iD.Way = iD.Entity.way = function iD_Way() {
    if (!(this instanceof iD_Way)) {
        return (new iD_Way()).initialize(arguments);
    } else if (arguments.length) {
        this.initialize(arguments);
    }
};

iD.Way.prototype = Object.create(iD.Entity.prototype);

_.extend(iD.Way.prototype, {
    type: 'way',
    nodes: [],

    extent: function(resolver) {
        return resolver.transient(this, 'extent', function() {
            return this.nodes.reduce(function(extent, id) {
                var node = resolver.hasEntity(id);
                if (node) {
                    return extent.extend(node.extent());
                } else {
                    return extent;
                }
            }, iD.geo.Extent());
        });
    },

    first: function() {
        return this.nodes[0];
    },

    last: function() {
        return this.nodes[this.nodes.length - 1];
    },

    contains: function(node) {
        return this.nodes.indexOf(node) >= 0;
    },

    affix: function(node) {
        if (this.nodes[0] === node) return 'prefix';
        if (this.nodes[this.nodes.length - 1] === node) return 'suffix';
    },

    isOneWay: function() {
        return this.tags.oneway === 'yes' ||
            this.tags.oneway === '1' ||
            this.tags.oneway === '-1' ||
            this.tags.waterway === 'river' ||
            this.tags.waterway === 'stream' ||
            this.tags.junction === 'roundabout';
    },

    isClosed: function() {
        return this.nodes.length > 0 && this.first() === this.last();
    },

    isArea: function() {
        if (this.tags.area === 'yes')
            return true;
        if (!this.isClosed() || this.tags.area === 'no')
            return false;
        for (var key in this.tags)
            if (key in iD.areaKeys && !(this.tags[key] in iD.areaKeys[key]))
                return true;
        return false;
    },

    isDegenerate: function() {
        return _.uniq(this.nodes).length < (this.isArea() ? 3 : 2);
    },

    areAdjacent: function(n1, n2) {
        for (var i = 0; i < this.nodes.length; i++) {
            if (this.nodes[i] === n1) {
                if (this.nodes[i - 1] === n2) return true;
                if (this.nodes[i + 1] === n2) return true;
            }
        }
        return false;
    },

    geometry: function(graph) {
        return graph.transient(this, 'geometry', function() {
            return this.isArea() ? 'area' : 'line';
        });
    },

    addNode: function(id, index) {
        var nodes = this.nodes.slice();
        nodes.splice(index === undefined ? nodes.length : index, 0, id);
        return this.update({nodes: nodes});
    },

    updateNode: function(id, index) {
        var nodes = this.nodes.slice();
        nodes.splice(index, 1, id);
        return this.update({nodes: nodes});
    },

    replaceNode: function(needle, replacement) {
        if (this.nodes.indexOf(needle) < 0)
            return this;

        var nodes = this.nodes.slice();
        for (var i = 0; i < nodes.length; i++) {
            if (nodes[i] === needle) {
                nodes[i] = replacement;
            }
        }
        return this.update({nodes: nodes});
    },

    removeNode: function(id) {
        var nodes = [];

        for (var i = 0; i < this.nodes.length; i++) {
            var node = this.nodes[i];
            if (node !== id && nodes[nodes.length - 1] !== node) {
                nodes.push(node);
            }
        }

        // Preserve circularity
        if (this.nodes.length > 1 && this.first() === id && this.last() === id && nodes[nodes.length - 1] !== nodes[0]) {
            nodes.push(nodes[0]);
        }

        return this.update({nodes: nodes});
    },

    asJXON: function(changeset_id) {
        var r = {
            way: {
                '@id': this.osmId(),
                '@version': this.version || 0,
                nd: _.map(this.nodes, function(id) {
                    return { keyAttributes: { ref: iD.Entity.id.toOSM(id) } };
                }),
                tag: _.map(this.tags, function(v, k) {
                    return { keyAttributes: { k: k, v: v } };
                })
            }
        };
        if (changeset_id) r.way['@changeset'] = changeset_id;
        return r;
    },

    asGeoJSON: function(resolver) {
        return resolver.transient(this, 'GeoJSON', function() {
            var coordinates = _.pluck(resolver.childNodes(this), 'loc');
            if (this.isArea() && this.isClosed()) {
                return {
                    type: 'Polygon',
                    coordinates: [coordinates]
                };
            } else {
                return {
                    type: 'LineString',
                    coordinates: coordinates
                };
            }
        });
    },

    area: function(resolver) {
        return resolver.transient(this, 'area', function() {
            var nodes = resolver.childNodes(this);

            if (!this.isClosed() && nodes.length) {
                nodes = nodes.concat([nodes[0]]);
            }

            var json = {
                type: 'Polygon',
                coordinates: [_.pluck(nodes, 'loc')]
            };

            var area = d3.geo.area(json);

            // Heuristic for detecting counterclockwise winding order. Assumes
            // that OpenStreetMap polygons are not hemisphere-spanning.
            if (d3.geo.area(json) > 2 * Math.PI) {
                json.coordinates[0] = json.coordinates[0].reverse();
                area = d3.geo.area(json);
            }

            return isNaN(area) ? 0 : area;
        });
    }
});