/*
 * Copyright 2015 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 GUI -- Topology Event Module.
 Defines event handling for events received from the server.
 */

(function () {
    'use strict';

    // injected refs
    var $log, fs, sus, is, ts, tis, uplink;

    var icfg;

    // configuration
    var labelConfig = {
            imgPad: 16,
            padLR: 4,
            padTB: 3,
            marginLR: 3,
            marginTB: 2,
            port: {
                gap: 3,
                width: 18,
                height: 14
            }
        };

    var deviceIconConfig = {
         xoff: -20,
         yoff: -18
    };

    var linkConfig = {
        light: {
            baseColor: '#666',
            inColor: '#66f',
            outColor: '#f00',
        },
        dark: {
            baseColor: '#666',
            inColor: '#66f',
            outColor: '#f00',
        },
        inWidth: 12,
        outWidth: 10
    };

    // internal state
    var settings,   // merged default settings and options
        force,      // force layout object
        drag,       // drag behavior handler
        network = {
            nodes: [],
            links: [],
            lookup: {},
            revLinkToKey: {}
        },
        lu = network.lookup,    // shorthand
        deviceLabelIndex = 0,   // for device label cycling
        hostLabelIndex = 0,     // for host label cycling
        showHosts = 1,          // whether hosts are displayed
        width, height;

    // SVG elements;
    var linkG, linkLabelG, nodeG;

    // D3 selections;
    var link, linkLabel, node;

    // default settings for force layout
    var defaultSettings = {
        gravity: 0.4,
        friction: 0.7,
        charge: {
            // note: key is node.class
            device: -8000,
            host: -5000,
            _def_: -12000
        },
        linkDistance: {
            // note: key is link.type
            direct: 100,
            optical: 120,
            hostLink: 3,
            _def_: 50
        },
        linkStrength: {
            // note: key is link.type
            // range: {0.0 ... 1.0}
            //direct: 1.0,
            //optical: 1.0,
            //hostLink: 1.0,
            _def_: 1.0
        }
    };


    // ==========================
    // === EVENT HANDLERS

    function addDevice(data) {
        var id = data.id,
            d;

        uplink.showNoDevs(false);

        // although this is an add device event, if we already have the
        //  device, treat it as an update instead..
        if (lu[id]) {
            updateDevice(data);
            return;
        }

        d = createDeviceNode(data);
        network.nodes.push(d);
        lu[id] = d;

        $log.debug("Created new device.. ", d.id, d.x, d.y);

        updateNodes();
        fStart();
    }

    function updateDevice(data) {
        var id = data.id,
            d = lu[id],
            wasOnline;

        if (d) {
            wasOnline = d.online;
            angular.extend(d, data);
            if (positionNode(d, true)) {
                sendUpdateMeta(d, true);
            }
            updateNodes();
            if (wasOnline !== d.online) {
                // TODO: re-instate link update, and offline visibility
                //findAttachedLinks(d.id).forEach(restyleLinkElement);
                //updateOfflineVisibility(d);
            }
        } else {
            // TODO: decide whether we want to capture logic errors
            //logicError('updateDevice lookup fail. ID = "' + id + '"');
        }
    }

    function removeDevice(data) {
        var id = data.id,
            d = lu[id];
        if (d) {
            removeDeviceElement(d);
        } else {
            // TODO: decide whether we want to capture logic errors
            //logicError('removeDevice lookup fail. ID = "' + id + '"');
        }
    }

    function addHost(data) {
        var id = data.id,
            d, lnk;

        // although this is an add host event, if we already have the
        //  host, treat it as an update instead..
        if (lu[id]) {
            updateHost(data);
            return;
        }

        d = createHostNode(data);
        network.nodes.push(d);
        lu[id] = d;

