/*
** Win32 Typing Test Program
**  v1.1.0 - Jan 19th 2024
**  by Allen Webster allenw@mr4th.com
**
** public domain example program
** NO WARRANTY IMPLIED; USE AT YOUR OWN RISK
**
**
** Tested on:
**  Windows 10 (English, Latvian, Emojis)
**
** This is an example and a tool for gathering information about
** Win32 text input APIs.
**
** You may use it as a starting point for your own Win32 text input
 ** implementation.
**
** Or you may contribute to the project by:
**  Trying typing in the test program and report any misbehavior you see.
**  Supplying references to relevant documentation/examples that perform
**   this task in a better way.
**
*/

#include <Windows.h>

typedef LONG S32;
typedef USHORT U16;
typedef ULONG U32;


////////////////////////////////
// App Functions

static void AppInit(HWND wnd);
static void AppRender(HWND wnd);
static void AppTypeBackspace(void);
static void AppTypeCodepoint(U32 cp);


////////////////////////////////
// Window Proc

static BOOL keep_running = 1;

static WCHAR lo_surrogate = 0;
static WCHAR hi_surrogate = 0;

static LRESULT
WindowProc(HWND   wnd,
           UINT   msg,
           WPARAM wparam,
           LPARAM lparam){
  LRESULT result = 0;
  
  switch (msg){
    case WM_CHAR:
    {
      // When a WM_CHAR generally represents text input that
      //  should be inserted, but there are a few twists.
      //
      // Sometimes WM_CHAR is triggered by controls that are
      //  not text input, like Ctrl + Letter. To filter out
      //  these cases we ignore values less than ' ' (0x20)
      //  and the value 0x7F. See WM_KEYDOWN for a little
      //  more on this issue.
      //
      // When the user types a character that does not fit
      //  in a single U16, a pair of WM_CHAR messages are sent.
      //  Each WM_CHAR message in the pair contains a
      //  "surrogate" (defined by UTF16) one "high" surrogate
      //  followed by a "low" surrogate. A pair of surrogates
      //  translates into a single typed codepoint.
      //
      // (Actually the docs don't clearly say one order
      //  or the other - I just support both)
      
      U32 c = (wparam & 0xFFFF);
      if (c >= ' ' && c != 0x7F){
        
        if (IS_LOW_SURROGATE(c)){
          lo_surrogate = c;
        }
        else if (IS_HIGH_SURROGATE(c)){
          hi_surrogate = c;
        }
        else{
          AppTypeCodepoint(c);
          lo_surrogate = 0;
          hi_surrogate = 0;
        }
        
        if (hi_surrogate != 0 && lo_surrogate != 0){
          if (IS_SURROGATE_PAIR(hi_surrogate, lo_surrogate)){
            U32 cp = (0x10000 +
                      ((hi_surrogate & 0x3FF) << 10) +
                      (lo_surrogate & 0x3FF) );
            AppTypeCodepoint(cp);
          }
          hi_surrogate = 0;
          lo_surrogate = 0;
        }
        
      }
    }break;
    
    case WM_KEYDOWN:
    {
      //  While it is possible to see newlines/carriage returns
      // and tabs through the WM_CHAR message, it is also possible
      // to get erroneous newlines and tabs in WM_CHAR.
      //
      //  "Erroneous" WM_CHAR messages are generated when a user
      // holds down "Ctrl" and presses any alphabetic character.
      // The erroneous values generated this way are always less
      // than 0x20 (0x20 is the ascii for the space character ' ').
      //
      //  Thus it's possible to get simple behavior by ignoring
      // all the WM_CHAR messages that have character values less
      // than 0x20 and then directly handle these two relevant
      // cases here.
      
      if (wparam == VK_RETURN){
        AppTypeCodepoint('\n');
      }
      if (wparam == VK_TAB){
        AppTypeCodepoint('\t');
      }
      
      if (wparam == VK_BACK){
        AppTypeBackspace();
      }
    }break;
    
    case WM_SYSCOMMAND:
    {
      //  Not directly relevant to the main goal, but if you don't
      // want your Alt+Key combos to play a bell sound you have to
      // disable default handling of this 'menu' path
      
      BOOL is_menu = (wparam == SC_KEYMENU && (lparam >> 16) <= 0);
      if (!is_menu){
        result = DefWindowProcW(wnd, msg, wparam, lparam);
      }
    }break;
    
    case WM_PAINT:
    {
      PAINTSTRUCT ps;
      BeginPaint(wnd, &ps);
      AppRender(wnd);
      EndPaint(wnd, &ps);
    }break;
    
    case WM_CLOSE:
    {
      keep_running = 0;
    }break;
    
    default:
    {
      result = DefWindowProcW(wnd, msg, wparam, lparam);
    }break;
  }
  
  return(result);
}


////////////////////////////////
// Main

static BOOL composition_enabled = 0;

int
WinMain(HINSTANCE hInstance,
        HINSTANCE hPrevInstance,
        LPSTR     lpCmdLine,
        int       nShowCmd){
  WNDCLASSW window_class = {0};
  window_class.style         = CS_HREDRAW|CS_VREDRAW;
  window_class.lpfnWndProc   = WindowProc;
  window_class.hInstance     = hInstance;
  window_class.hCursor       = LoadCursorA(0, IDC_ARROW);
  window_class.lpszClassName = L"WindowClass";
  
