import { afterEach, beforeEach, describe, expect, it, vi } from 'vitest'
import { readFile, rm } from 'fs/promises'
import { existsSync } from 'fs'
import { tmpdir } from 'os'
import { join } from 'path'

import type { ProjectSummary } from '../src/types.js'

import {
  addNewDays,
  currentTzKey,
  dailyCachePath,
  DAILY_CACHE_VERSION,
  type DailyCache,
  type DailyEntry,
  getDaysInRange,
  ensureCacheHydrated,
  loadDailyCache,
  saveDailyCache,
  withDailyCacheLock,
} from '../src/daily-cache.js'

function emptyDay(date: string, cost = 0, calls = 0): DailyEntry {
  return {
    date,
    cost,
    savingsUSD: 0,
    calls,
    sessions: 0,
    inputTokens: 0,
    outputTokens: 0,
    cacheReadTokens: 0,
    cacheWriteTokens: 0,
    editTurns: 0,
    oneShotTurns: 0,
    // A day's model rows have to account for its calls and cost, or loading it
    // credits the difference to the carried row.
    models: calls || cost
      ? { 'Opus 4.7': { calls, cost, savingsUSD: 0, inputTokens: 0, outputTokens: 0, cacheReadTokens: 0, cacheWriteTokens: 0 } }
      : {},
    categories: {},
    providers: {},
  }
}

const TMP_CACHE_ROOT = join(tmpdir(), `codeburn-cache-test-${Date.now()}-${Math.random().toString(36).slice(2, 8)}`)

beforeEach(() => {
  process.env['CODEBURN_CACHE_DIR'] = TMP_CACHE_ROOT
})

afterEach(async () => {
  vi.useRealTimers()
  if (existsSync(TMP_CACHE_ROOT)) {
    await rm(TMP_CACHE_ROOT, { recursive: true, force: true })
  }
})

describe('loadDailyCache', () => {
  it('returns an empty cache when the file does not exist', async () => {
    const cache = await loadDailyCache()
    expect(cache.version).toBe(DAILY_CACHE_VERSION)
    expect(cache.lastComputedDate).toBeNull()
    expect(cache.days).toEqual([])
  })

  it('returns an empty cache when the file contains invalid JSON', async () => {
    const { writeFile, mkdir } = await import('fs/promises')
    await mkdir(TMP_CACHE_ROOT, { recursive: true })
    await writeFile(join(TMP_CACHE_ROOT, 'daily-cache.json'), 'not valid json{{', 'utf-8')
    const cache = await loadDailyCache()
    expect(cache.days).toEqual([])
  })

  // With carry-forward (v14), a legacy unversioned file whose version is not
  // the current one is ADOPTED as a carried baseline — its days survive into
  // the new cache, marked `carried` and pending re-derivation. The legacy file
  // itself is never rewritten, backed up, or deleted (old binaries still own it).
  it('adopts a legacy file too old to trust as a carried baseline, without rewriting it', async () => {
    const saved = {
      version: 1,
      lastComputedDate: '2026-04-10',
      days: [{ date: '2026-04-10', cost: 10, calls: 5 }],
    }
    const { writeFile, mkdir } = await import('fs/promises')
    await mkdir(TMP_CACHE_ROOT, { recursive: true })
    const legacy = join(TMP_CACHE_ROOT, 'daily-cache.json')
    await writeFile(legacy, JSON.stringify(saved), 'utf-8')
    const cache = await loadDailyCache()
    expect(cache.days).toHaveLength(1)
    expect(cache.days[0]).toMatchObject({ date: '2026-04-10', cost: 10, calls: 5, carried: true })
    // Adopted days are not yet finalized under current accounting.
    expect(cache.complete).not.toBe(true)
    // Legacy file untouched (no .bak, contents intact); versioned file persisted.
    expect(existsSync(join(TMP_CACHE_ROOT, 'daily-cache.json.v1.bak'))).toBe(false)
    expect(JSON.parse(await readFile(legacy, 'utf-8'))).toEqual(saved)
    expect(existsSync(dailyCachePath())).toBe(true)
  })

