package simplelog

import (
	"context"
	"fmt"
	"log/slog"
	"os"
	"runtime"
	"time"

	"github.com/fatih/color"
)

// callerSkipFrames is the number of stack frames between runtime.Caller
// and the slog call site that produced the record.
const callerSkipFrames = 4

// ConsoleHandler writes human-readable, colored log lines to stdout.
type ConsoleHandler struct{}

// NewConsoleHandler returns a new ConsoleHandler.
func NewConsoleHandler() *ConsoleHandler {
	return &ConsoleHandler{}
}

// Handle writes the record to stdout as a colored, timestamped line
// including the caller file and line.
func (c *ConsoleHandler) Handle(
	_ context.Context,
	record slog.Record,
) error {
	timestamp := time.Now().UTC().Format("2006-01-02T15:04:05.000Z07:00")

	var colorFunc func(format string, a ...any) string

	switch record.Level {
	case slog.LevelDebug:
		colorFunc = color.New(color.FgWhite).SprintfFunc()
	case slog.LevelInfo:
		colorFunc = color.New(color.FgBlue).SprintfFunc()
	case slog.LevelWarn:
		colorFunc = color.New(color.FgYellow).SprintfFunc()
	case slog.LevelError:
		colorFunc = color.New(color.FgRed).SprintfFunc()
	default:
		colorFunc = color.New(color.FgWhite).SprintfFunc()
	}

	// Get the caller information
	_, file, line, ok := runtime.Caller(callerSkipFrames)
	if !ok {
		file = "???"
		line = 0
	}

	_, _ = fmt.Fprintln(
		os.Stdout,
		colorFunc(
			"%s [%s] %s:%d: %s",
			timestamp,
			record.Level,
			file,
			line,
			record.Message,
		),
	)

	return nil
}

// Enabled reports whether the handler processes records at the given
// level; it always returns true.
func (c *ConsoleHandler) Enabled(
	_ context.Context,
	_ slog.Level,
) bool {
	return true
}

// WithAttrs returns the handler unchanged; attributes are not rendered.
func (c *ConsoleHandler) WithAttrs(_ []slog.Attr) slog.Handler {
	return c
}

// WithGroup returns the handler unchanged; groups are not rendered.
func (c *ConsoleHandler) WithGroup(_ string) slog.Handler {
	return c
}