// Creating a node graph editor for ImGui
// Quick demo, not production code!
// See https://github.com/ocornut/imgui/issues/306
// v0.01
// Animated gif: https://cloud.githubusercontent.com/assets/8225057/9472357/c0263c04-4b4c-11e5-9fdf-2cd4f33f6582.gif

#include <math.h>
#include "imgui.h"

// NB: You can use math functions/operators on ImVec2 if you #define IMGUI_DEFINE_MATH_OPERATORS and #include "imgui_internal.h"
// Here we only declare simple +/- operators so others don't leak into the demo code.
static inline ImVec2 operator+(const ImVec2& lhs, const ImVec2& rhs) { return ImVec2(lhs.x+rhs.x, lhs.y+rhs.y); }
static inline ImVec2 operator-(const ImVec2& lhs, const ImVec2& rhs) { return ImVec2(lhs.x-rhs.x, lhs.y-rhs.y); }

// Really dumb data structure provided for the example.
// Note that we storing links are INDICES (not ID) to make example code shorter, obviously a bad idea for any general purpose code.
void ShowExampleAppCustomNodeGraph(bool* opened)
{
    ImGui::SetNextWindowSize(ImVec2(700,600), ImGuiSetCond_FirstUseEver);
    if (!ImGui::Begin("Example: Custom Node Graph", opened))
    {
        ImGui::End();
        return;
    }

    struct Node
    {
        int     ID;
        char    Name[32];
        ImVec2  Pos, Size;
        float   Value;
        int     InputsCount, OutputsCount;

        Node(int id, const char* name, const ImVec2& pos, float value, int inputs_count, int outputs_count) { ID = id; strncpy(Name, name, 31); Name[31] = 0; Pos = pos; Value = value; InputsCount = inputs_count; OutputsCount = outputs_count; }

        ImVec2 GetInputSlotPos(int slot_no) const   { return ImVec2(Pos.x, Pos.y + Size.y * ((float)slot_no+1) / ((float)InputsCount+1)); }
        ImVec2 GetOutputSlotPos(int slot_no) const  { return ImVec2(Pos.x + Size.x, Pos.y + Size.y * ((float)slot_no+1) / ((float)OutputsCount+1)); }
    };
    struct NodeLink
    {
        int     InputIdx, InputSlot, OutputIdx, OutputSlot;

        NodeLink(int input_idx, int input_slot, int output_idx, int output_slot) { InputIdx = input_idx; InputSlot = input_slot; OutputIdx = output_idx; OutputSlot = output_slot; }
    };

    static ImVector<Node> nodes;
    static ImVector<NodeLink> links;
    static bool inited = false;
    static ImVec2 scrolling = ImVec2(0.0f, 0.0f);
    static int node_selected = -1;
    if (!inited)
    {
        nodes.push_back(Node(0, "MainTex",  ImVec2(40,50), 0.5f, 1, 1));
        nodes.push_back(Node(1, "BumpMap",  ImVec2(40,150), 0.42f, 1, 1));
        nodes.push_back(Node(2, "Combine", ImVec2(270,80), 1.0f, 2, 2));
        links.push_back(NodeLink(0, 0, 2, 0));
        links.push_back(NodeLink(1, 0, 2, 1));
        inited = true;
    }

    // Draw a list of nodes on the left side
    bool open_context_menu = false;
    int node_hovered_in_list = -1;
    int node_hovered_in_scene = -1;
    ImGui::BeginChild("node_list", ImVec2(100,0));
    ImGui::Text("Nodes");
    ImGui::Separator();
    for (int node_idx = 0; node_idx < nodes.Size; node_idx++)
    {
        Node* node = &nodes[node_idx];
        ImGui::PushID(node->ID);
        if (ImGui::Selectable(node->Name, node->ID == node_selected))
            node_selected = node->ID;
        if (ImGui::IsItemHovered())
        {
            node_hovered_in_list = node->ID;
            open_context_menu |= ImGui::IsMouseClicked(1);
        }
        ImGui::PopID();
    }
    ImGui::EndChild();

