// Codex rollouts are append-only and the active ones are huge, so a run that
// re-read a grown session from byte 0 paid for the whole file to pick up a few
// KB. The parser now restarts from the last task boundary it recorded. What has
// to hold: the resumed decode is byte-identical to a full re-parse, and it
// really does start at an offset rather than quietly re-reading everything.
import { describe, it, expect, beforeEach, afterEach, vi } from 'vitest'
import { appendFile, mkdtemp, mkdir, rm, writeFile } from 'fs/promises'
import { join } from 'path'
import { tmpdir } from 'os'

const readLineCalls: Array<{ filePath: string; startByteOffset?: number }> = []
vi.mock('../../src/fs-utils.js', async (importOriginal) => {
  const actual = await importOriginal<typeof import('../../src/fs-utils.js')>()
  return {
    ...actual,
    readSessionLines: (filePath: string, skip?: unknown, options?: { startByteOffset?: number }) => {
      readLineCalls.push({ filePath, startByteOffset: options?.startByteOffset })
      // eslint-disable-next-line @typescript-eslint/no-explicit-any
      return (actual.readSessionLines as any)(filePath, skip, options)
    },
  }
})

import { clearCodexMemCaches, flushCodexCache, withCodexCacheDirectory } from '../../src/codex-cache.js'
import { createCodexProvider } from '../../src/providers/codex.js'
import type { ParsedProviderCall } from '../../src/providers/types.js'

let tmpDir: string
let sessionPath: string

beforeEach(async () => {
  tmpDir = await mkdtemp(join(tmpdir(), 'codex-resume-'))
  readLineCalls.length = 0
})

afterEach(async () => {
  await rm(tmpDir, { recursive: true, force: true })
})

function meta(): string {
  return JSON.stringify({
    type: 'session_meta',
    timestamp: '2026-04-14T10:00:00Z',
    payload: { cwd: '/Users/test/proj', originator: 'codex-cli', session_id: 'sess-1', model: 'gpt-5.3-codex' },
  })
}

// One complete task: user turn, tools, an edit, an MCP call, usage, completion.
function task(n: number, cumulative: { input: number; cached: number; output: number; reasoning: number }): string[] {
  const at = (s: number) => `2026-04-14T10:${String(n).padStart(2, '0')}:${String(s).padStart(2, '0')}Z`
  return [
    JSON.stringify({ type: 'event_msg', timestamp: at(0), payload: { type: 'task_started' } }),
    JSON.stringify({
      type: 'response_item', timestamp: at(1),
      payload: { type: 'message', role: 'user', content: [{ type: 'input_text', text: `task ${n}` }] },
    }),
    JSON.stringify({
      type: 'response_item', timestamp: at(2),
      payload: { type: 'function_call', name: 'shell', call_id: `c${n}`, arguments: JSON.stringify({ command: `ls ${n}` }) },
    }),
    JSON.stringify({
      type: 'response_item', timestamp: at(3),
      payload: { type: 'function_call_output', call_id: `c${n}` },
    }),
    JSON.stringify({
      type: 'event_msg', timestamp: at(4),
      payload: {
        type: 'patch_apply_end', success: n % 2 === 0,
        changes: { [`/Users/test/proj/f${n}.ts`]: { unified_diff: '@@ -1 +1,2 @@\n-old\n+new\n+extra\n' } },
      },
    }),
    JSON.stringify({
      type: 'event_msg', timestamp: at(5),
      payload: { type: 'mcp_tool_call_end', call_id: `m${n}`, invocation: { server: 'github', tool: 'list' }, duration_ms: 120, result: { Ok: {} } },
    }),
    JSON.stringify({
      type: 'response_item', timestamp: at(6),
      payload: { type: 'message', role: 'assistant', content: [{ type: 'output_text', text: 'x'.repeat(40) }] },
    }),
    JSON.stringify({
      type: 'event_msg', timestamp: at(7),
      payload: {
        type: 'token_count',
        info: {
          last_token_usage: { input_tokens: 100, cached_input_tokens: 20, output_tokens: 50, reasoning_output_tokens: 10, total_tokens: 180 },
          total_token_usage: {
            input_tokens: cumulative.input, cached_input_tokens: cumulative.cached,
            output_tokens: cumulative.output, reasoning_output_tokens: cumulative.reasoning,
            total_tokens: cumulative.input + cumulative.output + cumulative.reasoning,
          },
        },
      },
    }),
    JSON.stringify({ type: 'event_msg', timestamp: at(8), payload: { type: 'task_complete', duration_ms: 5000 } }),
  ]
}

function tasks(from: number, to: number): string[] {
  const lines: string[] = []
  for (let n = from; n <= to; n++) {
    lines.push(...task(n, { input: 100 * n, cached: 20 * n, output: 50 * n, reasoning: 10 * n }))
  }
  return lines
}

async function writeRollout(lines: string[]): Promise<string> {
  const dir = join(tmpDir, 'sessions', '2026', '04', '14')
  await mkdir(dir, { recursive: true })
  const path = join(dir, 'rollout-sess-1.jsonl')
  await writeFile(path, lines.join('\n') + '\n')
  return path
}

