# Nuke built-in rules.
.SUFFIXES:

# This is the name that our final executable will have.
# Change as needed.
override OUTPUT := kernel

# Target architecture to build for. Default to x86_64.
ARCH := x86_64

# Install prefix; /usr/local is a good, standard default pick.
PREFIX := /usr/local

# Check if the architecture is supported.
ifeq ($(filter $(ARCH),aarch64 loongarch64 riscv64 x86_64),)
    $(error Architecture $(ARCH) not supported)
endif

# User controllable toolchain and toolchain prefix.
TOOLCHAIN :=
TOOLCHAIN_PREFIX :=
ifneq ($(TOOLCHAIN),)
    ifeq ($(TOOLCHAIN_PREFIX),)
        TOOLCHAIN_PREFIX := $(TOOLCHAIN)-
    endif
endif

# User controllable C compiler command.
ifneq ($(TOOLCHAIN_PREFIX),)
    CC := $(TOOLCHAIN_PREFIX)gcc
else
    CC := cc
endif

# User controllable C++ compiler command.
CXX := $(TOOLCHAIN_PREFIX)c++

# User controllable linker command.
LD := $(TOOLCHAIN_PREFIX)ld

# Defaults overrides for variables if using "llvm" as toolchain.
ifeq ($(TOOLCHAIN),llvm)
    CC := clang
    CXX := clang++
    LD := ld.lld
endif

# User controllable C flags.
CFLAGS := -g -O3 -ffast-math -pipe -Werror -Wall -fomit-frame-pointer -funroll-loops -fno-exceptions -mllvm -force-vector-width=64 -mllvm -inline-threshold=1000

# User controllable C++ flags. We default to same as C flags.
CXXFLAGS := $(CFLAGS)

# User controllable C/C++ preprocessor flags. We set none by default.
CPPFLAGS :=

ifeq ($(ARCH),x86_64)
    # User controllable nasm flags.
    NASMFLAGS := -g
endif

# User controllable linker flags. We set none by default.
LDFLAGS :=

# Ensure the dependencies have been obtained.
ifneq ($(filter-out clean distclean,$(MAKECMDGOALS)),)
    ifeq ($(wildcard .deps-obtained),)
        $(error Please run the ./get-deps script first)
    endif
endif

# Check if CC is Clang.
override CC_IS_CLANG := $(shell ! $(CC) --version 2>/dev/null | grep -q '^Target: '; echo $$?)

# Check if CXX is Clang.
override CXX_IS_CLANG := $(shell ! $(CXX) --version 2>/dev/null | grep -q '^Target: '; echo $$?)

# Internal flags shared by both C and C++ compilers.
override SHARED_FLAGS := \
    -Wall \
    -Wextra \
    -nostdinc \
    -ffreestanding \
    -fno-stack-protector \
    -fno-stack-check \
    -flto \
    -fno-PIC -I uacpi/include \
    -ffunction-sections \
    -fdata-sections

# Internal C/C++ preprocessor flags that should not be changed by the user.
override CPPFLAGS_C := \
    -I src \
    -I limine-protocol/include -I flanterm/src -I nanoprintf -I stb -I src/klibc/c \
    -isystem freestnd-c-hdrs/$(ARCH)/include \
    $(CPPFLAGS) \
    -MMD \
    -MP

# Internal C++ only preprocessor flags.
override CPPFLAGS_CXX := \
    $(CPPFLAGS_C) \
    -isystem freestnd-cxx-hdrs/$(ARCH)/include

ifeq ($(ARCH),x86_64)
    # Internal nasm flags that should not be changed by the user.
    override NASMFLAGS := \
        $(patsubst -g,-g -F dwarf,$(NASMFLAGS)) \
        -Wall
endif

# Architecture specific internal flags.
ifeq ($(ARCH),x86_64)
    ifeq ($(CC_IS_CLANG),1)
        override CC += \
            -target x86_64-unknown-none-elf
    endif
    ifeq ($(CXX_IS_CLANG),1)
        override CXX += \
            -target x86_64-unknown-none-elf
    endif
    override SHARED_FLAGS += \
        -m64 \
        -march=x86-64 \
        -mabi=sysv \
        -mno-80387 \
        -mno-mmx \
        -mno-sse \
        -mno-sse2 \
        -mno-red-zone \
        -mcmodel=kernel
    override LDFLAGS += \
        -m elf_x86_64
    override NASMFLAGS := \
        -f elf64 \
        $(NASMFLAGS)
endif
ifeq ($(ARCH),aarch64)
    ifeq ($(CC_IS_CLANG),1)
        override CC += \
            -target aarch64-unknown-none-elf
    endif
    ifeq ($(CXX_IS_CLANG),1)
        override CXX += \
            -target aarch64-unknown-none-elf
    endif
    override SHARED_FLAGS += \
        -mcpu=generic \
        -march=armv8-a+nofp+nosimd \
        -mgeneral-regs-only
    override LDFLAGS += \
        -m aarch64elf
endif
ifeq ($(ARCH),riscv64)
    ifeq ($(CC_IS_CLANG),1)
        override CC += \
            -target riscv64-unknown-none-elf
    endif
    ifeq ($(CXX_IS_CLANG),1)
        override CXX += \
            -target riscv64-unknown-none-elf
    endif
    override SHARED_FLAGS += \
        -march=rv64imac_zicsr_zifencei \
        -mabi=lp64 \
        -mno-relax
    override LDFLAGS += \
        -m elf64lriscv \
        --no-relax
endif
ifeq ($(ARCH),loongarch64)
    ifeq ($(CC_IS_CLANG),1)
        override CC += \
            -target loongarch64-unknown-none-elf
    endif
    ifeq ($(CXX_IS_CLANG),1)
        override CXX += \
            -target loongarch64-unknown-none-elf
    endif
    override SHARED_FLAGS += \
        -march=loongarch64 \
        -mabi=lp64s \
        -mfpu=none \
        -msimd=none
    override LDFLAGS += \
        -m elf64loongarch
endif

