/**
 * Copyright 2013-2014 Facebook, Inc.
 *
 * 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.
 *
 * @providesModule ReactMultiChild
 * @typechecks static-only
 */

"use strict";

var ReactComponent = require('ReactComponent');
var ReactMultiChildUpdateTypes = require('ReactMultiChildUpdateTypes');

var flattenChildren = require('flattenChildren');
var instantiateReactComponent = require('instantiateReactComponent');
var shouldUpdateReactComponent = require('shouldUpdateReactComponent');

/**
 * Updating children of a component may trigger recursive updates. The depth is
 * used to batch recursive updates to render markup more efficiently.
 *
 * @type {number}
 * @private
 */
var updateDepth = 0;

/**
 * Queue of update configuration objects.
 *
 * Each object has a `type` property that is in `ReactMultiChildUpdateTypes`.
 *
 * @type {array<object>}
 * @private
 */
var updateQueue = [];

/**
 * Queue of markup to be rendered.
 *
 * @type {array<string>}
 * @private
 */
var markupQueue = [];

/**
 * Enqueues markup to be rendered and inserted at a supplied index.
 *
 * @param {string} parentID ID of the parent component.
 * @param {string} markup Markup that renders into an element.
 * @param {number} toIndex Destination index.
 * @private
 */
function enqueueMarkup(parentID, markup, toIndex) {
  // NOTE: Null values reduce hidden classes.
  updateQueue.push({
    parentID: parentID,
    parentNode: null,
    type: ReactMultiChildUpdateTypes.INSERT_MARKUP,
    markupIndex: markupQueue.push(markup) - 1,
    textContent: null,
    fromIndex: null,
    toIndex: toIndex
  });
}

/**
 * Enqueues moving an existing element to another index.
 *
 * @param {string} parentID ID of the parent component.
 * @param {number} fromIndex Source index of the existing element.
 * @param {number} toIndex Destination index of the element.
 * @private
 */
function enqueueMove(parentID, fromIndex, toIndex) {
  // NOTE: Null values reduce hidden classes.
  updateQueue.push({
    parentID: parentID,
    parentNode: null,
    type: ReactMultiChildUpdateTypes.MOVE_EXISTING,
    markupIndex: null,
    textContent: null,
    fromIndex: fromIndex,
    toIndex: toIndex
  });
}

/**
 * Enqueues removing an element at an index.
 *
 * @param {string} parentID ID of the parent component.
 * @param {number} fromIndex Index of the element to remove.
 * @private
 */
function enqueueRemove(parentID, fromIndex) {
  // NOTE: Null values reduce hidden classes.
  updateQueue.push({
    parentID: parentID,
    parentNode: null,
    type: ReactMultiChildUpdateTypes.REMOVE_NODE,
    markupIndex: null,
    textContent: null,
    fromIndex: fromIndex,
    toIndex: null
  });
}

/**
 * Enqueues setting the text content.
 *
 * @param {string} parentID ID of the parent component.
 * @param {string} textContent Text content to set.
 * @private
 */
function enqueueTextContent(parentID, textContent) {
  // NOTE: Null values reduce hidden classes.
  updateQueue.push({
    parentID: parentID,
    parentNode: null,
    type: ReactMultiChildUpdateTypes.TEXT_CONTENT,
    markupIndex: null,
    textContent: textContent,
    fromIndex: null,
    toIndex: null
  });
}

/**
 * Processes any enqueued updates.
 *
 * @private
 */
function processQueue() {
  if (updateQueue.length) {
    ReactComponent.BackendIDOperations.dangerouslyProcessChildrenUpdates(
      updateQueue,
      markupQueue
    );
    clearQueue();
  }
}

/**
 * Clears any enqueued updates.
 *
 * @private
 */
function clearQueue() {
  updateQueue.length = 0;
  markupQueue.length = 0;
}

