// ImGui Win32 + DirectX11 binding
// https://github.com/ocornut/imgui

#include <imgui.h>
#include "imgui_impl_dx11.h"

// DirectX
#include <d3d11.h>
#include <d3dcompiler.h>
#define DIRECTINPUT_VERSION 0x0800
#include <dinput.h>

// Data
static INT64                    g_Time = 0;
static INT64                    g_TicksPerSecond = 0;

static HWND                     g_hWnd = 0;
static ID3D11Device*            g_pd3dDevice = NULL;
static ID3D11DeviceContext*     g_pd3dDeviceContext = NULL;
static ID3D11Buffer*            g_pVB = NULL;
static ID3D10Blob *             g_pVertexShaderBlob = NULL;
static ID3D11VertexShader*      g_pVertexShader = NULL;
static ID3D11InputLayout*       g_pInputLayout = NULL;
static ID3D11Buffer*            g_pVertexConstantBuffer = NULL;
static ID3D10Blob *             g_pPixelShaderBlob = NULL;
static ID3D11PixelShader*       g_pPixelShader = NULL;
static ID3D11SamplerState*      g_pFontSampler = NULL;
static ID3D11ShaderResourceView*g_pFontTextureView = NULL;
static ID3D11BlendState*        g_blendState = NULL;
static int                      VERTEX_BUFFER_SIZE = 30000;     // TODO: Make vertex buffer smaller and grow dynamically as needed.

struct VERTEX_CONSTANT_BUFFER
{
    float        mvp[4][4];
};

// This is the main rendering function that you have to implement and provide to ImGui (via setting up 'RenderDrawListsFn' in the ImGuiIO structure)
// If text or lines are blurry when integrating ImGui in your engine:
// - in your Render function, try translating your projection matrix by (0.5f,0.5f) or (0.375f,0.375f)
static void ImGui_ImplDX11_RenderDrawLists(ImDrawList** const cmd_lists, int cmd_lists_count)
{
    // Copy and convert all vertices into a single contiguous buffer
    D3D11_MAPPED_SUBRESOURCE mappedResource;
    if (g_pd3dDeviceContext->Map(g_pVB, 0, D3D11_MAP_WRITE_DISCARD, 0, &mappedResource) != S_OK)
        return;
    ImDrawVert* vtx_dst = (ImDrawVert*)mappedResource.pData;
    for (int n = 0; n < cmd_lists_count; n++)
    {
        const ImDrawList* cmd_list = cmd_lists[n];
        const ImDrawVert* vtx_src = &cmd_list->vtx_buffer[0];
        memcpy(vtx_dst, vtx_src, cmd_list->vtx_buffer.size() * sizeof(ImDrawVert));
        vtx_dst += cmd_list->vtx_buffer.size();
    }
    g_pd3dDeviceContext->Unmap(g_pVB, 0);

    // Setup orthographic projection matrix into our constant buffer
    {
        D3D11_MAPPED_SUBRESOURCE mappedResource;
        if (g_pd3dDeviceContext->Map(g_pVertexConstantBuffer, 0, D3D11_MAP_WRITE_DISCARD, 0, &mappedResource) != S_OK)
            return;

        VERTEX_CONSTANT_BUFFER* pConstantBuffer = (VERTEX_CONSTANT_BUFFER*)mappedResource.pData;
        const float L = 0.0f;
        const float R = ImGui::GetIO().DisplaySize.x;
        const float B = ImGui::GetIO().DisplaySize.y;
        const float T = 0.0f;
        const float mvp[4][4] = 
        {
            { 2.0f/(R-L),   0.0f,           0.0f,       0.0f},
            { 0.0f,         2.0f/(T-B),     0.0f,       0.0f,},
            { 0.0f,         0.0f,           0.5f,       0.0f },
            { (R+L)/(L-R),  (T+B)/(B-T),    0.5f,       1.0f },
        };
        memcpy(&pConstantBuffer->mvp, mvp, sizeof(mvp));
        g_pd3dDeviceContext->Unmap(g_pVertexConstantBuffer, 0);
    }

    // Setup viewport
    {
        D3D11_VIEWPORT vp;
        memset(&vp, 0, sizeof(D3D11_VIEWPORT));
        vp.Width = ImGui::GetIO().DisplaySize.x;
        vp.Height = ImGui::GetIO().DisplaySize.y;
        vp.MinDepth = 0.0f;
        vp.MaxDepth = 1.0f;
        vp.TopLeftX = 0;
        vp.TopLeftY = 0;
        g_pd3dDeviceContext->RSSetViewports(1, &vp);
    }

