// Copyright 2024 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package repository

import (
	"context"
	"fmt"

	git_model "code.gitea.io/gitea/models/git"
	issue_model "code.gitea.io/gitea/models/issues"
	repo_model "code.gitea.io/gitea/models/repo"
	user_model "code.gitea.io/gitea/models/user"
	"code.gitea.io/gitea/modules/git"
	"code.gitea.io/gitea/modules/gitrepo"
	repo_module "code.gitea.io/gitea/modules/repository"
	"code.gitea.io/gitea/modules/util"
	"code.gitea.io/gitea/services/pull"
)

type UpstreamDivergingInfo struct {
	BaseHasNewCommits bool
	CommitsBehind     int
	CommitsAhead      int
}

// MergeUpstream merges the base repository's default branch into the fork repository's current branch.
func MergeUpstream(ctx context.Context, doer *user_model.User, repo *repo_model.Repository, branch string) (mergeStyle string, err error) {
	if err = repo.MustNotBeArchived(); err != nil {
		return "", err
	}
	if err = repo.GetBaseRepo(ctx); err != nil {
		return "", err
	}
	err = git.Push(ctx, repo.BaseRepo.RepoPath(), git.PushOptions{
		Remote: repo.RepoPath(),
		Branch: fmt.Sprintf("%s:%s", repo.BaseRepo.DefaultBranch, branch),
		Env:    repo_module.PushingEnvironment(doer, repo),
	})
	if err == nil {
		return "fast-forward", nil
	}
	if !git.IsErrPushOutOfDate(err) && !git.IsErrPushRejected(err) {
		return "", err
	}

	// TODO: FakePR: it is somewhat hacky, but it is the only way to "merge" at the moment
	// ideally in the future the "merge" functions should be refactored to decouple from the PullRequest
	fakeIssue := &issue_model.Issue{
		ID:       -1,
		RepoID:   repo.ID,
		Repo:     repo,
		Index:    -1,
		PosterID: doer.ID,
		Poster:   doer,
		IsPull:   true,
	}
	fakePR := &issue_model.PullRequest{
		ID:         -1,
		Status:     issue_model.PullRequestStatusMergeable,
		IssueID:    -1,
		Issue:      fakeIssue,
		Index:      -1,
		HeadRepoID: repo.ID,
		HeadRepo:   repo,
		BaseRepoID: repo.BaseRepo.ID,
		BaseRepo:   repo.BaseRepo,
		HeadBranch: branch, // maybe HeadCommitID is not needed
		BaseBranch: repo.BaseRepo.DefaultBranch,
	}
	fakeIssue.PullRequest = fakePR
	err = pull.Update(ctx, fakePR, doer, "merge upstream", false)
	if err != nil {
		return "", err
	}
	return "merge", nil
}

// GetUpstreamDivergingInfo returns the information about the divergence between the fork repository's branch and the base repository's default branch.
func GetUpstreamDivergingInfo(ctx context.Context, repo *repo_model.Repository, branch string) (*UpstreamDivergingInfo, error) {
	if !repo.IsFork {
		return nil, util.NewInvalidArgumentErrorf("repo is not a fork")
	}

	if repo.IsArchived {
		return nil, util.NewInvalidArgumentErrorf("repo is archived")
	}

	if err := repo.GetBaseRepo(ctx); err != nil {
		return nil, err
	}

	forkBranch, err := git_model.GetBranch(ctx, repo.ID, branch)
	if err != nil {
		return nil, err
	}

	baseBranch, err := git_model.GetBranch(ctx, repo.BaseRepo.ID, repo.BaseRepo.DefaultBranch)
	if err != nil {
		return nil, err
	}

	info := &UpstreamDivergingInfo{}
	if forkBranch.CommitID == baseBranch.CommitID {
		return info, nil
	}

	// if the fork repo has new commits, this call will fail because they are not in the base repo
	// exit status 128 - fatal: Invalid symmetric difference expression aaaaaaaaaaaa...bbbbbbbbbbbb
	// so at the moment, we first check the update time, then check whether the fork branch has base's head
	diff, err := git.GetDivergingCommits(ctx, repo.BaseRepo.RepoPath(), baseBranch.CommitID, forkBranch.CommitID)
	if err != nil {
		info.BaseHasNewCommits = baseBranch.UpdatedUnix > forkBranch.UpdatedUnix
		if info.BaseHasNewCommits {
			return info, nil
		}

		// if the base's update time is before the fork, check whether the base's head is in the fork
		baseGitRepo, baseGitRepoCloser, err := gitrepo.RepositoryFromContextOrOpen(ctx, repo.BaseRepo)
		if err != nil {
			return nil, err
		}
		defer baseGitRepoCloser.Close()

		headGitRepo, headGitRepoCloser, err := gitrepo.RepositoryFromContextOrOpen(ctx, repo)
		if err != nil {
			return nil, err
		}
		defer headGitRepoCloser.Close()

		baseCommitID, err := baseGitRepo.ConvertToGitID(baseBranch.CommitID)
		if err != nil {
			return nil, err
		}
		headCommit, err := headGitRepo.GetCommit(forkBranch.CommitID)
		if err != nil {
			return nil, err
		}
		hasPreviousCommit, _ := headCommit.HasPreviousCommit(baseCommitID)
		info.BaseHasNewCommits = !hasPreviousCommit
		return info, nil
	}

	info.CommitsBehind, info.CommitsAhead = diff.Behind, diff.Ahead
	return info, nil
}