/**
 * ReactMultiChild are capable of reconciling multiple children.
 *
 * @class ReactMultiChild
 * @internal
 */
var ReactMultiChild = {

  /**
   * Provides common functionality for components that must reconcile multiple
   * children. This is used by `ReactDOMComponent` to mount, update, and
   * unmount child components.
   *
   * @lends {ReactMultiChild.prototype}
   */
  Mixin: {

    /**
     * Generates a "mount image" for each of the supplied children. In the case
     * of `ReactDOMComponent`, a mount image is a string of markup.
     *
     * @param {?object} nestedChildren Nested child maps.
     * @return {array} An array of mounted representations.
     * @internal
     */
    mountChildren: function(nestedChildren, transaction) {
      var children = flattenChildren(nestedChildren);
      var mountImages = [];
      var index = 0;
      this._renderedChildren = children;
      for (var name in children) {
        var child = children[name];
        if (children.hasOwnProperty(name)) {
          // The rendered children must be turned into instances as they're
          // mounted.
          var childInstance = instantiateReactComponent(child);
          children[name] = childInstance;
          // Inlined for performance, see `ReactInstanceHandles.createReactID`.
          var rootID = this._rootNodeID + name;
          var mountImage = childInstance.mountComponent(
            rootID,
            transaction,
            this._mountDepth + 1
          );
          childInstance._mountIndex = index;
          mountImages.push(mountImage);
          index++;
        }
      }
      return mountImages;
    },

    /**
     * Replaces any rendered children with a text content string.
     *
     * @param {string} nextContent String of content.
     * @internal
     */
    updateTextContent: function(nextContent) {
      updateDepth++;
      var errorThrown = true;
      try {
        var prevChildren = this._renderedChildren;
        // Remove any rendered children.
        for (var name in prevChildren) {
          if (prevChildren.hasOwnProperty(name)) {
            this._unmountChildByName(prevChildren[name], name);
          }
        }
        // Set new text content.
        this.setTextContent(nextContent);
        errorThrown = false;
      } finally {
        updateDepth--;
        if (!updateDepth) {
          errorThrown ? clearQueue() : processQueue();
        }
      }
    },

    /**
     * Updates the rendered children with new children.
     *
     * @param {?object} nextNestedChildren Nested child maps.
     * @param {ReactReconcileTransaction} transaction
     * @internal
     */
    updateChildren: function(nextNestedChildren, transaction) {
      updateDepth++;
      var errorThrown = true;
      try {
        this._updateChildren(nextNestedChildren, transaction);
        errorThrown = false;
      } finally {
        updateDepth--;
        if (!updateDepth) {
          errorThrown ? clearQueue() : processQueue();
        }
      }
    },

    /**
     * Improve performance by isolating this hot code path from the try/catch
     * block in `updateChildren`.
     *
     * @param {?object} nextNestedChildren Nested child maps.
     * @param {ReactReconcileTransaction} transaction
     * @final
     * @protected
     */
    _updateChildren: function(nextNestedChildren, transaction) {
      var nextChildren = flattenChildren(nextNestedChildren);
      var prevChildren = this._renderedChildren;
      if (!nextChildren && !prevChildren) {
        return;
      }
      var name;
      // `nextIndex` will increment for each child in `nextChildren`, but
      // `lastIndex` will be the last index visited in `prevChildren`.
      var lastIndex = 0;
      var nextIndex = 0;
      for (name in nextChildren) {
        if (!nextChildren.hasOwnProperty(name)) {
          continue;
        }
        var prevChild = prevChildren && prevChildren[name];
        var nextChild = nextChildren[name];
        if (shouldUpdateReactComponent(prevChild, nextChild)) {
          this.moveChild(prevChild, nextIndex, lastIndex);
          lastIndex = Math.max(prevChild._mountIndex, lastIndex);
          prevChild.receiveComponent(nextChild, transaction);
          prevChild._mountIndex = nextIndex;
        } else {
          if (prevChild) {
            // Update `lastIndex` before `_mountIndex` gets unset by unmounting.
            lastIndex = Math.max(prevChild._mountIndex, lastIndex);
            this._unmountChildByName(prevChild, name);
          }
          // The child must be instantiated before it's mounted.
          var nextChildInstance = instantiateReactComponent(nextChild);
          this._mountChildByNameAtIndex(
            nextChildInstance, name, nextIndex, transaction
          );
        }
        nextIndex++;
      }
      // Remove children that are no longer present.
      for (name in prevChildren) {
        if (prevChildren.hasOwnProperty(name) &&
            !(nextChildren && nextChildren[name])) {
          this._unmountChildByName(prevChildren[name], name);
        }
      }
    },

