import { surroundingAgent } from '../host-defined/engine.mts';
import {
  Descriptor,
  Value,
  NumberValue,
  type Arguments,
} from '../value.mts';
import { Q, X, type ValueEvaluator } from '../completion.mts';
import { bootstrapPrototype } from './bootstrap.mts';
import {
  CreateBuiltinFunction,
  ToNumber,
  F, R,
  Realm,
  RequireObjectCoercible,
  GetIterator,
  IteratorStepValue,
  IteratorClose,
} from '#self';

/** https://tc39.es/ecma262/#sec-math.abs */
function* Math_abs([x = Value.undefined]: Arguments): ValueEvaluator {
  const n = Q(yield* ToNumber(x));
  if (n.isNaN()) {
    return n;
  } else if (Object.is(R(n), -0)) {
    return F(+0);
  } else if (n.isInfinity()) {
    return F(Infinity);
  }

  if (R(n) < 0) {
    return F(-R(n));
  }
  return n;
}

/** https://tc39.es/ecma262/#sec-math.acos */
function* Math_acos([x = Value.undefined]: Arguments): ValueEvaluator {
  const n = Q(yield* ToNumber(x));
  if (n.isNaN()) {
    return n;
  } else if (R(n) > 1) {
    return F(NaN);
  } else if (R(n) < -1) {
    return F(NaN);
  } else if (R(n) === 1) {
    return F(+0);
  }

  return F(Math.acos(R(n)));
}

/** https://tc39.es/ecma262/#sec-math.pow */
function* Math_pow([base = Value.undefined, exponent = Value.undefined]: Arguments): ValueEvaluator {
  // 1. Set base to ? ToNumber(base).
  base = Q(yield* ToNumber(base));
  // 2. Set exponent to ? ToNumber(exponent).
  exponent = Q(yield* ToNumber(exponent));
  // 3. Return ! Number::exponentiate(base, exponent).
  return X(NumberValue.exponentiate(base, exponent));
}

/** @param {bigint} h */
function fmix64(h: bigint) {
  h ^= h >> 33n;
  h *= 0xFF51AFD7ED558CCDn;
  h ^= h >> 33n;
  h *= 0xC4CEB9FE1A85EC53n;
  h ^= h >> 33n;
  return h;
}

const floatView = new Float64Array(1);
const big64View = new BigUint64Array(floatView.buffer);
/** https://tc39.es/ecma262/#sec-math.random */
function Math_random() {
  const realm = surroundingAgent.currentRealmRecord;
  if (realm.randomState === undefined) {
    const seed = realm.HostDefined.randomSeed
      ? BigInt(X(realm.HostDefined.randomSeed()))
      : BigInt(Math.round(Math.random() * (2 ** 32)));
    realm.randomState = new BigUint64Array([
      fmix64(BigInt.asUintN(64, seed)),
      fmix64(BigInt.asUintN(64, ~seed)),
    ]);
  }
  const s = realm.randomState;

  // XorShift128+
  let s1 = s[0];
  const s0 = s[1];
  s[0] = s0;
  s1 ^= s1 << 23n;
  s1 ^= s1 >> 17n;
  s1 ^= s0;
  s1 ^= s0 >> 26n;
  s[1] = s1;

  // Convert to double in [0, 1) range
  big64View[0] = (s0 >> 12n) | 0x3FF0000000000000n;
  const result = floatView[0] - 1;
  return F(result);
}

/** https://tc39.es/ecma262/#sec-math.sumprecise */
function* Math_sumPrecise([items = Value.undefined]: Arguments): ValueEvaluator {
  Q(RequireObjectCoercible(items));
  const iteratorRecord = Q(yield* GetIterator(items, 'sync'));
  let state: 'minus-zero' | 'not-a-number' | 'minus-infinity' | 'plus-infinity' | 'finite' = 'minus-zero';
  const sums: number[] = [];
  let count = 0;
  let next: 'not-started' | 'done' | Value = 'not-started';
  while (next !== 'done') {
    next = Q(yield* IteratorStepValue(iteratorRecord));
    if (next !== 'done') {
      if (count >= 2 ** 53 - 1) {
        const error = surroundingAgent.Throw('RangeError', 'OutOfRange', '');
        return Q(yield* IteratorClose(iteratorRecord, error));
      }
      if (!(next instanceof NumberValue)) {
        const error = surroundingAgent.Throw('TypeError', 'NotANumber', next);
        return Q(yield* IteratorClose(iteratorRecord, error));
      }
      const n = R(next);
      if (state !== 'not-a-number') {
        if (Number.isNaN(n)) {
          state = 'not-a-number';
        } else if (n === Infinity) {
          if (state === 'minus-infinity') {
            state = 'not-a-number';
          } else {
            state = 'plus-infinity';
          }
        } else if (n === -Infinity) {
          if (state === 'plus-infinity') {
            state = 'not-a-number';
          } else {
            state = 'minus-infinity';
          }
        } else if (!Object.is(n, -0) && (state === 'minus-zero' || state === 'finite')) {
          state = 'finite';
          sums.push(n);
        }
      }
      count += 1;
    }
  }
  if (state === 'not-a-number') {
    return F(NaN);
  }
  if (state === 'plus-infinity') {
    return F(Infinity);
  }
  if (state === 'minus-infinity') {
    return F(-Infinity);
  }
  if (state === 'minus-zero') {
    return F(-0);
  }
  return F(sum(sums));