# Internal C flags that should not be changed by the user.
override CFLAGS += \
    -std=gnu11 \
    $(SHARED_FLAGS)

# Internal C++ flags that should not be changed by the user.
override CXXFLAGS += \
    -std=c++26 -Wno-c23-extensions \
    -fno-rtti \
    -fno-exceptions \
    $(SHARED_FLAGS)

# Internal linker flags that should not be changed by the user.
override LDFLAGS += \
    -nostdlib \
    -static \
    -z max-page-size=0x1000 \
    --gc-sections \
    -T linker-scripts/$(ARCH).lds

# Use "find" to glob all *.c, *.cpp, *.S, and *.asm files in the tree
# (except the src/arch/* directories, as those are gonna be added
# in the next step).
override SRCFILES := $(shell find -L src cc-runtime/src flanterm/src uacpi/source -type f -not -path 'src/arch/*' 2>/dev/null | LC_ALL=C sort)
# Add architecture specific files, if they exist.
override SRCFILES += $(shell find -L src/arch/$(ARCH) -type f 2>/dev/null | LC_ALL=C sort)
# Obtain the object and header dependencies file names.
override CFILES := $(filter %.c,$(SRCFILES))
override CXXFILES := $(filter %.cpp,$(SRCFILES))
override ASFILES := $(filter %.S,$(SRCFILES))
ifeq ($(ARCH),x86_64)
override NASMFILES := $(filter %.asm,$(SRCFILES))
endif
override OBJ := $(addprefix obj-$(ARCH)/,$(CFILES:.c=.c.o) $(CXXFILES:.cpp=.cpp.o) $(ASFILES:.S=.S.o))
ifeq ($(ARCH),x86_64)
override OBJ += $(addprefix obj-$(ARCH)/,$(NASMFILES:.asm=.asm.o))
endif
override HEADER_DEPS := $(addprefix obj-$(ARCH)/,$(CFILES:.c=.c.d) $(CXXFILES:.cpp=.cpp.d) $(ASFILES:.S=.S.d))

# Default target. This must come first, before header dependencies.
.PHONY: all
all: bin-$(ARCH)/$(OUTPUT)

# Include header dependencies.
-include $(HEADER_DEPS)

# Link rules for the final executable.
bin-$(ARCH)/$(OUTPUT): GNUmakefile linker-scripts/$(ARCH).lds $(OBJ)
	mkdir -p "$(dir $@)"
	$(LD) $(LDFLAGS) $(OBJ) -o $@

# Compilation rules for *.c files.
obj-$(ARCH)/%.c.o: %.c GNUmakefile
	mkdir -p "$(dir $@)"
	$(CC) $(CFLAGS) $(CPPFLAGS_C) -c $< -o $@

# Compilation rules for *.cpp files.
obj-$(ARCH)/%.cpp.o: %.cpp GNUmakefile
	mkdir -p "$(dir $@)"
	$(CXX) $(CXXFLAGS) $(CPPFLAGS_CXX) -c $< -o $@

# Compilation rules for *.S files.
obj-$(ARCH)/%.S.o: %.S GNUmakefile
	mkdir -p "$(dir $@)"
	$(CC) $(CFLAGS) $(CPPFLAGS_C) -c $< -o $@

ifeq ($(ARCH),x86_64)
# Compilation rules for *.asm (nasm) files.
obj-$(ARCH)/%.asm.o: %.asm GNUmakefile
	mkdir -p "$(dir $@)"
	nasm $(NASMFLAGS) $< -o $@
endif

# Remove object files and the final executable.
.PHONY: clean
clean:
	rm -rf bin-$(ARCH) obj-$(ARCH)

# Remove everything built and generated including downloaded dependencies.
.PHONY: distclean
distclean:
	rm -rf bin-* obj-* .deps-obtained .cache compile_commands.json freestnd-c-hdrs freestnd-cxx-hdrs cc-runtime limine-protocol

# Install the final built executable to its final on-root location.
.PHONY: install
install: all
	install -d "$(DESTDIR)$(PREFIX)/share/$(OUTPUT)"
	install -m 644 bin-$(ARCH)/$(OUTPUT) "$(DESTDIR)$(PREFIX)/share/$(OUTPUT)/$(OUTPUT)-$(ARCH)"

# Try to undo whatever the "install" target did.
.PHONY: uninstall
uninstall:
	rm -f "$(DESTDIR)$(PREFIX)/share/$(OUTPUT)/$(OUTPUT)-$(ARCH)"
	-rmdir "$(DESTDIR)$(PREFIX)/share/$(OUTPUT)"