EXTERNAL_DIR=/yerba/external
BUILD_DIR=/yerba/build
LINUX_DIR=$(EXTERNAL_DIR)/linux
LINUX_REPO=https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
BUSYBOX_DIR=$(EXTERNAL_DIR)/busybox
BUSYBOX_REPO=https://git.busybox.net/busybox
INITRAMFS_INIT=initramfs_init

.PHONY: all kernel initramfs iso run clean

all: iso

$(EXTERNAL_DIR):
	@mkdir -p $(EXTERNAL_DIR)

$(BUILD_DIR):
	@mkdir -p $(BUILD_DIR)

$(LINUX_DIR): $(EXTERNAL_DIR)
	@echo "[yerba] cloning Linux kernel..."
	git clone --depth 1 $(LINUX_REPO) $(LINUX_DIR)

kernel: $(LINUX_DIR) $(BUILD_DIR)
	@echo "[yerba] building kernel (default defconfig)..."
	$(MAKE) -C $(LINUX_DIR) defconfig
	$(MAKE) -C $(LINUX_DIR) -j$(shell nproc) bzImage
	cp $(LINUX_DIR)/arch/x86/boot/bzImage $(BUILD_DIR)/bzImage


initramfs: busybox kernel
	@echo "[yerba] creating initramfs..."
	rm -rf $(BUILD_DIR)/initramfs
	mkdir -p $(BUILD_DIR)/initramfs/{bin,sbin,etc,proc,sys,dev}
	cp -a $(BUSYBOX_DIR)/_install/. $(BUILD_DIR)/initramfs/
	cp initramfs_init $(BUILD_DIR)/initramfs/init
	chmod +x $(BUILD_DIR)/initramfs/init
	cd $(BUILD_DIR)/initramfs && find . | cpio -o -H newc | gzip > $(BUILD_DIR)/initramfs.cpio.gz

$(BUSYBOX_DIR): $(EXTERNAL_DIR)
	@echo "[yerba] cloning BusyBox..."
	git clone --depth 1 $(BUSYBOX_REPO) $(BUSYBOX_DIR)

busybox: $(BUSYBOX_DIR) $(BUILD_DIR)
	@echo "[yerba] building BusyBox..."
	rm $(BUSYBOX_DIR)/.config
	cp busybox_config $(BUSYBOX_DIR)/.config
	$(MAKE) -C $(BUSYBOX_DIR) -j$(shell nproc)
	$(MAKE) -C $(BUSYBOX_DIR) CONFIG_PREFIX=$(BUSYBOX_DIR)/_install install

iso: kernel initramfs busybox
	@echo "[yerba] TODO: make this output an ISO when ready"
	@echo "[yerba] Kernel located at $(BUILD_DIR)/bzImage"
	@echo "[yerba] Initramfs located at $(BUILD_DIR)/initramfs.cpio.gz"

clean:
	rm -rf $(EXTERNAL_DIR) $(BUILD_DIR)

run: iso
	@echo "[yerba] booting in QEMU..."
	qemu-system-x86_64 -kernel $(BUILD_DIR)/bzImage -initrd $(BUILD_DIR)/initramfs.cpio.gz -nographic -append "console=ttyS0"