// Copyright 2019 The Gitea Authors. All rights reserved.
// SPDX-License-Identifier: MIT

package repo

import (
	"bufio"
	gocontext "context"
	"encoding/csv"
	"errors"
	"fmt"
	"io"
	"net/http"
	"net/url"
	"path/filepath"
	"sort"
	"strings"

	"code.gitea.io/gitea/models/db"
	git_model "code.gitea.io/gitea/models/git"
	issues_model "code.gitea.io/gitea/models/issues"
	access_model "code.gitea.io/gitea/models/perm/access"
	repo_model "code.gitea.io/gitea/models/repo"
	"code.gitea.io/gitea/models/unit"
	user_model "code.gitea.io/gitea/models/user"
	"code.gitea.io/gitea/modules/base"
	"code.gitea.io/gitea/modules/charset"
	csv_module "code.gitea.io/gitea/modules/csv"
	"code.gitea.io/gitea/modules/fileicon"
	"code.gitea.io/gitea/modules/git"
	"code.gitea.io/gitea/modules/git/gitcmd"
	"code.gitea.io/gitea/modules/gitrepo"
	"code.gitea.io/gitea/modules/log"
	"code.gitea.io/gitea/modules/markup"
	"code.gitea.io/gitea/modules/optional"
	"code.gitea.io/gitea/modules/setting"
	api "code.gitea.io/gitea/modules/structs"
	"code.gitea.io/gitea/modules/templates"
	"code.gitea.io/gitea/modules/typesniffer"
	"code.gitea.io/gitea/modules/util"
	"code.gitea.io/gitea/routers/common"
	"code.gitea.io/gitea/services/context"
	"code.gitea.io/gitea/services/context/upload"
	git_service "code.gitea.io/gitea/services/git"
	"code.gitea.io/gitea/services/gitdiff"
	user_service "code.gitea.io/gitea/services/user"
)

const (
	tplCompare     templates.TplName = "repo/diff/compare"
	tplBlobExcerpt templates.TplName = "repo/diff/blob_excerpt"
	tplDiffBox     templates.TplName = "repo/diff/box"
)

// setCompareContext sets context data.
func setCompareContext(ctx *context.Context, before, head *git.Commit, headOwner, headName string) {
	ctx.Data["BeforeCommit"] = before
	ctx.Data["HeadCommit"] = head

	ctx.Data["GetBlobByPathForCommit"] = func(commit *git.Commit, path string) *git.Blob {
		if commit == nil {
			return nil
		}

		blob, err := commit.GetBlobByPath(path)
		if err != nil {
			return nil
		}
		return blob
	}

	ctx.Data["GetSniffedTypeForBlob"] = func(blob *git.Blob) typesniffer.SniffedType {
		st := typesniffer.SniffedType{}

		if blob == nil {
			return st
		}

		st, err := blob.GuessContentType()
		if err != nil {
			log.Error("GuessContentType failed: %v", err)
			return st
		}
		return st
	}

	setPathsCompareContext(ctx, before, head, headOwner, headName)
	setImageCompareContext(ctx)
	setCsvCompareContext(ctx)
}

// SourceCommitURL creates a relative URL for a commit in the given repository
func SourceCommitURL(owner, name string, commit *git.Commit) string {
	return setting.AppSubURL + "/" + url.PathEscape(owner) + "/" + url.PathEscape(name) + "/src/commit/" + url.PathEscape(commit.ID.String())
}

// RawCommitURL creates a relative URL for the raw commit in the given repository
func RawCommitURL(owner, name string, commit *git.Commit) string {
	return setting.AppSubURL + "/" + url.PathEscape(owner) + "/" + url.PathEscape(name) + "/raw/commit/" + url.PathEscape(commit.ID.String())
}

// setPathsCompareContext sets context data for source and raw paths
func setPathsCompareContext(ctx *context.Context, base, head *git.Commit, headOwner, headName string) {
	ctx.Data["SourcePath"] = SourceCommitURL(headOwner, headName, head)
	ctx.Data["RawPath"] = RawCommitURL(headOwner, headName, head)
	if base != nil {
		ctx.Data["BeforeSourcePath"] = SourceCommitURL(headOwner, headName, base)
		ctx.Data["BeforeRawPath"] = RawCommitURL(headOwner, headName, base)
	}
}

// setImageCompareContext sets context data that is required by image compare template
func setImageCompareContext(ctx *context.Context) {
	ctx.Data["IsSniffedTypeAnImage"] = func(st typesniffer.SniffedType) bool {
		return st.IsImage() && (setting.UI.SVG.Enabled || !st.IsSvgImage())
	}
}