  it('adopts a legacy v2 cache as carried days and leaves the file intact', async () => {
    const saved = {
      version: 2,
      lastComputedDate: '2026-04-10',
      days: [{
        date: '2026-04-10', cost: 10, calls: 5, sessions: 2,
        inputTokens: 1000, outputTokens: 500, cacheReadTokens: 200, cacheWriteTokens: 100,
        models: { 'claude-opus-4-6': { calls: 5, cost: 10, inputTokens: 1000, outputTokens: 500, cacheReadTokens: 200, cacheWriteTokens: 100 } },
      }],
    }
    const { writeFile, mkdir } = await import('fs/promises')
    await mkdir(TMP_CACHE_ROOT, { recursive: true })
    const legacy = join(TMP_CACHE_ROOT, 'daily-cache.json')
    await writeFile(legacy, JSON.stringify(saved), 'utf-8')
    const cache = await loadDailyCache()
    expect(cache.version).toBe(DAILY_CACHE_VERSION)
    expect(cache.days).toHaveLength(1)
    expect(cache.days[0]).toMatchObject({ date: '2026-04-10', cost: 10, calls: 5, sessions: 2, carried: true })
    expect(cache.days[0]!.models['claude-opus-4-6']!.cost).toBe(10)
    expect(existsSync(join(TMP_CACHE_ROOT, 'daily-cache.json.v2.bak'))).toBe(false)
    expect(JSON.parse(await readFile(legacy, 'utf-8'))).toEqual(saved)
  })

  it('adopts a legacy v5 cache including its provider slices', async () => {
    const saved = {
      version: 5,
      lastComputedDate: '2026-05-01',
      days: [{
        date: '2026-05-01',
        cost: 0.37575,
        calls: 1,
        sessions: 1,
        inputTokens: 0,
        outputTokens: 0,
        cacheReadTokens: 0,
        cacheWriteTokens: 60_120,
        editTurns: 0,
        oneShotTurns: 0,
        models: { 'Opus 4.7': { calls: 1, cost: 0.37575, inputTokens: 0, outputTokens: 0, cacheReadTokens: 0, cacheWriteTokens: 60_120 } },
        categories: {},
        providers: { claude: { calls: 1, cost: 0.37575 } },
      }],
    }
    const { writeFile, mkdir } = await import('fs/promises')
    await mkdir(TMP_CACHE_ROOT, { recursive: true })
    const legacy = join(TMP_CACHE_ROOT, 'daily-cache.json')
    await writeFile(legacy, JSON.stringify(saved), 'utf-8')
    const cache = await loadDailyCache()
    expect(cache.version).toBe(DAILY_CACHE_VERSION)
    expect(cache.days).toHaveLength(1)
    expect(cache.days[0]).toMatchObject({ date: '2026-05-01', cost: 0.37575, calls: 1, carried: true })
    expect(cache.days[0]!.providers['claude']).toMatchObject({ calls: 1, cost: 0.37575 })
    expect(existsSync(join(TMP_CACHE_ROOT, 'daily-cache.json.v5.bak'))).toBe(false)
    expect(JSON.parse(await readFile(legacy, 'utf-8'))).toEqual(saved)
  })

