import {
  LuaBuiltinFunction,
  LuaMultiRes,
  LuaRuntimeError,
  LuaTable,
} from "../runtime.ts";
import { isNegativeZero, isTaggedFloat, makeLuaFloat } from "../numeric.ts";
import { LuaPRNG } from "./prng.ts";

// One PRNG per module load, auto-seeded at startup
const prng = new LuaPRNG();

// Fast unwrap: avoids function call overhead for the common plain-number case
function untagNumber(x: any): number {
  if (typeof x === "number") return x;
  if (isTaggedFloat(x)) return x.value;
  return Number(x);
}

export const mathApi = new LuaTable({
  // math constants
  huge: 1 / 0,
  pi: Math.PI,

  // math.type(x) => "integer" | "float" | nil
  type: new LuaBuiltinFunction((_sf, x?: any) => {
    if (x === undefined) {
      throw new LuaRuntimeError(
        "bad argument #1 to 'math.type' (value expected)",
        _sf,
      );
    }
    if (isTaggedFloat(x)) {
      return "float";
    }
    if (typeof x === "number") {
      if (!Number.isFinite(x) || isNegativeZero(x)) {
        return "float";
      }
      return Number.isInteger(x) ? "integer" : "float";
    }
    if (typeof x === "bigint") {
      return "integer";
    }
    return null;
  }),

  /**
   * If the value x is representable as a Lua integer, returns an integer
   * with that value. Otherwise returns nil.
   * Strings are NOT accepted — only Lua number values.
   */
  tointeger: new LuaBuiltinFunction((_sf, x?: any) => {
    if (typeof x === "number") {
      return Number.isInteger(x) && isFinite(x) ? x : null;
    }
    if (isTaggedFloat(x)) {
      const n = x.value;
      return Number.isInteger(n) && isFinite(n) ? n : null;
    }
    if (typeof x === "string") {
      const n = untagNumber(x); // Number(x) coerces the string
      if (isNaN(n) || !isFinite(n) || !Number.isInteger(n)) return null;
      return n;
    }
    return null;
  }),

  /**
   * When called without arguments, returns a pseudo-random float with
   * uniform distribution in the range [0,1). When called with two
   * integers m and n, math.random returns a pseudo-random integer
   * with uniform distribution in the range [m, n]. The call
   * math.random(n), for a positive n, is equivalent to
   * math.random(1,n). The call math.random(0) produces an integer
   * with all bits (pseudo)random.
   */
  random: new LuaBuiltinFunction((_sf, m?: number, n?: number) => {
    if (m !== undefined) m = untagNumber(m);
    if (n !== undefined) n = untagNumber(n);
    try {
      return prng.random(m, n);
    } catch (e: any) {
      throw new LuaRuntimeError(e.message, _sf);
    }
  }),
  /**
   * Seeds the pseudo-random generator. With no arguments, uses a
   * time-based seed. Returns the two seed integers used (Lua 5.4 contract).
   */
  randomseed: new LuaBuiltinFunction((_sf, x?: number, y?: number) => {
    if (x !== undefined) x = untagNumber(x);
    if (y !== undefined) y = untagNumber(y);
    const [s1, s2] = prng.randomseed(x, y);
    return new LuaMultiRes([s1, s2]);
  }),

  // Basic functions
  abs: new LuaBuiltinFunction((_sf, x: number) => Math.abs(untagNumber(x))),
  ceil: new LuaBuiltinFunction((_sf, x: number) => Math.ceil(untagNumber(x))),
  floor: new LuaBuiltinFunction((_sf, x: number) => Math.floor(untagNumber(x))),
  max: new LuaBuiltinFunction((_sf, ...args: number[]) =>
    Math.max(...args.map(untagNumber))
  ),
  min: new LuaBuiltinFunction((_sf, ...args: number[]) =>
    Math.min(...args.map(untagNumber))
  ),

  // Rounding and remainder
  fmod: new LuaBuiltinFunction((_sf, x: number, y: number) =>
    untagNumber(x) % untagNumber(y)
  ),
  modf: new LuaBuiltinFunction((_sf, x: number) => {
    const xn = untagNumber(x);
    const int = Math.trunc(xn);
    // Guarantee that the `frac` part is always Lua float
    const frac = makeLuaFloat(xn - int);
    return new LuaMultiRes([int, frac]);
  }),

