/*
 * Copyright 2014 Open Networking Laboratory
 *
 * 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.
 */

/*
 ONOS network topology viewer - version 1.1

 @author Simon Hunt
 */

(function (onos) {
    'use strict';

    // shorter names for library APIs
    var d3u = onos.lib.d3util,
        trace;

    // configuration data
    var config = {
        useLiveData: true,
        fnTrace: true,
        debugOn: false,
        debug: {
            showNodeXY: true,
            showKeyHandler: false
        },
        options: {
            layering: true,
            collisionPrevention: true,
            showBackground: true
        },
        backgroundUrl: 'img/us-map.png',
        webSockUrl: 'ws/topology',
        data: {
            live: {
                jsonUrl: 'rs/topology/graph',
                detailPrefix: 'rs/topology/graph/',
                detailSuffix: ''
            },
            fake: {
                jsonUrl: 'json/network2.json',
                detailPrefix: 'json/',
                detailSuffix: '.json'
            }
        },
        labels: {
            imgPad: 16,
            padLR: 4,
            padTB: 3,
            marginLR: 3,
            marginTB: 2,
            port: {
                gap: 3,
                width: 18,
                height: 14
            }
        },
        topo: {
            linkInColor: '#66f',
            linkInWidth: 14
        },
        icons: {
            w: 28,
            h: 28,
            xoff: -12,
            yoff: -8
        },
        iconUrl: {
            device: 'img/device.png',
            host: 'img/host.png',
            pkt: 'img/pkt.png',
            opt: 'img/opt.png'
        },
        force: {
            note_for_links: 'link.type is used to differentiate',
            linkDistance: {
                direct: 100,
                optical: 120,
                hostLink: 5
            },
            linkStrength: {
                direct: 1.0,
                optical: 1.0,
                hostLink: 1.0
            },
            note_for_nodes: 'node.class is used to differentiate',
            charge: {
                device: -8000,
                host: -300
            },
            pad: 20,
            translate: function() {
                return 'translate(' +
                    config.force.pad + ',' +
                    config.force.pad + ')';
            }
        }
    };

    // radio buttons
    var btnSet = [
        { text: 'All Layers', cb: showAllLayers },
        { text: 'Packet Only', cb: showPacketLayer },
        { text: 'Optical Only', cb: showOpticalLayer }
    ];

    // key bindings
    var keyDispatch = {
        M: testMe,                  // TODO: remove (testing only)
        S: injectStartupEvents,     // TODO: remove (testing only)
        space: injectTestEvent,     // TODO: remove (testing only)

        B: toggleBg,                // TODO: do we really need this?
        L: cycleLabels,
        P: togglePorts,
        U: unpin,

        X: requestPath
    };

    // state variables
    var network = {
            view: null,     // view token reference
            nodes: [],
            links: [],
            lookup: {}
        },
        scenario = {
            evDir: 'json/ev/',
            evScenario: '/scenario.json',
            evPrefix: '/ev_',
            evOnos: '_onos.json',
            evUi: '_ui.json',
            ctx: null,
            params: {},
            evNumber: 0,
            view: null,
            debug: false
        },
        webSock,
        deviceLabelIndex = 0,
        hostLabelIndex = 0,

        selectOrder = [],
        selections = {},

        highlighted = null,
        hovered = null,
        viewMode = 'showAll',
        portLabelsOn = false;

    // D3 selections
    var svg,
        bgImg,
        topoG,
        nodeG,
        linkG,
        node,
        link;

    // ==============================
    // For Debugging / Development

    function note(label, msg) {
        console.log('NOTE: ' + label + ': ' + msg);
    }

    function debug(what) {
        return config.debugOn && config.debug[what];
    }

    function fnTrace(msg, id) {
        if (config.fnTrace) {
            console.log('FN: ' + msg + ' [' + id + ']');
        }
    }

