import { Bool, Char, Double, Int, Unit } from "../primitives/types.js";
import { dictType, fnType, lsType, prodType, setType, sumType } from "../structures/types.js";

const bracketOperators = new Map([
  ['(', [')', null]],
  ['[', [']', lsType]],
  ['{', ['}', setType]],

  // can only occur at beginning
  // we use these to extract the type variables
  ['∀', [':', null]],
]);

const infixOperators = new Map([
  ['+', sumType],
  ['|', sumType],
  ['⨯', prodType],
  ['*', prodType],
  ['→', fnType],
  ['->', fnType],
  ['⇒', dictType],
  ['=>', dictType],

  // only used for type variables (e.g., ∀a,b,c:)
  [',', fnX => fnY => {
    const x = fnX();
    const y = fnY();
    return Array.isArray(x) ? x.concat(y) : [x].concat(y)
  }],
]);

const a = Symbol('a');
const b = Symbol('b');
const c = Symbol('c');
const d = Symbol('d');
const e = Symbol('e');

const primitives = new Map([
  ['Int', Int],
  ['Double', Double],
  ['Bool', Bool],
  ['Char', Char],
  ['Unit', Unit],
  ['a', a],
  ['b', b],
  ['c', c],
  ['d', d],
  ['e', e],
]);

const TOKENS = [
  ...bracketOperators.keys(),
  ...[...bracketOperators.values()].map(v => v[0]),
  ...infixOperators.keys(),
  ...primitives.keys(),
];

// console.log('TOKENS =', TOKENS);

const tokenize = expr => {
  const tokens = [];
  let i=0;
  outerloop: while (i<expr.length) {
    if (/\s/.test(expr[i])) {
      i++;
      continue outerloop; // skip whitespace
    }
    if (expr[i] === '#') {
      const label = '#' + parseInt(expr.slice(i+1));
      tokens.push(label);
      i += label.length;
      continue outerloop;
    }
    for (const token of TOKENS) {
      if (expr.startsWith(token, i)) {
        tokens.push(token);
        i += token.length;
        continue outerloop;
      }
    }
    throw new Error(`Couldn't match any token at position ${i} in\n  ${expr}\n  ${' '.repeat(i)}^`);
  }
  // console.log({tokens});
  return tokens;
}

const consumeGroup = (tokens) => {
  const bracket = bracketOperators.get(tokens[0]);
  if (bracket === undefined) {
    // no group, just a single token:
    const [firstToken, ...rest] = tokens;
    return [[firstToken], null, rest];
  }
  else {
    // find where group ends:
    const [closing, fn] = bracket;
    const opening = tokens[0]
    let depth = 1;
    let i = 1;
    for (; i<tokens.length; i++) {
      if (tokens[i] === opening) {
        depth++;
      }
      else if (tokens[i] === closing) {
        depth--;
      }
      if (depth === 0) {
        break;
      }
    }
    const tokensInGroup = tokens.slice(1, i); // don't include brackets
    const rest = tokens.slice(i+1);
    return [tokensInGroup, fn, rest];
  }
}

const parseGroup = (tokensInGroup, fn, labels, label) => {
  // console.log('parseGroup ', tokensInGroup, fn);
  return (fn === null)
    ? __parse(tokensInGroup, labels, label)
    : fn(self => {
        return __parse(tokensInGroup, extendLabels(labels, label, self));
      });
}

const extendLabels = (labels, label, self) => {
  return (label === null) ? labels : new Map([...labels, [label, self]])
};

const __parse = (tokens, labels = new Map(), label = null) => {
  // console.log('parse ', tokens);
  if (tokens[0].startsWith('#')) {
    if (labels.has(tokens[0])) {
      return labels.get(tokens[0]);
    }
    else {
      // pass label and parse 'rest'
      return __parse(tokens.slice(1), labels, tokens[0]);
    }
  }
  if (tokens.length === 1) {
    return primitives.get(tokens[0]);
  }
  else {
    const [lhsTokens, fnGrp, rest] = consumeGroup(tokens);
    if (rest.length === 0) {
      return parseGroup(lhsTokens, fnGrp, labels, label);
    }
    const [operator, ...rhsTokens] = rest;
    for (const [operatorChar, fn] of infixOperators) {
      if (operator === operatorChar) {
        return fn
          (self => {
            return parseGroup(lhsTokens, fnGrp, extendLabels(labels, label, self));
          })(self => {
            return __parse(rhsTokens, extendLabels(labels, label, self));
          });
      }
    }
    throw new Error("unknown operator: "+operator)
  }
};

export const parse = expr => {
  const tokens = tokenize(expr);
  if (tokens[0] === '∀') {
    // generic type
    const [typeVarTokens, _, rest] = consumeGroup(tokens);
    const typeVars = [].concat(__parse(typeVarTokens))
    const type = __parse(rest);
    return { typeVars, type };
  }
  return __parse(tokens);
}