Implement "local repo" functionality in github client

* Retrieving the current state (i.e. contents) of file at path in local
  repo
* Starting a commit
* Updating the contents (or creating) file at path in local repo and
  updating the "started" commit
* Finishing a commit
* Pushing commit to new remote branch (as part of creating a PR)
* Removing local repository on "shutdown"

vc/common.go

@@ -52,4 +52,14 @@ type VCClient interface {
 	// UpdateCodeChangeRequest updates an existing code change request on the version control server.
 	// UpdateCodeChangeRequest(id string, res llm.CodeChangeResponse)
 	// TODO: add/read comments to/from issues and code change requests
+	// GetLocalFile gets the current representation of the file at the provided path from the local git repo.
+	GetLocalFile(path string) (llm.File, error)
+	// StartCommit initiates a commit process, after which files can be modified and added to the commit.
+	StartCommit() error
+	// ReplaceOrAddLocalFile updates or adds a file in the locally cloned repo, and applies these changes to the current git worktree.
+	ReplaceOrAddLocalFile(newFile llm.File) error
+	// FinishCommit completes a commit, after which a code change request can be opened or updated.
+	FinishCommit(message string) error
+	// Close tears down the VCClient.
+	Close() error
 }

vc/github.go

@@ -6,12 +6,21 @@ import (
 	"encoding/hex"
 	"errors"
 	"fmt"
+	"go/format"
+	"io/ioutil"
+	"os"
+	"path/filepath"
 	"strconv"
+	"strings"
+
+	"github.com/mobyvb/pull-pal/llm"
 
 	"github.com/go-git/go-git/v5"
+	"github.com/go-git/go-git/v5/config"
+	"github.com/go-git/go-git/v5/plumbing"
+	"github.com/go-git/go-git/v5/plumbing/object"
 	"github.com/go-git/go-git/v5/plumbing/transport/http"
 	"github.com/google/go-github/github"
-	"github.com/mobyvb/pull-pal/llm"
 	"go.uber.org/zap"
 	"golang.org/x/oauth2"
 )
@@ -24,6 +33,8 @@ type GithubClient struct {
 	client *github.Client
 	self   Author
 	repo   Repository
+
+	worktree *git.Worktree
 }
 
 // NewGithubClient initializes a Github client and checks out a repository locally.
@@ -69,14 +80,16 @@ func NewGithubClient(ctx context.Context, log *zap.Logger, self Author, repo Rep
 	}, nil
 }
 
-// OpenCodeChangeRequest opens a new PR on Github based on the provided LLM request and response.
+// OpenCodeChangeRequest pushes to a new remote branch and opens a PR on Github.
 func (gc *GithubClient) OpenCodeChangeRequest(req llm.CodeChangeRequest, res llm.CodeChangeResponse) (id, url string, err error) {
 	// TODO handle gc.ctx canceled
 	gc.log.Debug("Creating a new pull request...")
 
 	title := req.Subject
 	branchName := randomBranchName()
+	branchRefName := plumbing.NewBranchReferenceName(branchName)
 	baseBranch := "main"
+	remoteName := "origin"
 	body := res.Notes
 	body += fmt.Sprintf("\n\nResolves #%s", req.IssueID)
 	issue, err := strconv.Atoi(req.IssueID)
@@ -85,6 +98,44 @@ func (gc *GithubClient) OpenCodeChangeRequest(req llm.CodeChangeRequest, res llm
 		return "", "", err
 	}
 
+	// Create new local branch
+	headRef, err := gc.repo.localRepo.Head()
+	if err != nil {
+		return "", "", err
+	}
+	err = gc.repo.localRepo.CreateBranch(&config.Branch{
+		Name:   branchName,
+		Remote: remoteName,
+		Merge:  branchRefName,
+	})
+	if err != nil {
+		return "", "", err
+	}
+
+	// Update the branch to point to the new commit
+	err = gc.repo.localRepo.Storer.SetReference(plumbing.NewHashReference(branchRefName, headRef.Hash()))
+	if err != nil {
+		return "", "", err
+	}
+
+	// Push the new branch to the remote repository
+	remote, err := gc.repo.localRepo.Remote(remoteName)
+	if err != nil {
+		return "", "", err
+	}
+
+	err = remote.Push(&git.PushOptions{
+		RefSpecs: []config.RefSpec{config.RefSpec(fmt.Sprintf("%s:refs/heads/%s", branchRefName, branchName))},
+		Auth: &http.BasicAuth{
+			Username: gc.self.Handle,
+			Password: gc.self.Token,
+		},
+	})
+	if err != nil {
+		return "", "", err
+	}
+
+	// Finally, open a pull request from the new branch.
 	pr, _, err := gc.client.PullRequests.Create(gc.ctx, gc.repo.Owner.Handle, gc.repo.Name, &github.NewPullRequest{
 		Title: &title,
 		Head:  &branchName,
@@ -136,3 +187,87 @@ func (gc *GithubClient) ListOpenIssues() ([]Issue, error) {
 
 	return toReturn, nil
 }
+
+// GetLocalFile gets the current representation of the file at the provided path from the local git repo.
+func (gc *GithubClient) GetLocalFile(path string) (llm.File, error) {
+	fullPath := filepath.Join(gc.repo.LocalPath, path)
+
+	data, err := ioutil.ReadFile(fullPath)
+	if err != nil {
+		return llm.File{}, err
+	}
+
+	return llm.File{
+		Path:     path,
+		Contents: string(data),
+	}, nil
+}
+
+// StartCommit creates a new worktree associated with this Github client.
+func (gc *GithubClient) StartCommit() error {
+	if gc.worktree != nil {
+		return errors.New("worktree is not nil - cannot start a new commit")
+	}
+
+	worktree, err := gc.repo.localRepo.Worktree()
+	if err != nil {
+		return err
+	}
+
+	gc.worktree = worktree
+
+	return nil
+}
+
+// ReplaceOrAddLocalFile updates or adds a file in the locally cloned repo, and applies these changes to the current git worktree.
+func (gc *GithubClient) ReplaceOrAddLocalFile(newFile llm.File) error {
+	if gc.worktree == nil {
+		return errors.New("worktree is nil - StartCommit must be called")
+	}
+
+	// TODO format non-go files as well
+	if strings.HasSuffix(newFile.Path, ".go") {
+		newContents, err := format.Source([]byte(newFile.Contents))
+		if err != nil {
+			return err
+		}
+		newFile.Contents = string(newContents)
+	}
+
+	fullPath := filepath.Join(gc.repo.LocalPath, newFile.Path)
+
+	err := ioutil.WriteFile(fullPath, []byte(newFile.Contents), 0644)
+	if err != nil {
+		return err
+	}
+
+	_, err = gc.worktree.Add(newFile.Path)
+
+	return err
+}
+
+// FinishCommit completes a commit, after which a code change request can be opened or updated.
+func (gc *GithubClient) FinishCommit(message string) error {
+	if gc.worktree == nil {
+		return errors.New("worktree is nil - StartCommit must be called")
+	}
+	_, err := gc.worktree.Commit(message, &git.CommitOptions{
+		Author: &object.Signature{
+			Name:  gc.self.Handle,
+			Email: gc.self.Email,
+		},
+	})
+
+	return err
+}
+
+func (gc *GithubClient) Close() error {
+	// Remove local repository
+	if gc.repo.LocalPath != "" {
+		err := os.RemoveAll(gc.repo.LocalPath)
+
+		return err
+	}
+
+	return nil
+}