feat(cmd): add VCS client abstraction for GitHub and Gitea

Adds vcs.go with:
- vcsClient interface that main.go uses for all VCS operations
- githubAdapter that wraps *github.Client and converts types to gitea types
- newVCSClient() factory: detects VCS type via GITHUB_API_URL env var
  (set by GitHub Actions runners; absent on Gitea) and returns the
  appropriate client
- buildRepoPersonaClient() adapter for LoadRepoPersonas
- detectVCSType() and githubAPIBaseURL() helpers

Detection logic mirrors action.yml: GITHUB_API_URL present → github,
absent → gitea. On GitHub/GHES, uses GITHUB_API_URL as the API base URL
(trusted platform value), never user-supplied vcsURL.

cmd/review-bot/vcs.go

@@ -0,0 +1,295 @@
+package main
+
+// vcs.go — VCS client abstraction for supporting both Gitea and GitHub.
+//
+// This file defines the vcsClient interface that main.go uses for all VCS
+// operations, and provides a githubAdapter that wraps *github.Client and
+// converts between github-package types and the gitea-package types used
+// throughout the rest of the binary.
+//
+// Design rationale: the entire codebase was written against gitea types.
+// Rather than introduce a third "shared" type package and update every call
+// site, the adapter converts at the boundary. The conversion is cheap — these
+// are small structs fetched once per run.
+
+import (
+	"context"
+	"os"
+
+	githubpkg "gitea.weiker.me/rodin/review-bot/github"
+	"gitea.weiker.me/rodin/review-bot/gitea"
+	"gitea.weiker.me/rodin/review-bot/review"
+)
+
+// vcsClient is the interface that main.go uses for all VCS API operations.
+// Both *gitea.Client (directly) and *githubAdapter (via this file) satisfy it.
+type vcsClient interface {
+	GetPullRequest(ctx context.Context, owner, repo string, number int) (*gitea.PullRequest, error)
+	GetPullRequestDiff(ctx context.Context, owner, repo string, number int) (string, error)
+	GetPullRequestFiles(ctx context.Context, owner, repo string, number int) ([]gitea.ChangedFile, error)
+	GetCommitStatuses(ctx context.Context, owner, repo, sha string) ([]gitea.CommitStatus, error)
+	GetFileContent(ctx context.Context, owner, repo, filepath string) (string, error)
+	GetFileContentRef(ctx context.Context, owner, repo, filepath, ref string) (string, error)
+	GetAllFilesInPath(ctx context.Context, owner, repo, path string) (map[string]string, error)
+	ListReviews(ctx context.Context, owner, repo string, number int) ([]gitea.Review, error)
+	GetAuthenticatedUser(ctx context.Context) (string, error)
+	RequestReviewer(ctx context.Context, owner, repo string, number int, reviewer string) error
+	PostReview(ctx context.Context, owner, repo string, number int, event, body, commitID string, comments []gitea.ReviewComment) (*gitea.Review, error)
+	GetTimelineReviewCommentIDForReview(ctx context.Context, owner, repo string, number int, reviewID int64) (int64, error)
+	EditComment(ctx context.Context, owner, repo string, commentID int64, newBody string) error
+	ListReviewComments(ctx context.Context, owner, repo string, prNumber int, reviewID int64) ([]gitea.ReviewComment, error)
+	ResolveComment(ctx context.Context, owner, repo string, commentID int64) error
+	ListContents(ctx context.Context, owner, repo, path string) ([]gitea.ContentEntry, error)
+}
+
+// vcsClientAdapterForPersona adapts vcsClient to review.GiteaClient.
+// Used by LoadRepoPersonas which needs only ListContents + GetFileContent.
+type vcsClientAdapterForPersona struct {
+	client vcsClient
+}
+
+func newVCSClientAdapterForPersona(c vcsClient) *vcsClientAdapterForPersona {
+	return &vcsClientAdapterForPersona{client: c}
+}
+
+func (a *vcsClientAdapterForPersona) ListContents(ctx context.Context, owner, repo, path string) ([]review.ContentEntry, error) {
+	entries, err := a.client.ListContents(ctx, owner, repo, path)
+	if err != nil {
+		return nil, err
+	}
+	result := make([]review.ContentEntry, len(entries))
+	for i, e := range entries {
+		result[i] = review.ContentEntry{
+			Name: e.Name,
+			Path: e.Path,
+			Type: e.Type,
+		}
+	}
+	return result, nil
+}
+
+func (a *vcsClientAdapterForPersona) GetFileContent(ctx context.Context, owner, repo, filepath string) (string, error) {
+	return a.client.GetFileContent(ctx, owner, repo, filepath)
+}
+
+// detectVCSType returns "github" if the environment indicates a GitHub or GHES
+// runner, "gitea" otherwise.
