/**
 * @fileOverview Contains definition of the core graph object.
 */

// TODO: need to change storage layer:
// 1. Be able to get all nodes O(1)
// 2. Be able to get number of links O(1)

/**
 * @example
 *  var graph = require('ngraph.graph')();
 *  graph.addNode(1);     // graph has one node.
 *  graph.addLink(2, 3);  // now graph contains three nodes and one link.
 *
 */
module.exports = createGraph;

var eventify = require('ngraph.events');

/**
 * Creates a new graph
 */
function createGraph(options) {
  // Graph structure is maintained as dictionary of nodes
  // and array of links. Each node has 'links' property which
  // hold all links related to that node. And general links
  // array is used to speed up all links enumeration. This is inefficient
  // in terms of memory, but simplifies coding.
  options = options || {};
  if ('uniqueLinkId' in options) {
    console.warn(
      'ngraph.graph: Starting from version 0.14 `uniqueLinkId` is deprecated.\n' +
      'Use `multigraph` option instead\n',
      '\n',
      'Note: there is also change in default behavior: From now on each graph\n'+
      'is considered to be not a multigraph by default (each edge is unique).'
    );

    options.multigraph = options.uniqueLinkId;
  }

  // Dear reader, the non-multigraphs do not guarantee that there is only
  // one link for a given pair of node. When this option is set to false
  // we can save some memory and CPU (18% faster for non-multigraph);
  if (options.multigraph === undefined) options.multigraph = false;

  if (typeof Map !== 'function') {
    // TODO: Should we polyfill it ourselves? We don't use much operations there..
    throw new Error('ngraph.graph requires `Map` to be defined. Please polyfill it before using ngraph');
  } 

  var nodes = new Map();
  var links = [],
    // Hash of multi-edges. Used to track ids of edges between same nodes
    multiEdges = {},
    suspendEvents = 0,

    createLink = options.multigraph ? createUniqueLink : createSingleLink,

    // Our graph API provides means to listen to graph changes. Users can subscribe
    // to be notified about changes in the graph by using `on` method. However
    // in some cases they don't use it. To avoid unnecessary memory consumption
    // we will not record graph changes until we have at least one subscriber.
    // Code below supports this optimization.
    //
    // Accumulates all changes made during graph updates.
    // Each change element contains:
    //  changeType - one of the strings: 'add', 'remove' or 'update';
    //  node - if change is related to node this property is set to changed graph's node;
    //  link - if change is related to link this property is set to changed graph's link;
    changes = [],
    recordLinkChange = noop,
    recordNodeChange = noop,
    enterModification = noop,
    exitModification = noop;

  // this is our public API:
  var graphPart = {
    /**
     * Adds node to the graph. If node with given id already exists in the graph
     * its data is extended with whatever comes in 'data' argument.
     *
     * @param nodeId the node's identifier. A string or number is preferred.
     * @param [data] additional data for the node being added. If node already
     *   exists its data object is augmented with the new one.
     *
     * @return {node} The newly added node or node with given id if it already exists.
     */
    addNode: addNode,

    /**
     * Adds a link to the graph. The function always create a new
     * link between two nodes. If one of the nodes does not exists
     * a new node is created.
     *
     * @param fromId link start node id;
     * @param toId link end node id;
     * @param [data] additional data to be set on the new link;
     *
     * @return {link} The newly created link
     */
    addLink: addLink,

    /**
     * Removes link from the graph. If link does not exist does nothing.
     *
     * @param link - object returned by addLink() or getLinks() methods.
     *
     * @returns true if link was removed; false otherwise.
     */
    removeLink: removeLink,

    /**
     * Removes node with given id from the graph. If node does not exist in the graph
     * does nothing.
     *
     * @param nodeId node's identifier passed to addNode() function.
     *
     * @returns true if node was removed; false otherwise.
     */
    removeNode: removeNode,

    /**
     * Gets node with given identifier. If node does not exist undefined value is returned.
     *
     * @param nodeId requested node identifier;
     *
     * @return {node} in with requested identifier or undefined if no such node exists.
     */
    getNode: getNode,

    /**
     * Gets number of nodes in this graph.
     *
     * @return number of nodes in the graph.
     */
    getNodeCount: getNodeCount,

    /**
     * Gets total number of links in the graph.
     */
    getLinkCount: getLinkCount,

    /**
     * Synonym for `getLinkCount()`
     */
    getLinksCount: getLinkCount,
    
    /**
     * Synonym for `getNodeCount()`
     */
    getNodesCount: getNodeCount,

    /**
     * Gets all links (inbound and outbound) from the node with given id.
     * If node with given id is not found null is returned.
     *
     * @param nodeId requested node identifier.
     *
     * @return Array of links from and to requested node if such node exists;
     *   otherwise null is returned.
     */
    getLinks: getLinks,

    /**
     * Invokes callback on each node of the graph.
     *
     * @param {Function(node)} callback Function to be invoked. The function
     *   is passed one argument: visited node.
     */
    forEachNode: forEachNode,

