// Copyright 2018 The Goma 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 remoteexec

import (
	"errors"
	"fmt"
	"strings"

	"go.chromium.org/goma/server/command/descriptor/posixpath"
	"go.chromium.org/goma/server/command/descriptor/winpath"
	gomapb "go.chromium.org/goma/server/proto/api"
)

func samePathElement(filepath clientFilePath, a, b []string) []string {
	for i, p := range a {
		if i >= len(b) {
			return a[:i]
		}
		switch filepath.(type) {
		case winpath.FilePath:
			if strings.ToLower(p) != strings.ToLower(b[i]) {
				return a[:i]
			}
		default:
			if p != b[i] {
				return a[:i]
			}
		}
	}
	return a
}

func commonDir(filepath clientFilePath, paths []string) string {
	if len(paths) == 0 {
		return ""
	}
	path := filepath.SplitElem(paths[0])
	for _, p := range paths[1:] {
		path = samePathElement(filepath, path, filepath.SplitElem(p))
	}
	return filepath.Join(path...)
}

// argv0InInputRoot checks argv0 should be in input root or not.
// when argv0 is /usr/bin/*, it might use
// the command in platform container image, so not
// considered it as part of input root.
// TODO: non-linux platforms?
func argv0InInputRoot(argv0 string) bool {
	for _, dir := range []string{"/bin/", "/sbin/", "/usr/bin/", "/usr/sbin/"} {
		if strings.HasPrefix(argv0, dir) {
			return false
		}
	}
	return true
}

func sysrootDir(args []string) (string, bool) {
	// https://github.com/llvm/llvm-project/blob/1d99472875100b230bac2d9ea70b5cd4b45e788b/clang/include/clang/Driver/Options.td
	//  def isysroot : JoinedOrSeparate<["-"], "isysroot">, Group<clang_i_Group>, Flags<[CC1Option]>,
	//     HelpText<"Set the system root directory (usually /)">, MetaVarName<"<dir>">;
	//  def _sysroot_EQ : Joined<["--"], "sysroot=">;
	//  def _sysroot : Separate<["--"], "sysroot">, Alias<_sysroot_EQ>;
	var sysrootDir, isysrootDir string
	var sysrootFlag, isysrootFlag bool
	// https://releases.llvm.org/10.0.0/tools/clang/docs/DiagnosticsReference.html#wmissing-sysroot
	// enabled by default
	need := true
	for _, arg := range args {
		if sysrootFlag {
			// separated, next arg of --sysroot
			sysrootDir = arg
			sysrootFlag = false
			continue
		}
		if isysrootFlag {
			// separated, next arg of -isysroot
			isysrootDir = arg
			isysrootFlag = false
			continue
		}
		switch arg {
		case "-Wall", "-Wmissing-sysroot":
			need = true
		case "-Wno-missing-sysroot":
			need = false
		case "-isysroot":
			isysrootFlag = true
		case "--sysroot":
			sysrootFlag = true
		default:
			// handled joined.
			switch {
			case strings.HasPrefix(arg, "-isysroot"):
				isysrootDir = strings.TrimPrefix(arg, "-isysroot")
			case strings.HasPrefix(arg, "--sysroot="):
				sysrootDir = strings.TrimPrefix(arg, "--sysroot=")
			}
		}
	}
	// https://gcc.gnu.org/onlinedocs/gcc/Directory-Options.html
	// If you use both this option and the -isysroot option, then
	// the --sysroot option applies to libraries, but the
	// -isysroot option applies to header files.
	if isysrootDir != "" {
		return isysrootDir, need
	}
	return sysrootDir, need
}

func inputPaths(filepath clientFilePath, req *gomapb.ExecReq, argv0 string) ([]string, error) {
	cwd := filepath.Clean(req.GetCwd())
	if !filepath.IsAbs(cwd) {
		return nil, fmt.Errorf("cwd is not abs path: %s", cwd)
	}
	paths := []string{cwd}
	for _, input := range req.Input {
		filename := input.GetFilename()
		if !filepath.IsAbs(filename) {
			filename = filepath.Join(cwd, filename)
		}
		paths = append(paths, filepath.Clean(filename))
	}
	if argv0InInputRoot(argv0) {
		if !filepath.IsAbs(argv0) {
			argv0 = filepath.Join(cwd, argv0)
		}
		paths = append(paths, filepath.Clean(argv0))
	}
	sysrootDir, need := sysrootDir(req.Arg)
	// if missing sysroot is allowed, no need to ensure it
	if need && sysrootDir != "" {
		// if request not allows missing sysroot, we
		// need to create the directory even if no input files
		// in dir are used. b/150421328

		// allow relative path only.
		// if dir is absolute, request would require
		// InputRootAbsolutePath.
		// TODO: cwdAgnosticReq should check input file path too.
		// http://b/167342635
		// http://crbug.com/1123938
		if !filepath.IsAbs(sysrootDir) {
			dir := filepath.Join(cwd, sysrootDir)
			paths = append(paths, filepath.Clean(dir))
		}
	}
	return paths, nil
}