    // ==============================
    // Key Callbacks

    function testMe(view) {
        view.alert('test');
    }

    function abortIfLive() {
        if (config.useLiveData) {
            scenario.view.alert("Sorry, currently using live data..");
            return true;
        }
        return false;
    }

    function testDebug(msg) {
        if (scenario.debug) {
            scenario.view.alert(msg);
        }
    }

    function injectTestEvent(view) {
        if (abortIfLive()) { return; }
        var sc = scenario,
            evn = ++sc.evNumber,
            pfx = sc.evDir + sc.ctx + sc.evPrefix + evn,
            onosUrl = pfx + sc.evOnos,
            uiUrl = pfx + sc.evUi,
            stack = [
                { url: onosUrl, cb: handleServerEvent },
                { url: uiUrl, cb: handleUiEvent }
            ];
        recurseFetchEvent(stack, evn);
    }

    function recurseFetchEvent(stack, evn) {
        var v = scenario.view,
            frame;
        if (stack.length === 0) {
            v.alert('Oops!\n\nNo event #' + evn + ' found.');
            return;
        }
        frame = stack.shift();

        d3.json(frame.url, function (err, data) {
            if (err) {
                if (err.status === 404) {
                    // if we didn't find the data, try the next stack frame
                    recurseFetchEvent(stack, evn);
                } else {
                    v.alert('non-404 error:\n\n' + frame.url + '\n\n' + err);
                }
            } else {
                testDebug('loaded: ' + frame.url);
                frame.cb(data);
            }
        });

    }

    function handleUiEvent(data) {
        scenario.view.alert('UI Tx: ' + data.event + '\n\n' +
            JSON.stringify(data));
    }

    function injectStartupEvents(view) {
        var last = scenario.params.lastAuto || 0;
        if (abortIfLive()) { return; }

        while (scenario.evNumber < last) {
            injectTestEvent(view);
        }
    }

    function toggleBg() {
        var vis = bgImg.style('visibility');
        bgImg.style('visibility', (vis === 'hidden') ? 'visible' : 'hidden');
    }

    function cycleLabels() {
        deviceLabelIndex = (deviceLabelIndex === network.deviceLabelCount - 1)
            ? 0 : deviceLabelIndex + 1;

        network.nodes.forEach(function (d) {
            if (d.class === 'device') {
                updateDeviceLabel(d);
            }
        });
    }

    function togglePorts(view) {
        view.alert('togglePorts() callback')
    }

    function unpin(view) {
        view.alert('unpin() callback')
    }

    function requestPath(view) {
        var payload = {
            one: selections[selectOrder[0]].obj.id,
            two: selections[selectOrder[1]].obj.id
        }
        sendMessage('requestPath', payload);
    }

    // ==============================
    // Radio Button Callbacks

    function showAllLayers() {
//        network.node.classed('inactive', false);
//        network.link.classed('inactive', false);
//        d3.selectAll('svg .port').classed('inactive', false);
//        d3.selectAll('svg .portText').classed('inactive', false);
        // TODO ...
        network.view.alert('showAllLayers() callback');
    }

    function showPacketLayer() {
        showAllLayers();
        // TODO ...
        network.view.alert('showPacketLayer() callback');
    }

    function showOpticalLayer() {
        showAllLayers();
        // TODO ...
        network.view.alert('showOpticalLayer() callback');
    }

    // ==============================
    // Private functions

    function safeId(s) {
        return s.replace(/[^a-z0-9]/gi, '-');
    }

    // set the size of the given element to that of the view (reduced if padded)
    function setSize(el, view, pad) {
        var padding = pad ? pad * 2 : 0;
        el.attr({
            width: view.width() - padding,
            height: view.height() - padding
        });
    }


    // ==============================
    // Event handlers for server-pushed events

    function logicError(msg) {
        // TODO, report logic error to server, via websock, so it can be logged
        network.view.alert('Logic Error:\n\n' + msg);
        console.warn(msg);
    }

    var eventDispatch = {
        addDevice: addDevice,
        addLink: addLink,
        addHost: addHost,
        updateDevice: updateDevice,
        updateLink: updateLink,
        updateHost: updateHost,
        removeDevice: stillToImplement,
        removeLink: removeLink,
        removeHost: stillToImplement,
        showPath: showPath
    };

    function addDevice(data) {
        fnTrace('addDevice', data.payload.id);
        var device = data.payload,
            nodeData = createDeviceNode(device);
        network.nodes.push(nodeData);
        network.lookup[nodeData.id] = nodeData;
        updateNodes();
        network.force.start();
    }

