package zim

import (
	"io"

	"github.com/pkg/errors"
)

type UncompressedBlobReader struct {
	reader          *Reader
	blobStartOffset uint64
	blobEndOffset   uint64
	blobSize        int
	readOffset      uint64
}

// Size implements BlobReader.
func (r *UncompressedBlobReader) Size() (int64, error) {
	return int64(r.blobEndOffset - r.blobStartOffset), nil
}

// Close implements io.ReadCloser.
func (*UncompressedBlobReader) Close() error {
	return nil
}

// Read implements io.ReadCloser.
func (r *UncompressedBlobReader) Read(p []byte) (n int, err error) {
	len := len(p)
	remaining := int(r.blobEndOffset - (r.blobStartOffset + r.readOffset))
	if len > remaining {
		len = remaining
	}

	data := make([]byte, len)

	err = r.reader.readRange(int64(r.blobStartOffset+r.readOffset), data)
	if err != nil {
		return len, errors.WithStack(err)
	}

	r.readOffset += uint64(len)

	copy(p, data)

	if len == remaining {
		return len, io.EOF
	}

	return len, nil
}

func NewUncompressedBlobReader(reader *Reader, blobStartOffset, blobEndOffset uint64, blobSize int) *UncompressedBlobReader {
	return &UncompressedBlobReader{
		reader:          reader,
		blobStartOffset: blobStartOffset,
		blobEndOffset:   blobEndOffset,
		blobSize:        blobSize,
		readOffset:      0,
	}
}

var _ BlobReader = &UncompressedBlobReader{}