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

Process expressions in map style.

import RuntimeError from '../runtime_error.js';
import { array, NumberType, ValueType } from '../types.js';

export default class At {
  constructor(type, index, input) {
    this.type = type;
    this.index = index;
    this.input = input;
  }

  static parse(args, context) {
    if (args.length !== 3) return context.error(`Expected 2 arguments, but found ${args.length - 1} instead.`);

    const index = context.parse(args[1], 1, NumberType);
    const input = context.parse(args[2], 2, array(context.expectedType || ValueType));

    if (!index || !input) return null;

    const t = input.type;
    return new At(t.itemType, index, input);
  }

  evaluate(ctx) {
    const index = this.index.evaluate(ctx);
    const array = this.input.evaluate(ctx);

    if (index < 0) {
      throw new RuntimeError(`Array index out of bounds: ${index} < 0.`);
    }

    if (index >= array.length) {
      throw new RuntimeError(`Array index out of bounds: ${index} > ${array.length - 1}.`);
    }

    if (index !== Math.floor(index)) {
      throw new RuntimeError(`Array index must be an integer, but found ${index} instead.`);
    }

    return array[index];
  }

  eachChild(fn) {
    fn(this.index);
    fn(this.input);
  }

  possibleOutputs() {
    return [undefined];
  }
}