    function addLink(data) {
        fnTrace('addLink', data.payload.id);
        var link = data.payload,
            lnk = createLink(link);
        if (lnk) {
            network.links.push(lnk);
            network.lookup[lnk.id] = lnk;
            updateLinks();
            network.force.start();
        }
    }

    function addHost(data) {
        fnTrace('addHost', data.payload.id);
        var host = data.payload,
            node = createHostNode(host),
            lnk;
        network.nodes.push(node);
        network.lookup[host.id] = node;
        updateNodes();

        lnk = createHostLink(host);
        if (lnk) {
            network.links.push(lnk);
            network.lookup[host.ingress] = lnk;
            network.lookup[host.egress] = lnk;
            updateLinks();
        }
        network.force.start();
    }

    function updateDevice(data) {
        fnTrace('updateDevice', data.payload.id);
        var device = data.payload,
            id = device.id,
            nodeData = network.lookup[id];
        if (nodeData) {
            $.extend(nodeData, device);
            updateDeviceState(nodeData);
        } else {
            logicError('updateDevice lookup fail. ID = "' + id + '"');
        }
    }

    function updateLink(data) {
        fnTrace('updateLink', data.payload.id);
        var link = data.payload,
            id = link.id,
            linkData = network.lookup[id];
        if (linkData) {
            $.extend(linkData, link);
            updateLinkState(linkData);
        } else {
            logicError('updateLink lookup fail. ID = "' + id + '"');
        }
    }

    function updateHost(data) {
        fnTrace('updateHost', data.payload.id);
        var host = data.payload,
            id = host.id,
            hostData = network.lookup[id];
        if (hostData) {
            $.extend(hostData, host);
            updateHostState(hostData);
        } else {
            logicError('updateHost lookup fail. ID = "' + id + '"');
        }
    }

    function removeLink(data) {
        fnTrace('removeLink', data.payload.id);
        var link = data.payload,
            id = link.id,
            linkData = network.lookup[id];
        if (linkData) {
            removeLinkElement(linkData);
        } else {
            logicError('removeLink lookup fail. ID = "' + id + '"');
        }
    }

    function showPath(data) {
        fnTrace('showPath', data.payload.id);
        var links = data.payload.links,
            s = [ data.event + "\n" + links.length ];
        links.forEach(function (d, i) {
            s.push(d);
        });
        network.view.alert(s.join('\n'));

        links.forEach(function (d, i) {
            var link = network.lookup[d];
            if (link) {
                link.el.classed('showPath', true);
            }
        });

        // TODO: add selection-highlite lines to links
    }

    // ...............................

    function stillToImplement(data) {
        var p = data.payload;
        note(data.event, p.id);
        network.view.alert('Not yet implemented: "' + data.event + '"');
    }

    function unknownEvent(data) {
        network.view.alert('Unknown event type: "' + data.event + '"');
    }

    function handleServerEvent(data) {
        var fn = eventDispatch[data.event] || unknownEvent;
        fn(data);
    }

    // ==============================
    // force layout modification functions

    function translate(x, y) {
        return 'translate(' + x + ',' + y + ')';
    }

    function missMsg(what, id) {
        return '\n[' + what + '] "' + id + '" missing ';
    }

    function linkEndPoints(srcId, dstId) {
        var srcNode = network.lookup[srcId],
            dstNode = network.lookup[dstId],
            sMiss = !srcNode ? missMsg('src', srcId) : '',
            dMiss = !dstNode ? missMsg('dst', dstId) : '';

        if (sMiss || dMiss) {
            logicError('Node(s) not on map for link:\n' + sMiss + dMiss);
            return null;
        }
        return {
            source: srcNode,
            target: dstNode,
            x1: srcNode.x,
            y1: srcNode.y,
            x2: dstNode.x,
            y2: dstNode.y
        };
    }

    function createHostLink(host) {
        var src = host.id,
            dst = host.cp.device,
            id = host.ingress,
            lnk = linkEndPoints(src, dst);

