import { afterEach, describe, expect, it } from 'vitest'
import express from 'express'
import type { AddressInfo } from 'node:net'
import type { Server } from 'node:http'
import { openDb, type DB } from '../src/db'
import { seedIfEmpty } from '../src/seed'
import { commitBill, createCustomer } from '../src/repos'
import { commitReturn } from '../src/repos-returns'
import { gstr1, gstr3b, hsnSummary, gstr1PortalJson } from '../src/repos-gst'
import { apiRouter } from '../src/api'

/**
 * GST returns — READ-ONLY compliance reporting over the period's immutable documents. These lock:
 * the B2B/B2CS split by buyer GSTIN, B2CS aggregation by rate, a credit note reducing its rate
 * bucket, HSN totals, the GSTR-3B 3.1(a) outward figures hand-checked against the bills, the
 * reconciliation identity (sections == source == HSN == 3B), the REPORT_VIEW gate, and valid JSON.
 *
 * Hermetic in-memory seed: item 103 Surf Excel (GST18, ₹145 incl), 107 Amul Butter (GST12, ₹275),
 * 104 Parle-G (GST5, ₹90). Store state 32. u1 Ramesh/cashier (4728), u3 Thomas/owner (9174).
 */
const PERIOD = '2026-07'
const DATE = '2026-07-10'
const CTIN = '27ABCDE1234F1Z0' // registered buyer in state 27 → inter-state B2B (IGST)

function itemId(db: DB, code: string): string {
  return (db.prepare(`SELECT id FROM item WHERE tenant_id='t1' AND code=?`).get(code) as { id: string }).id
}

interface Built { custA: string; bill1: string; bill2: string; bill3: string }

/** Build the known document set for a single month and return the ids. */
function buildMonth(db: DB): Built {
  const custA = createCustomer(db, 't1', 'Anand Traders', '9876543210', { gstin: CTIN }).id
  const line = (code: string, qty: number, price: number, cls: string, hsn: string, name: string) => ({
    itemId: itemId(db, code), name, hsn, qty, unitCode: 'PCS', unitPricePaise: price, priceIncludesTax: true, taxClassCode: cls,
  })
  const commit = (lines: ReturnType<typeof line>[], payable: number, customerId?: string) =>
    commitBill(db, {
      tenantId: 't1', storeId: 's1', counterId: 'c2', cashierId: 'u1', shiftId: 'sh1', businessDate: DATE,
      lines, payments: [{ mode: 'CASH', amountPaise: payable }], clientPayablePaise: payable,
      ...(customerId !== undefined ? { customerId } : {}),
    })
  // Bill 1 — B2B: 2 × Surf Excel to the GSTIN buyer (inter-state → IGST).
  const bill1 = commit([line('103', 2, 14_500, 'GST18', '3402', 'Surf Excel 1kg')], 29_000, custA).id
  // Bill 2 — B2C cash: 1 × Surf Excel + 1 × Amul Butter (intra → CGST/SGST).
  const bill2 = commit([line('103', 1, 14_500, 'GST18', '3402', 'Surf Excel 1kg'), line('107', 1, 27_500, 'GST12', '0405', 'Amul Butter 500g')], 42_000).id
  // Bill 3 — B2C cash: 3 × Parle-G.
  const bill3 = commit([line('104', 3, 9_000, 'GST5', '1905', 'Parle-G 800g')], 27_000).id
  // Return — the full Amul line from bill 2 (index 1) → nets into B2CS at GST12.
  commitReturn(db, {
    tenantId: 't1', storeId: 's1', counterId: 'c2', cashierId: 'u1', shiftId: 'sh1', businessDate: DATE,
    originalBillId: bill2, lines: [{ lineIndex: 1, qty: 1 }], reason: 'Damaged', refundMode: 'CASH',
  })
  return { custA, bill1, bill2, bill3 }
}

function fresh(): DB {
  const db = openDb(':memory:')
  seedIfEmpty(db)
  return db
}

describe('gstr1 — sections over the known month', () => {
  it('B2B shows the GSTIN invoice; B2CS aggregates the cash bills by rate; the return nets out', () => {
    const db = fresh()
    buildMonth(db)
    const r = gstr1(db, 't1', PERIOD)