        $log.debug("Created new host.. ", d.id, d.x, d.y);

        updateNodes();

        lnk = createHostLink(data);
        if (lnk) {

            $log.debug("Created new host-link.. ", lnk.key);

            d.linkData = lnk;    // cache ref on its host
            network.links.push(lnk);
            lu[d.ingress] = lnk;
            lu[d.egress] = lnk;
            updateLinks();
        }

        fStart();
    }

    function updateHost(data) {
        var id = data.id,
            d = lu[id];
        if (d) {
            angular.extend(d, data);
            if (positionNode(d, true)) {
                sendUpdateMeta(d, true);
            }
            updateNodes();
        } else {
            // TODO: decide whether we want to capture logic errors
            //logicError('updateHost lookup fail. ID = "' + id + '"');
        }
    }

    function removeHost(data) {
        var id = data.id,
            d = lu[id];
        if (d) {
            removeHostElement(d, true);
        } else {
            // may have already removed host, if attached to removed device
            //console.warn('removeHost lookup fail. ID = "' + id + '"');
        }
    }

    function addLink(data) {
        var result = findLink(data, 'add'),
            bad = result.badLogic,
            d = result.ldata;

        if (bad) {
            //logicError(bad + ': ' + link.id);
            return;
        }

        if (d) {
            // we already have a backing store link for src/dst nodes
            addLinkUpdate(d, data);
            return;
        }

        // no backing store link yet
        d = createLink(data);
        if (d) {
            network.links.push(d);
            lu[d.key] = d;
            updateLinks();
            fStart();
        }
    }

    function updateLink(data) {
        var result = findLink(data, 'update'),
            bad = result.badLogic;
        if (bad) {
            //logicError(bad + ': ' + link.id);
            return;
        }
        result.updateWith(link);
    }

    function removeLink(data) {
        var result = findLink(data, 'remove'),
            bad = result.badLogic;
        if (bad) {
            // may have already removed link, if attached to removed device
            //console.warn(bad + ': ' + link.id);
            return;
        }
        result.removeRawLink();
    }

    // ========================

    function addLinkUpdate(ldata, link) {
        // add link event, but we already have the reverse link installed
        ldata.fromTarget = link;
        network.revLinkToKey[link.id] = ldata.key;
        restyleLinkElement(ldata);
    }

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

        if (!lnk) {
            return null;
        }

        angular.extend(lnk, {
            key: link.id,
            class: 'link',
            fromSource: link,

            // functions to aggregate dual link state
            type: function () {
                var s = lnk.fromSource,
                    t = lnk.fromTarget;
                return (s && s.type) || (t && t.type) || defaultLinkType;
            },
            online: function () {
                var s = lnk.fromSource,
                    t = lnk.fromTarget,
                    both = lnk.source.online && lnk.target.online;
                return both && ((s && s.online) || (t && t.online));
            },
            linkWidth: function () {
                var s = lnk.fromSource,
                    t = lnk.fromTarget,
                    ws = (s && s.linkWidth) || 0,
                    wt = (t && t.linkWidth) || 0;
                return Math.max(ws, wt);
            }
        });
        return lnk;
    }


    function makeNodeKey(d, what) {
        var port = what + 'Port';
        return d[what] + '/' + d[port];
    }

    function makeLinkKey(d, flipped) {
        var one = flipped ? makeNodeKey(d, 'dst') : makeNodeKey(d, 'src'),
            two = flipped ? makeNodeKey(d, 'src') : makeNodeKey(d, 'dst');
        return one + '-' + two;
    }

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

    var allLinkTypes = 'direct indirect optical tunnel',
        defaultLinkType = 'direct';

    function restyleLinkElement(ldata) {
        // this fn's job is to look at raw links and decide what svg classes
        // need to be applied to the line element in the DOM
        var th = ts.theme(),
            el = ldata.el,
            type = ldata.type(),
            lw = ldata.linkWidth(),
            online = ldata.online();

        el.classed('link', true);
        el.classed('inactive', !online);
        el.classed(allLinkTypes, false);
        if (type) {
            el.classed(type, true);
        }
        el.transition()
            .duration(1000)
            .attr('stroke-width', linkScale(lw))
            .attr('stroke', linkConfig[th].baseColor);
    }

    function findLink(linkData, op) {
        var key = makeLinkKey(linkData),
            keyrev = makeLinkKey(linkData, 1),
            link = lu[key],
            linkRev = lu[keyrev],
            result = {},
            ldata = link || linkRev,
            rawLink;

        if (op === 'add') {
            if (link) {
                // trying to add a link that we already know about
                result.ldata = link;
                result.badLogic = 'addLink: link already added';