// setCsvCompareContext sets context data that is required by the CSV compare template
func setCsvCompareContext(ctx *context.Context) {
	ctx.Data["IsCsvFile"] = func(diffFile *gitdiff.DiffFile) bool {
		extension := strings.ToLower(filepath.Ext(diffFile.Name))
		return extension == ".csv" || extension == ".tsv"
	}

	type CsvDiffResult struct {
		Sections []*gitdiff.TableDiffSection
		Error    string
	}

	ctx.Data["CreateCsvDiff"] = func(diffFile *gitdiff.DiffFile, baseBlob, headBlob *git.Blob) CsvDiffResult {
		if diffFile == nil {
			return CsvDiffResult{nil, ""}
		}

		errTooLarge := errors.New(ctx.Locale.TrString("repo.error.csv.too_large"))

		csvReaderFromCommit := func(ctx *markup.RenderContext, blob *git.Blob) (*csv.Reader, io.Closer, error) {
			if blob == nil {
				// It's ok for blob to be nil (file added or deleted)
				return nil, nil, nil
			}

			if setting.UI.CSV.MaxFileSize != 0 && setting.UI.CSV.MaxFileSize < blob.Size() {
				return nil, nil, errTooLarge
			}

			reader, err := blob.DataAsync()
			if err != nil {
				return nil, nil, err
			}
			var closer io.Closer = reader
			csvReader, err := csv_module.CreateReaderAndDetermineDelimiter(ctx, charset.ToUTF8WithFallbackReader(reader, charset.ConvertOpts{}))
			return csvReader, closer, err
		}

		baseReader, baseBlobCloser, err := csvReaderFromCommit(markup.NewRenderContext(ctx).WithRelativePath(diffFile.OldName), baseBlob)
		if baseBlobCloser != nil {
			defer baseBlobCloser.Close()
		}
		if err != nil {
			if err == errTooLarge {
				return CsvDiffResult{nil, err.Error()}
			}
			log.Error("error whilst creating csv.Reader from file %s in base commit %s in %s: %v", diffFile.Name, baseBlob.ID.String(), ctx.Repo.Repository.Name, err)
			return CsvDiffResult{nil, "unable to load file"}
		}

		headReader, headBlobCloser, err := csvReaderFromCommit(markup.NewRenderContext(ctx).WithRelativePath(diffFile.Name), headBlob)
		if headBlobCloser != nil {
			defer headBlobCloser.Close()
		}
		if err != nil {
			if err == errTooLarge {
				return CsvDiffResult{nil, err.Error()}
			}
			log.Error("error whilst creating csv.Reader from file %s in head commit %s in %s: %v", diffFile.Name, headBlob.ID.String(), ctx.Repo.Repository.Name, err)
			return CsvDiffResult{nil, "unable to load file"}
		}

		sections, err := gitdiff.CreateCsvDiff(diffFile, baseReader, headReader)
		if err != nil {
			errMessage, err := csv_module.FormatError(err, ctx.Locale)
			if err != nil {
				log.Error("CreateCsvDiff FormatError failed: %v", err)
				return CsvDiffResult{nil, "unknown csv diff error"}
			}
			return CsvDiffResult{nil, errMessage}
		}
		return CsvDiffResult{sections, ""}
	}
}

// ParseCompareInfo parse compare info between two commit for preparing comparing references
func ParseCompareInfo(ctx *context.Context) *git_service.CompareInfo {
	baseRepo := ctx.Repo.Repository
	fileOnly := ctx.FormBool("file-only")

	// 1 Parse compare router param
	compareReq := common.ParseCompareRouterParam(ctx.PathParam("*"))

	// remove the check when we support compare with carets
	if compareReq.BaseOriRefSuffix != "" {
		ctx.HTTPError(http.StatusBadRequest, "Unsupported comparison syntax: ref with suffix")
		return nil
	}

	// 2 get repository and owner for head
	headOwner, headRepo, err := common.GetHeadOwnerAndRepo(ctx, baseRepo, compareReq)
	switch {
	case errors.Is(err, util.ErrInvalidArgument):
		ctx.HTTPError(http.StatusBadRequest, err.Error())
		return nil
	case errors.Is(err, util.ErrNotExist):
		ctx.NotFound(nil)
		return nil
	case err != nil:
		ctx.ServerError("GetHeadOwnerAndRepo", err)
		return nil
	}

	isSameRepo := baseRepo.ID == headRepo.ID

	// 3 permission check
	// base repository's code unit read permission check has been done on web.go
	permBase := ctx.Repo.Permission

