Publish comparison bundles safely

internal/app/output.go

@@ -6,6 +6,7 @@ import (
 	"path/filepath"
 	"strings"
 
+	"gitea.maximumdirect.net/eric/weatherreporter/internal/comparison"
 	"gitea.maximumdirect.net/eric/weatherreporter/internal/report"
 )
 
@@ -51,6 +52,35 @@ func resolveOutputDirWithConfigured(workingDir, override, configuredDir string)
 	return resolveOutputDir(workingDir, directory)
 }
 
+func resolveComparisonOutputDirectory(workingDir, override, configuredDir, reportOutputName string) (string, error) {
+	workingDir, err := validateWorkingDir(workingDir)
+	if err != nil {
+		return "", err
+	}
+	if override != "" {
+		return resolveComparisonDirectoryPath(workingDir, override)
+	}
+	outputDir, err := resolveOutputDir(workingDir, configuredDir)
+	if err != nil {
+		return "", err
+	}
+	name, err := comparison.DefaultDirectoryName(reportOutputName)
+	if err != nil {
+		return "", err
+	}
+	return filepath.Join(outputDir, name), nil
+}
+
+func resolveComparisonDirectoryPath(workingDir, directory string) (string, error) {
+	if strings.TrimSpace(directory) == "" {
+		return "", fmt.Errorf("comparison output directory is required")
+	}
+	if !filepath.IsAbs(directory) {
+		directory = filepath.Join(workingDir, directory)
+	}
+	return filepath.Clean(directory), nil
+}
+
 func resolveOutputDir(workingDir, override string) (string, error) {
 	workingDir, err := validateWorkingDir(workingDir)
 	if err != nil {

internal/app/output_test.go

@@ -6,6 +6,43 @@ import (
 	"testing"
 )
 
+func TestResolveComparisonOutputDirectory(t *testing.T) {
+	workingDir := t.TempDir()
+	configured := filepath.Join(workingDir, "configured")
+	blocked := filepath.Join(workingDir, "not-a-directory")
+	if err := os.WriteFile(blocked, []byte("blocked"), 0o600); err != nil {
+		t.Fatal(err)
+	}
+
+	tests := []struct {
+		name             string
+		override         string
+		configuredDir    string
+		reportOutputName string
+		want             string
+		wantErr          bool
+	}{
+		{name: "working directory default", reportOutputName: "today.md", want: filepath.Join(workingDir, "comparison-today")},
+		{name: "configured relative directory", configuredDir: "configured", reportOutputName: "tomorrow.md", want: filepath.Join(configured, "comparison-tomorrow")},
+		{name: "configured absolute directory", configuredDir: configured, reportOutputName: "hourly.md", want: filepath.Join(configured, "comparison-hourly")},
+		{name: "relative explicit directory", override: "exact", configuredDir: blocked, reportOutputName: "daily-2026-08-24.md", want: filepath.Join(workingDir, "exact")},
+		{name: "absolute explicit directory", override: filepath.Join(workingDir, "absolute"), reportOutputName: "today.md", want: filepath.Join(workingDir, "absolute")},
+		{name: "invalid report suffix", reportOutputName: "today.txt", wantErr: true},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got, err := resolveComparisonOutputDirectory(workingDir, test.override, test.configuredDir, test.reportOutputName)
+			if (err != nil) != test.wantErr {
+				t.Fatalf("resolveComparisonOutputDirectory() error = %v, want error %t", err, test.wantErr)
+			}
+			if !test.wantErr && got != test.want {
+				t.Fatalf("resolveComparisonOutputDirectory() = %q, want %q", got, test.want)
+			}
+		})
+	}
+}
+
 func TestResolveOutputDirRejectsDanglingSymlinkComponents(t *testing.T) {
 	workingDir := t.TempDir()
 	dangling := filepath.Join(workingDir, "dangling")