    /**
     * Invokes callback on every linked (adjacent) node to the given one.
     *
     * @param nodeId Identifier of the requested node.
     * @param {Function(node, link)} callback Function to be called on all linked nodes.
     *   The function is passed two parameters: adjacent node and link object itself.
     * @param oriented if true graph treated as oriented.
     */
    forEachLinkedNode: forEachLinkedNode,

    /**
     * Enumerates all links in the graph
     *
     * @param {Function(link)} callback Function to be called on all links in the graph.
     *   The function is passed one parameter: graph's link object.
     *
     * Link object contains at least the following fields:
     *  fromId - node id where link starts;
     *  toId - node id where link ends,
     *  data - additional data passed to graph.addLink() method.
     */
    forEachLink: forEachLink,

    /**
     * Suspend all notifications about graph changes until
     * endUpdate is called.
     */
    beginUpdate: enterModification,

    /**
     * Resumes all notifications about graph changes and fires
     * graph 'changed' event in case there are any pending changes.
     */
    endUpdate: exitModification,

    /**
     * Removes all nodes and links from the graph.
     */
    clear: clear,

    /**
     * Detects whether there is a link between two nodes.
     * Operation complexity is O(n) where n - number of links of a node.
     * NOTE: this function is synonim for getLink()
     *
     * @returns link if there is one. null otherwise.
     */
    hasLink: getLink,

    /**
     * Detects whether there is a node with given id
     * 
     * Operation complexity is O(1)
     * NOTE: this function is synonim for getNode()
     *
     * @returns node if there is one; Falsy value otherwise.
     */
    hasNode: getNode,

    /**
     * Gets an edge between two nodes.
     * Operation complexity is O(n) where n - number of links of a node.
     *
     * @param {string} fromId link start identifier
     * @param {string} toId link end identifier
     *
     * @returns link if there is one. null otherwise.
     */
    getLink: getLink
  };

  // this will add `on()` and `fire()` methods.
  eventify(graphPart);

  monitorSubscribers();

  return graphPart;

  function monitorSubscribers() {
    var realOn = graphPart.on;

    // replace real `on` with our temporary on, which will trigger change
    // modification monitoring:
    graphPart.on = on;

    function on() {
      // now it's time to start tracking stuff:
      graphPart.beginUpdate = enterModification = enterModificationReal;
      graphPart.endUpdate = exitModification = exitModificationReal;
      recordLinkChange = recordLinkChangeReal;
      recordNodeChange = recordNodeChangeReal;

      // this will replace current `on` method with real pub/sub from `eventify`.
      graphPart.on = realOn;
      // delegate to real `on` handler:
      return realOn.apply(graphPart, arguments);
    }
  }

  function recordLinkChangeReal(link, changeType) {
    changes.push({
      link: link,
      changeType: changeType
    });
  }

  function recordNodeChangeReal(node, changeType) {
    changes.push({
      node: node,
      changeType: changeType
    });
  }

  function addNode(nodeId, data) {
    if (nodeId === undefined) {
      throw new Error('Invalid node identifier');
    }

    enterModification();

    var node = getNode(nodeId);
    if (!node) {
      node = new Node(nodeId, data);
      recordNodeChange(node, 'add');
    } else {
      node.data = data;
      recordNodeChange(node, 'update');
    }

    nodes.set(nodeId, node);

    exitModification();
    return node;
  }

  function getNode(nodeId) {
    return nodes.get(nodeId);
  }

  function removeNode(nodeId) {
    var node = getNode(nodeId);
    if (!node) {
      return false;
    }

    enterModification();

    var prevLinks = node.links;
    if (prevLinks) {
      node.links = null;
      for(var i = 0; i < prevLinks.length; ++i) {
        removeLink(prevLinks[i]);
      }
    }

    nodes.delete(nodeId)

    recordNodeChange(node, 'remove');

    exitModification();

    return true;
  }


  function addLink(fromId, toId, data) {
    enterModification();

    var fromNode = getNode(fromId) || addNode(fromId);
    var toNode = getNode(toId) || addNode(toId);

    var link = createLink(fromId, toId, data);

    links.push(link);

