Add getting Merged Pull Requests function

Makefile

@@ -1,4 +1,4 @@
-.PHONY: lint tests mockgen
+.PHONY: lint tests generate
 
 lint:
 	golint -set_exit_status ./...

github.go

@@ -7,13 +7,15 @@ import (
 	"fmt"
 	"net/http"
 	"text/template"
+	"time"
 
 	"github.com/google/go-github/v28/github"
 	"golang.org/x/oauth2"
 )
 
 const (
 	baseBranch      = "master"
+	listPerPage     = 10
 	releaseTemplate = `
 ## Changelog
 - test (#10) by @p1ass
@@ -27,16 +29,22 @@ var (
 
 //go:generate mockgen -source=$GOFILE -destination=mock_$GOFILE -package=$GOPACKAGE
 
-// GitHubClient is a interface for calling GitHub API
-type GitHubClient interface {
+// GitHubRepositoriesClient is a interface for calling GitHub API about repositories
+type GitHubRepositoriesClient interface {
 	CreateRelease(ctx context.Context, owner, repo string, release *github.RepositoryRelease) (*github.RepositoryRelease, *github.Response, error)
 	GetLatestRelease(ctx context.Context, owner, repo string) (*github.RepositoryRelease, *github.Response, error)
 }
 
-// GitHubService calls GitHub API through GitHubClient
+// GitHubPullRequestsClient is a interface for calling GitHub API about pull requests
+type GitHubPullRequestsClient interface {
+	List(ctx context.Context, owner string, repo string, opt *github.PullRequestListOptions) ([]*github.PullRequest, *github.Response, error)
+}
+
+// GitHubService handles application logic using GitHub API
 type GitHubService struct {
-	owner string
-	cli   GitHubClient
+	owner   string
+	repoCli GitHubRepositoriesClient
+	prCli   GitHubPullRequestsClient
 }
 
 // NewGitHubService returns a pointer of GitHubService
@@ -49,13 +57,14 @@ func NewGitHubService(owner, accessToken string) *GitHubService {
 	tc := oauth2.NewClient(ctx, ts)
 	client := github.NewClient(tc)
 
-	return newGitHubService(owner, client.Repositories)
+	return newGitHubService(owner, client.Repositories, client.PullRequests)
 }
 
-func newGitHubService(owner string, githubCli GitHubClient) *GitHubService {
+func newGitHubService(owner string, githubCli GitHubRepositoriesClient, prCli GitHubPullRequestsClient) *GitHubService {
 	return &GitHubService{
-		owner: owner,
-		cli:   githubCli,
+		owner:   owner,
+		repoCli: githubCli,
+		prCli:   prCli,
 	}
 }
 
@@ -67,7 +76,7 @@ func (s *GitHubService) CreateReleaseByTagName(repo, tagName string) (*github.Re
 	}
 
 	ctx := context.Background()
-	release, _, err := s.cli.CreateRelease(ctx, s.owner, repo, &github.RepositoryRelease{
+	release, _, err := s.repoCli.CreateRelease(ctx, s.owner, repo, &github.RepositoryRelease{
 		TagName: github.String(tagName),
 		Name:    github.String(tagName),
 		Body:    github.String(body),
@@ -92,10 +101,10 @@ func generateReleaseBody() (string, error) {
 	return buff.String(), nil
 }
 
-// GetLatestRelease gets the latest release
-func (s *GitHubService) GetLatestRelease(repo string) (*github.RepositoryRelease, error) {
+// getLatestRelease gets the latest release
+func (s *GitHubService) getLatestRelease(repo string) (*github.RepositoryRelease, error) {
 	ctx := context.Background()
-	release, resp, err := s.cli.GetLatestRelease(ctx, s.owner, repo)
+	release, resp, err := s.repoCli.GetLatestRelease(ctx, s.owner, repo)
 	if err != nil {
 		if resp != nil && resp.StatusCode == http.StatusNotFound {
 			return nil, fmt.Errorf("%s: %w", repo, ErrReleaseNotFound)
@@ -104,3 +113,65 @@ func (s *GitHubService) GetLatestRelease(repo string) (*github.RepositoryRelease
 	}
 	return release, nil
 }
+
+// GetMergedPRsAfterLatestRelease gets pull requests which are merged after the latest release
+func (s *GitHubService) GetMergedPRsAfterLatestRelease(repo string) ([]*github.PullRequest, error) {
+	release, err := s.getLatestRelease(repo)
+	if err != nil {
+		return nil, fmt.Errorf("get latest release: %w", err)
+	}
+	prs, err := s.getMergedPRsAfter(repo, release.CreatedAt.Time)
+	if err != nil {
+		return nil, fmt.Errorf("get pull requests: %w", err)
+	}
+	return prs, nil
+}
+
+func (s *GitHubService) getMergedPRsAfter(repo string, after time.Time) ([]*github.PullRequest, error) {
+	opt := &github.PullRequestListOptions{
+		State:       "closed",
+		Base:        baseBranch,
+		Sort:        "updated",
+		Direction:   "desc",
+		ListOptions: github.ListOptions{PerPage: listPerPage},
+	}
+
+	var prList []*github.PullRequest
+	for {
+		ctx := context.Background()
+		prs, resp, err := s.prCli.List(ctx, s.owner, repo, opt)
+		if err != nil {
+			return nil, fmt.Errorf("call listing pull requests API: %w", err)
+		}
+
+		extractedPR, done := extractMergedPRsAfter(prs, after)
+		prList = append(prList, extractedPR...)
+		if done {
+			break
+		}
+
+		if resp.NextPage == 0 {
+			break
+		}
+		opt.Page = resp.NextPage
+	}
+
+	return prList, nil
+}
+
+// extractMergedPRsAfter extract merged PRs after a given time
+// Return PRs and boolean whether we got all PRs we want
+func extractMergedPRsAfter(prs []*github.PullRequest, after time.Time) ([]*github.PullRequest, bool) {
+	var prList []*github.PullRequest
+	done := false
+	for _, pr := range prs {
+		if pr.MergedAt != nil && pr.MergedAt.After(after) {
+			prList = append(prList, pr)
+		}
+		if pr.UpdatedAt != nil && !pr.UpdatedAt.After(after) {
+			done = true
+			break
+		}
+	}
+	return prList, done
+}