package log

import (
	"context"
	"fmt"
	"io"
	"log/slog"
	"os"
	"runtime"
	"strings"
	"sync"
)

type Handler struct {
	mu     sync.Mutex
	w      io.Writer
	level  slog.Level
	attrs  []slog.Attr
	groups []string
}

func New(w io.Writer, level slog.Level) *Handler {
	return &Handler{w: w, level: level}
}

func (h *Handler) Enabled(_ context.Context, l slog.Level) bool {
	return l >= h.level
}

func (h *Handler) Handle(_ context.Context, r slog.Record) error {
	h.mu.Lock()
	defer h.mu.Unlock()

	level := r.Level.String()
	switch r.Level {
	case slog.LevelDebug:
		level = "DEBUG"
	case slog.LevelInfo:
		level = "INFO"
	case slog.LevelWarn:
		level = "WARN"
	case slog.LevelError:
		level = "ERROR"
	}

	_, file, line, ok := runtime.Caller(4)
	if !ok {
		file = "???"
	}
	short := file
	for i := len(file) - 1; i > 0; i-- {
		if file[i] == '/' {
			short = file[i+1:]
			break
		}
	}

	t := r.Time.Format("2006-01-02 15:04:05.000")

	var b strings.Builder
	b.WriteString(fmt.Sprintf("[%s] [%s] [%s:%d]", level, t, short, line))

	if len(h.groups) > 0 {
		b.WriteString(" [" + strings.Join(h.groups, ".") + "]")
	}
	if r.Message != "" {
		b.WriteString(" " + r.Message)
	}

	r.Attrs(func(a slog.Attr) bool {
		b.WriteString(fmt.Sprintf(" %s=%v", a.Key, a.Value.Any()))
		return true
	})
	for _, a := range h.attrs {
		b.WriteString(fmt.Sprintf(" %s=%v", a.Key, a.Value.Any()))
	}

	b.WriteString("\n")
	_, err := h.w.Write([]byte(b.String()))
	return err
}

func (h *Handler) WithAttrs(attrs []slog.Attr) slog.Handler {
	if len(attrs) == 0 {
		return h
	}
	h2 := h.clone()
	h2.attrs = append(h2.attrs, attrs...)
	return h2
}

func (h *Handler) WithGroup(name string) slog.Handler {
	if name == "" {
		return h
	}
	h2 := h.clone()
	h2.groups = append(h2.groups, name)
	return h2
}

func (h *Handler) clone() *Handler {
	return &Handler{
		w:      h.w,
		level:  h.level,
		attrs:  append([]slog.Attr{}, h.attrs...),
		groups: append([]string{}, h.groups...),
	}
}

func Init(level string) {
	var l slog.Level
	switch strings.ToUpper(level) {
	case "DEBUG":
		l = slog.LevelDebug
	case "INFO":
		l = slog.LevelInfo
	case "WARN":
		l = slog.LevelWarn
	case "ERROR":
		l = slog.LevelError
	default:
		l = slog.LevelInfo
	}
	slog.SetDefault(slog.New(New(os.Stderr, l)))
}