    // Bind shader and vertex buffers
    unsigned int stride = sizeof(ImDrawVert);
    unsigned int offset = 0;
    g_pd3dDeviceContext->IASetInputLayout(g_pInputLayout);
    g_pd3dDeviceContext->IASetVertexBuffers(0, 1, &g_pVB, &stride, &offset);
    g_pd3dDeviceContext->IASetPrimitiveTopology(D3D11_PRIMITIVE_TOPOLOGY_TRIANGLELIST);
    g_pd3dDeviceContext->VSSetShader(g_pVertexShader, NULL, 0);
    g_pd3dDeviceContext->VSSetConstantBuffers(0, 1, &g_pVertexConstantBuffer);
    g_pd3dDeviceContext->PSSetShader(g_pPixelShader, NULL, 0);
    g_pd3dDeviceContext->PSSetSamplers(0, 1, &g_pFontSampler);

    // Setup render state
    const float blendFactor[4] = { 0.f, 0.f, 0.f, 0.f };
    g_pd3dDeviceContext->OMSetBlendState(g_blendState, blendFactor, 0xffffffff);

    // Render command lists
    int vtx_offset = 0;
    for (int n = 0; n < cmd_lists_count; n++)
    {
        const ImDrawList* cmd_list = cmd_lists[n];
        for (size_t cmd_i = 0; cmd_i < cmd_list->commands.size(); cmd_i++)
        {
            const ImDrawCmd* pcmd = &cmd_list->commands[cmd_i];
            if (pcmd->user_callback)
            {
                pcmd->user_callback(cmd_list, pcmd);
            }
            else
            {
                const D3D11_RECT r = { (LONG)pcmd->clip_rect.x, (LONG)pcmd->clip_rect.y, (LONG)pcmd->clip_rect.z, (LONG)pcmd->clip_rect.w };
                g_pd3dDeviceContext->PSSetShaderResources(0, 1, (ID3D11ShaderResourceView**)&pcmd->texture_id);
                g_pd3dDeviceContext->RSSetScissorRects(1, &r); 
                g_pd3dDeviceContext->Draw(pcmd->vtx_count, vtx_offset);
            }
            vtx_offset += pcmd->vtx_count;
        }
    }

    // Restore modified state
    g_pd3dDeviceContext->IASetInputLayout(NULL);
    g_pd3dDeviceContext->PSSetShader(NULL, NULL, 0);
    g_pd3dDeviceContext->VSSetShader(NULL, NULL, 0);
}

LRESULT ImGui_ImplDX11_WndProcHandler(HWND, UINT msg, WPARAM wParam, LPARAM lParam)
{
    ImGuiIO& io = ImGui::GetIO();
    switch (msg)
    {
    case WM_LBUTTONDOWN:
        io.MouseDown[0] = true;
        return true;
    case WM_LBUTTONUP:
        io.MouseDown[0] = false; 
        return true;
    case WM_RBUTTONDOWN:
        io.MouseDown[1] = true; 
        return true;
    case WM_RBUTTONUP:
        io.MouseDown[1] = false; 
        return true;
    case WM_MOUSEWHEEL:
        io.MouseWheel += GET_WHEEL_DELTA_WPARAM(wParam) > 0 ? +1.0f : -1.0f;
        return true;
    case WM_MOUSEMOVE:
        io.MousePos.x = (signed short)(lParam);
        io.MousePos.y = (signed short)(lParam >> 16); 
        return true;
    case WM_KEYDOWN:
        if (wParam < 256)
            io.KeysDown[wParam] = 1;
        return true;
    case WM_KEYUP:
        if (wParam < 256)
            io.KeysDown[wParam] = 0;
        return true;
    case WM_CHAR:
        // You can also use ToAscii()+GetKeyboardState() to retrieve characters.
        if (wParam > 0 && wParam < 0x10000)
            io.AddInputCharacter((unsigned short)wParam);
        return true;
    }
    return 0;
}

static void ImGui_ImplDX11_CreateFontsTexture()
{
    ImGuiIO& io = ImGui::GetIO();

    // Build
    unsigned char* pixels;
    int width, height;
    io.Fonts->GetTexDataAsRGBA32(&pixels, &width, &height);

    // Create DX11 texture
    {
        D3D11_TEXTURE2D_DESC texDesc;
        ZeroMemory(&texDesc, sizeof(texDesc));
        texDesc.Width = width;
        texDesc.Height = height;
        texDesc.MipLevels = 1;
        texDesc.ArraySize = 1;
        texDesc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
        texDesc.SampleDesc.Count = 1;
        texDesc.Usage = D3D11_USAGE_DEFAULT;
        texDesc.BindFlags = D3D11_BIND_SHADER_RESOURCE;
        texDesc.CPUAccessFlags = 0;

