import { queryRaw, queryRow } from "@/lib/db";
import { DEFAULT_OWNER_ID } from "@/lib/order-ingestion";

/**
 * Grocery receipts scanned in pantry-app, arriving as candidate spend.
 *
 * The shape deliberately mirrors the order lane rather than inventing a second mechanism,
 * but it makes one decision differently and the difference is the point: **nothing is
 * parked.** An order can wait for its statement because it is already visible as an email;
 * a gift-card grocery shop is visible nowhere at all, so a scan that does not produce a
 * transaction produces nothing a person can see. Every leg becomes a manual transaction
 * (`statement_id IS NULL`) immediately, and finance's existing pending-reconciliation queue
 * resolves the ones that have a card leg coming.
 *
 * Why one transaction per tender leg rather than one per receipt: a shop settled $40.75 on
 * a gift card and $73.82 on a Mastercard has a statement line for $73.82 and nothing for
 * the rest. A single $114.57 row marked `credits` is excluded from the queue and lets the
 * statement line double-count; marked `card` it is searched for at ±1% of $114.57 and never
 * matches, so it parks forever while the statement line still counts. Either way the shop
 * books $188.39. Per-leg rows make each amount exactly the settled amount, so the existing
 * matcher works untouched.
 */

export type TenderLeg = {
  leg_index: number;
  amount: number;
  card_last4?: string | null;
  card_product?: string | null;
  /** pantry's vocabulary; mapped to finance's payment_method below. */
  class?: "card" | "gift_card" | "cash" | null;
};

/**
 * Same keys the order lane uses, because the panel that renders an itemised receipt reads
 * `qty`/`description`/`amount` and a grocery shop is a receipt like any other. `unit` and
 * `category` are the two things a grocery line has and a delivery line does not; nothing
 * renders them yet, and the intra-transaction category composition will.
 */
export type ReceiptLineItem = {
  description: string;
  qty?: number | null;
  amount?: number | null;
  unit?: string | null;
  category?: string | null;
};

export type ParsedReceipt = {
  receipt_uid?: string | null;
  capture_event_id: number;
  image_sha256?: string | null;
  merchant_name: string;
  store_detail?: string | null;
  transaction_date: string;
  total: number;
  tax_amount?: number | null;
  tender_raw?: string | null;
  loyalty_card_number?: string | null;
  tender_legs: TenderLeg[];
  line_items: ReceiptLineItem[];
};

export type ReceiptIngestResult = {
  group: string;
  legs: { leg_index: number; transactionId: number; metadataId: number; paymentMethod: string | null; skipped?: string }[];
  flags: string[];
};

export class ReceiptValidationError extends Error {}

/**
 * `credits` rather than a new `gift_card`: prepaid value with no card leg is a concept
 * finance already has, and reusing it inherits both the `needsCardMatch()` exclusion that
 * keeps such rows out of the reconciliation queue and the "Gift Card" label `bankLabel()`
 * renders for them. A second word for one idea would have needed both taught again.
 *
 * An unknown class maps to NULL, which `needsCardMatch()` treats as reconcilable — so a leg
 * nobody could classify lands in the queue visibly unresolved instead of being silently
 * decided either way.
 */
function paymentMethodFor(legClass: TenderLeg["class"]): string | null {
  if (legClass === "gift_card") return "credits";
  if (legClass === "cash") return "cash";
  if (legClass === "card") return "card";
  return null;
}

const round2 = (value: number) => Number(value.toFixed(2));

/**
 * The whole shop is `groceries`. What it was actually made of — food versus household —
 * stays derived from `line_items` at display time rather than stored, because a mixed shop
 * is one payment and splitting the transaction to describe it would make the amount that
 * reconciles against the statement line stop matching it.
 */
const RECEIPT_CATEGORY = "groceries";

export function validateReceipt(receipt: ParsedReceipt): string[] {
  const flags: string[] = [];
  if (!receipt.tender_legs?.length) throw new ReceiptValidationError("at least one tender leg is required");
  if (!Number.isFinite(receipt.total) || receipt.total <= 0) throw new ReceiptValidationError("total must be a positive number");
  if (!/^\d{4}-\d{2}-\d{2}$/.test(receipt.transaction_date)) throw new ReceiptValidationError("transaction_date must be YYYY-MM-DD");

  // The check that detects a split at all, and the one that proves the payment side was
  // read whole. A leg missed here becomes spend that never appears.
  const legSum = round2(receipt.tender_legs.reduce((total, leg) => total + Number(leg.amount || 0), 0));
  if (Math.abs(legSum - round2(receipt.total)) > 0.02) {
    throw new ReceiptValidationError(`tender legs sum to ${legSum.toFixed(2)} but the receipt total is ${receipt.total.toFixed(2)}`);
  }

  // Lines are allowed to disagree: promotional rows are deliberately skipped during
  // extraction, so this flags rather than rejects. The money is the tender, not the lines.
  const lineSum = round2((receipt.line_items ?? []).reduce((total, line) => total + Number(line.amount || 0), 0));
  if (receipt.line_items?.length && Math.abs(lineSum - round2(receipt.total)) > 0.02) flags.push(`line_items_sum_${lineSum.toFixed(2)}`);
  if (receipt.tender_legs.length > 1) flags.push("split_tender");
  if (receipt.tender_legs.some((leg) => !leg.class)) flags.push("unclassified_tender");
  return flags;
}

