package logging

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

	"go.uber.org/zap"
	"go.uber.org/zap/zapcore"
	"gopkg.in/natefinch/lumberjack.v2"
)

type Config struct {
	AppName        string
	Environment    string
	BasePath       string
	Level          string
	MaxSizeMB      int
	MaxBackups     int
	MaxAgeDays     int
	Compress       bool
	ConsoleEnabled bool
}

func New(cfg Config) (*zap.Logger, func() error, error) {
	cfg = finalizeConfig(cfg)

	infoWriter, err := newDailyRollingWriter(cfg, "info.log")
	if err != nil {
		return nil, nil, err
	}
	errorWriter, err := newDailyRollingWriter(cfg, "error.log")
	if err != nil {
		_ = infoWriter.Close()
		return nil, nil, err
	}

	level := parseLevel(cfg.Level)
	encoderConfig := zapcore.EncoderConfig{
		TimeKey:        "time",
		LevelKey:       "level",
		NameKey:        "logger",
		CallerKey:      "caller",
		MessageKey:     "msg",
		StacktraceKey:  "stacktrace",
		LineEnding:     zapcore.DefaultLineEnding,
		EncodeLevel:    zapcore.CapitalLevelEncoder,
		EncodeTime:     zapcore.TimeEncoderOfLayout("2006-01-02 15:04:05.000"),
		EncodeDuration: zapcore.StringDurationEncoder,
		EncodeCaller:   zapcore.ShortCallerEncoder,
	}
	jsonEncoder := zapcore.NewJSONEncoder(encoderConfig)
	consoleEncoder := zapcore.NewConsoleEncoder(encoderConfig)

	cores := make([]zapcore.Core, 0, 3)
	cores = append(cores, zapcore.NewCore(
		jsonEncoder,
		zapcore.AddSync(io.Writer(infoWriter)),
		zap.LevelEnablerFunc(func(l zapcore.Level) bool {
			return l >= level && l < zapcore.ErrorLevel
		}),
	))
	cores = append(cores, zapcore.NewCore(
		jsonEncoder,
		zapcore.AddSync(io.Writer(errorWriter)),
		zap.LevelEnablerFunc(func(l zapcore.Level) bool {
			return l >= maxLevel(level, zapcore.ErrorLevel)
		}),
	))
	if cfg.ConsoleEnabled {
		cores = append(cores, zapcore.NewCore(
			consoleEncoder,
			zapcore.AddSync(os.Stdout),
			zap.LevelEnablerFunc(func(l zapcore.Level) bool {
				return l >= level
			}),
		))
	}

	logger := zap.New(
		zapcore.NewTee(cores...),
		zap.AddCaller(),
		zap.AddCallerSkip(1),
		zap.AddStacktrace(zapcore.ErrorLevel),
		zap.Fields(
			zap.String("app", cfg.AppName),
			zap.String("env", cfg.Environment),
		),
	)

	cleanup := func() error {
		var finalErr error
		if err := infoWriter.Close(); err != nil && finalErr == nil {
			finalErr = err
		}
		if err := errorWriter.Close(); err != nil && finalErr == nil {
			finalErr = err
		}
		if err := logger.Sync(); err != nil && finalErr == nil {
			finalErr = err
		}
		return finalErr
	}
	return logger, cleanup, nil
}

type dailyRollingWriter struct {
	mu sync.Mutex

	cfg      Config
	fileName string

	dayKey string
	writer *lumberjack.Logger
}

func newDailyRollingWriter(cfg Config, fileName string) (*dailyRollingWriter, error) {
	w := &dailyRollingWriter{
		cfg:      cfg,
		fileName: fileName,
	}
	if err := w.ensureWriter(time.Now()); err != nil {
		return nil, err
	}
	return w, nil
}

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

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

func (w *dailyRollingWriter) ensureWriter(now time.Time) error {
	dayKey := now.Format("2006-01-02")
	if w.writer != nil && w.dayKey == dayKey {
		return nil
	}

	monthDir := now.Format("2006-01")
	logDir := filepath.Join(w.cfg.BasePath, monthDir, dayKey)
	if err := os.MkdirAll(logDir, 0o755); err != nil {
		return fmt.Errorf("mkdir log dir failed: %w", err)
	}

	next := &lumberjack.Logger{
		Filename:   filepath.Join(logDir, w.fileName),
		MaxSize:    w.cfg.MaxSizeMB,
		MaxBackups: w.cfg.MaxBackups,
		MaxAge:     w.cfg.MaxAgeDays,
		Compress:   w.cfg.Compress,
	}

	if w.writer != nil {
		_ = w.writer.Close()
	}
	w.writer = next
	w.dayKey = dayKey
	return nil
}

func finalizeConfig(cfg Config) Config {
	if strings.TrimSpace(cfg.AppName) == "" {
		cfg.AppName = "lsp-gateway"
	}
	if strings.TrimSpace(cfg.Environment) == "" {
		cfg.Environment = "dev"
	}
	if strings.TrimSpace(cfg.BasePath) == "" {
		cfg.BasePath = filepath.Join(".", "logs", cfg.AppName)
	}
	if strings.TrimSpace(cfg.Level) == "" {
		cfg.Level = "info"
	}
	if cfg.MaxSizeMB <= 0 {
		cfg.MaxSizeMB = 100
	}
	if cfg.MaxBackups <= 0 {
		cfg.MaxBackups = 31
	}
	if cfg.MaxAgeDays <= 0 {
		cfg.MaxAgeDays = 31
	}
	return cfg
}

func parseLevel(level string) zapcore.Level {
	switch strings.ToLower(strings.TrimSpace(level)) {
	case "debug":
		return zapcore.DebugLevel
	case "info":
		return zapcore.InfoLevel
	case "warn", "warning":
		return zapcore.WarnLevel
	case "error":
		return zapcore.ErrorLevel
	default:
		return zapcore.InfoLevel
	}
}

func maxLevel(a, b zapcore.Level) zapcore.Level {
	if a > b {
		return a
	}
	return b
}