Add a --write and --diff flag; require --write to be set before making any changes, for safety

tesseract/genconf/main.go

@@ -5,8 +5,12 @@ import (
 	"fmt"
 	"log"
 	"os"
+	"strings"
 	"time"
 
+	"github.com/hexops/gotextdiff"
+	"github.com/hexops/gotextdiff/myers"
+	"github.com/hexops/gotextdiff/span"
 	"gopkg.in/yaml.v3"
 )
 
@@ -41,6 +45,9 @@ type Log struct {
 
 func main() {
 	configFile := flag.String("c", "./tesseract-staging.yaml", "Path to the YAML configuration file")
+	wantDiff := flag.Bool("diff", false, "Show unified diff of changes")
+	allowWrite := flag.Bool("write", false, "Allow writing files (required for actual file modifications)")
+	noColor := flag.Bool("no-color", false, "Disable colored diff output")
 	flag.Parse()
 
 	args := flag.Args()
@@ -51,15 +58,15 @@ func main() {
 
 	switch args[0] {
 	case "gen-html":
-		generateHTML(*configFile)
+		generateHTML(*configFile, *wantDiff, *allowWrite, !*noColor)
 	case "gen-env":
-		generateEnv(*configFile)
+		generateEnv(*configFile, *wantDiff, *allowWrite, !*noColor)
 	case "gen-key":
-		generateKeys(*configFile)
+		generateKeys(*configFile, *wantDiff, *allowWrite, !*noColor)
 	case "gen-nginx":
-		generateNginx(*configFile)
+		generateNginx(*configFile, *wantDiff, *allowWrite, !*noColor)
 	case "gen-roots":
-		generateRoots(args[1:])
+		generateRoots(args[1:], *wantDiff, *allowWrite, !*noColor)
 	default:
 		fmt.Fprintf(os.Stderr, "Unknown command: %s\n", args[0])
 		showHelp()
@@ -97,17 +104,94 @@ func loadConfig(yamlFile string) Config {
 	return config
 }
 
-func writeFileWithStatus(filename string, content []byte) error {
+// ANSI color codes
+const (
+	colorReset  = "\033[0m"
+	colorRed    = "\033[31m"
+	colorGreen  = "\033[32m"
+	colorYellow = "\033[33m"
+	colorCyan   = "\033[36m"
+)
+
+// colorizeUnifiedDiff adds ANSI color codes to unified diff output
+func colorizeUnifiedDiff(diff string) string {
+	lines := strings.Split(diff, "\n")
+	var colorizedLines []string
+
+	for _, line := range lines {
+		switch {
+		case strings.HasPrefix(line, "---"):
+			// File deletion header in cyan
+			colorizedLines = append(colorizedLines, colorCyan+line+colorReset)
+		case strings.HasPrefix(line, "+++"):
+			// File addition header in cyan
+			colorizedLines = append(colorizedLines, colorCyan+line+colorReset)
+		case strings.HasPrefix(line, "@@"):
+			// Hunk header in yellow
+			colorizedLines = append(colorizedLines, colorYellow+line+colorReset)
+		case strings.HasPrefix(line, "-"):
+			// Deleted lines in red
+			colorizedLines = append(colorizedLines, colorRed+line+colorReset)
+		case strings.HasPrefix(line, "+"):
+			// Added lines in green
+			colorizedLines = append(colorizedLines, colorGreen+line+colorReset)
+		default:
+			// Context lines unchanged
+			colorizedLines = append(colorizedLines, line)
+		}
+	}
+
+	return strings.Join(colorizedLines, "\n")
+}
+
+func writeFileWithStatus(filename string, content []byte, wantDiff bool, allowWrite bool, useColor bool) error {
 	existingContent, err := os.ReadFile(filename)
-	if os.IsNotExist(err) {
-		fmt.Printf("Creating %s\n", filename)
+	isNew := os.IsNotExist(err)
+	isUnchanged := false
+
+	if isNew {
+		if allowWrite {
+			fmt.Printf("Creating %s\n", filename)
+		} else {
+			fmt.Printf("Would create %s\n", filename)
+		}
 	} else if err != nil {
 		return fmt.Errorf("failed to read existing file %s: %v", filename, err)
 	} else if string(existingContent) == string(content) {
 		fmt.Printf("Unchanged %s\n", filename)
-		return nil
+		isUnchanged = true
 	} else {
-		fmt.Printf("Updating %s\n", filename)
+		if allowWrite {
+			fmt.Printf("Updating %s\n", filename)
+		} else {
+			fmt.Printf("Would update %s\n", filename)
+		}
+	}
+
+	if wantDiff && !isUnchanged {
+		if isNew {
+			// For new files, show the entire content as added
+			edits := myers.ComputeEdits(span.URIFromPath(filename), "", string(content))
+			diff := fmt.Sprint(gotextdiff.ToUnified("/dev/null", filename, "", edits))
+			if useColor {
+				fmt.Print(colorizeUnifiedDiff(diff))
+			} else {
+				fmt.Print(diff)
+			}
+		} else {
+			// For existing files, show the diff
+			edits := myers.ComputeEdits(span.URIFromPath(filename), string(existingContent), string(content))
+			diff := fmt.Sprint(gotextdiff.ToUnified(filename, filename+".new", string(existingContent), edits))
+			if useColor {
+				fmt.Print(colorizeUnifiedDiff(diff))
+			} else {
+				fmt.Print(diff)
+			}
+		}
+	}
+
+	if isUnchanged || !allowWrite {
+		return nil
 	}
 
 	err = os.WriteFile(filename, content, 0644)
@@ -119,8 +203,17 @@ func writeFileWithStatus(filename string, content []byte) error {
 
 func showHelp() {
 	fmt.Printf("Usage: %s [options] <command>\n\n", os.Args[0])
+	fmt.Printf("Note: Flags must come before the command name.\n\n")
 	fmt.Printf("Options:\n")
-	fmt.Printf("  -c <file>    Path to YAML configuration file (default: ./tesseract-staging.yaml)\n\n")
+	fmt.Printf("  -c <file>    Path to YAML configuration file (default: ./tesseract-staging.yaml)\n")
+	fmt.Printf("  --diff       Show unified diff of changes without writing files\n")
+	fmt.Printf("  --write      Allow writing files (required for actual file modifications)\n")
+	fmt.Printf("  --no-color   Disable colored diff output\n\n")
+	fmt.Printf("Examples:\n")
+	fmt.Printf("  %s --diff gen-html            # Show colored diffs without writing\n", os.Args[0])
+	fmt.Printf("  %s --diff --no-color gen-html # Show plain diffs without writing\n", os.Args[0])
+	fmt.Printf("  %s --write gen-html           # Write files\n", os.Args[0])
+	fmt.Printf("  %s --diff --write gen-html    # Show colored diffs and write files\n\n", os.Args[0])
 	fmt.Printf("Commands:\n")
 	fmt.Printf("  gen-html     Generate index.html and log.v3.json files in each log's localdirectory.\n")
 	fmt.Printf("               Creates HTML pages with log information and CT log metadata JSON.\n")