            } else if (linkRev) {
                // we found the reverse of the link to be added
                result.ldata = linkRev;
                if (linkRev.fromTarget) {
                    result.badLogic = 'addLink: link already added';
                }
            }
        } else if (op === 'update') {
            if (!ldata) {
                result.badLogic = 'updateLink: link not found';
            } else {
                rawLink = link ? ldata.fromSource : ldata.fromTarget;
                result.updateWith = function (data) {
                    angular.extend(rawLink, data);
                    restyleLinkElement(ldata);
                }
            }
        } else if (op === 'remove') {
            if (!ldata) {
                result.badLogic = 'removeLink: link not found';
            } else {
                rawLink = link ? ldata.fromSource : ldata.fromTarget;

                if (!rawLink) {
                    result.badLogic = 'removeLink: link not found';

                } else {
                    result.removeRawLink = function () {
                        if (link) {
                            // remove fromSource
                            ldata.fromSource = null;
                            if (ldata.fromTarget) {
                                // promote target into source position
                                ldata.fromSource = ldata.fromTarget;
                                ldata.fromTarget = null;
                                ldata.key = keyrev;
                                delete network.lookup[key];
                                network.lookup[keyrev] = ldata;
                                delete network.revLinkToKey[keyrev];
                            }
                        } else {
                            // remove fromTarget
                            ldata.fromTarget = null;
                            delete network.revLinkToKey[keyrev];
                        }
                        if (ldata.fromSource) {
                            restyleLinkElement(ldata);
                        } else {
                            removeLinkElement(ldata);
                        }
                    }
                }
            }
        }
        return result;
    }


    function findAttachedHosts(devId) {
        var hosts = [];
        network.nodes.forEach(function (d) {
            if (d.class === 'host' && d.cp.device === devId) {
                hosts.push(d);
            }
        });
        return hosts;
    }

    function findAttachedLinks(devId) {
        var links = [];
        network.links.forEach(function (d) {
            if (d.source.id === devId || d.target.id === devId) {
                links.push(d);
            }
        });
        return links;
    }

    function removeLinkElement(d) {
        var idx = fs.find(d.key, network.links, 'key'),
            removed;
        if (idx >=0) {
            // remove from links array
            removed = network.links.splice(idx, 1);
            // remove from lookup cache
            delete lu[removed[0].key];
            updateLinks();
            fResume();
        }
    }

    function removeHostElement(d, upd) {
        // first, remove associated hostLink...
        removeLinkElement(d.linkData);

        // remove hostLink bindings
        delete lu[d.ingress];
        delete lu[d.egress];

        // remove from lookup cache
        delete lu[d.id];
        // remove from nodes array
        var idx = fs.find(d.id, network.nodes);
        network.nodes.splice(idx, 1);

        // remove from SVG
        // NOTE: upd is false if we were called from removeDeviceElement()
        if (upd) {
            updateNodes();
            fResume();
        }
    }

    function removeDeviceElement(d) {
        var id = d.id;
        // first, remove associated hosts and links..
        findAttachedHosts(id).forEach(removeHostElement);
        findAttachedLinks(id).forEach(removeLinkElement);

