/**
 * `findPriceListBySku` — SKU → catalogue row matcher.
 *
 * Used by the "Check pricing" button on the quote process page
 * (and, in v2, by the email-intake Code node + the AI rewriter).
 *
 * The match has two tiers, ranked by specificity:
 *
 *   Tier 1 — exact equality on the canonical form:
 *     - `sku = "${raw}"`              (buyer typed it exactly)
 *     - `sku_normalised = "${norm}"`  (canonical form — dashes,
 *                                     case, and other noise stripped)
 *
 *   Tier 2 — substring fallback (only if Tier 1 yields zero hits):
 *     - `sku ~ "${norm}"`             (substring on canonical form;
 *                                     catches "TS-12" inside "TS-12-55"
 *                                     or vice-versa)
 *
 * Returns the candidates sorted with the **most recently updated
 * row first** — that's the v1 policy ("newest match wins") we
 * agreed for multi-supplier SKUs in the brainstorm. If the v1
 * callers want a different policy they can use the `preferNewest`
 * option (default true).
 *
 * The function uses admin PB (no user session). Caller-side
 * permissions/feature gating lives in the route handler.
 */
import type PocketBase from "pocketbase";
import { getAdminPocketBase } from "./pocketbase-admin";
import type { PriceList } from "../types";

/** A catalogue row slimmed down to the fields the matcher
 *  consumer actually needs. Includes `specifications` and
 *  `search_text` so the picker modal's explainer can show why a
 *  fuzzy candidate matched (e.g. "brand = BOSCH + description
 *  contains grinder"). The shape is a structural superset of
 *  the catalogue's typed fields — `PriceList` is assignable here. */
export type PriceListMatch = Pick<
  PriceList,
  | "id"
  | "sku"
  | "description"
  | "cost_price"
  | "selling_price"
  | "unit"
  | "supplier"
  | "brand"
  | "category"
  | "subcategory"
  | "sku_normalised"
  | "updated"
  | "specifications"
  | "search_text"
>;

export type FindPriceListBySkuOptions = {
  /** When true (default), sort the candidates newest-first. */
  preferNewest?: boolean;
  /** Hard cap on the number of rows we look at. Default 25. Tier 3
   *  has its own tighter cap regardless. */
  limit?: number;
  /** Set false from bulk auto-fill paths (Check pricing) so fuzzy
   *  description/brand hits don't silently patch 10 unrelated rows.
   *  The picker UI passes true. Default true. */
  enableTier3?: boolean;
};

/** Canonicalise a SKU: uppercase, strip everything that's not A-Z
 *  / 0-9. Exported so callers (and tests) can use the same helper
 *  the matcher uses to compare inputs. */
export function normaliseSku(raw: string | null | undefined): string {
  if (!raw) return "";
  return raw.toUpperCase().replace(/[^A-Z0-9]/g, "");
}

/** Escape a literal string for embedding inside a double-quoted PB
 *  filter token. Doubles the only special character (`"` → `\"`).
 *  Exported for unit tests + callers that build their own filters
 *  on top of the matcher. */
export function escapeForPbString(value: string): string {
  return value.replace(/"/g, '\\"');
}

/**
 * Look up `price_list` rows by SKU. Returns an empty array if no
 * row matches the input — callers translate that into a "no
 * match" UI badge.
 *
 * Three tiers, ranked by specificity:
 *
 *   Tier 1 — exact equality on the SKU (raw + canonical form).
 *            Catches "JEITD-06" and "JEITD06" against the canonical
 *            "JEITD-06".
 *
 *   Tier 2 — substring fallback on the SKU (raw + canonical form).
 *            Catches "JEITD" matching "JEITD-D11", and partial
 *            prefix hits like "TS-12" against "TS-12-55".
 *
 *   Tier 3 — `search_text` fuzzy (only consulted when Tiers 1+2
 *            yield zero hits). `search_text` already contains the
 *            SKU, the description, the brand, the category, the
 *            supplier name, and every spec key/value/synonym — so
 *            `search_text ~ "bosch grinder"` matches both rows
 *            where brand="BOSCH" AND rows where a synonym contains
 *            "grinder". This is the "M20 X 50 BOLTS or BOSCH GRINDER
 *            still finds something" tier — it's broad, so we cap
 *            it tighter than the SKU tiers AND only surface it
 *            through the picker modal (the auto-fill rule still
 *            requires Tier 1+2 because Tier 3 is high-risk on
 *            common words).
 *
 * @param rawInput  The buyer's SKU string. May be empty.
 * @param options   `{ preferNewest, limit, enableTier3 }`.
 *                  `enableTier3` defaults to true — the picker
 *                  needs it. Pass false from the bulk "Check
 *                  pricing" path so a fuzzy hit on "BOSCH" doesn't
 *                  auto-populate 10 unrelated rows.
 * @param pb        Optional PocketBase instance.
 */
export async function findPriceListBySku(
  rawInput: string,
  options: FindPriceListBySkuOptions = {},
  pb?: PocketBase,
): Promise<PriceListMatch[]> {
  const client = pb ?? (await getAdminPocketBase());
  const raw = (rawInput ?? "").trim();
  if (!raw) return [];
  const normalised = normaliseSku(raw);
  if (!normalised) return [];