  it('credits a token remainder to the carried row even when cost and calls reconcile', async () => {
    const saved = {
      version: 5,
      lastComputedDate: '2026-05-02',
      days: [
        {
          // cost + calls reconcile with the model rows, but the model tokens
          // fall 200 input / 100 output short of the day totals.
          date: '2026-05-02',
          cost: 10, calls: 5, sessions: 1,
          inputTokens: 1000, outputTokens: 500, cacheReadTokens: 0, cacheWriteTokens: 0,
          editTurns: 0, oneShotTurns: 0,
          models: { 'Opus 4.7': { calls: 5, cost: 10, savingsUSD: 0, inputTokens: 800, outputTokens: 400, cacheReadTokens: 0, cacheWriteTokens: 0 } },
          categories: {}, providers: {},
        },
        {
          // Fully reconciled — must not grow a carried row.
          date: '2026-05-03',
          cost: 4, calls: 2, sessions: 1,
          inputTokens: 600, outputTokens: 300, cacheReadTokens: 0, cacheWriteTokens: 0,
          editTurns: 0, oneShotTurns: 0,
          models: { 'Opus 4.7': { calls: 2, cost: 4, savingsUSD: 0, inputTokens: 600, outputTokens: 300, cacheReadTokens: 0, cacheWriteTokens: 0 } },
          categories: {}, providers: {},
        },
      ],
    }
    const { writeFile, mkdir } = await import('fs/promises')
    await mkdir(TMP_CACHE_ROOT, { recursive: true })
    await writeFile(join(TMP_CACHE_ROOT, 'daily-cache.json'), JSON.stringify(saved), 'utf-8')

    const cache = await loadDailyCache()
    const short = cache.days.find(d => d.date === '2026-05-02')!
    const reconciled = cache.days.find(d => d.date === '2026-05-03')!

    // The carried row picks up exactly the missing tokens, with no calls/cost.
    const carried = short.models['Unknown (carried)']!
    expect(carried).toBeDefined()
    expect(carried.inputTokens).toBe(200)
    expect(carried.outputTokens).toBe(100)
    expect(carried.calls).toBe(0)
    expect(carried.cost).toBe(0)
    // Cost and calls are untouched; token sums now reconcile.
    expect(short.cost).toBe(10)
    expect(short.calls).toBe(5)
    const sum = (k: 'inputTokens' | 'outputTokens') => Object.values(short.models).reduce((a, m) => a + m[k], 0)
    expect(sum('inputTokens')).toBe(short.inputTokens)
    expect(sum('outputTokens')).toBe(short.outputTokens)

    // A fully reconciled day gets no carried row (idempotent).
    expect(reconciled.models['Unknown (carried)']).toBeUndefined()
  })

  it('adopts a legacy file whose version matches the current one, once, without deleting it', async () => {
    const saved = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: 'legacy-hash',
      lastComputedDate: '2026-05-01',
      days: [emptyDay('2026-05-01', 3.5, 9)],
    }
    const { writeFile, mkdir } = await import('fs/promises')
    await mkdir(TMP_CACHE_ROOT, { recursive: true })
    const legacy = join(TMP_CACHE_ROOT, 'daily-cache.json')
    await writeFile(legacy, JSON.stringify(saved), 'utf-8')

    // First load: versioned file absent → adopt-copy from legacy.
    const first = await loadDailyCache()
    expect(first.days).toEqual(saved.days)
    expect(first.savingsConfigHash).toBe('legacy-hash')
    expect(existsSync(dailyCachePath())).toBe(true)
    // Legacy file is NOT deleted.
    expect(existsSync(legacy)).toBe(true)

    // Adoption is one-time: mutate the legacy file, load again — the versioned
    // file now wins and the stale legacy edit is never re-adopted.
    await writeFile(legacy, JSON.stringify({ ...saved, days: [emptyDay('2000-01-01', 999)] }), 'utf-8')
    const second = await loadDailyCache()
    expect(second.days).toEqual(saved.days)
  })

  it('round-trips a valid cache through save and load', async () => {
    const saved: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: 'cfg-hash-1',
      lastComputedDate: '2026-04-10',
      days: [emptyDay('2026-04-09', 12.5, 40), emptyDay('2026-04-10', 7.25, 28)],
      complete: true,
      watermarkTrusted: true,
    }
    await saveDailyCache(saved)
    const loaded = await loadDailyCache()
    expect(loaded).toEqual(saved)
  })
})

