feat: add slog structured logging

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

pkg/logger/logger.go

@@ -1,11 +1,49 @@
 package logger
 
 import (
-	"log"
+	"fmt"
+	"log/slog"
 	"os"
+	"strings"
+
+	"codespace/pkg/config"
 )
 
-// New returns a standard library logger writing to stdout with a codespace prefix.
-func New() *log.Logger {
-	return log.New(os.Stdout, "codespace ", log.LstdFlags|log.Lshortfile)
+// New creates a *slog.Logger from the given log configuration.
+// It also sets the logger as the default slog logger.
+func New(cfg config.LogConfig) (*slog.Logger, error) {
+	level, err := parseLevel(cfg.Level)
+	if err != nil {
+		return nil, err
+	}
+
+	opts := &slog.HandlerOptions{Level: level}
+	var handler slog.Handler
+	switch strings.ToLower(cfg.Format) {
+	case "json", "":
+		handler = slog.NewJSONHandler(os.Stdout, opts)
+	case "text":
+		handler = slog.NewTextHandler(os.Stdout, opts)
+	default:
+		return nil, fmt.Errorf("invalid log format %q", cfg.Format)
+	}
+
+	lg := slog.New(handler)
+	slog.SetDefault(lg)
+	return lg, nil
+}
+
+func parseLevel(value string) (slog.Level, error) {
+	switch strings.ToLower(value) {
+	case "debug":
+		return slog.LevelDebug, nil
+	case "info", "":
+		return slog.LevelInfo, nil
+	case "warn":
+		return slog.LevelWarn, nil
+	case "error":
+		return slog.LevelError, nil
+	default:
+		return slog.LevelInfo, fmt.Errorf("invalid log level %q", value)
+	}
 }

pkg/logger/logger_test.go

@@ -0,0 +1,39 @@
+package logger
+
+import (
+	"testing"
+
+	"codespace/pkg/config"
+)
+
+func TestNewJSONInfoLogger(t *testing.T) {
+	lg, err := New(config.LogConfig{Level: "info", Format: "json"})
+	if err != nil {
+		t.Fatalf("New returned error: %v", err)
+	}
+	if lg == nil {
+		t.Fatal("logger is nil")
+	}
+}
+
+func TestNewTextDebugLogger(t *testing.T) {
+	lg, err := New(config.LogConfig{Level: "debug", Format: "text"})
+	if err != nil {
+		t.Fatalf("New returned error: %v", err)
+	}
+	if lg == nil {
+		t.Fatal("logger is nil")
+	}
+}
+
+func TestNewRejectsInvalidLevel(t *testing.T) {
+	if _, err := New(config.LogConfig{Level: "verbose", Format: "json"}); err == nil {
+		t.Fatal("expected invalid level error")
+	}
+}
+
+func TestNewRejectsInvalidFormat(t *testing.T) {
+	if _, err := New(config.LogConfig{Level: "info", Format: "xml"}); err == nil {
+		t.Fatal("expected invalid format error")
+	}
+}