+//
+// Detection logic mirrors the action.yml composite action:
+//   - GITHUB_API_URL is set by GitHub Actions runners (github.com and GHES)
+//   - On Gitea Actions runners it is empty or absent
+func detectVCSType() string {
+	if os.Getenv("GITHUB_API_URL") != "" {
+		return "github"
+	}
+	return "gitea"
+}
+
+// githubAPIBaseURL returns the GitHub API base URL from the environment.
+// On GitHub.com this is https://api.github.com.
+// On GHES this is https://<host>/api/v3.
+func githubAPIBaseURL() string {
+	if u := os.Getenv("GITHUB_API_URL"); u != "" {
+		return u
+	}
+	return "https://api.github.com"
+}
+
+// githubAdapter wraps *github.Client and translates github-package types to
+// gitea-package types so that the rest of main.go can remain unchanged.
+type githubAdapter struct {
+	c *githubpkg.Client
+}
+
+func newGitHubAdapter(token, apiBaseURL string) *githubAdapter {
+	return &githubAdapter{c: githubpkg.NewClient(token, apiBaseURL)}
+}
+
+func (a *githubAdapter) GetPullRequest(ctx context.Context, owner, repo string, number int) (*gitea.PullRequest, error) {
+	pr, err := a.c.GetPullRequest(ctx, owner, repo, number)
+	if err != nil {
+		return nil, err
+	}
+	return &gitea.PullRequest{
+		Title: pr.Title,
+		Body:  pr.Body,
+		Head: struct {
+			Sha string "json:\"sha\""
+			Ref string "json:\"ref\""
+		}{Sha: pr.Head.Sha, Ref: pr.Head.Ref},
+	}, nil
+}
+
+func (a *githubAdapter) GetPullRequestDiff(ctx context.Context, owner, repo string, number int) (string, error) {
+	return a.c.GetPullRequestDiff(ctx, owner, repo, number)
+}
+
+func (a *githubAdapter) GetPullRequestFiles(ctx context.Context, owner, repo string, number int) ([]gitea.ChangedFile, error) {
+	files, err := a.c.GetPullRequestFiles(ctx, owner, repo, number)
+	if err != nil {
+		return nil, err
+	}
+	result := make([]gitea.ChangedFile, len(files))
+	for i, f := range files {
+		result[i] = gitea.ChangedFile{
+			Filename: f.Filename,
+			Status:   f.Status,
+		}
+	}
+	return result, nil
+}
+
+func (a *githubAdapter) GetCommitStatuses(ctx context.Context, owner, repo, sha string) ([]gitea.CommitStatus, error) {
+	statuses, err := a.c.GetCommitStatuses(ctx, owner, repo, sha)
+	if err != nil {
+		return nil, err
+	}
+	result := make([]gitea.CommitStatus, len(statuses))
+	for i, s := range statuses {
+		// GitHub uses "state" with values: success, failure, pending, error.
+		// Gitea uses "status" with values: success, failure, pending, warning, error.
+		// Map GitHub's "state" to gitea's "status" field for evaluateCIStatus().
+		result[i] = gitea.CommitStatus{
+			Status:      s.State,
+			Context:     s.Context,
+			Description: s.Description,
+			TargetURL:   s.TargetURL,
+		}
+	}
+	return result, nil
+}
+
+func (a *githubAdapter) GetFileContent(ctx context.Context, owner, repo, filepath string) (string, error) {
+	return a.c.GetFileContent(ctx, owner, repo, filepath)
+}
+
+func (a *githubAdapter) GetFileContentRef(ctx context.Context, owner, repo, filepath, ref string) (string, error) {
+	return a.c.GetFileContentRef(ctx, owner, repo, filepath, ref)
+}
+
+func (a *githubAdapter) GetAllFilesInPath(ctx context.Context, owner, repo, path string) (map[string]string, error) {
+	return a.c.GetAllFilesInPath(ctx, owner, repo, path)
+}
+
+func (a *githubAdapter) ListReviews(ctx context.Context, owner, repo string, number int) ([]gitea.Review, error) {
+	reviews, err := a.c.ListReviews(ctx, owner, repo, number)
+	if err != nil {
+		return nil, err
+	}
+	result := make([]gitea.Review, len(reviews))
+	for i, r := range reviews {
+		result[i] = gitea.Review{
+			ID:   r.ID,
+			Body: r.Body,
+			User: struct {
+				Login string "json:\"login\""
+			}{Login: r.User.Login},
+			State:    r.State,
+			CommitID: r.CommitID,
+		}
+	}
+	return result, nil
+}
+
+func (a *githubAdapter) GetAuthenticatedUser(ctx context.Context) (string, error) {
+	return a.c.GetAuthenticatedUser(ctx)
+}
+
+func (a *githubAdapter) RequestReviewer(ctx context.Context, owner, repo string, number int, reviewer string) error {
+	return a.c.RequestReviewer(ctx, owner, repo, number, reviewer)
+}
+
+func (a *githubAdapter) PostReview(ctx context.Context, owner, repo string, number int, event, body, commitID string, comments []gitea.ReviewComment) (*gitea.Review, error) {
+	// Convert gitea ReviewComments to github ReviewComments.