describe('saveDailyCache', () => {
  it('writes atomically so no temp file is left after a successful save', async () => {
    const saved: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: 'cfg-hash-1',
      lastComputedDate: '2026-04-10',
      days: [emptyDay('2026-04-10', 5)],
    }
    await saveDailyCache(saved)
    const { readdir } = await import('fs/promises')
    const files = await readdir(TMP_CACHE_ROOT)
    const tempLeftovers = files.filter(f => f.endsWith('.tmp'))
    expect(tempLeftovers).toEqual([])
    const finalFile = await readFile(dailyCachePath(), 'utf-8')
    expect(JSON.parse(finalFile)).toEqual(saved)
  })
})

describe('addNewDays', () => {
  it('returns a new cache with the added days sorted ascending by date', () => {
    const base: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: '',
      lastComputedDate: '2026-04-08',
      days: [emptyDay('2026-04-07', 3), emptyDay('2026-04-08', 5)],
    }
    const updated = addNewDays(base, [emptyDay('2026-04-10', 9), emptyDay('2026-04-09', 7)], '2026-04-10')
    expect(updated.days.map(d => d.date)).toEqual(['2026-04-07', '2026-04-08', '2026-04-09', '2026-04-10'])
    expect(updated.lastComputedDate).toBe('2026-04-10')
  })

  it('replaces existing days with incoming data (last write wins)', () => {
    const base: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: '',
      lastComputedDate: '2026-04-08',
      days: [emptyDay('2026-04-08', 5)],
    }
    const updated = addNewDays(base, [emptyDay('2026-04-08', 99)], '2026-04-08')
    const aprilEight = updated.days.find(d => d.date === '2026-04-08')!
    expect(aprilEight.cost).toBe(99)
  })

  it('does not regress lastComputedDate if incoming newestDate is older', () => {
    const base: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: '',
      lastComputedDate: '2026-04-10',
      days: [emptyDay('2026-04-10', 5)],
    }
    const updated = addNewDays(base, [emptyDay('2026-04-05', 3)], '2026-04-05')
    expect(updated.lastComputedDate).toBe('2026-04-10')
  })

  it('skips prune when newestDate is malformed (does not silently drop all days)', () => {
    // Regression guard: a corrupt newestDate string used to produce a NaN
    // cutoff, which made `d.date >= "Invalid Date"` always false and
    // wiped every cached day on the next merge. The guard now leaves
    // the entries untouched so the next valid run can prune normally.
    const base: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: '',
      lastComputedDate: '2026-04-10',
      days: [emptyDay('2026-04-08', 1), emptyDay('2026-04-09', 2), emptyDay('2026-04-10', 3)],
    }
    const updated = addNewDays(base, [], 'not-a-date')
    expect(updated.days.map(d => d.date)).toEqual(['2026-04-08', '2026-04-09', '2026-04-10'])
  })

  it('still prunes when newestDate is valid', () => {
    const old = '2010-01-01'
    const recent = '2026-04-10'
    const base: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: '',
      lastComputedDate: recent,
      days: [emptyDay(old, 1), emptyDay(recent, 2)],
    }
    const updated = addNewDays(base, [], recent)
    // 3650-day retention from 2026-04-10 puts the cutoff in 2016; 2010-01-01 must be gone.
    expect(updated.days.find(d => d.date === old)).toBeUndefined()
    expect(updated.days.find(d => d.date === recent)).toBeDefined()
  })
})

describe('getDaysInRange', () => {
  const cache: DailyCache = {
    version: DAILY_CACHE_VERSION,
    savingsConfigHash: '',
    lastComputedDate: '2026-04-10',
    days: [
      emptyDay('2026-04-05', 1),
      emptyDay('2026-04-06', 2),
      emptyDay('2026-04-07', 3),
      emptyDay('2026-04-08', 4),
      emptyDay('2026-04-09', 5),
      emptyDay('2026-04-10', 6),
    ],
  }

