'use strict';

const crypto = require('crypto');
const { getDb } = require('../db/database');
const { decorateTransaction, ensureManualDataSource } = require('./transactionService');

const SESSION_TTL_MS = 24 * 60 * 60 * 1000;
const MAX_ROWS = 25000;
const SAMPLE_SIZE = 10;

const FIELD_LABELS = {
  posted_date: 'Posted date',
  transacted_at: 'Transaction date/time',
  amount: 'Amount',
  debit_amount: 'Debit amount',
  credit_amount: 'Credit amount',
  description: 'Description',
  payee: 'Payee',
  memo: 'Memo',
  category: 'Category',
  account: 'Account',
  transaction_id: 'Transaction ID',
  transaction_type: 'Transaction type',
  currency: 'Currency',
};

function importError(status, message, code, details = []) {
  const err = new Error(message);
  err.status = status;
  err.code = code;
  err.details = details;
  return err;
}

function makeSessionId() {
  return crypto.randomBytes(16).toString('hex');
}

function cleanFilename(value) {
  return value
    ? String(value).replace(/[^a-zA-Z0-9._\-\s]/g, '').trim().slice(0, 255)
    : null;
}

function normalizeHeader(value, index) {
  const text = String(value ?? '').trim();
  return text || `Column ${index + 1}`;
}

function parseCsv(text) {
  const rows = [];
  let row = [];
  let cell = '';
  let inQuotes = false;

  for (let i = 0; i < text.length; i++) {
    const ch = text[i];
    const next = text[i + 1];

    if (inQuotes) {
      if (ch === '"' && next === '"') {
        cell += '"';
        i++;
      } else if (ch === '"') {
        inQuotes = false;
      } else {
        cell += ch;
      }
      continue;
    }

    if (ch === '"') {
      inQuotes = true;
    } else if (ch === ',') {
      row.push(cell);
      cell = '';
    } else if (ch === '\n') {
      row.push(cell);
      rows.push(row);
      row = [];
      cell = '';
    } else if (ch === '\r') {
      if (next === '\n') continue;
      row.push(cell);
      rows.push(row);
      row = [];
      cell = '';
    } else {
      cell += ch;
    }
  }

  if (inQuotes) {
    throw importError(400, 'CSV has an unterminated quoted field.', 'CSV_PARSE_ERROR');
  }
  if (cell !== '' || row.length > 0) {
    row.push(cell);
    rows.push(row);
  }

  return rows.filter(r => r.some(c => String(c ?? '').trim() !== ''));
}

function csvBufferToText(buffer) {
  if (!Buffer.isBuffer(buffer) || buffer.length === 0) {
    throw importError(400, 'CSV file is required.', 'CSV_REQUIRED');
  }
  return buffer.toString('utf8').replace(/^\uFEFF/, '');
}

function rowToObject(headers, row) {
  const out = {};
  headers.forEach((header, index) => {
    out[header] = String(row[index] ?? '').trim();
  });
  return out;
}

function normalizeHeaderToken(value) {
  return String(value || '').toLowerCase().replace(/[^a-z0-9]+/g, ' ').trim();
}

function headerMatches(header, patterns) {
  const token = normalizeHeaderToken(header);
  return patterns.some(pattern => (
    pattern instanceof RegExp ? pattern.test(token) : token === pattern
  ));
}

function suggestMapping(headers) {
  const mapping = {};
  const candidates = [
    ['posted_date', [/^date$/, 'posted date', 'post date', 'posting date', 'transaction date', 'trans date']],
    ['transacted_at', ['authorized date', 'authorization date', 'datetime', 'date time', 'timestamp']],
    ['transaction_id', ['transaction id', 'transaction number', 'trans id', 'id', 'fitid', 'reference', 'reference number']],
    ['description', ['description', 'transaction description', 'name', 'details', 'details description']],
    ['payee', ['payee', 'merchant', 'merchant name', 'vendor', 'name']],
    ['memo', ['memo', 'notes', 'note']],
    ['amount', [/^amount$/, 'transaction amount', 'net amount']],
    ['debit_amount', ['debit', 'debits', 'withdrawal', 'withdrawals', 'charge', 'charges']],
    ['credit_amount', ['credit', 'credits', 'deposit', 'deposits']],
    ['category', ['category', 'transaction category']],
    ['account', ['account', 'account name', 'account number']],
    ['transaction_type', ['type', 'transaction type']],
    ['currency', ['currency', 'currency code']],
  ];