+	// NewPosition in Gitea maps to Position in GitHub (diff line position).
+	ghComments := make([]githubpkg.ReviewComment, len(comments))
+	for i, c := range comments {
+		ghComments[i] = githubpkg.ReviewComment{
+			Path:     c.Path,
+			Position: c.NewPosition,
+			Body:     c.Body,
+		}
+	}
+	review, err := a.c.PostReview(ctx, owner, repo, number, event, body, commitID, ghComments)
+	if err != nil {
+		return nil, err
+	}
+	return &gitea.Review{
+		ID:   review.ID,
+		Body: review.Body,
+		User: struct {
+			Login string "json:\"login\""
+		}{Login: review.User.Login},
+		State:    review.State,
+		CommitID: review.CommitID,
+	}, nil
+}
+
+func (a *githubAdapter) GetTimelineReviewCommentIDForReview(ctx context.Context, owner, repo string, number int, reviewID int64) (int64, error) {
+	return a.c.GetTimelineReviewCommentIDForReview(ctx, owner, repo, number, reviewID)
+}
+
+func (a *githubAdapter) EditComment(ctx context.Context, owner, repo string, commentID int64, newBody string) error {
+	return a.c.EditComment(ctx, owner, repo, commentID, newBody)
+}
+
+func (a *githubAdapter) ListReviewComments(ctx context.Context, owner, repo string, prNumber int, reviewID int64) ([]gitea.ReviewComment, error) {
+	comments, err := a.c.ListReviewComments(ctx, owner, repo, prNumber, reviewID)
+	if err != nil {
+		return nil, err
+	}
+	result := make([]gitea.ReviewComment, len(comments))
+	for i, c := range comments {
+		result[i] = gitea.ReviewComment{
+			ID:          c.ID,
+			Path:        c.Path,
+			NewPosition: c.Position,
+			Body:        c.Body,
+		}
+	}
+	return result, nil
+}
+
+func (a *githubAdapter) ResolveComment(ctx context.Context, owner, repo string, commentID int64) error {
+	return a.c.ResolveComment(ctx, owner, repo, commentID)
+}
+
+func (a *githubAdapter) ListContents(ctx context.Context, owner, repo, path string) ([]gitea.ContentEntry, error) {
+	entries, err := a.c.ListContents(ctx, owner, repo, path)
+	if err != nil {
+		return nil, err
+	}
+	result := make([]gitea.ContentEntry, len(entries))
+	for i, e := range entries {
+		result[i] = gitea.ContentEntry{
+			Name: e.Name,
+			Path: e.Path,
+			Type: e.Type,
+		}
+	}
+	return result, nil
+}
+
+// newVCSClient creates the appropriate VCS client based on detected VCS type.
+// On GitHub/GHES (GITHUB_API_URL set), returns a githubAdapter.
+// On Gitea (GITHUB_API_URL absent), returns *gitea.Client directly.
+//
+// For GitHub: uses GITHUB_API_URL as the API base URL (trusted platform value).
+// For Gitea: uses vcsURL (validated before this call).
+func newVCSClient(vcsType, vcsURL, reviewerToken string) vcsClient {
+	switch vcsType {
+	case "github":
+		apiURL := githubAPIBaseURL()
+		return newGitHubAdapter(reviewerToken, apiURL)
+	default:
+		return gitea.NewClient(vcsURL, reviewerToken)
+	}
+}
+
+// buildRepoPersonaClient creates a review.GiteaClient from the active vcsClient.
+// This exists because LoadRepoPersonas expects the review.GiteaClient interface
+// (which only requires ListContents + GetFileContent).
+func buildRepoPersonaClient(c vcsClient) review.GiteaClient {
+	return newVCSClientAdapterForPersona(c)
+}
+