package handler

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

	"github.com/databricks/cli/libs/log"
)

// friendlyHandler implements a custom [slog.Handler] that writes
// human readable (and colorized) log lines to a terminal.
//
// The implementation is based on the guide at:
// https://github.com/golang/example/blob/master/slog-handler-guide/README.md
type friendlyHandler struct {
	opts Options
	mu   *sync.Mutex
	out  io.Writer

	// List of colors to use for formatting.
	ttyColors

	// Cache (colorized) level strings.
	levelTrace string
	levelDebug string
	levelInfo  string
	levelWarn  string
	levelError string
}

func NewFriendlyHandler(out io.Writer, opts *Options) slog.Handler {
	h := &friendlyHandler{out: out, mu: &sync.Mutex{}}
	if opts != nil {
		h.opts = *opts
	}
	if h.opts.Level == nil {
		h.opts.Level = slog.LevelInfo
	}

	h.ttyColors = newColors(opts.Color)

	// Cache (colorized) level strings.
	// The colors to use for each level are configured in `colors.go`.
	h.levelTrace = h.sprintf(ttyColorLevelTrace, "%s", "Trace: ")
	h.levelDebug = h.sprintf(ttyColorLevelDebug, "%s", "Debug: ")
	h.levelInfo = h.sprintf(ttyColorLevelInfo, "%s", "Info: ")
	h.levelWarn = h.sprintf(ttyColorLevelWarn, "%s", "Warn: ")
	h.levelError = h.sprintf(ttyColorLevelError, "%s", "Error: ")
	return h
}

func (h *friendlyHandler) sprint(color ttyColor, args ...any) string {
	return h.ttyColors[color].Sprint(args...)
}

func (h *friendlyHandler) sprintf(color ttyColor, format string, args ...any) string {
	return h.ttyColors[color].Sprintf(format, args...)
}

func (h *friendlyHandler) coloredLevel(r slog.Record) string {
	switch r.Level {
	case log.LevelTrace:
		return h.levelTrace
	case log.LevelDebug:
		return h.levelDebug
	case log.LevelInfo:
		return h.levelInfo
	case log.LevelWarn:
		return h.levelWarn
	case log.LevelError:
		return h.levelError
	}
	return ""
}

// Enabled implements slog.Handler.
func (h *friendlyHandler) Enabled(ctx context.Context, level slog.Level) bool {
	return level >= h.opts.Level.Level()
}

// Handle implements slog.Handler.
func (h *friendlyHandler) Handle(ctx context.Context, r slog.Record) error {
	out := fmt.Sprintf("%s%s\n", h.coloredLevel(r), h.sprint(ttyColorMessage, r.Message))

	h.mu.Lock()
	defer h.mu.Unlock()
	_, err := h.out.Write([]byte(out))
	return err
}

// WithGroup implements slog.Handler.
func (h *friendlyHandler) WithGroup(name string) slog.Handler {
	return h
}

// WithAttrs implements slog.Handler.
func (h *friendlyHandler) WithAttrs(attrs []slog.Attr) slog.Handler {
	return h
}