package gpgbin

import (
	"bufio"
	"bytes"
	"errors"
	"fmt"
	"io"
	"io/ioutil"
	"log"
	"os"
	"os/exec"
	"strconv"
	"strings"

	"git.sr.ht/~rjarry/aerc/models"
	"github.com/mattn/go-isatty"
)

// gpg represents a gpg command with buffers attached to stdout and stderr
type gpg struct {
	cmd    *exec.Cmd
	stdout bytes.Buffer
	stderr bytes.Buffer
}

// newGpg creates a new gpg command with buffers attached
func newGpg(stdin io.Reader, args []string) *gpg {
	g := new(gpg)
	g.cmd = exec.Command("gpg", "--status-fd", "1", "--batch")
	g.cmd.Args = append(g.cmd.Args, args...)
	g.cmd.Stdin = stdin
	g.cmd.Stdout = &g.stdout
	g.cmd.Stderr = &g.stderr

	return g
}

// parseError parses errors returned by gpg that don't show up with a [GNUPG:]
// prefix
func parseError(s string) error {
	lines := strings.Split(s, "\n")
	for _, line := range lines {
		line = strings.ToLower(line)
		if GPGErrors[line] > 0 {
			return errors.New(line)
		}
	}
	return errors.New(strings.Join(lines, ", "))
}

// fields returns the field name from --status-fd output. See:
// https://github.com/gpg/gnupg/blob/master/doc/DETAILS
func field(s string) string {
	tokens := strings.SplitN(s, " ", 3)
	if tokens[0] == "[GNUPG:]" {
		return tokens[1]
	}
	return ""
}

// getIdentity returns the identity of the given key
func getIdentity(key uint64) string {
	fpr := fmt.Sprintf("%X", key)
	cmd := exec.Command("gpg", "--with-colons", "--batch", "--list-keys", fpr)

	var outbuf strings.Builder
	cmd.Stdout = &outbuf
	cmd.Run()
	out := strings.Split(outbuf.String(), "\n")
	for _, line := range out {
		if strings.HasPrefix(line, "uid") {
			flds := strings.Split(line, ":")
			return flds[9]
		}
	}
	return ""
}

// getKeyId returns the 16 digit key id, if key exists
func getKeyId(s string, private bool) string {
	cmd := exec.Command("gpg", "--with-colons", "--batch")
	listArg := "--list-keys"
	if private {
		listArg = "--list-secret-keys"
	}
	cmd.Args = append(cmd.Args, listArg, s)

	var outbuf strings.Builder
	cmd.Stdout = &outbuf
	cmd.Run()
	out := strings.Split(outbuf.String(), "\n")
	for _, line := range out {
		if strings.HasPrefix(line, "fpr") {
			flds := strings.Split(line, ":")
			id := flds[9]
			return id[len(id)-16:]
		}
	}
	return ""
}

// longKeyToUint64 returns a uint64 version of the given key
func longKeyToUint64(key string) (uint64, error) {
	fpr := string(key[len(key)-16:])
	fprUint64, err := strconv.ParseUint(fpr, 16, 64)
	if err != nil {
		return 0, err
	}
	return fprUint64, nil
}

// parse parses the output of gpg --status-fd
func parse(r io.Reader, md *models.MessageDetails) error {
	var (
		logOut io.Writer
		logger *log.Logger
	)
	if !isatty.IsTerminal(os.Stdout.Fd()) {
		logOut = os.Stdout
	} else {
		logOut = ioutil.Discard
		os.Stdout, _ = os.Open(os.DevNull)
	}
	logger = log.New(logOut, "", log.LstdFlags)
	var err error
	var msgContent []byte
	var msgCollecting bool
	newLine := []byte("\r\n")
	scanner := bufio.NewScanner(r)
	for scanner.Scan() {
		line := scanner.Text()
		if field(line) == "PLAINTEXT_LENGTH" {
			continue
		}
		if strings.HasPrefix(line, "[GNUPG:]") {
			msgCollecting = false
			logger.Println(line)
		}
		if msgCollecting {
			msgContent = append(msgContent, scanner.Bytes()...)
			msgContent = append(msgContent, newLine...)
		}

