commands: add a nice terminal progress bar when building the cache

One issue remaining is that writing the cache takes significant time, but I don't know how to reflect that nicely to the user.

2 files changed, 91 insertions, 49 deletions

diff --git a/cache/repo_cache.go b/cache/repo_cache.go
index 99e9abbd..9c7e945a 100644
--- a/cache/repo_cache.go
+++ b/cache/repo_cache.go
@@ -30,7 +30,7 @@ var _ repository.RepoKeyring = &RepoCache{}
 type cacheMgmt interface {
 	Typename() string
 	Load() error
-	Build() error
+	Build() <-chan BuildEvent
 	SetCacheSize(size int)
 	MergeAll(remote string) <-chan entity.MergeResult
 	GetNamespace() string
@@ -212,6 +212,7 @@ const (
 	BuildEventCacheIsBuilt
 	BuildEventRemoveLock
 	BuildEventStarted
+	BuildEventProgress
 	BuildEventFinished
 )
 
@@ -223,6 +224,10 @@ type BuildEvent struct {
 	Typename string
 	// Event is the type of the event.
 	Event BuildEventType
+	// Total is the total number of element being built. Set if Event is BuildEventStarted.
+	Total int64
+	// Progress is the current count of processed element. Set if Event is BuildEventProgress.
+	Progress int64
 }
 
 func (c *RepoCache) buildCache(events chan BuildEvent) {
@@ -233,23 +238,13 @@ func (c *RepoCache) buildCache(events chan BuildEvent) {
 		wg.Add(1)
 		go func(subcache cacheMgmt) {
 			defer wg.Done()
-			events <- BuildEvent{
-				Typename: subcache.Typename(),
-				Event:    BuildEventStarted,
-			}
 
-			err := subcache.Build()
-			if err != nil {
-				events <- BuildEvent{
-					Typename: subcache.Typename(),
-					Err:      err,
+			buildEvents := subcache.Build()
+			for buildEvent := range buildEvents {
+				events <- buildEvent
+				if buildEvent.Err != nil {
+					return
 				}
-				return
-			}
-
-			events <- BuildEvent{
-				Typename: subcache.Typename(),
-				Event:    BuildEventFinished,
 			}
 		}(subcache)
 	}
diff --git a/cache/subcache.go b/cache/subcache.go
index 7b599b10..29155e82 100644
--- a/cache/subcache.go
+++ b/cache/subcache.go
@@ -185,51 +185,98 @@ func (sc *SubCache[EntityT, ExcerptT, CacheT]) write() error {
 	return f.Close()
 }
 
-func (sc *SubCache[EntityT, ExcerptT, CacheT]) Build() error {
-	sc.excerpts = make(map[entity.Id]ExcerptT)
+func (sc *SubCache[EntityT, ExcerptT, CacheT]) Build() <-chan BuildEvent {
+	out := make(chan BuildEvent)
 
-	allEntities := sc.actions.ReadAllWithResolver(sc.repo, sc.resolvers())
+	go func() {
+		defer close(out)
 
-	index, err := sc.repo.GetIndex(sc.namespace)
-	if err != nil {
-		return err
-	}
+		out <- BuildEvent{
+			Typename: sc.typename,
+			Event:    BuildEventStarted,
+		}
 
-	// wipe the index just to be sure
-	err = index.Clear()
-	if err != nil {
-		return err
-	}
+		sc.excerpts = make(map[entity.Id]ExcerptT)
+
+		allEntities := sc.actions.ReadAllWithResolver(sc.repo, sc.resolvers())
 
-	indexer, indexEnd := index.IndexBatch()
+		index, err := sc.repo.GetIndex(sc.namespace)
+		if err != nil {
+			out <- BuildEvent{
+				Typename: sc.typename,
+				Err:      err,
+			}
+			return
+		}
 
-	for e := range allEntities {
-		if e.Err != nil {
-			return e.Err
+		// wipe the index just to be sure
+		err = index.Clear()
+		if err != nil {
+			out <- BuildEvent{
+				Typename: sc.typename,
+				Err:      err,
+			}
+			return
 		}
 
-		cached := sc.makeCached(e.Entity, sc.entityUpdated)
-		sc.excerpts[e.Entity.Id()] = sc.makeExcerpt(cached)
-		// might as well keep them in memory
-		sc.cached[e.Entity.Id()] = cached
+		indexer, indexEnd := index.IndexBatch()
+
+		for e := range allEntities {
+			if e.Err != nil {
+				out <- BuildEvent{
+					Typename: sc.typename,
+					Err:      e.Err,
+				}
+				return
+			}
+
+			cached := sc.makeCached(e.Entity, sc.entityUpdated)
+			sc.excerpts[e.Entity.Id()] = sc.makeExcerpt(cached)
+			// might as well keep them in memory
+			sc.cached[e.Entity.Id()] = cached
+
+			indexData := sc.makeIndexData(cached)
+			if err := indexer(e.Entity.Id().String(), indexData); err != nil {
+				out <- BuildEvent{
+					Typename: sc.typename,
+					Err:      err,
+				}
+				return
+			}
+
+			out <- BuildEvent{
+				Typename: sc.typename,
+				Event:    BuildEventProgress,
+				Progress: e.CurrentEntity,
+				Total:    e.TotalEntities,
+			}
+		}
 
-		indexData := sc.makeIndexData(cached)
-		if err := indexer(e.Entity.Id().String(), indexData); err != nil {
-			return err
+		err = indexEnd()
+		if err != nil {
+			out <- BuildEvent{
+				Typename: sc.typename,
+				Err:      err,
+			}
+			return
 		}
-	}
 
-	err = indexEnd()
-	if err != nil {
-		return err
-	}
+		err = sc.write()
+		if err != nil {
+			out <- BuildEvent{
+				Typename: sc.typename,
+				Err:      err,
+			}
+			return
+		}
 
-	err = sc.write()
-	if err != nil {
-		return err
-	}
+		out <- BuildEvent{
+			Typename: sc.typename,
+			Event:    BuildEventFinished,
+		}
+	}()
 
-	return nil
+	return out
 }
 
 func (sc *SubCache[EntityT, ExcerptT, CacheT]) SetCacheSize(size int) {