// Copyright 2017 The Fuchsia Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

// Generates a Debian based sysroot.
package main

import (
	"bufio"
	"bytes"
	"compress/gzip"
	"context"
	"crypto/sha256"
	"encoding/hex"
	"flag"
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"net/url"
	"os"
	"os/exec"
	"path"
	"path/filepath"
	"regexp"
	"sort"
	"strings"
	"time"

	"github.com/google/subcommands"
	"golang.org/x/crypto/openpgp"
	"gopkg.in/yaml.v2"
)

// gpg keyring file generated using:
//   export KEYS="46925553 2B90D010 518E17E1 1A7B6500"
//   gpg --keyserver keys.gnupg.net --recv-keys $KEYS
//   gpg --output ./debian-archive-stretch-stable.gpg --export $KEYS

const (
	aptRepo = "http://http.us.debian.org/debian"
)

type stringsValue []string

func (i *stringsValue) String() string {
	return strings.Join(*i, ",")
}

func (i *stringsValue) Set(value string) error {
	*i = strings.Split(value, ",")
	return nil
}

type Config struct {
	Dists      []string  `yaml:"dists"`
	Components []string  `yaml:"components"`
	Keyring    string    `yaml:"keyring"`
	Packages   []Package `yaml:"packages"`
}

type Package struct {
	Name string   `yaml:"package"`
	Arch []string `yaml:"arch,omitempty"`
}

type Lockfile struct {
	Hash     string    `yaml:"hash"`
	Updated  time.Time `yaml:"updated"`
	Packages []Lock    `yaml:"packages"`
}

type Lock struct {
	Name     string `yaml:"package"`
	Version  string `yaml:"version"`
	Filename string `yaml:"filename"`
	Hash     string `yaml:"hash"`
}

type Arch struct {
	Name     string `yaml:"name"`
	Filename string `yaml:"filename"`
	Hash     string `yaml:"hash"`
}

type Locks []Lock

func (l Locks) Len() int {
	return len(l)
}

func (l Locks) Swap(i, j int) {
	l[i], l[j] = l[j], l[i]
}

func (l Locks) Less(i, j int) bool {
	return l[i].Name < l[j].Name
}

// Descriptor represents a Debian package description.
type Descriptor map[string]string

// parsePackages parses Debian's control file which described packages.
//
// See chapter 5.1 (Syntax of control files) of the Debian Policy Manual:
// http://www.debian.org/doc/debian-policy/ch-controlfields.html
func parsePackages(r io.Reader) ([]Descriptor, error) {
	// Packages are separated by double newline, use scanner to split them.
	scanner := bufio.NewScanner(r)
	scanner.Split(func(data []byte, atEOF bool) (int, []byte, error) {
		const separator = "\n\n"
		if i := bytes.Index(data, []byte(separator)); i != -1 {
			return i + len(separator), data[:i], nil
		}
		return 0, nil, nil
	})
	exp := regexp.MustCompile(`(?m)^(?P<key>\S+): (?P<value>(.*)(?:$\s^ .*)*)$`)
	var descriptors []Descriptor
	for scanner.Scan() {
		descriptor := make(Descriptor)
		for _, m := range exp.FindAllStringSubmatch(scanner.Text(), -1) {
			descriptor[m[1]] = m[2]
		}
		descriptors = append(descriptors, descriptor)
	}
	if err := scanner.Err(); err != nil {
		return nil, err
	}
	return descriptors, nil
}

func downloadPackageList(config *Config, arch string) ([]Lock, error) {
	pkgs := map[string]Descriptor{}

	file, err := os.Open(config.Keyring)
	if err != nil {
		return nil, err
	}
	defer file.Close()
	keyring, err := openpgp.ReadKeyRing(file)
	if err != nil {
		return nil, err
	}

	for _, dist := range config.Dists {
		u, err := url.Parse(aptRepo)
		u.Path = path.Join(u.Path, "dists", dist, "Release")
		r, err := http.Get(u.String())
		if err != nil {
			return nil, err
		}
		defer r.Body.Close()

		b, err := ioutil.ReadAll(r.Body)
		if err != nil {
			return nil, err
		}

		u, err = url.Parse(aptRepo)
		u.Path = path.Join(u.Path, "dists", dist, "Release.gpg")
		r, err = http.Get(u.String())
		if err != nil {
			return nil, err
		}
		defer r.Body.Close()

