// an expression language

function run(code: string, ctx: { [name: string]: any } = {}): any {
  const tokens = lex(code);
  const tree = parse(tokens);
  const result = expr(tree, ctx);
  return result;
}

function expr(tree, ctx: { [name: string]: any } = {}): any {
  switch (tree.type) {
    case "int": return parseInt(tree.val);
    case "float": return parseFloat(tree.val);
    case "str": return tree.val.slice(1, -1);
    case "ident": 
      switch (tree.val) {
        case "true": return true;
        case "false": return false;
        case "null": return null;
        default: return Object.hasOwn(ctx, tree.val) && ctx[tree.val];
      }
  }
  
  if (tree.op) {
    if (tree.op.val === ".") {
      if (tree.cons[1].type !== "ident") throw "expected ident";
      const obj = expr(tree.cons[0], ctx);
      const idx = tree.cons[1].val;
      if (!Object.hasOwn(obj, idx)) throw `${idx} doesn't exist on object`;
      return obj[idx];
    }
    const op = ({
      "**": (a, b) => a ** b,
      "*": (a, b) => a * b,
      "/": (a, b) => a / b,
      "%": (a, b) => a % b,
      "+": (a, b) => a + b,
      "-": (a, b) => b === undefined ? -a : a - b,
      "==": (a, b) => a == b,
      "!=": (a, b) => a != b,
      ">=": (a, b) => a >= b,
      "<=": (a, b) => a <= b,
      ">": (a, b) => a > b,
      "<": (a, b) => a < b,      
      "in": (a, b) => {
        if (!Array.isArray(b)) throw "can only use `in` on arrays";
        return b.includes(a);
      },
      "&&": (a, b) => a && b,
      "||": (a, b) => a || b,
      "?": (cond, a, b) => cond ? a : b,
      ",": (a, b) => (a, b),
    })[tree.op.val];
    if (!op) throw `invalid operator ${op}`;
    return op(...tree.cons.map(i => expr(i, ctx)));
  }
  
  if (tree.array) return tree.array.map(i => expr(i, ctx));  
  if (tree.func) return expr(tree.func, ctx)(...tree.cons.map(i => expr(i, ctx)));
  
  if (tree.index) {
    const obj = expr(tree.index, ctx);
    const idx = expr(tree.with, ctx);
    if (!Object.hasOwn(obj, idx)) throw `${idx} doesn't exist on object`;
    return obj[idx];
  }
}

function parse(tokens, min = 0) {
  const bp = {
    ".": [24, 25],
    "(": [22, 23],
    "[": [20, 21],
    // negation/not: 19
    "**": [18, 17],
    "*": [15, 16],
    "/": [15, 16],
    "%": [15, 16],
    "+": [13, 14],
    "-": [13, 14],
    "==": [11, 12],
    "!=": [11, 12],
    ">=": [11, 12],
    "<=": [11, 12],
    ">": [11, 12],
    "<": [11, 12],
    "in": [9, 10],
    "&&": [7, 8],
    "||": [5, 6],
    "?": [4, 3],
    ",": [2, 1],
  };
  
  let lhs = tokens.next();
  if (lhs.val === "-" || lhs.val === "!") {
    lhs = { op: lhs, cons: [parse(tokens, 19)] };
  } else if (lhs.val === "(") {
    if (tokens.peek()?.val === ")") throw "empty paranthases";
    const newlhs = parse(tokens, 0);
    if (tokens.next()?.val !== ")") throw "missing a closing paranthase";
    lhs = newlhs;
  } else if (lhs.val === "[") {
    const cons = [];
    let next;
    if (tokens.peek()?.val === "]") {
      next = tokens.peek();
    } else {
      do {
        cons.push(parse(tokens, 0));
        next = tokens.next();
      } while (next.val === ",");
    }    
    if (next?.val !== "]") throw "missing a closing bracket";
    lhs = { array: cons };
  } else if (lhs.type === "symb" || lhs.val === "in") {
    throw "unexpected token " + lhs.val;
  }
  
  while (true) {
    const next = tokens.peek();
    if (!next) break;
    if (next.type !== "symb" && next.type !== "paran" && next.val !== "in") throw "unexpected token " + next.val;
    if ([")", "]", ",", ":"].includes(next.val)) break;
    if (!bp[next.val]) throw "invalid symbol";
    const [left, right] = bp[next.val];
    if (left < min) break;

