# ==============================================================================
# Makefile for Simple UEFI Operating System
# ==============================================================================

# ---- Architecture -----------------------------------------------------------
ARCH = x86_64

# ---- Tools ------------------------------------------------------------------
CC      = gcc
LD      = ld
OBJCOPY = objcopy

# ---- Directories ------------------------------------------------------------
SRC_DIR   = .
BUILD_DIR = build
EFI_DIR   = $(BUILD_DIR)/EFI/BOOT
IMAGE_DIR = $(BUILD_DIR)/image

# ---- GNU-EFI paths ---------------------------------------------------------
EFI_INC       = /usr/include/efi
EFI_INCLUDES  = -I$(EFI_INC) -I$(EFI_INC)/$(ARCH) -I$(EFI_INC)/protocol
EFI_LDS       = /usr/lib/elf_$(ARCH)_efi.lds
EFI_CRT_OBJS  = /usr/lib/crt0-efi-$(ARCH).o
EFI_LIB_PATHS = -L/usr/lib

# ---- Compiler / linker flags ------------------------------------------------

# Flags shared by both the UEFI loader and the kernel
COMMON_CFLAGS = -ffreestanding -fno-stack-protector -fshort-wchar \
                -mno-red-zone -Wall -Wextra $(EFI_INCLUDES)

# UEFI loader: position-independent (shared object → PE32+ conversion)
LOADER_CFLAGS = $(COMMON_CFLAGS) -fpic -DEFI_FUNCTION_WRAPPER

# Kernel: position-dependent static ELF
KERNEL_CFLAGS = $(COMMON_CFLAGS) -fno-pic

LDFLAGS = -nostdlib -znocombreloc -T $(EFI_LDS) -shared \
          -Bsymbolic $(EFI_LIB_PATHS) $(EFI_CRT_OBJS)

LIBS = -lefi -lgnuefi

# ---- Targets / objects ------------------------------------------------------
TARGET        = BOOTX64.EFI
TARGET_SO     = bootx64.so
LOADER_OBJ    = $(BUILD_DIR)/main.o

KERNEL_TARGET = kernel.elf
KERNEL_LD     = kernel.ld
KERNEL_C_SRCS = kernel.c string_utils.c commands.c idt.c memory.c task.c
KERNEL_S_SRCS = isr.S context_switch.S
KERNEL_OBJS   = $(patsubst %.c,$(BUILD_DIR)/%.o,$(KERNEL_C_SRCS)) \
                $(patsubst %.S,$(BUILD_DIR)/%.o,$(KERNEL_S_SRCS))

# QEMU settings
QEMU = qemu-system-x86_64

# Try to find OVMF firmware (different locations on different distros)
OVMF_CODE := $(shell \
	if [ -f /usr/share/OVMF/OVMF_CODE_4M.fd ]; then \
		echo /usr/share/OVMF/OVMF_CODE_4M.fd; \
	elif [ -f /usr/share/OVMF/OVMF_CODE.fd ]; then \
		echo /usr/share/OVMF/OVMF_CODE.fd; \
	elif [ -f /usr/share/qemu/OVMF_CODE.fd ]; then \
		echo /usr/share/qemu/OVMF_CODE.fd; \
	elif [ -f /usr/share/edk2-ovmf/x64/OVMF_CODE.fd ]; then \
		echo /usr/share/edk2-ovmf/x64/OVMF_CODE.fd; \
	else \
		echo /usr/share/OVMF/OVMF_CODE.fd; \
	fi)

OVMF_VARS_TEMPLATE := $(shell \
	if [ -f /usr/share/OVMF/OVMF_VARS_4M.fd ]; then \
		echo /usr/share/OVMF/OVMF_VARS_4M.fd; \
	elif [ -f /usr/share/OVMF/OVMF_VARS.fd ]; then \
		echo /usr/share/OVMF/OVMF_VARS.fd; \
	elif [ -f /usr/share/qemu/OVMF_VARS.fd ]; then \
		echo /usr/share/qemu/OVMF_VARS.fd; \
	elif [ -f /usr/share/edk2-ovmf/x64/OVMF_VARS.fd ]; then \
		echo /usr/share/edk2-ovmf/x64/OVMF_VARS.fd; \
	else \
		echo /usr/share/OVMF/OVMF_VARS.fd; \
	fi)

