//! exFAT through the VFS. Cargo.toml's test-args attach two exFAT images
//! that build.rs makes (snapshot=on, so writes vanish after the test):
//!
//!   vdc  target/exfat.img      /mnt/disk2  4 KiB clusters, disk3/ + more
//!   vdg  target/exfat-512.img  /mnt/disk6  512-byte clusters, small tree
//!
//! scripts/exfat-check.sh runs this kernel on *writable* copies and then
//! checks them with the host's fsck.exfat.
#![no_std]
#![no_main]
#![feature(custom_test_frameworks)]
#![test_runner(rustbelt::test_runner)]
#![reexport_test_harness_main = "test_main"]

extern crate alloc;

use alloc::{format, string::String, vec, vec::Vec};
use bootloader::{BootInfo, entry_point};
use core::panic::PanicInfo;
use rustbelt::block;
use rustbelt::errno::Errno;
use rustbelt::fs::{self, InodeKind, exfat::ExfatFs};

entry_point!(main);

fn main(boot_info: &'static BootInfo) -> ! {
    rustbelt::init();
    rustbelt::init_memory(boot_info);
    fs::init();
    rustbelt::init_storage();
    test_main();
    rustbelt::hlt_loop();
}

const DISK: &str = "/mnt/disk2";
const SMALL: &str = "/mnt/disk6";
/// The small disk's root is one 512-byte cluster with 1 free entry left, so
/// its write tests run in Photos/ (which has room): growing the root is
/// tested on its own, because a directory never shrinks again.
const SMALL_DIR: &str = "/mnt/disk6/Photos";

fn read(path: &str, offset: usize, len: usize) -> Vec<u8> {
    let mut buf = vec![0u8; len];
    let n = fs::lookup(path).unwrap().read_at(offset, &mut buf).unwrap();
    buf.truncate(n);
    buf
}

fn names(path: &str) -> Vec<String> {
    let mut names: Vec<String> = fs::lookup(path).unwrap().list().unwrap().into_iter().map(|e| e.name).collect();
    names.sort();
    names
}

/// (clusters marked used in the allocation bitmap, PercentInUse), read
/// straight from the disk with a few lines of independent parsing: boot
/// sector -> root directory -> bitmap entry (0x81). On a freshly made
/// volume the bitmap and root are both single, contiguous runs.
fn usage(device: &str) -> (u32, u8) {
    let dev = block::get(device).unwrap();
    let mut boot = [0u8; 512];
    dev.read_sectors(0, &mut boot).unwrap();
    let get32 = |b: &[u8], at: usize| u32::from_le_bytes(b[at..at + 4].try_into().unwrap());
    let sector_shift = boot[108] as u32;
    let cluster_bytes = 1usize << (sector_shift + boot[109] as u32);
    let heap = (get32(&boot, 88) as u64) << sector_shift;
    let count = get32(&boot, 92);
    let pos = |cluster: u32| heap + (cluster as u64 - 2) * cluster_bytes as u64;
    let read = |at: u64, len: usize| {
        let mut b = vec![0u8; len.div_ceil(512) * 512];
        dev.read_sectors(at / 512, &mut b).unwrap();
        b
    };
    let root = read(pos(get32(&boot, 96)), cluster_bytes);
    let e = root.chunks(32).find(|e| e[0] == 0x81).unwrap();
    let bitmap = read(pos(get32(e, 20)), count.div_ceil(8) as usize);
    let used = (0..count as usize).filter(|&i| bitmap[i / 8] & (1 << (i % 8)) != 0).count();
    (used as u32, boot[112])
}

#[test_case]
fn mounted_as_exfat() {
    let mounts = fs::mounts();
    for path in [DISK, SMALL] {
        assert!(mounts.iter().any(|(p, name)| p == path && *name == "exfat"), "{} not exFAT", path);
    }
    // A second instance on the same device, just to read its description.
    let d = ExfatFs::mount(block::get("vdc").unwrap()).unwrap().describe();
    assert_eq!(d, "exFAT volume \"TYLEREXFAT\" (4 KiB clusters, 7680 clusters)");
    let d = ExfatFs::mount(block::get("vdg").unwrap()).unwrap().describe();
    assert!(d.starts_with("exFAT volume \"SMALLCLUST\" (512 byte clusters"), "{}", d);
}

