// Copyright 2017 syzkaller project authors. All rights reserved.
// Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.

// Package git provides helper functions for working with git repositories.
package git

import (
	"bytes"
	"fmt"
	"os"
	"regexp"
	"strings"
	"time"

	"github.com/google/syzkaller/pkg/osutil"
)

const timeout = time.Hour // timeout for all git invocations

// Poll checkouts the specified repository/branch in dir.
// This involves fetching/resetting/cloning as necessary to recover from all possible problems.
// Returns hash of the HEAD commit in the specified branch.
func Poll(dir, repo, branch string) (string, error) {
	runSandboxed(dir, "git", "reset", "--hard")
	origin, err := runSandboxed(dir, "git", "remote", "get-url", "origin")
	if err != nil || strings.TrimSpace(string(origin)) != repo {
		// The repo is here, but it has wrong origin (e.g. repo in config has changed), re-clone.
		if err := clone(dir, repo, branch); err != nil {
			return "", err
		}
	}
	// Use origin/branch for the case the branch was force-pushed,
	// in such case branch is not the same is origin/branch and we will
	// stuck with the local version forever (git checkout won't fail).
	if _, err := runSandboxed(dir, "git", "checkout", "origin/"+branch); err != nil {
		// No such branch (e.g. branch in config has changed), re-clone.
		if err := clone(dir, repo, branch); err != nil {
			return "", err
		}
	}
	if _, err := runSandboxed(dir, "git", "fetch", "--no-tags"); err != nil {
		// Something else is wrong, re-clone.
		if err := clone(dir, repo, branch); err != nil {
			return "", err
		}
	}
	if _, err := runSandboxed(dir, "git", "checkout", "origin/"+branch); err != nil {
		return "", err
	}
	return HeadCommit(dir)
}

// Checkout checkouts the specified repository/branch in dir.
// It does not fetch history and efficiently supports checkouts of different repos in the same dir.
func Checkout(dir, repo, branch string) (string, error) {
	if _, err := runSandboxed(dir, "git", "reset", "--hard"); err != nil {
		if err := initRepo(dir); err != nil {
			return "", err
		}
	}
	_, err := runSandboxed(dir, "git", "fetch", "--no-tags", "--depth=1", repo, branch)
	if err != nil {
		return "", err
	}
	if _, err := runSandboxed(dir, "git", "checkout", "FETCH_HEAD"); err != nil {
		return "", err
	}
	return HeadCommit(dir)
}

func clone(dir, repo, branch string) error {
	if err := initRepo(dir); err != nil {
		return err
	}
	if _, err := runSandboxed(dir, "git", "remote", "add", "origin", repo); err != nil {
		return err
	}
	if _, err := runSandboxed(dir, "git", "fetch", "origin", branch); err != nil {
		return err
	}
	return nil
}

func initRepo(dir string) error {
	if err := os.RemoveAll(dir); err != nil {
		return fmt.Errorf("failed to remove repo dir: %v", err)
	}
	if err := osutil.MkdirAll(dir); err != nil {
		return fmt.Errorf("failed to create repo dir: %v", err)
	}
	if err := osutil.SandboxChown(dir); err != nil {
		return err
	}
	if _, err := runSandboxed(dir, "git", "init"); err != nil {
		return err
	}
	return nil
}

// HeadCommit returns hash of the HEAD commit of the current branch of git repository in dir.
func HeadCommit(dir string) (string, error) {
	output, err := runSandboxed(dir, "git", "log", "--pretty=format:%H", "-n", "1")
	if err != nil {
		return "", err
	}
	if len(output) != 0 && output[len(output)-1] == '\n' {
		output = output[:len(output)-1]
	}
	if len(output) != 40 {
		return "", fmt.Errorf("unexpected git log output, want commit hash: %q", output)
	}
	return string(output), nil
}

// ListRecentCommits returns list of recent commit titles starting from baseCommit.
func ListRecentCommits(dir, baseCommit string) ([]string, error) {
	// On upstream kernel this produces ~11MB of output.
	// Somewhat inefficient to collect whole output in a slice
	// and then convert to string, but should be bearable.
	output, err := runSandboxed(dir, "git", "log",
		"--pretty=format:%s", "--no-merges", "-n", "200000", baseCommit)
	if err != nil {
		return nil, err
	}
	return strings.Split(string(output), "\n"), nil
}

// CanonicalizeCommit returns commit title that can be used when checking
// if a particular commit is present in a git tree.
// Some trees add prefixes to commit titles during backporting,
// so we want e.g. commit "foo bar" match "BACKPORT: foo bar".
func CanonicalizeCommit(title string) string {
	for _, prefix := range commitPrefixes {
		if strings.HasPrefix(title, prefix) {
			title = title[len(prefix):]
			break
		}
	}
	return strings.TrimSpace(title)
}

var commitPrefixes = []string{
	"UPSTREAM:",
	"CHROMIUM:",
	"FROMLIST:",
	"BACKPORT:",
	"FROMGIT:",
	"net-backports:",
}

func Patch(dir string, patch []byte) error {
	// Do --dry-run first to not mess with partially consistent state.
	cmd := osutil.Command("patch", "-p1", "--force", "--ignore-whitespace", "--dry-run")
	if err := osutil.Sandbox(cmd, true, true); err != nil {
		return err
	}
	cmd.Stdin = bytes.NewReader(patch)
	cmd.Dir = dir
	if output, err := cmd.CombinedOutput(); err != nil {
		// If it reverses clean, then it's already applied
		// (seems to be the easiest way to detect it).
		cmd = osutil.Command("patch", "-p1", "--force", "--ignore-whitespace", "--reverse", "--dry-run")
		if err := osutil.Sandbox(cmd, true, true); err != nil {
			return err
		}
		cmd.Stdin = bytes.NewReader(patch)
		cmd.Dir = dir
		if _, err := cmd.CombinedOutput(); err == nil {
			return fmt.Errorf("patch is already applied")
		}
		return fmt.Errorf("failed to apply patch:\n%s", output)
	}
	// Now apply for real.
	cmd = osutil.Command("patch", "-p1", "--force", "--ignore-whitespace")
	if err := osutil.Sandbox(cmd, true, true); err != nil {
		return err
	}
	cmd.Stdin = bytes.NewReader(patch)
	cmd.Dir = dir
	if output, err := cmd.CombinedOutput(); err != nil {
		return fmt.Errorf("failed to apply patch after dry run:\n%s", output)
	}
	return nil
}

func runSandboxed(dir, command string, args ...string) ([]byte, error) {
	cmd := osutil.Command(command, args...)
	cmd.Dir = dir
	if err := osutil.Sandbox(cmd, true, false); err != nil {
		return nil, err
	}
	return osutil.Run(timeout, cmd)
}

// CheckRepoAddress does a best-effort approximate check of a git repo address.
func CheckRepoAddress(repo string) bool {
	return gitRepoRe.MatchString(repo)
}

var gitRepoRe = regexp.MustCompile("^(git|ssh|http|https|ftp|ftps)://[a-zA-Z0-9-_]+(\\.[a-zA-Z0-9-_]+)+(:[0-9]+)?/[a-zA-Z0-9-_./]+\\.git(/)?$")

// CheckBranch does a best-effort approximate check of a git branch name.
func CheckBranch(branch string) bool {
	return gitBranchRe.MatchString(branch)
}

var gitBranchRe = regexp.MustCompile("^[a-zA-Z0-9-_/.]{2,200}$")