async function parse(cacheDir: string, codexDir = tmpDir): Promise<ParsedProviderCall[]> {
  clearCodexMemCaches()
  return withCodexCacheDirectory(cacheDir, async () => {
    const provider = createCodexProvider(codexDir)
    const sources = await provider.discoverSessions()
    const seenKeys = new Set<string>()
    const calls: ParsedProviderCall[] = []
    for (const source of sources) {
      for await (const call of provider.createSessionParser!(source, seenKeys).parse()) calls.push(call)
    }
    await flushCodexCache()
    clearCodexMemCaches()
    return calls
  })
}

describe('codex incremental resume', () => {
  it('resumes at a task boundary and matches a full re-parse exactly', async () => {
    const warmCache = join(tmpDir, 'cache-warm')
    const coldCache = join(tmpDir, 'cache-cold')

    sessionPath = await writeRollout([meta(), ...tasks(1, 3)])
    const first = await parse(warmCache)
    expect(first.length).toBe(3)

    await appendFile(sessionPath, tasks(4, 6).join('\n') + '\n')

    readLineCalls.length = 0
    const resumed = await parse(warmCache)
    const resumeReads = readLineCalls.filter(c => c.filePath === sessionPath)
    // The parse re-entered the file at a boundary rather than at byte 0.
    expect(resumeReads.some(c => (c.startByteOffset ?? 0) > 0)).toBe(true)
    expect(resumeReads.every(c => (c.startByteOffset ?? 0) > 0)).toBe(true)

    // Byte-for-byte agreement with a decode that never saw a cache.
    const full = await parse(coldCache)
    expect(resumed.length).toBe(6)
    expect(JSON.stringify(resumed)).toBe(JSON.stringify(full))
  })

  it('stays exact across successive appends, resuming from a resumed state', async () => {
    const warmCache = join(tmpDir, 'cache-warm')

    sessionPath = await writeRollout([meta(), ...tasks(1, 2)])
    await parse(warmCache)
    await appendFile(sessionPath, tasks(3, 4).join('\n') + '\n')
    await parse(warmCache)
    // A tail with no task boundary at all: the next run restarts from the same
    // boundary and re-decodes the open task.
    await appendFile(sessionPath, tasks(5, 5).slice(1).join('\n') + '\n')
    const resumed = await parse(warmCache)

    const full = await parse(join(tmpDir, 'cache-cold'))
    expect(JSON.stringify(resumed)).toBe(JSON.stringify(full))
  })

  it('serves an unchanged file from the cache without reading it', async () => {
    const cacheDir = join(tmpDir, 'cache')
    sessionPath = await writeRollout([meta(), ...tasks(1, 2)])
    const first = await parse(cacheDir)

    readLineCalls.length = 0
    const second = await parse(cacheDir)
    expect(readLineCalls.filter(c => c.filePath === sessionPath)).toHaveLength(0)
    expect(JSON.stringify(second)).toBe(JSON.stringify(first))
  })

  it('falls back to a full re-parse when the stored resume state is unusable', async () => {
    const cacheDir = join(tmpDir, 'cache')
    sessionPath = await writeRollout([meta(), ...tasks(1, 2)])
    await parse(cacheDir)

    const cachePath = join(cacheDir, 'codex-results.json')
    const { readFile } = await import('fs/promises')
    const raw = JSON.parse(await readFile(cachePath, 'utf-8'))
    raw.files[sessionPath].resumeState = { garbage: true }
    await writeFile(cachePath, JSON.stringify(raw))
    const { clearCodexMemCaches } = await import('../../src/codex-cache.js')
    clearCodexMemCaches()

    await appendFile(sessionPath, tasks(3, 3).join('\n') + '\n')
    readLineCalls.length = 0
    const resumed = await parse(cacheDir)
    expect(readLineCalls.filter(c => c.filePath === sessionPath).every(c => (c.startByteOffset ?? 0) === 0)).toBe(true)

    const full = await parse(join(tmpDir, 'cache-cold'))
    expect(JSON.stringify(resumed)).toBe(JSON.stringify(full))
  })
})

// The resume snapshot has to carry EVERY field the decode reads from an earlier
// line. Missing one shows up only when the split lands between the line that
// sets it and the line that reads it — so split at every line boundary and
// require the resumed decode to equal a full one each time.
const J = (o: unknown) => JSON.stringify(o)
const ts = (n: number, s: number) => `2026-04-14T${String(10 + Math.floor(n / 60)).padStart(2, '0')}:${String(n % 60).padStart(2, '0')}:${String(s).padStart(2, '0')}Z`

