import { useCallback, useEffect, useState } from 'react'
import type { LedgerEntry, LedgerKind } from './api'
import { syncAppLedger } from './api'
import { dayOffsetIso, pickInt, pickOne, rng, seedOf, todayIso } from './demo/seed'

/*
 * Offline-first ledger.
 *
 * Every entry is written to localStorage first and marked PENDING; a sync pass
 * flips it to SYNCED. This is what makes the deck's "works with zero
 * connectivity" claim true in the prototype — the owner never sees a spinner
 * and never loses a tap.
 */

const KEY = 'ul-ledger'
const SYNC_KEY = 'ul-last-sync'

export const CATEGORIES: Record<LedgerKind, { code: string; en: string; hi: string }[]> = {
  IN: [
    { code: 'SALE', en: 'Sale', hi: 'बिक्री' },
    { code: 'UPI', en: 'UPI received', hi: 'UPI आया' },
    { code: 'RECOVERY', en: 'Udhaar recovered', hi: 'उधारी वसूली' },
    { code: 'OTHER_IN', en: 'Other', hi: 'अन्य' },
  ],
  OUT: [
    { code: 'INPUT', en: 'Raw material / feed', hi: 'कच्चा माल / दाना' },
    { code: 'WAGES', en: 'Wages', hi: 'मज़दूरी' },
    { code: 'TRANSPORT', en: 'Transport', hi: 'भाड़ा' },
    { code: 'EMI', en: 'Instalment', hi: 'किस्त' },
    { code: 'OTHER_OUT', en: 'Other', hi: 'अन्य' },
  ],
  STOCK: [
    { code: 'STOCK_IN', en: 'Stock added', hi: 'स्टॉक आया' },
    { code: 'STOCK_OUT', en: 'Stock sold', hi: 'स्टॉक गया' },
  ],
}

function read(): LedgerEntry[] {
  try {
    const raw = localStorage.getItem(KEY)
    return raw ? (JSON.parse(raw) as LedgerEntry[]) : []
  } catch {
    return []
  }
}

function write(entries: LedgerEntry[]) {
  localStorage.setItem(KEY, JSON.stringify(entries))
  window.dispatchEvent(new Event('ul-ledger-changed'))
}

/** 30 days of plausible history, generated once per enterprise so the app is never empty. */
function seedHistory(enterpriseId: string): LedgerEntry[] {
  const r = rng(seedOf(`${enterpriseId}:ledger`))
  const out: LedgerEntry[] = []
  for (let d = 30; d >= 0; d--) {
    const entries = pickInt(r, 1, 3)
    for (let i = 0; i < entries; i++) {
      const kind: LedgerKind = r() > 0.45 ? 'IN' : 'OUT'
      const cat = pickOne(r, CATEGORIES[kind])
      out.push({
        id: `seed-${enterpriseId}-${d}-${i}`,
        enterpriseId,
        kind,
        amount: kind === 'IN' ? pickInt(r, 6, 52) * 100 : pickInt(r, 4, 38) * 100,
        category: cat.code,
        note: null,
        entryDate: dayOffsetIso(-d),
        syncState: 'SYNCED',
        createdAt: new Date().toISOString(),
      })
    }
  }
  return out
}

export function loadLedger(enterpriseId: string): LedgerEntry[] {
  const all = read()
  const mine = all.filter((e) => e.enterpriseId === enterpriseId)
  if (mine.length) return mine.sort((a, b) => b.entryDate.localeCompare(a.entryDate))
  const seeded = seedHistory(enterpriseId)
  write([...all, ...seeded])
  return seeded.sort((a, b) => b.entryDate.localeCompare(a.entryDate))
}

/** Three-tap write: amount → category → save. Always succeeds, online or not. */
export function addEntry(input: {
  enterpriseId: string
  kind: LedgerKind
  amount: number
  category: string
  note?: string
}): LedgerEntry {
  const entry: LedgerEntry = {
    id: `local-${Date.now()}-${Math.round(Math.random() * 1e6)}`,
    enterpriseId: input.enterpriseId,
    kind: input.kind,
    amount: input.amount,
    category: input.category,
    note: input.note ?? null,
    entryDate: todayIso(),
    syncState: 'PENDING',
    createdAt: new Date().toISOString(),
  }
  write([...read(), entry])
  return entry
}

export function pendingCount(enterpriseId: string): number {
  return read().filter((e) => e.enterpriseId === enterpriseId && e.syncState === 'PENDING').length
}

