// Copyright 2014 The Go Authors.  All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package main

import (
	"bytes"
	"crypto/rand"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"regexp"
	"strings"
)

var hookFiles = []string{
	"commit-msg",
	"pre-commit",
}

// installHook installs Git hooks to enforce code review conventions.
//
// auto is whether hooks are being installed automatically as part of
// running another git-codereview command, rather than an explicit
// invocation of the 'hooks' command itself.
func installHook(args []string, auto bool) {
	flags.Parse(args)
	hooksDir := gitPath("hooks")
	var existingHooks []string
	for _, hookFile := range hookFiles {
		filename := filepath.Join(hooksDir, hookFile)
		hookContent := fmt.Sprintf(hookScript, hookFile)

		if data, err := os.ReadFile(filename); err == nil {
			// Special case: remove old hooks that use 'git-review'
			oldHookContent := fmt.Sprintf(oldHookScript, hookFile)
			if string(data) == oldHookContent {
				verbosef("removing old %v hook", hookFile)
				os.Remove(filename)
			}
			// Special case: remove old commit-msg shell script
			// in favor of invoking the git-codereview hook
			// implementation, which will be easier to change in
			// the future.
			if hookFile == "commit-msg" && string(data) == oldCommitMsgHook {
				verbosef("removing old commit-msg hook")
				os.Remove(filename)
			}
		}

		// If hook file exists but has different content, let the user know.
		_, err := os.Stat(filename)
		if err == nil {
			data, err := os.ReadFile(filename)
			if err != nil {
				verbosef("reading hook: %v", err)
			} else if string(data) != hookContent {
				verbosef("unexpected hook content in %s", filename)
				if !auto {
					existingHooks = append(existingHooks, filename)
				}
			}
			continue
		}

		if !os.IsNotExist(err) {
			dief("checking hook: %v", err)
		}

		verbosef("installing %s hook", hookFile)
		if _, err := os.Stat(hooksDir); os.IsNotExist(err) {
			verbosef("creating hooks directory %s", hooksDir)
			if err := os.Mkdir(hooksDir, 0777); err != nil {
				dief("creating hooks directory: %v", err)
			}
		}
		if err := os.WriteFile(filename, []byte(hookContent), 0700); err != nil {
			dief("writing hook: %v", err)
		}
	}

	switch {
	case len(existingHooks) == 1:
		dief("Hooks file %s already exists."+
			"\nTo install git-codereview hooks, delete that"+
			" file and re-run 'git-codereview hooks'.",
			existingHooks[0])
	case len(existingHooks) > 1:
		dief("Hooks files %s already exist."+
			"\nTo install git-codereview hooks, delete these"+
			" files and re-run 'git-codereview hooks'.",
			strings.Join(existingHooks, ", "))
	}
}

// repoRoot returns the root of the currently selected git repo, or
// worktree root if this is an alternate worktree of a repo.
func repoRoot() string {
	return filepath.Clean(trim(cmdOutput("git", "rev-parse", "--show-toplevel")))
}

// gitPathDir returns the directory used by git to store temporary
// files such as COMMIT_EDITMSG, FETCH_HEAD, and such for the repo.
// For a simple git repo, this will be <root>/.git, and for an
// alternate worktree of a repo it will be in
// <root>/.git/worktrees/<worktreename>.
func gitPathDir() string {
	gcd := trim(cmdOutput("git", "rev-parse", "--git-path", "."))
	result, err := filepath.Abs(gcd)
	if err != nil {
		dief("%v", err)
	}
	return result
}

// gitPath resolve the $GIT_DIR/path, taking in consideration
// all other path relocations, e.g. hooks for linked worktrees
// are not kept in their gitdir, but shared in the main one.
func gitPath(path string) string {
	root := repoRoot()
	// git 2.13.0 changed the behavior of --git-path from printing
	// a path relative to the repo root to printing a path
	// relative to the working directory (issue #19477). Normalize
	// both behaviors by running the command from the repo root.
	p, err := trimErr(cmdOutputErr("git", "-C", root, "rev-parse", "--git-path", path))
	if err != nil {
		// When --git-path is not available, assume the common case.
		p = filepath.Join(".git", path)
	}
	if !filepath.IsAbs(p) {
		p = filepath.Join(root, p)
	}
	return p
}

var hookScript = `#!/bin/sh
exec git-codereview hook-invoke %s "$@"
`

var oldHookScript = `#!/bin/sh
exec git-review hook-invoke %s "$@"
`

func cmdHookInvoke(args []string) {
	flags.Parse(args)
	args = flags.Args()
	if len(args) == 0 {
		dief("usage: git-codereview hook-invoke <hook-name> [args...]")
	}
	switch args[0] {
	case "commit-msg":
		hookCommitMsg(args[1:])
	case "pre-commit":
		hookPreCommit(args[1:])
	}
}

var (
	issueRefRE         = regexp.MustCompile(`(?P<space>\s)(?P<ref>#\d+\w)`)
	oldFixesRETemplate = `Fixes +(issue +(%s)?#?)?(?P<issueNum>[0-9]+)`
)

