//! Build script, two jobs:
//!
//! 1. Compile the user programs in user/ into ELF executables in OUT_DIR.
//!    They're compiled with plain `rustc` for the built-in
//!    `x86_64-unknown-none` target (prebuilt `core`, so no build-std
//!    needed), as static executables (`relocation-model=static`) linked at a
//!    high user address -- which needs the `large` code model (the default
//!    ones assume code in the low/high 2 GiB).
//!
//! 2. Build the second QEMU disk, `target/disk.img` (64 MiB):
//!      * a GPT partition table (made with `sfdisk`) with one partition
//!        starting at sector 2048 (1 MiB, the usual alignment),
//!      * in it a FAT32 file system (`mkfs.vfat`), filled with `mtools`
//!        (`mmd`/`mcopy` write into an image file directly -- no root, no
//!        loop-mounting needed): everything in disk/ plus the user programs
//!        in /bin.
//!    The kernel finds the disk on the PCI bus, reads the GPT, mounts the
//!    FAT32 partition at /mnt/disk0 and loads programs from /mnt/disk0/bin.
//!    QEMU opens it with `snapshot=on`, so the kernel's writes never change
//!    this file (every boot and every test starts from the same disk).
//!
//! 3. Build the third QEMU disk, `target/ext2.img` (32 MiB): a whole-disk
//!    ext2 file system (no partition table) made by `mke2fs -d`, which
//!    copies a directory tree into the new file system. The tree is disk2/
//!    plus generated files: big.txt (big enough for double-indirect blocks),
//!    sparse.bin (66 MiB of mostly holes, reaching the triple-indirect
//!    blocks), and two symlinks (one short = "fast", one long = "slow").
//!    Mounted at /mnt/disk1 (drive C: in the shell).
//!    Two more small images are for `cargo test` only (see Cargo.toml
//!    test-args): ext2-4k.img (4 KiB blocks) and ext2-rev0.img (the original
//!    1993 revision 0 format: fixed 128-byte inodes, no file types in
//!    directory entries).
//!
//! Needs dosfstools (mkfs.vfat), mtools (mmd, mcopy), fdisk (sfdisk) and
//! e2fsprogs (mke2fs):
//!     sudo apt install dosfstools mtools fdisk e2fsprogs

use std::{env, fs, io::Write, path::{Path, PathBuf}, process::{Command, Stdio}};

/// Everything in /bin on the disk: the shell, its tools, and the test and
/// demo programs of the earlier stages.
const PROGRAMS: &[&str] = &[
    "sh", "ls", "cat", "wc", "grep", "mkdir", "rm", "touch", "cp", "sleep", // the shell + tools
    "hello", "evil", "spin", "demo", "child", // stage 5/6 demos and tests
];

const DISK_SECTORS: u64 = 64 * 1024 * 1024 / 512;
const PART_START: u64 = 2048;
/// Leave 1 MiB at the end too (the backup GPT lives in the last 33 sectors).
const PART_SECTORS: u64 = DISK_SECTORS - 2 * PART_START;

fn main() {
    let manifest = PathBuf::from(env::var("CARGO_MANIFEST_DIR").unwrap());
    let out_dir = PathBuf::from(env::var("OUT_DIR").unwrap());
    let user_dir = manifest.join("user");
    println!("cargo:rerun-if-changed=user");
    println!("cargo:rerun-if-changed=disk");
    println!("cargo:rerun-if-changed=disk2");
    println!("cargo:rerun-if-changed=build.rs");

    for program in PROGRAMS {
        build_program(&user_dir, &out_dir, program);
    }
    build_disk(&manifest, &out_dir);
    build_ext2_disks(&manifest, &out_dir);
}

fn build_program(user_dir: &Path, out_dir: &Path, program: &str) {
    let rustc = env::var("RUSTC").unwrap_or_else(|_| "rustc".into());
    let status = Command::new(&rustc)
        .args(["--edition", "2024", "--target", "x86_64-unknown-none"])
        .args(["-C", "panic=abort", "-C", "opt-level=2", "-C", "debuginfo=0", "-C", "strip=debuginfo"])
        .args(["-C", "relocation-model=static", "-C", "code-model=large"])
        .arg("-C")
        .arg(format!("link-arg=-T{}", user_dir.join("link.ld").display()))
        .arg("-o")
        .arg(out_dir.join(program))
        .arg(user_dir.join(format!("{program}.rs")))
        .status()
        .expect("failed to run rustc for a user program");
    assert!(status.success(), "building user program {program} failed");
}

