feat(orchestrator): add Progress type and OnProgress callback

Adds atomic counters for books_found, chapters_scraped, chapters_skipped,
and errors. The new OnProgress callback fires after each counter update
and once more at the end of Run, giving callers a live progress feed.

scraper/internal/orchestrator/orchestrator.go

@@ -17,11 +17,20 @@ import (
 	"log/slog"
 	"runtime"
 	"sync"
+	"sync/atomic"
 
 	"github.com/libnovel/scraper/internal/scraper"
 	"github.com/libnovel/scraper/internal/storage"
 )
 
+// Progress is a snapshot of counters at a point in time.
+type Progress struct {
+	BooksFound      int
+	ChaptersScraped int
+	ChaptersSkipped int
+	Errors          int
+}
+
 // Config holds tunable parameters for the orchestrator.
 type Config struct {
 	// Workers is the number of goroutines used to scrape chapters in parallel.
@@ -35,6 +44,10 @@ type Config struct {
 	// SingleBookURL when non-empty causes the orchestrator to scrape only
 	// that one book instead of walking the full catalogue.
 	SingleBookURL string
+
+	// OnProgress is called periodically with the current progress counters.
+	// It is always called on completion (success or failure). May be nil.
+	OnProgress func(p Progress)
 }
 
 // Orchestrator coordinates the full scrape pipeline.
@@ -69,6 +82,29 @@ func (o *Orchestrator) Run(ctx context.Context) error {
 		"workers", o.workers,
 	)
 
+	// Atomic counters updated by concurrent goroutines.
+	var (
+		booksFound      atomic.Int64
+		chaptersScraped atomic.Int64
+		chaptersSkipped atomic.Int64
+		errors          atomic.Int64
+	)
+
+	snapshot := func() Progress {
+		return Progress{
+			BooksFound:      int(booksFound.Load()),
+			ChaptersScraped: int(chaptersScraped.Load()),
+			ChaptersSkipped: int(chaptersSkipped.Load()),
+			Errors:          int(errors.Load()),
+		}
+	}
+
+	notify := func() {
+		if o.cfg.OnProgress != nil {
+			o.cfg.OnProgress(snapshot())
+		}
+	}
+
 	// chapterWork is the shared queue consumed by chapter worker goroutines.
 	type chapterJob struct {
 		slug string
@@ -93,6 +129,8 @@ func (o *Orchestrator) Run(ctx context.Context) error {
 				if o.store.ChapterExists(ctx, job.slug, job.ref) {
 					o.log.Debug("chapter already exists, skipping",
 						"book", job.slug, "chapter", job.ref.Number)
+					chaptersSkipped.Add(1)
+					notify()
 					continue
 				}
 
@@ -104,6 +142,8 @@ func (o *Orchestrator) Run(ctx context.Context) error {
 						"url", job.ref.URL,
 						"err", err,
 					)
+					errors.Add(1)
+					notify()
 					continue
 				}
 
@@ -113,9 +153,13 @@ func (o *Orchestrator) Run(ctx context.Context) error {
 						"chapter", job.ref.Number,
 						"err", err,
 					)
+					errors.Add(1)
+					notify()
 					continue
 				}
 
+				chaptersScraped.Add(1)
+				notify()
 				o.log.Info("chapter saved",
 					"book", job.slug,
 					"chapter", job.ref.Number,
@@ -132,6 +176,8 @@ func (o *Orchestrator) Run(ctx context.Context) error {
 		meta, err := o.novel.ScrapeMetadata(ctx, bookURL)
 		if err != nil {
 			o.log.Error("metadata scrape failed", "url", bookURL, "err", err)
+			errors.Add(1)
+			notify()
 			return
 		}
 
@@ -141,12 +187,16 @@ func (o *Orchestrator) Run(ctx context.Context) error {
 			// Continue — chapters can still be scraped.
 		}
 
+		booksFound.Add(1)
+		notify()
 		o.log.Info("metadata saved", "slug", meta.Slug, "title", meta.Title)
 
 		// Fetch chapter list.
 		refs, err := o.novel.ScrapeChapterList(ctx, bookURL)
 		if err != nil {
 			o.log.Error("chapter list scrape failed", "slug", meta.Slug, "err", err)
+			errors.Add(1)
+			notify()
 			return
 		}
 
@@ -174,6 +224,8 @@ func (o *Orchestrator) Run(ctx context.Context) error {
 		go func() {
 			for err := range catErrs {
 				o.log.Error("catalogue error", "err", err)
+				errors.Add(1)
+				notify()
 			}
 		}()
 
@@ -204,6 +256,9 @@ func (o *Orchestrator) Run(ctx context.Context) error {
 	// Wait for all in-flight chapter scrapes to finish.
 	chapterWG.Wait()
 
+	// Final progress notification.
+	notify()
+
 	if ctx.Err() != nil {
 		return fmt.Errorf("orchestrator: context cancelled: %w", ctx.Err())
 	}