// Copyright 2017 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 cfg holds configuration shared by multiple parts
// of the go command.
package cfg

import (
	"bytes"
	"fmt"
	"go/build"
	"io/ioutil"
	"os"
	"path/filepath"
	"runtime"
	"strings"
	"sync"

	"cmd/internal/objabi"
)

// These are general "build flags" used by build and other commands.
var (
	BuildA                 bool   // -a flag
	BuildBuildmode         string // -buildmode flag
	BuildContext           = defaultContext()
	BuildMod               string             // -mod flag
	BuildI                 bool               // -i flag
	BuildLinkshared        bool               // -linkshared flag
	BuildMSan              bool               // -msan flag
	BuildN                 bool               // -n flag
	BuildO                 string             // -o flag
	BuildP                 = runtime.NumCPU() // -p flag
	BuildPkgdir            string             // -pkgdir flag
	BuildRace              bool               // -race flag
	BuildToolexec          []string           // -toolexec flag
	BuildToolchainName     string
	BuildToolchainCompiler func() string
	BuildToolchainLinker   func() string
	BuildTrimpath          bool // -trimpath flag
	BuildV                 bool // -v flag
	BuildWork              bool // -work flag
	BuildX                 bool // -x flag

	CmdName string // "build", "install", "list", "mod tidy", etc.

	DebugActiongraph string // -debug-actiongraph flag (undocumented, unstable)
)

func defaultContext() build.Context {
	ctxt := build.Default
	ctxt.JoinPath = filepath.Join // back door to say "do not use go command"

	ctxt.GOROOT = findGOROOT()
	if runtime.Compiler != "gccgo" {
		// Note that we must use runtime.GOOS and runtime.GOARCH here,
		// as the tool directory does not move based on environment
		// variables. This matches the initialization of ToolDir in
		// go/build, except for using ctxt.GOROOT rather than
		// runtime.GOROOT.
		build.ToolDir = filepath.Join(ctxt.GOROOT, "pkg/tool/"+runtime.GOOS+"_"+runtime.GOARCH)
	}

	ctxt.GOPATH = envOr("GOPATH", ctxt.GOPATH)

	// Override defaults computed in go/build with defaults
	// from go environment configuration file, if known.
	ctxt.GOOS = envOr("GOOS", ctxt.GOOS)
	ctxt.GOARCH = envOr("GOARCH", ctxt.GOARCH)

	// The go/build rule for whether cgo is enabled is:
	//	1. If $CGO_ENABLED is set, respect it.
	//	2. Otherwise, if this is a cross-compile, disable cgo.
	//	3. Otherwise, use built-in default for GOOS/GOARCH.
	// Recreate that logic here with the new GOOS/GOARCH setting.
	if v := Getenv("CGO_ENABLED"); v == "0" || v == "1" {
		ctxt.CgoEnabled = v[0] == '1'
	} else if ctxt.GOOS != runtime.GOOS || ctxt.GOARCH != runtime.GOARCH {
		ctxt.CgoEnabled = false
	} else {
		// Use built-in default cgo setting for GOOS/GOARCH.
		// Note that ctxt.GOOS/GOARCH are derived from the preference list
		// (1) environment, (2) go/env file, (3) runtime constants,
		// while go/build.Default.GOOS/GOARCH are derived from the preference list
		// (1) environment, (2) runtime constants.
		// We know ctxt.GOOS/GOARCH == runtime.GOOS/GOARCH;
		// no matter how that happened, go/build.Default will make the
		// same decision (either the environment variables are set explicitly
		// to match the runtime constants, or else they are unset, in which
		// case go/build falls back to the runtime constants), so
		// go/build.Default.GOOS/GOARCH == runtime.GOOS/GOARCH.
		// So ctxt.CgoEnabled (== go/build.Default.CgoEnabled) is correct
		// as is and can be left unmodified.
		// Nothing to do here.
	}

	return ctxt
}

func init() {
	BuildToolchainCompiler = func() string { return "missing-compiler" }
	BuildToolchainLinker = func() string { return "missing-linker" }
}

// An EnvVar is an environment variable Name=Value.
type EnvVar struct {
	Name  string
	Value string
}

// OrigEnv is the original environment of the program at startup.
var OrigEnv []string

// CmdEnv is the new environment for running go tool commands.
// User binaries (during go test or go run) are run with OrigEnv,
// not CmdEnv.
var CmdEnv []EnvVar

// Global build parameters (used during package load)
var (
	Goarch = BuildContext.GOARCH
	Goos   = BuildContext.GOOS

