package azblob

import (

	"errors"

	"fmt"

	"io"

	"strconv"

)

// httpRange defines a range of bytes within an HTTP resource, starting at offset and

// ending at offset+count. A zero-value httpRange indicates the entire resource. An httpRange

// which has an offset but na zero value count indicates from the offset to the resource's end.

type httpRange struct {

	offset int64

	count  int64

}

func (r httpRange) pointers() *string {

	if r.offset == 0 && r.count == CountToEnd { // Do common case first for performance

		return nil // No specified range

	}

	endOffset := "" // if count == CountToEnd (0)

	if r.count > 0 {

		endOffset = strconv.FormatInt((r.offset+r.count)-1, 10)

	}

	dataRange := fmt.Sprintf("bytes=%v-%s", r.offset, endOffset)

	return &dataRange

}

////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////

func validateSeekableStreamAt0AndGetCount(body io.ReadSeeker) (int64, error) {

	if body == nil { // nil body's are "logically" seekable to 0 and are 0 bytes long

		return 0, nil

	}

	err := validateSeekableStreamAt0(body)

	if err != nil {

		return 0, err

	}

	count, err := body.Seek(0, io.SeekEnd)

	if err != nil {

		return 0, errors.New("body stream must be seekable")

	}

	body.Seek(0, io.SeekStart)

	return count, nil

}

// return an error if body is not a valid seekable stream at 0

func validateSeekableStreamAt0(body io.ReadSeeker) error {

	if body == nil { // nil body's are "logically" seekable to 0

		return nil

	}

	if pos, err := body.Seek(0, io.SeekCurrent); pos != 0 || err != nil {

		// Help detect programmer error

		if err != nil {

			return errors.New("body stream must be seekable")

		}

		return errors.New("body stream must be set to position 0")

	}

	return nil

}