	// If we're not merging from the same repo:
	if !isSameRepo {
		// Assert ctx.Doer has permission to read headRepo's codes
		permHead, err := access_model.GetUserRepoPermission(ctx, headRepo, ctx.Doer)
		if err != nil {
			ctx.ServerError("GetUserRepoPermission", err)
			return nil
		}
		if !permHead.CanRead(unit.TypeCode) {
			if log.IsTrace() {
				log.Trace("Permission Denied: User: %-v cannot read code in Repo: %-v\nUser in headRepo has Permissions: %-+v",
					ctx.Doer,
					headRepo,
					permHead)
			}
			ctx.NotFound(nil)
			return nil
		}
		ctx.Data["CanWriteToHeadRepo"] = permHead.CanWrite(unit.TypeCode)
	}

	// 4 get base and head refs
	baseRefName := util.IfZero(compareReq.BaseOriRef, baseRepo.DefaultBranch)
	headRefName := util.IfZero(compareReq.HeadOriRef, headRepo.DefaultBranch)

	baseRef := ctx.Repo.GitRepo.UnstableGuessRefByShortName(baseRefName)
	if baseRef == "" {
		ctx.NotFound(nil)
		return nil
	}
	var headGitRepo *git.Repository
	if isSameRepo {
		headGitRepo = ctx.Repo.GitRepo
	} else {
		headGitRepo, err = gitrepo.OpenRepository(ctx, headRepo)
		if err != nil {
			ctx.ServerError("OpenRepository", err)
			return nil
		}
		defer headGitRepo.Close()
	}
	headRef := headGitRepo.UnstableGuessRefByShortName(headRefName)
	if headRef == "" {
		ctx.NotFound(nil)
		return nil
	}

	ctx.Data["BaseName"] = baseRepo.OwnerName
	ctx.Data["BaseBranch"] = baseRef.ShortName() // for legacy templates
	ctx.Data["HeadUser"] = headOwner
	ctx.Data["HeadBranch"] = headRef.ShortName() // for legacy templates
	ctx.Repo.PullRequest.SameRepo = isSameRepo

	ctx.Data["IsPull"] = true

	// The current base and head repositories and branches may not
	// actually be the intended branches that the user wants to
	// create a pull-request from - but also determining the head
	// repo is difficult.

	// We will want therefore to offer a few repositories to set as
	// our base and head

	// 1. First if the baseRepo is a fork get the "RootRepo" it was
	// forked from
	var rootRepo *repo_model.Repository
	if baseRepo.IsFork {
		err = baseRepo.GetBaseRepo(ctx)
		if err != nil {
			if !repo_model.IsErrRepoNotExist(err) {
				ctx.ServerError("Unable to find root repo", err)
				return nil
			}
		} else {
			rootRepo = baseRepo.BaseRepo
		}
	}

	// 2. Now if the current user is not the owner of the baseRepo,
	// check if they have a fork of the base repo and offer that as
	// "OwnForkRepo"
	var ownForkRepo *repo_model.Repository
	if ctx.Doer != nil && baseRepo.OwnerID != ctx.Doer.ID {
		repo := repo_model.GetForkedRepo(ctx, ctx.Doer.ID, baseRepo.ID)
		if repo != nil {
			ownForkRepo = repo
			ctx.Data["OwnForkRepo"] = ownForkRepo
		}
	}

	has := headRepo != nil
	// 3. If the base is a forked from "RootRepo" and the owner of
	// the "RootRepo" is the :headUser - set headRepo to that
	if !has && rootRepo != nil && rootRepo.OwnerID == headOwner.ID {
		headRepo = rootRepo
		has = true
	}

	// 4. If the ctx.Doer has their own fork of the baseRepo and the headUser is the ctx.Doer
	// set the headRepo to the ownFork
	if !has && ownForkRepo != nil && ownForkRepo.OwnerID == headOwner.ID {
		headRepo = ownForkRepo
		has = true
	}

	// 5. If the headOwner has a fork of the baseRepo - use that
	if !has {
		headRepo = repo_model.GetForkedRepo(ctx, headOwner.ID, baseRepo.ID)
		has = headRepo != nil
	}

	// 6. If the baseRepo is a fork and the headUser has a fork of that use that
	if !has && baseRepo.IsFork {
		headRepo = repo_model.GetForkedRepo(ctx, headOwner.ID, baseRepo.ForkID)
		has = headRepo != nil
	}