  for (const [field, patterns] of candidates) {
    const found = headers.find(header => !Object.values(mapping).includes(header) && headerMatches(header, patterns));
    if (found) mapping[field] = found;
  }

  if (!mapping.payee && mapping.description) {
    const payee = headers.find(header => header !== mapping.description && headerMatches(header, ['name', 'merchant name']));
    if (payee) mapping.payee = payee;
  }

  return mapping;
}

function parseCsvPreview(buffer, options = {}) {
  const text = csvBufferToText(buffer);
  const parsed = parseCsv(text);
  if (parsed.length < 2) {
    throw importError(400, 'CSV must include a header row and at least one data row.', 'CSV_EMPTY');
  }

  const headers = parsed[0].map(normalizeHeader);
  const seenHeaders = new Set();
  const duplicateHeaders = [];
  for (const header of headers) {
    const key = header.toLowerCase();
    if (seenHeaders.has(key)) duplicateHeaders.push(header);
    seenHeaders.add(key);
  }
  if (duplicateHeaders.length > 0) {
    throw importError(400, `CSV contains duplicate headers: ${duplicateHeaders.join(', ')}`, 'CSV_DUPLICATE_HEADERS');
  }

  const dataRows = parsed.slice(1).slice(0, MAX_ROWS).map(row => rowToObject(headers, row));
  const truncated = parsed.length - 1 > MAX_ROWS;
  const suggestedMapping = suggestMapping(headers);
  const errors = [];

  if (!suggestedMapping.posted_date) {
    errors.push({ field: 'posted_date', message: 'Could not detect a posted date column.' });
  }
  if (!suggestedMapping.amount && !(suggestedMapping.debit_amount || suggestedMapping.credit_amount)) {
    errors.push({ field: 'amount', message: 'Could not detect an amount column.' });
  }
  if (!suggestedMapping.description && !suggestedMapping.payee && !suggestedMapping.memo) {
    errors.push({ field: 'description', message: 'No description, payee, or memo column was detected. Dedupe will be less useful.' });
  }
  if (truncated) {
    errors.push({ field: 'file', message: `Only the first ${MAX_ROWS} rows will be imported from this CSV.` });
  }

  return {
    headers,
    rows: dataRows,
    rowCount: dataRows.length,
    sampleRows: dataRows.slice(0, SAMPLE_SIZE),
    suggestedMapping,
    errors,
    original_filename: cleanFilename(options.original_filename),
  };
}

function pruneExpiredSessions(db) {
  db.prepare('DELETE FROM import_sessions WHERE expires_at <= ?').run(new Date().toISOString());
}

function saveImportSession(db, userId, sessionData) {
  const id = makeSessionId();
  const now = new Date().toISOString();
  const expiresAt = new Date(Date.now() + SESSION_TTL_MS).toISOString();
  db.prepare(`
    INSERT INTO import_sessions (id, user_id, created_at, expires_at, preview_json)
    VALUES (?, ?, ?, ?, ?)
  `).run(id, userId, now, expiresAt, JSON.stringify(sessionData));
  return id;
}

function loadImportSession(db, userId, sessionId) {
  const row = db.prepare(`
    SELECT preview_json
    FROM import_sessions
    WHERE id = ? AND user_id = ? AND expires_at > ?
  `).get(sessionId, userId, new Date().toISOString());

  if (!row) {
    throw importError(404, 'CSV import session not found or expired. Please re-upload the file.', 'CSV_SESSION_NOT_FOUND');
  }
  return JSON.parse(row.preview_json);
}

function deleteImportSession(db, sessionId) {
  db.prepare('DELETE FROM import_sessions WHERE id = ?').run(sessionId);
}

