// Copyright 2020 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package pull

import (
	"context"
	"errors"
	"fmt"

	git_model "gitea.dev/models/git"
	issues_model "gitea.dev/models/issues"
	access_model "gitea.dev/models/perm/access"
	repo_model "gitea.dev/models/repo"
	"gitea.dev/models/unit"
	user_model "gitea.dev/models/user"
	"gitea.dev/modules/gitrepo"
	"gitea.dev/modules/globallock"
	"gitea.dev/modules/graceful"
	"gitea.dev/modules/log"
	"gitea.dev/modules/repository"
)

// Update updates pull request with base branch.
func Update(pr *issues_model.PullRequest, doer *user_model.User, message string, rebase bool) error {
	ctx := graceful.GetManager().HammerContext() // don't abort the git operation even if the user's request is canceled
	if pr.Flow == issues_model.PullRequestFlowAGit {
		// TODO: update of agit flow pull request's head branch is unsupported
		return errors.New("update of agit flow pull request's head branch is unsupported")
	}

	releaser, err := globallock.Lock(ctx, getPullWorkingLockKey(pr.ID))
	if err != nil {
		log.Error("lock.Lock(): %v", err)
		return fmt.Errorf("lock.Lock: %w", err)
	}
	defer releaser()

	if err := pr.LoadBaseRepo(ctx); err != nil {
		log.Error("unable to load BaseRepo for %-v during update-by-merge: %v", pr, err)
		return fmt.Errorf("unable to load BaseRepo for PR[%d] during update-by-merge: %w", pr.ID, err)
	}

	// TODO: FakePR: if the PR is a fake PR (for example: from Merge Upstream), then no need to check diverging
	if pr.ID > 0 {
		diffCount, err := gitrepo.GetDivergingCommits(ctx, pr.BaseRepo, pr.BaseBranch, pr.GetGitHeadRefName())
		if err != nil {
			return err
		} else if diffCount.Behind == 0 {
			return fmt.Errorf("HeadBranch of PR %d is up to date", pr.Index)
		}
	}

	if err := pr.LoadHeadRepo(ctx); err != nil {
		log.Error("unable to load HeadRepo for PR %-v during update-by-merge: %v", pr, err)
		return fmt.Errorf("unable to load HeadRepo for PR[%d] during update-by-merge: %w", pr.ID, err)
	}
	if pr.HeadRepo == nil {
		// LoadHeadRepo will swallow ErrRepoNotExist so if pr.HeadRepo is still nil recreate the error
		err := repo_model.ErrRepoNotExist{
			ID: pr.HeadRepoID,
		}
		log.Error("unable to load HeadRepo for PR %-v during update-by-merge: %v", pr, err)
		return fmt.Errorf("unable to load HeadRepo for PR[%d] during update-by-merge: %w", pr.ID, err)
	}

	// TODO: The code is from https://github.com/go-gitea/gitea/pull/9784,
	// it seems a simple copy-paste from https://github.com/go-gitea/gitea/pull/7082 without a real reason.
	// TODO: DUPLICATE-PR-TASK: search and see another TODO comment for more details
	defer addTestPullRequestTaskAfterWebOperation(pr, doer)

	if rebase {
		return updateHeadByRebaseOnToBase(ctx, pr, doer)
	}

	// 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
	// now use a fake reverse PR to switch head&base repos/branches
	reversePR := &issues_model.PullRequest{
		ID: pr.ID,

		HeadRepoID: pr.BaseRepoID,
		HeadRepo:   pr.BaseRepo,
		HeadBranch: pr.BaseBranch,

		BaseRepoID: pr.HeadRepoID,
		BaseRepo:   pr.HeadRepo,
		BaseBranch: pr.HeadBranch,
	}

	_, err = doMergeAndPush(ctx, reversePR, doer, repo_model.MergeStyleMerge, "", message, repository.PushTriggerPRUpdateWithBase)
	// TODO: the "update" (merge target branch to PR head branch) operation has finished, there could still be some edge cases:
	// * the database was already out of sync: the target branch was already in head branch:
	//   * so no post-receive hook is really executed, no PR status update
	//   * then the PR status is stuck in "behind the target branch" (a new push can be used as a workaround)
	// * "merge" operation does finish, but the post-receive hook isn't correctly executed due to other reasons:
	//   * although the target branch is merged into head branch by this "update" (head branch receives new commits)
	//   * but database isn't updated, so the PR status is still "behind the target branch"
	return err
}

// isUserAllowedToPushOrForcePushInRepoBranch checks whether user is allowed to push or force push in the given repo and branch
// it will check both user permission and branch protection rules
func isUserAllowedToPushOrForcePushInRepoBranch(ctx context.Context, user *user_model.User, repo *repo_model.Repository, branch string) (pushAllowed, forcePushAllowed bool, err error) {
	if user == nil {
		return false, false, nil
	}