        // remove from lookup cache
        delete lu[id];
        // remove from nodes array
        var idx = fs.find(id, network.nodes);
        network.nodes.splice(idx, 1);

        if (!network.nodes.length) {
            xlink.showNoDevs(true);
        }

        // remove from SVG
        updateNodes();
        fResume();
    }


    function sendUpdateMeta(d, store) {
        var metaUi = {},
            ll;

        if (store) {
            ll = lngLatFromCoord([d.x, d.y]);
            metaUi = {
                x: d.x,
                y: d.y,
                lng: ll[0],
                lat: ll[1]
            };
        }
        d.metaUi = metaUi;
        uplink.sendEvent('updateMeta', {
            id: d.id,
            'class': d.class,
            memento: metaUi
        });
    }


    function fStart() {
        $log.debug('TODO fStart()...');
        // TODO...
    }

    function fResume() {
        $log.debug('TODO fResume()...');
        // TODO...
    }

    // ==========================
    // === Devices and hosts - helper functions

    function coordFromLngLat(loc) {
        var p = uplink.projection();
        return p ? p([loc.lng, loc.lat]) : [0, 0];
    }

    function lngLatFromCoord(coord) {
        var p = uplink.projection();
        return p ? p.invert([coord.x, coord.y]) : [0, 0];
    }

    function positionNode(node, forUpdate) {
        var meta = node.metaUi,
            x = meta && meta.x,
            y = meta && meta.y,
            xy;

        // If we have [x,y] already, use that...
        if (x && y) {
            node.fixed = true;
            node.px = node.x = x;
            node.py = node.y = y;
            return;
        }

        var location = node.location,
            coord;

        if (location && location.type === 'latlng') {
            coord = coordFromLngLat(location);
            node.fixed = true;
            node.px = node.x = coord[0];
            node.py = node.y = coord[1];
            return true;
        }

        // if this is a node update (not a node add).. skip randomizer
        if (forUpdate) {
            return;
        }

        // Note: Placing incoming unpinned nodes at exactly the same point
        //        (center of the view) causes them to explode outwards when
        //        the force layout kicks in. So, we spread them out a bit
        //        initially, to provide a more serene layout convergence.
        //       Additionally, if the node is a host, we place it near
        //        the device it is connected to.

        function spread(s) {
            return Math.floor((Math.random() * s) - s/2);
        }

        function randDim(dim) {
            return dim / 2 + spread(dim * 0.7071);
        }

        function rand() {
            return {
                x: randDim(width),
                y: randDim(height)
            };
        }

        function near(node) {
            var min = 12,
                dx = spread(12),
                dy = spread(12);
            return {
                x: node.x + min + dx,
                y: node.y + min + dy
            };
        }

        function getDevice(cp) {
            var d = lu[cp.device];
            return d || rand();
        }

        xy = (node.class === 'host') ? near(getDevice(node.cp)) : rand();
        angular.extend(node, xy);
    }

    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);
        return node;
    }

    function createHostNode(host) {
        var node = host;

        // Augment as needed...
        node.class = 'host';
        if (!node.type) {
            node.type = 'endstation';
        }
        node.svgClass = 'node host ' + node.type;
        positionNode(node);
        return node;
    }

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

        if (!lnk) {
            return null;
        }

        // Synthesize link ...
        angular.extend(lnk, {
            key: id,
            class: 'link',

            type: function () { return 'hostLink'; },
            online: function () {
                // hostlink target is edge switch
                return lnk.target.online;
            },
            linkWidth: function () { return 1; }
        });
        return lnk;
    }

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

        if (sMiss || dMiss) {
            $log.error('Node(s) not on map for link:\n' + 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 missMsg(what, id) {
        return '\n[' + what + '] "' + id + '" missing ';
    }

    // ==========================
    // === Devices and hosts - D3 rendering

    function nodeMouseOver(m) {
        // TODO
        $log.debug("TODO nodeMouseOver()...", m);
    }

    function nodeMouseOut(m) {
        // TODO
        $log.debug("TODO nodeMouseOut()...", m);
    }


