feat: get matching PRs from GitHub

forge.go

@@ -1,38 +1,231 @@
 package rp
 
 import (
+	"context"
 	"fmt"
+	"log/slog"
+
+	"github.com/google/go-github/v63/github"
 )
 
+type Changeset struct {
+	URL              string
+	Identifier       string
+	ChangelogEntries []AnalyzedCommit
+}
+
 type Forge interface {
 	RepoURL() string
+
+	// LatestTag returns the last tag created on the main branch. If no tag is found, it returns nil.
+	LatestTag(context.Context) (*Tag, error)
+
+	// CommitsSince returns all commits to main branch after the Tag. The tag can be `nil`, in which case this
+	// function should return all commits.
+	CommitsSince(context.Context, *Tag) ([]Commit, error)
+
+	// Changesets looks up the Pull/Merge Requests for each commit, returning its parsed metadata.
+	Changesets(context.Context, []Commit) ([]Changeset, error)
 }
 
 type ForgeOptions struct {
 	Repository string
+	BaseBranch string
 }
 
 var _ Forge = &GitHub{}
-var _ Forge = &GitLab{}
+
+// var _ Forge = &GitLab{}
 
 type GitHub struct {
-	options ForgeOptions
+	options *GitHubOptions
+
+	client *github.Client
+	log    *slog.Logger
 }
 
 func (g *GitHub) RepoURL() string {
 	return fmt.Sprintf("https://github.com/%s", g.options.Repository)
 }
 
-func (g *GitHub) autodiscover() {
-	// Read settings from GitHub Actions env vars
-}
-
-func NewGitHub(options ForgeOptions) *GitHub {
-	gh := &GitHub{
-		options: options,
+func (g *GitHub) LatestTag(ctx context.Context) (*Tag, error) {
+	g.log.Debug("listing all tags in github repository")
+	// We only get the first page because the latest tag is returned as the first item
+	tags, _, err := g.client.Repositories.ListTags(ctx, g.options.Owner, g.options.Repo, nil)
+	if err != nil {
+		return nil, err
 	}
 
-	gh.autodiscover()
+	if len(tags) > 0 {
+		// TODO: Is tags sorted?
+		tag := tags[0]
+		return &Tag{
+			Hash: tag.GetCommit().GetSHA(),
+			Name: tag.GetName(),
+		}, nil
+	}
+
+	return nil, nil
+}
+
+func (g *GitHub) CommitsSince(ctx context.Context, tag *Tag) ([]Commit, error) {
+	var repositoryCommits []*github.RepositoryCommit
+	var err error
+	if tag != nil {
+		repositoryCommits, err = g.commitsSinceTag(ctx, tag)
+	} else {
+		return nil, fmt.Errorf("not implemented")
+	}
+
+	if err != nil {
+		return nil, err
+	}
+
+	var commits = make([]Commit, 0, len(repositoryCommits))
+	for _, ghCommit := range repositoryCommits {
+		commits = append(commits, Commit{
+			Hash:    ghCommit.GetSHA(),
+			Message: ghCommit.GetCommit().GetMessage(),
+		})
+	}
+
+	return commits, nil
+}
+
+func (g *GitHub) commitsSinceTag(ctx context.Context, tag *Tag) ([]*github.RepositoryCommit, error) {
+	head := g.options.BaseBranch
+	log := g.log.With("base", tag.Hash, "head", head)
+	log.Debug("comparing commits", "base", tag.Hash, "head", head)
+
+	page := 1
+
+	var repositoryCommits []*github.RepositoryCommit
+	for {
+		log.Debug("fetching page", "page", page)
+		comparison, resp, err := g.client.Repositories.CompareCommits(
+			ctx, g.options.Owner, g.options.Repo,
+			tag.Hash, head, &github.ListOptions{
+				Page:    page,
+				PerPage: 100,
+			})
+		if err != nil {
+			return nil, err
+		}
+
+		if repositoryCommits == nil {
+			// Pre-initialize slice on first request
+			log.Debug("found commits", "length", comparison.GetTotalCommits())
+			repositoryCommits = make([]*github.RepositoryCommit, 0, comparison.GetTotalCommits())
+		}
+
+		repositoryCommits = append(repositoryCommits, comparison.Commits...)
+
+		if page == resp.LastPage || resp.LastPage == 0 {
+			break
+		}
+
+		page = resp.NextPage
+	}
+
+	return repositoryCommits, nil
+}
+
+func (g *GitHub) Changesets(ctx context.Context, commits []Commit) ([]Changeset, error) {
+	// We naively look up the associated PR for each commit through the "List pull requests associated with a commit"
+	// endpoint. This requires len(commits) requests.
+	// Using the "List pull requests" endpoint might be faster, as it allows us to fetch 100 arbitrary PRs per request,
+	// but worst case we need to look up all PRs made in the repository ever.
+
+	changesets := make([]Changeset, 0, len(commits))
+
+	for _, commit := range commits {
+		log := g.log.With("commit.hash", commit.Hash)
+		page := 1
+		var associatedPRs []*github.PullRequest
+
+		for {
+			log.Debug("fetching pull requests associated with commit", "page", page)
+			prs, resp, err := g.client.PullRequests.ListPullRequestsWithCommit(
+				ctx, g.options.Owner, g.options.Repo,
+				commit.Hash, &github.ListOptions{
+					Page:    page,
+					PerPage: 100,
+				})
+			if err != nil {
+				return nil, err
+			}
+
+			associatedPRs = append(associatedPRs, prs...)
+
+			if page == resp.LastPage || resp.LastPage == 0 {
+				break
+			}
+			page = resp.NextPage
+		}
+
+		var pullrequest *github.PullRequest
+		for _, pr := range associatedPRs {
+			// We only look for the PR that has this commit set as the "merge commit" => The result of squashing this branch onto main
+			if pr.GetMergeCommitSHA() == commit.Hash {
+				pullrequest = pr
+				break
+			}
+		}
+		if pullrequest == nil {
+			log.Warn("did not find associated pull request, not considering it for changesets")
+			// No pull request was found for this commit, nothing to do here
+			// TODO: We could also return the minimal changeset for this commit, so at least it would come up in the changelog.
+			continue
+		}
+
+		log = log.With("pullrequest.id", pullrequest.GetID())
+
+		// TODO: Parse PR description for overrides
+		changelogEntries, _, err := AnalyzeCommits([]Commit{commit})
+		if err != nil {
+			log.Warn("unable to parse changelog entries", "error", err)
+			continue
+		}
+
+		if len(changelogEntries) > 0 {
+			changesets = append(changesets, Changeset{
+				URL:              pullrequest.GetHTMLURL(),
+				Identifier:       fmt.Sprintf("#%d", pullrequest.GetNumber()),
+				ChangelogEntries: changelogEntries,
+			})
+		}
+	}
+
+	return changesets, nil
+}
+
+func (g *GitHubOptions) autodiscover() {
+	// TODO: Read settings from GitHub Actions env vars
+}
+
+type GitHubOptions struct {
+	ForgeOptions
+
+	Owner string
+	Repo  string
+
+	APIToken string
+}
+
+func NewGitHub(log *slog.Logger, options *GitHubOptions) *GitHub {
+	options.autodiscover()
+
+	client := github.NewClient(nil)
+	if options.APIToken != "" {
+		client = client.WithAuthToken(options.APIToken)
+	}
+
+	gh := &GitHub{
+		options: options,
+
+		client: client,
+		log:    log.With("forge", "github"),
+	}
 
 	return gh
 }