        if (!lnk) {
            return null;
        }

        // Synthesize link ...
        $.extend(lnk, {
            id: id,
            class: 'link',
            type: 'hostLink',
            svgClass: 'link hostLink',
            linkWidth: 1
        });
        return lnk;
    }

    function createLink(link) {
        var lnk = linkEndPoints(link.src, link.dst),
            type = link.type;

        if (!lnk) {
            return null;
        }

        // merge in remaining data
        $.extend(lnk, link, {
            class: 'link',
            svgClass: type ? 'link ' + type : 'link'
        });
        return lnk;
    }

    var widthRatio = 1.4,
        linkScale = d3.scale.linear()
            .domain([1, 12])
            .range([widthRatio, 12 * widthRatio])
            .clamp(true);

    function updateLinkWidth (d) {
        // TODO: watch out for .showPath/.showTraffic classes
        d.el.transition()
            .duration(1000)
            .attr('stroke-width', linkScale(d.linkWidth));
    }


    function updateLinks() {
        link = linkG.selectAll('.link')
            .data(network.links, function (d) { return d.id; });

        // operate on existing links, if necessary
        // link .foo() .bar() ...

        // operate on entering links:
        var entering = link.enter()
            .append('line')
            .attr({
                class: function (d) { return d.svgClass; },
                x1: function (d) { return d.x1; },
                y1: function (d) { return d.y1; },
                x2: function (d) { return d.x2; },
                y2: function (d) { return d.y2; },
                stroke: config.topo.linkInColor,
                'stroke-width': config.topo.linkInWidth
            })
            .transition().duration(1000)
            .attr({
                'stroke-width': function (d) { return linkScale(d.linkWidth); },
                stroke: '#666'      // TODO: remove explicit stroke, rather...
            });

        // augment links
        entering.each(function (d) {
            var link = d3.select(this);
            // provide ref to element selection from backing data....
            d.el = link;

            // TODO: add src/dst port labels etc.
        });

        // operate on both existing and new links, if necessary
        //link .foo() .bar() ...

        // operate on exiting links:
        // TODO: better transition (longer as a dashed, grey line)
        link.exit()
            .attr({
                'stroke-dasharray': '3, 3'
            })
            .style('opacity', 0.4)
            .transition()
            .duration(2000)
            .attr({
                'stroke-dasharray': '3, 12'
            })
            .transition()
            .duration(1000)
            .style('opacity', 0.0)
            .remove();
    }

    function createDeviceNode(device) {
        // start with the object as is
        var node = device,
            type = device.type,
            svgCls = type ? 'node device ' + type : 'node device';

        // Augment as needed...
        node.class = 'device';
        node.svgClass = device.online ? svgCls + ' online' : svgCls;
        positionNode(node);

        // cache label array length
        network.deviceLabelCount = device.labels.length;
        return node;
    }

    function createHostNode(host) {
        // start with the object as is
        var node = host;

        // Augment as needed...
        node.class = 'host';
        if (!node.type) {
            // TODO: perhaps type would be: {phone, tablet, laptop, endstation} ?
            node.type = 'endstation';
        }
        node.svgClass = 'node host';
        // TODO: consider placing near its switch, if [x,y] not defined
        positionNode(node);

        // cache label array length
        network.hostLabelCount = host.labels.length;
        return node;
    }

    function positionNode(node) {
        var meta = node.metaUi,
            x = 0,
            y = 0;

        if (meta) {
            x = meta.x;
            y = meta.y;
        }
        if (x && y) {
            node.fixed = true;
        }
        node.x = x || network.view.width() / 2;
        node.y = y || network.view.height() / 2;
    }

    function iconUrl(d) {
        return 'img/' + d.type + '.png';
    }

    // returns the newly computed bounding box of the rectangle
    function adjustRectToFitText(n) {
        var text = n.select('text'),
            box = text.node().getBBox(),
            lab = config.labels;

        text.attr('text-anchor', 'middle')
            .attr('y', '-0.8em')
            .attr('x', lab.imgPad/2);

        // translate the bbox so that it is centered on [x,y]
        box.x = -box.width / 2;
        box.y = -box.height / 2;

