/*
Copyright 2020 SAP SE

Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at

    http://www.apache.org/licenses/LICENSE-2.0

Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
*/

package encoding

import (
	"encoding/binary"
	"io"
	"math"

	"github.com/SAP/go-hdb/internal/unicode"
	"golang.org/x/text/transform"
)

const readScratchSize = 512 // used for skip as well - size not too small!

// Decoder decodes hdb protocol datatypes an basis of an io.Reader.
type Decoder struct {
	rd  io.Reader
	err error
	b   [readScratchSize]byte // scratch buffer
	tr  transform.Transformer
	cnt int
	dfv int
}

// NewDecoder creates a new Decoder instance based on an io.Reader.
func NewDecoder(rd io.Reader) *Decoder {
	return &Decoder{
		rd: rd,
		tr: unicode.Cesu8ToUtf8Transformer,
	}
}

// Dfv returns the data format version.
func (d *Decoder) Dfv() int {
	return d.dfv
}

// SetDfv sets the data format version.
func (d *Decoder) SetDfv(dfv int) {
	d.dfv = dfv
}

// ResetCnt resets the byte read counter.
func (d *Decoder) ResetCnt() {
	d.cnt = 0
}

// Cnt returns the value of the byte read counter.
func (d *Decoder) Cnt() int {
	return d.cnt
}

// Error returns the reader error.
func (d *Decoder) Error() error {
	return d.err
}

// ResetError return and resets reader error.
func (d *Decoder) ResetError() error {
	err := d.err
	d.err = nil
	return err
}

// Skip skips cnt bytes from reading.
func (d *Decoder) Skip(cnt int) {
	var n int
	for n < cnt {
		if d.err != nil {
			return
		}
		to := cnt - n
		if to > readScratchSize {
			to = readScratchSize
		}
		var m int
		m, d.err = io.ReadFull(d.rd, d.b[:to])
		n += m
		d.cnt += m
	}
}

// Byte reads and returns a byte.
func (d *Decoder) Byte() byte { // ReadB as sig differs from ReadByte (vet issues)
	if d.err != nil {
		return 0
	}
	var n int
	n, d.err = io.ReadFull(d.rd, d.b[:1])
	d.cnt += n
	if d.err != nil {
		return 0
	}
	return byte(d.b[0])
}

// Bytes reads and returns a byte slice.
func (d *Decoder) Bytes(p []byte) {
	if d.err != nil {
		return
	}
	var n int
	n, d.err = io.ReadFull(d.rd, p)
	d.cnt += n
}

// Bool reads and returns a boolean.
func (d *Decoder) Bool() bool {
	if d.err != nil {
		return false
	}
	return d.Byte() != 0
}

// Int8 reads and returns an int8.
func (d *Decoder) Int8() int8 {
	return int8(d.Byte())
}

// Int16 reads and returns an int16.
func (d *Decoder) Int16() int16 {
	if d.err != nil {
		return 0
	}
	var n int
	n, d.err = io.ReadFull(d.rd, d.b[:2])
	d.cnt += n
	if d.err != nil {
		return 0
	}
	return int16(binary.LittleEndian.Uint16(d.b[:2]))
}

// Uint16 reads and returns an uint16.
func (d *Decoder) Uint16() uint16 {
	if d.err != nil {
		return 0
	}
	var n int
	n, d.err = io.ReadFull(d.rd, d.b[:2])
	d.cnt += n
	if d.err != nil {
		return 0
	}
	return binary.LittleEndian.Uint16(d.b[:2])
}

// Int32 reads and returns an int32.
func (d *Decoder) Int32() int32 {
	if d.err != nil {
		return 0
	}
	var n int
	n, d.err = io.ReadFull(d.rd, d.b[:4])
	d.cnt += n
	if d.err != nil {
		return 0
	}
	return int32(binary.LittleEndian.Uint32(d.b[:4]))
}

// Uint32 reads and returns an uint32.
func (d *Decoder) Uint32() uint32 {
	if d.err != nil {
		return 0
	}
	var n int
	n, d.err = io.ReadFull(d.rd, d.b[:4])
	d.cnt += n
	if d.err != nil {
		return 0
	}
	return binary.LittleEndian.Uint32(d.b[:4])
}

// Uint32ByteOrder reads and returns an uint32 in given byte order.
func (d *Decoder) Uint32ByteOrder(byteOrder binary.ByteOrder) uint32 {
	if d.err != nil {
		return 0
	}
	var n int
	n, d.err = io.ReadFull(d.rd, d.b[:4])
	d.cnt += n
	if d.err != nil {
		return 0
	}
	return byteOrder.Uint32(d.b[:4])
}

// Int64 reads and returns an int64.
func (d *Decoder) Int64() int64 {
	if d.err != nil {
		return 0
	}
	var n int
	n, d.err = io.ReadFull(d.rd, d.b[:8])
	d.cnt += n
	if d.err != nil {
		return 0
	}
	return int64(binary.LittleEndian.Uint64(d.b[:8]))
}

// Uint64 reads and returns an uint64.
func (d *Decoder) Uint64() uint64 {
	if d.err != nil {
		return 0
	}
	var n int
	n, d.err = io.ReadFull(d.rd, d.b[:8])
	d.cnt += n
	if d.err != nil {
		return 0
	}
	return binary.LittleEndian.Uint64(d.b[:8])
}

// Float32 reads and returns a float32.
func (d *Decoder) Float32() float32 {
	if d.err != nil {
		return 0
	}
	var n int
	n, d.err = io.ReadFull(d.rd, d.b[:4])
	d.cnt += n
	if d.err != nil {
		return 0
	}
	bits := binary.LittleEndian.Uint32(d.b[:4])
	return math.Float32frombits(bits)
}

// Float64 reads and returns a float64.
func (d *Decoder) Float64() float64 {
	if d.err != nil {
		return 0
	}
	var n int
	n, d.err = io.ReadFull(d.rd, d.b[:8])
	d.cnt += n
	if d.err != nil {
		return 0
	}
	bits := binary.LittleEndian.Uint64(d.b[:8])
	return math.Float64frombits(bits)
}

// CESU8Bytes reads a size CESU-8 encoded byte sequence and returns an UTF-8 byte slice.
func (d *Decoder) CESU8Bytes(size int) []byte {
	if d.err != nil {
		return nil
	}
	p := make([]byte, size)
	var n int
	n, d.err = io.ReadFull(d.rd, p)
	d.cnt += n
	if d.err != nil {
		return nil
	}
	d.tr.Reset()
	if n, _, d.err = d.tr.Transform(p, p, true); d.err != nil { // inplace transformation
		return nil
	}
	return p[:n]
}

// // ShortCESU8Bytes reads a CESU-8 encoded byte sequence and returns an UTF-8 byte slice.
// // Size is encoded in one byte.
// func (d *Decoder) ShortCESU8Bytes() ([]byte, int) {
// 	size := d.Byte()
// 	return d.CESU8Bytes(int(size)), int(size)
// }

// // ShortCESU8String reads a CESU-8 encoded byte sequence and returns an UTF-8 string.
// // Size is encoded in one byte.
// func (d *Decoder) ShortCESU8Bytes() (string, int) {
// 	b, n := d.ShortCESU8Bytes()
// 	return b, n
// }

// // ShortBytes reads a byte sequence and returns a byte slice.
// // Size is encoded in one byte.
// func (d *Decoder) ShortBytes() ([]byte, int) {
// 	size := d.Byte()
// 	b := make([]byte, size)
// 	d.Bytes(b)
// 	return b
// }