	ExeSuffix = exeSuffix()

	// ModulesEnabled specifies whether the go command is running
	// in module-aware mode (as opposed to GOPATH mode).
	// It is equal to modload.Enabled, but not all packages can import modload.
	ModulesEnabled bool
)

func exeSuffix() string {
	if Goos == "windows" {
		return ".exe"
	}
	return ""
}

var envCache struct {
	once sync.Once
	m    map[string]string
}

// EnvFile returns the name of the Go environment configuration file.
func EnvFile() (string, error) {
	if file := os.Getenv("GOENV"); file != "" {
		if file == "off" {
			return "", fmt.Errorf("GOENV=off")
		}
		return file, nil
	}
	dir, err := os.UserConfigDir()
	if err != nil {
		return "", err
	}
	if dir == "" {
		return "", fmt.Errorf("missing user-config dir")
	}
	return filepath.Join(dir, "go/env"), nil
}

func initEnvCache() {
	envCache.m = make(map[string]string)
	file, _ := EnvFile()
	if file == "" {
		return
	}
	data, err := ioutil.ReadFile(file)
	if err != nil {
		return
	}

	for len(data) > 0 {
		// Get next line.
		line := data
		i := bytes.IndexByte(data, '\n')
		if i >= 0 {
			line, data = line[:i], data[i+1:]
		} else {
			data = nil
		}

		i = bytes.IndexByte(line, '=')
		if i < 0 || line[0] < 'A' || 'Z' < line[0] {
			// Line is missing = (or empty) or a comment or not a valid env name. Ignore.
			// (This should not happen, since the file should be maintained almost
			// exclusively by "go env -w", but better to silently ignore than to make
			// the go command unusable just because somehow the env file has
			// gotten corrupted.)
			continue
		}
		key, val := line[:i], line[i+1:]
		envCache.m[string(key)] = string(val)
	}
}

// Getenv gets the value for the configuration key.
// It consults the operating system environment
// and then the go/env file.
// If Getenv is called for a key that cannot be set
// in the go/env file (for example GODEBUG), it panics.
// This ensures that CanGetenv is accurate, so that
// 'go env -w' stays in sync with what Getenv can retrieve.
func Getenv(key string) string {
	if !CanGetenv(key) {
		switch key {
		case "CGO_TEST_ALLOW", "CGO_TEST_DISALLOW", "CGO_test_ALLOW", "CGO_test_DISALLOW":
			// used by internal/work/security_test.go; allow
		default:
			panic("internal error: invalid Getenv " + key)
		}
	}
	val := os.Getenv(key)
	if val != "" {
		return val
	}
	envCache.once.Do(initEnvCache)
	return envCache.m[key]
}

// CanGetenv reports whether key is a valid go/env configuration key.
func CanGetenv(key string) bool {
	return strings.Contains(knownEnv, "\t"+key+"\n")
}

var knownEnv = `
	AR
	CC
	CGO_CFLAGS
	CGO_CFLAGS_ALLOW
	CGO_CFLAGS_DISALLOW
	CGO_CPPFLAGS
	CGO_CPPFLAGS_ALLOW
	CGO_CPPFLAGS_DISALLOW
	CGO_CXXFLAGS
	CGO_CXXFLAGS_ALLOW
	CGO_CXXFLAGS_DISALLOW
	CGO_ENABLED
	CGO_FFLAGS
	CGO_FFLAGS_ALLOW
	CGO_FFLAGS_DISALLOW
	CGO_LDFLAGS
	CGO_LDFLAGS_ALLOW
	CGO_LDFLAGS_DISALLOW
	CXX
	FC
	GCCGO
	GO111MODULE
	GO386
	GOARCH
	GOARM
	GOBIN
	GOCACHE
	GOENV
	GOEXE
	GOFLAGS
	GOGCCFLAGS
	GOHOSTARCH
	GOHOSTOS
	GOMIPS
	GOMIPS64
	GONOPROXY
	GONOSUMDB
	GOOS
	GOPATH
	GOPPC64
	GOPRIVATE
	GOPROXY
	GOROOT
	GOSUMDB
	GOTMPDIR
	GOTOOLDIR
	GOWASM
	GO_EXTLINK_ENABLED
	PKG_CONFIG
`

var (
	GOROOT       = BuildContext.GOROOT
	GOBIN        = Getenv("GOBIN")
	GOROOTbin    = filepath.Join(GOROOT, "bin")
	GOROOTpkg    = filepath.Join(GOROOT, "pkg")
	GOROOTsrc    = filepath.Join(GOROOT, "src")
	GOROOT_FINAL = findGOROOT_FINAL()

