package codec

import "io"

// Decoder wraps an [io.Reader] and decodes data from it.
type Decoder struct {
	io.Reader
}

// ReadFull calls [io.ReadFull] on the reader.
func (this *Decoder) ReadFull(buffer []byte) (n int, err error) {
	return io.ReadFull(this, buffer)
}

// ReadByte decodes a single byte from the input reader.
func (this *Decoder) ReadByte() (value byte, n int, err error) {
	uncasted, n, err := this.ReadUint8()
	return byte(uncasted), n, err
}

// ReadInt8 decodes an 8-bit signed integer from the input reader.
func (this *Decoder) ReadInt8() (value int8, n int, err error) {
	uncasted, n, err := this.ReadUint8()
	return int8(uncasted), n, err
}

// ReadUint8 decodes an 8-bit unsigned integer from the input reader.
func (this *Decoder) ReadUint8() (value uint8, n int, err error) {
	buffer := [1]byte { }
	n, err = this.ReadFull(buffer[:])
	return uint8(buffer[0]), n, err
}

// ReadInt16 decodes an 16-bit signed integer from the input reader.
func (this *Decoder) ReadInt16() (value int16, n int, err error) {
	uncasted, n, err := this.ReadUint16()
	return int16(uncasted), n, err
}

// ReadUint16 decodes an 16-bit unsigned integer from the input reader.
func (this *Decoder) ReadUint16() (value uint16, n int, err error) {
	buffer := [2]byte { }
	n, err = this.ReadFull(buffer[:])
	return uint16(buffer[0]) << 8 |
		uint16(buffer[1]), n, err
}

// ReadInt32 decodes an 32-bit signed integer from the input reader.
func (this *Decoder) ReadInt32() (value int32, n int, err error) {
	uncasted, n, err := this.ReadUint32()
	return int32(uncasted), n, err
}

// ReadUint32 decodes an 32-bit unsigned integer from the input reader.
func (this *Decoder) ReadUint32() (value uint32, n int, err error) {
	buffer := [4]byte { }
	n, err = this.ReadFull(buffer[:])
	return uint32(buffer[0]) << 24 |
		uint32(buffer[1]) << 16 |
		uint32(buffer[2]) << 8 |
		uint32(buffer[3]), n, err
}

// ReadInt64 decodes an 64-bit signed integer from the input reader.
func (this *Decoder) ReadInt64() (value int64, n int, err error) {
	uncasted, n, err := this.ReadUint64()
	return int64(uncasted), n, err
}

// ReadUint64 decodes an 64-bit unsigned integer from the input reader.
func (this *Decoder) ReadUint64() (value uint64, n int, err error) {
	buffer := [8]byte { }
	n, err = this.ReadFull(buffer[:])
	return uint64(buffer[0]) << 56 |
		uint64(buffer[1]) << 48 |
		uint64(buffer[2]) << 48 |
		uint64(buffer[3]) << 32 |
		uint64(buffer[4]) << 24 |
		uint64(buffer[5]) << 16 |
		uint64(buffer[6]) << 8 |
		uint64(buffer[7]), n, err
}

// ReadGBEU decodes a growing unsigned integer of up to 64 bits from the input
// reader.
func (this *Decoder) ReadGBEU() (value uint64, n int, err error) {
	var fullValue uint64
	for {
		chunk, nn, err := this.ReadByte()
		if err != nil { return 0, n, err }
		n += nn
		
		fullValue *= 0x80
		fullValue += uint64(chunk & 0x7F)
		ccb := chunk >> 7
		if ccb == 0 {
			return fullValue, n, nil
		}
	}
}