        ID3D11Texture2D *pTexture = NULL;
        D3D11_SUBRESOURCE_DATA subResource;
        subResource.pSysMem = pixels;
        subResource.SysMemPitch = texDesc.Width * 4;
        subResource.SysMemSlicePitch = 0;
        g_pd3dDevice->CreateTexture2D(&texDesc, &subResource, &pTexture);

        // Create texture view
        D3D11_SHADER_RESOURCE_VIEW_DESC srvDesc;
        ZeroMemory(&srvDesc, sizeof(srvDesc));
        srvDesc.Format = DXGI_FORMAT_R8G8B8A8_UNORM;
        srvDesc.ViewDimension = D3D11_SRV_DIMENSION_TEXTURE2D;
        srvDesc.Texture2D.MipLevels = texDesc.MipLevels;
        srvDesc.Texture2D.MostDetailedMip = 0;
        g_pd3dDevice->CreateShaderResourceView(pTexture, &srvDesc, &g_pFontTextureView);
        pTexture->Release();
    }

    // Store our identifier
    io.Fonts->TexID = (void *)g_pFontTextureView;

    // Create texture sampler
    {
        D3D11_SAMPLER_DESC samplerDesc;
        ZeroMemory(&samplerDesc, sizeof(samplerDesc));
        samplerDesc.Filter = D3D11_FILTER_MIN_MAG_MIP_LINEAR;
        samplerDesc.AddressU = D3D11_TEXTURE_ADDRESS_WRAP;
        samplerDesc.AddressV = D3D11_TEXTURE_ADDRESS_WRAP;
        samplerDesc.AddressW = D3D11_TEXTURE_ADDRESS_WRAP;
        samplerDesc.MipLODBias = 0.f;
        samplerDesc.ComparisonFunc = D3D11_COMPARISON_ALWAYS;
        samplerDesc.MinLOD = 0.f;
        samplerDesc.MaxLOD = 0.f;
        g_pd3dDevice->CreateSamplerState(&samplerDesc, &g_pFontSampler);
    }
}

bool    ImGui_ImplDX11_CreateDeviceObjects()
{
    if (!g_pd3dDevice)
        return false;
    if (g_pVB)
        ImGui_ImplDX11_InvalidateDeviceObjects();

    // Create the vertex shader
    {
        static const char* vertexShader = 
            "cbuffer vertexBuffer : register(c0) \
            {\
            float4x4 ProjectionMatrix; \
            };\
            struct VS_INPUT\
            {\
            float2 pos : POSITION;\
            float4 col : COLOR0;\
            float2 uv  : TEXCOORD0;\
            };\
            \
            struct PS_INPUT\
            {\
            float4 pos : SV_POSITION;\
            float4 col : COLOR0;\
            float2 uv  : TEXCOORD0;\
            };\
            \
            PS_INPUT main(VS_INPUT input)\
            {\
            PS_INPUT output;\
            output.pos = mul( ProjectionMatrix, float4(input.pos.xy, 0.f, 1.f));\
            output.col = input.col;\
            output.uv  = input.uv;\
            return output;\
            }";

        D3DCompile(vertexShader, strlen(vertexShader), NULL, NULL, NULL, "main", "vs_5_0", 0, 0, &g_pVertexShaderBlob, NULL);
        if (g_pVertexShaderBlob == NULL) // NB: Pass ID3D10Blob* pErrorBlob to D3DCompile() to get error showing in (const char*)pErrorBlob->GetBufferPointer(). Make sure to Release() the blob!
            return false;
        if (g_pd3dDevice->CreateVertexShader((DWORD*)g_pVertexShaderBlob->GetBufferPointer(), g_pVertexShaderBlob->GetBufferSize(), NULL, &g_pVertexShader) != S_OK)
            return false;

        // Create the input layout
        D3D11_INPUT_ELEMENT_DESC localLayout[] = {
            { "POSITION", 0, DXGI_FORMAT_R32G32B32A32_FLOAT, 0, (size_t)(&((ImDrawVert*)0)->pos), D3D11_INPUT_PER_VERTEX_DATA, 0 },
            { "TEXCOORD", 0, DXGI_FORMAT_R32G32_FLOAT,       0, (size_t)(&((ImDrawVert*)0)->uv),  D3D11_INPUT_PER_VERTEX_DATA, 0 },
            { "COLOR",    0, DXGI_FORMAT_R8G8B8A8_UNORM,     0, (size_t)(&((ImDrawVert*)0)->col), D3D11_INPUT_PER_VERTEX_DATA, 0 },
        };

        if (g_pd3dDevice->CreateInputLayout(localLayout, 3, g_pVertexShaderBlob->GetBufferPointer(), g_pVertexShaderBlob->GetBufferSize(), &g_pInputLayout) != S_OK)
            return false;