  const limit = Math.max(1, Math.min(200, options.limit ?? 25));
  const preferNewest = options.preferNewest ?? true;
  const enableTier3 = options.enableTier3 ?? true;

  // Tier 1 — exact equality on both raw and canonical forms. We
  // OR-chain (PB 0.26 has no `IN`) and ask for `-updated` so the
  // newest match comes back first; tier 2 below is only consulted
  // when this tier yields zero hits.
  const tier1Filter = `sku = "${escapeForPbString(raw)}" || sku_normalised = "${escapeForPbString(normalised)}"`;
  const tier1 = await client.collection("price_list").getList<PriceListMatch>(1, limit, {
    filter: tier1Filter,
    sort: preferNewest ? "-updated" : "sku",
    fields:
      "id,sku,description,cost_price,selling_price,unit,supplier,brand,category,subcategory,sku_normalised,updated",
  });
  if (tier1.items.length > 0) return tier1.items;

  // Tier 2 — substring fallback on the canonical form (catches
  // "JEITD" matching "JEITD-06-EXTRA", and partial-prefix hits
  // like the buyer typing "TS-12" against a catalogue "TS-12-55").
  const tier2Filter = `(sku_normalised ~ "${escapeForPbString(normalised)}" || sku ~ "${escapeForPbString(raw)}")`;
  const tier2 = await client.collection("price_list").getList<PriceListMatch>(1, limit, {
    filter: tier2Filter,
    sort: preferNewest ? "-updated" : "sku",
    fields:
      "id,sku,description,cost_price,selling_price,unit,supplier,brand,category,subcategory,sku_normalised,updated",
  });
  if (tier2.items.length > 0) return tier2.items;

  // Tier 3 — fuzzy `search_text`. Catches description / brand /
  // category / synonyms matches that have no SKU overlap at all,
  // e.g. "BOSCH GRINDER" or "M20 X 50 BOLTS" — neither text has
  // a SKU substring, but the rows contain those tokens in their
  // description / brand fields.
  if (!enableTier3) return [];
  // Tighten the cap so a noisy input ("BOLT") doesn't return
  // thousands of rows. 10 candidates is plenty for the picker
  // modal to feel useful.
  const tier3 = await client.collection("price_list").getList<PriceListMatch>(1, 10, {
    filter: `search_text ~ "${escapeForPbString(raw)}"`,
    sort: preferNewest ? "-updated" : "sku",
    fields:
      "id,sku,description,cost_price,selling_price,unit,supplier,brand,category,subcategory,sku_normalised,updated,specifications,search_text",
  });
  return tier3.items;
}

/**
 * Per-tier label for a match. Used by the picker modal to badge
 * each candidate with how it was found. The numeric tier is what
 * the auto-fill rule uses; the label is for the operator's eyes
 * only.
 */
export function matchTierLabel(tier: 1 | 2 | 3): string {
  switch (tier) {
    case 1:
      return "Exact SKU";
    case 2:
      return "SKU substring";
    case 3:
      return "Description / brand match";
  }
}

/**
 * Compute the tier (1, 2, or 3) that produced a match for a given
 * input. The endpoint uses this to decide whether to auto-fill
 * (`tier <= 2`) or show the picker (`tier === 3`).
 *
 * Cheap and pure — does not call PB.
 */
export function classifyMatch(
  rawInput: string,
  match: Pick<PriceListMatch, "sku" | "sku_normalised">,
): 1 | 2 | 3 {
  const raw = rawInput.trim();
  const normalised = normaliseSku(raw);
  if (
    match.sku === raw ||
    (normalised && match.sku_normalised === normalised)
  ) {
    return 1;
  }
  if (
    (normalised && match.sku_normalised.includes(normalised)) ||
    (raw && match.sku.includes(raw))
  ) {
    return 2;
  }
  return 3;
}

