const IsNanError = TypeError('resulted in NaN');
const FailedToConvergeError = Error('failed to converge');
const InvalidInputsError = Error('invalid inputs');

export default async function GoalSeek(options) {
  const {
    fn,
    fnParams,
    percentTolerance,
    customToleranceFn,
    maxIterations,
    maxStep,
    goal,
    independentVariableIdx,
  } = options;
  if (typeof customToleranceFn !== 'function') {
    if (!percentTolerance) {
      throw InvalidInputsError;
    }
  }
  let g;
  let y;
  let oldY = 0;
  let oldGuess = fnParams[independentVariableIdx];
  let newGuess;
  let res;
  let max;
  let min;
  const absoluteTolerance = ((percentTolerance || 0) / 100) * goal;
  
  async function getMin(minGuest) {
    let copyParams = [...fnParams]
    copyParams[independentVariableIdx] = minGuest
    res = await fn(...copyParams);
    if (res > goal) {
      minGuest -= oldGuess / 2;
      await getMin(minGuest);
    }
    return minGuest;
  }

  async function getMax(maxGuest) {
    let copyParams = [...fnParams]
    copyParams[independentVariableIdx] = maxGuest
    res = await fn(...copyParams);
    if (res < goal) {
      maxGuest += oldGuess / 2;
      await getMax(maxGuest);
    }
    return maxGuest;
  }
  // iterate through the guesses
  for (let i = 0; i < maxIterations; i++) {
    // define the root of the function as the error
    res = await fn(...fnParams);
    y = res - goal;
    if (isNaN(y)) throw IsNanError;
    // 判断是否满足条件
    if (typeof customToleranceFn !== 'function') {
      if (Math.abs(y) <= Math.abs(absoluteTolerance)) return fnParams[independentVariableIdx];
    } else {
      if (customToleranceFn(res)) return fnParams[independentVariableIdx];
    }
    // 获取要改变的变量
    oldGuess = fnParams[independentVariableIdx];

    // newGuess = oldGuess + y;
    // if (Math.abs(newGuess - oldGuess) > maxStep) {
    //   if (newGuess > oldGuess) {
    //     newGuess = oldGuess + maxStep;
    //   } else {
    //     newGuess = oldGuess - maxStep;
    //   }
    // }
    // 获取最大值和最小值
    if (y > 0) {
      max = oldGuess;
      if (!min) {
        min = await getMin(oldGuess / 2);
      }
    } else {
      min = oldGuess;
      if (!max) {
        max = await getMax(oldGuess * 2);
      }
    }
    // if(oldY) {
    //   if(y > oldY) {

    //   }
    // }
    // oldY = y;
    // 利用二分法查询
    newGuess = (min + max) / 2;
    fnParams[independentVariableIdx] = newGuess;
  }
  // done with iterations, and we failed to converge
  throw FailedToConvergeError;
}

// const fn = (x, y) => x / y;
// const fnParams = [2037375, 15897178];
// const customToleranceFn = (x) => {
//   return x < 1;
// };

// try {
//   const result = goalSeek({
//     fn,
//     fnParams,
//     customToleranceFn,
//     maxIterations: 1000,
//     maxStep: 0.01,
//     goal: 0.15,
//     independentVariableIdx: 0,
//   });

//   console.log(`result: ${result}`);
// } catch (e) {
//   console.log("error", e);
// }