'use strict';
const express   = require('express');
const router    = express.Router();
const https     = require('https');
const axios     = require('axios');
const FormData  = require('form-data');
const { verifyToken } = require('../middleware/auth');
const { getPool }     = require('../services/sqlPool');

const httpsAgent = new https.Agent({ rejectUnauthorized: false });

// ── TCS GSP config ────────────────────────────────────────────────────────
const CFG = {
  M2JW: {
    mappingCd:  process.env.ITC04_M2JW_MAPPING_CD  || 'MFHGSTTN0000880',
    templateCd: process.env.ITC04_M2JW_TEMPLATE_CD || 'ITC04M2JWTemplate880',
  },
  JW2M: {
    mappingCd:  process.env.ITC04_JW2M_MAPPING_CD  || 'MFHGSTTN0000881',
    templateCd: process.env.ITC04_JW2M_TEMPLATE_CD || 'ITC04JW2MTemplate881',
  },
};

// DB column name → CSV header name mapping
// (desc is a SQL reserved word; SQL returns it as desc_field, CSV header must be desc)
const COL_MAP = [
  ['trans_type_code','trans_type_code'],
  ['fp',            'fp'],
  ['ack_sr_no',     'ack_sr_no'],
  ['self_gstin',    'self_gstin'],
  ['resultflag',    'resultflag'],
  ['ctin',          'ctin'],
  ['ctin_name',     'ctin_name'],
  ['jw_stcd',       'jw_stcd'],
  ['chnum',         'chnum'],
  ['chdt',          'chdt'],
  ['goods_ty',      'goods_ty'],
  ['uqc',           'uqc'],
  ['qty',           'qty'],
  ['desc_field',    'desc'],      // SQL alias → TCS CSV header
  ['txval',         'txval'],
  ['tx_i',          'tx_i'],
  ['tx_c',          'tx_c'],
  ['tx_s',          'tx_s'],
  ['tx_cs',         'tx_cs'],
];
const COLS = COL_MAP.map(([db]) => db);

// ── Quarter period helpers ─────────────────────────────────────────────────
// SQL generates fp as MMYYYY (e.g. 042026 = Q1 Apr-Jun 2026)
// TCS GSP URL requires a different code: 13yyyy / 14yyyy / 15yyyy / 16yyyy
function toTcsPeriod(fp) {
  // fp = 'MMYYYY' e.g. '042026'
  const mm   = parseInt(fp.substring(0, 2), 10);
  const yyyy = fp.substring(2);
  let code;
  if      (mm === 4)  code = '13'; // Q1 Apr-Jun
  else if (mm === 7)  code = '14'; // Q2 Jul-Sep
  else if (mm === 10) code = '15'; // Q3 Oct-Dec
  else if (mm === 1)  code = '16'; // Q4 Jan-Mar
  else                code = '13'; // fallback
  return code + yyyy;              // e.g. '132026'
}

// ── SQL query builders ────────────────────────────────────────────────────
function buildSQL(transType, series, resultflag = 'A') {
  const selfGstin = process.env.TCS_GSP_GSTIN || '06AAACM4564C1ZT';
  const flag      = ['A','M','D'].includes(resultflag) ? resultflag : 'A';
  return `
    SELECT
      '${transType}' AS trans_type_code,
      -- TCS format: Q1=13yyyy, Q2=14yyyy, Q3=15yyyy, Q4=16yyyy
      CAST(
        CASE
          WHEN MONTH(T0.DocDate) BETWEEN 4  AND 6  THEN '13'
          WHEN MONTH(T0.DocDate) BETWEEN 7  AND 9  THEN '14'
          WHEN MONTH(T0.DocDate) BETWEEN 10 AND 12 THEN '15'
          ELSE '16'
        END
        + CAST(
            CASE WHEN MONTH(T0.DocDate) >= 4 THEN YEAR(T0.DocDate)
                 ELSE YEAR(T0.DocDate) - 1
            END AS VARCHAR(4))
      AS VARCHAR(6)) AS fp,
      ROW_NUMBER() OVER (ORDER BY T0.DocEntry, T2.LineNum) AS ack_sr_no,
      '${selfGstin}' AS self_gstin,
      '${flag}'      AS resultflag,
      CASE WHEN CRD1.GSTRegnNo IS NOT NULL AND CRD1.GSTRegnNo <> ''
           THEN CRD1.GSTRegnNo ELSE '' END AS ctin,
      T0.CardName    AS ctin_name,
      CASE WHEN CRD1.GSTRegnNo IS NULL OR CRD1.GSTRegnNo = ''
           THEN T0.U_State ELSE '' END AS jw_stcd,
      CAST(T0.DocNum AS VARCHAR(16)) AS chnum,
      CONVERT(VARCHAR(10), T0.DocDate, 105) AS chdt,
      '8b' AS goods_ty,
      T2.unitMsr AS uqc,
      CAST(T2.Quantity AS DECIMAL(15,2)) AS qty,
      -- Cast to VARCHAR, truncate to 70 chars, fall back to ItemCode if empty
      CAST(LEFT(ISNULL(NULLIF(LTRIM(RTRIM(T2.Dscription)), ''), T2.ItemCode), 70) AS VARCHAR(70)) AS desc_field,
      CAST(T2.LineTotal AS DECIMAL(11,2)) AS txval,
      CAST(ISNULL(T2.U_IGST_Rate1, 0) AS DECIMAL(11,2)) AS tx_i,
      CAST(ISNULL(T2.U_CGST_RATE1, 0) AS DECIMAL(11,2)) AS tx_c,
      CAST(ISNULL(T2.U_SGST_RATE1, 0) AS DECIMAL(11,2)) AS tx_s,
      CAST(0.00 AS DECIMAL(11,2)) AS tx_cs
    FROM OWTR T0
    INNER JOIN WTR1 T2  ON T0.DocEntry = T2.DocEntry
    LEFT  JOIN NNM1 T1  ON T0.Series   = T1.Series
    LEFT  JOIN CRD1
           ON CRD1.CardCode  = T0.CardCode
          AND CRD1.AdresType = 'S'
          AND CRD1.Address   = T0.ShipToCode
    WHERE T0.DocDate BETWEEN @from AND @to
      AND T1.SeriesName LIKE '${series}%'
    ORDER BY T0.DocEntry, T2.LineNum`;
}