	// 7. Otherwise if we're not the same repo and haven't found a repo give up
	if !isSameRepo && !has {
		ctx.Data["PageIsComparePull"] = false
	}

	ctx.Data["HeadRepo"] = headRepo
	ctx.Data["BaseCompareRepo"] = ctx.Repo.Repository

	// If we have a rootRepo and it's different from:
	// 1. the computed base
	// 2. the computed head
	// then get the branches of it
	if rootRepo != nil &&
		rootRepo.ID != headRepo.ID &&
		rootRepo.ID != baseRepo.ID {
		canRead := access_model.CheckRepoUnitUser(ctx, rootRepo, ctx.Doer, unit.TypeCode)
		if canRead {
			ctx.Data["RootRepo"] = rootRepo
			if !fileOnly {
				branches, tags, err := getBranchesAndTagsForRepo(ctx, rootRepo)
				if err != nil {
					ctx.ServerError("GetBranchesForRepo", err)
					return nil
				}

				ctx.Data["RootRepoBranches"] = branches
				ctx.Data["RootRepoTags"] = tags
			}
		}
	}

	// If we have a ownForkRepo and it's different from:
	// 1. The computed base
	// 2. The computed head
	// 3. The rootRepo (if we have one)
	// then get the branches from it.
	if ownForkRepo != nil &&
		ownForkRepo.ID != headRepo.ID &&
		ownForkRepo.ID != baseRepo.ID &&
		(rootRepo == nil || ownForkRepo.ID != rootRepo.ID) {
		canRead := access_model.CheckRepoUnitUser(ctx, ownForkRepo, ctx.Doer, unit.TypeCode)
		if canRead {
			ctx.Data["OwnForkRepo"] = ownForkRepo
			if !fileOnly {
				branches, tags, err := getBranchesAndTagsForRepo(ctx, ownForkRepo)
				if err != nil {
					ctx.ServerError("GetBranchesForRepo", err)
					return nil
				}
				ctx.Data["OwnForkRepoBranches"] = branches
				ctx.Data["OwnForkRepoTags"] = tags
			}
		}
	}

	// Treat as pull request if both references are branches
	if ctx.Data["PageIsComparePull"] == nil {
		ctx.Data["PageIsComparePull"] = baseRef.IsBranch() && headRef.IsBranch() && permBase.CanReadIssuesOrPulls(true)
	}

	if ctx.Data["PageIsComparePull"] == true && !permBase.CanReadIssuesOrPulls(true) {
		if log.IsTrace() {
			log.Trace("Permission Denied: User: %-v cannot create/read pull requests in Repo: %-v\nUser in baseRepo has Permissions: %-+v",
				ctx.Doer,
				baseRepo,
				permBase)
		}
		ctx.NotFound(nil)
		return nil
	}

	compareInfo, err := git_service.GetCompareInfo(ctx, baseRepo, headRepo, headGitRepo, baseRef, headRef, compareReq.DirectComparison(), fileOnly)
	if err != nil {
		ctx.ServerError("GetCompareInfo", err)
		return nil
	}
	if compareReq.DirectComparison() {
		ctx.Data["BeforeCommitID"] = compareInfo.BaseCommitID
	} else {
		ctx.Data["BeforeCommitID"] = compareInfo.MergeBase
	}

	return compareInfo
}

// PrepareCompareDiff renders compare diff page
func PrepareCompareDiff(
	ctx *context.Context,
	ci *git_service.CompareInfo,
	whitespaceBehavior gitcmd.TrustedCmdArgs,
) (nothingToCompare bool) {
	repo := ctx.Repo.Repository
	headCommitID := ci.HeadCommitID

	ctx.Data["CommitRepoLink"] = ci.HeadRepo.Link()
	ctx.Data["AfterCommitID"] = headCommitID

	// follow GitHub's behavior: autofill the form and expand
	newPrFormTitle := ctx.FormTrim("title")
	newPrFormBody := ctx.FormTrim("body")
	ctx.Data["ExpandNewPrForm"] = ctx.FormBool("expand") || ctx.FormBool("quick_pull") || newPrFormTitle != "" || newPrFormBody != ""
	ctx.Data["TitleQuery"] = newPrFormTitle
	ctx.Data["BodyQuery"] = newPrFormBody

	if (headCommitID == ci.MergeBase && !ci.DirectComparison()) ||
		headCommitID == ci.BaseCommitID {
		ctx.Data["IsNothingToCompare"] = true
		if unit, err := repo.GetUnit(ctx, unit.TypePullRequests); err == nil {
			config := unit.PullRequestsConfig()