/**
 * Drain the offline queue to the server.
 *
 * <p>This was the missing half of the offline promise. Entries were written to
 * localStorage and marked PENDING, and this function flipped them to SYNCED
 * without anything leaving the phone — so an owner could record a sale with no
 * signal, which was the point, but it never reached the lender and the officer's
 * screen never saw it.
 *
 * <p>Safe to call whenever. The server dedupes on `clientId`, which the phone
 * minted, so a retry after a half-failed sync writes nothing twice. Entries that
 * fail to send stay PENDING and go again on the next pass rather than being
 * dropped — losing an owner's tap is the one failure this app cannot have, so a
 * network error is deliberately silent from their side.
 */
export async function syncPending(enterpriseId: string): Promise<number> {
  const pending = read().filter(
    (e) => e.enterpriseId === enterpriseId && e.syncState === 'PENDING',
  )
  if (pending.length === 0) return 0

  try {
    await syncAppLedger(pending)
  } catch {
    return 0
  }

  // Re-read rather than reusing the snapshot: the owner may have tapped save
  // again while the request was in flight, and that entry must stay PENDING.
  const sent = new Set(pending.map((e) => e.id))
  write(read().map((e) => (sent.has(e.id) ? { ...e, syncState: 'SYNCED' as const } : e)))
  localStorage.setItem(SYNC_KEY, new Date().toISOString())
  return pending.length
}

export function lastSyncedAt(): string | null {
  return localStorage.getItem(SYNC_KEY)
}

export function dayTotals(entries: LedgerEntry[], date = todayIso()) {
  const today = entries.filter((e) => e.entryDate === date)
  return {
    in: today.filter((e) => e.kind === 'IN').reduce((a, e) => a + e.amount, 0),
    out: today.filter((e) => e.kind === 'OUT').reduce((a, e) => a + e.amount, 0),
    count: today.length,
  }
}

/** Live ledger for a given enterprise, re-reading whenever an entry is written. */
/**
 * The borrower.s ledger: what the server holds, plus anything typed on this
 * device that has not synced yet.
 *
 * <p>Local entries come first and win on `clientId`, which is minted on the
 * phone. That is what makes the offline path honest — an entry recorded with no
 * signal is visible immediately, and when it syncs the server copy replaces it
 * without ever appearing twice.
 */
export function useLedger(enterpriseId: string, server: LedgerEntry[] = []) {
  const [local, setLocal] = useState<LedgerEntry[]>(() => loadLedger(enterpriseId))

  const refresh = useCallback(() => setLocal(loadLedger(enterpriseId)), [enterpriseId])

  useEffect(() => {
    refresh()
    window.addEventListener("ul-ledger-changed", refresh)
    return () => window.removeEventListener("ul-ledger-changed", refresh)
  }, [refresh])

  const seen = new Set(local.map((e) => e.id))
  const entries = [...local, ...server.filter((e) => !seen.has(e.id))]
    .sort((a, b) => b.entryDate.localeCompare(a.entryDate))

  return { entries, refresh }
}

/**
 * Drain the queue whenever the network comes back.
 *
 * <p>Without this the offline promise was only half kept: an entry recorded with
 * no signal reached the lender on the owner's <em>next</em> save or manual tap,
 * and an owner who recorded a sale and put the phone away never synced at all.
 * The browser tells us when the radio returns; that is the moment to try.
 *
 * <p>Also runs once on mount, because the app is commonly opened <em>after</em>
 * connectivity is restored rather than while it is being restored — in that
 * case no `online` event ever fires.
 */
export function useAutoSync(enterpriseId: string | undefined) {
  useEffect(() => {
    if (!enterpriseId) return
    const drain = () => {
      void syncPending(enterpriseId)
    }
    drain()
    window.addEventListener('online', drain)
    return () => window.removeEventListener('online', drain)
  }, [enterpriseId])
}