import { isPromise } from "./rp.ts";

export function evalPromiseValues(vals: any[]): Promise<any[]> | any[] {
  const promises = [];
  const promiseResults = new Array(vals.length);
  for (let i = 0; i < vals.length; i++) {
    if (isPromise(vals[i])) {
      promises.push(
        (vals[i] as Promise<any>).then((v: any) => (promiseResults[i] = v)),
      );
    } else {
      promiseResults[i] = vals[i];
    }
  }
  if (promises.length === 0) {
    return promiseResults;
  }
  return Promise.all(promises).then(() => promiseResults);
}

/**
 * return the mid value among x, y, and z
 * @param x
 * @param y
 * @param z
 * @param compare
 * @returns {Promise.<*>}
 */
async function getPivot(
  x: any,
  y: any,
  z: any,
  compare: (a: any, b: any) => Promise<number>,
) {
  if ((await compare(x, y)) < 0) {
    if ((await compare(y, z)) < 0) {
      return y;
    }
    if ((await compare(z, x)) < 0) {
      return x;
    }
    return z;
  }
  if ((await compare(y, z)) > 0) {
    return y;
  }
  if ((await compare(z, x)) > 0) {
    return x;
  }
  return z;
}

/**
 * asynchronous quick sort
 * @param arr array to sort
 * @param compare asynchronous comparing function
 * @param left index where the range of elements to be sorted starts
 * @param right index where the range of elements to be sorted ends
 * @returns {Promise.<*>}
 */
export async function asyncQuickSort(
  arr: any[],
  compare: (a: any, b: any) => Promise<number>,
  left = 0,
  right = arr.length - 1,
) {
  if (left < right) {
    let i = left,
      j = right,
      tmp;
    const pivot = await getPivot(
      arr[i],
      arr[i + Math.floor((j - i) / 2)],
      arr[j],
      compare,
    );
    while (true) {
      while ((await compare(arr[i], pivot)) < 0) {
        i++;
      }
      while ((await compare(pivot, arr[j])) < 0) {
        j--;
      }
      if (i >= j) {
        break;
      }
      tmp = arr[i];
      arr[i] = arr[j];
      arr[j] = tmp;

      i++;
      j--;
    }
    await asyncQuickSort(arr, compare, left, i - 1);
    await asyncQuickSort(arr, compare, j + 1, right);
  }
  return arr;
}

/**
 * iterative async merge sort
 * @param arr tagged array of { val, idx } elements
 * @param compare async comparator returning <0, 0, or >0
 */
export async function asyncMergeSort(
  arr: { val: any; idx: number }[],
  compare: (
    a: { val: any; idx: number },
    b: { val: any; idx: number },
  ) => Promise<number>,
): Promise<void> {
  const n = arr.length;
  if (n <= 1) return;
  const work = new Array(n);

  for (let size = 1; size < n; size *= 2) {
    for (let left = 0; left < n; left += 2 * size) {
      const mid = Math.min(left + size, n);
      const right = Math.min(left + 2 * size, n);

      let i = left,
        j = mid,
        k = left;
      while (i < mid && j < right) {
        const cmp = await compare(arr[i], arr[j]);
        if (cmp <= 0) work[k++] = arr[i++];
        else work[k++] = arr[j++];
      }
      while (i < mid) work[k++] = arr[i++];
      while (j < right) work[k++] = arr[j++];
      for (let m = left; m < right; m++) arr[m] = work[m];
    }
  }
}