        // Create the constant buffer
        {
            D3D11_BUFFER_DESC cbDesc;
            cbDesc.ByteWidth = sizeof(VERTEX_CONSTANT_BUFFER);
            cbDesc.Usage = D3D11_USAGE_DYNAMIC;
            cbDesc.BindFlags = D3D11_BIND_CONSTANT_BUFFER;
            cbDesc.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
            cbDesc.MiscFlags = 0;
            g_pd3dDevice->CreateBuffer(&cbDesc, NULL, &g_pVertexConstantBuffer);
        }
    }

    // Create the pixel shader
    {
        static const char* pixelShader = 
            "struct PS_INPUT\
            {\
            float4 pos : SV_POSITION;\
            float4 col : COLOR0;\
            float2 uv  : TEXCOORD0;\
            };\
            sampler sampler0;\
            Texture2D texture0;\
            \
            float4 main(PS_INPUT input) : SV_Target\
            {\
            float4 out_col = input.col * texture0.Sample(sampler0, input.uv); \
            return out_col; \
            }";

        D3DCompile(pixelShader, strlen(pixelShader), NULL, NULL, NULL, "main", "ps_5_0", 0, 0, &g_pPixelShaderBlob, NULL);
        if (g_pPixelShaderBlob == NULL)  // NB: Pass ID3D10Blob* pErrorBlob to D3DCompile() to get error showing in (const char*)pErrorBlob->GetBufferPointer(). Make sure to Release() the blob!
            return false;
        if (g_pd3dDevice->CreatePixelShader((DWORD*)g_pPixelShaderBlob->GetBufferPointer(), g_pPixelShaderBlob->GetBufferSize(), NULL, &g_pPixelShader) != S_OK)
            return false;
    }

    // Create the blending setup
    {
        D3D11_BLEND_DESC desc;
        ZeroMemory(&desc, sizeof(desc));
        desc.AlphaToCoverageEnable = false;
        desc.RenderTarget[0].BlendEnable = true;
        desc.RenderTarget[0].SrcBlend = D3D11_BLEND_SRC_ALPHA;
        desc.RenderTarget[0].DestBlend = D3D11_BLEND_INV_SRC_ALPHA;
        desc.RenderTarget[0].BlendOp = D3D11_BLEND_OP_ADD;
        desc.RenderTarget[0].SrcBlendAlpha = D3D11_BLEND_INV_SRC_ALPHA;
        desc.RenderTarget[0].DestBlendAlpha = D3D11_BLEND_ZERO;
        desc.RenderTarget[0].BlendOpAlpha = D3D11_BLEND_OP_ADD;
        desc.RenderTarget[0].RenderTargetWriteMask = D3D11_COLOR_WRITE_ENABLE_ALL;
        g_pd3dDevice->CreateBlendState(&desc, &g_blendState);
    }

    // Create the vertex buffer
    {
        D3D11_BUFFER_DESC bufferDesc;
        memset(&bufferDesc, 0, sizeof(D3D11_BUFFER_DESC));
        bufferDesc.Usage = D3D11_USAGE_DYNAMIC;
        bufferDesc.ByteWidth = VERTEX_BUFFER_SIZE * sizeof(ImDrawVert);
        bufferDesc.BindFlags = D3D11_BIND_VERTEX_BUFFER;
        bufferDesc.CPUAccessFlags = D3D11_CPU_ACCESS_WRITE;
        bufferDesc.MiscFlags = 0;
        if (g_pd3dDevice->CreateBuffer(&bufferDesc, NULL, &g_pVB) < 0)
            return false;
    }

