Add a build system

build.bat

@@ -0,0 +1,120 @@
+@echo off
+setlocal enabledelayedexpansion
+
+:: ============================================================================
+:: build.bat - Build script with compiler preference: clang-cl > gcc > clang
+:: Usage: build [Release|Debug] [clean]
+:: ============================================================================
+
+set BUILD_TYPE=Release
+set CLEAN_BUILD=0
+
+:: Parse arguments
+:parse_args
+if "%~1"=="" goto :main
+
+if /i "%~1"=="Release" (
+    set BUILD_TYPE=Release
+    shift
+    goto :parse_args
+)
+if /i "%~1"=="Debug" (
+    set BUILD_TYPE=Debug
+    shift
+    goto :parse_args
+)
+if /i "%~1"=="clean" (
+    set CLEAN_BUILD=1
+    shift
+    goto :parse_args
+)
+
+:: Unknown argument fallback (the *)
+echo Unknown argument: %~1
+echo Usage: .\%~nx0 [Release^|Debug] [clean]
+exit /b 1
+
+:main
+set BUILD_DIR=build\windows\%BUILD_TYPE%
+echo === Building filehasher (%BUILD_TYPE%) ===
+
+:: Clean if requested
+if %CLEAN_BUILD%==1 (
+    echo Cleaning...
+    if exist "%BUILD_DIR%" rmdir /s /q "%BUILD_DIR%" 2>nul
+)
+
+:: Create build dir
+if not exist "%BUILD_DIR%" mkdir "%BUILD_DIR%"
+pushd "%BUILD_DIR%"
+
+:: Find compiler in preferred order
+set CC=
+where clang-cl >nul 2>&1
+if !ERRORLEVEL! equ 0 (
+    echo Compiler: clang-cl ^(preferred^)
+    set "CC=-DCMAKE_C_COMPILER=clang-cl"
+    goto :find_generator
+)
+
+where gcc >nul 2>&1
+if !ERRORLEVEL! equ 0 (
+    echo Compiler: gcc ^(fallback^)
+    set "CC=-DCMAKE_C_COMPILER=gcc"
+    goto :find_generator
+)
+
+where clang >nul 2>&1
+if !ERRORLEVEL! equ 0 (
+    echo Compiler: clang ^(last resort^)
+    set "CC=-DCMAKE_C_COMPILER=clang"
+    goto :find_generator
+)
+
+echo ERROR: No suitable compiler found! (clang-cl, gcc, or clang required)
+popd
+exit /b 1
+
+:find_generator
+:: Find Ninja for build system
+set GEN=
+where ninja >nul 2>&1
+if !ERRORLEVEL! equ 0 (
+    echo Generator: Ninja
+    set "GEN=-G Ninja"
+) else (
+    echo Generator: Default
+)
+
+:: Configure
+echo.
+echo Configuring CMake...
+set CMD=cmake ../../.. %GEN% %CC% -DCMAKE_BUILD_TYPE=%BUILD_TYPE% -DCMAKE_EXPORT_COMPILE_COMMANDS=ON
+echo !CMD!
+!CMD!
+if !ERRORLEVEL! neq 0 (echo ERROR: Configuration failed & popd & exit /b 1)
+
+:: Build
+echo.
+echo Building...
+cmake --build . --config %BUILD_TYPE%
+if !ERRORLEVEL! neq 0 (echo ERROR: Build failed & popd & exit /b 1)
+
+:: Check if compile_commands.json exists in the current build directory
+if exist "compile_commands.json" (
+    echo.
+    echo   clangd: compile_commands.json generated
+    
+    :: Copy from current build dir up two levels to the project root
+    copy /Y "compile_commands.json" "..\..\..\compile_commands.json" >nul 2>&1
+    if !ERRORLEVEL! equ 0 (
+        echo   clangd: Copied to project root
+    ) else (
+        echo   clangd: Could not copy to project root
+    )
+)
+
+popd
+echo.
+echo === Build Complete ===
+echo Executable: %BUILD_DIR%\filehasher.exe