handler.go

package main

import (
    "context"
    "encoding/json"
    "io"
    "log"
    "log/slog"

    "github.com/fatih/color"
)

// Custom log levels
const (
    LevelTrace = slog.Level(-8)
    LevelFatal = slog.Level(12)
)

var LevelNames = map[slog.Leveler]string{
    LevelTrace: "TRACE",
    LevelFatal: "FATAL",
    slog.LevelDebug: "DEBUG",
    slog.LevelInfo:  "INFO",
    slog.LevelWarn:  "WARN",
    slog.LevelError: "ERROR",
}

type PrettyHandlerOptions struct {
    SlogOpts slog.HandlerOptions
}

type PrettyHandler struct {
    slog.Handler
    l *log.Logger
}

func (h *PrettyHandler) Handle(ctx context.Context, r slog.Record) error {
    level := r.Level.String() + ":"
    switch r.Level {
    case LevelTrace:
        level = color.MagentaString(level)
    case slog.LevelDebug:
        level = color.MagentaString(level)
    case slog.LevelInfo:
        level = color.BlueString(level)
    case slog.LevelWarn:
        level = color.YellowString(level)
    case slog.LevelError, LevelFatal:
        level = color.RedString(level)
    }

    fields := make(map[string]interface{}, r.NumAttrs())
    r.Attrs(func(a slog.Attr) bool {
        fields[a.Key] = a.Value.Any()
        return true
    })

    b, err := json.MarshalIndent(fields, "", "  ")
    if err != nil {
        return err
    }

    timeStr := r.Time.Format("[15:05:05.000]")
    msg := color.CyanString(r.Message)
    h.l.Println(timeStr, level, msg, color.WhiteString(string(b)))
    return nil
}

func NewPrettyHandler(out io.Writer, opts PrettyHandlerOptions) *PrettyHandler {
    return &PrettyHandler{
        Handler: slog.NewJSONHandler(out, &opts.SlogOpts),
        l:       log.New(out, "", 0),
    }
}