# Nuke built-in rules and variables.
MAKEFLAGS += -rR
.SUFFIXES:

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

# User controllable C compiler command.
CC := cc

# User controllable archiver command.
AR := ar

# User controllable C flags.
CFLAGS := -g -O2 -pipe

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

# User controllable nasm flags.
NASMFLAGS := -F dwarf -g

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

# Check if CC is Clang.
override CC_IS_CLANG := $(shell ! $(CC) --version 2>/dev/null | grep 'clang' >/dev/null 2>&1; echo $$?)

# If the C compiler is Clang, set the target as needed.
ifeq ($(CC_IS_CLANG),1)
    override CC += \
        -target x86_64-unknown-none
endif

# Internal C flags that should not be changed by the user.
override CFLAGS += \
    -Wall \
    -Wextra \
    -std=gnu11 \
    -ffreestanding \
    -fno-stack-protector \
    -fno-stack-check \
    -fno-PIC \
    -ffunction-sections \
    -fdata-sections \
    -m64 \
    -march=x86-64 \
    -mno-80387 \
    -mno-mmx \
    -mno-sse \
    -mno-sse2 \
    -mno-red-zone \
    -mcmodel=kernel

# Internal C preprocessor flags that should not be changed by the user.
override CPPFLAGS := \
    -I src \
    -I src/lib \
    $(CPPFLAGS) \
    -DLIMINE_API_REVISION=3 \
    -MMD \
    -MP

# Internal nasm flags that should not be changed by the user.
override NASMFLAGS += \
    -Wall \
    -f elf64

# Internal linker flags that should not be changed by the user.
override LDFLAGS += \
    -Wl,-m,elf_x86_64 \
    -Wl,--build-id=none \
    -nostdlib \
    -static \
    -z max-page-size=0x1000 \
    -Wl,--gc-sections \
    -T linker.ld

# Use "find" to glob all *.c, *.S, and *.asm files in the tree and obtain the
# object and header dependency file names.
override SRCFILES := $(shell cd src && find -L * -type f | LC_ALL=C sort)
override CFILES := $(filter %.c,$(SRCFILES))
override ASFILES := $(filter %.S,$(SRCFILES))
override NASMFILES := $(filter %.asm,$(SRCFILES))
override OBJ := $(addprefix obj/,$(CFILES:.c=.c.o) $(ASFILES:.S=.S.o) $(NASMFILES:.asm=.asm.o))
override HEADER_DEPS := $(addprefix obj/,$(CFILES:.c=.c.d) $(ASFILES:.S=.S.d))

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

# Include header dependencies.
-include $(HEADER_DEPS)

src/limine.h:
	curl -Lo $@ https://github.com/limine-bootloader/limine/raw/trunk/limine.h || cp ../build/limine/limine.h src/limine.h || echo "ERROR"

# Link rules for the final executable.
bin/$(OUTPUT): GNUmakefile linker.ld $(OBJ)
	mkdir -p "$$(dirname $@)"
	$(CC) $(CFLAGS) $(LDFLAGS) $(OBJ) -o $@

# Compilation rules for *.c files.
obj/%.c.o: src/%.c GNUmakefile src/limine.h
	mkdir -p "$$(dirname $@)"
	$(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $@

# Compilation rules for *.S files.
obj/%.S.o: src/%.S GNUmakefile src/limine.h
	mkdir -p "$$(dirname $@)"
	$(CC) $(CFLAGS) $(CPPFLAGS) -c $< -o $@

# Compilation rules for *.asm (nasm) files.
obj/%.asm.o: src/%.asm GNUmakefile
	mkdir -p "$$(dirname $@)"
	nasm $(NASMFLAGS) $< -o $@

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

# Remove everything built and generated including downloaded dependencies.
.PHONY: distclean
distclean: clean
	rm -f src/limine.h