QEMU_FLAGS = -machine q35 \
             -drive if=pflash,format=raw,readonly=on,file=$(OVMF_CODE) \
             -drive if=pflash,format=raw,file=$(BUILD_DIR)/OVMF_VARS.fd \
             -drive format=raw,file=fat:rw:$(BUILD_DIR) \
             -net none \
             -no-reboot

# ==============================================================================
#  Phony targets
# ==============================================================================

.PHONY: all clean run setup install-deps iso runiso help

# ---- Default ----------------------------------------------------------------

all: setup $(EFI_DIR)/$(TARGET) $(BUILD_DIR)/$(KERNEL_TARGET)
# ==============================================================================
#  ISO image
# ==============================================================================

ISO_FILE = $(IMAGE_DIR)/os.iso
ESP_IMG  = $(IMAGE_DIR)/staging/esp.img

iso: all
	@echo "Creating FAT ESP image for UEFI boot..."
	@mkdir -p $(IMAGE_DIR)/staging
	@# Calculate size: EFI binary + kernel + overhead, rounded up to MiB
	@SIZE_KB=$$(( ($$(stat -c%s $(EFI_DIR)/$(TARGET)) + $$(stat -c%s $(BUILD_DIR)/$(KERNEL_TARGET)) + 1048576) / 1024 )); \
	dd if=/dev/zero of=$(ESP_IMG) bs=1K count=$$SIZE_KB 2>/dev/null
	mkfs.fat -F 12 $(ESP_IMG) >/dev/null
	mmd -i $(ESP_IMG) ::EFI
	mmd -i $(ESP_IMG) ::EFI/BOOT
	mcopy -i $(ESP_IMG) $(EFI_DIR)/$(TARGET) ::EFI/BOOT/BOOTX64.EFI
	mcopy -i $(ESP_IMG) $(BUILD_DIR)/$(KERNEL_TARGET) ::kernel.elf
	@echo "Creating ISO image..."
	xorriso -as mkisofs \
		-o $(ISO_FILE) \
		-e esp.img \
		-no-emul-boot \
		$(IMAGE_DIR)/staging
	@echo "ISO image created: $(ISO_FILE)"

# ==============================================================================
#  Run targets
# ==============================================================================

# Run from ISO with QEMU
runiso: iso
	@echo "Starting QEMU from ISO..."
	@echo "Using OVMF firmware: $(OVMF_CODE)"
	@if [ ! -f $(BUILD_DIR)/OVMF_VARS.fd ]; then \
		echo "Creating OVMF_VARS.fd from template..."; \
		cp $(OVMF_VARS_TEMPLATE) $(BUILD_DIR)/OVMF_VARS.fd 2>/dev/null || \
		dd if=/dev/zero of=$(BUILD_DIR)/OVMF_VARS.fd bs=1M count=64 2>/dev/null; \
	fi
	$(QEMU) -machine q35 \
		-drive if=pflash,format=raw,readonly=on,file=$(OVMF_CODE) \
		-drive if=pflash,format=raw,file=$(BUILD_DIR)/OVMF_VARS.fd \
		-cdrom $(ISO_FILE) \
		-net none \
		-nographic \
		-no-reboot

# ==============================================================================
#  Directory setup
# ==============================================================================

setup:
	@mkdir -p $(BUILD_DIR)
	@mkdir -p $(EFI_DIR)
	@mkdir -p $(IMAGE_DIR)

# ==============================================================================
#  Compilation rules
# ==============================================================================

# ---- UEFI loader object (PIC, linked as shared object → PE32+) ----

$(BUILD_DIR)/main.o: $(SRC_DIR)/main.c
	@echo "  CC    $<"
	@$(CC) $(LOADER_CFLAGS) -c $< -o $@

# ---- Kernel objects (position-dependent, linked into static ELF) ----
# Pattern rules replace the per-file rules for every kernel source.

