/**
 * ═══════════════════════════════════════════════════════════════════════════
 * AAMOS Ledger — SIE4 Export
 * Exporterar bokföringsdata i SIE4-format (svensk standard, typ 4)
 *
 * Endpoints:
 *   GET /api/ledger/export/sie4          → SIE4-fil (text/plain download)
 *   GET /api/ledger/export/sie4/preview  → JSON-förhandsgranskning
 *
 * SIE4 standard: https://sie.se/
 * Teckenset: UTF-8 (moderna program accepterar detta; CP437/PC8 är äldre norm)
 * Radslut: CRLF per SIE-standard
 * ═══════════════════════════════════════════════════════════════════════════
 */

// ── Hjälpfunktioner ──────────────────────────────────────────────────────────

/**
 * Mappar source_type till SIE4-serie:
 *   A = manuella verifikationer
 *   B = bankimport
 *   S = SIE-import
 */
function sourceTypeToSeries(sourceType) {
  switch (sourceType) {
    case 'import_bank':
    case 'bank':
      return 'B';
    case 'import_sie':
      return 'S';
    default:
      return 'A';
  }
}

/**
 * Formaterar Date eller ISO-sträng till YYYYMMDD (SIE-datumformat).
 */
function fmtDate(d) {
  if (!d) return '';
  const dt = typeof d === 'string' ? new Date(d) : d;
  const y  = dt.getUTCFullYear();
  const m  = String(dt.getUTCMonth() + 1).padStart(2, '0');
  const day = String(dt.getUTCDate()).padStart(2, '0');
  return `${y}${m}${day}`;
}

/**
 * Formaterar numeriskt belopp till SIE4-format (punkt, 2 decimaler).
 * Debet = positivt, Kredit = negativt.
 */
function fmtAmount(n) {
  return (parseFloat(n) || 0).toFixed(2);
}

/**
 * Escapar citattecken i SIE4-strängar: " → \"
 */
function escapeStr(s) {
  if (s == null) return '';
  return String(s).replace(/\\/g, '\\\\').replace(/"/g, '\\"');
}

// ── Databas-hämtning ─────────────────────────────────────────────────────────

/**
 * Hämtar all data som behövs för en SIE4-export.
 *
 * @param {object} pool          - pg.Pool
 * @param {string} tenant_id
 * @param {number} fiscal_year
 * @param {string|null} period   - "YYYY-MM" eller null (= hela räkenskapsåret)
 * @param {boolean} include_unposted
 * @returns {Promise<object>}    { entries, accountMap, accountNumbers, ibMap, ubMap, dateFrom, dateTo }
 */
async function fetchExportData(pool, tenant_id, fiscal_year, period, include_unposted) {
  // ── Datumintervall ──────────────────────────────────────────────────────────
  let dateFromUtc, dateToUtc;
  if (period) {
    const [py, pm] = period.split('-').map(Number);
    dateFromUtc = new Date(Date.UTC(py, pm - 1, 1));
    dateToUtc   = new Date(Date.UTC(py, pm, 0)); // sista dagen i månaden
  } else {
    dateFromUtc = new Date(Date.UTC(fiscal_year, 0, 1));   // 1 jan
    dateToUtc   = new Date(Date.UTC(fiscal_year, 11, 31)); // 31 dec
  }
  const dateFromStr = dateFromUtc.toISOString().split('T')[0];
  const dateToStr   = dateToUtc.toISOString().split('T')[0];

  // ── Verifikationer med rader ────────────────────────────────────────────────
  const statusFilter       = include_unposted ? ['draft', 'posted'] : ['posted'];
  const statusPlaceholders = statusFilter.map((_, i) => `$${i + 3}`).join(',');
  const dateFromIdx        = statusFilter.length + 3;
  const dateToIdx          = statusFilter.length + 4;

  const entriesSQL = `
    SELECT
      e.id,
      e.entry_number,
      e.entry_date,
      e.description,
      e.reference,
      e.source_type,
      e.status,
      e.posted_at,
      e.created_at,
      json_agg(
        json_build_object(
          'account_number', l.account_number,
          'account_name',   l.account_name,
          'debit',          l.debit,
          'credit',         l.credit,
          'description',    l.description
        ) ORDER BY l.line_number
      ) AS lines
    FROM ledger_journal_entries e
    JOIN ledger_journal_lines l ON l.entry_id = e.id
    WHERE e.tenant_id = $1
      AND e.fiscal_year = $2
      AND e.status IN (${statusPlaceholders})
      AND e.entry_date >= $${dateFromIdx}
      AND e.entry_date <= $${dateToIdx}
    GROUP BY e.id
    ORDER BY e.entry_date ASC,
             e.entry_number ASC NULLS LAST,
             e.created_at ASC
  `;
  const { rows: entries } = await pool.query(entriesSQL, [
    tenant_id, fiscal_year, ...statusFilter, dateFromStr, dateToStr,
  ]);

