geniusrun/backend/internal/log/log.go

// Package applog provides geniusrun's structured JSON logging: a
// log/slog-based logger writing to stdout, plus the App helper that tags
// records with the mandatory schema fields every geniusrun log line
// carries -- "type" ("app" | "http" | "wrapper"), "class" (Go type with
// its package, or the package/module name for free functions), and
// "method" (the Go or Python function emitting the record). "msg" is
// optional: NewLogger's handler drops it when empty.
package applog

import (
	"io"
	"log/slog"
	"strings"
)

// NewLogger builds a JSON-handler *slog.Logger writing to w at the given
// level ("debug"|"info"|"warn"|"error", case-insensitive; anything else
// defaults to info). Empty msg values are omitted from the output --
// records whose meaning is fully carried by type/class/method and attrs
// (e.g. the HTTP request line) don't need one.
func NewLogger(level string, w io.Writer) *slog.Logger {
	return slog.New(slog.NewJSONHandler(w, &slog.HandlerOptions{
		Level: parseLevel(level),
		ReplaceAttr: func(groups []string, a slog.Attr) slog.Attr {
			if len(groups) == 0 && a.Key == slog.MessageKey && a.Value.String() == "" {
				return slog.Attr{}
			}
			return a
		},
	}))
}

// App returns the default logger tagged with the mandatory schema fields
// for an ordinary application record: type=app, plus the emitting class
// and method. The http and wrapper emitters (internal/api's logging
// middleware, internal/garmin's execute/forwardWrapperStderr) tag their
// own type instead.
func App(class, method string) *slog.Logger {
	return slog.Default().With("type", "app", "class", class, "method", method)
}

func parseLevel(level string) slog.Level {
	switch strings.ToLower(level) {
	case "debug":
		return slog.LevelDebug
	case "warn":
		return slog.LevelWarn
	case "error":
		return slog.LevelError
	default:
		return slog.LevelInfo
	}
}