feat(cli): add --watch mode to convert (#39)

Poll source files/directories and regenerate output on change. Output path is excluded from watching; errors don't stop the loop. Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>
2026-10-03 10:29:42 +02:00
parent b38f53c603
commit d36806047b
4 changed files with 270 additions and 1 deletions
@@ -0,0 +1,152 @@
+package main
+
+import (
+	"context"
+	"fmt"
+	"io"
+	"io/fs"
+	"os"
+	"os/signal"
+	"path/filepath"
+	"strings"
+	"syscall"
+	"time"
+)
+
+// watchSnapshot maps a file path to its modification time and size.
+type watchSnapshot map[string]string
+
+// takeWatchSnapshot records the state of every file under the given paths.
+// Directories are walked recursively. Anything at or below the excluded path
+// (typically the output path) is skipped so regenerating output does not
+// retrigger the watcher. Missing paths are simply absent from the snapshot, so
+// creating them later counts as a change.
+func takeWatchSnapshot(paths []string, exclude string) watchSnapshot {
+	snap := watchSnapshot{}
+	exclude = absPathOrSelf(exclude)
+	for _, root := range paths {
+		_ = filepath.WalkDir(root, func(p string, d fs.DirEntry, err error) error {
+			if err != nil {
+				return nil
+			}
+			if exclude != "" && isWithin(absPathOrSelf(p), exclude) {
+				if d.IsDir() {
+					return filepath.SkipDir
+				}
+				return nil
+			}
+			if d.IsDir() {
+				return nil
+			}
+			info, err := d.Info()
+			if err != nil {
+				return nil
+			}
+			snap[p] = fmt.Sprintf("%d-%d", info.ModTime().UnixNano(), info.Size())
+			return nil
+		})
+	}
+	return snap
+}
+
+func (s watchSnapshot) equal(o watchSnapshot) bool {
+	if len(s) != len(o) {
+		return false
+	}
+	for k, v := range s {
+		if o[k] != v {
+			return false
+		}
+	}
+	return true
+}
+
+func absPathOrSelf(p string) string {
+	if p == "" {
+		return ""
+	}
+	if abs, err := filepath.Abs(p); err == nil {
+		return abs
+	}
+	return p
+}
+
+// isWithin reports whether path equals dir or is located below it.
+func isWithin(path, dir string) bool {
+	if path == dir {
+		return true
+	}
+	return strings.HasPrefix(path, dir+string(filepath.Separator))
+}
+
+// watchLoop runs fn once immediately and again whenever the watched paths
+// change, until ctx is cancelled. Changes are debounced: fn runs only after
+// the snapshot has stayed unchanged for one poll interval. Errors from fn are
+// reported to w and do not stop the loop.
+func watchLoop(ctx context.Context, w io.Writer, paths []string, exclude string, interval time.Duration, fn func() error) {
+	run := func() {
+		if err := fn(); err != nil {
+			fmt.Fprintf(w, "Error: %v\n", err)
+		}
+		fmt.Fprintf(w, "Watching for changes (Ctrl-C to stop)...\n")
+	}
+
+	last := takeWatchSnapshot(paths, exclude)
+	run()
+
+	ticker := time.NewTicker(interval)
+	defer ticker.Stop()
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-ticker.C:
+		}
+		cur := takeWatchSnapshot(paths, exclude)
+		if cur.equal(last) {
+			continue
+		}
+		// Debounce: wait until writes settle.
+		for settled := false; !settled; {
+			select {
+			case <-ctx.Done():
+				return
+			case <-time.After(interval):
+			}
+			next := takeWatchSnapshot(paths, exclude)
+			settled = next.equal(cur)
+			cur = next
+		}
+		fmt.Fprintf(w, "\nChange detected, regenerating...\n")
+		last = cur
+		run()
+	}
+}
+
+// runConvertWatch runs the conversion once and then again whenever the source
+// files change, until interrupted.
+func runConvertWatch(parent context.Context, w io.Writer, run func() error) error {
+	var paths []string
+	switch {
+	case len(convertFromList) > 0:
+		paths = convertFromList
+	case convertSourcePath != "":
+		paths = []string{convertSourcePath}
+	default:
+		return fmt.Errorf("--watch requires --from-path or --from-list (live database connections cannot be watched)")
+	}
+	if convertDryRun {
+		return fmt.Errorf("--watch cannot be combined with --dry-run")
+	}
+	if convertWatchInterval <= 0 {
+		return fmt.Errorf("--watch-interval must be positive")
+	}
+	if parent == nil {
+		parent = context.Background()
+	}
+
+	ctx, stop := signal.NotifyContext(parent, os.Interrupt, syscall.SIGTERM)
+	defer stop()
+	watchLoop(ctx, w, paths, convertTargetPath, convertWatchInterval, run)
+	return nil
+}