			if !config.AutodetectManualMerge {
				ctx.Data["AllowEmptyPr"] = !ci.IsSameRef()
				return ci.IsSameRef()
			}

			ctx.Data["AllowEmptyPr"] = false
		}
		return true
	}

	beforeCommitID := ci.MergeBase
	if ci.DirectComparison() {
		beforeCommitID = ci.BaseCommitID
	}

	maxLines, maxFiles := setting.Git.MaxGitDiffLines, setting.Git.MaxGitDiffFiles
	files := ctx.FormStrings("files")
	if len(files) == 2 || len(files) == 1 {
		maxLines, maxFiles = -1, -1
	}

	fileOnly := ctx.FormBool("file-only")

	diff, err := gitdiff.GetDiffForRender(ctx, ci.HeadRepo.Link(), ci.HeadGitRepo,
		&gitdiff.DiffOptions{
			BeforeCommitID:     beforeCommitID,
			AfterCommitID:      headCommitID,
			SkipTo:             ctx.FormString("skip-to"),
			MaxLines:           maxLines,
			MaxLineCharacters:  setting.Git.MaxGitDiffLineCharacters,
			MaxFiles:           maxFiles,
			WhitespaceBehavior: whitespaceBehavior,
			DirectComparison:   ci.DirectComparison(),
		}, ctx.FormStrings("files")...)
	if err != nil {
		ctx.ServerError("GetDiff", err)
		return false
	}
	diffShortStat, err := gitdiff.GetDiffShortStat(ctx, ci.HeadRepo, ci.HeadGitRepo, beforeCommitID, headCommitID)
	if err != nil {
		ctx.ServerError("GetDiffShortStat", err)
		return false
	}
	ctx.Data["DiffShortStat"] = diffShortStat
	ctx.Data["Diff"] = diff
	ctx.Data["DiffBlobExcerptData"] = &gitdiff.DiffBlobExcerptData{
		BaseLink:      ci.HeadRepo.Link() + "/blob_excerpt",
		DiffStyle:     GetDiffViewStyle(ctx),
		AfterCommitID: headCommitID,
	}
	ctx.Data["DiffNotAvailable"] = diffShortStat.NumFiles == 0

	if !fileOnly {
		diffTree, err := gitdiff.GetDiffTree(ctx, ci.HeadGitRepo, false, beforeCommitID, headCommitID)
		if err != nil {
			ctx.ServerError("GetDiffTree", err)
			return false
		}

		renderedIconPool := fileicon.NewRenderedIconPool()
		ctx.PageData["DiffFileTree"] = transformDiffTreeForWeb(renderedIconPool, diffTree, nil)
		ctx.PageData["FolderIcon"] = fileicon.RenderEntryIconHTML(renderedIconPool, fileicon.EntryInfoFolder())
		ctx.PageData["FolderOpenIcon"] = fileicon.RenderEntryIconHTML(renderedIconPool, fileicon.EntryInfoFolderOpen())
		ctx.Data["FileIconPoolHTML"] = renderedIconPool.RenderToHTML()
	}

	headCommit, err := ci.HeadGitRepo.GetCommit(headCommitID)
	if err != nil {
		ctx.ServerError("GetCommit", err)
		return false
	}

	baseGitRepo := ctx.Repo.GitRepo

	beforeCommit, err := baseGitRepo.GetCommit(beforeCommitID)
	if err != nil {
		ctx.ServerError("GetCommit", err)
		return false
	}

	commits, err := processGitCommits(ctx, ci.Commits)
	if err != nil {
		ctx.ServerError("processGitCommits", err)
		return false
	}
	ctx.Data["Commits"] = commits
	ctx.Data["CommitCount"] = len(commits)

	title := ci.HeadRef.ShortName()
	if len(commits) == 1 {
		c := commits[0]
		title = strings.TrimSpace(c.UserCommit.Summary())

		body := strings.Split(strings.TrimSpace(c.UserCommit.Message()), "\n")
		if len(body) > 1 {
			ctx.Data["content"] = strings.Join(body[1:], "\n")
		}
	}

	if len(title) > 255 {
		var trailer string
		title, trailer = util.EllipsisDisplayStringX(title, 255)
		if len(trailer) > 0 {
			if ctx.Data["content"] != nil {
				ctx.Data["content"] = fmt.Sprintf("%s\n\n%s", trailer, ctx.Data["content"])
			} else {
				ctx.Data["content"] = trailer + "\n"
			}
		}
	}

	ctx.Data["title"] = title
	ctx.Data["Username"] = ci.HeadRepo.OwnerName
	ctx.Data["Reponame"] = ci.HeadRepo.Name

