feat(config): allow optional config file with default fallback

2 files changed, 89 insertions, 5 deletions

diff --git a/internal/config/config.go b/internal/config/config.go
index 69173fd..47f5842 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -89,11 +89,13 @@ func Load(path string) (Config, error) {
 		b, err := os.ReadFile(path)
 
 		if err != nil {
-			return Config{}, fmt.Errorf("read config: %w", err)
-		}
-
-		if err := yaml.Unmarshal(b, &cfg); err != nil {
-			return Config{}, fmt.Errorf("parse config: %w", err)
+			if !errors.Is(err, os.ErrNotExist) {
+				return Config{}, fmt.Errorf("read config: %w", err)
+			}
+		} else {
+			if err := yaml.Unmarshal(b, &cfg); err != nil {
+				return Config{}, fmt.Errorf("parse config: %w", err)
+			}
 		}
 	}
 
diff --git a/internal/config/config_load_test.go b/internal/config/config_load_test.go
new file mode 100644
index 0000000..516dd93
--- /dev/null
+++ b/internal/config/config_load_test.go
@@ -0,0 +1,82 @@
+package config
+
+import (
+	"os"
+	"path/filepath"
+	"testing"
+	"time"
+)
+
+func TestLoadMissingConfigFileFallsBackToDefaults(t *testing.T) {
+	cfg, err := Load(filepath.Join(t.TempDir(), "missing.yaml"))
+	if err != nil {
+		t.Fatalf("load missing config: %v", err)
+	}
+
+	def := Default()
+	if cfg.Mode != def.Mode {
+		t.Fatalf("mode mismatch: got %q want %q", cfg.Mode, def.Mode)
+	}
+	if cfg.VerifyPolicy != def.VerifyPolicy {
+		t.Fatalf("verify policy mismatch: got %q want %q", cfg.VerifyPolicy, def.VerifyPolicy)
+	}
+	if cfg.CheckpointInterval != def.CheckpointInterval {
+		t.Fatalf("checkpoint interval mismatch: got %d want %d", cfg.CheckpointInterval, def.CheckpointInterval)
+	}
+	if cfg.VerifyWorkers != def.VerifyWorkers {
+		t.Fatalf("verify workers mismatch: got %d want %d", cfg.VerifyWorkers, def.VerifyWorkers)
+	}
+}
+
+func TestLoadPartialConfigRetainsDefaultValues(t *testing.T) {
+	configPath := filepath.Join(t.TempDir(), "partial.yaml")
+	content := []byte("mode: thin\nverify: full\n")
+
+	if err := os.WriteFile(configPath, content, 0o644); err != nil {
+		t.Fatalf("write partial config: %v", err)
+	}
+
+	cfg, err := Load(configPath)
+	if err != nil {
+		t.Fatalf("load partial config: %v", err)
+	}
+
+	if cfg.Mode != ModeThin {
+		t.Fatalf("mode mismatch: got %q want %q", cfg.Mode, ModeThin)
+	}
+	if cfg.VerifyPolicy != VerifyFull {
+		t.Fatalf("verify policy mismatch: got %q want %q", cfg.VerifyPolicy, VerifyFull)
+	}
+
+	def := Default()
+	if cfg.PLCSource != def.PLCSource {
+		t.Fatalf("plc_source mismatch: got %q want %q", cfg.PLCSource, def.PLCSource)
+	}
+	if cfg.RequestTimeout != 10*time.Second {
+		t.Fatalf("request_timeout mismatch: got %s want 10s", cfg.RequestTimeout)
+	}
+	if cfg.CommitBatchSize != def.CommitBatchSize {
+		t.Fatalf("commit_batch_size mismatch: got %d want %d", cfg.CommitBatchSize, def.CommitBatchSize)
+	}
+}
+
+func TestLoadMissingConfigFileAppliesEnvOverrides(t *testing.T) {
+	t.Setenv("PLUTIA_MODE", ModeThin)
+	t.Setenv("PLUTIA_VERIFY", VerifyFull)
+	t.Setenv("PLUTIA_REQUEST_TIMEOUT", "15s")
+
+	cfg, err := Load(filepath.Join(t.TempDir(), "missing.yaml"))
+	if err != nil {
+		t.Fatalf("load missing config with env overrides: %v", err)
+	}
+
+	if cfg.Mode != ModeThin {
+		t.Fatalf("mode mismatch: got %q want %q", cfg.Mode, ModeThin)
+	}
+	if cfg.VerifyPolicy != VerifyFull {
+		t.Fatalf("verify policy mismatch: got %q want %q", cfg.VerifyPolicy, VerifyFull)
+	}
+	if cfg.RequestTimeout != 15*time.Second {
+		t.Fatalf("request_timeout mismatch: got %s want 15s", cfg.RequestTimeout)
+	}
+}