$(BUILD_DIR)/%.o: $(SRC_DIR)/%.c
	@echo "  CC    $<"
	@$(CC) $(KERNEL_CFLAGS) -c $< -o $@

$(BUILD_DIR)/%.o: $(SRC_DIR)/%.S
	@echo "  AS    $<"
	@$(CC) $(KERNEL_CFLAGS) -c $< -o $@

# ==============================================================================
#  Linking
# ==============================================================================

# ---- Kernel ELF ----

$(BUILD_DIR)/$(KERNEL_TARGET): $(KERNEL_OBJS) $(KERNEL_LD)
	@echo "  LD    $@"
	@$(LD) -nostdlib -T $(KERNEL_LD) $(KERNEL_OBJS) -o $@

# ---- UEFI loader shared object ----

$(BUILD_DIR)/$(TARGET_SO): $(LOADER_OBJ)
	@echo "  LD    $@"
	@$(LD) $(LDFLAGS) $(LOADER_OBJ) -o $@ $(LIBS)

# ---- Convert to PE32+ EFI application ----

$(EFI_DIR)/$(TARGET): $(BUILD_DIR)/$(TARGET_SO)
	@echo "  OBJCOPY $@"
	@$(OBJCOPY) -j .text -j .sdata -j .data -j .dynamic \
	            -j .dynsym -j .rel -j .rela -j .reloc \
	            --target=efi-app-$(ARCH) $< $@
	@echo "Build complete: $@"

# Run with QEMU (FAT directory)
run: all
	@echo "Starting QEMU..."
	@echo "Using OVMF firmware: $(OVMF_CODE)"
	@if [ ! -f $(BUILD_DIR)/OVMF_VARS.fd ]; then \
		echo "Creating OVMF_VARS.fd from template..."; \
		cp $(OVMF_VARS_TEMPLATE) $(BUILD_DIR)/OVMF_VARS.fd 2>/dev/null || \
		dd if=/dev/zero of=$(BUILD_DIR)/OVMF_VARS.fd bs=1M count=64 2>/dev/null; \
	fi
	@echo "================================================"
	@echo "QEMU is starting in nographic mode"
	@echo "To exit QEMU: Press Ctrl+A, then X"
	@echo "In the OS: Press 'q' to shutdown"
	@echo "================================================"
	$(QEMU) $(QEMU_FLAGS)

# ==============================================================================
#  Maintenance
# ==============================================================================

# Clean build artifacts
clean:
	@echo "Cleaning build directory..."
	rm -rf $(BUILD_DIR)
	@echo "Clean complete."

# Install dependencies (Debian/Ubuntu)
install-deps:
	@echo "Installing dependencies..."
	sudo apt-get update
	sudo apt-get install -y gnu-efi qemu-system-x86 ovmf gcc binutils make xorriso mtools
	@echo "Dependencies installed."

# ==============================================================================
#  Help
# ==============================================================================

help:
	@echo "UEFI Operating System Makefile"
	@echo ""
	@echo "Targets:"
	@echo "  all          - Build the UEFI application (default)"
	@echo "  run          - Build and run with QEMU"
	@echo "  iso          - Create a bootable ISO image"
	@echo "  runiso       - Build, create ISO, and run in QEMU from ISO"
	@echo "  clean        - Remove build artifacts"
	@echo "  install-deps - Install required dependencies (Debian/Ubuntu)"
	@echo "  help         - Display this help message"
	@echo ""
	@echo "Usage:"
	@echo "  make              # Build the OS"
	@echo "  make run          # Build and run in QEMU"
	@echo "  make iso          # Create ISO image"
	@echo "  make runiso       # Build, create ISO, and run in QEMU from ISO"
	@echo "  make clean        # Clean build files"
	@echo "  make install-deps # Install dependencies"