function previewCsvTransactions(userId, buffer, options = {}) {
  const db = getDb();
  pruneExpiredSessions(db);
  const preview = parseCsvPreview(buffer, options);
  const sessionId = saveImportSession(db, userId, {
    kind: 'csv_transactions',
    ...preview,
  });

  return {
    import_session_id: sessionId,
    headers: preview.headers,
    sampleRows: preview.sampleRows,
    rowCount: preview.rowCount,
    suggestedMapping: preview.suggestedMapping,
    errors: preview.errors,
    fields: FIELD_LABELS,
  };
}

function headerValue(row, mapping, field) {
  const header = mapping?.[field];
  if (!header) return '';
  return String(row[header] ?? '').trim();
}

function parseDateValue(value, field, rowNumber) {
  const text = String(value || '').trim();
  if (!text) {
    throw importError(400, `${FIELD_LABELS[field] || field} is required`, 'CSV_ROW_VALIDATION', [
      { row: rowNumber, field, message: `${FIELD_LABELS[field] || field} is required` },
    ]);
  }

  const iso = /^(\d{4})-(\d{1,2})-(\d{1,2})/.exec(text);
  if (iso) {
    const normalized = `${iso[1]}-${iso[2].padStart(2, '0')}-${iso[3].padStart(2, '0')}`;
    if (isRealDate(normalized)) return normalized;
  }

  const slash = /^(\d{1,2})\/(\d{1,2})\/(\d{2,4})$/.exec(text);
  if (slash) {
    const year = slash[3].length === 2 ? `20${slash[3]}` : slash[3];
    const normalized = `${year}-${slash[1].padStart(2, '0')}-${slash[2].padStart(2, '0')}`;
    if (isRealDate(normalized)) return normalized;
  }

  throw importError(400, `${FIELD_LABELS[field] || field} must be a valid date`, 'CSV_ROW_VALIDATION', [
    { row: rowNumber, field, value: text, message: `${FIELD_LABELS[field] || field} must be YYYY-MM-DD or MM/DD/YYYY` },
  ]);
}

function isRealDate(value) {
  const [year, month, day] = String(value).split('-').map(Number);
  const date = new Date(Date.UTC(year, month - 1, day));
  return date.getUTCFullYear() === year
    && date.getUTCMonth() === month - 1
    && date.getUTCDate() === day;
}

function parseCents(value, { negative = false } = {}) {
  const text = String(value ?? '').trim();
  if (!text) return null;
  const parenNegative = /^\(.*\)$/.test(text);
  const cleaned = text.replace(/[,$\s]/g, '').replace(/^\((.*)\)$/, '$1');
  if (!/^[+-]?\d+(?:\.\d{1,4})?$/.test(cleaned)) return null;
  const number = Number(cleaned);
  if (!Number.isFinite(number)) return null;
  const explicitNegative = cleaned.startsWith('-') || parenNegative;
  const sign = explicitNegative || negative ? -1 : 1;
  return Math.round(Math.abs(number) * 100) * sign;
}

function parseMappedAmount(row, mapping) {
  const amount = parseCents(headerValue(row, mapping, 'amount'));
  if (amount !== null) return amount;

  const debit = parseCents(headerValue(row, mapping, 'debit_amount'), { negative: true });
  if (debit !== null) return debit;

  const credit = parseCents(headerValue(row, mapping, 'credit_amount'));
  if (credit !== null) return credit;

  return null;
}

function stableHash(parts) {
  return crypto
    .createHash('sha256')
    .update(parts.map(part => String(part || '').trim().toLowerCase()).join('\u001f'))
    .digest('hex')
    .slice(0, 48);
}

function getOrCreateCsvDataSource(db, userId) {
  ensureManualDataSource(db, userId);
  const existing = db.prepare(`
    SELECT *
    FROM data_sources
    WHERE user_id = ? AND type = 'file_import' AND provider = 'csv' AND name = 'CSV Import'
    ORDER BY id ASC
    LIMIT 1
  `).get(userId);
  if (existing) return existing;