  it('returns inclusive start and end range', () => {
    const days = getDaysInRange(cache, '2026-04-07', '2026-04-09')
    expect(days.map(d => d.date)).toEqual(['2026-04-07', '2026-04-08', '2026-04-09'])
  })

  it('returns empty when range is entirely outside cache', () => {
    expect(getDaysInRange(cache, '2026-03-01', '2026-03-10')).toEqual([])
    expect(getDaysInRange(cache, '2026-05-01', '2026-05-10')).toEqual([])
  })

  it('clips to available cache days when range extends beyond', () => {
    const days = getDaysInRange(cache, '2026-04-09', '2026-04-20')
    expect(days.map(d => d.date)).toEqual(['2026-04-09', '2026-04-10'])
  })
})

describe('ensureCacheHydrated', () => {
  it('does not recompute yesterday after it has already been cached', async () => {
    vi.useFakeTimers()
    vi.setSystemTime(new Date('2026-06-12T12:00:00.000Z'))

    const saved: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: '',
      tzKey: currentTzKey(),
      lastComputedDate: '2026-06-11',
      days: [emptyDay('2026-06-11', 5, 10)],
      complete: true,
      watermarkTrusted: true,
    }
    await saveDailyCache(saved)

    let parseCalls = 0
    const hydrated = await ensureCacheHydrated(
      async () => {
        parseCalls += 1
        return []
      },
      () => [],
    )

    expect(parseCalls).toBe(0)
    expect(hydrated).toEqual(saved)
  })

  it('drops a cached today/future entry so it is recomputed live, keeping yesterday cached', async () => {
    vi.useFakeTimers()
    vi.setSystemTime(new Date('2026-06-12T12:00:00.000Z'))

    // A "today" entry can only exist via a backward clock change or a stale
    // cache; it must be purged so today is served live, not from a frozen entry.
    const saved: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: '',
      lastComputedDate: '2026-06-12',
      days: [emptyDay('2026-06-11', 5, 10), emptyDay('2026-06-12', 9, 20)],
      complete: true,
    }
    await saveDailyCache(saved)

    let parseCalls = 0
    const hydrated = await ensureCacheHydrated(
      async () => {
        parseCalls += 1
        return []
      },
      () => [],
    )

    expect(parseCalls).toBe(0)
    expect(hydrated.days.map(d => d.date)).toEqual(['2026-06-11'])
    expect(hydrated.lastComputedDate).toBe('2026-06-11')
  })
})

// Codex discovery went structural in v16 (#873/#626), admitting rollouts from
// third-party frontends that v15 rollups never counted. Every historical day is
// served from this cache (usage-aggregator only recomputes today) and retention
// is ten years, so without a schema bump an upgrading user keeps the pre-fix
// numbers forever: the session COUNT moves because discovery reruns, while
// cost/calls stay frozen — a self-contradicting report that reads as "fixed".
describe('ensureCacheHydrated: schema version invalidation (#873)', () => {
  it('re-derives a warm v15 cache instead of serving its pre-fix rollups', async () => {
    vi.useFakeTimers()
    vi.setSystemTime(new Date('2026-06-12T12:00:00.000Z'))

    const { writeFile, mkdir } = await import('fs/promises')
    await mkdir(TMP_CACHE_ROOT, { recursive: true })
    // A cache exactly as a pre-fix release left it: current schema at the time,
    // finalized off a complete parse, watermark at yesterday, matching tz.
    // Nothing but the version bump can invalidate it.
    const v15 = {
      version: 15,
      savingsConfigHash: '',
      tzKey: currentTzKey(),
      lastComputedDate: '2026-06-11',
      days: [emptyDay('2026-06-11', 4.55, 1)],
      complete: true,
      watermarkTrusted: true,
    }
    await writeFile(join(TMP_CACHE_ROOT, 'daily-cache.v15.json'), JSON.stringify(v15), 'utf-8')

    let parseCalls = 0
    const hydrated = await ensureCacheHydrated(
      async () => {
        parseCalls += 1
        return []
      },
      () => [emptyDay('2026-06-11', 18.2, 2)],
    )