		switch field(line) {
		case "ENC_TO":
			md.IsEncrypted = true
		case "DECRYPTION_KEY":
			md.DecryptedWithKeyId, err = parseDecryptionKey(line)
			md.DecryptedWith = getIdentity(md.DecryptedWithKeyId)
			if err != nil {
				return err
			}
		case "DECRYPTION_FAILED":
			return fmt.Errorf("gpg: decryption failed")
		case "PLAINTEXT":
			msgCollecting = true
		case "NEWSIG":
			md.IsSigned = true
		case "GOODSIG":
			t := strings.SplitN(line, " ", 4)
			md.SignedByKeyId, err = longKeyToUint64(t[2])
			if err != nil {
				return err
			}
			md.SignedBy = t[3]
		case "BADSIG":
			t := strings.SplitN(line, " ", 4)
			md.SignedByKeyId, err = longKeyToUint64(t[2])
			if err != nil {
				return err
			}
			md.SignatureError = "gpg: invalid signature"
			md.SignedBy = t[3]
		case "EXPSIG":
			t := strings.SplitN(line, " ", 4)
			md.SignedByKeyId, err = longKeyToUint64(t[2])
			if err != nil {
				return err
			}
			md.SignatureError = "gpg: expired signature"
			md.SignedBy = t[3]
		case "EXPKEYSIG":
			t := strings.SplitN(line, " ", 4)
			md.SignedByKeyId, err = longKeyToUint64(t[2])
			if err != nil {
				return err
			}
			md.SignatureError = "gpg: signature made with expired key"
			md.SignedBy = t[3]
		case "REVKEYSIG":
			t := strings.SplitN(line, " ", 4)
			md.SignedByKeyId, err = longKeyToUint64(t[2])
			if err != nil {
				return err
			}
			md.SignatureError = "gpg: signature made with revoked key"
			md.SignedBy = t[3]
		case "ERRSIG":
			t := strings.SplitN(line, " ", 9)
			md.SignedByKeyId, err = longKeyToUint64(t[2])
			if err != nil {
				return err
			}
			if t[7] == "9" {
				md.SignatureError = "gpg: missing public key"
			}
			if t[7] == "4" {
				md.SignatureError = "gpg: unsupported algorithm"
			}
			md.SignedBy = "(unknown signer)"
		case "BEGIN_ENCRYPTION":
			msgCollecting = true
		case "SIG_CREATED":
			fields := strings.Split(line, " ")
			micalg, err := strconv.Atoi(fields[4])
			if err != nil {
				return fmt.Errorf("gpg: micalg not found")
			}
			md.Micalg = micalgs[micalg]
			msgCollecting = true
		case "VALIDSIG":
			fields := strings.Split(line, " ")
			micalg, err := strconv.Atoi(fields[9])
			if err != nil {
				return fmt.Errorf("gpg: micalg not found")
			}
			md.Micalg = micalgs[micalg]
		case "NODATA":
			md.SignatureError = "gpg: no signature packet found"
		case "FAILURE":
			return fmt.Errorf(strings.TrimPrefix(line, "[GNUPG:] "))
		}
	}
	md.Body = bytes.NewReader(msgContent)
	return nil
}

// parseDecryptionKey returns primary key from DECRYPTION_KEY line
func parseDecryptionKey(l string) (uint64, error) {
	key := strings.Split(l, " ")[3]
	fpr := string(key[len(key)-16:])
	fprUint64, err := longKeyToUint64(fpr)
	if err != nil {
		return 0, err
	}
	getIdentity(fprUint64)
	return fprUint64, nil
}

type GPGError int32

const (
	ERROR_NO_PGP_DATA_FOUND GPGError = iota + 1
)

var GPGErrors = map[string]GPGError{
	"gpg: no valid openpgp data found.": ERROR_NO_PGP_DATA_FOUND,
}

// micalgs represent hash algorithms for signatures. These are ignored by many
// email clients, but can be used as an additional verification so are sent.
// Both gpgmail and pgpmail implementations in aerc check for matching micalgs
var micalgs = map[int]string{
	1:  "pgp-md5",
	2:  "pgp-sha1",
	3:  "pgp-ripemd160",
	8:  "pgp-sha256",
	9:  "pgp-sha384",
	10: "pgp-sha512",
	11: "pgp-sha224",
}

func logger(s string) {
	var (
		logOut io.Writer
		logger *log.Logger
	)
	if !isatty.IsTerminal(os.Stdout.Fd()) {
		logOut = os.Stdout
	} else {
		logOut = ioutil.Discard
		os.Stdout, _ = os.Open(os.DevNull)
	}
	logger = log.New(logOut, "", log.LstdFlags)
	logger.Println(s)
}