// validCommonDir takes a path `dir` generated by commonDir() and returns
// true if it represents a valid common path.
func validCommonDir(filepath clientFilePath, dir string) bool {
	if dir == "" {
		return false
	}
	switch filepath.(type) {
	case posixpath.FilePath:
		if dir == "/" {
			return false
		}
	case winpath.FilePath:
		// The drive should be considered as root on Win.
		// e.g. c:\ will return false.
		if len(dir) == 3 && dir[1:] == `:\` {
			return false
		}

	default:
		// unknown filepath?
		return true
	}

	return true
}

// needChroot returns true if chroot is needed to run the task with
// given common `dir`
func needChroot(filepath clientFilePath, dir string) bool {
	return !validCommonDir(filepath, dir)
}

// getPathsWithNoCommonDir returns two or more paths from the input paths that
// don't have a common dir above the root directory. If there is a common dir,
// then returns an empty array. Does not guarantee any kind of order.
func getPathsWithNoCommonDir(filepath clientFilePath, paths []string) []string {
	if len(paths) < 2 {
		return nil
	}

	p0 := paths[0]
	// If there are any pairs of paths in `paths` that have no common directories,
	// then there should be a mismatch between paths[0] and paths[i] for some i > 0.
	for _, p1 := range paths[1:] {
		pair := []string{p0, p1}
		dir := commonDir(filepath, pair)
		if !validCommonDir(filepath, dir) {
			return pair
		}
	}
	return nil
}

func checkInputRootDir(filepath clientFilePath, dir string) error {
	switch filepath.(type) {
	case posixpath.FilePath:
		// if dir covers these paths, command (e.g. clang) won't
		// work because required *.so etc would not be accessible.
		for _, p := range []string{
			"/lib/x86_64-linux-gnu/",
			"/usr/lib/x86_64-linux-gnu/",
			"/lib64/",
		} {
			if strings.HasPrefix(p, dir+"/") {
				return fmt.Errorf("bad input root: %s", dir)
			}
		}
		return nil

	case winpath.FilePath:
		// TODO: check for win path.
		return nil

	default:
		// unknown filepath?
		return nil
	}
}

// inputRootDir returns common root of paths.
// if execRootDir is not empty, use it as root of paths.
// If second return value is true, chroot must be used.  It become true only
// if `allowChroot` is true and common input root is "/".
func inputRootDir(filepath clientFilePath, paths []string, allowChroot bool, execRootDir string) (string, bool, error) {
	if execRootDir != "" {
		return execRootDir, execRootDir == "/" && allowChroot, nil
	}
	root := commonDir(filepath, paths)
	if needChroot(filepath, root) && allowChroot {
		switch filepath.(type) {
		// TODO: support non-posix platform
		case posixpath.FilePath:
			return "/", true, nil
		}
	}
	if !validCommonDir(filepath, root) {
		pair := getPathsWithNoCommonDir(filepath, paths)
		return "", false, fmt.Errorf("no common paths in inputs: %v", pair)
	}
	err := checkInputRootDir(filepath, root)
	if err != nil {
		return "", false, err
	}
	return root, false, nil
}

var errOutOfRoot = errors.New("out of root")

// rootRel returns relative path from rootDir for fname,
// which is relative path from cwd, or absolute path.
// cwd and rootDir should be clean path.
func rootRel(filepath clientFilePath, fname, cwd, rootDir string) (string, error) {
	if filepath == nil {
		return "", errors.New("rootRel: client filepath unknown")
	}
	if !filepath.IsAbs(fname) {
		fname = filepath.Join(cwd, fname)
	}
	// filepath.Rel cleans paths, so we can't use it here.
	// suppose rootdir and cwd are clean path, and
	// cwd is under rootdir.
	rootElems := filepath.SplitElem(rootDir)
	fileElems := filepath.SplitElem(fname)

	if len(fileElems) < len(rootElems) {
		return "", errOutOfRoot
	}
	commonElems := samePathElement(filepath, rootElems, fileElems)
	if len(commonElems) != len(rootElems) {
		return "", errOutOfRoot
	}
	fileElems = fileElems[len(rootElems):]
	relname := filepath.Join(fileElems...)
	fileElems = filepath.SplitElem(filepath.Clean(relname))
	if len(fileElems) > 0 && fileElems[0] == ".." {
		return "", errOutOfRoot
	}
	return relname, nil
}

// hasPrefixDir returns true if p has prefix as a directory name.
// Note: it is case sensitive.
// TODO: support non-posix platforms.
func hasPrefixDir(p, prefix string) bool {
	prefix = strings.TrimRight(prefix, "/")
	if !strings.HasPrefix(p, prefix) {
		return false
	}
	if len(p) == len(prefix) {
		return true
	}
	return p[len(prefix)] == '/'
}