package ssh

import (
	"crypto/rand"
	"crypto/rsa"
	"crypto/x509"
	"encoding/binary"
	"encoding/pem"
	"fmt"

	"golang.org/x/crypto/ssh"
)

func signerFromBlock(block *pem.Block) (ssh.Signer, error) {
	var key interface{}
	var err error
	switch block.Type {
	case "RSA PRIVATE KEY":
		key, err = x509.ParsePKCS1PrivateKey(block.Bytes)
	case "EC PRIVATE KEY":
		key, err = x509.ParseECPrivateKey(block.Bytes)
	case "DSA PRIVATE KEY":
		key, err = ssh.ParseDSAPrivateKey(block.Bytes)
	default:
		return nil, fmt.Errorf("unsupported key type %q", block.Type)
	}
	if err != nil {
		return nil, err
	}
	signer, err := ssh.NewSignerFromKey(key)
	if err != nil {
		return nil, err
	}
	return signer, nil
}

func decodePemBlocks(pemData []byte) []*pem.Block {
	var blocks []*pem.Block
	var block *pem.Block
	for {
		block, pemData = pem.Decode(pemData)
		if block == nil {
			return blocks
		}
		blocks = append(blocks, block)
	}
}

func generateSigner() (ssh.Signer, error) {
	key, err := rsa.GenerateKey(rand.Reader, 768)
	if err != nil {
		return nil, err
	}
	return ssh.NewSignerFromKey(key)
}

func parsePtyRequest(s []byte) (pty Pty, ok bool) {
	term, s, ok := parseString(s)
	if !ok {
		return
	}
	width32, s, ok := parseUint32(s)
	if width32 < 1 {
		ok = false
	}
	if !ok {
		return
	}
	height32, _, ok := parseUint32(s)
	if height32 < 1 {
		ok = false
	}
	if !ok {
		return
	}
	pty = Pty{
		Term: term,
		Window: Window{
			Width:  int(width32),
			Height: int(height32),
		},
	}
	return
}

func parseWinchRequest(s []byte) (win Window, ok bool) {
	width32, s, ok := parseUint32(s)
	if width32 < 1 {
		ok = false
	}
	if !ok {
		return
	}
	height32, _, ok := parseUint32(s)
	if height32 < 1 {
		ok = false
	}
	if !ok {
		return
	}
	win = Window{
		Width:  int(width32),
		Height: int(height32),
	}
	return
}

func parseString(in []byte) (out string, rest []byte, ok bool) {
	if len(in) < 4 {
		return
	}
	length := binary.BigEndian.Uint32(in)
	if uint32(len(in)) < 4+length {
		return
	}
	out = string(in[4 : 4+length])
	rest = in[4+length:]
	ok = true
	return
}

func parseUint32(in []byte) (uint32, []byte, bool) {
	if len(in) < 4 {
		return 0, nil, false
	}
	return binary.BigEndian.Uint32(in), in[4:], true
}