/**
 * Build a short human-readable explanation of why this catalogue
 * row matched the input. Rule-based today (no LLM call) — runs in
 * <1ms per candidate so the picker modal renders synchronously
 * and feels snappy. Designed so an LLM explainer can replace it
 * in one swap: the picker renders whatever string this returns,
 * so a future `llmExplainMatch()` can be called instead and its
 * output dropped in. Once we have a workflow (an n8n hook or a
 * direct model call) that runs in <500ms reliably, the modal
 * shows the rule-based line immediately and replaces it when the
 * LLM returns — instant fill, enriched reading.
 *
 * @param rawInput  The buyer's SKU / description / brand / etc.
 * @param match     The catalogue row we matched against.
 * @returns         One short sentence (≤120 chars) explaining the
 *                  match in the operator's voice.
 */
export function explainMatch(
  rawInput: string,
  match: PriceListMatch,
): string {
  const tier = classifyMatch(rawInput, match);
  const raw = rawInput.trim();
  const inputLower = raw.toLowerCase();
  const inputWords = inputLower.split(/\s+/).filter((w) => w.length >= 2);

  const bits: string[] = [];

  // Always anchor on the row's headline identifier.
  bits.push(match.sku);

  // Tier 1 & 2 — explain the SKU dimension.
  if (tier === 1) {
    bits.push("exact SKU match");
  } else if (tier === 2) {
    bits.push("SKU substring");
  }

  // Tier 3 — explain the description / brand / spec hits. We
  // surface what concretely matched so the operator can scan
  // 5 candidates and pick fast.
  if (tier === 3) {
    const detailBits: string[] = [];
    if (match.brand && inputWords.some((w) => match.brand!.toLowerCase().includes(w))) {
      detailBits.push(`brand: ${match.brand}`);
    }
    if (match.category && inputWords.some((w) => match.category!.toLowerCase().includes(w))) {
      detailBits.push(`category: ${match.category}`);
    }
    if (match.supplier && inputWords.some((w) => match.supplier!.toLowerCase().includes(w))) {
      detailBits.push(`supplier: ${match.supplier}`);
    }
    if (match.description) {
      const descLower = match.description.toLowerCase();
      const matchedWords = inputWords.filter((w) => descLower.includes(w));
      if (matchedWords.length > 0) {
        detailBits.push(`description matches "${matchedWords.slice(0, 3).join(", ")}"`);
      }
    }
    // Spec keys & values. `search_text` flattens everything in
    // `specifications` into one blob, so a substring hit on
    // `material` showing in the spec means there was a hit.
    if (match.specifications && typeof match.specifications === "object") {
      for (const [k, v] of Object.entries(match.specifications)) {
        if (typeof v === "string" && inputWords.some((w) => v.toLowerCase().includes(w))) {
          detailBits.push(`${k}: ${v}`);
          break; // one spec fact per line is enough noise-wise
        }
        if (Array.isArray(v) && v.some((sv) => typeof sv === "string" && inputWords.some((w) => sv.toLowerCase().includes(w)))) {
          detailBits.push(`synonym matches "${k}"`);
          break;
        }
      }
    }
    if (detailBits.length === 0) {
      // Generic fallback so we never render an empty explanation.
      detailBits.push(`"${raw}" found in catalogue text`);
    }
    bits.push(detailBits.join("; "));
  }

  // Closing hint for the supplier so the operator knows where
  // the price comes from without needing a second lookup.
  if (match.supplier) {
    bits.push(`from ${match.supplier}`);
  }

  return bits.slice(0, 4).join(" — ").slice(0, 240);
}

/** Quick "did we match anything" helper. Useful in UI code that
 *  only needs a yes/no/which-row. */
export async function findFirstPriceListBySku(
  rawInput: string,
  options?: FindPriceListBySkuOptions,
  pb?: PocketBase,
): Promise<PriceListMatch | null> {
  const matches = await findPriceListBySku(rawInput, options, pb);
  return matches[0] ?? null;
}