package mysql

import (
	"bytes"
	"encoding/binary"
)

// parseHandshakeResponseHeader parses the common header of SSLRequest and HandshakeResponse41.
func parseHandshakeResponseHeader(packet *handshakeResponse41, data []byte) (parsedBytes int, err error) {
	// Ensure there are enough data to read:
	// http://dev.mysql.com/doc/internals/en/connection-phase-packets.html#packet-Protocol::SSLRequest
	if len(data) < 4+4+1+23 {
		return 0, ErrMalformPacket
	}

	offset := 0
	// capability
	capability := binary.LittleEndian.Uint32(data[:4])
	packet.Capability = capability
	offset += 4
	// skip max packet size
	offset += 4
	// charset, skip, if you want to use another charset, use set names
	packet.Collation = data[offset]
	offset++
	// skip reserved 23[00]
	offset += 23

	return offset, nil
}

// parseHandshakeResponseBody parse the HandshakeResponse (except the common header part).
func parseHandshakeResponseBody(packet *handshakeResponse41, data []byte, offset int) (err error) {
	defer func() {
		// Check malformat packet cause out of range is disgusting, but don't panic!
		if r := recover(); r != nil {
			err = ErrMalformPacket
		}
	}()
	// user name
	packet.User = string(data[offset : offset+bytes.IndexByte(data[offset:], 0)])
	offset += len(packet.User) + 1

	if packet.Capability&ClientPluginAuthLenencClientData > 0 {
		// MySQL client sets the wrong capability, it will set this bit even server doesn't
		// support ClientPluginAuthLenencClientData.
		// https://github.com/mysql/mysql-server/blob/5.7/sql-common/client.c#L3478
		num, null, off := parseLengthEncodedInt(data[offset:])
		offset += off
		if !null {
			packet.Auth = data[offset : offset+int(num)]
			offset += int(num)
		}
	} else if packet.Capability&ClientSecureConnection > 0 {
		// auth length and auth
		authLen := int(data[offset])
		offset++
		packet.Auth = data[offset : offset+authLen]
		offset += authLen
	} else {
		packet.Auth = data[offset : offset+bytes.IndexByte(data[offset:], 0)]
		offset += len(packet.Auth) + 1
	}

	if packet.Capability&ClientConnectWithDB > 0 {
		if len(data[offset:]) > 0 {
			idx := bytes.IndexByte(data[offset:], 0)
			packet.DBName = string(data[offset : offset+idx])
			offset = offset + idx + 1
		}
	}

	if packet.Capability&ClientPluginAuth > 0 {
		// TODO: Support mysql.ClientPluginAuth, skip it now
		idx := bytes.IndexByte(data[offset:], 0)
		offset = offset + idx + 1
	}

	if packet.Capability&ClientConnectAtts > 0 {
		if len(data[offset:]) == 0 {
			// Defend some ill-formated packet, connection attribute is not important and can be ignored.
			return nil
		}
	}

	return nil
}

func parseLengthEncodedInt(b []byte) (num uint64, isNull bool, n int) {
	switch b[0] {
	// 251: NULL
	case 0xfb:
		n = 1
		isNull = true
		return

	// 252: value of following 2
	case 0xfc:
		num = uint64(b[1]) | uint64(b[2])<<8
		n = 3
		return

	// 253: value of following 3
	case 0xfd:
		num = uint64(b[1]) | uint64(b[2])<<8 | uint64(b[3])<<16
		n = 4
		return

	// 254: value of following 8
	case 0xfe:
		num = uint64(b[1]) | uint64(b[2])<<8 | uint64(b[3])<<16 |
			uint64(b[4])<<24 | uint64(b[5])<<32 | uint64(b[6])<<40 |
			uint64(b[7])<<48 | uint64(b[8])<<56
		n = 9
		return
	}

	// 0-250: value of first byte
	num = uint64(b[0])
	n = 1
	return
}

func extractMysqlPayloadSize(header []byte) int {
	return int(uint32(header[0]) | uint32(header[1])<<8 | uint32(header[2])<<16)
}

func bytesToInt(contents []byte) int {
	return int(uint32(contents[0]) | uint32(contents[1])<<8 | uint32(contents[2])<<16 | uint32(contents[3])<<24)
}