'use strict';

const Promise = require("bluebird");
const bhttp = require("bhttp");
const debug = require("debug")("seekable:http");

function generateRangeHeader(start, end) {
    if (start != null && end != null) {
        return `bytes=${start}-${end}`;
    } else if (start != null && end == null) {
        return `bytes=${start}-`;
    } else if (start == null && end != null) {
        return `bytes=-${end}`;
    } else {
        return null;
    }
}

module.exports = function getHttpSeekable(targetUrl) {
    return {
        createReadStream: function createReadStream(start, end) {
            return Promise.try(() => {
                debug(`${start}-${end} -- ${targetUrl}`);

                return bhttp.get(targetUrl, {
                    stream: true,
                    headers: {
                        "range": generateRangeHeader(start, end) // FIXME: What if there is no range specified at all? Is `null` valid then?
                    }
                });
            });
        }
    }
};