package logger

import (
	"fmt"
	"io"
	"log"
	"os"
	"path/filepath"
	"strings"
	"sync"
	"sync/atomic"
	"time"

	"douyu_go/internal/constants"
	"douyu_go/internal/types"
)

const (
	asyncLogBufferSize = 8192
	logTimeLayout      = "2006/01/02 15:04:05.000"
	logEntryTimeLayout = "2006-01-02 15:04:05.000"
)

// minLevel 日志最低等级，低于此等级的日志不输出。0=info, 1=warn, 2=error。
var minLevel atomic.Int32

var douyuOffset atomic.Int64

// SetMinLevel 设置日志最低显示等级。
func SetMinLevel(level string) {
	minLevel.Store(int32(levelPriority(level)))
}

// SetDouyuOffset 设置斗鱼服务端时间与本地时间的偏移量，用于日志双时间显示。
func SetDouyuOffset(offset time.Duration) {
	douyuOffset.Store(int64(offset))
}

func levelPriority(level string) int {
	switch strings.ToLower(level) {
	case "debug":
		return -1
	case "info":
		return 0
	case "warn":
		return 1
	case "error":
		return 2
	default:
		return 0
	}
}

// AsyncLogWriter 异步日志写入器，队列满时丢弃日志以保护主链路。
type AsyncLogWriter struct {
	mu      sync.RWMutex
	dst     io.Writer
	ch      chan []byte
	wg      sync.WaitGroup
	closed  uint32
	dropped uint64
}

// NewAsyncLogWriter 创建异步日志写入器。
func NewAsyncLogWriter(dst io.Writer, buffer int) *AsyncLogWriter {
	if buffer <= 0 {
		buffer = 1024
	}
	w := &AsyncLogWriter{
		dst: dst,
		ch:  make(chan []byte, buffer),
	}
	w.wg.Add(1)
	go w.run()
	return w
}

// Write 异步写日志；队列满时丢弃，避免抢购请求被磁盘 I/O 阻塞。
func (w *AsyncLogWriter) Write(p []byte) (int, error) {
	if w == nil {
		return len(p), nil
	}
	w.mu.RLock()
	defer w.mu.RUnlock()
	if atomic.LoadUint32(&w.closed) == 1 {
		return len(p), nil
	}
	buf := append([]byte(nil), p...)
	select {
	case w.ch <- buf:
	default:
		atomic.AddUint64(&w.dropped, 1)
	}
	return len(p), nil
}

func (w *AsyncLogWriter) run() {
	defer w.wg.Done()
	for p := range w.ch {
		_, _ = w.dst.Write(p)
	}
	if dropped := atomic.LoadUint64(&w.dropped); dropped > 0 {
		_, _ = fmt.Fprintln(w.dst, formatLogLine(time.Now(), "日志", "warn", "", fmt.Sprintf("日志队列已丢弃 %d 条，已优先保护抢购链路", dropped)))
	}
}

// Close 关闭写入器，等待队列清空。
func (w *AsyncLogWriter) Close() error {
	if w == nil {
		return nil
	}
	w.mu.Lock()
	defer w.mu.Unlock()
	if atomic.CompareAndSwapUint32(&w.closed, 0, 1) {
		close(w.ch)
		w.wg.Wait()
	}
	return nil
}

// sink 日志输出汇集点，把结构化日志条目分发到内存、文件和终端。
type sink struct {
	async  *AsyncLogWriter // 文件异步写入（无文件时为 nil，仅写内存+终端）
	store  *MemoryLogStore
	stdout bool
}