  ATOM atom = RegisterClassW(&window_class);
  if (atom == 0){
    MessageBoxW(0, (WCHAR*)L"RegisterClassW failed\n", (WCHAR*)L"Fatal", MB_OK);
    ExitProcess(1);
  }
  
  DWORD style = WS_OVERLAPPEDWINDOW;
  HWND wnd = CreateWindowW(L"WindowClass", L"Type Test", style,
                           CW_USEDEFAULT, CW_USEDEFAULT,
                           CW_USEDEFAULT, CW_USEDEFAULT,
                           0, 0, hInstance, 0);
  
  // init
  AppInit(wnd);
  
  // main loop
  ShowWindow(wnd, SW_SHOW);
  
  keep_running = 1;
  for (;keep_running;){
    
    // Handle Message Queue
    BOOL wait = 1;
    MSG msg;
    for (;(wait?GetMessageW(&msg, 0, 0, 0):
           PeekMessageW(&msg, 0, 0, 0, PM_REMOVE));){
      wait = 0;
      TranslateMessage(&msg);
      DispatchMessageW(&msg);
    }
    
    // render
    AppRender(wnd);
    
    // sleep
    Sleep(33);
  }
}


////////////////////////////////
// App Implementation

static HFONT font = 0;

#define TEXT_CAP (1 << 14)
static U16 text_memory[TEXT_CAP];
static U32 text_len = 0;

static void
AppInsertCodepoint(U32 cp){
  // convert codepoint to UTF16
  U16 encode_buf[2];
  U32 encode_len = 0;
  if (cp < 0x10000){
    encode_buf[0] = cp;
    encode_len = 1;
  }
  else{
    U32 cpj = cp - 0x10000;
    encode_buf[0] = (cpj >> 10) + 0xD800;
    encode_buf[1] = (cpj & 0x3FF) + 0xDC00;
    encode_len = 2;
  }
  
  // insert into string
  if (text_len + encode_len < TEXT_CAP){
    for (U32 i = 0; i < encode_len; i += 1){
      text_memory[text_len] = encode_buf[i];
      text_len += 1;
    }
  }
}

static void
AppTypeBackspace(void){
  text_len = 0;
}

static void
AppTypeCodepoint(U32 cp){
  if (cp == '\n'){
    AppInsertCodepoint('\\');
    AppInsertCodepoint('n');
  }
  else if (cp == '\t'){
    AppInsertCodepoint('\\');
    AppInsertCodepoint('t');
  }
  else{
    AppInsertCodepoint(cp);
  }
}

static void
AppInit(HWND wnd){
  LOGFONT logfont = {0};
  logfont.lfHeight = 24;
  memcpy(logfont.lfFaceName, "Arial", sizeof("Arial"));
  font = CreateFontIndirectA(&logfont);
}

static void
AppRender(HWND wnd){
  
  // window dimensions
  RECT wnd_rect = {0};
  GetClientRect(wnd, &wnd_rect);
  
  // render begin
  HDC wnd_dc = GetDC(wnd);
  HDC dc = CreateCompatibleDC(wnd_dc);
  HBITMAP bitmap =
    CreateCompatibleBitmap(wnd_dc, wnd_rect.right, wnd_rect.bottom);
  SelectObject(dc, bitmap);
  
  // render body
  {
    SelectObject(dc, GetStockObject(DC_PEN));
    SelectObject(dc, GetStockObject(DC_BRUSH));
    SetBkMode(dc, TRANSPARENT);
    SelectObject(dc, font);
    
    // background
    {
      SetDCPenColor(dc, RGB(255, 255, 255));
      SetDCBrushColor(dc, RGB(255, 255, 255));
      Rectangle(dc, wnd_rect.left, wnd_rect.top, wnd_rect.right, wnd_rect.bottom);
    }
    
    // string
    {
      SIZE dim = {0};
      GetTextExtentPoint32W(dc, (WCHAR*)text_memory, text_len, &dim);
      
      S32 cx = (wnd_rect.right  - wnd_rect.left)/2;
      S32 cy = (wnd_rect.bottom - wnd_rect.top)/2;
      
      S32 x = cx - dim.cx/2;
      S32 y = cy - dim.cy/2;
      
      TextOutW(dc, x, y, (WCHAR*)text_memory, text_len);
    }
  }
  
  // render end
  BitBlt(wnd_dc, 0, 0, wnd_rect.right, wnd_rect.bottom, dc, 0, 0, SRCCOPY);
  DeleteObject(bitmap);
  DeleteDC(dc);
  ReleaseDC(wnd, wnd_dc);
}


//$ graphical //