1 files changed, 95 insertions, 0 deletions
diff --git a/internal/gitutil/tag.go b/internal/gitutil/tag.go
new file mode 100644
index 00000000..86efd6cd
--- /dev/null
+++ b/internal/gitutil/tag.go
@@ -0,0 +1,95 @@
+// Copyright 2020 The Gogs Authors. All rights reserved.
+// Use of this source code is governed by a MIT-style
+// license that can be found in the LICENSE file.
+
+package gitutil
+
+import (
+	"github.com/pkg/errors"
+)
+
+// TagsPage contains a list of tags and pagination information.
+type TagsPage struct {
+	// List of tags in the current page.
+	Tags []string
+	// Whether the results include the latest tag.
+	HasLatest bool
+	// When results do not include the latest tag, an indicator of 'after' to go back.
+	PreviousAfter string
+	// Whether there are more tags in the next page.
+	HasNext bool
+}
+
+func (moduler) ListTagsAfter(repoPath, after string, limit int) (*TagsPage, error) {
+	all, err := Module.RepoTags(repoPath)
+	if err != nil {
+		return nil, errors.Wrap(err, "get tags")
+	}
+	total := len(all)
+
+	if limit < 0 {
+		limit = 0
+	}
+
+	// Returns everything when no filter and no limit
+	if after == "" && limit == 0 {
+		return &TagsPage{
+			Tags:      all,
+			HasLatest: true,
+		}, nil
+	}
+
+	// No filter but has a limit, returns first X tags
+	if after == "" && limit > 0 {
+		endIdx := limit
+		if limit > total {
+			endIdx = total
+		}
+		return &TagsPage{
+			Tags:      all[:endIdx],
+			HasLatest: true,
+			HasNext:   limit < total,
+		}, nil
+	}
+
+	// Loop over all tags see if we can find the filter
+	previousAfter := ""
+	found := false
+	tags := make([]string, 0, len(all))
+	for i := range all {
+		if all[i] != after {
+			continue
+		}
+
+		found = true
+		if limit > 0 && i-limit >= 0 {
+			previousAfter = all[i-limit]
+		}
+
+		// In case filter is the oldest one
+		if i+1 < total {
+			tags = all[i+1:]
+		}
+		break
+	}
+
+	if !found {
+		tags = all
+	}
+
+	// If all tags after match is equal to the limit, it reaches the oldest tag as well.
+	if limit == 0 || len(tags) <= limit {
+		return &TagsPage{
+			Tags:          tags,
+			HasLatest:     !found,
+			PreviousAfter: previousAfter,
+		}, nil
+	}
+
+	return &TagsPage{
+		Tags:          tags[:limit],
+		HasLatest:     !found,
+		PreviousAfter: previousAfter,
+		HasNext:       true,
+	}, nil
+}