  const result = db.prepare(`
    INSERT INTO data_sources (user_id, type, provider, name, status)
    VALUES (?, 'file_import', 'csv', 'CSV Import', 'active')
  `).run(userId);
  return db.prepare('SELECT * FROM data_sources WHERE id = ? AND user_id = ?').get(result.lastInsertRowid, userId);
}

function getOrCreateAccount(db, userId, dataSourceId, name) {
  const accountName = String(name || '').trim();
  if (!accountName) return null;
  const providerAccountId = stableHash([accountName]).slice(0, 32);
  const existing = db.prepare(`
    SELECT *
    FROM financial_accounts
    WHERE user_id = ? AND data_source_id = ? AND provider_account_id = ?
  `).get(userId, dataSourceId, providerAccountId);
  if (existing) return existing;

  const result = db.prepare(`
    INSERT INTO financial_accounts
      (user_id, data_source_id, provider_account_id, name, account_type, currency)
    VALUES (?, ?, ?, ?, 'csv', 'USD')
  `).run(userId, dataSourceId, providerAccountId, accountName);
  return db.prepare('SELECT * FROM financial_accounts WHERE id = ? AND user_id = ?').get(result.lastInsertRowid, userId);
}

function validateMapping(headers, mapping = {}) {
  const headerSet = new Set(headers);
  const required = [];
  if (!mapping.posted_date) required.push('posted_date');
  if (!mapping.amount && !(mapping.debit_amount || mapping.credit_amount)) required.push('amount');
  if (required.length) {
    throw importError(400, `Missing required mapping: ${required.map(f => FIELD_LABELS[f] || f).join(', ')}`, 'CSV_MAPPING_REQUIRED');
  }

  for (const [field, header] of Object.entries(mapping)) {
    if (!FIELD_LABELS[field]) {
      throw importError(400, `Unsupported mapping field: ${field}`, 'CSV_MAPPING_INVALID');
    }
    if (header && !headerSet.has(header)) {
      throw importError(400, `Mapped column "${header}" for ${field} was not found in the CSV headers.`, 'CSV_MAPPING_INVALID');
    }
  }
}

function parseOptionalDateTimeValue(value, field, rowNumber) {
  const text = String(value || '').trim();
  if (!text) return null;

  const match = /^(\d{4}-\d{2}-\d{2})(?:[T ]\d{2}:\d{2}(?::\d{2}(?:\.\d{1,9})?)?(?:Z|[+-]\d{2}:?\d{2})?)?$/.exec(text);
  if (!match || !isRealDate(match[1])) {
    throw importError(400, `${FIELD_LABELS[field] || field} must be a valid ISO date or date-time`, 'CSV_ROW_VALIDATION', [
      { row: rowNumber, field, value: text, message: `${FIELD_LABELS[field] || field} must be YYYY-MM-DD or an ISO date-time` },
    ]);
  }
  return text;
}

function normalizeCsvTransaction(row, mapping, rowNumber) {
  const postedDate = parseDateValue(headerValue(row, mapping, 'posted_date'), 'posted_date', rowNumber);
  const transactedAt = parseOptionalDateTimeValue(headerValue(row, mapping, 'transacted_at'), 'transacted_at', rowNumber);
  const amount = parseMappedAmount(row, mapping);
  if (!Number.isSafeInteger(amount) || amount === 0) {
    throw importError(400, 'Amount must be a non-zero number.', 'CSV_ROW_VALIDATION', [
      { row: rowNumber, field: 'amount', message: 'Amount must be a non-zero number.' },
    ]);
  }

  const description = headerValue(row, mapping, 'description');
  const payee = headerValue(row, mapping, 'payee');
  const memo = headerValue(row, mapping, 'memo');
  const accountName = headerValue(row, mapping, 'account');
  const transactionId = headerValue(row, mapping, 'transaction_id');
  const providerTransactionId = transactionId
    ? `csv:id:${transactionId}`
    : `csv:hash:${stableHash([postedDate, amount, description, payee, accountName])}`;