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

        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 trimLabel(label) {
        return (label && label.trim()) || '';
    }

    function emptyBox() {
        return {
            x: -2,
            y: -2,
            width: 4,
            height: 4
        };
    }


    function updateDeviceLabel(d) {
        var label = trimLabel(deviceLabel(d)),
            noLabel = !label,
            node = d.el,
            dim = icfg.device.dim,
            devCfg = deviceIconConfig,
            box, dx, dy;

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

        if (noLabel) {
            box = emptyBox();
            dx = -dim/2;
            dy = -dim/2;
        } else {
            box = adjustRectToFitText(node);
            dx = box.x + devCfg.xoff;
            dy = box.y + devCfg.yoff;
        }

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

        node.select('g.deviceIcon')
            .transition()
            .attr('transform', sus.translate(dx, dy));
    }

    function updateHostLabel(d) {
        var label = trimLabel(hostLabel(d));
        d.el.select('text').text(label);
    }

    function updateDeviceColors(d) {
        if (d) {
            setDeviceColor(d);
        } else {
            node.filter('.device').each(function (d) {
                setDeviceColor(d);
            });
        }
    }

    var dCol = {
        black: '#000',
        paleblue: '#acf',
        offwhite: '#ddd',
        darkgrey: '#444',
        midgrey: '#888',
        lightgrey: '#bbb',
        orange: '#f90'
    };

    // note: these are the device icon colors without affinity
    var dColTheme = {
        light: {
            rfill: dCol.offwhite,
            online: {
                glyph: dCol.darkgrey,
                rect: dCol.paleblue
            },
            offline: {
                glyph: dCol.midgrey,
                rect: dCol.lightgrey
            }
        },
        dark: {
            rfill: dCol.midgrey,
            online: {
                glyph: dCol.darkgrey,
                rect: dCol.paleblue
            },
            offline: {
                glyph: dCol.midgrey,
                rect: dCol.darkgrey
            }
        }
    };

    function devBaseColor(d) {
        var o = d.online ? 'online' : 'offline';
        return dColTheme[ts.theme()][o];
    }

    function setDeviceColor(d) {
        var o = d.online,
            s = d.el.classed('selected'),
            c = devBaseColor(d),
            a = instColor(d.master, o),
            icon = d.el.select('g.deviceIcon'),
            g, r;

        if (s) {
            g = c.glyph;
            r = dCol.orange;
        } else if (tis.isVisible()) {
            g = o ? a : c.glyph;
            r = o ? c.rfill : a;
        } else {
            g = c.glyph;
            r = c.rect;
        }

        icon.select('use').style('fill', g);
        icon.select('rect').style('fill', r);
    }

    function instColor(id, online) {
        return sus.cat7().getColor(id, !online, ts.theme());
    }

    // ==========================

    function updateNodes() {
        // select all the nodes in the layout:
        node = nodeG.selectAll('.node')
            .data(network.nodes, function (d) { return d.id; });

        // operate on existing nodes:
        node.filter('.device').each(deviceExisting);
        node.filter('.host').each(hostExisting);

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

        // augment entering nodes:
        entering.filter('.device').each(deviceEnter);
        entering.filter('.host').each(hostEnter);

        // operate on both existing and new nodes:
        updateDeviceColors();

        // operate on exiting nodes:
        // Note that the node is removed after 2 seconds.
        // Sub element animations should be shorter than 2 seconds.
        var exiting = node.exit()
            .transition()
            .duration(2000)
            .style('opacity', 0)
            .remove();

        // exiting node specifics:
        exiting.filter('.host').each(hostExit);
        exiting.filter('.device').each(deviceExit);

        // finally, resume the force layout
        fResume();
    }

    // ==========================
    // updateNodes - subfunctions

    function deviceExisting(d) {
        var node = d.el;
        node.classed('online', d.online);
        updateDeviceLabel(d);
        positionNode(d, true);
    }

    function hostExisting(d) {
        updateHostLabel(d);
        positionNode(d, true);
    }

    function deviceEnter(d) {
        var node = d3.select(this),
            glyphId = d.type || 'unknown',
            label = trimLabel(deviceLabel(d)),
            devCfg = deviceIconConfig,
            noLabel = !label,
            box, dx, dy, icon;