    // B2B: one party, one invoice, GST18, taxable 24576 + IGST 4424 (₹290 incl of 2×₹145).
    expect(r.b2b).toHaveLength(1)
    expect(r.b2b[0]!.ctin).toBe(CTIN)
    expect(r.b2b[0]!.invoiceCount).toBe(1)
    expect(r.b2b[0]!.totals.taxablePaise).toBe(24_576)
    expect(r.b2b[0]!.totals.igstPaise).toBe(4_424)

    // B2CS: Surf (GST18) and Parle (GST5) survive; the Amul (GST12) bucket nets to zero and is dropped.
    const b18 = r.b2cs.find((b) => b.rateBp === 1800)!
    expect(b18.taxablePaise).toBe(12_288)
    expect(b18.cgstPaise).toBe(1_106)
    expect(r.b2cs.find((b) => b.rateBp === 500)!.taxablePaise).toBe(25_714)
    expect(r.b2cs.some((b) => b.rateBp === 1200)).toBe(false)

    // No B2CL / CDNR / CDNUR in this set (nothing large, no registered return).
    expect(r.b2cl).toHaveLength(0)
    expect(r.cdnr).toHaveLength(0)
    expect(r.cdnur).toHaveLength(0)

    // HSN: Surf 3402 aggregates B2B + B2C (qty 3); Amul 0405 nets to zero and drops.
    const surf = r.hsn.find((h) => h.hsn === '3402')!
    expect(surf.taxablePaise).toBe(36_864)
    expect(surf.qty).toBe(3)
    expect(r.hsn.some((h) => h.hsn === '0405')).toBe(false)
    expect(r.totals.hsn.taxablePaise).toBe(62_578)

    // Documents issued: 3 invoices + 1 credit note.
    expect(r.docs.find((d) => d.natureOfDocument === 'Invoices for outward supply')!.totalNumber).toBe(3)
    expect(r.docs.find((d) => d.natureOfDocument === 'Credit notes')!.totalNumber).toBe(1)
  })
})

describe('gstr3b — 3.1(a) hand-checked against the bills', () => {
  it('outward = Σ bill tax − credit-note tax, at captured rates', () => {
    const db = fresh()
    buildMonth(db)
    const r = gstr3b(db, 't1', PERIOD)
    // Sales tax: IGST 4424 + CGST 3222 + SGST 3222 = 10868; credit note: CGST 1473 + SGST 1473 = 2946.
    expect(r.salesTax.igstPaise + r.salesTax.cgstPaise + r.salesTax.sgstPaise).toBe(10_868)
    expect(r.returnsTax.cgstPaise + r.returnsTax.sgstPaise).toBe(2_946)
    expect(r.outward.taxablePaise).toBe(62_578)
    expect(r.outward.igstPaise).toBe(4_424)
    expect(r.outward.cgstPaise).toBe(1_749)
    expect(r.outward.sgstPaise).toBe(1_749)
    expect(r.outward.igstPaise + r.outward.cgstPaise + r.outward.sgstPaise).toBe(7_922) // 10868 − 2946
    expect(r.itc.igstPaise).toBe(0) // ITC stub
  })
})

describe('reconciliation — the compliance gate ties out', () => {
  it('GSTR-1 sections == source == HSN == GSTR-3B (taxable and tax)', () => {
    const db = fresh()
    buildMonth(db)
    const r = gstr1(db, 't1', PERIOD)
    expect(r.reconciliation.ok).toBe(true)
    expect(r.reconciliation.mismatches).toEqual([])
    expect(r.reconciliation.sourceTaxablePaise).toBe(62_578)
    expect(r.reconciliation.gstr1NetTaxablePaise).toBe(62_578)
    expect(r.reconciliation.hsnTaxablePaise).toBe(62_578)
    expect(r.reconciliation.gstr3bTaxablePaise).toBe(62_578)
    expect(r.reconciliation.sourceTaxPaise).toBe(7_922)
    expect(r.reconciliation.gstr3bTaxPaise).toBe(7_922)
  })

  it('an empty period reconciles to zero, not an error', () => {
    const db = fresh()
    const r = gstr1(db, 't1', '2026-01')
    expect(r.reconciliation.ok).toBe(true)
    expect(r.reconciliation.sourceTaxablePaise).toBe(0)
    expect(r.b2b).toHaveLength(0)
    expect(r.docs).toHaveLength(0)
  })
})