// ── Fetch data from SAP ───────────────────────────────────────────────────
async function fetchData(pool, from, to, type, resultflag = 'A') {
  const series = type === 'JW2M' ? 'JWR' : 'JW';
  const sql    = buildSQL(type, series, resultflag);
  const r      = await pool.request()
    .input('from', from)
    .input('to',   to)
    .query(sql);
  return r.recordset || [];
}

// ── Sanitize description for TCS ITC04 ────────────────────────────────────
// TCS CLNDESC validator rejects: & ( ) . and other special chars.
// Allowed: A-Z a-z 0-9 space / - , _ '
function sanitizeDesc(v) {
  return String(v || '')
    .replace(/[\r\n\t]/g, ' ')          // newlines/tabs → space
    .replace(/[^\x20-\x7E]/g, '')       // strip non-ASCII
    .replace(/&/g, 'and')               // & → and
    .replace(/\(/g, ' ')                // ( → space
    .replace(/\)/g, ' ')                // ) → space
    .replace(/\./g, ' ')                // . → space  (TCS rejects decimal points in desc)
    .replace(/[^A-Za-z0-9 /,\-_']/g, ' ')  // strip remaining special chars
    .replace(/\s+/g, ' ')               // collapse multiple spaces
    .trim()
    .substring(0, 50);                  // TCS ITC04 template: max 50 chars
}

// Numeric columns — written as plain numbers, no quotes ever
const NUMERIC_COLS = new Set(['ack_sr_no','qty','txval','tx_i','tx_c','tx_s','tx_cs']);

// ── Build CSV buffer ──────────────────────────────────────────────────────
function buildCsv(rows) {
  const header = COL_MAP.map(([, csvName]) => csvName).join(',');
  const lines  = rows.map(r =>
    COL_MAP.map(([dbCol]) => {
      const raw = r[dbCol] ?? '';

      if (NUMERIC_COLS.has(dbCol)) return raw;  // plain number, no quoting

      const v = dbCol === 'desc_field' ? sanitizeDesc(raw) : String(raw).trim();

      // TCS does not expect RFC-quoted CSV — strip commas instead of quoting
      return v.replace(/,/g, ' ');
    }).join(',')
  );
  return Buffer.from([header, ...lines].join('\r\n'), 'utf8');
}

// ── TCS auth token ────────────────────────────────────────────────────────
async function getTcsToken() {
  const baseUrl  = process.env.TCS_GSP_BASE_URL || 'https://g31.tcsgsp.in';
  const username = process.env.TCS_GSP_USERNAME  || '';
  const password = process.env.TCS_GSP_PASSWORD  || '';
  const resp = await axios.get(
    `${baseUrl}/Tax-Tool-Core/services/accessMgmt/generateToken`,
    { headers: { 'Content-Type': 'application/json', username, password }, httpsAgent }
  );
  const token = resp.data?.access_token || resp.data?.token || resp.data?.accessToken;
  if (!token) throw new Error('TCS token missing: ' + JSON.stringify(resp.data));
  return token;
}

// ── GET /api/itc04/data ───────────────────────────────────────────────────
router.get('/data', verifyToken, async (req, res) => {
  try {
    const { from, to, type = 'M2JW', resultflag = 'A' } = req.query;
    if (!from || !to) return res.status(400).json({ success: false, message: 'from and to dates are required' });
    if (!['M2JW','JW2M'].includes(type)) return res.status(400).json({ success: false, message: 'type must be M2JW or JW2M' });

    const pool = await getPool();
    const rows = await fetchData(pool, from, to, type, resultflag);
    const total = rows.reduce((s, r) => s + (parseFloat(r.txval) || 0), 0);

    res.json({ success: true, data: rows, count: rows.length, totalValue: parseFloat(total.toFixed(2)) });
  } catch (err) {
    res.status(500).json({ success: false, message: err.message });
  }
});

