package client

// Paginate returns the correct starting and ending index for a paginated query,
// given that client provides a desired page and limit of objects and the handler
// provides the total number of objects. The start page is assumed to be 1-indexed.
// If the start page is invalid, non-positive values are returned signaling the
// request is invalid; it returns non-positive values if limit is non-positive and
// defLimit is negative.
func Paginate(numObjs, page, limit, defLimit int) (start, end int) {
	if page <= 0 {
		// invalid start page
		return -1, -1
	}

	// fallback to default limit if supplied limit is invalid
	if limit <= 0 {
		if defLimit < 0 {
			// invalid default limit
			return -1, -1
		}
		limit = defLimit
	}

	start = (page - 1) * limit
	end = limit + start

	if end >= numObjs {
		end = numObjs
	}

	if start >= numObjs {
		// page is out of bounds
		return -1, -1
	}

	return start, end
}