package config

import (
	"os"
	"path/filepath"
	"testing"
)

// Regression: Load used yaml.Decoder.Decode for KnownFields, which returns
// io.EOF for an empty or comment-only config.yaml. cmd/thoi treats any non-
// IsNotExist error as fatal, so an empty config aborted startup instead of
// booting on defaults (yaml.Unmarshal had returned nil).

func writeEmptyConfig(t *testing.T, body string) string {
	t.Helper()
	path := filepath.Join(t.TempDir(), "config.yaml")
	if err := os.WriteFile(path, []byte(body), 0o644); err != nil {
		t.Fatal(err)
	}
	return path
}

func TestLoadEmptyFileBootsOnDefaults(t *testing.T) {
	cfg, err := Load(writeEmptyConfig(t, ""))
	if err != nil {
		t.Fatalf("empty config.yaml must load on defaults, got: %v", err)
	}
	if cfg.TickLength != Default().TickLength {
		t.Errorf("TickLength = %d, want default %d", cfg.TickLength, Default().TickLength)
	}
	if cfg.Telnet.Port != Default().Telnet.Port {
		t.Errorf("Telnet.Port = %d, want default %d", cfg.Telnet.Port, Default().Telnet.Port)
	}
}

func TestLoadCommentOnlyFileBootsOnDefaults(t *testing.T) {
	cfg, err := Load(writeEmptyConfig(t, "# nothing configured yet\n\n# ports come from defaults\n"))
	if err != nil {
		t.Fatalf("comment-only config.yaml must load on defaults, got: %v", err)
	}
	if cfg.StartingRoom != Default().StartingRoom {
		t.Errorf("StartingRoom = %d, want default %d", cfg.StartingRoom, Default().StartingRoom)
	}
}

func TestLoadEmptyFileStillRejectsUnknownKey(t *testing.T) {
	if _, err := Load(writeEmptyConfig(t, "not_a_real_key: 1\n")); err == nil {
		t.Fatal("unknown key must still be rejected after the io.EOF fix")
	}
}