exactly the arrays passed to
  // it. Both arrays below are built with a single `.map()` over
  // `orderItems`/`quoteItems` — `.map()` is index-preserving by
  // definition, so `orderLineIdx`/`quoteLineIdx` always refer back to
  // the same position in `orderItems`/`quoteItems`. No sort or filter
  // runs on either array between the fetch and this call, so the
  // mapping can't be thrown off.
  const pairs = pairQuoteLines(
    orderItems.map((r) => ({ description: r.description || "" })),
    quoteItems.map((r) => ({ description: r.description || "" })),
  );

  const confident: PairedLine[] = [];
  const possible: PairedLine[] = [];
  const pairedOrderIdx = new Set<number>();

  for (const p of pairs) {
    pairedOrderIdx.add(p.orderLineIdx);
    const entry: PairedLine = {
      orderItemId: orderItems[p.orderLineIdx].id,
      quoteItemId: quoteItems[p.quoteLineIdx].id,
      confidence: p.jaccard,
    };
    if (p.tier === "confident") confident.push(entry);
    else possible.push(entry);
  }

  // Quote lines already claimed by an order line's existing DB value.
  // Seeded up front, before any write — a stale link (the line's
  // description drifted since it was set, or an operator hand-picked
  // it) still occupies that quote line. Without this, a fresh
  // confident pair on a *different* order line can point a second
  // line at the same quote_item: both would then render the same
  // estimator's note and attachments, which is exactly the failure
  // this feature exists to prevent, just reached from the other
  // direction (`row?.quote_item` below only guards the pair's own
  // order line, not the quote line it targets).
  const claimedQuoteItemIds = new Set(
    orderItems.map((r) => r.quote_item).filter((v): v is string => Boolean(v)),
  );

  // Persist confident pairs only, and never clobber an existing link
  // (a line paired by createOrderFromQuote, or confirmed by hand).
  //
  // Sequential, one write per line — same tradeoff as the bulk-cancel
  // and delivery loops elsewhere in orders-service.ts ("one PB
  // round-trip per write is fine here; we cap at a few dozen items
  // per order in practice"). Parallelizing with Promise.all would add
  // concurrent-write risk against PB for no real gain at this volume.
  for (const c of confident) {
    const row = orderItems.find((r) => r.id === c.orderItemId);
    if (row?.quote_item) continue;
    if (claimedQuoteItemIds.has(c.quoteItemId)) continue;
    await pb.collection(ORDER_ITEMS_COLLECTION).update(c.orderItemId, {
      quote_item: c.quoteItemId,
    });
  }

  return {
    confident,
    possible,
    // A line already carrying a `quote_item` in the DB is matched
    // even if this run's algorithm didn't (re-)propose a pair for
    // it — e.g. its description drifted away from its original
    // counterpart. Only a line with neither an existing link nor a
    // fresh pair counts as genuinely unmatched.
    unmatchedOrderItemIds: orderItems
      .filter((r, idx) => !pairedOrderIdx.has(idx) && !r.quote_item)
      .map((r) => r.id),
  };
}

/* ============================================================================
 * Backlog sweep
 *
 * Auto-detection at intake only covers orders created from now on.
 * This walks the orders that were never attempted — the historical
 * backlog, plus any order whose lines were corrected after creation.
 *
 * The age-gap histogram exists so the FUZZY_WINDOW_DAYS default (90)
 * can be re-tuned against what actually happens in this business
 * rather than left at an estimate.
 * ========================================================================== */

export interface AgeGapHistogram {
  d0_30: number;
  d31_60: number;
  d61_90: number;
  d91_180: number;
  d181_365: number;
  d365_plus: number;
  total: number;
}

export interface SweepResult {
  processed: number;
  suggested: number;
  noMatch: number;
  failed: number;
  /** Total orders still awaiting a sweep after this batch. */
  remaining: number;
  ageGaps: AgeGapHistogram;
}

/** Bucket quote→order age gaps. Exported for direct unit testing.
 *
 *  Uses `|g|` because a negative gap (quote created AFTER the order)
 *  is a real observation on back-dated orders; treating it as a
 *  positive day count preserves the bucket semantics.
 *
 *  Boundary days are counted in the LOWER bucket (≤ 30 stays in
 *  d0_30) so the histogram's edges line up with how operators
 *  describe ranges ("within a month"). */
export function bucketAgeGaps(gaps: ReadonlyArray<number>): AgeGapHistogram {
  const h: AgeGapHistogram = {
    d0_30: 0,
    d31_60: 0,
    d61_90: 0,
    d91_180: 0,
    d181_365: 0,
    d365_plus: 0,
    total: 0,
  };
  for (const g of gaps) {
    const d = Math.abs(g);
    if (d <= 30) h.d0_30++;
    else if (d <= 60) h.d31_60++;
    else if (d <= 90) h.d61_90++;
    else if (d <= 180) h.d91_180++;
    else if (d <= 365) h.d181_365++;
    else h.d365_plus++;
    h.total++;
  }
  return h;
}

export interface SweepOptions {
  /** Max orders to process in this batch. */
  limit?: number;
}

export async function sweepUnmatchedOrders(
  options: SweepOptions = {},
): Promise<SweepResult> {
  const limit = Math.min(Math.max(options.limit ?? 100, 1), 500);
  const pb = await getAdminPocketBase();
  pb.autoCancellation(false);

  // Scope: orders where the matcher has never run AND no hard link
  // exists. `quote = ""` is the codebase's pattern for "no relation"
  // (verified against orders-service.ts:3749).
  //
  // Projection: `id` only. We re-fetch the order inside
  // suggestQuoteForOrder with the fields the matcher actually reads;
  // pulling the full record here just bloats the wire.
  const page = await pb.collection(ORDER_COLLECTION).getList<{ id: string }>(1, limit, {
    filter: `quote_matching_attempted = false && quote = ""`,
    sort: "-created",
    fields: "id",
  });

  let suggested = 0;
  let noMatch = 0;
  let failed = 0;
  const gaps: number[] = [];

  // Sequential on purpose: each order fans out into a candidate scan,
  // and running them in parallel would hammer PB during a backlog run.
  for (const row of page.items) {
    try {
      const res = await suggestQuoteForOrder(row.id);
      if (res.best) {
        suggested++;
        if (res.ageGapDays !== null) gaps.push(res.ageGapDays);
      } else {
        // Skipped orders (already_linked) and true no_matches both
        // land here — distinguish via `res.skipped` if a future caller
        // needs to. For now they're both "nothing new to show."
        noMatch++;
      }
    } catch (err) {
      failed++;
      console.error(
        `[sweepUnmatchedOrders] order ${row.id} failed:`,
        err instanceof Error ? err.message : err,
      );
    }
  }

  return {
    processed: page.items.length,
    suggested,
    noMatch,
    failed,
    remaining: Math.max(0, (page.totalItems ?? 0) - page.items.length),
    ageGaps: bucketAgeGaps(gaps),
  };
}