		_, err = openpgp.CheckArmoredDetachedSignature(keyring, bytes.NewReader(b), r.Body)
		if err != nil {
			return nil, err
		}

		for _, c := range config.Components {
			u, err := url.Parse(aptRepo)
			u.Path = path.Join(u.Path, "dists", dist, c, "binary-"+arch, "Packages.gz")
			r, err := http.Get(u.String())
			if err != nil {
				return nil, err
			}
			defer r.Body.Close()

			buf, err := ioutil.ReadAll(r.Body)
			if err != nil {
				return nil, err
			}

			f := path.Join(c, "binary-"+arch, "Packages.gz")
			l := regexp.MustCompile(`([0-9a-z]{64})\s+\d+\s+` + f)
			m := l.FindStringSubmatch(string(b))

			sum := sha256.Sum256(buf)
			if m[1] != hex.EncodeToString(sum[:]) {
				return nil, fmt.Errorf("%s: checksum doesn't match", f)
			}

			g, err := gzip.NewReader(bytes.NewReader(buf))
			if err != nil {
				return nil, err
			}

			ps, err := parsePackages(g)
			if err != nil {
				return nil, err
			}

			// We only want development libraries, filter out everything else.
			for _, p := range ps {
				// Use sections as a coarse grained filter.
				var section bool
				switch p["Section"] {
				case "libs", "libdevel", "devel", "x11":
					section = true
				}
				// Use tags as a more fine-grained filter.
				var tag bool
				for _, n := range strings.Split(p["Tag"], ", ") {
					t := strings.Split(strings.TrimSpace(n), " ")[0]
					switch t {
					case "devel::library", "x11::library", "role::devel-lib", "role::shared-lib":
						tag = true
					}
				}
				// Skip everything that doesn't match.
				if section && tag {
					pkgs[p["Package"]] = p
				}
			}
		}
	}

	var queue []string
	for _, p := range config.Packages {
		if pkg, ok := pkgs[p.Name]; ok {
			queue = append(queue, pkg["Package"])
		} else {
			for _, a := range p.Arch {
				if a == arch {
					fmt.Printf("Package %s not found\n", p.Name)
				}
			}
		}
	}

	locks := map[string]Lock{}
	for len(queue) > 0 {
		p := queue[0]
		queue = queue[1:]
		if _, ok := locks[p]; ok {
			continue
		}
		if pkg, ok := pkgs[p]; ok {
			locks[p] = Lock{
				Name:     pkg["Package"],
				Version:  pkg["Version"],
				Filename: pkg["Filename"],
				Hash:     pkg["SHA256"],
			}
			for _, n := range strings.Split(pkg["Depends"], ", ") {
				d := strings.Split(strings.TrimSpace(n), " ")[0]
				queue = append(queue, d)
			}
		}
	}

	var list []Lock
	for _, p := range locks {
		list = append(list, p)
	}

	return list, nil
}

func relativize(link, target, dir string, patterns []string) error {
	for _, p := range patterns {
		matches, err := filepath.Glob(filepath.Join(dir, p))
		if err != nil {
			return err
		}
		for _, m := range matches {
			if link == m {
				if err := os.Remove(link); err != nil {
					return err
				}
				relDir := ".." + strings.Repeat("/..", strings.Count(p, "/")-1)
				if err := os.Symlink(relDir+target, link); err != nil {
					return err
				}
				return nil
			}
		}
	}
	return nil
}

func installSysroot(list []Lock, installDir, debsCache string) error {
	if err := os.MkdirAll(debsCache, 0777); err != nil {
		return err
	}

	if err := os.RemoveAll(installDir); err != nil {
		return err
	}

	// This is only needed when running dpkg-shlibdeps.
	if err := os.MkdirAll(filepath.Join(installDir, "debian"), 0777); err != nil {
		return err
	}