/// Find a tool in PATH or the sbin directories (often not in a user's PATH).
fn tool(name: &str) -> PathBuf {
    let path = env::var("PATH").unwrap_or_default();
    for dir in path.split(':').chain(["/usr/sbin", "/sbin", "/usr/bin"]) {
        let candidate = Path::new(dir).join(name);
        if candidate.is_file() {
            return candidate;
        }
    }
    panic!("`{name}` not found: install it with `sudo apt install dosfstools mtools fdisk e2fsprogs`");
}

fn run(cmd: &mut Command, stdin: Option<&str>) {
    cmd.stdin(if stdin.is_some() { Stdio::piped() } else { Stdio::null() });
    let mut child = cmd.spawn().unwrap_or_else(|e| panic!("can't run {cmd:?}: {e}"));
    if let Some(input) = stdin {
        child.stdin.take().unwrap().write_all(input.as_bytes()).unwrap();
    }
    let status = child.wait().unwrap();
    assert!(status.success(), "{cmd:?} failed");
}

fn build_disk(manifest: &Path, out_dir: &Path) {
    let target_dir = env::var("CARGO_TARGET_DIR").map(PathBuf::from).unwrap_or_else(|_| manifest.join("target"));
    fs::create_dir_all(&target_dir).unwrap();
    let disk = target_dir.join("disk.img");
    let part = out_dir.join("part.img");

    // 1. The FAT32 file system, as its own image first. -s 1: one sector per
    //    cluster (FAT32 needs >= 65525 clusters, so small disks need small
    //    clusters). -n: volume label.
    let _ = fs::remove_file(&part);
    run(
        Command::new(tool("mkfs.vfat"))
            .args(["-F", "32", "-s", "1", "-n", "TYLERDISK", "-C"])
            .arg(&part)
            .arg((PART_SECTORS / 2).to_string()), // size in KiB
        None,
    );
    let mtools = |name: &str, args: &[&str]| {
        let mut cmd = Command::new(tool(name));
        cmd.env("MTOOLS_SKIP_CHECK", "1").arg("-i").arg(&part).args(args);
        run(&mut cmd, None);
    };
    // Copy disk/ (text files, subdirectories) to the root of the volume...
    for entry in fs::read_dir(manifest.join("disk")).unwrap() {
        let path = entry.unwrap().path();
        mtools("mcopy", &["-s", path.to_str().unwrap(), "::/"]);
    }
    // ...and the user programs to /bin.
    mtools("mmd", &["::/bin"]);
    for program in PROGRAMS {
        mtools("mcopy", &[out_dir.join(program).to_str().unwrap(), &format!("::/bin/{program}")]);
    }

    // 2. The whole disk: zeros + GPT partition table (sfdisk works on image
    //    files too), then the FAT32 image copied into the partition.
    let _ = fs::remove_file(&disk);
    fs::File::create(&disk).unwrap().set_len(DISK_SECTORS * 512).unwrap();
    let layout = format!(
        "label: gpt\nstart={PART_START}, size={PART_SECTORS}, type=EBD0A0A2-B9E5-4433-87C0-68B6B72699C7, name=\"fat32\"\n"
    );
    run(Command::new(tool("sfdisk")).arg("--quiet").arg(&disk), Some(&layout));
    let fat = fs::read(&part).unwrap();
    assert_eq!(fat.len() as u64, PART_SECTORS * 512);
    let mut file = fs::OpenOptions::new().write(true).open(&disk).unwrap();
    use std::io::{Seek, SeekFrom};
    file.seek(SeekFrom::Start(PART_START * 512)).unwrap();
    file.write_all(&fat).unwrap();
}

/// The lines of big.txt: line i is `big.txt line {i:05}` (19 bytes with the
/// newline), so tests can check any offset. 16000 lines = 304000 bytes:
/// with 1 KiB blocks that's past the 12 direct + 256 single-indirect blocks.
pub const BIG_LINES: usize = 16000;