	setCompareContext(ctx, beforeCommit, headCommit, ci.HeadRepo.OwnerName, repo.Name)

	return false
}

func getBranchesAndTagsForRepo(ctx gocontext.Context, repo *repo_model.Repository) (branches, tags []string, err error) {
	branches, err = git_model.FindBranchNames(ctx, git_model.FindBranchOptions{
		RepoID:          repo.ID,
		ListOptions:     db.ListOptionsAll,
		IsDeletedBranch: optional.Some(false),
	})
	if err != nil {
		return nil, nil, err
	}
	tags, err = repo_model.GetTagNamesByRepoID(ctx, repo.ID)
	if err != nil {
		return nil, nil, err
	}
	return branches, tags, nil
}

// CompareDiff show different from one commit to another commit
func CompareDiff(ctx *context.Context) {
	ci := ParseCompareInfo(ctx)
	if ctx.Written() {
		return
	}

	ctx.Data["PageIsViewCode"] = true
	ctx.Data["PullRequestWorkInProgressPrefixes"] = setting.Repository.PullRequest.WorkInProgressPrefixes
	ctx.Data["CompareInfo"] = ci

	nothingToCompare := PrepareCompareDiff(ctx, ci, gitdiff.GetWhitespaceFlag(ctx.Data["WhitespaceBehavior"].(string)))
	if ctx.Written() {
		return
	}

	baseTags, err := repo_model.GetTagNamesByRepoID(ctx, ctx.Repo.Repository.ID)
	if err != nil {
		ctx.ServerError("GetTagNamesByRepoID", err)
		return
	}
	ctx.Data["Tags"] = baseTags

	fileOnly := ctx.FormBool("file-only")
	if fileOnly {
		ctx.HTML(http.StatusOK, tplDiffBox)
		return
	}

	headBranches, err := git_model.FindBranchNames(ctx, git_model.FindBranchOptions{
		RepoID:          ci.HeadRepo.ID,
		ListOptions:     db.ListOptionsAll,
		IsDeletedBranch: optional.Some(false),
	})
	if err != nil {
		ctx.ServerError("GetBranches", err)
		return
	}
	ctx.Data["HeadBranches"] = headBranches

	// For compare repo branches
	PrepareBranchList(ctx)
	if ctx.Written() {
		return
	}

	headTags, err := repo_model.GetTagNamesByRepoID(ctx, ci.HeadRepo.ID)
	if err != nil {
		ctx.ServerError("GetTagNamesByRepoID", err)
		return
	}
	ctx.Data["HeadTags"] = headTags

	if ctx.Data["PageIsComparePull"] == true {
		pr, err := issues_model.GetUnmergedPullRequest(ctx, ci.HeadRepo.ID, ctx.Repo.Repository.ID, ci.HeadRef.ShortName(), ci.BaseRef.ShortName(), issues_model.PullRequestFlowGithub)
		if err != nil {
			if !issues_model.IsErrPullRequestNotExist(err) {
				ctx.ServerError("GetUnmergedPullRequest", err)
				return
			}
		} else {
			ctx.Data["HasPullRequest"] = true
			if err := pr.LoadIssue(ctx); err != nil {
				ctx.ServerError("LoadIssue", err)
				return
			}
			ctx.Data["PullRequest"] = pr
			ctx.HTML(http.StatusOK, tplCompareDiff)
			return
		}

		if !nothingToCompare {
			// Setup information for new form.
			pageMetaData := retrieveRepoIssueMetaData(ctx, ctx.Repo.Repository, nil, true)
			if ctx.Written() {
				return
			}
			_, templateErrs := setTemplateIfExists(ctx, pullRequestTemplateKey, pullRequestTemplateCandidates, pageMetaData)
			if len(templateErrs) > 0 {
				ctx.Flash.Warning(renderErrorOfTemplates(ctx, templateErrs), true)
			}
		}
	}
	beforeCommitID := ctx.Data["BeforeCommitID"].(string)
	afterCommitID := ctx.Data["AfterCommitID"].(string)

	ctx.Data["Title"] = "Comparing " + base.ShortSha(beforeCommitID) + ci.CompareSeparator + base.ShortSha(afterCommitID)

	ctx.Data["IsDiffCompare"] = true

	if content, ok := ctx.Data["content"].(string); ok && content != "" {
		// If a template content is set, prepend the "content". In this case that's only
		// applicable if you have one commit to compare and that commit has a message.
		// In that case the commit message will be prepend to the template body.
		if templateContent, ok := ctx.Data[pullRequestTemplateKey].(string); ok && templateContent != "" {
			// Re-use the same key as that's prioritized over the "content" key.
			// Add two new lines between the content to ensure there's always at least
			// one empty line between them.
			ctx.Data[pullRequestTemplateKey] = content + "\n\n" + templateContent
		}