        // add padding
        box.x -= (lab.padLR + lab.imgPad/2);
        box.width += lab.padLR * 2 + lab.imgPad;
        box.y -= lab.padTB;
        box.height += lab.padTB * 2;

        return box;
    }

    function mkSvgClass(d) {
        return d.fixed ? d.svgClass + ' fixed' : d.svgClass;
    }

    function hostLabel(d) {
        var idx = (hostLabelIndex < d.labels.length) ? hostLabelIndex : 0;
        return d.labels[idx];
    }
    function deviceLabel(d) {
        var idx = (deviceLabelIndex < d.labels.length) ? deviceLabelIndex : 0;
        return d.labels[idx];
    }
    function niceLabel(label) {
        return (label && label.trim()) ? label : '.';
    }

    function updateDeviceLabel(d) {
        var label = niceLabel(deviceLabel(d)),
            node = d.el,
            box;

        node.select('text')
            .text(label)
            .style('opacity', 0)
            .transition()
            .style('opacity', 1);

        box = adjustRectToFitText(node);

        node.select('rect')
            .transition()
            .attr(box);

        node.select('image')
            .transition()
            .attr('x', box.x + config.icons.xoff)
            .attr('y', box.y + config.icons.yoff);
    }

    function updateHostLabel(d) {
        var label = hostLabel(d),
            host = d.el;

        host.select('text').text(label);
    }

    function updateDeviceState(nodeData) {
        nodeData.el.classed('online', nodeData.online);
        updateDeviceLabel(nodeData);
        // TODO: review what else might need to be updated
    }

    function updateLinkState(linkData) {
        updateLinkWidth(linkData);
        // TODO: review what else might need to be updated
        //  update label, if showing
    }

    function updateHostState(hostData) {
        updateHostLabel(hostData);
        // TODO: review what else might need to be updated
    }


    function updateNodes() {
        node = nodeG.selectAll('.node')
            .data(network.nodes, function (d) { return d.id; });

        // operate on existing nodes, if necessary
        //  update host labels
        //node .foo() .bar() ...

        // operate on entering nodes:
        var entering = node.enter()
            .append('g')
            .attr({
                id: function (d) { return safeId(d.id); },
                class: mkSvgClass,
                transform: function (d) { return translate(d.x, d.y); },
                opacity: 0
            })
            .call(network.drag)
            //.on('mouseover', function (d) {})
            //.on('mouseover', function (d) {})
            .transition()
            .attr('opacity', 1);

        // augment device nodes...
        entering.filter('.device').each(function (d) {
            var node = d3.select(this),
                icon = iconUrl(d),
                label = niceLabel(deviceLabel(d)),
                box;

            // provide ref to element from backing data....
            d.el = node;

            node.append('rect')
                .attr({
                    'rx': 5,
                    'ry': 5
                });

            node.append('text')
                .text(label)
                .attr('dy', '1.1em');

            box = adjustRectToFitText(node);

            node.select('rect')
                .attr(box);

            if (icon) {
                var cfg = config.icons;
                node.append('svg:image')
                    .attr({
                        x: box.x + config.icons.xoff,
                        y: box.y + config.icons.yoff,
                        width: cfg.w,
                        height: cfg.h,
                        'xlink:href': icon
                    });
            }

            // debug function to show the modelled x,y coordinates of nodes...
            if (debug('showNodeXY')) {
                node.select('rect').attr('fill-opacity', 0.5);
                node.append('circle')
                    .attr({
                        class: 'debug',
                        cx: 0,
                        cy: 0,
                        r: '3px'
                    });
            }
        });

        // augment host nodes...
        entering.filter('.host').each(function (d) {
            var node = d3.select(this),
                box;

            // provide ref to element from backing data....
            d.el = node;

            node.append('circle')
                .attr('r', 8);     // TODO: define host circle radius

            // TODO: are we attaching labels to hosts?
            node.append('text')
                .text(hostLabel)
                .attr('dy', '1.3em')
                .attr('text-anchor', 'middle');

            // debug function to show the modelled x,y coordinates of nodes...
            if (debug('showNodeXY')) {
                node.select('circle').attr('fill-opacity', 0.5);
                node.append('circle')
                    .attr({
                        class: 'debug',
                        cx: 0,
                        cy: 0,
                        r: '3px'
                    });
            }
        });

        // operate on both existing and new nodes, if necessary
        //node .foo() .bar() ...

