package applog

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

	"github.com/gin-gonic/gin"
	"gorm.io/gorm/logger"
)

// logRetainDays 保留最近多少天的日志文件；<=0 不清理。
var logRetainDays = 30

// SetRetainDays 设置日志文件保留天数（可在 main 里按配置覆盖）。
func SetRetainDays(days int) {
	if days > 0 {
		logRetainDays = days
	}
}

// dailyFileWriter 按天轮转的日志 writer。
// 文件命名：<前缀>-20060102<扩展>，如 app-20260803.log；跨天自动切换并清理过期文件。
type dailyFileWriter struct {
	dir         string
	prefix      string
	ext         string
	mu          sync.Mutex
	current     *os.File
	currentDate string
}

func newDailyFileWriter(logFile string) (*dailyFileWriter, error) {
	abs, err := filepath.Abs(logFile)
	if err != nil {
		return nil, err
	}
	dir := filepath.Dir(abs)
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return nil, err
	}
	base := filepath.Base(abs)
	ext := filepath.Ext(base)
	prefix := strings.TrimSuffix(base, ext)
	w := &dailyFileWriter{dir: dir, prefix: prefix, ext: ext}
	if err := w.rotateIfNeeded(time.Now()); err != nil {
		return nil, err
	}
	return w, nil
}

// pathFor 当天日志文件路径。
func (w *dailyFileWriter) pathFor(t time.Time) string {
	return filepath.Join(w.dir, fmt.Sprintf("%s-%s%s", w.prefix, t.Format("20060102"), w.ext))
}

func (w *dailyFileWriter) rotateIfNeeded(now time.Time) error {
	date := now.Format("20060102")
	if w.current != nil && w.currentDate == date {
		return nil
	}
	if w.current != nil {
		_ = w.current.Close()
		w.current = nil
	}
	f, err := os.OpenFile(w.pathFor(now), os.O_CREATE|os.O_APPEND|os.O_WRONLY, 0o644)
	if err != nil {
		return err
	}
	w.current = f
	w.currentDate = date
	go w.cleanup(now)
	return nil
}

// cleanup 删除超出保留天数的历史日志文件。
func (w *dailyFileWriter) cleanup(now time.Time) {
	if logRetainDays <= 0 {
		return
	}
	cutoff := now.AddDate(0, 0, -logRetainDays).Format("20060102")
	entries, err := os.ReadDir(w.dir)
	if err != nil {
		return
	}
	for _, entry := range entries {
		if entry.IsDir() {
			continue
		}
		name := entry.Name()
		if !strings.HasPrefix(name, w.prefix+"-") || !strings.HasSuffix(name, w.ext) {
			continue
		}
		datePart := strings.TrimSuffix(strings.TrimPrefix(name, w.prefix+"-"), w.ext)
		if len(datePart) != 8 || datePart >= cutoff {
			continue
		}
		_ = os.Remove(filepath.Join(w.dir, name))
	}
}

func (w *dailyFileWriter) Write(p []byte) (int, error) {
	w.mu.Lock()
	defer w.mu.Unlock()
	if err := w.rotateIfNeeded(time.Now()); err != nil {
		return 0, err
	}
	return w.current.Write(p)
}

func (w *dailyFileWriter) Close() error {
	w.mu.Lock()
	defer w.mu.Unlock()
	if w.current != nil {
		err := w.current.Close()
		w.current = nil
		return err
	}
	return nil
}

// Setup 将标准库 log、Gin 请求日志同时写到控制台与按天分割的文件。
// logFile 为空则仅控制台。返回文件句柄供进程结束时 Close（可为 nil）。
func Setup(logFile string) (*os.File, error) {
	writers := []io.Writer{os.Stdout}
	var f *os.File
	if logFile != "" {
		daily, err := newDailyFileWriter(logFile)
		if err != nil {
			return nil, err
		}
		f = daily.current
		writers = append(writers, daily)
	}

	mw := io.MultiWriter(writers...)
	log.SetOutput(mw)
	log.SetFlags(log.LstdFlags | log.Lmicroseconds)

	// Gin access / recovery 日志
	gin.DefaultWriter = mw
	gin.DefaultErrorWriter = mw

	if logFile != "" {
		abs, _ := filepath.Abs(logFile)
		log.Printf("[applog] 日志按天分割输出到 %s-YYYYMMDD.log（保留 %d 天）", strings.TrimSuffix(abs, filepath.Ext(abs)), logRetainDays)
	}
	return f, nil
}

// NewGormLogger 返回写到当前 log 输出（已含 MultiWriter）的 GORM 日志
func NewGormLogger(mode string) logger.Interface {
	level := logger.Info
	if mode == "release" {
		level = logger.Warn
	}
	return logger.New(
		log.New(log.Writer(), "\r\n", log.LstdFlags),
		logger.Config{
			SlowThreshold:             200 * time.Millisecond,
			LogLevel:                  level,
			IgnoreRecordNotFoundError: true,
			Colorful:                  false,
		},
	)
}