/**
 * @fileoverview Check that there's a Services.(prefs|obs).removeObserver for
 * each addObserver.
 *
 * 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/.
 */

"use strict";

// -----------------------------------------------------------------------------
// Rule Definition
// -----------------------------------------------------------------------------

module.exports = function(context) {
  // ---------------------------------------------------------------------------
  // Helpers
  // ---------------------------------------------------------------------------

  var addedObservers = [];
  var removedObservers = [];

  function getObserverAPI(node) {
    const object = node.callee.object;
    if (
      object.type == "MemberExpression" &&
      object.property.type == "Identifier"
    ) {
      return object.property.name;
    }
    return null;
  }

  function isServicesObserver(api) {
    return api == "obs" || api == "prefs";
  }

  function getObservableName(node, api) {
    if (api === "obs") {
      return node.arguments[1].value;
    }
    return node.arguments[0].value;
  }

  function addAddedObserver(node) {
    const api = getObserverAPI(node);
    if (!isServicesObserver(api)) {
      return;
    }

    addedObservers.push({
      functionName: node.callee.property.name,
      observable: getObservableName(node, api),
      node: node.callee.property,
    });
  }

  function addRemovedObserver(node) {
    const api = getObserverAPI(node);
    if (!isServicesObserver(api)) {
      return;
    }

    removedObservers.push({
      functionName: node.callee.property.name,
      observable: getObservableName(node, api),
    });
  }

  function getUnbalancedObservers() {
    const unbalanced = addedObservers.filter(
      observer => !hasRemovedObserver(observer)
    );
    addedObservers = removedObservers = [];

    return unbalanced;
  }

  function hasRemovedObserver(addedObserver) {
    return removedObservers.some(
      observer => addedObserver.observable === observer.observable
    );
  }

  // ---------------------------------------------------------------------------
  // Public
  // ---------------------------------------------------------------------------

  return {
    CallExpression(node) {
      if (node.arguments.length === 0) {
        return;
      }

      if (node.callee.type === "MemberExpression") {
        var methodName = node.callee.property.name;

        if (methodName === "addObserver") {
          addAddedObserver(node);
        } else if (methodName === "removeObserver") {
          addRemovedObserver(node);
        }
      }
    },

    "Program:exit": function() {
      getUnbalancedObservers().forEach(function(observer) {
        context.report(
          observer.node,
          "No corresponding 'removeObserver(\"{{observable}}\")' was found.",
          {
            observable: observer.observable,
          }
        );
      });
    },
  };
};