  // ── Samla berörda kontonummer ───────────────────────────────────────────────
  const accountNumberSet = new Set();
  for (const e of entries) {
    for (const l of (e.lines || [])) {
      if (l.account_number) accountNumberSet.add(l.account_number);
    }
  }
  const accountNumbers = Array.from(accountNumberSet).sort();

  // ── Kontoinformation ────────────────────────────────────────────────────────
  const accountMap = {};
  if (accountNumbers.length > 0) {
    const placeholders = accountNumbers.map((_, i) => `$${i + 2}`).join(',');
    const { rows: acctRows } = await pool.query(
      `SELECT account_number, name, account_type, normal_balance
       FROM ledger_accounts
       WHERE tenant_id = $1 AND account_number IN (${placeholders})`,
      [tenant_id, ...accountNumbers]
    );
    for (const a of acctRows) {
      accountMap[a.account_number] = a;
    }
  }

  // ── IB — ingångssaldo (alla poster INNAN perioden startar) ──────────────────
  // IB = kumulativt nettosaldo t.o.m. dagen FÖRE periodens start
  const ibDate    = new Date(dateFromUtc.getTime() - 86_400_000); // -1 dag
  const ibDateStr = ibDate.toISOString().split('T')[0];

  const ibMap = {};
  if (accountNumbers.length > 0) {
    const placeholders = accountNumbers.map((_, i) => `$${i + 3}`).join(',');
    const { rows: ibRows } = await pool.query(
      `SELECT
         l.account_number,
         COALESCE(SUM(l.debit), 0) - COALESCE(SUM(l.credit), 0) AS balance
       FROM ledger_journal_lines l
       JOIN ledger_journal_entries e ON e.id = l.entry_id
       WHERE e.tenant_id = $1
         AND e.status = 'posted'
         AND e.entry_date <= $2
         AND l.account_number IN (${placeholders})
       GROUP BY l.account_number`,
      [tenant_id, ibDateStr, ...accountNumbers]
    );
    for (const r of ibRows) {
      ibMap[r.account_number] = parseFloat(r.balance) || 0;
    }
  }

  // ── UB — utgångssaldo (alla poster T.O.M. periodens slut) ──────────────────
  const ubMap = {};
  if (accountNumbers.length > 0) {
    const placeholders = accountNumbers.map((_, i) => `$${i + 3}`).join(',');
    const { rows: ubRows } = await pool.query(
      `SELECT
         l.account_number,
         COALESCE(SUM(l.debit), 0) - COALESCE(SUM(l.credit), 0) AS balance
       FROM ledger_journal_lines l
       JOIN ledger_journal_entries e ON e.id = l.entry_id
       WHERE e.tenant_id = $1
         AND e.status = 'posted'
         AND e.entry_date <= $2
         AND l.account_number IN (${placeholders})
       GROUP BY l.account_number`,
      [tenant_id, dateToStr, ...accountNumbers]
    );
    for (const r of ubRows) {
      ubMap[r.account_number] = parseFloat(r.balance) || 0;
    }
  }

  return { entries, accountMap, accountNumbers, ibMap, ubMap, dateFrom: dateFromStr, dateTo: dateToStr };
}

// ── SIE4-textgenerator ───────────────────────────────────────────────────────

/**
 * Bygger SIE4-textfilen från exportdata och alternativ.
 *
 * @param {object} data  - Returnerat från fetchExportData
 * @param {object} opts  - { fiscal_year, org_nr, company_name }
 * @returns {string}     - SIE4-text med CRLF-radslut
 */
function buildSIE4(data, opts) {
  const { entries, accountMap, accountNumbers, ibMap, ubMap } = data;
  const { fiscal_year, org_nr, company_name } = opts;

  // Dagens datum för #GEN
  const now     = new Date();
  const genDate = [
    now.getUTCFullYear(),
    String(now.getUTCMonth() + 1).padStart(2, '0'),
    String(now.getUTCDate()).padStart(2, '0'),
  ].join('');

  const fyStart = `${fiscal_year}0101`;
  const fyEnd   = `${fiscal_year}1231`;

  const out = [];

  // ── Huvudblock ─────────────────────────────────────────────────────────────
  out.push('#FLAGGA 0');
  out.push('#PROGRAM "AAMOS Ledger" 1.0');
  out.push('#FORMAT PC8');
  out.push(`#GEN ${genDate} system`);
  out.push('#SIETYP 4');
  if (org_nr)       out.push(`#ORGNR ${org_nr}`);
  if (company_name) out.push(`#FNAMN "${escapeStr(company_name)}"`);
  out.push(`#RAR 0 ${fyStart} ${fyEnd}`);
  out.push('');

