springboard 3.0.1

use anyhow::Context;
use std::{
   fs,
   io::{self, Seek, Write},
   path::Path,
   process::Command,
};
use thiserror::Error;

/// Creates a bootable disk image from the given bootloader executable.
pub fn create_disk_image(
   bootloader_elf_path: &Path,
   output_bin_path: &Path,
   kernel_binary: &Path,
) -> anyhow::Result<()> {
   let llvm_tools =
      llvm_tools::LlvmTools::new().map_err(|err| anyhow::anyhow!("failed to get llvm tools"))?;
   let objcopy = llvm_tools
      .tool(&llvm_tools::exe("llvm-objcopy"))
      .ok_or(DiskImageError::LlvmObjcopyNotFound)?;

   // convert first stage to binary
   let mut cmd = Command::new(objcopy);
   cmd.arg("-I").arg("elf64-x86-64");
   cmd.arg("-O").arg("binary");
   cmd.arg("--binary-architecture=i386:x86-64");
   cmd.arg(bootloader_elf_path);
   cmd.arg(output_bin_path);
   let output = cmd.output().map_err(|err| DiskImageError::Io {
      message: "failed to execute llvm-objcopy command",
      error: err,
   })?;
   if !output.status.success() {
      return Err(DiskImageError::ObjcopyFailed {
         stderr: output.stderr,
      })
         .context("objcopy failed");
   }

   use std::fs::OpenOptions;
   let mut disk_image = OpenOptions::new()
      .write(true)
      .open(&output_bin_path)
      .map_err(|err| DiskImageError::Io {
         message: "failed to open boot image",
         error: err,
      })?;
   let file_size = disk_image
      .metadata()
      .map_err(|err| DiskImageError::Io {
         message: "failed to get size of boot image",
         error: err,
      })?
      .len();
   const BLOCK_SIZE: u64 = 512;
   assert_eq!(file_size, BLOCK_SIZE);

   let kernel_size = fs::metadata(&kernel_binary)
      .context("failed to read metadata of kernel binary")?
      .len();

   // create fat partition
   const MB: u64 = 1024 * 1024;
   let fat_size = kernel_size; // TODO plus second stage size
   let fat_size_padded_and_rounded = ((fat_size + 1024 * 64 - 1) / MB + 1) * MB;
   let fat_file_path = {
      let fat_path = output_bin_path.with_extension("fat");
      let fat_file = fs::OpenOptions::new()
         .read(true)
         .write(true)
         .create(true)
         .truncate(true)
         .open(&fat_path)
         .context("Failed to create UEFI FAT file")?;
      fat_file
         .set_len(fat_size_padded_and_rounded)
         .context("failed to set UEFI FAT file length")?;

      // create new FAT partition
      let format_options = fatfs::FormatVolumeOptions::new().volume_label(*b"BOOT       ");
      fatfs::format_volume(&fat_file, format_options)
         .context("Failed to format UEFI FAT file")?;

      // copy kernel to FAT filesystem
      let partition = fatfs::FileSystem::new(&fat_file, fatfs::FsOptions::new())
         .context("Failed to open FAT file system of UEFI FAT file")?;
      let root_dir = partition.root_dir();
      let mut kernel_file = root_dir.create_file("kernel-x86_64")?;
      kernel_file.truncate()?;
      io::copy(&mut fs::File::open(&kernel_binary)?, &mut kernel_file)?;

      fat_path
   };

   disk_image.seek(io::SeekFrom::Start(446))?;
   disk_image.write_all(&[0x80, 0, 0, 0, 0x04, 0, 0, 0])?;
   let start_sector = 1u32.to_le_bytes();
   let size_sectors = u32::try_from(&fat_size_padded_and_rounded / 512)
      .unwrap()
      .to_le_bytes();
   disk_image.write_all(&start_sector)?;
   disk_image.write_all(&size_sectors)?;

   disk_image.seek(io::SeekFrom::Start(512))?;
   io::copy(&mut fs::File::open(&kernel_binary)?, &mut disk_image)?;

   pad_to_nearest_block_size(output_bin_path)?;
   Ok(())
}

fn pad_to_nearest_block_size(output_bin_path: &Path) -> Result<(), DiskImageError> {
   const BLOCK_SIZE: u64 = 512;
   use std::fs::OpenOptions;
   let file = OpenOptions::new()
      .write(true)
      .open(&output_bin_path)
      .map_err(|err| DiskImageError::Io {
         message: "failed to open boot image",
         error: err,
      })?;
   let file_size = file
      .metadata()
      .map_err(|err| DiskImageError::Io {
         message: "failed to get size of boot image",
         error: err,
      })?
      .len();
   let remainder = file_size % BLOCK_SIZE;
   let padding = if remainder > 0 {
      BLOCK_SIZE - remainder
   } else {
      0
   };
   file.set_len(file_size + padding)
      .map_err(|err| DiskImageError::Io {
         message: "failed to pad boot image to a multiple of the block size",
         error: err,
      })
}

/// Creating the disk image failed.
#[derive(Debug, Error)]
pub enum DiskImageError {
   /// The `llvm-tools-preview` rustup component was not found
   #[error(
   "Could not find the `llvm-tools-preview` rustup component.\n\n\
        You can install by executing `rustup component add llvm-tools-preview`."
   )]
   LlvmToolsNotFound,

   /// There was another problem locating the `llvm-tools-preview` rustup component
   #[error("Failed to locate the `llvm-tools-preview` rustup component: {0:?}")]
   LlvmTools(llvm_tools::Error),

   /// The llvm-tools component did not contain the required `llvm-objcopy` executable
   #[error("Could not find `llvm-objcopy` in the `llvm-tools-preview` rustup component.")]
   LlvmObjcopyNotFound,

   /// The `llvm-objcopy` command failed
   #[error("Failed to run `llvm-objcopy`: {}", String::from_utf8_lossy(.stderr))]
   ObjcopyFailed {
      /// The output of `llvm-objcopy` to standard error
      stderr: Vec<u8>,
   },

   /// An unexpected I/O error occurred
   #[error("I/O error: {message}:\n{error}")]
   Io {
      /// Description of the failed I/O operation
      message: &'static str,
      /// The I/O error that occurred
      error: io::Error,
   },
}

impl From<llvm_tools::Error> for DiskImageError {
   fn from(err: llvm_tools::Error) -> Self {
      match err {
         llvm_tools::Error::NotFound => DiskImageError::LlvmToolsNotFound,
         other => DiskImageError::LlvmTools(other),
      }
   }
}