// Copyright 2025 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package pull

import (
	"context"
	"fmt"

	repo_model "code.gitea.io/gitea/models/repo"
	"code.gitea.io/gitea/modules/git"
	"code.gitea.io/gitea/modules/gitrepo"
)

// CompareInfo represents needed information for comparing references.
type CompareInfo struct {
	MergeBase    string
	BaseCommitID string
	HeadCommitID string
	Commits      []*git.Commit
	NumFiles     int
}

// GetCompareInfo generates and returns compare information between base and head branches of repositories.
func GetCompareInfo(ctx context.Context, baseRepo, headRepo *repo_model.Repository, headGitRepo *git.Repository, baseBranch, headBranch string, directComparison, fileOnly bool) (_ *CompareInfo, err error) {
	compareInfo := new(CompareInfo)

	compareInfo.HeadCommitID, err = gitrepo.GetFullCommitID(ctx, headRepo, headBranch)
	if err != nil {
		compareInfo.HeadCommitID = headBranch
	}
	compareInfo.BaseCommitID, err = gitrepo.GetFullCommitID(ctx, baseRepo, baseBranch)
	if err != nil {
		compareInfo.BaseCommitID = baseBranch
	}

	compareInfo.MergeBase, err = gitrepo.MergeBaseFromRemote(ctx, baseRepo, headRepo, compareInfo.BaseCommitID, compareInfo.HeadCommitID)
	if err == nil {
		separator := "..."
		startCommitID := compareInfo.MergeBase
		if directComparison {
			separator = ".."
			startCommitID = compareInfo.BaseCommitID
		}

		// We have a common base - therefore we know that ... should work
		if !fileOnly {
			compareInfo.Commits, err = headGitRepo.ShowPrettyFormatLogToList(ctx, startCommitID+separator+headBranch)
			if err != nil {
				return nil, fmt.Errorf("ShowPrettyFormatLogToList: %w", err)
			}
		} else {
			compareInfo.Commits = []*git.Commit{}
		}
	} else {
		compareInfo.Commits = []*git.Commit{}
		compareInfo.MergeBase = compareInfo.BaseCommitID
	}

	// Count number of changed files.
	// This probably should be removed as we need to use shortstat elsewhere
	// Now there is git diff --shortstat but this appears to be slower than simply iterating with --nameonly
	compareInfo.NumFiles, err = headGitRepo.GetDiffNumChangedFiles(compareInfo.BaseCommitID, compareInfo.HeadCommitID, directComparison)
	if err != nil {
		return nil, err
	}
	return compareInfo, nil
}