// hookCommitMsg is installed as the git commit-msg hook.
// It adds a Change-Id line to the bottom of the commit message
// if there is not one already.
func hookCommitMsg(args []string) {
	if len(args) != 1 {
		dief("usage: git-codereview hook-invoke commit-msg message.txt\n")
	}

	// We used to bail in detached head mode, but it's very common
	// to be modifying things during git rebase -i and it's annoying
	// that those new commits made don't get Commit-Msg lines.
	// Let's try keeping the hook on and see what breaks.
	/*
		b := CurrentBranch()
		if b.DetachedHead() {
			// Likely executing rebase or some other internal operation.
			// Probably a mistake to make commit message changes.
			return
		}
	*/

	file := args[0]
	oldData, err := os.ReadFile(file)
	if err != nil {
		dief("%v", err)
	}

	data := fixCommitMessage(oldData)

	// Write back.
	if !bytes.Equal(data, oldData) {
		if err := os.WriteFile(file, data, 0666); err != nil {
			dief("%v", err)
		}
	}
}

// fixCommitMessage fixes various commit message issues,
// including adding a Change-Id line and rewriting #12345
// into repo#12345 as directed by codereview.cfg.
func fixCommitMessage(msg []byte) []byte {
	data := append([]byte{}, msg...)
	data = stripComments(data)

	// Empty message not allowed.
	if len(bytes.TrimSpace(data)) == 0 {
		dief("empty commit message")
	}

	// Insert a blank line between first line and subsequent lines if not present.
	eol := bytes.IndexByte(data, '\n')
	if eol != -1 && len(data) > eol+1 && data[eol+1] != '\n' {
		data = append(data, 0)
		copy(data[eol+1:], data[eol:])
		data[eol+1] = '\n'
	}

	issueRepo := config()["issuerepo"]
	// Update issue references to point to issue repo, if set.
	if issueRepo != "" {
		data = issueRefRE.ReplaceAll(data, []byte("${space}"+issueRepo+"${ref}"))
	}
	// TestHookCommitMsgIssueRepoRewrite makes sure the regex is valid
	oldFixesRE := regexp.MustCompile(fmt.Sprintf(oldFixesRETemplate, regexp.QuoteMeta(issueRepo)))
	data = oldFixesRE.ReplaceAll(data, []byte("Fixes "+issueRepo+"#${issueNum}"))

	if haveGerrit() {
		// Complain if two Change-Ids are present.
		// This can happen during an interactive rebase;
		// it is easy to forget to remove one of them.
		nChangeId := bytes.Count(data, []byte("\nChange-Id: "))
		if nChangeId > 1 {
			dief("multiple Change-Id lines")
		}

		// Add Change-Id to commit message if not present.
		if nChangeId == 0 {
			data = bytes.TrimRight(data, "\n")
			sep := "\n\n"
			if endsWithMetadataLine(data) {
				sep = "\n"
			}
			data = append(data, fmt.Sprintf("%sChange-Id: I%x\n", sep, randomBytes())...)
		}

		// Add branch prefix to commit message if not present and on a
		// dev or release branch and not a special Git fixup! or
		// squash! commit message.
		b := CurrentBranch()
		branch := strings.TrimPrefix(b.OriginBranch(), "origin/")
		if strings.HasPrefix(branch, "dev.") || strings.HasPrefix(branch, "release-branch.") {
			prefix := "[" + branch + "] "
			if !bytes.HasPrefix(data, []byte(prefix)) && !isFixup(data) {
				data = []byte(prefix + string(data))
			}
		}
	}

	return data
}

// randomBytes returns 20 random bytes suitable for use in a Change-Id line.
func randomBytes() []byte {
	var id [20]byte
	if _, err := io.ReadFull(rand.Reader, id[:]); err != nil {
		dief("generating Change-Id: %v", err)
	}
	return id[:]
}

var metadataLineRE = regexp.MustCompile(`^[a-zA-Z0-9-]+: `)

// endsWithMetadataLine reports whether the given commit message ends with a
// metadata line such as "Bug: #42" or "Signed-off-by: Al <al@example.com>".
func endsWithMetadataLine(msg []byte) bool {
	i := bytes.LastIndexByte(msg, '\n')
	return i >= 0 && metadataLineRE.Match(msg[i+1:])
}

var (
	fixupBang  = []byte("fixup!")
	squashBang = []byte("squash!")

	ignoreBelow = []byte("\n# ------------------------ >8 ------------------------\n")
)