describe('gstr1PortalJson — pragmatic GSTN-shaped export', () => {
  it('produces valid, serialisable JSON with the seller GSTIN and section keys', () => {
    const db = fresh()
    buildMonth(db)
    const j = gstr1PortalJson(db, 't1', PERIOD)
    // Round-trips through JSON.stringify/parse (no NaN, no cycles) and carries the shape.
    const round = JSON.parse(JSON.stringify(j)) as Record<string, unknown>
    expect(round['gstin']).toBe('32ABCDE1234F1Z5')
    expect(round['fp']).toBe('072026')
    expect(Array.isArray(round['b2b'])).toBe(true)
    expect((round['b2b'] as unknown[]).length).toBe(1)
    expect(round['_note']).toMatch(/NOT a certified/i)
    const hsn = round['hsn'] as { data: unknown[] }
    expect(Array.isArray(hsn.data)).toBe(true)
  })
})

// ---- HTTP surface: the REPORT_VIEW gate + period validation ----
interface Harness { db: DB; url: string; server: Server }
async function start(): Promise<Harness> {
  const db = openDb(':memory:')
  seedIfEmpty(db)
  buildMonth(db)
  const app = express()
  app.use(express.json({ limit: '1mb' }))
  app.use('/api', apiRouter(db))
  app.use((err: unknown, _req: express.Request, res: express.Response, _next: express.NextFunction) => {
    const e = (err ?? {}) as { status?: number; code?: string; message?: string }
    const status = typeof e.status === 'number' ? e.status : 500
    if (res.headersSent) return
    res.status(status).json({ error: status >= 500 ? 'Something went wrong' : (e.message ?? 'Bad request'), code: e.code ?? 'E-5000' })
  })
  const server: Server = await new Promise((resolve) => { const s = app.listen(0, () => resolve(s)) })
  const port = (server.address() as AddressInfo).port
  return { db, url: `http://127.0.0.1:${port}`, server }
}
async function login(url: string, userId: string, pin: string): Promise<string> {
  const res = await fetch(`${url}/api/auth/pin`, {
    method: 'POST', headers: { 'content-type': 'application/json' }, body: JSON.stringify({ userId, pin }),
  })
  const body = (await res.json()) as { token?: string }
  if (body.token === undefined) throw new Error(`login failed for ${userId}`)
  return body.token
}
const get = (url: string, path: string, token?: string) =>
  fetch(`${url}${path}`, { headers: { ...(token !== undefined ? { authorization: `Bearer ${token}` } : {}) } })

describe('GST HTTP routes — REPORT_VIEW gate + validation', () => {
  let h: Harness
  afterEach(() => { h.server.close() })

  it('owner (REPORT_VIEW) reads the returns; a cashier is 403; unauth is 401; a bad period is 400', async () => {
    h = await start()
    // unauthenticated
    expect((await get(h.url, `/api/gst/gstr1?period=${PERIOD}`)).status).toBe(401)
    // a cashier lacks REPORT_VIEW → 403 E-6105
    const cashier = await login(h.url, 'u1', '4728')
    const denied = await get(h.url, `/api/gst/gstr1?period=${PERIOD}`, cashier)
    expect(denied.status).toBe(403)
    expect(((await denied.json()) as { code?: string }).code).toBe('E-6105')
    // the owner reads it → 200 with the reconciled numbers
    const owner = await login(h.url, 'u3', '9174')
    const ok = await get(h.url, `/api/gst/gstr1?period=${PERIOD}`, owner)
    expect(ok.status).toBe(200)
    const body = (await ok.json()) as { reconciliation: { ok: boolean }; totals: { net: { taxablePaise: number } } }
    expect(body.reconciliation.ok).toBe(true)
    expect(body.totals.net.taxablePaise).toBe(62_578)
    // 3B + hsn + json all 200 for the owner
    expect((await get(h.url, `/api/gst/gstr3b?period=${PERIOD}`, owner)).status).toBe(200)
    expect((await get(h.url, `/api/gst/hsn?period=${PERIOD}`, owner)).status).toBe(200)
    const j = await get(h.url, `/api/gst/gstr1.json?period=${PERIOD}`, owner)
    expect(j.status).toBe(200)
    expect(((await j.json()) as { fp?: string }).fp).toBe('072026')
    // a malformed period → 400 E-1330
    const bad = await get(h.url, `/api/gst/gstr1?period=2026-13`, owner)
    expect(bad.status).toBe(400)
    expect(((await bad.json()) as { code?: string }).code).toBe('E-1330')
  })
})