@mapwhit/style-expressions/lib/expression/definitions/assertion.js

Process expressions in map style.

import assert from 'assert';
import RuntimeError from '../runtime_error.js';
import { array, BooleanType, checkSubtype, NumberType, ObjectType, StringType, toString, ValueType } from '../types.js';
import { typeOf } from '../values.js';

const types = {
  string: StringType,
  number: NumberType,
  boolean: BooleanType,
  object: ObjectType
};

export default class Assertion {
  constructor(type, args) {
    this.type = type;
    this.args = args;
  }

  static parse(args, context) {
    if (args.length < 2) return context.error('Expected at least one argument.');

    let i = 1;
    let type;

    const name = args[0];
    if (name === 'array') {
      let itemType;
      if (args.length > 2) {
        const type = args[1];
        if (typeof type !== 'string' || !(type in types) || type === 'object')
          return context.error('The item type argument of "array" must be one of string, number, boolean', 1);
        itemType = types[type];
        i++;
      } else {
        itemType = ValueType;
      }

      let N;
      if (args.length > 3) {
        if (args[2] !== null && (typeof args[2] !== 'number' || args[2] < 0 || args[2] !== Math.floor(args[2]))) {
          return context.error('The length argument to "array" must be a positive integer literal', 2);
        }
        N = args[2];
        i++;
      }

      type = array(itemType, N);
    } else {
      assert(types[name], name);
      type = types[name];
    }

    const parsed = [];
    for (; i < args.length; i++) {
      const input = context.parse(args[i], i, ValueType);
      if (!input) return null;
      parsed.push(input);
    }

    return new Assertion(type, parsed);
  }

  evaluate(ctx) {
    for (let i = 0; i < this.args.length; i++) {
      const value = this.args[i].evaluate(ctx);
      const error = checkSubtype(this.type, typeOf(value));
      if (!error) {
        return value;
      }
      if (i === this.args.length - 1) {
        throw new RuntimeError(
          `Expected value to be of type ${toString(this.type)}, but found ${toString(typeOf(value))} instead.`
        );
      }
    }

    assert(false);
    return null;
  }

  eachChild(fn) {
    this.args.forEach(fn);
  }

  possibleOutputs() {
    return [].concat(...this.args.map(arg => arg.possibleOutputs()));
  }
}