#[test_case]
fn root_listing_keeps_case_and_long_names() {
    let long = format!("a-really-long-file-name-that-takes-several-file-name-directory-entries-in-exfat-{}.txt", "x".repeat(20));
    let want = vec![
        String::from("Long File Name With Spaces.txt"),
        "MixedCase.TXT".into(),
        "Photos".into(),
        long.clone(),
        "frag-chain.txt".into(),
        "numbers.txt".into(),
        "readme.txt".into(),
        "Ünïcödé café.txt".into(),
    ];
    // (Contains, not equals: tests run in name order, and the copy test
    // adds files to this directory first.)
    let have = names(DISK);
    for name in &want {
        assert!(have.contains(name), "{} missing from {:?}", name, have);
    }
    assert_eq!(read(&format!("{}/{}", DISK, long), 0, 13), b"A name longer");
    assert_eq!(fs::lookup(&format!("{}/Photos", DISK)).unwrap().kind(), InodeKind::Directory);
}

#[test_case]
fn lookup_ignores_case() {
    assert!(read("/mnt/disk2/mixedcase.txt", 0, 100).starts_with(b"MixedCase.TXT: exFAT keeps"));
    assert!(read("/mnt/disk2/LONG FILE NAME WITH SPACES.TXT", 0, 100).starts_with(b"This file has a long name"));
    // Non-ASCII: the volume's up-case table maps ü -> Ü, é -> É.
    assert!(read("/mnt/disk2/ÜNÏCÖDÉ CAFÉ.TXT", 0, 100).starts_with("Ünïcödé names work".as_bytes()));
    assert_eq!(read("/mnt/disk2/photos/2026 TRIP/Trip Notes.txt", 0, 100), b"Notes from the 2026 trip, two directories down.\n");
    assert_eq!(fs::lookup("/mnt/disk2/mixedcase.tx").err(), Some(Errno::ENOENT));
    assert_eq!(fs::lookup("/mnt/disk2/readme.txt/x").err(), Some(Errno::ENOTDIR));
}

#[test_case]
fn contiguous_file() {
    // numbers.txt: 20 000 lines "exfat line NNNNN\n", one NoFatChain run.
    let path = "/mnt/disk2/numbers.txt";
    assert_eq!(fs::lookup(path).unwrap().size(), 340_000);
    assert_eq!(read(path, 12345 * 17, 17), b"exfat line 12345\n");
    assert_eq!(read(path, 4090, 12), b" 00240\nexfat"); // across a cluster boundary
    assert_eq!(read(path, 339_983, 100), b"exfat line 19999\n"); // the end
    assert_eq!(read(path, 400_000, 10), b"");
}

#[test_case]
fn fragmented_file() {
    // frag-chain.txt uses every other cluster, linked through the FAT.
    let want: String = (0..2000).map(|i| format!("fragment line {:04}\n", i)).collect();
    for disk in [DISK, SMALL] {
        assert_eq!(fs::read_all(&format!("{}/frag-chain.txt", disk)).unwrap(), want.as_bytes(), "{}", disk);
    }
}

#[test_case]
fn bad_names() {
    assert_eq!(fs::create("/mnt/disk2/a:b.txt", InodeKind::File).err(), Some(Errno::EINVAL));
    assert_eq!(fs::create("/mnt/disk2/what?.txt", InodeKind::File).err(), Some(Errno::EINVAL));
    assert_eq!(fs::create(&format!("/mnt/disk2/{}", "n".repeat(256)), InodeKind::File).err(), Some(Errno::ENAMETOOLONG));
    // Same name in other case = the same file.
    assert_eq!(fs::create("/mnt/disk2/README.TXT", InodeKind::File).err(), Some(Errno::EEXIST));
}

