package repo

import (
	"context"
	"errors"
	"fmt"

	"polar/internal/git"
)

var ErrForkNotFound = errors.New("fork repository not found")

// MergePullRequest merges an open pull request into its base branch and
// records the merge. Same-repository pull requests merge local branches;
// cross-repository (fork) pull requests are merged through a temporary ref
// fetched from the fork.
func (s *Service) MergePullRequest(ctx context.Context, base *Repository, pr *PullRequest, authorName, authorEmail string, mergedByID int64) error {
	if pr == nil || base == nil {
		return errors.New("pull request and repository are required")
	}
	if pr.Status != "open" {
		return errors.New("only open pull requests can be merged")
	}

	baseDisk, err := s.DiskPath(base.OwnerUsername, base.Name)
	if err != nil {
		return err
	}

	headLabel := pr.HeadBranch
	if pr.HeadRepoID != nil && *pr.HeadRepoID != base.ID {
		headLabel = fmt.Sprintf("%s/%s:%s", pr.HeadRepoOwner, pr.HeadRepoName, pr.HeadBranch)
	}
	msg := fmt.Sprintf("Merge pull request #%d from %s\n\n%s", pr.Number, headLabel, pr.Title)

	if pr.HeadRepoID != nil && *pr.HeadRepoID != base.ID {
		head, err := s.GetByID(ctx, *pr.HeadRepoID)
		if err != nil || head == nil {
			return ErrForkNotFound
		}
		forkDisk, err := s.DiskPath(head.OwnerUsername, head.Name)
		if err != nil {
			return err
		}
		tmpRef := fmt.Sprintf("refs/polar/tmp-merge-%d", pr.ID)
		if _, err := git.MergeFromPath(ctx, baseDisk, forkDisk, pr.BaseBranch, pr.HeadBranch, tmpRef, msg, authorName, authorEmail); err != nil {
			return err
		}
	} else {
		if _, err := git.MergeBranches(ctx, baseDisk, pr.BaseBranch, pr.HeadBranch, msg, authorName, authorEmail); err != nil {
			return err
		}
	}

	if err := s.SetPullRequestStatus(ctx, pr.ID, "merged", &mergedByID); err != nil {
		return err
	}
	s.TouchUpdatedAt(ctx, base.ID)
	return nil
}