export default {
  methods: {
    predicate() {
      var fields = [],
        n_fields = arguments.length,
        field,
        name,
        cmp;

      var default_cmp = function(a, b) {
          if (a == undefined) a = 0;
          if (b == undefined) b = 0;
          if (a === b) return 0;
          return a < b ? -1 : 1;
        },
        getCmpFunc = function(primer, reverse) {
          var dfc = default_cmp,
            // closer in scope
            cmp = default_cmp;
          if (primer) {
            cmp = function(a, b) {
              return dfc(primer(a), primer(b));
            };
          }
          if (reverse) {
            return function(a, b) {
              return -1 * cmp(a, b);
            };
          }
          return cmp;
        };

      // preprocess sorting options
      for (var i = 0; i < n_fields; i++) {
        field = arguments[i];
        if (typeof field === "string") {
          name = field;
          cmp = default_cmp;
        } else {
          name = field.name;
          cmp = getCmpFunc(field.primer, field.reverse);
        }
        fields.push({
          name: name,
          cmp: cmp
        });
      }

      // final comparison function
      return function(A, B) {
        var name, result;
        for (var i = 0; i < n_fields; i++) {
          result = 0;
          field = fields[i];
          name = field.name;

          result = field.cmp(A[name], B[name]);
          if (result !== 0) break;
        }
        return result;
      };
    }
  }
};