    // TODO: this is not cool. On large graphs potentially would consume more memory.
    addLinkToNode(fromNode, link);
    if (fromId !== toId) {
      // make sure we are not duplicating links for self-loops
      addLinkToNode(toNode, link);
    }

    recordLinkChange(link, 'add');

    exitModification();

    return link;
  }

  function createSingleLink(fromId, toId, data) {
    var linkId = makeLinkId(fromId, toId);
    return new Link(fromId, toId, data, linkId);
  }

  function createUniqueLink(fromId, toId, data) {
    // TODO: Get rid of this method.
    var linkId = makeLinkId(fromId, toId);
    var isMultiEdge = multiEdges.hasOwnProperty(linkId);
    if (isMultiEdge || getLink(fromId, toId)) {
      if (!isMultiEdge) {
        multiEdges[linkId] = 0;
      }
      var suffix = '@' + (++multiEdges[linkId]);
      linkId = makeLinkId(fromId + suffix, toId + suffix);
    }

    return new Link(fromId, toId, data, linkId);
  }

  function getNodeCount() {
    return nodes.size;
  }

  function getLinkCount() {
    return links.length;
  }

  function getLinks(nodeId) {
    var node = getNode(nodeId);
    return node ? node.links : null;
  }

  function removeLink(link) {
    if (!link) {
      return false;
    }
    var idx = indexOfElementInArray(link, links);
    if (idx < 0) {
      return false;
    }

    enterModification();

    links.splice(idx, 1);

    var fromNode = getNode(link.fromId);
    var toNode = getNode(link.toId);

    if (fromNode) {
      idx = indexOfElementInArray(link, fromNode.links);
      if (idx >= 0) {
        fromNode.links.splice(idx, 1);
      }
    }

    if (toNode) {
      idx = indexOfElementInArray(link, toNode.links);
      if (idx >= 0) {
        toNode.links.splice(idx, 1);
      }
    }

    recordLinkChange(link, 'remove');

    exitModification();

    return true;
  }

  function getLink(fromNodeId, toNodeId) {
    // TODO: Use sorted links to speed this up
    var node = getNode(fromNodeId),
      i;
    if (!node || !node.links) {
      return null;
    }

    for (i = 0; i < node.links.length; ++i) {
      var link = node.links[i];
      if (link.fromId === fromNodeId && link.toId === toNodeId) {
        return link;
      }
    }

    return null; // no link.
  }

  function clear() {
    enterModification();
    forEachNode(function(node) {
      removeNode(node.id);
    });
    exitModification();
  }

  function forEachLink(callback) {
    var i, length;
    if (typeof callback === 'function') {
      for (i = 0, length = links.length; i < length; ++i) {
        callback(links[i]);
      }
    }
  }

  function forEachLinkedNode(nodeId, callback, oriented) {
    var node = getNode(nodeId);

    if (node && node.links && typeof callback === 'function') {
      if (oriented) {
        return forEachOrientedLink(node.links, nodeId, callback);
      } else {
        return forEachNonOrientedLink(node.links, nodeId, callback);
      }
    }
  }

  function forEachNonOrientedLink(links, nodeId, callback) {
    var quitFast;
    for (var i = 0; i < links.length; ++i) {
      var link = links[i];
      var linkedNodeId = link.fromId === nodeId ? link.toId : link.fromId;

      quitFast = callback(nodes.get(linkedNodeId), link);
      if (quitFast) {
        return true; // Client does not need more iterations. Break now.
      }
    }
  }

  function forEachOrientedLink(links, nodeId, callback) {
    var quitFast;
    for (var i = 0; i < links.length; ++i) {
      var link = links[i];
      if (link.fromId === nodeId) {
        quitFast = callback(nodes.get(link.toId), link)
        if (quitFast) {
          return true; // Client does not need more iterations. Break now.
        }
      }
    }
  }

  // we will not fire anything until users of this library explicitly call `on()`
  // method.
  function noop() {}

  // Enter, Exit modification allows bulk graph updates without firing events.
  function enterModificationReal() {
    suspendEvents += 1;
  }

  function exitModificationReal() {
    suspendEvents -= 1;
    if (suspendEvents === 0 && changes.length > 0) {
      graphPart.fire('changed', changes);
      changes.length = 0;
    }
  }

  function forEachNode(callback) {
    if (typeof callback !== 'function') {
      throw new Error('Function is expected to iterate over graph nodes. You passed ' + callback);
    }

    var valuesIterator = nodes.values();
    var nextValue = valuesIterator.next();
    while (!nextValue.done) {
      if (callback(nextValue.value)) {
        return true; // client doesn't want to proceed. Return.
      }
      nextValue = valuesIterator.next();
    }
  }
}

// need this for old browsers. Should this be a separate module?
function indexOfElementInArray(element, array) {
  if (!array) return -1;

  if (array.indexOf) {
    return array.indexOf(element);
  }

  var len = array.length,
    i;

  for (i = 0; i < len; i += 1) {
    if (array[i] === element) {
      return i;
    }
  }

  return -1;
}

/**
 * Internal structure to represent node;
 */
function Node(id, data) {
  this.id = id;
  this.links = null;
  this.data = data;
}

function addLinkToNode(node, link) {
  if (node.links) {
    node.links.push(link);
  } else {
    node.links = [link];
  }
}

/**
 * Internal structure to represent links;
 */
function Link(fromId, toId, data, id) {
  this.fromId = fromId;
  this.toId = toId;
  this.data = data;
  this.id = id;
}

function makeLinkId(fromId, toId) {
  return fromId.toString() + '👉 ' + toId.toString();
}