// ── GET /api/itc04/download?from=&to=&type= ───────────────────────────────
router.get('/download', verifyToken, async (req, res) => {
  try {
    const { from, to, type = 'M2JW', resultflag = 'A', period } = req.query;
    if (!from || !to) return res.status(400).json({ success: false, message: 'from and to required' });

    const pool = await getPool();
    const rows = await fetchData(pool, from, to, type, resultflag);
    if (!rows.length) return res.status(404).json({ success: false, message: 'No data found for the selected period' });

    const fp       = period || rows[0]?.fp || 'period';
    const csv      = buildCsv(rows);
    const filename = `ITC04_${type}_${fp}.csv`;

    res.setHeader('Content-Type', 'text/csv');
    res.setHeader('Content-Disposition', `attachment; filename="${filename}"`);
    res.send(csv);
  } catch (err) {
    res.status(500).json({ success: false, message: err.message });
  }
});

// ── POST /api/itc04/upload ────────────────────────────────────────────────
router.post('/upload', verifyToken, async (req, res) => {
  try {
    const { from, to, type = 'M2JW', resultflag = 'A', period } = req.body;
    if (!from || !to) return res.status(400).json({ success: false, message: 'from and to dates are required' });

    const baseUrl    = process.env.TCS_GSP_BASE_URL   || 'https://g31.tcsgsp.in';
    const gstin      = process.env.TCS_GSP_GSTIN       || '';
    const clientCode = process.env.TCS_GSP_CLIENT_CODE || '';
    const cfg        = CFG[type] || CFG.M2JW;

    if (!gstin || !clientCode) return res.status(400).json({ success: false, message: 'TCS_GSP_GSTIN and TCS_GSP_CLIENT_CODE must be set in .env' });

    const pool = await getPool();
    const rows = await fetchData(pool, from, to, type, resultflag);
    if (!rows.length) return res.status(404).json({ success: false, message: 'No data found for the selected period' });

    // Use manually entered period if provided, otherwise derive from data
    const fp    = (period && /^\d{6}$/.test(period)) ? period : (rows[0]?.fp || '132026');
    const csv   = buildCsv(rows);
    const token = await getTcsToken();

    console.log(`[ITC04] fp=${fp}  records=${rows.length}`);

    const form = new FormData();
    form.append('upldGstinLst', `"${gstin}"`);
    form.append('file', csv, { filename: `ITC04_${type}_${fp}.csv`, contentType: 'text/csv' });

    const url = `${baseUrl}/Tax-Tool-Core/services/auth/invoiceUpload/challanUploadITC04CSV/${clientCode}/${cfg.mappingCd}/${cfg.templateCd}/${gstin}/CSV/${fp}?oprFlag=SALES`;

    const uploadResp = await axios.post(url, form, {
      headers: {
        ...form.getHeaders(),
        authorization: `Bearer ${token}`,
        clientCode,
        gstin,
      },
      httpsAgent,
      maxContentLength: Infinity,
      maxBodyLength:    Infinity,
    });

    const d = uploadResp.data;
    console.log('[ITC04] Upload HTTP status:', uploadResp.status);
    console.log('[ITC04] Upload response   :', JSON.stringify(d, null, 2));

    // TCS GSP can return ackNo at root level OR nested inside data/result/response
    function extractAckNo(obj) {
      if (!obj || typeof obj !== 'object') return null;
      const keys = ['ackNo','AckNo','ack_no','ackno','acknowledgeNo','acknowledgementNo','ackNumber'];
      for (const k of keys) {
        if (obj[k] != null && obj[k] !== '') return String(obj[k]);
      }
      // Check one level deeper (data / result / response wrappers)
      for (const wrap of ['data','result','response','Result','Data']) {
        if (obj[wrap] && typeof obj[wrap] === 'object') {
          const nested = extractAckNo(obj[wrap]);
          if (nested) return nested;
        }
      }
      return null;
    }

    const ackNo  = extractAckNo(d);
    const status = d.Status || d.status || d.statusCd || uploadResp.status;
    const msg    = d.Message || d.message || d.msg || 'Upload submitted';

    // Treat statusCd 400 as error
    if (String(status) === '400') {
      return res.status(400).json({ success: false, message: msg, raw: d });
    }

    res.json({ success: true, ackNo, status, message: msg, raw: d });
  } catch (err) {
    const msg = err.response?.data ? JSON.stringify(err.response.data) : err.message;
    console.error('[ITC04] Upload error:', msg);
    res.status(500).json({ success: false, message: msg });
  }
});

module.exports = router;