const std = @import("std");
const elf = std.elf;
const Allocator = std.mem.Allocator;
const root = @import("root");
const Block = root.Block;

pub fn create_elf(allocator: Allocator, block: Block) ![]u8 {
    _ = block;

    const base_addr = 0x10000000;
    const elf_header: elf.Elf64_Ehdr = .{
        .e_ident = elf.MAGIC.* ++ [_]u8{
            elf.ELFCLASS64, // EI_CLASS
            elf.ELFDATA2LSB, // EI_DATA
            1, // EI_VERSION
            @intFromEnum(elf.OSABI.NONE), // EI_OSABI
            0, // EI_ABIVERSION
        } ++ [1]u8{0} ** 7, // EI_PAD
        .e_type = .EXEC,
        .e_machine = elf.EM.RISCV,
        .e_version = 1,
        .e_entry = base_addr + @sizeOf(elf.Elf64_Ehdr) + @sizeOf(elf.Elf64_Phdr), // we place the code directly after the headers
        .e_phoff = @sizeOf(elf.Elf64_Ehdr), // we place the program header(s) directly after the elf header
        .e_shoff = 0,
        .e_flags = 0, // ?
        .e_ehsize = @sizeOf(elf.Elf64_Ehdr),
        .e_phentsize = @sizeOf(elf.Elf64_Phdr),
        .e_phnum = 1,
        .e_shentsize = @sizeOf(elf.Elf64_Shdr),
        .e_shnum = 0,
        .e_shstrndx = 0,
    };
    const program_header: elf.Elf64_Phdr = .{
        .p_type = elf.PT_LOAD,
        .p_flags = elf.PF_R | elf.PF_X,
        .p_offset = 0,
        .p_vaddr = base_addr,
        .p_paddr = base_addr,
        .p_filesz = @sizeOf(elf.Elf64_Ehdr) + @sizeOf(elf.Elf64_Phdr) + 40,
        .p_memsz = @sizeOf(elf.Elf64_Ehdr) + @sizeOf(elf.Elf64_Phdr) + 40,
        .p_align = 0x1000,
    };

    var output_buffer: std.ArrayList(u8) = .init(allocator);
    errdefer output_buffer.deinit();
    const output = output_buffer.writer();
    try output.writeAll(std.mem.asBytes(&elf_header));
    try output.writeAll(std.mem.asBytes(&program_header));
    for (0..10) |_| try output.writeAll(&std.mem.toBytes(@as(u32, 0x13)));
    return output_buffer.toOwnedSlice();
}