<?php

namespace WikiPEG;

class Expectation implements \JsonSerializable {
  /** @var string */
  public $type;
  /** @var string|null */
  public $value;
  /** @var string */
  public $description;

  /**
   * @param array $info The expectation array, which comes from the generated code, with keys:
   *   - type: The failed node type
   *   - value: The actual string which failed to match, may be absent for some node types
   *   - description: A readable description of the value
   */
  public function __construct($info) {
    $this->type = $info['type'];
    $this->value = $info['value'] ?? null;
    $this->description = $info['description'];
  }

  /**
   * Compare two Expectation objects, and return a value less than, equal to,
   * or greater than zero, depending on whether $a is less than, equal to, or
   * greater than $b respectively.
   *
   * This is used to sort expectations before combining them into SyntaxError
   * descriptions.
   *
   * @param Expectation $a
   * @param Expectation $b
   * @return int
   */
  public static function compare(Expectation $a, Expectation $b) {
    return $a->type <=> $b->type
      ?: $a->value <=> $b->value
      ?: $a->description <=> $b->description;
  }

  /**
   * Emit a JSON serialization similar to JS, for testing
   * @return array
   */
  public function jsonSerialize() {
    return [
      'type' => $this->type,
      'value' => $this->value,
      'description' => $this->description
    ];
  }
}