	// 1. check user push permission on the given repository
	repoPerm, err := access_model.GetDoerRepoPermission(ctx, repo, user)
	if err != nil {
		if repo_model.IsErrUnitTypeNotExist(err) {
			return false, false, nil
		}
		return false, false, err
	}
	pushAllowed = repoPerm.CanWrite(unit.TypeCode)
	forcePushAllowed = pushAllowed

	// 2. check branch protection whether user can push or force push
	pb, err := git_model.GetFirstMatchProtectedBranchRule(ctx, repo.ID, branch)
	if err != nil {
		return false, false, err
	}
	if pb != nil { // override previous results if there is a branch protection rule
		pb.Repo = repo
		pushAllowed = pb.CanUserPush(ctx, user)
		forcePushAllowed = pb.CanUserForcePush(ctx, user)
	}
	return pushAllowed, forcePushAllowed, nil
}

// CheckUserAllowedToUpdate check if user is allowed to update PR with given permissions and branch protections
// update PR means send new commits to PR head branch from base branch
func CheckUserAllowedToUpdate(ctx context.Context, pull *issues_model.PullRequest, user *user_model.User) (ret struct {
	MergeAllowed, RebaseAllowed bool
	DefaultUpdateStyle          repo_model.UpdateStyle
}, err error,
) {
	if user == nil {
		return ret, nil
	}
	if err := pull.LoadBaseRepo(ctx); err != nil {
		return ret, err
	}
	if err := pull.LoadHeadRepo(ctx); err != nil {
		return ret, err
	}

	// 1. check whether pull request enabled.
	prBaseUnit, err := pull.BaseRepo.GetUnit(ctx, unit.TypePullRequests)
	if repo_model.IsErrUnitTypeNotExist(err) {
		return ret, nil // the PR unit is disabled in base repo means no update allowed
	} else if err != nil {
		return ret, fmt.Errorf("get base repo unit: %v", err)
	}

	// 2. only support Github style pull request
	if pull.Flow == issues_model.PullRequestFlowAGit {
		return ret, nil
	}

	// 3. check user push permission on head repository
	ret.MergeAllowed, ret.RebaseAllowed, err = isUserAllowedToPushOrForcePushInRepoBranch(ctx, user, pull.HeadRepo, pull.HeadBranch)
	if err != nil {
		return ret, err
	}

	// 4. if the pull creator allows maintainer to edit, we need to check whether
	// user is a maintainer (has permission to merge into base branch) and inherit pull request poster's permission
	if pull.AllowMaintainerEdit && (!ret.MergeAllowed || !ret.RebaseAllowed) {
		baseRepoPerm, err := access_model.GetDoerRepoPermission(ctx, pull.BaseRepo, user)
		if err != nil {
			return ret, err
		}
		userAllowedToMergePR, err := isUserAllowedToMergeInRepoBranch(ctx, pull.BaseRepoID, pull.BaseBranch, baseRepoPerm, user)
		if err != nil {
			return ret, err
		}
		if userAllowedToMergePR {
			// the user is maintainer (can merge PR), and this PR is allowed to be edited by maintainers,
			// then the user should inherit the PR poster's push/rebase permission for the head branch
			if err := pull.LoadIssue(ctx); err != nil {
				return ret, err
			}
			if err := pull.Issue.LoadPoster(ctx); err != nil {
				return ret, err
			}
			posterPushAllowed, posterRebaseAllowed, err := isUserAllowedToPushOrForcePushInRepoBranch(ctx, pull.Issue.Poster, pull.HeadRepo, pull.HeadBranch)
			if err != nil {
				return ret, err
			}
			if !ret.MergeAllowed {
				ret.MergeAllowed = posterPushAllowed
			}
			if !ret.RebaseAllowed {
				ret.RebaseAllowed = posterRebaseAllowed
			}
		}
	}

	// 5. apply base repository's update configuration; it is a config on the base repo,
	// but it controls the head (fork) repo's "Update" behavior.
	prConfig := prBaseUnit.PullRequestsConfig()
	ret.MergeAllowed = ret.MergeAllowed && prConfig.AllowMergeUpdate
	ret.RebaseAllowed = ret.RebaseAllowed && prConfig.AllowRebaseUpdate
	ret.DefaultUpdateStyle = prConfig.DefaultUpdateStyle
	return ret, nil
}

func syncCommitDivergence(ctx context.Context, pr *issues_model.PullRequest) error {
	if err := pr.LoadBaseRepo(ctx); err != nil {
		return err
	}
	divergence, err := gitrepo.GetDivergingCommits(ctx, pr.BaseRepo, pr.BaseBranch, pr.GetGitHeadRefName())
	if err != nil {
		return err
	}
	return pr.UpdateCommitDivergence(ctx, divergence.Ahead, divergence.Behind)
}