		// When using form fields, also add content to field with id "body".
		if fields, ok := ctx.Data["Fields"].([]*api.IssueFormField); ok {
			for _, field := range fields {
				if field.ID == "body" {
					if fieldValue, ok := field.Attributes["value"].(string); ok && fieldValue != "" {
						field.Attributes["value"] = content + "\n\n" + fieldValue
					} else {
						field.Attributes["value"] = content
					}
				}
			}
		}
	}

	ctx.Data["IsProjectsEnabled"] = ctx.Repo.CanWrite(unit.TypeProjects)
	ctx.Data["IsAttachmentEnabled"] = setting.Attachment.Enabled
	upload.AddUploadContext(ctx, "comment")

	ctx.Data["HasIssuesOrPullsWritePermission"] = ctx.Repo.CanWrite(unit.TypePullRequests)

	if unit, err := ctx.Repo.Repository.GetUnit(ctx, unit.TypePullRequests); err == nil {
		config := unit.PullRequestsConfig()
		ctx.Data["AllowMaintainerEdit"] = config.DefaultAllowMaintainerEdit
	} else {
		ctx.Data["AllowMaintainerEdit"] = false
	}

	ctx.HTML(http.StatusOK, tplCompare)
}

// attachCommentsToLines attaches comments to their corresponding diff lines
func attachCommentsToLines(section *gitdiff.DiffSection, lineComments map[int64][]*issues_model.Comment) {
	for _, line := range section.Lines {
		if comments, ok := lineComments[int64(line.LeftIdx*-1)]; ok {
			line.Comments = append(line.Comments, comments...)
		}
		if comments, ok := lineComments[int64(line.RightIdx)]; ok {
			line.Comments = append(line.Comments, comments...)
		}
		sort.SliceStable(line.Comments, func(i, j int) bool {
			return line.Comments[i].CreatedUnix < line.Comments[j].CreatedUnix
		})
	}
}

// attachHiddenCommentIDs calculates and attaches hidden comment IDs to expand buttons
func attachHiddenCommentIDs(section *gitdiff.DiffSection, lineComments map[int64][]*issues_model.Comment) {
	for _, line := range section.Lines {
		gitdiff.FillHiddenCommentIDsForDiffLine(line, lineComments)
	}
}

// ExcerptBlob render blob excerpt contents
func ExcerptBlob(ctx *context.Context) {
	commitID := ctx.PathParam("sha")
	lastLeft := ctx.FormInt("last_left")
	lastRight := ctx.FormInt("last_right")
	idxLeft := ctx.FormInt("left")
	idxRight := ctx.FormInt("right")
	leftHunkSize := ctx.FormInt("left_hunk_size")
	rightHunkSize := ctx.FormInt("right_hunk_size")
	direction := ctx.FormString("direction")
	filePath := ctx.FormString("path")
	gitRepo := ctx.Repo.GitRepo

	diffBlobExcerptData := &gitdiff.DiffBlobExcerptData{
		BaseLink:      ctx.Repo.RepoLink + "/blob_excerpt",
		DiffStyle:     GetDiffViewStyle(ctx),
		AfterCommitID: commitID,
	}

	if ctx.Data["PageIsWiki"] == true {
		var err error
		gitRepo, err = gitrepo.RepositoryFromRequestContextOrOpen(ctx, ctx.Repo.Repository.WikiStorageRepo())
		if err != nil {
			ctx.ServerError("OpenRepository", err)
			return
		}
		diffBlobExcerptData.BaseLink = ctx.Repo.RepoLink + "/wiki/blob_excerpt"
	}