/**
 * The receipt's own identity, not the capture's. A photo and the store's e-receipt PDF of
 * one purchase are different files with different hashes, so keying on the capture would
 * let the same shop arrive twice as two unrelated sets of transactions. Falls back to the
 * capture id when the receipt did not print enough to identify itself — that risks a
 * duplicate, which is visible and removable, rather than a merge, which silently hides a
 * real shop.
 */
export function receiptGroup(receipt: ParsedReceipt): string {
  return `pantry:${receipt.receipt_uid || `capture:${receipt.capture_event_id}`}`;
}

export async function processReceiptIngestion(receipt: ParsedReceipt): Promise<ReceiptIngestResult> {
  const flags = validateReceipt(receipt);
  const group = receiptGroup(receipt);
  // Line items describe the whole shop but can only attach to one row —
  // expense_metadata.transaction_id is UNIQUE, and duplicating them would double any
  // composition derived from them. They go on the card leg because that is the row which
  // reconciles onto the statement line, which is where an unreadable `COLES 0556` descriptor
  // actually gets its contents. With no card leg, the largest leg carries them.
  const cardLeg = receipt.tender_legs.find((leg) => leg.class === "card" || !leg.class)
    ?? [...receipt.tender_legs].sort((a, b) => Number(b.amount) - Number(a.amount))[0];

  const legs: ReceiptIngestResult["legs"] = [];
  for (const leg of receipt.tender_legs) {
    const reference = `${group}#${leg.leg_index}`;
    const existing = await queryRow<{ id: number; transaction_id: number | null }>(
      `SELECT id, transaction_id FROM expense_metadata WHERE source = 'pantry' AND order_reference = $1`,
      [reference]
    );
    if (existing) {
      legs.push({ leg_index: leg.leg_index, transactionId: existing.transaction_id ?? 0, metadataId: existing.id, paymentMethod: null, skipped: "already_ingested" });
      continue;
    }

    const paymentMethod = paymentMethodFor(leg.class);
    const amount = round2(Number(leg.amount));
    const description = receipt.store_detail ? `${receipt.merchant_name} ${receipt.store_detail}` : receipt.merchant_name;
    const txn = await queryRow<{ id: number }>(
      `INSERT INTO transactions (
         transaction_date, description, amount, amount_aud, category, payment_method,
         merchant_name, merchant_normalized, transaction_type, owner_id
       ) VALUES ($1,$2,$3,$3,$4,$5,$6,$6,'debit',$7) RETURNING id`,
      [receipt.transaction_date, description, amount, RECEIPT_CATEGORY, paymentMethod, receipt.merchant_name, DEFAULT_OWNER_ID]
    );

    const carriesLines = leg.leg_index === cardLeg?.leg_index;
    const meta = await queryRow<{ id: number }>(
      `INSERT INTO expense_metadata (
         transaction_id, source, order_reference, line_items, subtotal, amount,
         merchant_normalized, transaction_date, card_last4, currency, flags,
         reconciled_at, payment_method, payment_method_detail, tender_raw,
         receipt_sha256, receipt_group, extraction_model
       ) VALUES ($1,'pantry',$2,$3::jsonb,$4,$5,$6,$7,$8,'AUD',$9::jsonb,NULL,$10,$11,$12,$13,$14,'cloud-budget')
       RETURNING id`,
      [
        txn!.id,
        reference,
        JSON.stringify(carriesLines ? receipt.line_items ?? [] : []),
        receipt.tax_amount ?? null,
        amount,
        receipt.merchant_name,
        receipt.transaction_date,
        leg.card_last4 ?? null,
        JSON.stringify(carriesLines ? flags : [...flags, "line_items_on_card_leg"]),
        paymentMethod,
        leg.card_product ?? null,
        receipt.tender_raw ?? null,
        receipt.image_sha256 ?? null,
        group,
      ]
    );
    legs.push({ leg_index: leg.leg_index, transactionId: txn!.id, metadataId: meta!.id, paymentMethod });
  }
  return { group, legs, flags };
}

/**
 * Statement lines that look like a pantry row already marked as needing no card leg.
 *
 * Such rows never enter the reconciliation queue — that is the whole point of classifying
 * them — so a mis-learned card would otherwise double-count in silence. This only flags: the
 * same uncertainty that makes the classification fallible makes the match a suggestion, and
 * auto-reconciling on it would trade a visible error for an invisible one. A confirmed
 * conflict is a reason to correct the card's stored class, which fixes every later receipt
 * from it at once.
 */
export async function pantryTenderConflicts(): Promise<{ transactionId: number; statementTransactionId: number; amount: string; merchant: string | null; date: string }[]> {
  return queryRaw(
    `SELECT p.id AS "transactionId", s.id AS "statementTransactionId", p.amount::text AS amount,
            p.merchant_normalized AS merchant, p.transaction_date::text AS date
       FROM transactions p
       JOIN expense_metadata em ON em.transaction_id = p.id AND em.source = 'pantry'
       JOIN transactions s ON s.statement_id IS NOT NULL
        AND s.transaction_date BETWEEN p.transaction_date - 3 AND p.transaction_date + 3
        AND s.amount BETWEEN p.amount * 0.99 AND p.amount * 1.01
        AND upper(coalesce(s.description, '')) LIKE '%' || upper(p.merchant_name) || '%'
      WHERE p.statement_id IS NULL
        AND p.reconciled_with_id IS NULL
        AND p.payment_method IN ('cash', 'credits')
      ORDER BY p.transaction_date DESC`
  );
}