/// sparse.bin: 66 MiB, all holes except these 1 KiB chunks of text. With
/// 1 KiB blocks, 40 MiB is in the double-indirect range and 65 MiB in the
/// triple-indirect range (which starts at 12 + 256 + 256*256 KiB ~ 64.3 MiB).
pub const SPARSE_SIZE: u64 = 66 * 1024 * 1024;
pub const SPARSE_MARKS: &[u64] = &[0, 40 * 1024 * 1024, 65 * 1024 * 1024];

/// Copy a directory tree (files and directories only).
fn copy_tree(from: &Path, to: &Path) {
    fs::create_dir_all(to).unwrap();
    for entry in fs::read_dir(from).unwrap() {
        let path = entry.unwrap().path();
        let dest = to.join(path.file_name().unwrap());
        if path.is_dir() {
            copy_tree(&path, &dest);
        } else {
            fs::copy(&path, &dest).unwrap();
        }
    }
}

fn build_ext2_disks(manifest: &Path, out_dir: &Path) {
    use std::os::unix::fs::symlink;
    let target_dir = env::var("CARGO_TARGET_DIR").map(PathBuf::from).unwrap_or_else(|_| manifest.join("target"));

    // The tree to copy in: disk2/ + generated files.
    let tree = out_dir.join("ext2-tree");
    let _ = fs::remove_dir_all(&tree);
    copy_tree(&manifest.join("disk2"), &tree);
    let big: String = (0..BIG_LINES).map(|i| format!("big.txt line {i:05}\n")).collect();
    fs::write(tree.join("big.txt"), &big).unwrap();
    {
        use std::io::{Seek, SeekFrom};
        let mut f = fs::File::create(tree.join("sparse.bin")).unwrap();
        f.set_len(SPARSE_SIZE).unwrap(); // a file of holes...
        for &at in SPARSE_MARKS {
            // ...with a few 1 KiB blocks of text (mke2fs -d keeps all-zero
            // blocks as holes, so the image stays small).
            let text = format!("sparse.bin data at offset {at}\n");
            let mut block = text.repeat(1024 / text.len()).into_bytes();
            block.resize(1024, b'.');
            f.seek(SeekFrom::Start(at)).unwrap();
            f.write_all(&block).unwrap();
        }
    }
    // A "fast" symlink: the target (< 60 bytes) fits inside the inode.
    symlink("hello.txt", tree.join("hello-link")).unwrap();
    // A "slow" symlink: the target is too long, so it gets a data block.
    symlink("./deep/../deep/er/../er/./../../../docs/./deep/er/../../deep/er/nested.txt", tree.join("docs/long-link")).unwrap();

    // -t ext2: no journal, no extents. -b 1024: 1 KiB blocks. -m 0: no
    // blocks reserved for root. -E root_owner: the root directory belongs to
    // root (the other files keep their owner from the build machine).
    // -F: it's a file, not a block device; just do it.
    let mke2fs = |img: &Path, size: &str, extra: &[&str], src: &Path| {
        let _ = fs::remove_file(img);
        run(
            Command::new(tool("mke2fs"))
                .args(["-q", "-F", "-t", "ext2", "-m", "0"])
                .args(extra)
                .arg("-d")
                .arg(src)
                .arg(img)
                .arg(size),
            None,
        );
    };
    mke2fs(&target_dir.join("ext2.img"), "32M", &["-b", "1024", "-L", "RUSTBELT", "-E", "root_owner=0:0"], &tree);

    // Smaller tree for the test-only images.
    let small = out_dir.join("ext2-small");
    let _ = fs::remove_dir_all(&small);
    copy_tree(&manifest.join("disk2/docs"), &small.join("docs"));
    fs::copy(manifest.join("disk2/hello.txt"), small.join("hello.txt")).unwrap();
    fs::write(small.join("big.txt"), &big).unwrap();
    symlink("hello.txt", small.join("hello-link")).unwrap();
    mke2fs(&target_dir.join("ext2-4k.img"), "8M", &["-b", "4096", "-L", "FOURK", "-E", "root_owner=0:0"], &small);
    mke2fs(&target_dir.join("ext2-rev0.img"), "4M", &["-b", "1024", "-E", "root_owner=0:0,revision=0"], &small);
}