    /**
     * Unmounts all rendered children. This should be used to clean up children
     * when this component is unmounted.
     *
     * @internal
     */
    unmountChildren: function() {
      var renderedChildren = this._renderedChildren;
      for (var name in renderedChildren) {
        var renderedChild = renderedChildren[name];
        // TODO: When is this not true?
        if (renderedChild.unmountComponent) {
          renderedChild.unmountComponent();
        }
      }
      this._renderedChildren = null;
    },

    /**
     * Moves a child component to the supplied index.
     *
     * @param {ReactComponent} child Component to move.
     * @param {number} toIndex Destination index of the element.
     * @param {number} lastIndex Last index visited of the siblings of `child`.
     * @protected
     */
    moveChild: function(child, toIndex, lastIndex) {
      // If the index of `child` is less than `lastIndex`, then it needs to
      // be moved. Otherwise, we do not need to move it because a child will be
      // inserted or moved before `child`.
      if (child._mountIndex < lastIndex) {
        enqueueMove(this._rootNodeID, child._mountIndex, toIndex);
      }
    },

    /**
     * Creates a child component.
     *
     * @param {ReactComponent} child Component to create.
     * @param {string} mountImage Markup to insert.
     * @protected
     */
    createChild: function(child, mountImage) {
      enqueueMarkup(this._rootNodeID, mountImage, child._mountIndex);
    },

    /**
     * Removes a child component.
     *
     * @param {ReactComponent} child Child to remove.
     * @protected
     */
    removeChild: function(child) {
      enqueueRemove(this._rootNodeID, child._mountIndex);
    },

    /**
     * Sets this text content string.
     *
     * @param {string} textContent Text content to set.
     * @protected
     */
    setTextContent: function(textContent) {
      enqueueTextContent(this._rootNodeID, textContent);
    },

    /**
     * Mounts a child with the supplied name.
     *
     * NOTE: This is part of `updateChildren` and is here for readability.
     *
     * @param {ReactComponent} child Component to mount.
     * @param {string} name Name of the child.
     * @param {number} index Index at which to insert the child.
     * @param {ReactReconcileTransaction} transaction
     * @private
     */
    _mountChildByNameAtIndex: function(child, name, index, transaction) {
      // Inlined for performance, see `ReactInstanceHandles.createReactID`.
      var rootID = this._rootNodeID + name;
      var mountImage = child.mountComponent(
        rootID,
        transaction,
        this._mountDepth + 1
      );
      child._mountIndex = index;
      this.createChild(child, mountImage);
      this._renderedChildren = this._renderedChildren || {};
      this._renderedChildren[name] = child;
    },

    /**
     * Unmounts a rendered child by name.
     *
     * NOTE: This is part of `updateChildren` and is here for readability.
     *
     * @param {ReactComponent} child Component to unmount.
     * @param {string} name Name of the child in `this._renderedChildren`.
     * @private
     */
    _unmountChildByName: function(child, name) {
      // TODO: When is this not true?
      if (ReactComponent.isValidComponent(child)) {
        this.removeChild(child);
        child._mountIndex = null;
        child.unmountComponent();
        delete this._renderedChildren[name];
      }
    }

  }

};

module.exports = ReactMultiChild;