    // The whole point: the window is re-parsed rather than served frozen.
    expect(parseCalls).toBe(1)
    // ...and the fresh derivation wins over the stale v15 day.
    expect(hydrated.days.find(d => d.date === '2026-06-11')?.cost).toBe(18.2)
    expect(hydrated.days.find(d => d.date === '2026-06-11')?.calls).toBe(2)
    expect(hydrated.version).toBe(DAILY_CACHE_VERSION)
    // The v15 file is never rewritten or deleted — old binaries still own it.
    expect(JSON.parse(await readFile(join(TMP_CACHE_ROOT, 'daily-cache.v15.json'), 'utf-8')).version).toBe(15)
  })

  it('carries a v15 day forward when its sources can no longer re-derive it', async () => {
    vi.useFakeTimers()
    vi.setSystemTime(new Date('2026-06-12T12:00:00.000Z'))

    const { writeFile, mkdir } = await import('fs/promises')
    await mkdir(TMP_CACHE_ROOT, { recursive: true })
    const v15 = {
      version: 15,
      savingsConfigHash: '',
      tzKey: currentTzKey(),
      lastComputedDate: '2026-06-11',
      days: [emptyDay('2026-04-02', 7, 3), emptyDay('2026-06-11', 4.55, 1)],
      complete: true,
      watermarkTrusted: true,
    }
    await writeFile(join(TMP_CACHE_ROOT, 'daily-cache.v15.json'), JSON.stringify(v15), 'utf-8')

    // The parse can only still see the recent day; April's sources are gone.
    const hydrated = await ensureCacheHydrated(
      async () => [],
      () => [emptyDay('2026-06-11', 18.2, 2)],
    )

    // NEVER-LOSE (v14) still holds across this bump: the sourceless day keeps
    // its old accounting rather than being dropped or zeroed.
    expect(hydrated.days.find(d => d.date === '2026-04-02')?.cost).toBe(7)
    expect(hydrated.days.find(d => d.date === '2026-06-11')?.cost).toBe(18.2)
  })
})

describe('ensureCacheHydrated: Codex usage-record accounting migration', () => {
  it.each([40, 42])('re-derives shrinking Codex slices from v%i and carries days with missing sources', async sourceVersion => {
    vi.useFakeTimers()
    vi.setSystemTime(new Date('2026-09-27T12:00:00.000Z'))

    const { writeFile, mkdir } = await import('fs/promises')
    await mkdir(TMP_CACHE_ROOT, { recursive: true })
    const model = 'GPT-5.5'
    const codexDay = (date: string, calls: number, inputTokens: number): DailyEntry => {
      const cost = calls * 0.5
      const modelStats = {
        calls,
        cost,
        savingsUSD: 0,
        inputTokens,
        outputTokens: calls * 100,
        cacheReadTokens: 0,
        cacheWriteTokens: 0,
      }
      const providerSlice = {
        calls,
        cost,
        savingsUSD: 0,
        sessions: 1,
        inputTokens,
        outputTokens: calls * 100,
        cacheReadTokens: 0,
        cacheWriteTokens: 0,
        models: { [model]: modelStats },
        categories: {},
      }
      return {
        date,
        cost,
        savingsUSD: 0,
        calls,
        sessions: 1,
        inputTokens,
        outputTokens: calls * 100,
        cacheReadTokens: 0,
        cacheWriteTokens: 0,
        editTurns: 0,
        oneShotTurns: 0,
        models: { [model]: modelStats },
        categories: {},
        providers: { codex: providerSlice },
      }
    }