	// An empty control file is necessary to run dpkg-shlibdeps.
	if file, err := os.OpenFile(filepath.Join(installDir, "debian", "control"), os.O_RDONLY|os.O_CREATE, 0644); err != nil {
		return err
	} else {
		file.Close()
	}

	for _, pkg := range list {
		filename := filepath.Base(pkg.Filename)
		deb := filepath.Join(debsCache, filename)
		if _, err := os.Stat(deb); os.IsNotExist(err) {
			fmt.Printf("Downloading %s...\n", filename)

			u, err := url.Parse(aptRepo)
			u.Path = path.Join(u.Path, pkg.Filename)
			r, err := http.Get(u.String())
			if err != nil {
				return err
			}
			defer r.Body.Close()

			buf, err := ioutil.ReadAll(r.Body)
			if err != nil {
				return err
			}

			sum := sha256.Sum256(buf)
			if pkg.Hash != hex.EncodeToString(sum[:]) {
				return fmt.Errorf("%s: checksum doesn't match", filename)
			}

			if err := ioutil.WriteFile(deb, buf, 0644); err != nil {
				return err
			}
		}

		fmt.Printf("Installing %s...\n", filename)
		// Extract the content of the package into the install directory.
		err := exec.Command("dpkg-deb", "-x", deb, installDir).Run()
		if err != nil {
			return err
		}
		// Get the package name.
		cmd := exec.Command("dpkg-deb", "--field", deb, "Package")
		stdout, err := cmd.StdoutPipe()
		if err != nil {
			return err
		}
		if err := cmd.Start(); err != nil {
			return err
		}
		r := bufio.NewReader(stdout)
		baseDir, _, err := r.ReadLine()
		if err != nil {
			return err
		}
		if err := cmd.Wait(); err != nil {
			return err
		}
		// Construct the path which contains the control information files.
		controlDir := filepath.Join(installDir, "debian", string(baseDir), "DEBIAN")
		if err := os.MkdirAll(controlDir, 0777); err != nil {
			return err
		}
		// Extract the control information files.
		err = exec.Command("dpkg-deb", "-e", deb, controlDir).Run()
		if err != nil {
			return err
		}
	}

	// Prune /usr/share, leave only pkgconfig files.
	files, err := ioutil.ReadDir(filepath.Join(installDir, "usr", "share"))
	if err != nil {
		return err
	}
	for _, file := range files {
		if file.Name() != "pkgconfig" {
			if err := os.RemoveAll(filepath.Join(installDir, "usr", "share", file.Name())); err != nil {
				return err
			}
		}
	}

	// Relativize all symlinks within the sysroot.
	for _, d := range []string{"usr/lib", "lib64", "lib"} {
		p := filepath.Join(installDir, d)
		if _, err := os.Stat(p); os.IsNotExist(err) {
			continue
		}
		if err := filepath.Walk(p, func(path string, info os.FileInfo, err error) error {
			if err != nil {
				return err
			}
			if info.Mode()&os.ModeSymlink == os.ModeSymlink {
				target, err := os.Readlink(path)
				if err != nil {
					return err
				}
				if !filepath.IsAbs(target) {
					return nil
				}
				patterns := []string{
					"usr/lib/gcc/*-linux-gnu/*/*",
					"usr/lib/*-linux-gnu/*",
					"usr/lib/*",
					"lib64/*",
					"lib/*",
				}
				if err := relativize(path, target, installDir, patterns); err != nil {
					return err
				}
				if _, err := os.Stat(path); os.IsNotExist(err) {
					return fmt.Errorf("%s: broken link", path)
				}
			}
			return nil
		}); err != nil {
			return err
		}
	}

	// Rewrite and relativize all linkerscripts.
	linkerscripts := []string{
		"usr/lib/*-linux-gnu/libpthread.so",
		"usr/lib/*-linux-gnu/libc.so",
	}
	for _, l := range linkerscripts {
		matches, err := filepath.Glob(filepath.Join(installDir, l))
		if err != nil {
			return err
		}
		for _, path := range matches {
			read, err := ioutil.ReadFile(path)
			if err != nil {
				return err
			}
			sub := regexp.MustCompile(`(/usr)?/lib/[a-z0-9_]+-linux-gnu/`)
			contents := sub.ReplaceAllString(string(read), "")
			if err := ioutil.WriteFile(path, []byte(contents), 0644); err != nil {
				return err
			}
		}
	}