/// Create, write across clusters, append, truncate, mkdir, rmdir, unlink:
/// afterwards the bitmap and PercentInUse are back where they started.
fn write_round_trip(disk: &str, device: &str) {
    let before = usage(device);
    let dir = format!("{}/New Folder", disk);
    fs::create(&dir, InodeKind::Directory).unwrap();
    let path = format!("{}/Data File.BIN", dir);
    let f = fs::create(&path, InodeKind::File).unwrap();
    assert_eq!(f.size(), 0);
    let data: Vec<u8> = (0..10_000u32).map(|i| (i * 7 % 251) as u8).collect();
    f.write_at(0, &data[..3000]).unwrap();
    f.write_at(3000, &data[3000..]).unwrap();
    assert_eq!(fs::read_all(&path).unwrap(), data);
    // Same file, other case.
    f.write_at(10_000, b"appended").unwrap();
    assert_eq!(read(&format!("{}/new folder/data file.bin", disk), 9_998, 20), [&data[9998..], b"appended"].concat());
    assert_eq!(fs::remove(&dir, true), Err(Errno::ENOTEMPTY));
    f.truncate().unwrap();
    assert_eq!(f.size(), 0);
    f.write_at(0, b"short").unwrap();
    assert_eq!(fs::read_all(&path).unwrap(), b"short");
    // Writing past the end leaves a gap of zeros.
    f.write_at(5000, b"!").unwrap();
    let all = fs::read_all(&path).unwrap();
    assert_eq!(all.len(), 5001);
    assert!(all[5..5000].iter().all(|&b| b == 0));
    fs::remove(&path, false).unwrap();
    assert_eq!(names(&dir), Vec::<String>::new());
    fs::remove(&dir, true).unwrap();
    assert_eq!(fs::lookup(&dir).err(), Some(Errno::ENOENT));
    assert_eq!(usage(device), before);
}

#[test_case]
fn write_4k_clusters() {
    write_round_trip(DISK, "vdc");
}

#[test_case]
fn write_512_byte_clusters() {
    write_round_trip(SMALL_DIR, "vdg");
}

#[test_case]
fn contiguous_file_turns_into_a_fat_chain() {
    // a.bin gets a cluster, b.bin the very next one. Growing a.bin can't
    // stay contiguous, so its clusters get FAT links (NoFatChain cleared).
    let before = usage("vdg");
    let a = fs::create("/mnt/disk6/Photos/a.bin", InodeKind::File).unwrap();
    a.write_at(0, &[b'a'; 500]).unwrap();
    let b = fs::create("/mnt/disk6/Photos/b.bin", InodeKind::File).unwrap();
    b.write_at(0, &[b'b'; 1500]).unwrap();
    a.write_at(500, &[b'A'; 3000]).unwrap();
    let all = fs::read_all("/mnt/disk6/Photos/a.bin").unwrap();
    assert_eq!(all.len(), 3500);
    assert!(all[..500].iter().all(|&c| c == b'a') && all[500..].iter().all(|&c| c == b'A'));
    assert_eq!(fs::read_all("/mnt/disk6/Photos/b.bin").unwrap(), [b'b'; 1500]);
    fs::remove("/mnt/disk6/Photos/a.bin", false).unwrap();
    fs::remove("/mnt/disk6/Photos/b.bin", false).unwrap();
    assert_eq!(usage("vdg"), before);
}

#[test_case]
fn many_files_grow_a_directory() {
    // 200 entry sets of 3 entries need 38 clusters of 512 bytes: the
    // directory grows (and, with file data in between, becomes a FAT chain).
    let before = usage("vdg");
    fs::create("/mnt/disk6/Photos/many", InodeKind::Directory).unwrap();
    for i in 0..200 {
        let f = fs::create(&format!("/mnt/disk6/Photos/many/File Number {:03}.txt", i), InodeKind::File).unwrap();
        f.write_at(0, format!("{}\n", i).as_bytes()).unwrap();
    }
    assert_eq!(fs::lookup("/mnt/disk6/Photos/many").unwrap().size(), 200);
    assert_eq!(read("/mnt/disk6/PHOTOS/MANY/file number 123.TXT", 0, 10), b"123\n");
    assert_eq!(read("/mnt/disk6/Photos/many/File Number 199.txt", 0, 10), b"199\n");
    for i in 0..200 {
        fs::remove(&format!("/mnt/disk6/Photos/many/file number {:03}.txt", i), false).unwrap();
    }
    fs::remove("/mnt/disk6/Photos/many", true).unwrap();
    assert_eq!(usage("vdg"), before);
}