  function sum(items: number[]) {
    if ('sumPrecise' in Math) {
      // @ts-expect-error
      return Math.sumPrecise(items);
    }
    const fractional_parts: number[] = [];
    let whole_part_sum = 0n;
    items.forEach((n) => {
      const whole_num = Math.trunc(n);
      fractional_parts.push(n - whole_num);
      whole_part_sum += BigInt(whole_num);
    });
    const fractional_parts_as_hex = fractional_parts.map((n) => n.toString(32));

    const fractional: number[] = [];
    for (const fractional_str of fractional_parts_as_hex) {
      const neg = fractional_str[0] === '-';
      const prefix = neg ? 3 : 2; // -0.xxx or 0.xxx
      for (let index = prefix; index < fractional_str.length; index += 1) {
        fractional[index - prefix] ??= 0;
        if (neg) {
          fractional[index - prefix] -= parseInt(fractional_str[index], 32);
        } else {
          fractional[index - prefix] += parseInt(fractional_str[index], 32);
        }
      }
    }
    for (let index = fractional.length - 1; index >= 0; index -= 1) {
      const element = fractional[index];
      if (element >= 32) {
        fractional[index] = element % 32;
        fractional[index - 1] ??= 0;
        fractional[index - 1] += Math.floor(element / 32);
      }
      if (element < 0) {
        fractional[index] = 32 + element;
        fractional[index - 1] ??= 0;
        fractional[index - 1] -= 1;
      }
    }
    const fractional_part = fractional.reduceRight((acc, digit, index) => acc + digit * 32 ** -(index + 1), 0);
    if (fractional[-1]) {
      whole_part_sum += BigInt(fractional[-1]);
    }
    return Number(whole_part_sum) + fractional_part;
  }
}

/** https://tc39.es/ecma262/#sec-math-object */
export function bootstrapMath(realmRec: Realm) {
  /** https://tc39.es/ecma262/#sec-value-properties-of-the-math-object */
  const readonly = { Writable: Value.false, Configurable: Value.false };

  // @@toStringTag is handled in the bootstrapPrototype() call.
  const mathObj = bootstrapPrototype(realmRec, [
    ['E', F(2.718281828459045), undefined, readonly],
    ['LN10', F(2.302585092994046), undefined, readonly],
    ['LN2', F(0.6931471805599453), undefined, readonly],
    ['LOG10E', F(0.4342944819032518), undefined, readonly],
    ['LOG2E', F(1.4426950408889634), undefined, readonly],
    ['PI', F(3.141592653589793), undefined, readonly],
    ['SQRT1_2', F(0.7071067811865476), undefined, readonly],
    ['SQRT2', F(1.4142135623730951), undefined, readonly],
    ['abs', Math_abs, 1],
    ['acos', Math_acos, 1],
    ['pow', Math_pow, 2],
    ['random', Math_random, 0],
    ['sumPrecise', Math_sumPrecise, 1],
  ], realmRec.Intrinsics['%Object.prototype%'], 'Math');

  /** https://tc39.es/ecma262/#sec-function-properties-of-the-math-object */

  ([
    ['acosh', 1],
    ['asin', 1],
    ['asinh', 1],
    ['atan', 1],
    ['atanh', 1],
    ['atan2', 2],
    ['cbrt', 1],
    ['ceil', 1],
    ['clz32', 1],
    ['cos', 1],
    ['cosh', 1],
    ['exp', 1],
    ['expm1', 1],
    ['floor', 1],
    ['fround', 1],
    ['hypot', 2],
    ['imul', 2],
    ['log', 1],
    ['log1p', 1],
    ['log10', 1],
    ['log2', 1],
    ['max', 2],
    ['min', 2],
    ['round', 1],
    ['sign', 1],
    ['sin', 1],
    ['sinh', 1],
    ['sqrt', 1],
    ['tan', 1],
    ['tanh', 1],
    ['trunc', 1],
  ] as const).forEach(([name, length]) => {
    // TODO(18): Math
    /** https://tc39.es/ecma262/#sec-function-properties-of-the-math-object */
    const method = function* method(args: Arguments): ValueEvaluator {
      const nextArgs: number[] = [];
      for (let i = 0; i < args.length; i += 1) {
        nextArgs[i] = R(Q(yield* ToNumber(args[i]!)));
      }
      // we're calling host Math functions here.
      return F((Math[name] as (...args: unknown[]) => number)(...nextArgs));
    };
    const func = CreateBuiltinFunction(method, length, Value(name), [], realmRec);
    X(mathObj.DefineOwnProperty(Value(name), Descriptor({
      Value: func,
      Writable: Value.true,
      Enumerable: Value.false,
      Configurable: Value.true,
    })));
  });

  realmRec.Intrinsics['%Math%'] = mathObj;
}