    const oldCodexDay = codexDay('2026-09-01', 2, 1_000)
    const sourceGoneDay = codexDay('2026-08-01', 4, 2_000)
    await writeFile(join(TMP_CACHE_ROOT, `daily-cache.v${sourceVersion}.json`), JSON.stringify({
      version: sourceVersion,
      savingsConfigHash: '',
      tzKey: currentTzKey(),
      lastComputedDate: '2026-09-01',
      days: [sourceGoneDay, oldCodexDay],
      complete: true,
      watermarkTrusted: true,
    }), 'utf-8')

    let parseCalls = 0
    const freshCodexDay = codexDay('2026-09-01', 1, 700)
    const hydrated = await ensureCacheHydrated(
      async () => { parseCalls += 1; return [] },
      () => [freshCodexDay],
    )

    expect(parseCalls).toBe(1)
    expect(hydrated.version).toBe(DAILY_CACHE_VERSION)
    expect(hydrated.days.find(day => day.date === '2026-09-01')?.providers['codex']?.calls).toBe(1)
    expect(hydrated.days.find(day => day.date === '2026-08-01')).toMatchObject({
      calls: 4,
      carried: true,
      providers: { codex: { calls: 4 } },
    })
  })
})

describe('ensureCacheHydrated: Claude queued prompt categories', () => {
  it.each([39, 43])('re-derives a settled v%i day when turns are reclassified but calls stay equal', async sourceVersion => {
    vi.useFakeTimers()
    vi.setSystemTime(new Date('2026-09-27T12:00:00.000Z'))

    const { writeFile, mkdir } = await import('fs/promises')
    await mkdir(TMP_CACHE_ROOT, { recursive: true })
    const date = '2026-09-01'
    const category = { turns: 1, cost: 1, savingsUSD: 0, editTurns: 0, oneShotTurns: 0 }
    const oldDay = emptyDay(date, 1, 1)
    oldDay.categories = { exploration: category }
    oldDay.providers = { claude: { calls: 1, cost: 1, savingsUSD: 0, categories: oldDay.categories } }
    const freshDay = emptyDay(date, 1, 1)
    freshDay.categories = { feature: category }
    freshDay.providers = { claude: { calls: 1, cost: 1, savingsUSD: 0, categories: freshDay.categories } }

    await writeFile(join(TMP_CACHE_ROOT, `daily-cache.v${sourceVersion}.json`), JSON.stringify({
      version: sourceVersion,
      savingsConfigHash: '',
      tzKey: currentTzKey(),
      lastComputedDate: date,
      days: [oldDay],
      complete: true,
      watermarkTrusted: true,
    }), 'utf-8')

    let parseCalls = 0
    const hydrated = await ensureCacheHydrated(
      async () => { parseCalls += 1; return [] },
      () => [freshDay],
    )

    expect(parseCalls).toBe(1)
    expect(hydrated.version).toBe(DAILY_CACHE_VERSION)
    expect(hydrated.days.find(day => day.date === date)?.providers['claude']?.categories)
      .toEqual({ feature: category })
  })
})

describe('withDailyCacheLock', () => {
  it('serializes concurrent operations', async () => {
    const sequence: string[] = []
    const op = async (tag: string): Promise<void> => {
      await withDailyCacheLock(async () => {
        sequence.push(`start-${tag}`)
        await new Promise(r => setTimeout(r, 20))
        sequence.push(`end-${tag}`)
      })
    }
    await Promise.all([op('a'), op('b'), op('c')])
    for (let i = 0; i < sequence.length; i += 2) {
      expect(sequence[i]?.startsWith('start-')).toBe(true)
      expect(sequence[i + 1]?.startsWith('end-')).toBe(true)
      expect(sequence[i]!.slice(6)).toBe(sequence[i + 1]!.slice(4))
    }
  })
})

describe('ensureCacheHydrated: savings config invalidation', () => {
  it('re-derives on savingsConfigHash change but CARRIES days the parse cannot re-derive', async () => {
    // Seed a cache with a day OLDER than yesterday so the hydration window
    // (which keeps `d.date < yesterdayStr`) actually retains it.
    const twoDaysAgo = new Date(Date.now() - 2 * 24 * 60 * 60 * 1000)
    const twoDaysAgoStr = `${twoDaysAgo.getFullYear()}-${String(twoDaysAgo.getMonth() + 1).padStart(2, '0')}-${String(twoDaysAgo.getDate()).padStart(2, '0')}`
    const seeded: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: 'cfg-A',
      lastComputedDate: twoDaysAgoStr,
      days: [emptyDay(twoDaysAgoStr, 1.5, 3)],
      complete: true,
    }
    await saveDailyCache(seeded)