  // ── Kontoplan (#KONTO) ──────────────────────────────────────────────────────
  for (const acctNr of accountNumbers) {
    const acct = accountMap[acctNr];
    const name = acct ? acct.name : acctNr;
    out.push(`#KONTO ${acctNr} "${escapeStr(name)}"`);
  }
  out.push('');

  // ── Saldon (#IB / #UB / #RES) ──────────────────────────────────────────────
  // Balansräkningskonton    → #IB + #UB
  // Resultaträkningskonton  → #RES (periodens netto: UB − IB)
  for (const acctNr of accountNumbers) {
    const acct = accountMap[acctNr];
    const ib   = ibMap[acctNr] || 0;
    const ub   = ubMap[acctNr] || 0;

    if (acct && (acct.account_type === 'revenue' || acct.account_type === 'expense')) {
      out.push(`#RES 0 ${acctNr} ${fmtAmount(ub - ib)}`);
    } else {
      out.push(`#IB 0 ${acctNr} ${fmtAmount(ib)}`);
      out.push(`#UB 0 ${acctNr} ${fmtAmount(ub)}`);
    }
  }
  out.push('');

  // ── Verifikationer (#VER med #TRANS) ───────────────────────────────────────
  let fallbackIdx = 1;
  for (const entry of entries) {
    const series  = sourceTypeToSeries(entry.source_type);
    const verNr   = entry.entry_number != null ? String(entry.entry_number) : String(fallbackIdx);
    fallbackIdx++;

    const verDate = fmtDate(entry.entry_date);
    const regDate = entry.posted_at ? fmtDate(entry.posted_at) : verDate;
    const desc    = escapeStr(entry.description);

    out.push(`#VER ${series} ${verNr} ${verDate} "${desc}" ${regDate}`);
    out.push('{');

    for (const l of (entry.lines || [])) {
      // Debet = positivt, Kredit = negativt i SIE4
      const amount = (parseFloat(l.debit) || 0) - (parseFloat(l.credit) || 0);
      out.push(`#TRANS ${l.account_number} {} ${fmtAmount(amount)}`);
    }

    out.push('}');
  }

  // SIE4-standard: CRLF radslut
  return out.join('\r\n') + '\r\n';
}

// ── Route-registrering ───────────────────────────────────────────────────────

/**
 * Registrerar SIE4 export-endpoints på Express-appen.
 *
 * @param {import('express').Application} app
 * @param {import('pg').Pool} pool
 * @param {Function} buildCtx  - Context-byggare från index.mjs (används ej — read-only export)
 * @param {object}   hermes    - Event-fabric (används ej — read-only export)
 */
export function register(app, pool, buildCtx, hermes) {

  // ── GET /api/ledger/export/sie4 ────────────────────────────────────────────
  // Returnerar SIE4-fil som nedladdningsbar bifogad fil (text/plain).
  //
  // Query params:
  //   fiscal_year      (krävs)    t.ex. 2026
  //   period           (valfritt) t.ex. 2026-01; utelämnad = hela räkenskapsåret
  //   org_nr           (valfritt) organisationsnummer
  //   company_name     (valfritt) företagsnamn
  //   include_unposted (valfritt, default "false") inkludera draft-poster
  app.get('/api/ledger/export/sie4', async (req, res) => {
    const tenant_id = req.headers['x-tenant-id'] || 'wavult-group';
    const {
      fiscal_year,
      period           = null,
      org_nr           = null,
      company_name     = null,
      include_unposted = 'false',
    } = req.query;

    if (!fiscal_year) {
      return res.status(400).json({ ok: false, error: 'fiscal_year krävs' });
    }
    const fy = parseInt(fiscal_year, 10);
    if (isNaN(fy) || fy < 1900 || fy > 2100) {
      return res.status(400).json({ ok: false, error: 'Ogiltigt fiscal_year' });
    }
    if (period && !/^\d{4}-\d{2}$/.test(period)) {
      return res.status(400).json({ ok: false, error: 'period måste vara i format YYYY-MM' });
    }

    const incUnposted = include_unposted === 'true';

    try {
      console.log(`[sie4-export] Export: tenant=${tenant_id} fy=${fy} period=${period ?? 'hela året'} unposted=${incUnposted}`);

      const data    = await fetchExportData(pool, tenant_id, fy, period, incUnposted);
      const sieText = buildSIE4(data, { fiscal_year: fy, org_nr, company_name });
      const filename = period ? `SIE4_${period}.se` : `SIE4_${fy}.se`;

      console.log(
        `[sie4-export] OK: ${data.entries.length} verifikationer, ` +
        `${data.accountNumbers.length} konton → ${filename}`
      );

      res.set('Content-Type', 'text/plain; charset=utf-8');
      res.set('Content-Disposition', `attachment; filename="${filename}"`);
      res.send(sieText);