  return {
    provider_transaction_id: providerTransactionId,
    transaction_type: headerValue(row, mapping, 'transaction_type') || null,
    posted_date: postedDate,
    transacted_at: transactedAt,
    amount,
    currency: headerValue(row, mapping, 'currency') || 'USD',
    description: description || payee || memo || null,
    payee: payee || null,
    memo: memo || null,
    category: headerValue(row, mapping, 'category') || null,
    account_name: accountName || null,
    raw_data: JSON.stringify(row),
  };
}

function commitCsvTransactions(userId, importSessionId, mapping, options = {}) {
  const db = getDb();
  const session = loadImportSession(db, userId, importSessionId);
  if (session.kind !== 'csv_transactions') {
    throw importError(400, 'Import session is not a CSV transaction preview.', 'CSV_SESSION_INVALID');
  }

  validateMapping(session.headers, mapping);
  const dataSource = getOrCreateCsvDataSource(db, userId);
  const details = [];
  const counts = { imported: 0, skipped: 0, failed: 0 };
  const insert = db.prepare(`
    INSERT INTO transactions
      (user_id, data_source_id, account_id, provider_transaction_id, source_type,
       transaction_type, posted_date, transacted_at, amount, currency, description,
       payee, memo, category, raw_data, match_status, ignored)
    VALUES (?, ?, ?, ?, 'file_import', ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, 'unmatched', 0)
  `);
  const existing = db.prepare(`
    SELECT id
    FROM transactions
    WHERE user_id = ? AND data_source_id = ? AND provider_transaction_id = ?
  `);

  const run = db.transaction(() => {
    session.rows.forEach((row, index) => {
      const rowNumber = index + 2;
      try {
        const tx = normalizeCsvTransaction(row, mapping, rowNumber);
        if (existing.get(userId, dataSource.id, tx.provider_transaction_id)) {
          counts.skipped++;
          details.push({ row: rowNumber, result: 'skipped_duplicate', provider_transaction_id: tx.provider_transaction_id });
          return;
        }

        const account = getOrCreateAccount(db, userId, dataSource.id, tx.account_name);
        const result = insert.run(
          userId,
          dataSource.id,
          account?.id ?? null,
          tx.provider_transaction_id,
          tx.transaction_type,
          tx.posted_date,
          tx.transacted_at,
          tx.amount,
          tx.currency,
          tx.description,
          tx.payee,
          tx.memo,
          tx.category,
          tx.raw_data,
        );
        counts.imported++;
        details.push({
          row: rowNumber,
          result: 'imported',
          transaction: decorateTransaction({
            ...tx,
            id: result.lastInsertRowid,
            user_id: userId,
            data_source_id: dataSource.id,
            source_type: 'file_import',
            data_source_type: dataSource.type,
            data_source_provider: dataSource.provider,
            data_source_name: dataSource.name,
            data_source_status: dataSource.status,
            account_id: account?.id ?? null,
            account_name: account?.name ?? null,
            match_status: 'unmatched',
            ignored: 0,
          }),
        });
      } catch (err) {
        counts.failed++;
        details.push({ row: rowNumber, result: 'failed', message: err.message, details: err.details || [] });
      }
    });

    db.prepare(`
      INSERT INTO import_history (
        user_id, imported_at, source_filename, file_type, sheet_name,
        rows_parsed, rows_created, rows_updated, rows_skipped, rows_ambiguous,
        rows_errored, options_json, summary_json
      ) VALUES (?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?, ?)
    `).run(
      userId,
      new Date().toISOString(),
      session.original_filename,
      'csv_transactions',
      null,
      session.rows.length,
      counts.imported,
      0,
      counts.skipped,
      0,
      counts.failed,
      JSON.stringify({ mapping, options }),
      JSON.stringify(details.slice(0, 500)),
    );
  });

  run();
  deleteImportSession(db, importSessionId);

  return {
    success: true,
    imported: counts.imported,
    skipped: counts.skipped,
    failed: counts.failed,
    details,
  };
}

module.exports = {
  FIELD_LABELS,
  commitCsvTransactions,
  previewCsvTransactions,
};