package gpg

import (
	"context"
	"encoding/hex"
	"fmt"
	"io"
	"io/ioutil"
	"os"
	"os/exec"
	"path"
	"strings"
	"time"
)

var ExecutionTimeLimit = 30 * time.Second
var BinaryPath = "gpg"

type Encryptor interface {
	ReadCipherText(size int) ([]byte, error)
	WritePlainText(chunk []byte) error
	Finish()
	Close()
}

type EncryptorFactory interface {
	Get(recipient []byte, keyRing []byte) (Encryptor, error)
}

type CLIEncryptorFactory struct {
}

func (CLIEncryptorFactory) Get(recipient []byte, keyRing []byte) (Encryptor, error) {
	return NewCLIEncryptor(recipient, keyRing)
}

type CLIEncryptor struct {
	tempDir     string
	recipient   []byte
	cmd         *exec.Cmd
	stdout      io.ReadCloser
	stderr      io.ReadCloser
	stdin       io.WriteCloser
	initialized bool
}

func NewCLIEncryptor(recipient []byte, keyRing []byte) (*CLIEncryptor, error) {
	temp, err := getGpgTempDir()
	if err != nil {
		return nil, err
	}

	keyRingTempPath := path.Join(temp, "_keyring")
	err = ioutil.WriteFile(keyRingTempPath, keyRing, 0600)
	if err != nil {
		return nil, err
	}

	// TODO(lb5tr): test for command injection
	importParams := []string{
		"--homedir", temp,
		"--import", keyRingTempPath,
	}

	ctx, cancel := context.WithTimeout(context.Background(), ExecutionTimeLimit)
	defer cancel()

	cmd := exec.CommandContext(ctx, BinaryPath, importParams...)
	err = cmd.Start()
	if err != nil {
		return nil, fmt.Errorf("failed to start import command: %v", err)
	}

	err = cmd.Wait()
	if err != nil {
		return nil, fmt.Errorf("workspace initialization failed: %v", err)
	}

	ok, err := isOkExitCode(cmd)
	if !ok || err != nil {
		return nil, fmt.Errorf("failed to initialize gpg workspace due to gpg execution failure")
	}

	// spawn background encryption process
	// TODO(lb5tr): test for command injection
	encryptParams := []string{
		"--encrypt",
		"--homedir", temp,
		"--recipient", strings.ToUpper(hex.EncodeToString(recipient)),
		"--trust-model", "always",
		"--yes",
		"--batch",
	}

	cmd = exec.Command(BinaryPath, encryptParams...)
	stdout, stderr, stdin, err := makePipes(cmd)
	if err != nil {
		return nil, err
	}

	err = cmd.Start()
	if err != nil {
		return nil, fmt.Errorf("failed to start encryptor process: %v", err)
	}

	encryptor := CLIEncryptor{
		tempDir:     temp,
		recipient:   recipient,
		cmd:         cmd,
		stdin:       stdin,
		stderr:      stderr,
		stdout:      stdout,
		initialized: true,
	}

	return &encryptor, nil
}

func (encryptor *CLIEncryptor) WritePlainText(chunk []byte) error {
	if !encryptor.initialized {
		return fmt.Errorf("encryptor is not initialized")
	}

	encryptor.stdin.Write(chunk)
	return nil
}

func (encryptor *CLIEncryptor) ReadCipherText(size int) ([]byte, error) {
	if !encryptor.initialized {
		return nil, fmt.Errorf("encryptor is not initialized")
	}

	buf := make([]byte, size)
	n, err := encryptor.stdout.Read(buf)

	return buf[:n], err
}

func (encryptor *CLIEncryptor) Finish() {
	encryptor.stdin.Close()
}

func (encryptor *CLIEncryptor) Close() {
	encryptor.stdout.Close()
	encryptor.stderr.Close()
	encryptor.stdin.Close()

	os.RemoveAll(encryptor.tempDir)
}

func getGpgTempDir() (string, error) {
	temp, err := ioutil.TempDir("", "gpg-")
	if err != nil {
		return "", fmt.Errorf("failed to create temporary gpg workspace %v", err)
	}

	return temp, nil
}

func cleanupProcess(cmd *exec.Cmd) {
	if !cmd.ProcessState.Exited() {
		cmd.Process.Kill()
	}
}

func isOkExitCode(cmd *exec.Cmd) (bool, error) {
	exitCode := cmd.ProcessState.ExitCode()

	if exitCode == -1 {
		return false, fmt.Errorf("process is either still runing or was terminated by a signal")
	}

	return exitCode == 0, nil
}

func makePipes(cmd *exec.Cmd) (stdout io.ReadCloser, stderr io.ReadCloser, stdin io.WriteCloser, error error) {
	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return nil, nil, nil, fmt.Errorf("cmd.StdoutPipe() failed %v", err)
	}

	stdin, err = cmd.StdinPipe()
	if err != nil {
		return nil, nil, nil, fmt.Errorf("cmd.StdinPipe() failed %v", err)
	}

	stderr, err = cmd.StderrPipe()
	if err != nil {
		return nil, nil, nil, fmt.Errorf("cmd.StderrPipe() failed %v", err)
	}

	return stdout, stderr, stdin, nil
}