function richTask(n: number, opts: { tokens?: false | 'empty'; reasoning?: number; model?: string; noComplete?: boolean } = {}): string[] {
  const lines: string[] = [J({ type: 'event_msg', timestamp: ts(n, 0), payload: { type: 'task_started' } })]
  if (opts.model) lines.push(J({ type: 'turn_context', timestamp: ts(n, 0), payload: { model: opts.model } }))
  lines.push(
    J({ type: 'response_item', timestamp: ts(n, 1), payload: { type: 'message', role: 'user', content: [{ type: 'input_text', text: `please do task ${n} with some length` }] } }),
    J({ type: 'response_item', timestamp: ts(n, 2), payload: { type: 'function_call', name: 'shell', call_id: `c${n}`, arguments: J({ command: `ls ${n}` }) } }),
    J({ type: 'response_item', timestamp: ts(n, 3), payload: { type: 'function_call_output', call_id: `c${n}` } }),
    J({ type: 'event_msg', timestamp: ts(n, 4), payload: { type: 'patch_apply_end', success: n % 3 !== 0, changes: { [`/Users/test/proj/f${n}.ts`]: { unified_diff: '@@ -1 +1,2 @@\n-old\n+new\n+extra\n' } } } }),
    J({ type: 'event_msg', timestamp: ts(n, 5), payload: { type: 'mcp_tool_call_end', call_id: `m${n}`, invocation: { server: 'github', tool: 'list' }, duration_ms: 120, result: { Ok: {} } } }),
    J({ type: 'response_item', timestamp: ts(n, 6), payload: { type: 'message', role: 'assistant', content: [{ type: 'output_text', text: 'y'.repeat(120) }] } }),
  )
  if (opts.tokens === 'empty') {
    // No `info`: the estimated-usage path, which advances estCounter.
    lines.push(J({ type: 'event_msg', timestamp: ts(n, 7), payload: { type: 'token_count' } }))
  } else if (opts.tokens !== false) {
    const c = { input: 100 * n, cached: 20 * n, output: 50 * n, reasoning: (opts.reasoning ?? 10) * n }
    lines.push(J({ type: 'event_msg', timestamp: ts(n, 7), payload: { type: 'token_count', info: {
      last_token_usage: { input_tokens: 100, cached_input_tokens: 20, output_tokens: 50, reasoning_output_tokens: opts.reasoning ?? 10, total_tokens: 180 },
      total_token_usage: { input_tokens: c.input, cached_input_tokens: c.cached, output_tokens: c.output, reasoning_output_tokens: c.reasoning, total_tokens: c.input + c.output + c.reasoning },
    } } }))
  }
  if (!opts.noComplete) lines.push(J({ type: 'event_msg', timestamp: ts(n, 8), payload: { type: 'task_complete', duration_ms: 5000 } }))
  return lines
}

const RICH_LINES = [
  J({ type: 'session_meta', timestamp: ts(0, 0), payload: { cwd: '/Users/test/proj', originator: 'codex-cli', session_id: 'sess-1', model: 'gpt-5.3-codex' } }),
  ...richTask(1),
  ...richTask(2, { tokens: 'empty' }),
  ...richTask(7, { tokens: 'empty' }),
  ...richTask(3, { model: 'gpt-5.3-codex-mini' }),
  ...richTask(4, { reasoning: 33 }),
  ...richTask(5, { noComplete: true }),
  ...richTask(6),
]

const FORK_LINES = [
  J({ type: 'session_meta', timestamp: ts(0, 0), payload: { cwd: '/Users/test/proj', originator: 'codex-cli', session_id: 'sess-2', forked_from_id: 'sess-1', model: 'gpt-5.3-codex' } }),
  // Parent history replayed inside the 5s fork cutoff: must stay skipped across a split.
  ...richTask(0).map(l => l.replace(/2026-04-14T10:00:0\d/g, '2026-04-14T10:00:01')),
  ...richTask(11),
  ...richTask(12, { tokens: 'empty' }),
]

describe('codex resume differential', () => {
  async function rollout(lines: string[]): Promise<{ codexDir: string; path: string }> {
    const codexDir = await mkdtemp(join(tmpdir(), 'codex-split-'))
    const dir = join(codexDir, 'sessions', '2026', '04', '14')
    await mkdir(dir, { recursive: true })
    const path = join(dir, 'rollout-sess-1.jsonl')
    await writeFile(path, lines.join('\n') + '\n')
    return { codexDir, path }
  }

  async function assertEverySplitMatches(lines: string[]): Promise<void> {
    const base = await rollout(lines)
    const full = await parse(await mkdtemp(join(tmpdir(), 'codex-c-')), base.codexDir)
    expect(full.length).toBeGreaterThan(0)

    for (let k = 1; k < lines.length; k++) {
      const split = await rollout(lines.slice(0, k))
      const cacheDir = await mkdtemp(join(tmpdir(), 'codex-c-'))
      await parse(cacheDir, split.codexDir)
      await appendFile(split.path, lines.slice(k).join('\n') + '\n')
      const resumed = await parse(cacheDir, split.codexDir)
      expect(JSON.stringify(resumed), `split after line ${k}: ${lines[k - 1]!.slice(0, 80)}`).toBe(JSON.stringify(full))
    }
  }

  it('matches a full re-parse at every line boundary of a rich session', async () => {
    await assertEverySplitMatches(RICH_LINES)
  }, 60_000)

  it('matches a full re-parse at every line boundary of a forked session', async () => {
    await assertEverySplitMatches(FORK_LINES)
  }, 60_000)
})