configure do
  check_c_compiler "i686-elf-gcc"
  check_program "genext2fs"
  check_program "grub-mkstandalone"
  check_program "mformat", on_fail: "Install the mtools package"
  check_program "xorriso"
  check_cfg package: "freetype2", on_fail: "Install libfreetype-dev", use: "freetype"
end

build do
  require "tmpdir"

  # EFI (w/ GRUB) partition size (MiB)
  EFI_PART_SIZE = 8
  # HOS partition size (MiB)
  HOS_PART_SIZE = 4
  # Kernel default font size
  KFONT_SIZE = 12

  class BiosImage < Builder
    def run(options)
      unless @cache.up_to_date?(@target, nil, @sources, @env)
        print_run_message("Generating BIOS boot image #{@target}", nil)
        Dir.mktmpdir do |tmpdir|
          # Create iso directory.
          FileUtils.mkdir_p("#{tmpdir}/iso/boot/grub")
          File.open("#{tmpdir}/iso/boot/grub/grub.cfg", "wb") do |fh|
            fh.write(<<EOF)
set default="0"
set timeout=1
menuentry "HOS" {
  insmod multiboot2
  multiboot2 /hos.elf
}
EOF
          end
          @sources.each do |source|
            FileUtils.cp(source, "#{tmpdir}/iso")
          end
          # Build bootable GRUB image.
          system(*%W[grub-mkrescue -o #{@target} #{tmpdir}/iso], err: "#{@env.build_root}/grub-mkrescue.log")
        end
        @cache.register_build(@target, nil, @sources, @env)
      end
      true
    end
  end

  class EfiImage < Builder
    def run(options)
      unless @cache.up_to_date?(@target, nil, @sources, @env)
        print_run_message("Generating EFI boot image #{@target}", nil)
        Dir.mktmpdir do |tmpdir|
          # Build a standalone GRUB.
          File.open("#{tmpdir}/grub.cfg", "wb") do |fh|
            fh.write(<<EOF)
insmod part_gpt
configfile (hd0,gpt2)/grub.cfg
EOF
          end
          system(*%W[grub-mkstandalone -O x86_64-efi -o #{tmpdir}/BOOTX64.EFI boot/grub/grub.cfg=#{tmpdir}/grub.cfg])
          # Create EFI partition.
          system(*%W[dd if=/dev/zero of=#{tmpdir}/efi.part bs=1M count=#{EFI_PART_SIZE}], err: "/dev/null")
          system(*%W[mformat -i #{tmpdir}/efi.part ::])
          system(*%W[mmd -i #{tmpdir}/efi.part ::/EFI])
          system(*%W[mmd -i #{tmpdir}/efi.part ::/EFI/BOOT])
          system(*%W[mcopy -i #{tmpdir}/efi.part #{tmpdir}/BOOTX64.EFI ::/EFI/BOOT])
          # Create ext2 HOS partition.
          FileUtils.mkdir_p("#{tmpdir}/ext2")
          @sources.each do |source|
            FileUtils.cp(source, "#{tmpdir}/ext2")
          end
          File.open("#{tmpdir}/ext2/grub.cfg", "wb") do |fh|
            fh.write(<<EOF)
set default="0"
set timeout=1
menuentry "HOS" {
  insmod part_gpt
  insmod multiboot2
  set root=(hd0,gpt2)
  multiboot2 /hos.elf
}
EOF
          end
          system(*%W[genext2fs -b #{HOS_PART_SIZE * 1024} -d #{tmpdir}/ext2 #{tmpdir}/ext2.part])
          # Create full disk image.
          system(*%W[dd if=/dev/zero of=#{@target} bs=1M count=#{EFI_PART_SIZE + HOS_PART_SIZE + 2}], err: "/dev/null")
          system(*%W[parted -s #{@target} mklabel gpt])
          system(*%W[parted -s #{@target} mkpart efi 1MiB #{EFI_PART_SIZE + 1}MiB])
          system(*%W[parted -s #{@target} mkpart hos #{EFI_PART_SIZE + 1}MiB #{EFI_PART_SIZE + HOS_PART_SIZE + 1}MiB])
          system(*%W[dd if=#{tmpdir}/efi.part of=#{@target} bs=1M seek=1 conv=notrunc], err: "/dev/null")
          system(*%W[dd if=#{tmpdir}/ext2.part of=#{@target} bs=1M seek=#{1 + EFI_PART_SIZE} conv=notrunc], err: "/dev/null")
        end
        @cache.register_build(@target, nil, @sources, @env)
      end
      true
    end
  end

  class FontGen < Builder
    def run(options)
      if @command
        finalize_command
      else
        @sources += ["build/fontgen"]
        command = %W[build/fontgen #{@sources.first} #{KFONT_SIZE} #{@target}]
        standard_command("FontGen <target>#{@target}<reset>", command, {})
      end
    end
  end

  # FontGen Environment
  Environment.new(use: "freetype") do |env|
    env["CC"] = "gcc"
    env.Program("build/fontgen", glob("fontgen/**/*.c"))
  end

  # Kernel Environment
  Environment.new do |env|
    env.add_builder(EfiImage)
    env.add_builder(BiosImage)
    env.add_builder(FontGen)
    env["CCFLAGS"] += %w[-ffreestanding -Wall -O2]
    env["LDFLAGS"] += %w[-ffreestanding -nostdlib -T src/link.ld]
    env["LIBS"] += %w[gcc]
    env["OBJDUMP"] = "i686-elf-objdump"
    env.FontGen("^/kfont/kfont.c", "font/Hack-Regular.ttf")
    env["CPPPATH"] += ["#{env.build_root}/kfont"]
    env.Program("^/hos.elf", glob("src/**/*.{S,c}") + ["^/kfont/kfont.c"])
    env.depends("#{env.build_root}/hos.elf", "src/link.ld")
    env.Disassemble("^/hos.elf.txt", "^/hos.elf")
    env.EfiImage("build/hos-efi.img", %w[^/hos.elf])
    env.BiosImage("build/hos.img", %w[^/hos.elf])
  end
end