/* This Source Code Form is subject to the terms of the Mozilla Public
 * License, v. 2.0. If a copy of the MPL was not distributed with this
 * file, You can obtain one at <http://mozilla.org/MPL/2.0/>. */

import { getThreadContext } from "../selectors";

// Context encapsulates the main parameters of the current redux state, which
// impact most other information tracked by the debugger.
//
// The main use of Context is to control when asynchronous operations are
// allowed to make changes to the program state. Such operations might be
// invalidated as the state changes from the time the operation was originally
// initiated. For example, operations on pause state might still continue even
// after the thread unpauses.
//
// The methods below can be used to compare an old context with the current one
// and see if the operation is now invalid and should be abandoned. Actions can
// also include a 'cx' Context property, which will be checked by the context
// middleware. If the action fails validateContextAction() then it will not be
// dispatched.
//
// Context can additionally be used as a shortcut to access the main properties
// of the pause state.

// A normal Context is invalidated if the target navigates.

// A ThreadContext is invalidated if the target navigates, or if the current
// thread changes, pauses, or resumes.

export class ContextError extends Error {}

export function validateNavigateContext(state, cx) {
  const newcx = getThreadContext(state);

  if (newcx.navigateCounter != cx.navigateCounter) {
    throw new ContextError("Page has navigated");
  }
}

export function validateThreadContext(state, cx) {
  const newcx = getThreadContext(state);

  if (cx.thread != newcx.thread) {
    throw new ContextError("Current thread has changed");
  }

  if (cx.pauseCounter != newcx.pauseCounter) {
    throw new ContextError("Current thread has paused or resumed");
  }
}

export function validateContext(state, cx) {
  validateNavigateContext(state, cx);

  if ("thread" in cx) {
    validateThreadContext(state, cx);
  }
}

export function isValidThreadContext(state, cx) {
  const newcx = getThreadContext(state);
  return cx.thread == newcx.thread && cx.pauseCounter == newcx.pauseCounter;
}