const common = require('./common')

function hasRel(x) {
  return x && x.rel;
}

function intoRels (acc, x) {
  function splitRel (rel) {
    acc[rel] = xtend(x, { rel: rel });
  }

  x.rel.split(/\s+/).forEach(splitRel);

  return acc;
}

function createObjects (acc, p) {
  // rel="next" => 1: rel 2: next
  var m = p.match(/\s*(.+)\s*=\s*"?([^"]+)"?/)
  if (m) acc[m[1]] = m[2];
  return acc;
}

var hasOwnProperty = Object.prototype.hasOwnProperty;

function extend() {
    var target = {}

    for (var i = 0; i < arguments.length; i++) {
        var source = arguments[i]

        for (var key in source) {
            if (hasOwnProperty.call(source, key)) {
                target[key] = source[key]
            }
        }
    }

    return target
}

function parseLink(link) {
  try {
    var m         =  link.match(/<?([^>]*)>(.*)/)
      , linkUrl   =  m[1]
      , parts     =  m[2].split(';')
      , qry       =  new URL(linkUrl).searchParams;

    parts.shift();

    var info = parts
      .reduce(createObjects, {});
    
    info = extend(qry, info);
    info.url = linkUrl;
    return info;
  } catch (e) {
    return null;
  }
}

function parse(linkHeader) {
  return linkHeader.split(/,\s*</)
    .map(parseLink)
    .filter(hasRel)
    .reduce(intoRels, {});
}

exports.fetchPage = function(url) {
  return common.sendRequest({
    method: 'GET',
    url: url,
  }, true)
  .then(function(result) {
    return {
      data: result.data,
      links: parse(result.headers.link || ''),
      total: Number(result.headers.pagination_total || '0'),
    }
  })
}