// Program aedeploy assists with deploying Go Managed VM apps to production.
// A temporary directory is created; the app, its subdirectories, and all its
// dependencies from $GOPATH are copied into the directory; then the app
// is deployed to production with the provided command.
//
// The app must be in "package main".
//
// This command must be issued from within the root directory of the app
// (where the app.yaml file is located).
//
// A sample Dockerfile to be used with this tool could look like this:
//     FROM gcr.io/google_appengine/go-compat
//     ADD . /app
//     RUN GOPATH=/app/_gopath go build -tags appenginevm -o /app/_ah/exe
package main

import (
	"flag"
	"fmt"
	"go/build"
	"io"
	"io/ioutil"
	"os"
	"os/exec"
	"path/filepath"
	"strings"
)

var (
	skipFiles = map[string]bool{
		".git":        true,
		".gitconfig":  true,
		".hg":         true,
		".travis.yml": true,
	}

	gopathCache = map[string]string{}
)

func usage() {
	fmt.Fprintf(os.Stderr, "Usage of %s:\n", os.Args[0])
	fmt.Fprintf(os.Stderr, "\t%s gcloud --verbosity debug preview app deploy --version myversion ./app.yaml\tDeploy app to production\n", os.Args[0])
}

func main() {
	flag.Usage = usage
	flag.Parse()
	if flag.NArg() < 1 {
		usage()
		os.Exit(1)
	}

	if err := aedeploy(); err != nil {
		fmt.Fprintf(os.Stderr, os.Args[0]+": Error: %v\n", err)
		os.Exit(1)
	}
}

func aedeploy() error {
	tags := []string{"appenginevm"}
	app, err := analyze(tags)
	if err != nil {
		return err
	}

	tmpDir, err := app.bundle()
	if tmpDir != "" {
		defer os.RemoveAll(tmpDir)
	}
	if err != nil {
		return err
	}

	if err := os.Chdir(tmpDir); err != nil {
		return fmt.Errorf("unable to chdir to %v: %v", tmpDir, err)
	}
	return deploy()
}

// deploy calls the provided command to deploy the app from the temporary directory.
func deploy() error {
	cmd := exec.Command(flag.Arg(0), flag.Args()[1:]...)
	cmd.Stdin, cmd.Stdout, cmd.Stderr = os.Stdin, os.Stdout, os.Stderr
	if err := cmd.Run(); err != nil {
		return fmt.Errorf("unable to run %q: %v", strings.Join(flag.Args(), " "), err)
	}
	return nil
}

type app struct {
	appFiles []string
	imports  map[string]string
}

// analyze checks the app for building with the given build tags and returns
// app files, and a map of full directory import names to original import names.
func analyze(tags []string) (*app, error) {
	ctxt := buildContext(tags)
	appFiles, err := appFiles(ctxt)
	if err != nil {
		return nil, err
	}
	gopath := filepath.SplitList(ctxt.GOPATH)
	im, err := imports(ctxt, ".", gopath)
	return &app{
		appFiles: appFiles,
		imports:  im,
	}, err
}

// buildContext returns the context for building the source.
func buildContext(tags []string) *build.Context {
	return &build.Context{
		GOARCH:    "amd64",
		GOOS:      "linux",
		GOROOT:    build.Default.GOROOT,
		GOPATH:    build.Default.GOPATH,
		Compiler:  build.Default.Compiler,
		BuildTags: append(build.Default.BuildTags, tags...),
	}
}

// bundle bundles the app into a temporary directory.
func (s *app) bundle() (tmpdir string, err error) {
	workDir, err := ioutil.TempDir("", os.Args[0])
	if err != nil {
		return "", fmt.Errorf("unable to create tmpdir: %v", err)
	}

	for srcDir, importName := range s.imports {
		dstDir := "_gopath/src/" + importName
		if err := copyTree(workDir, dstDir, srcDir); err != nil {
			return workDir, fmt.Errorf("unable to copy directory %v to %v: %v", srcDir, dstDir, err)
		}
	}
	if err := copyTree(workDir, ".", "."); err != nil {
		return workDir, fmt.Errorf("unable to copy root directory to /app: %v", err)
	}
	return workDir, nil
}