    if (next.val === "(" || next.val === "[") {
      const cons = [];
      do {
        tokens.next();
        if (tokens.peek()?.val === ")") break;
        cons.push(parse(tokens, 0));
      } while (next.val === "(" && tokens.peek()?.val === ",");
      if (next.val === "(") {
        if (tokens.next()?.val !== ")") throw "missing a closing paranthase";
        lhs = { func: lhs, cons };
      } else {
        if (tokens.next()?.val !== "]") throw "missing a closing bracket";
        lhs = { index: lhs, with: cons[0] };
      }
      continue;
    } else if (next.val === "?") {
      tokens.next();
      const middle = parse(tokens, 0);
      if (tokens.next()?.val !== ":") throw "missing a colon";
      lhs = { op: next, cons: [lhs, middle, parse(tokens, right)] };
    } else {
      tokens.next();
      lhs = { op: next, cons: [lhs, parse(tokens, right)] };
    }
  }
  
  return lhs;
}

function lex(input: string) {
  let code = input;
  const tokens = [];
  while (code.length) {
    for (let [name, reg] of [
      ["space", /^[ \n\t]+/],
      ["int",   /^0(x[0-9a-f]+|b[01]+|o[0-7]+)/i],
      ["float", /^[0-9]+(\.[0-9]+)?/],
      ["str",   /^"(.*?[^\\])?"/],
      ["str",   /^'(.*?[^\\])?'/],
      ["ident", /^[a-z_][a-z0-9_]*/i],
      ["paran", /^[\[\]\(\)]/i],
      ["symb",  /^[^ \n\ta-z0-9_]{1,2}/i],
    ]) {
      const match = code.match(reg);
      if (match) {
        tokens.push({ type: name, val: match[0] });
        code = code.slice(match[0].length);
        break;
      }
    }
  }
  return {
    i: 0,
    tokens: tokens.filter(i => i.type !== "space"),
    peek() { return this.tokens[this.i] },
    next() { return this.tokens[this.i++] },
  };
}

function test(code: string) {
  const ctx = {
    math: {
      rand: ()  => Math.random(),
      abs:  (n) => Math.abs(n),
      sin:  (n) => Math.sin(n),
      cos:  (n) => Math.cos(n),
      tan:  (n) => Math.tan(n),
      log:  (n) => Math.log10(n),
      log2: (n) => Math.log2(n),
      sqrt: (n) => Math.sqrt(n),
      floor: (n) => Math.floor(n),
      ceil:  (n) => Math.ceil(n),
      round: (n) => Math.round(n),
      max:  (...n) => Math.max(...n),
      min:  (...n) => Math.min(...n),
      sum:  (...n) => n.reduce((a, i) => a + i),
      avg:  (...n) => n.reduce((a, i) => a + i) / n,
      pi: Math.PI,
      tau: Math.PI * 2,
      e: Math.E,
    },
    obj: {
      keys:    (obj) => [...Object.keys(obj)],
      vals:    (obj) => [...Object.values(obj)],
      entries: (obj) => [...Object.entries(obj)],
      has:     (obj) => Object.hasOwn(obj),
    },
    str: {
      capitalize: (str) => str.split(" ").map(i => i[0].toUpperCase() + i.slice(1).toLowerCase()).join(" "),
      upper:      (str) => str.toUpperCase(),
      lower:      (str) => str.toLowerCase(),
      trim:       (str) => str.trim(),
      trimStart:  (str) => str.trimStart(),
      trimEnd:    (str) => str.trimEnd(),
      split:      (str, by = " ") => str.split(by),
      slice:      (str, start, end) => str.slice(by),
    },
  };
  console.log(code, "\x1b[90m=>\x1b[0m", run(code, ctx));
}

test("2 + 3 * 4");
test("(2 + 3) * 4");
test("math.sin");
test("math.sin(10 * math.pi)");
test('"foo" in ["fooo", "bar", "baz"]');
test('"foo" ? 1 : 4');
test('"hello" + ", " + "world"');
test('"hello".length');
test('[1, 2, 3].length');
test('str.capitalize("hello world")');
test('"apple" in str.split("apple banana orange") ? "apple exists" : "apple doesn\'t exist"');