Add campaign configuration support

internal/app/campaign_config_path.go

@@ -0,0 +1,49 @@
+package app
+
+import (
+	"errors"
+	"fmt"
+	"os"
+	"path/filepath"
+	"strings"
+
+	"gitea.maximumdirect.net/eric/narratio/internal/config"
+)
+
+func resolveCampaignConfigPath(flagValue string) (string, error) {
+	return resolveCampaignConfigPathWithCandidates(flagValue, config.DefaultCampaignConfigSearchPaths)
+}
+
+func resolveCampaignConfigPathWithCandidates(flagValue string, candidates []string) (string, error) {
+	if explicit := strings.TrimSpace(flagValue); explicit != "" {
+		return explicit, nil
+	}
+
+	ordered := make([]string, 0, len(candidates))
+	for _, raw := range candidates {
+		path := strings.TrimSpace(raw)
+		if path == "" {
+			continue
+		}
+		ordered = append(ordered, path)
+		info, err := os.Stat(path)
+		if err == nil {
+			if info.IsDir() {
+				continue
+			}
+			return filepath.Clean(path), nil
+		}
+		if errors.Is(err, os.ErrNotExist) {
+			continue
+		}
+		return "", fmt.Errorf("check default campaign config %q: %w", path, err)
+	}
+
+	if len(ordered) == 0 {
+		return "", fmt.Errorf("no campaign config path provided and no default locations configured")
+	}
+	return "", fmt.Errorf(
+		"no campaign config path provided and no default campaign config found; searched: %s; pass --campaign to use an explicit path",
+		strings.Join(ordered, ", "),
+	)
+}