/*
Copyright 2017 Google Inc. All rights reserved.

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 s2

import (
	"encoding/binary"
	"io"
)

const (
	// encodingVersion is the current version of the encoding
	// format that is compatible with C++ and other S2 libraries.
	encodingVersion = int8(1)

	// encodingCompressedVersion is the current version of the
	// compressed format.
	encodingCompressedVersion = int8(4)
)

// encoder handles the specifics of encoding for S2 types.
type encoder struct {
	w   io.Writer // the real writer passed to Encode
	err error
}

func (e *encoder) writeUvarint(x uint64) {
	if e.err != nil {
		return
	}
	var buf [binary.MaxVarintLen64]byte
	n := binary.PutUvarint(buf[:], x)
	_, e.err = e.w.Write(buf[:n])
}

func (e *encoder) writeBool(x bool) {
	if e.err != nil {
		return
	}
	var val int8
	if x {
		val = 1
	}
	e.err = binary.Write(e.w, binary.LittleEndian, val)
}

func (e *encoder) writeInt8(x int8) {
	if e.err != nil {
		return
	}
	e.err = binary.Write(e.w, binary.LittleEndian, x)
}

func (e *encoder) writeInt16(x int16) {
	if e.err != nil {
		return
	}
	e.err = binary.Write(e.w, binary.LittleEndian, x)
}

func (e *encoder) writeInt32(x int32) {
	if e.err != nil {
		return
	}
	e.err = binary.Write(e.w, binary.LittleEndian, x)
}

func (e *encoder) writeInt64(x int64) {
	if e.err != nil {
		return
	}
	e.err = binary.Write(e.w, binary.LittleEndian, x)
}

func (e *encoder) writeUint8(x uint8) {
	if e.err != nil {
		return
	}
	_, e.err = e.w.Write([]byte{x})
}

func (e *encoder) writeUint32(x uint32) {
	if e.err != nil {
		return
	}
	e.err = binary.Write(e.w, binary.LittleEndian, x)
}

func (e *encoder) writeUint64(x uint64) {
	if e.err != nil {
		return
	}
	e.err = binary.Write(e.w, binary.LittleEndian, x)
}

func (e *encoder) writeFloat32(x float32) {
	if e.err != nil {
		return
	}
	e.err = binary.Write(e.w, binary.LittleEndian, x)
}

func (e *encoder) writeFloat64(x float64) {
	if e.err != nil {
		return
	}
	e.err = binary.Write(e.w, binary.LittleEndian, x)
}

type byteReader interface {
	io.Reader
	io.ByteReader
}

// byteReaderAdapter embellishes an io.Reader with a ReadByte method,
// so that it implements the io.ByteReader interface.
type byteReaderAdapter struct {
	io.Reader
}

func (b byteReaderAdapter) ReadByte() (byte, error) {
	buf := []byte{0}
	_, err := io.ReadFull(b, buf)
	return buf[0], err
}

func asByteReader(r io.Reader) byteReader {
	if br, ok := r.(byteReader); ok {
		return br
	}
	return byteReaderAdapter{r}
}

type decoder struct {
	r   byteReader // the real reader passed to Decode
	err error
}

func (d *decoder) readBool() (x bool) {
	if d.err != nil {
		return
	}
	var val int8
	d.err = binary.Read(d.r, binary.LittleEndian, &val)
	return val == 1
}

func (d *decoder) readInt8() (x int8) {
	if d.err != nil {
		return
	}
	d.err = binary.Read(d.r, binary.LittleEndian, &x)
	return
}

func (d *decoder) readInt16() (x int16) {
	if d.err != nil {
		return
	}
	d.err = binary.Read(d.r, binary.LittleEndian, &x)
	return
}

func (d *decoder) readInt32() (x int32) {
	if d.err != nil {
		return
	}
	d.err = binary.Read(d.r, binary.LittleEndian, &x)
	return
}

func (d *decoder) readInt64() (x int64) {
	if d.err != nil {
		return
	}
	d.err = binary.Read(d.r, binary.LittleEndian, &x)
	return
}

func (d *decoder) readUint8() (x uint8) {
	if d.err != nil {
		return
	}
	x, d.err = d.r.ReadByte()
	return
}

func (d *decoder) readUint32() (x uint32) {
	if d.err != nil {
		return
	}
	d.err = binary.Read(d.r, binary.LittleEndian, &x)
	return
}

func (d *decoder) readUint64() (x uint64) {
	if d.err != nil {
		return
	}
	d.err = binary.Read(d.r, binary.LittleEndian, &x)
	return
}

func (d *decoder) readFloat32() (x float32) {
	if d.err != nil {
		return
	}
	d.err = binary.Read(d.r, binary.LittleEndian, &x)
	return
}

func (d *decoder) readFloat64() (x float64) {
	if d.err != nil {
		return
	}
	d.err = binary.Read(d.r, binary.LittleEndian, &x)
	return
}

func (d *decoder) readUvarint() (x uint64) {
	if d.err != nil {
		return
	}
	x, d.err = binary.ReadUvarint(d.r)
	return
}
