Add initial support for pagination in ListComments, ListEvents.

Only implemented in fs service implementation for now.

Helps github.com/shurcooL/home/idiomaticgo rendering performance.
Helps https://dmitri.shuralyov.com/issues/github.com/shurcooL/issuesapp/14.

asanaapi/asanaapi.go

@@ -151,7 +151,9 @@ func (s service) canEdit(isCollaborator bool, isCollaboratorErr error, authorID
 	}
 }
 
-func (s service) ListComments(ctx context.Context, _ issues.RepoSpec, id uint64, opt interface{}) ([]issues.Comment, error) {
+func (s service) ListComments(ctx context.Context, _ issues.RepoSpec, id uint64, opt *issues.ListOptions) ([]issues.Comment, error) {
+	// TODO: Pagination. Respect opt.Start and opt.Length, if given.
+
 	var comments []issues.Comment
 
 	// TODO: Figure this out.
@@ -215,7 +217,9 @@ func (s service) ListComments(ctx context.Context, _ issues.RepoSpec, id uint64,
 	return comments, nil
 }
 
-func (s service) ListEvents(ctx context.Context, _ issues.RepoSpec, id uint64, opt interface{}) ([]issues.Event, error) {
+func (s service) ListEvents(ctx context.Context, _ issues.RepoSpec, id uint64, opt *issues.ListOptions) ([]issues.Event, error) {
+	// TODO: Pagination. Respect opt.Start and opt.Length, if given.
+
 	stories, err := s.cl.ListTaskStories(ctx, int64(id), &asana.Filter{OptExpand: []string{"created_by"}})
 	if err != nil {
 		return nil, err

fs/fs.go

@@ -150,7 +150,7 @@ func (s service) Get(ctx context.Context, repo issues.RepoSpec, id uint64) (issu
 	}, nil
 }
 
-func (s service) ListComments(ctx context.Context, repo issues.RepoSpec, id uint64, opt interface{}) ([]issues.Comment, error) {
+func (s service) ListComments(ctx context.Context, repo issues.RepoSpec, id uint64, opt *issues.ListOptions) ([]issues.Comment, error) {
 	currentUser, err := s.users.GetAuthenticated(ctx)
 	if err != nil {
 		return nil, err
@@ -162,7 +162,7 @@ func (s service) ListComments(ctx context.Context, repo issues.RepoSpec, id uint
 	if err != nil {
 		return comments, err
 	}
-	for _, fi := range fis {
+	for _, fi := range paginate(fis, opt) {
 		var comment comment
 		err = jsonDecodeFile(s.fs, issueCommentPath(repo, id, fi.ID), &comment)
 		if err != nil {
@@ -203,14 +203,14 @@ func (s service) ListComments(ctx context.Context, repo issues.RepoSpec, id uint
 	return comments, nil
 }
 
-func (s service) ListEvents(ctx context.Context, repo issues.RepoSpec, id uint64, opt interface{}) ([]issues.Event, error) {
+func (s service) ListEvents(ctx context.Context, repo issues.RepoSpec, id uint64, opt *issues.ListOptions) ([]issues.Event, error) {
 	var events []issues.Event
 
 	fis, err := readDirIDs(s.fs, issueEventsDir(repo, id))
 	if err != nil {
 		return events, err
 	}
-	for _, fi := range fis {
+	for _, fi := range paginate(fis, opt) {
 		var event event
 		err = jsonDecodeFile(s.fs, issueEventPath(repo, id, fi.ID), &event)
 		if err != nil {
@@ -697,6 +697,21 @@ func (s service) EditComment(ctx context.Context, repo issues.RepoSpec, id uint6
 	}, nil
 }
 
+func paginate(fis []fileInfoID, opt *issues.ListOptions) []fileInfoID {
+	if opt == nil {
+		return fis
+	}
+	start := opt.Start
+	if start > len(fis) {
+		start = len(fis)
+	}
+	end := opt.Start + opt.Length
+	if end > len(fis) {
+		end = len(fis)
+	}
+	return fis[start:end]
+}
+
 // toggleReaction toggles reaction emojiID to comment c for specified user u.
 // If user is creating a new reaction, they get added to the end of reaction authors.
 func toggleReaction(c *comment, u users.UserSpec, emojiID reactions.EmojiID) error {

githubapi/githubapi.go

@@ -214,7 +214,9 @@ func (s service) Get(ctx context.Context, rs issues.RepoSpec, id uint64) (issues
 	}, nil
 }
 
-func (s service) ListComments(ctx context.Context, rs issues.RepoSpec, id uint64, opt interface{}) ([]issues.Comment, error) {
+func (s service) ListComments(ctx context.Context, rs issues.RepoSpec, id uint64, opt *issues.ListOptions) ([]issues.Comment, error) {
+	// TODO: Respect opt.Start and opt.Length, if given.
+
 	repo, err := ghRepoSpec(rs)
 	if err != nil {
 		return nil, err
@@ -296,14 +298,16 @@ func (s service) ListComments(ctx context.Context, rs issues.RepoSpec, id uint64
 	return comments, nil
 }
 
-func (s service) ListEvents(_ context.Context, rs issues.RepoSpec, id uint64, opt interface{}) ([]issues.Event, error) {
+func (s service) ListEvents(_ context.Context, rs issues.RepoSpec, id uint64, opt *issues.ListOptions) ([]issues.Event, error) {
+	// TODO: Pagination. Respect opt.Start and opt.Length, if given.
+
 	repo, err := ghRepoSpec(rs)
 	if err != nil {
 		return nil, err
 	}
 	var events []issues.Event
 
-	ghEvents, _, err := s.cl.Issues.ListIssueEvents(repo.Owner, repo.Repo, int(id), nil) // TODO: Pagination.
+	ghEvents, _, err := s.cl.Issues.ListIssueEvents(repo.Owner, repo.Repo, int(id), nil)
 	if err != nil {
 		return events, err
 	}

issues.go

@@ -33,9 +33,9 @@ type Service interface {
 	Get(ctx context.Context, repo RepoSpec, id uint64) (Issue, error)
 
 	// ListComments lists comments for specified issue id.
-	ListComments(ctx context.Context, repo RepoSpec, id uint64, opt interface{}) ([]Comment, error)
+	ListComments(ctx context.Context, repo RepoSpec, id uint64, opt *ListOptions) ([]Comment, error)
 	// ListEvents lists events for specified issue id.
-	ListEvents(ctx context.Context, repo RepoSpec, id uint64, opt interface{}) ([]Event, error)
+	ListEvents(ctx context.Context, repo RepoSpec, id uint64, opt *ListOptions) ([]Event, error)
 
 	// Create a new issue.
 	Create(ctx context.Context, repo RepoSpec, issue Issue) (Issue, error)

options.go

@@ -12,3 +12,12 @@ const (
 	// AllStates is a state filter that includes all issues.
 	AllStates StateFilter = "all"
 )
+
+// ListOptions controls pagination.
+type ListOptions struct {
+	// Start is the index of first result to retrieve, zero-indexed.
+	Start int
+
+	// Length is the number of results to include.
+	Length int
+}