    // The re-derive parse finds NOTHING (session files already deleted). The
    // day must survive as carried — this exact path used to wipe it.
    const parseSessions = async (): Promise<ProjectSummary[]> => []
    const aggregateDays = (): DailyEntry[] => []

    const rehydrated = await ensureCacheHydrated(parseSessions, aggregateDays, 'cfg-B')
    expect(rehydrated.savingsConfigHash).toBe('cfg-B')
    expect(rehydrated.days).toHaveLength(1)
    expect(rehydrated.days[0]).toMatchObject({ date: twoDaysAgoStr, cost: 1.5, calls: 3, carried: true })
    expect(rehydrated.complete).toBe(true)

    // Same hash → cached days survive untouched (no carried marker).
    const seeded2: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: 'cfg-C',
      lastComputedDate: twoDaysAgoStr,
      days: [emptyDay(twoDaysAgoStr, 1.5, 3)],
      complete: true,
    }
    await saveDailyCache(seeded2)
    const preserved = await ensureCacheHydrated(parseSessions, aggregateDays, 'cfg-C')
    expect(preserved.days).toHaveLength(1)
    expect(preserved.days[0]!.date).toBe(twoDaysAgoStr)
    expect(preserved.days[0]!.carried).toBeUndefined()
  })
})

describe('ensureCacheHydrated: timezone invalidation', () => {
  const twoDaysAgo = new Date(Date.now() - 2 * 24 * 60 * 60 * 1000)
  const twoDaysAgoStr = `${twoDaysAgo.getFullYear()}-${String(twoDaysAgo.getMonth() + 1).padStart(2, '0')}-${String(twoDaysAgo.getDate()).padStart(2, '0')}`
  const parseSessions = async (): Promise<ProjectSummary[]> => []
  const aggregateDays = (): DailyEntry[] => []

  it('re-derives on timezone change but keeps days whose sources are gone', async () => {
    // Days are bucketed by local midnight, so a cache tagged under a different
    // timezone re-derives everything. Days that can no longer be re-derived stay
    // (old-tz bucketing beats a silent zero). 'Test/OtherZone' can never equal a
    // real IANA zone.
    const seeded: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: '',
      tzKey: 'Test/OtherZone',
      lastComputedDate: twoDaysAgoStr,
      days: [emptyDay(twoDaysAgoStr, 1.5, 3)],
      complete: true,
    }
    await saveDailyCache(seeded)
    const rehydrated = await ensureCacheHydrated(parseSessions, aggregateDays, '')
    expect(rehydrated.tzKey).toBe(currentTzKey())
    expect(rehydrated.days).toHaveLength(1)
    expect(rehydrated.days[0]).toMatchObject({ date: twoDaysAgoStr, cost: 1.5, carried: true })
  })

  it('keeps cached days when the tzKey matches the current timezone', async () => {
    const seeded: DailyCache = {
      version: DAILY_CACHE_VERSION,
      savingsConfigHash: '',
      tzKey: currentTzKey(),
      lastComputedDate: twoDaysAgoStr,
      days: [emptyDay(twoDaysAgoStr, 1.5, 3)],
      complete: true,
    }
    await saveDailyCache(seeded)
    const preserved = await ensureCacheHydrated(parseSessions, aggregateDays, '')
    expect(preserved.days).toHaveLength(1)
    expect(preserved.days[0]!.date).toBe(twoDaysAgoStr)
  })
})