        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);

        icon = is.addDeviceIcon(node, glyphId);

        if (noLabel) {
            dx = -icon.dim/2;
            dy = -icon.dim/2;
        } else {
            box = adjustRectToFitText(node);
            dx = box.x + devCfg.xoff;
            dy = box.y + devCfg.yoff;
        }

        icon.attr('transform', sus.translate(dx, dy));
    }

    function hostEnter(d) {
        var node = d3.select(this),
            gid = d.type || 'unknown',
            rad = icfg.host.radius,
            r = d.type ? rad.withGlyph : rad.noGlyph,
            textDy = r + 10;

        d.el = node;
        sus.makeVisible(node, showHosts);

        is.addHostIcon(node, r, gid);

        node.append('text')
            .text(hostLabel)
            .attr('dy', textDy)
            .attr('text-anchor', 'middle');
    }

    function hostExit(d) {
        var node = d.el;
        node.select('use')
            .style('opacity', 0.5)
            .transition()
            .duration(800)
            .style('opacity', 0);

        node.select('text')
            .style('opacity', 0.5)
            .transition()
            .duration(800)
            .style('opacity', 0);

        node.select('circle')
            .style('stroke-fill', '#555')
            .style('fill', '#888')
            .style('opacity', 0.5)
            .transition()
            .duration(1500)
            .attr('r', 0);
    }

    function deviceExit(d) {
        var node = d.el;
        node.select('use')
            .style('opacity', 0.5)
            .transition()
            .duration(800)
            .style('opacity', 0);

        node.selectAll('rect')
            .style('stroke-fill', '#555')
            .style('fill', '#888')
            .style('opacity', 0.5);
    }

    // ==========================

    function updateLinks() {
        var th = ts.theme();

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

        // operate on existing links:
        //link.each(linkExisting);

        // operate on entering links:
        var entering = link.enter()
            .append('line')
            .attr({
                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: linkConfig[th].inColor,
                'stroke-width': linkConfig.inWidth
            });

        // augment links
        entering.each(linkEntering);

        // operate on both existing and new links:
        //link.each(...)

        // apply or remove labels
        var labelData = getLabelData();
        applyLinkLabels(labelData);

        // operate on exiting links:
        link.exit()
            .attr('stroke-dasharray', '3 3')
            .style('opacity', 0.5)
            .transition()
            .duration(1500)
            .attr({
                'stroke-dasharray': '3 12',
                stroke: linkConfig[th].outColor,
                'stroke-width': linkConfig.outWidth
            })
            .style('opacity', 0.0)
            .remove();

        // NOTE: invoke a single tick to force the labels to position
        //        onto their links.
        tick();
        // FIXME: this is a bug when in oblique view
        // It causes the nodes to jump into "overhead" view positions, even
        //  though the oblique planes are still showing...
    }

    // ==========================
    // updateLinks - subfunctions

    function getLabelData() {
        // create the backing data for showing labels..
        var data = [];
        link.each(function (d) {
            if (d.label) {
                data.push({
                    id: 'lab-' + d.key,
                    key: d.key,
                    label: d.label,
                    ldata: d
                });
            }
        });
        return data;
    }

    //function linkExisting(d) { }

    function linkEntering(d) {
        var link = d3.select(this);
        d.el = link;
        restyleLinkElement(d);
        if (d.type() === 'hostLink') {
            sus.makeVisible(link, showHosts);
        }
    }

    //function linkExiting(d) { }

    var linkLabelOffset = '0.3em';

    function applyLinkLabels(data) {
        var entering;

        linkLabel = linkLabelG.selectAll('.linkLabel')
            .data(data, function (d) { return d.id; });

