package compress

import (
	"fmt"
	"github.com/DataDog/zstd"
)

// ZstdLevel compression level used by Zstd
const ZstdLevel = 1 // fastest

type noOp struct{}

func (n noOp) Name() string            { return "Noop" }
func (n noOp) CompressBound(l int) int { return l }
func (n noOp) Compress(dst, src []byte) (int, error) {
	if len(dst) < len(src) {
		return 0, fmt.Errorf("buffer too short: %d < %d", len(dst), len(src))
	}
	copy(dst, src)
	return len(src), nil
}
func (n noOp) Decompress(dst, src []byte) (int, error) {
	if len(dst) < len(src) {
		return 0, fmt.Errorf("buffer too short: %d < %d", len(dst), len(src))
	}
	copy(dst, src)
	return len(src), nil
}

// ZStandard implements Compressor interface using zstd library
type ZStandard struct {
	level int
}

// Name returns name of the algorithm Zstd
func (n ZStandard) Name() string { return "Zstd" }

// CompressBound max size of compressed data
func (n ZStandard) CompressBound(l int) int { return zstd.CompressBound(l) }

// Compress using Zstd
func (n ZStandard) Compress(dst, src []byte) (int, error) {
	d, err := zstd.CompressLevel(dst, src, n.level)
	if err != nil {
		return 0, err
	}
	if len(d) > 0 && len(dst) > 0 && &d[0] != &dst[0] {
		return 0, fmt.Errorf("buffer too short: %d < %d", cap(dst), cap(d))
	}
	return len(d), err
}

// Decompress using Zstd
func (n ZStandard) Decompress(dst, src []byte) (int, error) {
	d, err := zstd.Decompress(dst, src)
	if err != nil {
		return 0, err
	}
	if len(d) > 0 && len(dst) > 0 && &d[0] != &dst[0] {
		return 0, fmt.Errorf("buffer too short: %d < %d", len(dst), len(d))
	}
	return len(d), err
}