// isFixup reports whether text is a Git fixup! or squash! commit,
// which must not have a prefix.
func isFixup(text []byte) bool {
	return bytes.HasPrefix(text, fixupBang) || bytes.HasPrefix(text, squashBang)
}

// stripComments strips lines that begin with "#" and removes the
// "everything below will be removed" section containing the diff when
// using commit --verbose.
func stripComments(in []byte) []byte {
	// Issue 16376
	if i := bytes.Index(in, ignoreBelow); i >= 0 {
		in = in[:i+1]
	}
	return regexp.MustCompile(`(?m)^#.*\n`).ReplaceAll(in, nil)
}

// hookPreCommit is installed as the git pre-commit hook.
// It prevents commits to the master branch.
// It checks that the Go files added, copied, or modified by
// the change are gofmt'd, and if not it prints gofmt instructions
// and exits with nonzero status.
func hookPreCommit(args []string) {
	// We used to bail in detached head mode, but it's very common
	// to be modifying things during git rebase -i and it's annoying
	// that those new commits made don't get the gofmt check.
	// Let's try keeping the hook on and see what breaks.
	/*
		b := CurrentBranch()
		if b.DetachedHead() {
			// This is an internal commit such as during git rebase.
			// Don't die, and don't force gofmt.
			return
		}
	*/

	hookGofmt()
}

func hookGofmt() {
	if os.Getenv("GIT_GOFMT_HOOK") == "off" {
		fmt.Fprintf(stderr(), "git-codereview pre-commit gofmt hook disabled by $GIT_GOFMT_HOOK=off\n")
		return
	}

	files, stderr := runGofmt(gofmtPreCommit)

	if stderr != "" {
		msgf := printf
		if len(files) == 0 {
			msgf = dief
		}
		msgf("gofmt reported errors:\n\t%s", strings.Replace(strings.TrimSpace(stderr), "\n", "\n\t", -1))
	}

	if len(files) == 0 {
		return
	}

	dief("gofmt needs to format these files (run 'git gofmt'):\n\t%s",
		strings.Join(files, "\n\t"))
}

// This is NOT USED ANYMORE.
// It is here only for comparing against old commit-hook files.
var oldCommitMsgHook = `#!/bin/sh
# From Gerrit Code Review 2.2.1
#
# Part of Gerrit Code Review (http://code.google.com/p/gerrit/)
#
# Copyright (C) 2009 The Android Open Source Project
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
# http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
#

CHANGE_ID_AFTER="Bug|Issue"
MSG="$1"

# Check for, and add if missing, a unique Change-Id
#
add_ChangeId() {
	clean_message=` + "`" + `sed -e '
		/^diff --git a\/.*/{
			s///
			q
		}
		/^Signed-off-by:/d
		/^#/d
	' "$MSG" | git stripspace` + "`" + `
	if test -z "$clean_message"
	then
		return
	fi

	if grep -i '^Change-Id:' "$MSG" >/dev/null
	then
		return
	fi

	id=` + "`" + `_gen_ChangeId` + "`" + `
	perl -e '
		$MSG = shift;
		$id = shift;
		$CHANGE_ID_AFTER = shift;

		undef $/;
		open(I, $MSG); $_ = <I>; close I;
		s|^diff --git a/.*||ms;
		s|^#.*$||mg;
		exit unless $_;

		@message = split /\n/;
		$haveFooter = 0;
		$startFooter = @message;
		for($line = @message - 1; $line >= 0; $line--) {
			$_ = $message[$line];

			if (/^[a-zA-Z0-9-]+:/ && !m,^[a-z0-9-]+://,) {
				$haveFooter++;
				next;
			}
			next if /^[ []/;
			$startFooter = $line if ($haveFooter && /^\r?$/);
			last;
		}

		@footer = @message[$startFooter+1..@message];
		@message = @message[0..$startFooter];
		push(@footer, "") unless @footer;

		for ($line = 0; $line < @footer; $line++) {
			$_ = $footer[$line];
			next if /^($CHANGE_ID_AFTER):/i;
			last;
		}
		splice(@footer, $line, 0, "Change-Id: I$id");

		$_ = join("\n", @message, @footer);
		open(O, ">$MSG"); print O; close O;
	' "$MSG" "$id" "$CHANGE_ID_AFTER"
}
_gen_ChangeIdInput() {
	echo "tree ` + "`" + `git write-tree` + "`" + `"
	if parent=` + "`" + `git rev-parse HEAD^0 2>/dev/null` + "`" + `
	then
		echo "parent $parent"
	fi
	echo "author ` + "`" + `git var GIT_AUTHOR_IDENT` + "`" + `"
	echo "committer ` + "`" + `git var GIT_COMMITTER_IDENT` + "`" + `"
	echo
	printf '%s' "$clean_message"
}
_gen_ChangeId() {
	_gen_ChangeIdInput |
	git hash-object -t commit --stdin
}


add_ChangeId
`