// imports returns a map of all import directories (recursively) used by the app.
// The return value maps full directory names to original import names.
func imports(ctxt *build.Context, srcDir string, gopath []string) (map[string]string, error) {
	pkg, err := ctxt.ImportDir(srcDir, 0)
	if err != nil {
		return nil, err
	}

	// Resolve all non-standard-library imports
	result := make(map[string]string)
	for _, v := range pkg.Imports {
		if !strings.Contains(v, ".") {
			continue
		}
		src, err := findInGopath(v, gopath)
		if err != nil {
			return nil, fmt.Errorf("unable to find import %v in gopath %v: %v", v, gopath, err)
		}
		if _, ok := result[src]; ok { // Already processed
			continue
		}
		result[src] = v
		im, err := imports(ctxt, src, gopath)
		if err != nil {
			return nil, fmt.Errorf("unable to parse package %v: %v", src, err)
		}
		for k, v := range im {
			result[k] = v
		}
	}
	return result, nil
}

// findInGopath searches the gopath for the named import directory.
func findInGopath(dir string, gopath []string) (string, error) {
	if v, ok := gopathCache[dir]; ok {
		return v, nil
	}
	for _, v := range gopath {
		dst := filepath.Join(v, "src", dir)
		if _, err := os.Stat(dst); err == nil {
			gopathCache[dir] = dst
			return dst, nil
		}
	}
	return "", fmt.Errorf("unable to find package %v in gopath %v", dir, gopath)
}

// copyTree copies srcDir to dstDir relative to dstRoot, ignoring skipFiles.
func copyTree(dstRoot, dstDir, srcDir string) error {
	d := filepath.Join(dstRoot, dstDir)
	if err := os.MkdirAll(d, 0755); err != nil {
		return fmt.Errorf("unable to create directory %v: %v", d, err)
	}

	entries, err := ioutil.ReadDir(srcDir)
	if err != nil {
		return fmt.Errorf("unable to read dir %v: %v", srcDir, err)
	}
	for _, entry := range entries {
		n := entry.Name()
		if skipFiles[n] {
			continue
		}
		s := filepath.Join(srcDir, n)
		d := filepath.Join(dstDir, n)
		if entry.IsDir() {
			if err := copyTree(dstRoot, d, s); err != nil {
				return fmt.Errorf("unable to copy dir %v to %v: %v", s, d, err)
			}
			continue
		}
		if err := copyFile(dstRoot, d, s); err != nil {
			return fmt.Errorf("unable to copy dir %v to %v: %v", s, d, err)
		}
	}
	return nil
}

// copyFile copies src to dst relative to dstRoot.
func copyFile(dstRoot, dst, src string) error {
	s, err := os.Open(src)
	if err != nil {
		return fmt.Errorf("unable to open %v: %v", src, err)
	}
	defer s.Close()

	dst = filepath.Join(dstRoot, dst)
	d, err := os.Create(dst)
	if err != nil {
		return fmt.Errorf("unable to create %v: %v", dst)
	}
	_, err = io.Copy(d, s)
	if err != nil {
		d.Close() // ignore error, copy already failed.
		return fmt.Errorf("unable to copy %v to %v: %v", src, dst, err)
	}
	if err := d.Close(); err != nil {
		return fmt.Errorf("unable to close %v: %v", dst, err)
	}
	return nil
}

// appFiles returns a list of all Go source files in the app.
func appFiles(ctxt *build.Context) ([]string, error) {
	pkg, err := ctxt.ImportDir(".", 0)
	if err != nil {
		return nil, err
	}
	if !pkg.IsCommand() {
		return nil, fmt.Errorf(`the root of your app needs to be package "main" (currently %q). Please see https://cloud.google.com/appengine/docs/go/managed-vms for more details on structuring your app.`, pkg.Name)
	}
	var appFiles []string
	for _, f := range pkg.GoFiles {
		n := filepath.Join(".", f)
		appFiles = append(appFiles, n)
	}
	return appFiles, nil
}