// Copyright 2015 The Gogs Authors. All rights reserved.
// Copyright 2019 The Gitea Authors. All rights reserved.
// Use of this source code is governed by a MIT-style
// license that can be found in the LICENSE file.

package git

import (
	"bytes"
	"container/list"
	"fmt"
	"io"
	"strconv"
	"strings"
	"time"

	logger "code.gitea.io/gitea/modules/log"
)

// CompareInfo represents needed information for comparing references.
type CompareInfo struct {
	MergeBase string
	Commits   *list.List
	NumFiles  int
}

// GetMergeBase checks and returns merge base of two branches and the reference used as base.
func (repo *Repository) GetMergeBase(tmpRemote string, base, head string) (string, string, error) {
	if tmpRemote == "" {
		tmpRemote = "origin"
	}

	if tmpRemote != "origin" {
		tmpBaseName := "refs/remotes/" + tmpRemote + "/tmp_" + base
		// Fetch commit into a temporary branch in order to be able to handle commits and tags
		_, err := NewCommand("fetch", tmpRemote, base+":"+tmpBaseName).RunInDir(repo.Path)
		if err == nil {
			base = tmpBaseName
		}
	}

	stdout, err := NewCommand("merge-base", "--", base, head).RunInDir(repo.Path)
	return strings.TrimSpace(stdout), base, err
}

// GetCompareInfo generates and returns compare information between base and head branches of repositories.
func (repo *Repository) GetCompareInfo(basePath, baseBranch, headBranch string) (_ *CompareInfo, err error) {
	var (
		remoteBranch string
		tmpRemote    string
	)

	// We don't need a temporary remote for same repository.
	if repo.Path != basePath {
		// Add a temporary remote
		tmpRemote = strconv.FormatInt(time.Now().UnixNano(), 10)
		if err = repo.AddRemote(tmpRemote, basePath, false); err != nil {
			return nil, fmt.Errorf("AddRemote: %v", err)
		}
		defer func() {
			if err := repo.RemoveRemote(tmpRemote); err != nil {
				logger.Error("GetPullRequestInfo: RemoveRemote: %v", err)
			}
		}()
	}

	compareInfo := new(CompareInfo)
	compareInfo.MergeBase, remoteBranch, err = repo.GetMergeBase(tmpRemote, baseBranch, headBranch)
	if err == nil {
		// We have a common base - therefore we know that ... should work
		logs, err := NewCommand("log", compareInfo.MergeBase+"..."+headBranch, prettyLogFormat).RunInDirBytes(repo.Path)
		if err != nil {
			return nil, err
		}
		compareInfo.Commits, err = repo.parsePrettyFormatLogToList(logs)
		if err != nil {
			return nil, fmt.Errorf("parsePrettyFormatLogToList: %v", err)
		}
	} else {
		compareInfo.Commits = list.New()
		compareInfo.MergeBase, err = GetFullCommitID(repo.Path, remoteBranch)
		if err != nil {
			compareInfo.MergeBase = remoteBranch
		}
	}

	// Count number of changed files.
	stdout, err := NewCommand("diff", "--name-only", remoteBranch+"..."+headBranch).RunInDir(repo.Path)
	if err != nil && strings.Contains(err.Error(), "no merge base") {
		// git >= 2.28 now returns an error if base and head have become unrelated.
		// previously it would return the results of git diff --name-only base head so let's try that...
		stdout, err = NewCommand("diff", "--name-only", remoteBranch, headBranch).RunInDir(repo.Path)
	}
	if err != nil {
		return nil, err
	}
	compareInfo.NumFiles = len(strings.Split(stdout, "\n")) - 1
	return compareInfo, nil
}

// GetDiffOrPatch generates either diff or formatted patch data between given revisions
func (repo *Repository) GetDiffOrPatch(base, head string, w io.Writer, formatted bool) error {
	if formatted {
		return repo.GetPatch(base, head, w)
	}
	return repo.GetDiff(base, head, w)
}

// GetDiff generates and returns patch data between given revisions.
func (repo *Repository) GetDiff(base, head string, w io.Writer) error {
	return NewCommand("diff", "-p", "--binary", base, head).
		RunInDirPipeline(repo.Path, w, nil)
}

// GetPatch generates and returns format-patch data between given revisions.
func (repo *Repository) GetPatch(base, head string, w io.Writer) error {
	stderr := new(bytes.Buffer)
	err := NewCommand("format-patch", "--binary", "--stdout", base+"..."+head).
		RunInDirPipeline(repo.Path, w, stderr)
	if err != nil && bytes.Contains(stderr.Bytes(), []byte("no merge base")) {
		return NewCommand("format-patch", "--binary", "--stdout", base, head).
			RunInDirPipeline(repo.Path, w, nil)
	}
	return err
}

// GetDiffFromMergeBase generates and return patch data from merge base to head
func (repo *Repository) GetDiffFromMergeBase(base, head string, w io.Writer) error {
	stderr := new(bytes.Buffer)
	err := NewCommand("diff", "-p", "--binary", base+"..."+head).
		RunInDirPipeline(repo.Path, w, stderr)
	if err != nil && bytes.Contains(stderr.Bytes(), []byte("no merge base")) {
		return NewCommand("diff", "-p", "--binary", base, head).
			RunInDirPipeline(repo.Path, w, nil)
	}
	return err
}