    ImGui_ImplDX11_CreateFontsTexture();

    return true;
}

void    ImGui_ImplDX11_InvalidateDeviceObjects()
{
    if (!g_pd3dDevice)
        return;

    if (g_pFontSampler) { g_pFontSampler->Release(); g_pFontSampler = NULL; }
    if (g_pFontTextureView) { g_pFontTextureView->Release(); ImGui::GetIO().Fonts->TexID = 0; }
    if (g_pVB) { g_pVB->Release(); g_pVB = NULL; }

    if (g_blendState) { g_blendState->Release(); g_blendState = NULL; }
    if (g_pPixelShader) { g_pPixelShader->Release(); g_pPixelShader = NULL; }
    if (g_pPixelShaderBlob) { g_pPixelShaderBlob->Release(); g_pPixelShaderBlob = NULL; }
    if (g_pVertexConstantBuffer) { g_pVertexConstantBuffer->Release(); g_pVertexConstantBuffer = NULL; }
    if (g_pInputLayout) { g_pInputLayout->Release(); g_pInputLayout = NULL; }
    if (g_pVertexShader) { g_pVertexShader->Release(); g_pVertexShader = NULL; }
    if (g_pVertexShaderBlob) { g_pVertexShaderBlob->Release(); g_pVertexShaderBlob = NULL; }
}

bool    ImGui_ImplDX11_Init(void* hwnd, ID3D11Device* device, ID3D11DeviceContext* device_context)
{
    g_hWnd = (HWND)hwnd;
    g_pd3dDevice = device;
    g_pd3dDeviceContext = device_context;

    if (!QueryPerformanceFrequency((LARGE_INTEGER *)&g_TicksPerSecond)) 
        return false;
    if (!QueryPerformanceCounter((LARGE_INTEGER *)&g_Time))
        return false;

    ImGuiIO& io = ImGui::GetIO();
    io.KeyMap[ImGuiKey_Tab] = VK_TAB;                              // Keyboard mapping. ImGui will use those indices to peek into the io.KeyDown[] array that we will update during the application lifetime.
    io.KeyMap[ImGuiKey_LeftArrow] = VK_LEFT;
    io.KeyMap[ImGuiKey_RightArrow] = VK_RIGHT;
    io.KeyMap[ImGuiKey_UpArrow] = VK_UP;
    io.KeyMap[ImGuiKey_DownArrow] = VK_UP;
    io.KeyMap[ImGuiKey_Home] = VK_HOME;
    io.KeyMap[ImGuiKey_End] = VK_END;
    io.KeyMap[ImGuiKey_Delete] = VK_DELETE;
    io.KeyMap[ImGuiKey_Backspace] = VK_BACK;
    io.KeyMap[ImGuiKey_Enter] = VK_RETURN;
    io.KeyMap[ImGuiKey_Escape] = VK_ESCAPE;
    io.KeyMap[ImGuiKey_A] = 'A';
    io.KeyMap[ImGuiKey_C] = 'C';
    io.KeyMap[ImGuiKey_V] = 'V';
    io.KeyMap[ImGuiKey_X] = 'X';
    io.KeyMap[ImGuiKey_Y] = 'Y';
    io.KeyMap[ImGuiKey_Z] = 'Z';

    io.RenderDrawListsFn = ImGui_ImplDX11_RenderDrawLists;
    io.ImeWindowHandle = g_hWnd;

    return true;
}

void ImGui_ImplDX11_Shutdown()
{
    ImGui_ImplDX11_InvalidateDeviceObjects();
    ImGui::Shutdown();
    g_pd3dDevice = NULL;
    g_pd3dDeviceContext = NULL;
    g_hWnd = (HWND)0;
}

void ImGui_ImplDX11_NewFrame()
{
    if (!g_pVB)
        ImGui_ImplDX11_CreateDeviceObjects();

    ImGuiIO& io = ImGui::GetIO();

    // Setup display size (every frame to accommodate for window resizing)
    RECT rect;
    GetClientRect(g_hWnd, &rect);
    io.DisplaySize = ImVec2((float)(rect.right - rect.left), (float)(rect.bottom - rect.top));

    // Setup time step
    INT64 current_time;
    QueryPerformanceCounter((LARGE_INTEGER *)&current_time); 
    io.DeltaTime = (float)(current_time - g_Time) / g_TicksPerSecond;
    g_Time = current_time;

    // Read keyboard modifiers inputs
    io.KeyCtrl = (GetKeyState(VK_CONTROL) & 0x8000) != 0;
    io.KeyShift = (GetKeyState(VK_SHIFT) & 0x8000) != 0;
    io.KeyAlt = (GetKeyState(VK_MENU) & 0x8000) != 0;
    // io.KeysDown : filled by WM_KEYDOWN/WM_KEYUP events
    // io.MousePos : filled by WM_MOUSEMOVE events
    // io.MouseDown : filled by WM_*BUTTON* events
    // io.MouseWheel : filled by WM_MOUSEWHEEL events

    // Start the frame
    ImGui::NewFrame();
}