import { spawn } from 'node:child_process'
import type { SubagentBackend, SubagentInput, SubagentResult } from './types.js'
import { logger } from '../logger.js'

const CODEX_BIN = process.env.CODEX_BIN ?? 'codex'
const DEFAULT_TIMEOUT_MS = 900_000

function parseTokenUsage(text: string): { total?: number } {
  const m = /tokens used\s*(\d[\d,]*)/i.exec(text)
  if (!m || !m[1]) return {}
  const n = Number.parseInt(m[1].replace(/,/g, ''), 10)
  return Number.isFinite(n) ? { total: n } : {}
}

function stripBanner(raw: string): string {
  // Codex CLI prints a header ("model: ...", "provider: ...") and a trailing "tokens used" line.
  // Extract the body between the "codex" label and "tokens used" line, or return raw if unstructured.
  const codexIdx = raw.lastIndexOf('\ncodex\n')
  const tokensIdx = raw.indexOf('\ntokens used\n')
  const start = codexIdx >= 0 ? codexIdx + '\ncodex\n'.length : 0
  const end = tokensIdx >= 0 ? tokensIdx : raw.length
  return raw.slice(start, end).trim()
}

export class CodexBackend implements SubagentBackend {
  readonly name = 'codex'

  async run(input: SubagentInput): Promise<SubagentResult> {
    const start = Date.now()
    const timeoutMs = (input.timeoutMs ?? Number.parseInt(process.env.CODEX_TIMEOUT_MS ?? '', 10)) || DEFAULT_TIMEOUT_MS
    const args = ['exec', '--skip-git-repo-check', '-s', 'read-only', input.prompt]
    const result: SubagentResult = { backend: this.name, text: '', durationMs: 0 }

    return await new Promise<SubagentResult>((resolve) => {
      const child = spawn(CODEX_BIN, args, { stdio: ['ignore', 'pipe', 'pipe'] })
      const stdout: Buffer[] = []
      const stderr: Buffer[] = []
      const timer = setTimeout(() => {
        child.kill('SIGKILL')
        result.error = `codex timeout after ${timeoutMs}ms`
      }, timeoutMs)
      timer.unref()

      child.stdout.on('data', chunk => stdout.push(chunk))
      child.stderr.on('data', chunk => stderr.push(chunk))
      child.on('error', err => {
        clearTimeout(timer)
        result.error = err.message
        result.durationMs = Date.now() - start
        resolve(result)
      })
      child.on('close', code => {
        clearTimeout(timer)
        const raw = Buffer.concat(stdout).toString('utf8')
        const errTxt = Buffer.concat(stderr).toString('utf8').trim()
        result.durationMs = Date.now() - start
        if (code !== 0 && !result.error) {
          result.error = `codex exit ${code}: ${errTxt.slice(0, 400)}`
          result.text = stripBanner(raw)
          resolve(result)
          return
        }
        const body = stripBanner(raw)
        const usage = parseTokenUsage(raw)
        result.text = body
        result.outputTokens = usage.total
        if (result.error) logger.warn({ err: result.error }, 'codex partial')
        resolve(result)
      })
    })
  }
}