    } catch (e) {
      console.error('[sie4-export] Export misslyckades:', e.message);
      res.status(500).json({ ok: false, error: e.message });
    }
  });

  // ── GET /api/ledger/export/sie4/preview ───────────────────────────────────
  // Returnerar JSON med metadata + max 20 verifikationer för förhandsgranskning.
  // Samma query-params som /sie4.
  app.get('/api/ledger/export/sie4/preview', async (req, res) => {
    const tenant_id = req.headers['x-tenant-id'] || 'wavult-group';
    const {
      fiscal_year,
      period           = null,
      org_nr           = null,
      company_name     = null,
      include_unposted = 'false',
    } = req.query;

    if (!fiscal_year) {
      return res.status(400).json({ ok: false, error: 'fiscal_year krävs' });
    }
    const fy = parseInt(fiscal_year, 10);
    if (isNaN(fy) || fy < 1900 || fy > 2100) {
      return res.status(400).json({ ok: false, error: 'Ogiltigt fiscal_year' });
    }
    if (period && !/^\d{4}-\d{2}$/.test(period)) {
      return res.status(400).json({ ok: false, error: 'period måste vara i format YYYY-MM' });
    }

    const incUnposted = include_unposted === 'true';

    try {
      console.log(`[sie4-export] Preview: tenant=${tenant_id} fy=${fy} period=${period ?? 'hela året'}`);

      const data = await fetchExportData(pool, tenant_id, fy, period, incUnposted);

      // Förhandsgranskning (max 20 verifikationer)
      let fallbackIdx = 1;
      const previewEntries = data.entries.slice(0, 20).map(e => {
        const verNr = e.entry_number != null ? String(e.entry_number) : String(fallbackIdx);
        fallbackIdx++;
        return {
          series:      sourceTypeToSeries(e.source_type),
          ver_nr:      verNr,
          date:        fmtDate(e.entry_date),
          reg_date:    e.posted_at ? fmtDate(e.posted_at) : fmtDate(e.entry_date),
          description: e.description,
          source_type: e.source_type,
          status:      e.status,
          lines: (e.lines || []).map(l => ({
            account_number: l.account_number,
            account_name:   l.account_name || null,
            amount:         (parseFloat(l.debit) || 0) - (parseFloat(l.credit) || 0),
          })),
        };
      });

      // Kontosaldo-sammanfattning
      const accountSummary = data.accountNumbers.map(acctNr => {
        const acct      = data.accountMap[acctNr];
        const ib        = data.ibMap[acctNr] || 0;
        const ub        = data.ubMap[acctNr] || 0;
        const isResultat = acct && (acct.account_type === 'revenue' || acct.account_type === 'expense');
        return {
          account_number: acctNr,
          name:           acct ? acct.name : null,
          account_type:   acct ? acct.account_type : 'unknown',
          sie4_type:      isResultat ? 'RES' : 'IB/UB',
          ib:             isResultat ? null : ib,
          ub:             isResultat ? null : ub,
          res:            isResultat ? (ub - ib) : null,
        };
      });

      // Totaler för balans-check
      const totalDebit  = data.entries.reduce(
        (s, e) => s + (e.lines || []).reduce((ls, l) => ls + (parseFloat(l.debit)  || 0), 0), 0
      );
      const totalCredit = data.entries.reduce(
        (s, e) => s + (e.lines || []).reduce((ls, l) => ls + (parseFloat(l.credit) || 0), 0), 0
      );

      res.json({
        ok: true,
        meta: {
          tenant_id,
          fiscal_year:      fy,
          period:           period ?? `${fy} (hela räkenskapsåret)`,
          date_from:        data.dateFrom,
          date_to:          data.dateTo,
          org_nr:           org_nr   ?? null,
          company_name:     company_name ?? null,
          include_unposted: incUnposted,
          entry_count:      data.entries.length,
          account_count:    data.accountNumbers.length,
          total_debit:      totalDebit,
          total_credit:     totalCredit,
          balanced:         Math.abs(totalDebit - totalCredit) < 0.01,
        },
        accounts:        accountSummary,
        preview_entries: previewEntries,
        note: data.entries.length > 20
          ? `Visar 20 av ${data.entries.length} verifikationer`
          : `Visar alla ${data.entries.length} verifikationer`,
      });

    } catch (e) {
      console.error('[sie4-export] Preview misslyckades:', e.message);
      res.status(500).json({ ok: false, error: e.message });
    }
  });

  console.log('[aamos-ledger] SIE4 Export registrerad: /api/ledger/export/sie4 · /api/ledger/export/sie4/preview');
}