	if err := os.RemoveAll(filepath.Join(installDir, "debian")); err != nil {
		return err
	}

	return nil
}

type updateCmd struct {
	arch     string
	config   string
	lockfile string
}

func (*updateCmd) Name() string     { return "update" }
func (*updateCmd) Synopsis() string { return "Update the lock file." }
func (*updateCmd) Usage() string {
	return `update [-arch] [-packages] [-list]:
	Update the lock file to include specific package versions.
`
}

func (c *updateCmd) SetFlags(f *flag.FlagSet) {
	f.StringVar(&c.arch, "arch", "amd64", "Target architecture")
	f.StringVar(&c.config, "config", "packages.yml", "Package configuration")
	f.StringVar(&c.lockfile, "lock", "packages.lock", "Lockfile filename")
}

func (c *updateCmd) Execute(_ context.Context, f *flag.FlagSet, _ ...interface{}) subcommands.ExitStatus {
	d, err := ioutil.ReadFile(c.config)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to read config: %v\n", err)
		return subcommands.ExitFailure
	}
	config := &Config{}
	if err := yaml.Unmarshal(d, &config); err != nil {
		fmt.Fprintf(os.Stderr, "failed to unmarshal config: %v\n", err)
		return subcommands.ExitFailure
	}

	if _, err := os.Stat(config.Keyring); os.IsNotExist(err) {
		fmt.Fprintf(os.Stderr, "keyring file '%s' missing\n", config.Keyring)
		return subcommands.ExitUsageError
	}

	list, err := downloadPackageList(config, c.arch)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to download package list: %v\n", err)
		return subcommands.ExitFailure
	}
	sort.Sort(Locks(list))

	hash := sha256.New()
	hash.Write(d)

	pkgs := Lockfile{
		Updated:  time.Now(),
		Hash:     fmt.Sprintf("%x", hash.Sum(nil)),
		Packages: list,
	}

	l, err := yaml.Marshal(&pkgs)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to marshal lockfile: %v\n", err)
		return subcommands.ExitFailure
	}

	if err := ioutil.WriteFile(c.lockfile, l, 0666); err != nil {
		fmt.Fprintf(os.Stderr, "failed to write lockfile: %v\n", err)
		return subcommands.ExitFailure
	}

	return subcommands.ExitSuccess
}

type installCmd struct {
	arch      string
	outDir    string
	debsCache string
}

func (*installCmd) Name() string     { return "install" }
func (*installCmd) Synopsis() string { return "Install packages" }
func (*installCmd) Usage() string {
	return `install [-out] [-cache] <lockfile>:
  Install the specific versions from the lock file.
`
}

func (c *installCmd) SetFlags(f *flag.FlagSet) {
	f.StringVar(&c.outDir, "out", "sysroot", "Output directory")
	f.StringVar(&c.debsCache, "cache", "debs", "Cache for .deb files")
}

func (c *installCmd) Execute(_ context.Context, f *flag.FlagSet, _ ...interface{}) subcommands.ExitStatus {
	if len(f.Args()) != 1 {
		fmt.Fprintln(os.Stderr, "missing lockfile argument")
		return subcommands.ExitUsageError
	}
	lockfile := f.Args()[0]

	d, err := ioutil.ReadFile(lockfile)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed to read lockfile: %v\n", err)
		return subcommands.ExitFailure
	}
	var lock Lockfile
	if err := yaml.Unmarshal(d, &lock); err != nil {
		fmt.Fprintf(os.Stderr, "failed to unmarshal lockfile: %v\n", err)
		return subcommands.ExitFailure
	}

	if err := installSysroot(lock.Packages, c.outDir, c.debsCache); err != nil {
		fmt.Fprintf(os.Stderr, "failed to install sysroot: %v\n", err)
		return subcommands.ExitFailure
	}
	return subcommands.ExitSuccess
}

func main() {
	subcommands.Register(subcommands.HelpCommand(), "")
	subcommands.Register(subcommands.FlagsCommand(), "")
	subcommands.Register(subcommands.CommandsCommand(), "")
	subcommands.Register(&updateCmd{}, "")
	subcommands.Register(&installCmd{}, "")

	flag.Parse()
	ctx := context.Background()
	os.Exit(int(subcommands.Execute(ctx)))
}