'use strict'

const fs = require('fs')
const path = require('path')

// 日志总线：内存环形缓冲供管理窗口实时查看，同时落一份文件供现场排障。
// 现场没有外网也没有终端，文件日志是事后定位问题的唯一线索。
class LogBus {
  constructor(options = {}) {
    const { maxLines = 2000, file = null, maxFileBytes = 4 * 1024 * 1024 } = options
    this.maxLines = maxLines
    this.maxFileBytes = maxFileBytes
    this.lines = []
    this.listeners = new Set()
    // 子进程的输出是流式分片的，可能把一行拆到两次 data 事件里
    this.pending = new Map()
    this.stream = null
    this.file = null
    this.bytesWritten = 0
    this.rotating = false
    this.closed = false
    if (file) this.openFile(file)
  }

  openFile(file) {
    this.file = file
    try {
      fs.mkdirSync(path.dirname(file), { recursive: true })
      if (fs.existsSync(file) && fs.statSync(file).size > this.maxFileBytes) this.rotateFile()
      this.stream = fs.createWriteStream(file, { flags: 'a' })
      this.bytesWritten = fs.existsSync(file) ? fs.statSync(file).size : 0
    } catch (err) {
      this.stream = null
      this.push('console', `日志文件不可写，仅保留内存日志：${err.message}`)
    }
  }

  // 把当前日志改名成 .1：Windows 上 rename 到已存在的目标会失败，先删掉旧 .1
  rotateFile() {
    const rotated = `${this.file}.1`
    try {
      fs.rmSync(rotated, { force: true })
    } catch {
      // 删不掉就让 rename 失败，由调用方落到「仅内存日志」兜底
    }
    if (fs.existsSync(this.file)) fs.renameSync(this.file, rotated)
  }

  // 运行中轮转：push 时按累计字节数触发，否则长赛事跑满一天文件会无限增长。
  // 必须先关流把缓冲刷盘再改名（Windows 下打开中的文件不能改名），
  // 轮转窗口内新日志只进内存缓冲，窗口很短。
  rotate() {
    if (!this.file || this.rotating) return
    this.rotating = true
    const stream = this.stream
    this.stream = null
    this.bytesWritten = 0
    const reopen = () => {
      this.rotating = false
      if (this.closed) return
      try {
        this.rotateFile()
      } catch (err) {
        this.push('console', `日志文件轮转失败，仅保留内存日志：${err.message}`)
        return
      }
      this.stream = fs.createWriteStream(this.file, { flags: 'a' })
    }
    if (stream) stream.end(reopen)
    else reopen()
  }

  append(source, chunk) {
    const text = `${this.pending.get(source) || ''}${String(chunk)}`
    const parts = text.split(/\r?\n/)
    // 最后一段是没有换行的残行，留到下一次拼接
    this.pending.set(source, parts.pop() || '')
    for (const part of parts) this.push(source, part)
  }

  push(source, message) {
    const line = `[${new Date().toISOString()}] [${source}] ${message}`
    this.lines.push(line)
    if (this.lines.length > this.maxLines) {
      this.lines.splice(0, this.lines.length - this.maxLines)
    }
    if (this.stream) {
      const text = `${line}\n`
      const bytes = Buffer.byteLength(text)
      if (this.maxFileBytes > 0 && this.bytesWritten + bytes > this.maxFileBytes) this.rotate()
      if (this.stream) {
        this.stream.write(text)
        this.bytesWritten += bytes
      }
    }
    for (const listener of this.listeners) {
      try {
        listener(line)
      } catch {
        // 单个订阅者出错不能拖垮日志链路
      }
    }
  }

  tail() {
    return this.lines.slice()
  }

  clear() {
    this.lines = []
  }

  onLine(listener) {
    this.listeners.add(listener)
    return () => this.listeners.delete(listener)
  }

  close() {
    this.closed = true
    if (this.stream) {
      this.stream.end()
      this.stream = null
    }
  }
}

module.exports = { LogBus }