local Node = require('Node');
local Edge = require('Edge');

local Graph = {};

function Graph.new()
    local self = {};

    local nodes = {};
    local edges = {};
    local edgeIDs = 0;

    local attractionPoint;

    ---
    -- Creates a new graph based on the information passed via the table
    -- parameter. It creates all nodes and connects them via edges.
    -- @param table - A table containing information about nodes and edges.
    -- @param x - The minimum x value to use when randomly spawning nodes.
    -- @param y - The minimum y value to use when randomly spawning nodes.
    -- @param w - The maximum x value to use when randomly spawning nodes.
    -- @param h - The maximum y value to use when randomly spawning nodes.
    --
    function self:create( table, x, y, w, h )
        math.randomseed( os.time() );

        for _, id in pairs( table.nodes ) do
            local rx, ry = math.random( x, w ), math.random( y, h );
            self:addNode( Node.new( id, rx, ry ));
        end

        for _, edge in pairs( table.edges ) do
            self:addEdge( nodes[edge.origin], nodes[edge.target] );
        end
    end

    ---
    -- Add a node to the graph.
    -- @param node - The node to add to the graph.
    --
    function self:addNode( node )
        assert( not nodes[node:getID()], "Node IDs must be unique." );
        nodes[node:getID()] = node;
    end

    ---
    -- Remove a node from the graph. This will also remove all edges pointing to
    -- or originating from this node.
    -- @param node - The node to remove from the graph.
    --
    function self:removeNode( node )
        nodes[node:getID()] = nil;

        self:removeEdges( node );
    end

    ---
    -- Adds a global attraction point.
    -- This point won't show up in the graph itself and can not be interacted
    -- with. Instead it only has the purpose to attract all nodes in the graph.
    -- This can be useful if you have unconnected nodes and want to prevent
    -- them from floating away.
    -- @param ncx - The x-coordinate of the attraction point.
    -- @param ncy - The y-coordinate of the attraction point.
    function self:addAttractionPoint( ncx, ncy )
        attractionPoint = Node.new( 'center', ncx, ncy );
    end

    ---
    -- Adds a new edge between two nodes.
    -- @param origin - The node from which the edge originates.
    -- @param target - The node to which the edge is pointing to.
    --
    function self:addEdge( origin, target )
        for _, edge in pairs(edges) do
            if edge.origin == origin and edge.target == target then
                error "Trying to connect nodes which are already connected.";
            end
        end

        assert(origin ~= target, "Tried to connect a node with itself.");
        edges[edgeIDs] = Edge.new( edgeIDs, origin, target );
        edgeIDs = edgeIDs + 1;
    end

    ---
    -- Removes all edges leading to or originating from a node.
    -- @param node - The node to remove all edges from.
    --
    function self:removeEdges( node )
        for id, edge in pairs( edges ) do
            if edge.origin == node or edge.target == node then
                edges[id] = nil;
            end
        end
    end

    ---
    -- Updates the graph.
    -- @param dt - The delta time between frames.
    --
    function self:update( dt )
        for _, edge in pairs( edges ) do
            edge.origin:attractTo( edge.target );
            edge.target:attractTo( edge.origin );
        end

        for _, nodeA in pairs( nodes ) do
            if attractionPoint then
                nodeA:attractTo( attractionPoint );
            end

            for _, nodeB in pairs( nodes ) do
                if nodeA ~= nodeB then
                    nodeA:repelFrom( nodeB );
                end
            end
            nodeA:move( dt );
        end
    end

    ---
    -- This function receives a single parameter of type function to which it
    -- will pass the edges and nodes tables. This means the user has to provide
    -- his own drawing function.
    -- @param func - The function to pass the tables to.
    --
    function self:draw( func )
        func( edges, nodes );
    end

    ---
    -- Gets a node at a certain point in the graph.
    -- @param x - The x coordinate to check.
    -- @param y - The y coordinate to check.
    -- @param range - The range in which to check around the given coordinates.
    --
    function self:getNodeAt(x, y, range)
        for _, node in pairs( nodes ) do
            local nx, ny = node:getPosition();
            if x < nx + range and x > nx - range and y < ny + range and y > ny - range then
                return node;
            end
        end
    end

    return self;
end

return Graph;