const NUM_DATA_POINTS = 30;
let _seed = 1234;

// Create a set of data with predicatable "randomness"
export function getData(
  start = [100, 100, 100, 100],
  variance = 2,
  offset = 0,
  length = NUM_DATA_POINTS,
  seed = _seed,
) {
  // Vary the datum by a random proportion of the variance +ve or -ve
  const vary = (n: number) =>
    Math.max(0, n + variance * random() * 2 - variance);

  _seed = seed;
  const data: Array<{
    year: number;
    one: number;
    two: number;
    three: number;
    four: number;
    five: number;
  }> = [
    {
      year: new Date().getFullYear() - NUM_DATA_POINTS,
      one: start[0],
      two: start[1],
      three: start[2],
      four: start[3],
      five: start[4],
    },
  ];
  for (let i = 1; i < NUM_DATA_POINTS + offset; i++) {
    data.push({
      year: new Date().getFullYear() - NUM_DATA_POINTS + i,
      one: vary(data[i - 1].one),
      two: vary(data[i - 1].two),
      three: vary(data[i - 1].three),
      four: vary(data[i - 1].four),
      five: vary(data[i - 1].five),
    });
  }
  return data.slice(offset - (length - NUM_DATA_POINTS));
}

export function random() {
  _seed = (_seed * 16807) % 2147483647;
  return (_seed - 1) / 2147483646;
}