please work on the first commit

CMakeLists.txt

@@ -0,0 +1,129 @@
+cmake_minimum_required(VERSION 3.22)
+
+# -----------------------------
+# Safely force Clang
+# -----------------------------
+if(NOT DEFINED CMAKE_C_COMPILER)
+    set(CMAKE_C_COMPILER clang CACHE STRING "C compiler" FORCE)
+endif()
+if(NOT DEFINED CMAKE_CXX_COMPILER)
+    set(CMAKE_CXX_COMPILER clang++ CACHE STRING "C++ compiler" FORCE)
+endif()
+
+# -----------------------------
+# Project setup
+# -----------------------------
+project(advent-of-code
+    LANGUAGES CXX
+    VERSION 2025.12
+)
+
+set(CMAKE_CXX_STANDARD 23)
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
+set(CMAKE_CXX_EXTENSIONS OFF)
+set(CMAKE_EXPORT_COMPILE_COMMANDS ON)
+set(CMAKE_BUILD_TYPE Release CACHE STRING "Build type")
+
+# -----------------------------
+# Dependencies
+# -----------------------------
+add_subdirectory(external/fmt)
+add_subdirectory(external/spdlog)
+
+set(COMMON_LIBS fmt::fmt spdlog::spdlog)
+
+# -----------------------------
+# 1. Collect ALL .cpp files under src/
+# -----------------------------
+file(GLOB_RECURSE ALL_CPP_FILES
+    RELATIVE ${CMAKE_CURRENT_SOURCE_DIR}
+    "src/*.cpp"
+)
+
+# -----------------------------
+# 2. Separate day solution mains from everything else
+# -----------------------------
+set(DAY_MAIN_PATTERN "^day-[0-9]+-solution\\.cpp$")
+
+set(DAY_MAINS "")
+set(COMMON_SOURCES "")
+
+foreach(file ${ALL_CPP_FILES})
+    get_filename_component(fname ${file} NAME)
+    if(fname MATCHES ${DAY_MAIN_PATTERN})
+        list(APPEND DAY_MAINS "${CMAKE_CURRENT_SOURCE_DIR}/${file}")
+    else()
+        list(APPEND COMMON_SOURCES "${CMAKE_CURRENT_SOURCE_DIR}/${file}")
+    endif()
+endforeach()
+
+# -----------------------------
+# 3. Include directories (all subfolders under src/)
+# -----------------------------
+file(GLOB_RECURSE SRC_SUBDIRS LIST_DIRECTORIES true "src/*")
+set(PROJECT_INCLUDE_DIRS "")
+foreach(dir ${SRC_SUBDIRS})
+    if(IS_DIRECTORY ${dir})
+        list(APPEND PROJECT_INCLUDE_DIRS ${dir})
+    endif()
+endforeach()
+
+# -----------------------------
+# 4. Common code → object library (only if we actually have common files)
+# -----------------------------
+if(COMMON_SOURCES)
+    add_library(common_objects OBJECT ${COMMON_SOURCES})
+    target_include_directories(common_objects PRIVATE ${PROJECT_INCLUDE_DIRS})
+    target_link_libraries(common_objects PRIVATE ${COMMON_LIBS})
+    target_compile_features(common_objects PRIVATE cxx_std_23)
+else()
+    # Create a dummy interface target so the rest of the script stays simple
+    add_library(common_objects INTERFACE)
+    message(STATUS "No common source files found – each day will compile independently")
+endif()
+
+# -----------------------------
+# 5. Build one executable per day solution
+# -----------------------------
+foreach(MAIN_FILE ${DAY_MAINS})
+    get_filename_component(MAIN_NAME ${MAIN_FILE} NAME_WE)      # day-1-solution
+    set(EXE_NAME "aoc-${MAIN_NAME}")
+
+    add_executable(${EXE_NAME} ${MAIN_FILE})
+
+    # If we have common_objects as OBJECT library → reuse compiled objects
+    # Otherwise it's just an INTERFACE → nothing added
+    if(COMMON_SOURCES)
+        target_sources(${EXE_NAME} PRIVATE $<TARGET_OBJECTS:common_objects>)
+    endif()
+
+    target_include_directories(${EXE_NAME} PRIVATE ${PROJECT_INCLUDE_DIRS})
+    target_link_libraries(${EXE_NAME} PRIVATE ${COMMON_LIBS} common_objects)
+    target_compile_features(${EXE_NAME} PRIVATE cxx_std_23)
+
+    # Warnings + optimizations
+    if(CMAKE_CXX_COMPILER_ID MATCHES "Clang|GNU")
+        target_compile_options(${EXE_NAME} PRIVATE
+            -Wall -Wextra -Wpedantic -Wconversion -Wshadow -Wformat=2 -Werror=main
+        )
+    endif()
+
+    target_compile_options(${EXE_NAME} PRIVATE -O3 -march=native)
+    if(CMAKE_CXX_COMPILER_ID MATCHES "Clang|GNU")
+        target_link_options(${EXE_NAME} PRIVATE -flto=auto)
+    endif()
+endforeach()
+
+# -----------------------------
+# Final summary
+# -----------------------------
+list(LENGTH DAY_MAINS DAY_COUNT)
+message(STATUS "Advent of Code 2025 – Building ${DAY_COUNT} solution(s):")
+foreach(MAIN ${DAY_MAINS})
+    get_filename_component(NAME ${MAIN} NAME)
+    message(STATUS "   • ${NAME} → aoc-${NAME_WE}")
+endforeach()
+
+if(NOT DAY_MAINS)
+    message(FATAL_ERROR "No files matching 'day-N-solution.cpp' found in src/ – nothing to build!")
+endif()