        // operate on exiting nodes:
        // TODO: figure out how to remove the node 'g' AND its children
        node.exit()
            .transition()
            .duration(750)
            .attr({
                opacity: 0,
                cx: 0,
                cy: 0,
                r: 0
            })
            .remove();
    }

    function find(id, array) {
        for (var idx = 0, n = array.length; idx < n; idx++) {
            if (array[idx].id === id) {
                return idx;
            }
        }
        return -1;
    }

    function removeLinkElement(linkData) {
        // remove from lookup cache
        delete network.lookup[linkData.id];
        // remove from links array
        var idx = find(linkData.id, network.links);

        network.links.splice(idx, 1);
        // remove from SVG
        updateLinks();
    }

    function tick() {
        node.attr({
            transform: function (d) { return translate(d.x, d.y); }
        });

        link.attr({
            x1: function (d) { return d.source.x; },
            y1: function (d) { return d.source.y; },
            x2: function (d) { return d.target.x; },
            y2: function (d) { return d.target.y; }
        });
    }

    // ==============================
    // Web-Socket for live data

    function webSockUrl() {
        return document.location.toString()
            .replace(/\#.*/, '')
            .replace('http://', 'ws://')
            .replace('https://', 'wss://')
            .replace('index2.html', config.webSockUrl);
    }

    webSock = {
        ws : null,

        connect : function() {
            webSock.ws = new WebSocket(webSockUrl());

            webSock.ws.onopen = function() {
            };

            webSock.ws.onmessage = function(m) {
                if (m.data) {
                    wsTraceRx(m.data);
                    handleServerEvent(JSON.parse(m.data));
                }
            };

            webSock.ws.onclose = function(m) {
                webSock.ws = null;
            };
        },

        send : function(text) {
            if (text != null) {
                webSock._send(text);
            }
        },

        _send : function(message) {
            if (webSock.ws) {
                webSock.ws.send(message);
            } else {
                network.view.alert('no web socket open\n\n' + message);
            }
        }

    };

    var sid = 0;

    function sendMessage(evType, payload) {
        var toSend = {
                event: evType,
                sid: ++sid,
                payload: payload
            },
            asText = JSON.stringify(toSend);
        wsTraceTx(asText);
        webSock.send(asText);
    }

    function wsTraceTx(msg) {
        wsTrace('tx', msg);
    }
    function wsTraceRx(msg) {
        wsTrace('rx', msg);
    }
    function wsTrace(rxtx, msg) {

        console.log('[' + rxtx + '] ' + msg);
        // TODO: integrate with trace view
        //if (trace) {
        //    trace.output(rxtx, msg);
        //}
    }


    // ==============================
    // Selection stuff

    function selectObject(obj, el) {
        var n,
            meta = d3.event.sourceEvent.metaKey;

        if (el) {
            n = d3.select(el);
        } else {
            node.each(function(d) {
                if (d == obj) {
                    n = d3.select(el = this);
                }
            });
        }
        if (!n) return;

        if (meta && n.classed('selected')) {
            deselectObject(obj.id);
            //flyinPane(null);
            return;
        }

        if (!meta) {
            deselectAll();
        }

        selections[obj.id] = { obj: obj, el  : el};
        selectOrder.push(obj.id);

        n.classed('selected', true);
        //flyinPane(obj);
    }

    function deselectObject(id) {
        var obj = selections[id];
        if (obj) {
            d3.select(obj.el).classed('selected', false);
            selections[id] = null;
            // TODO: use splice to remove element
        }
        //flyinPane(null);
    }

    function deselectAll() {
        // deselect all nodes in the network...
        node.classed('selected', false);
        selections = {};
        selectOrder = [];
        //flyinPane(null);
    }

