/**
 * Expense duplicate detection — heuristic match on
 * (port + vendor + amount + date ± 3d). PR1 ships the function shape;
 * PR8 wires the BullMQ trigger and the merge service.
 */

import { and, between, eq, ne, sql } from 'drizzle-orm';

import { db } from '@/lib/db';
import { expenses } from '@/lib/db/schema/financial';

const DEDUP_WINDOW_DAYS = 3;

export interface DedupCandidate {
  /** Existing expense that the new one likely duplicates. */
  candidateId: string;
  /** 0..1 confidence; 1.0 = exact vendor + amount + same day. */
  confidence: number;
}

export async function scanForDuplicates(expenseId: string): Promise<DedupCandidate[]> {
  const target = await db.query.expenses.findFirst({ where: eq(expenses.id, expenseId) });
  if (!target) return [];

  const { portId, establishmentName, amount, expenseDate } = target;
  if (!establishmentName || !amount || !expenseDate) return [];

  const lo = new Date(expenseDate);
  lo.setDate(lo.getDate() - DEDUP_WINDOW_DAYS);
  const hi = new Date(expenseDate);
  hi.setDate(hi.getDate() + DEDUP_WINDOW_DAYS);

  const matches = await db.query.expenses.findMany({
    where: and(
      eq(expenses.portId, portId),
      sql`lower(${expenses.establishmentName}) = lower(${establishmentName})`,
      eq(expenses.amount, amount),
      between(expenses.expenseDate, lo, hi),
      ne(expenses.id, expenseId),
    ),
    limit: 5,
  });

  return matches.map((m) => ({
    candidateId: m.id,
    confidence: dayDiff(m.expenseDate, expenseDate) === 0 ? 1.0 : 0.85,
  }));
}

function dayDiff(a: Date, b: Date): number {
  const ms = Math.abs(a.getTime() - b.getTime());
  return Math.round(ms / 86_400_000);
}

/** Mark an expense as a duplicate of the candidate with the highest score. */
export async function markBestDuplicate(expenseId: string): Promise<string | null> {
  const candidates = await scanForDuplicates(expenseId);
  if (candidates.length === 0) {
    await db
      .update(expenses)
      .set({ dedupScannedAt: sql`now()` })
      .where(eq(expenses.id, expenseId));
    return null;
  }
  const best = candidates.reduce((a, b) => (a.confidence >= b.confidence ? a : b));
  await db
    .update(expenses)
    .set({ duplicateOf: best.candidateId, dedupScannedAt: sql`now()` })
    .where(eq(expenses.id, expenseId));
  return best.candidateId;
}

/**
 * Clear the duplicate flag — operator confirmed this is a real expense.
 * Leaves `dedupScannedAt` populated so the engine doesn't re-flag it.
 */
export async function clearDuplicate(expenseId: string, portId: string): Promise<void> {
  await db
    .update(expenses)
    .set({ duplicateOf: null, dedupScannedAt: sql`now()` })
    .where(and(eq(expenses.id, expenseId), eq(expenses.portId, portId)));
}

/**
 * Merge `sourceId` into `targetId`: combine receipt files, archive the
 * source, and clear the duplicate-of pointer. Both rows must belong to
 * the same port; runs inside a single transaction so a partial failure
 * leaves both rows untouched.
 */
export async function mergeDuplicate(
  sourceId: string,
  targetId: string,
  portId: string,
): Promise<void> {
  if (sourceId === targetId) {
    throw new Error('Cannot merge an expense into itself');
  }

  await db.transaction(async (tx) => {
    const [source] = await tx
      .select()
      .from(expenses)
      .where(and(eq(expenses.id, sourceId), eq(expenses.portId, portId)));
    const [target] = await tx
      .select()
      .from(expenses)
      .where(and(eq(expenses.id, targetId), eq(expenses.portId, portId)));
    if (!source || !target) {
      throw new Error('Source or target expense not found in this port');
    }

    const mergedReceipts = Array.from(
      new Set([...(target.receiptFileIds ?? []), ...(source.receiptFileIds ?? [])]),
    );

    await tx
      .update(expenses)
      .set({ receiptFileIds: mergedReceipts })
      .where(eq(expenses.id, targetId));

    // Archive the source — preserves audit history, keeps any FKs alive.
    await tx
      .update(expenses)
      .set({ archivedAt: sql`now()`, duplicateOf: null })
      .where(eq(expenses.id, sourceId));
  });
}