    ImGui::SameLine();
    ImGui::BeginGroup();

    const float NODE_SLOT_RADIUS = 4.0f;
    const ImVec2 NODE_WINDOW_PADDING(8.0f, 8.0f);

    // Create our child canvas
    ImGui::Text("Hold middle mouse button to scroll (%.2f,%.2f)", scrolling.x, scrolling.y);
    ImGui::PushStyleVar(ImGuiStyleVar_FramePadding, ImVec2(1,1));
    ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(0,0));
    ImGui::PushStyleColor(ImGuiCol_ChildWindowBg, ImColor(40,40,40,200));
    ImGui::BeginChild("scrolling_region", ImVec2(0,0), true, ImGuiWindowFlags_NoScrollbar|ImGuiWindowFlags_NoMove);
    ImGui::PushItemWidth(120.0f);

    ImDrawList* draw_list = ImGui::GetWindowDrawList();
    draw_list->ChannelsSplit(2);
    ImVec2 offset = ImGui::GetCursorScreenPos() - scrolling;

    // Display links
    draw_list->ChannelsSetCurrent(0); // Background
    for (int link_idx = 0; link_idx < links.Size; link_idx++)
    {
        NodeLink* link = &links[link_idx];
        Node* node_inp = &nodes[link->InputIdx];
        Node* node_out = &nodes[link->OutputIdx];

#if 1
        // Hermite spline
        // TODO: move to ImDrawList path API
        ImVec2 p1 = offset+node_inp->GetOutputSlotPos(link->InputSlot);
        ImVec2 t1 = ImVec2(+80.0f, 0.0f);
        ImVec2 p2 = offset+node_out->GetInputSlotPos(link->OutputSlot);
        ImVec2 t2 = ImVec2(+80.0f, 0.0f);
        const int STEPS = 12;
        for (int step = 0; step <= STEPS; step++)
        {
            float t = (float)step / (float)STEPS;
            float h1 = +2*t*t*t - 3*t*t + 1.0f;
            float h2 = -2*t*t*t + 3*t*t;
            float h3 =    t*t*t - 2*t*t + t;
            float h4 =    t*t*t -   t*t;
            draw_list->PathLineTo(ImVec2(h1*p1.x + h2*p2.x + h3*t1.x + h4*t2.x, h1*p1.y + h2*p2.y + h3*t1.y + h4*t2.y));
        }
        draw_list->PathStroke(ImColor(200,200,100), false, 3.0f);
#else
        draw_list->AddLine(offset+node_inp->GetOutputSlotPos(link->InputSlot), offset+node_out->GetInputSlotPos(link->OutputSlot), ImColor(200,200,100), 3.0f);
#endif
    }

    // Display nodes
    for (int node_idx = 0; node_idx < nodes.Size; node_idx++)
    {
        Node* node = &nodes[node_idx];
        ImGui::PushID(node->ID);
        ImVec2 node_rect_min = offset + node->Pos;

        // Display node contents first
        draw_list->ChannelsSetCurrent(1); // Foreground
        bool old_any_active = ImGui::IsAnyItemActive();
        ImGui::SetCursorScreenPos(node_rect_min + NODE_WINDOW_PADDING);
        ImGui::BeginGroup(); // Lock horizontal position
        ImGui::Text("%s", node->Name);
        ImGui::SliderFloat("##value", &node->Value, 0.0f, 1.0f, "Alpha %.2f");
        float dummy_color[3] = { node->Pos.x / ImGui::GetWindowWidth(), node->Pos.y / ImGui::GetWindowHeight(), fmodf((float)node->ID * 0.5f, 1.0f) };
        ImGui::ColorEdit3("##color", &dummy_color[0]);
        ImGui::EndGroup();