        // for elements already existing, we need to update the text
        // and adjust the rectangle size to fit
        linkLabel.each(function (d) {
            var el = d3.select(this),
                rect = el.select('rect'),
                text = el.select('text');
            text.text(d.label);
            rect.attr(rectAroundText(el));
        });

        entering = linkLabel.enter().append('g')
            .classed('linkLabel', true)
            .attr('id', function (d) { return d.id; });

        entering.each(function (d) {
            var el = d3.select(this),
                rect,
                text,
                parms = {
                    x1: d.ldata.x1,
                    y1: d.ldata.y1,
                    x2: d.ldata.x2,
                    y2: d.ldata.y2
                };

            d.el = el;
            rect = el.append('rect');
            text = el.append('text').text(d.label);
            rect.attr(rectAroundText(el));
            text.attr('dy', linkLabelOffset);

            el.attr('transform', transformLabel(parms));
        });

        // Remove any labels that are no longer required.
        linkLabel.exit().remove();
    }

    function rectAroundText(el) {
        var text = el.select('text'),
            box = text.node().getBBox();

        // 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 -= 1;
        box.width += 2;
        return box;
    }

    function transformLabel(p) {
        var dx = p.x2 - p.x1,
            dy = p.y2 - p.y1,
            xMid = dx/2 + p.x1,
            yMid = dy/2 + p.y1;
        return sus.translate(xMid, yMid);
    }

    // ==========================
    // force layout tick function
    function tick() {

    }


    // ==========================
    // === MOUSE GESTURE HANDLERS

    function selectCb() { }
    function atDragEnd() {}
    function dragEnabled() {}
    function clickEnabled() {}


    // ==========================
    // Module definition

    angular.module('ovTopo')
    .factory('TopoForceService',
        ['$log', 'FnService', 'SvgUtilService', 'IconService', 'ThemeService',
            'TopoInstService',

        function (_$log_, _fs_, _sus_, _is_, _ts_, _tis_) {
            $log = _$log_;
            fs = _fs_;
            sus = _sus_;
            is = _is_;
            ts = _ts_;
            tis = _tis_;

            icfg = is.iconConfig();

            // forceG is the SVG group to display the force layout in
            // xlink is the cross-link api from the main topo source file
            // w, h are the initial dimensions of the SVG
            // opts are, well, optional :)
            function initForce(forceG, _uplink_, w, h, opts) {
                $log.debug('initForce().. WxH = ' + w + 'x' + h);
                uplink = _uplink_;
                width = w;
                height = h;

                settings = angular.extend({}, defaultSettings, opts);

                linkG = forceG.append('g').attr('id', 'topo-links');
                linkLabelG = forceG.append('g').attr('id', 'topo-linkLabels');
                nodeG = forceG.append('g').attr('id', 'topo-nodes');

                link = linkG.selectAll('.link');
                linkLabel = linkLabelG.selectAll('.linkLabel');
                node = nodeG.selectAll('.node');

                force = d3.layout.force()
                    .size([w, h])
                    .nodes(network.nodes)
                    .links(network.links)
                    .gravity(settings.gravity)
                    .friction(settings.friction)
                    .charge(settings.charge._def_)
                    .linkDistance(settings.linkDistance._def_)
                    .linkStrength(settings.linkStrength._def_)
                    .on('tick', tick);

                drag = sus.createDragBehavior(force,
                    selectCb, atDragEnd, dragEnabled, clickEnabled);
            }

            function resize(dim) {
                width = dim.width;
                height = dim.height;
                force.size([width, height]);
                // Review -- do we need to nudge the layout ?
            }

            return {
                initForce: initForce,
                resize: resize,

                updateDeviceColors: updateDeviceColors,

                addDevice: addDevice,
                updateDevice: updateDevice,
                removeDevice: removeDevice,
                addHost: addHost,
                updateHost: updateHost,
                removeHost: removeHost,
                addLink: addLink,
                updateLink: updateLink,
                removeLink: removeLink
            };
        }]);
}());