export let re2 = /^(?:([-+]?(?:\d+|\d+\.\d+))\s*,\s*)?([-+]?(?:\d+|\d+\.\d+))(?:\s*\.\.(\.?)\s*([-+]?(?:\d+|\d+\.\d+)))?$/;
export let re = /^([-+]?(?:\d+|\d+\.\d+))(?:\s*,\s*([-+]?(?:\d+|\d+\.\d+)))?(?:\s*(\.\.\.?)\s*([-+]?(?:\d+|\d+\.\d+)))?$/;


function toArray(value) {
  if (Array.isArray(value)) {
    return value.slice();
  }
  if (typeof value !== "string") {
    return [ value ];
  }

  var matched = re.exec(value.trim());

  if (!matched) {
    return [];
  }

  let [ _, first, second, dots, last ] = matched;

  first = +first;

  if (typeof last === "undefined") {
    return [ first ];
  }

  last = +last;

  let a = [];
  let step = (typeof second !== "undefined") ? (+second - first) : (first < last) ? 1 : -1;

  // console.log(first, step, last);

  let x = first;

  if (dots === "...") {
    if (0 < step) {
      while (x < last) {
        a.push(x);
        x += step;
      }
    } else if (step < 0) {
      while (x > last) {
        a.push(x);
        x += step;
      }
    }
  } else {
    if (0 < step) {
      while (x <= last) {
        a.push(x);
        x += step;
      }
    } else if (step < 0) {
      while (x >= last) {
        a.push(x);
        x += step;
      }
    }
  }

  return a;
}


function test(str) {
  let result = toArray(str);

  console.log(str, result);

  // let matched = re.exec(str);
  //
  // if (!matched) {
  //   return;
  // }
  //
  // let [ _, first, second, dots, last ] = matched;
  //
  // console.log(`first: ${first}`);
  // console.log(`second: ${second}`);
  // console.log(`last: ${last}`);
  // console.log(`dots: ${dots}`);
  // console.log("=======================");
}

test("1");
test("1..20");
test("1...20");
test("0, 2..20");
test("0, 2...20");
test("0, -2..20");
test("0, 0..20");
test("0, 1");