	// Used in envcmd.MkEnv and build ID computations.
	GOARM    = envOr("GOARM", fmt.Sprint(objabi.GOARM))
	GO386    = envOr("GO386", objabi.GO386)
	GOMIPS   = envOr("GOMIPS", objabi.GOMIPS)
	GOMIPS64 = envOr("GOMIPS64", objabi.GOMIPS64)
	GOPPC64  = envOr("GOPPC64", fmt.Sprintf("%s%d", "power", objabi.GOPPC64))
	GOWASM   = envOr("GOWASM", fmt.Sprint(objabi.GOWASM))

	GOPROXY   = envOr("GOPROXY", "https://proxy.golang.org,direct")
	GOSUMDB   = envOr("GOSUMDB", "sum.golang.org")
	GOPRIVATE = Getenv("GOPRIVATE")
	GONOPROXY = envOr("GONOPROXY", GOPRIVATE)
	GONOSUMDB = envOr("GONOSUMDB", GOPRIVATE)
)

// GetArchEnv returns the name and setting of the
// GOARCH-specific architecture environment variable.
// If the current architecture has no GOARCH-specific variable,
// GetArchEnv returns empty key and value.
func GetArchEnv() (key, val string) {
	switch Goarch {
	case "arm":
		return "GOARM", GOARM
	case "386":
		return "GO386", GO386
	case "mips", "mipsle":
		return "GOMIPS", GOMIPS
	case "mips64", "mips64le":
		return "GOMIPS64", GOMIPS64
	case "ppc64", "ppc64le":
		return "GOPPC64", GOPPC64
	case "wasm":
		return "GOWASM", GOWASM
	}
	return "", ""
}

// envOr returns Getenv(key) if set, or else def.
func envOr(key, def string) string {
	val := Getenv(key)
	if val == "" {
		val = def
	}
	return val
}

// There is a copy of findGOROOT, isSameDir, and isGOROOT in
// x/tools/cmd/godoc/goroot.go.
// Try to keep them in sync for now.

// findGOROOT returns the GOROOT value, using either an explicitly
// provided environment variable, a GOROOT that contains the current
// os.Executable value, or else the GOROOT that the binary was built
// with from runtime.GOROOT().
//
// There is a copy of this code in x/tools/cmd/godoc/goroot.go.
func findGOROOT() string {
	if env := Getenv("GOROOT"); env != "" {
		return filepath.Clean(env)
	}
	def := filepath.Clean(runtime.GOROOT())
	if runtime.Compiler == "gccgo" {
		// gccgo has no real GOROOT, and it certainly doesn't
		// depend on the executable's location.
		return def
	}
	exe, err := os.Executable()
	if err == nil {
		exe, err = filepath.Abs(exe)
		if err == nil {
			if dir := filepath.Join(exe, "../.."); isGOROOT(dir) {
				// If def (runtime.GOROOT()) and dir are the same
				// directory, prefer the spelling used in def.
				if isSameDir(def, dir) {
					return def
				}
				return dir
			}
			exe, err = filepath.EvalSymlinks(exe)
			if err == nil {
				if dir := filepath.Join(exe, "../.."); isGOROOT(dir) {
					if isSameDir(def, dir) {
						return def
					}
					return dir
				}
			}
		}
	}
	return def
}

func findGOROOT_FINAL() string {
	// $GOROOT_FINAL is only for use during make.bash
	// so it is not settable using go/env, so we use os.Getenv here.
	def := GOROOT
	if env := os.Getenv("GOROOT_FINAL"); env != "" {
		def = filepath.Clean(env)
	}
	return def
}

// isSameDir reports whether dir1 and dir2 are the same directory.
func isSameDir(dir1, dir2 string) bool {
	if dir1 == dir2 {
		return true
	}
	info1, err1 := os.Stat(dir1)
	info2, err2 := os.Stat(dir2)
	return err1 == nil && err2 == nil && os.SameFile(info1, info2)
}

// isGOROOT reports whether path looks like a GOROOT.
//
// It does this by looking for the path/pkg/tool directory,
// which is necessary for useful operation of the cmd/go tool,
// and is not typically present in a GOPATH.
//
// There is a copy of this code in x/tools/cmd/godoc/goroot.go.
func isGOROOT(path string) bool {
	stat, err := os.Stat(filepath.Join(path, "pkg", "tool"))
	if err != nil {
		return false
	}
	return stat.IsDir()
}