        // Save the size of what we have emitted and weither any of the widgets are being used
        bool node_widgets_active = (!old_any_active && ImGui::IsAnyItemActive());
        node->Size = ImGui::GetItemRectSize() + NODE_WINDOW_PADDING + NODE_WINDOW_PADDING;
        ImVec2 node_rect_max = node_rect_min + node->Size;

        // Display node box
        draw_list->ChannelsSetCurrent(0); // Background
        ImGui::SetCursorScreenPos(node_rect_min);
        ImGui::InvisibleButton("node", node->Size);
        if (ImGui::IsItemHovered())
        {
            node_hovered_in_scene = node->ID;
            open_context_menu |= ImGui::IsMouseClicked(1);
        }
        bool node_moving_active = ImGui::IsItemActive();
        if (node_widgets_active || node_moving_active)
            node_selected = node->ID;
        if (node_moving_active && ImGui::IsMouseDragging(0))
            node->Pos = node->Pos + ImGui::GetIO().MouseDelta;

        ImU32 node_bg_color = (node_hovered_in_list == node->ID || node_hovered_in_scene == node->ID || (node_hovered_in_list == -1 && node_selected == node->ID)) ? ImColor(75,75,75) : ImColor(60,60,60);
        draw_list->AddRectFilled(node_rect_min, node_rect_max, node_bg_color, 4.0f); 
        draw_list->AddRect(node_rect_min, node_rect_max, ImColor(100,100,100), 4.0f); 
        for (int slot_idx = 0; slot_idx < node->InputsCount; slot_idx++)
            draw_list->AddCircleFilled(offset + node->GetInputSlotPos(slot_idx), NODE_SLOT_RADIUS, ImColor(150,150,150,150));
        for (int slot_idx = 0; slot_idx < node->OutputsCount; slot_idx++)
            draw_list->AddCircleFilled(offset + node->GetOutputSlotPos(slot_idx), NODE_SLOT_RADIUS, ImColor(150,150,150,150));

        ImGui::PopID();
    }
    draw_list->ChannelsMerge();

    // Open context menu
    if (!ImGui::IsAnyItemHovered() && ImGui::IsMouseHoveringWindow() && ImGui::IsMouseClicked(1))
    {
        node_selected = node_hovered_in_list = node_hovered_in_scene = -1;
        open_context_menu = true;
    }
    if (open_context_menu)
    {
        ImGui::OpenPopup("context_menu");
        if (node_hovered_in_list != -1)
            node_selected = node_hovered_in_list;
        if (node_hovered_in_scene != -1)
            node_selected = node_hovered_in_scene;
    }

    // Draw context menu
    ImGui::PushStyleVar(ImGuiStyleVar_WindowPadding, ImVec2(8,8));
    if (ImGui::BeginPopup("context_menu"))
    {
        Node* node = node_selected != -1 ? &nodes[node_selected] : NULL;
        ImVec2 scene_pos = ImGui::GetMousePosOnOpeningCurrentPopup() - offset;
        if (node)
        {
            ImGui::Text("Node '%s'", node->Name);
            ImGui::Separator();
            if (ImGui::MenuItem("Rename..", NULL, false, false)) {}
            if (ImGui::MenuItem("Delete", NULL, false, false)) {}
            if (ImGui::MenuItem("Copy", NULL, false, false)) {}
        }
        else
        {
            if (ImGui::MenuItem("Add")) { nodes.push_back(Node(nodes.Size, "New node", scene_pos, 0.5f, 2, 2)); }
            if (ImGui::MenuItem("Paste", NULL, false, false)) {}
        }
        ImGui::EndPopup();
    }
    ImGui::PopStyleVar();

    // Scrolling
    if (ImGui::IsWindowHovered() && !ImGui::IsAnyItemActive() && ImGui::IsMouseDragging(2, 0.0f))
        scrolling = scrolling - ImGui::GetIO().MouseDelta;

    ImGui::PopItemWidth();
    ImGui::EndChild();
    ImGui::PopStyleColor();
    ImGui::PopStyleVar(2);
    ImGui::EndGroup();

    ImGui::End();
}