package ledger

import (
	"encoding/binary"
	"fmt"

	"github.com/golang/protobuf/proto"
	"github.com/pkg/errors"
)

func EncodeUint64(number uint64) []byte {
	bytes := make([]byte, 8)
	binary.BigEndian.PutUint64(bytes, number)
	startingIndex := 0
	size := 0
	for i, b := range bytes {
		if b != 0x00 {
			startingIndex = i
			size = 8 - i
			break
		}
	}
	sizeBytes := proto.EncodeVarint(uint64(size))
	if len(sizeBytes) > 1 {
		panic(fmt.Errorf("[]sizeBytes should not be more than one byte because the max number it needs to hold is 8. size=%d", size))
	}
	encodedBytes := make([]byte, size+1)
	encodedBytes[0] = sizeBytes[0]
	copy(encodedBytes[1:], bytes[startingIndex:])
	return encodedBytes
}

func DecodeUint64(bytes []byte) (uint64, int, error) {
	s, numBytes := proto.DecodeVarint(bytes)

	switch {
	case numBytes != 1:
		return 0, 0, errors.Errorf("number of consumed bytes from DecodeVarint is invalid, expected 1, but got %d", numBytes)
	case s > 8:
		return 0, 0, errors.Errorf("decoded size from DecodeVarint is invalid, expected <=8, but got %d", s)
	case int(s) > len(bytes)-1:
		return 0, 0, errors.Errorf("decoded size (%d) from DecodeVarint is more than available bytes (%d)", s, len(bytes)-1)
	default:
		// no error
		size := int(s)
		decodedBytes := make([]byte, 8)
		copy(decodedBytes[8-size:], bytes[1:size+1])
		numBytesConsumed := size + 1
		return binary.BigEndian.Uint64(decodedBytes), numBytesConsumed, nil
	}
}