// write 分发一条日志：内存同步写入，文件异步写入，终端尽力写入。
func (s *sink) write(entry types.LogEntry) {
	s.store.Append(entry)
	if s.async != nil {
		_, _ = s.async.Write([]byte(entry.Message + "\n"))
	}
	if s.stdout {
		_, _ = os.Stdout.Write([]byte(entry.Message + "\n"))
	}
}

var globalSink *sink

// InitLogging 初始化日志输出：日志文件和内存缓冲同时写入。
// 终端输出通过 sink 同步写入（Windows GUI 应用无控制台时自动跳过）。
func InitLogging(store *MemoryLogStore, logDir string) func() {
	log.SetFlags(0)
	log.SetPrefix("")

	if logDir == "" {
		logDir = constants.DefaultLogDir
	}

	// 解析为绝对路径，避免打包后工作目录不同导致日志写到意外位置
	logDir = resolveAbsolutePath(logDir)

	if err := os.MkdirAll(logDir, 0755); err != nil {
		globalSink = &sink{store: store, stdout: true}
		LogEvent("日志", "warn", "日志目录创建失败，仅写入内存: %v", err)
		return func() {}
	}

	filePath := filepath.Join(logDir, "douyu_"+time.Now().In(constants.CST).Format("20060102_150405")+".log")
	file, err := os.OpenFile(filePath, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0644)
	if err != nil {
		globalSink = &sink{store: store, stdout: true}
		LogEvent("日志", "warn", "日志文件创建失败，仅写入内存: %v", err)
		return func() {}
	}

	store.SetFilePath(filePath)
	globalSink = &sink{
		async:  NewAsyncLogWriter(file, asyncLogBufferSize),
		store:  store,
		stdout: true,
	}
	LogEvent("日志", "success", "日志文件已启用: %s", filePath)
	return func() {
		if globalSink != nil && globalSink.async != nil {
			_ = globalSink.async.Close()
		}
		_ = file.Close()
	}
}

// LogEvent 输出带分类和级别的结构化文本日志。低于当前最低等级的日志会被丢弃。
func LogEvent(category, level, format string, args ...any) {
	logStructuredEvent(category, level, "", format, args...)
}

// LogAccountEvent 输出带账号标签的结构化日志，便于前端按账号观察抢购链路。
func LogAccountEvent(category, level, account, format string, args ...any) {
	logStructuredEvent(category, level, account, format, args...)
}

func logStructuredEvent(category, level, account, format string, args ...any) {
	if category == "" {
		category = "系统"
	}
	if level == "" {
		level = "info"
	}
	if levelPriority(level) < int(minLevel.Load()) {
		return
	}
	now := time.Now()
	message := fmt.Sprintf(format, args...)
	entry := types.LogEntry{
		Time:     now.In(constants.CST).Format(logEntryTimeLayout),
		Level:    level,
		Category: category,
		Account:  account,
		Message:  formatLogLine(now, category, level, account, message),
	}
	if globalSink != nil {
		globalSink.write(entry)
	}
}

func formatLogLine(now time.Time, category, level, account, message string) string {
	ts := now.In(constants.CST).Format(logTimeLayout)
	offset := time.Duration(douyuOffset.Load())
	var prefix string
	if offset != 0 {
		dyTime := now.Add(offset)
		prefix = fmt.Sprintf("%s(D%02d:%02d:%02d.%03d) ", ts,
			dyTime.Hour(), dyTime.Minute(), dyTime.Second(), dyTime.Nanosecond()/1e6)
	} else {
		prefix = ts + " "
	}
	if account != "" {
		return fmt.Sprintf("%s[%s][%s][账号:%s] %s", prefix, category, level, account, message)
	}
	return fmt.Sprintf("%s[%s][%s] %s", prefix, category, level, message)
}

// resolveAbsolutePath 将相对路径解析为绝对路径。
// 如果路径已经是绝对路径则直接返回；否则基于可执行文件所在目录解析。
func resolveAbsolutePath(path string) string {
	if filepath.IsAbs(path) {
		return path
	}
	// 先尝试基于当前工作目录解析
	if abs, err := filepath.Abs(path); err == nil {
		return abs
	}
	// 兜底：基于可执行文件所在目录
	if exe, err := os.Executable(); err == nil {
		return filepath.Join(filepath.Dir(exe), path)
	}
	return path
}