package logging

import (
	"context"
	"fmt"
	"io"
	"log/slog"
	"slices"
	"sync"
)

// ANSI color codes
const (
	dim    = "\033[2m"
	red    = "\033[31m"
	yellow = "\033[33m"
	cyan   = "\033[36m"
	reset  = "\033[0m"
)

// ConsoleHandler formats log output for human readability on terminals.
// It produces compact, color-coded lines:
//
//	20:15:54 INF daemon started addr=:5055
//	20:15:54 ERR backup failed component=backup error="connection refused"
type ConsoleHandler struct {
	w     io.Writer
	level slog.Leveler
	attrs []slog.Attr
	mu    *sync.Mutex
}

// NewConsoleHandler creates a handler that writes human-friendly colored logs.
func NewConsoleHandler(w io.Writer, opts *slog.HandlerOptions) *ConsoleHandler {
	level := slog.LevelInfo
	if opts != nil && opts.Level != nil {
		level = opts.Level.Level()
	}
	return &ConsoleHandler{
		w:     w,
		level: level,
		mu:    &sync.Mutex{},
	}
}

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

func (h *ConsoleHandler) Handle(_ context.Context, r slog.Record) error {
	// Time
	buf := []byte(dim + r.Time.Format("15:04:05") + reset + " ")

	// Level badge
	switch {
	case r.Level >= slog.LevelError:
		buf = append(buf, red+"ERR"+reset+" "...)
	case r.Level >= slog.LevelWarn:
		buf = append(buf, yellow+"WRN"+reset+" "...)
	default:
		buf = append(buf, cyan+"INF"+reset+" "...)
	}

	// Message
	buf = append(buf, r.Message...)

	// Pre-set attrs (from slog.With)
	for _, a := range h.attrs {
		buf = appendAttr(buf, a)
	}

	// Inline attrs
	r.Attrs(func(a slog.Attr) bool {
		buf = appendAttr(buf, a)
		return true
	})

	buf = append(buf, '\n')

	h.mu.Lock()
	defer h.mu.Unlock()
	_, err := h.w.Write(buf)
	return err
}

func (h *ConsoleHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
	return &ConsoleHandler{
		w:     h.w,
		level: h.level,
		attrs: append(slices.Clone(h.attrs), attrs...),
		mu:    h.mu,
	}
}

func (h *ConsoleHandler) WithGroup(name string) slog.Handler {
	// Groups are rare in this codebase; treat as a prefixed attr set
	return &ConsoleHandler{
		w:     h.w,
		level: h.level,
		attrs: append(slices.Clone(h.attrs), slog.String("group", name)),
		mu:    h.mu,
	}
}

func appendAttr(buf []byte, a slog.Attr) []byte {
	if a.Equal(slog.Attr{}) {
		return buf
	}
	v := a.Value.Resolve()
	buf = append(buf, ' ')
	buf = append(buf, dim...)
	buf = append(buf, a.Key...)
	buf = append(buf, '=')
	buf = append(buf, reset...)

	s := v.String()
	if needsQuote(s) {
		buf = append(buf, fmt.Sprintf("%q", s)...)
	} else {
		buf = append(buf, s...)
	}
	return buf
}

func needsQuote(s string) bool {
	if s == "" {
		return true
	}
	for _, c := range s {
		if c <= ' ' || c == '"' || c == '\\' {
			return true
		}
	}
	return false
}

// Verify interface compliance at compile time.
var _ slog.Handler = (*ConsoleHandler)(nil)