@toryt/contracts/lib/Contract.js

Design-by-Contract and Test-by-Contract for JavaScript

/*
  Copyright 2016–2024 Jan Dockx

  Licensed under the Apache License, Version 2.0 (the "License");
  you may not use this file except in compliance with the License.
  You may obtain a copy of the License at

  http://www.apache.org/licenses/LICENSE-2.0

  Unless required by applicable law or agreed to in writing, software
  distributed under the License is distributed on an "AS IS" BASIS,
  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  See the License for the specific language governing permissions and
  limitations under the License.
 */

'use strict'

const stack = require('./_private/stack')
const ConditionError = require('./ConditionError')
const AbstractContract = require('./AbstractContract')
const PreconditionViolation = require('./PreconditionViolation')
const PostconditionViolation = require('./PostconditionViolation')
const ExceptionConditionViolation = require('./ExceptionConditionViolation')
const assert = require('assert')
const PromiseContract = require('./PromiseContract')

/**
 * The separation between AbstractContract and Contract is necessary to break a dependency
 * cycle with ConditionError.
 *
 * @constructor
 */
function Contract(kwargs) {
  assert.ok(kwargs)
  assert(!kwargs.pre || Array.isArray(kwargs.pre), 'optional kwargs.pre is an array')
  assert(!kwargs.post || Array.isArray(kwargs.post), 'optional kwargs.post is an array')
  assert(!kwargs.exception || Array.isArray(kwargs.exception), 'optional kwargs.exception is an array')

  AbstractContract.call(this, kwargs, stack.location(1))
}

Contract.prototype = new AbstractContract({ pre: AbstractContract.mustNotHappen }, AbstractContract.internalLocation)
Contract.prototype.constructor = Contract
Contract.prototype.implementation = function (implFunction) {
  assert.strictEqual(typeof implFunction, 'function')

  const contract = this
  const location = stack.location(1)

  function contractFunction() {
    // cfThis: the `this` of the contract function call
    const cfThis = this
    if (!contractFunction.contract.verify) {
      /* Shortcut if there is no verification.
         This is not contract.verify: contractFunction.contract is a separate object, that has contract as a
         prototype. */
      return implFunction.apply(cfThis, arguments)
    }

    // noinspection JSUnresolvedReference
    PreconditionViolation.prototype.verifyAll(contractFunction, contract.pre, cfThis, arguments)
    if (!contractFunction.contract.verifyPostconditions) {
      /* Shortcut if there is no verification.
         This is not contract.verifyPostconditions: contractFunction.contract is a separate object, that has contract as
         a prototype. */
      return implFunction.apply(cfThis, arguments)
    }

    const extendedArgs = Array.prototype.slice.call(arguments)
    try {
      const result = implFunction.apply(cfThis, arguments)
      extendedArgs.push(result)
      extendedArgs.push(contractFunction.bind(cfThis))
      // noinspection JSUnresolvedReference
      PostconditionViolation.prototype.verifyAll(contractFunction, contract.post, cfThis, extendedArgs)
      return result
    } catch (exc) {
      if (exc instanceof ConditionError) {
        // necessary to report only the deepest failure clearly
        throw exc
      }
      extendedArgs.push(exc)
      extendedArgs.push(contractFunction.bind(cfThis))
      // noinspection JSUnresolvedReference
      ExceptionConditionViolation.prototype.verifyAll(contractFunction, contract.exception, cfThis, extendedArgs)
      throw exc
    }
  }

  AbstractContract.bless(contractFunction, contract, implFunction, location)

  return contractFunction
}

Contract.falseCondition = AbstractContract.falseCondition
Contract.mustNotHappen = AbstractContract.mustNotHappen
Contract.root = AbstractContract.root
Contract.isAContractFunction = AbstractContract.isAContractFunction
Contract.outcome = AbstractContract.outcome
// noinspection JSAnnotator
Contract.callee = AbstractContract.callee

Contract.Promise = PromiseContract

module.exports = Contract