	chunkSize := gitdiff.BlobExcerptChunkSize
	commit, err := gitRepo.GetCommit(commitID)
	if err != nil {
		ctx.HTTPError(http.StatusInternalServerError, "GetCommit")
		return
	}
	section := &gitdiff.DiffSection{
		FileName: filePath,
	}
	if direction == "up" && (idxLeft-lastLeft) > chunkSize {
		idxLeft -= chunkSize
		idxRight -= chunkSize
		leftHunkSize += chunkSize
		rightHunkSize += chunkSize
		section.Lines, err = getExcerptLines(commit, filePath, idxLeft-1, idxRight-1, chunkSize)
	} else if direction == "down" && (idxLeft-lastLeft) > chunkSize {
		section.Lines, err = getExcerptLines(commit, filePath, lastLeft, lastRight, chunkSize)
		lastLeft += chunkSize
		lastRight += chunkSize
	} else {
		offset := -1
		if direction == "down" {
			offset = 0
		}
		section.Lines, err = getExcerptLines(commit, filePath, lastLeft, lastRight, idxRight-lastRight+offset)
		leftHunkSize = 0
		rightHunkSize = 0
		idxLeft = lastLeft
		idxRight = lastRight
	}
	if err != nil {
		ctx.HTTPError(http.StatusInternalServerError, "getExcerptLines")
		return
	}

	newLineSection := &gitdiff.DiffLine{
		Type: gitdiff.DiffLineSection,
		SectionInfo: &gitdiff.DiffLineSectionInfo{
			Path:          filePath,
			LastLeftIdx:   lastLeft,
			LastRightIdx:  lastRight,
			LeftIdx:       idxLeft,
			RightIdx:      idxRight,
			LeftHunkSize:  leftHunkSize,
			RightHunkSize: rightHunkSize,
		},
	}
	if newLineSection.GetExpandDirection() != "" {
		newLineSection.Content = fmt.Sprintf("@@ -%d,%d +%d,%d @@\n", idxLeft, leftHunkSize, idxRight, rightHunkSize)
		switch direction {
		case "up":
			section.Lines = append([]*gitdiff.DiffLine{newLineSection}, section.Lines...)
		case "down":
			section.Lines = append(section.Lines, newLineSection)
		}
	}

	diffBlobExcerptData.PullIssueIndex = ctx.FormInt64("pull_issue_index")
	if diffBlobExcerptData.PullIssueIndex > 0 {
		if !ctx.Repo.CanRead(unit.TypePullRequests) {
			ctx.NotFound(nil)
			return
		}

		issue, err := issues_model.GetIssueByIndex(ctx, ctx.Repo.Repository.ID, diffBlobExcerptData.PullIssueIndex)
		if err != nil {
			log.Error("GetIssueByIndex error: %v", err)
		} else if issue.IsPull {
			// FIXME: DIFF-CONVERSATION-DATA: the following data assignment is fragile
			ctx.Data["Issue"] = issue
			ctx.Data["CanBlockUser"] = func(blocker, blockee *user_model.User) bool {
				return user_service.CanBlockUser(ctx, ctx.Doer, blocker, blockee)
			}
			// and "diff/comment_form.tmpl" (reply comment) needs them
			ctx.Data["PageIsPullFiles"] = true
			ctx.Data["AfterCommitID"] = diffBlobExcerptData.AfterCommitID

			allComments, err := issues_model.FetchCodeComments(ctx, issue, ctx.Doer, ctx.FormBool("show_outdated"))
			if err != nil {
				log.Error("FetchCodeComments error: %v", err)
			} else {
				if lineComments, ok := allComments[filePath]; ok {
					attachCommentsToLines(section, lineComments)
					attachHiddenCommentIDs(section, lineComments)
				}
			}
		}
	}

	ctx.Data["section"] = section
	ctx.Data["FileNameHash"] = git.HashFilePathForWebUI(filePath)
	ctx.Data["DiffBlobExcerptData"] = diffBlobExcerptData

	ctx.HTML(http.StatusOK, tplBlobExcerpt)
}

func getExcerptLines(commit *git.Commit, filePath string, idxLeft, idxRight, chunkSize int) ([]*gitdiff.DiffLine, error) {
	blob, err := commit.Tree.GetBlobByPath(filePath)
	if err != nil {
		return nil, err
	}
	reader, err := blob.DataAsync()
	if err != nil {
		return nil, err
	}
	defer reader.Close()
	scanner := bufio.NewScanner(reader)
	var diffLines []*gitdiff.DiffLine
	for line := 0; line < idxRight+chunkSize; line++ {
		if ok := scanner.Scan(); !ok {
			break
		}
		if line < idxRight {
			continue
		}
		lineText := scanner.Text()
		diffLine := &gitdiff.DiffLine{
			LeftIdx:  idxLeft + (line - idxRight) + 1,
			RightIdx: line + 1,
			Type:     gitdiff.DiffLinePlain,
			Content:  " " + lineText,
		}
		diffLines = append(diffLines, diffLine)
	}
	if err = scanner.Err(); err != nil {
		return nil, fmt.Errorf("getExcerptLines scan: %w", err)
	}
	return diffLines, nil
}