    // TODO: this click handler does not get unloaded when the view does
    $('#view').on('click', function(e) {
        if (!$(e.target).closest('.node').length) {
            if (!e.metaKey) {
                deselectAll();
            }
        }
    });


    function prepareScenario(view, ctx, dbg) {
        var sc = scenario,
            urlSc = sc.evDir + ctx + sc.evScenario;

        if (!ctx) {
            view.alert("No scenario specified (null ctx)");
            return;
        }

        sc.view = view;
        sc.ctx = ctx;
        sc.debug = dbg;
        sc.evNumber = 0;

        d3.json(urlSc, function(err, data) {
            var p = data && data.params || {},
                desc = data && data.description || null,
                intro = data && data.title;

            if (err) {
                view.alert('No scenario found:\n\n' + urlSc + '\n\n' + err);
            } else {
                sc.params = p;
                if (desc) {
                    intro += '\n\n  ' + desc.join('\n  ');
                }
                view.alert(intro);
            }
        });

    }

    // ==============================
    // View life-cycle callbacks

    function preload(view, ctx, flags) {
        var w = view.width(),
            h = view.height(),
            idBg = view.uid('bg'),
            showBg = config.options.showBackground ? 'visible' : 'hidden',
            fcfg = config.force,
            fpad = fcfg.pad,
            forceDim = [w - 2*fpad, h - 2*fpad];

        // TODO: set trace api
        //trace = onos.exported.webSockTrace;

        // NOTE: view.$div is a D3 selection of the view's div
        svg = view.$div.append('svg');
        setSize(svg, view);

        // add blue glow filter to svg layer
        d3u.appendGlow(svg);

        // load the background image
        bgImg = svg.append('svg:image')
            .attr({
                id: idBg,
                width: w,
                height: h,
                'xlink:href': config.backgroundUrl
            })
            .style({
                visibility: showBg
            });

        // group for the topology
        topoG = svg.append('g')
            .attr('transform', fcfg.translate());

        // subgroups for links and nodes
        linkG = topoG.append('g').attr('id', 'links');
        nodeG = topoG.append('g').attr('id', 'nodes');

        // selection of nodes and links
        link = linkG.selectAll('.link');
        node = nodeG.selectAll('.node');

        function chrg(d) {
            return fcfg.charge[d.class] || -12000;
        }
        function ldist(d) {
            return fcfg.linkDistance[d.type] || 50;
        }
        function lstrg(d) {
            // 0.0 - 1.0
            return fcfg.linkStrength[d.type] || 1.0;
        }

        function selectCb(d, self) {
            selectObject(d, self);
        }

        function atDragEnd(d, self) {
            // once we've finished moving, pin the node in position
            d.fixed = true;
            d3.select(self).classed('fixed', true);
            if (config.useLiveData) {
                sendUpdateMeta(d);
            }
        }

        function sendUpdateMeta(d) {
            sendMessage('updateMeta', {
                id: d.id,
                'class': d.class,
                'memento': {
                    x: Math.floor(d.x),
                    y: Math.floor(d.y)
                }
            });
        }

        // set up the force layout
        network.force = d3.layout.force()
            .size(forceDim)
            .nodes(network.nodes)
            .links(network.links)
            .gravity(0.4)
            .friction(0.7)
            .charge(chrg)
            .linkDistance(ldist)
            .linkStrength(lstrg)
            .on('tick', tick);

        network.drag = d3u.createDragBehavior(network.force, selectCb, atDragEnd);
    }

    function load(view, ctx, flags) {
        // resize, in case the window was resized while we were not loaded
        resize(view, ctx, flags);

        // cache the view token, so network topo functions can access it
        network.view = view;
        config.useLiveData = !flags.local;

        if (!config.useLiveData) {
            prepareScenario(view, ctx, flags.debug);
        }

        // set our radio buttons and key bindings
        view.setRadio(btnSet);
        view.setKeys(keyDispatch);

        if (config.useLiveData) {
            webSock.connect();
        }
    }

    function resize(view, ctx, flags) {
        setSize(svg, view);
        setSize(bgImg, view);

        // TODO: hook to recompute layout, perhaps? work with zoom/pan code
        // adjust force layout size
    }


    // ==============================
    // View registration

    onos.ui.addView('topo', {
        preload: preload,
        load: load,
        resize: resize
    });

}(ONOS));