  // Returns m and e such that x = m * 2^e, 0.5 <= |m| < 1 (or m=0 when x=0).
  // e is an integer. Mirrors C99/Lua.
  // Special cases: frexp(0) = (0, 0); frexp(+-inf/nan) = (x, 0).
  frexp: new LuaBuiltinFunction((_sf, x: number) => {
    const xn = untagNumber(x);
    if (xn === 0 || !isFinite(xn) || isNaN(xn)) {
      return new LuaMultiRes([xn, 0]);
    }
    const abs = Math.abs(xn);
    let e = Math.floor(Math.log2(abs)) + 1;
    let m = xn / Math.pow(2, e);
    if (Math.abs(m) >= 1.0) {
      e += 1;
      m /= 2;
    }
    if (Math.abs(m) < 0.5) {
      e -= 1;
      m *= 2;
    }
    return new LuaMultiRes([m, e]);
  }),

  // Returns m * 2^e (the inverse of frexp).  Mirrors C99/Lua.
  ldexp: new LuaBuiltinFunction((_sf, m: number, e: number) =>
    untagNumber(m) * Math.pow(2, untagNumber(e))
  ),

  // Power and logarithms
  exp: new LuaBuiltinFunction((_sf, x: number) => Math.exp(untagNumber(x))),
  log: new LuaBuiltinFunction((_sf, x: number, base?: number) => {
    if (base === undefined) {
      return Math.log(untagNumber(x));
    }
    return Math.log(untagNumber(x)) / Math.log(untagNumber(base));
  }),
  // Power function (deprecated in Lua 5.4 but retained for compatibility)
  pow: new LuaBuiltinFunction((_sf, x: number, y: number) =>
    Math.pow(untagNumber(x), untagNumber(y))
  ),
  sqrt: new LuaBuiltinFunction((_sf, x: number) => Math.sqrt(untagNumber(x))),

  // Trigonometric functions
  cos: new LuaBuiltinFunction((_sf, x: number) => Math.cos(untagNumber(x))),
  sin: new LuaBuiltinFunction((_sf, x: number) => Math.sin(untagNumber(x))),
  tan: new LuaBuiltinFunction((_sf, x: number) => Math.tan(untagNumber(x))),
  acos: new LuaBuiltinFunction((_sf, x: number) => Math.acos(untagNumber(x))),
  asin: new LuaBuiltinFunction((_sf, x: number) => Math.asin(untagNumber(x))),
  atan: new LuaBuiltinFunction((_sf, y: number, x?: number) => {
    if (x === undefined) {
      return Math.atan(untagNumber(y));
    }
    return Math.atan2(untagNumber(y), untagNumber(x));
  }),

  // Hyperbolic functions (deprecated in Lua 5.4 but retained for compatibility)
  cosh: new LuaBuiltinFunction((_sf, x: number) => Math.cosh(untagNumber(x))),
  sinh: new LuaBuiltinFunction((_sf, x: number) => Math.sinh(untagNumber(x))),
  tanh: new LuaBuiltinFunction((_sf, x: number) => Math.tanh(untagNumber(x))),

  // Additional utility
  deg: new LuaBuiltinFunction((_sf, x: number) =>
    untagNumber(x) * 180 / Math.PI
  ),
  rad: new LuaBuiltinFunction((_sf, x: number) =>
    untagNumber(x) * Math.PI / 180
  ),
  ult: new LuaBuiltinFunction((_sf, m: number, n: number) => {
    return (untagNumber(m) >>> 0) < (untagNumber(n) >>> 0);
  }),

  // Keep the cosineSimilarity utility function
  cosineSimilarity: new LuaBuiltinFunction(
    (sf, vecA: LuaTable | number[], vecB: LuaTable | number[]) => {
      if (vecA instanceof LuaTable) {
        vecA = vecA.toJSArray();
      }
      if (vecB instanceof LuaTable) {
        vecB = vecB.toJSArray();
      }

      if (vecA.length !== vecB.length) {
        throw new LuaRuntimeError("Vectors must be of the same length", sf);
      }

      let dotProduct = 0;
      let normA = 0;
      let normB = 0;

      for (let i = 0; i < vecA.length; i++) {
        dotProduct += vecA[i] * vecB[i];
        normA += vecA[i] ** 2;
        normB += vecB[i] ** 2;
      }

      return dotProduct / (Math.sqrt(normA) * Math.sqrt(normB));
    },
  ),
});