#[test_case]
fn root_directory_grows() {
    // The root has no entry set: its size is its FAT chain. Two new files
    // don't fit in its one 512-byte cluster, so it gains a second one.
    let (used, _) = usage("vdg");
    for name in ["First New File.txt", "Second New File.txt"] {
        let f = fs::create(&format!("{}/{}", SMALL, name), InodeKind::File).unwrap();
        f.write_at(0, name.as_bytes()).unwrap();
    }
    assert_eq!(read("/mnt/disk6/second new file.txt", 0, 100), b"Second New File.txt");
    assert!(names(SMALL).contains(&String::from("First New File.txt")));
    assert_eq!(usage("vdg").0, used + 3); // one root cluster + one per file
    for name in ["First New File.txt", "Second New File.txt"] {
        fs::remove(&format!("{}/{}", SMALL, name), false).unwrap();
    }
    assert_eq!(usage("vdg").0, used + 1); // the root keeps its new cluster
    assert_eq!(read("/mnt/disk6/numbers.txt", 17, 17), b"exfat line 00001\n");
}

#[test_case]
fn copy_from_fat_and_ext2() {
    // What `cp B:/notes/todo.txt D:/` and `cp C:/hello.txt D:/` do.
    for (from, to) in [("/mnt/disk0/notes/todo.txt", "/mnt/disk2/todo.txt"), ("/mnt/disk1/hello.txt", "/mnt/disk2/Copied From Ext2.txt")] {
        let bytes = fs::read_all(from).unwrap();
        fs::create(to, InodeKind::File).unwrap().write_at(0, &bytes).unwrap();
        assert_eq!(fs::read_all(to).unwrap(), bytes);
    }
    // And the 340 KB file the other way, onto ext2.
    let numbers = fs::read_all("/mnt/disk2/numbers.txt").unwrap();
    fs::create("/mnt/disk1/numbers.txt", InodeKind::File).unwrap().write_at(0, &numbers).unwrap();
    assert_eq!(fs::read_all("/mnt/disk1/numbers.txt").unwrap(), numbers);
}

#[test_case]
fn written_files_stay_for_fsck() {
    // Runs last (tests go in name order) and deletes nothing, so that
    // scripts/exfat-check.sh's fsck.exfat sees the tricky cases on disk: a
    // grown directory that became a FAT chain, a file that went from
    // NoFatChain to a FAT chain, deleted entries in the middle of a
    // directory, and the grown root.
    for (disk, n) in [(SMALL_DIR, 40usize), (DISK, 300)] {
        let dir = format!("{}/Kept For fsck", disk);
        fs::create(&dir, InodeKind::Directory).unwrap();
        for i in 0..n {
            let f = fs::create(&format!("{}/Kept File {:03}.txt", dir, i), InodeKind::File).unwrap();
            f.write_at(0, format!("kept {}\n", i).as_bytes()).unwrap();
        }
        for i in (0..n).step_by(3) {
            fs::remove(&format!("{}/kept file {:03}.TXT", dir, i), false).unwrap();
        }
        let a = fs::create(&format!("{}/Grows Into A Chain.bin", dir), InodeKind::File).unwrap();
        a.write_at(0, &[1; 100]).unwrap();
        fs::create(&format!("{}/Blocker.txt", dir), InodeKind::File).unwrap().write_at(0, b"in the way\n").unwrap();
        a.write_at(100, &[2; 9000]).unwrap();
        assert_eq!(a.size(), 9100);
        assert_eq!(fs::lookup(&dir).unwrap().size(), n - n.div_ceil(3) + 2);
    }
    assert_eq!(read("/mnt/disk2/kept for FSCK/KEPT FILE 299.txt", 0, 20), b"kept 299\n");
}

#[panic_handler]
fn panic(info: &PanicInfo) -> ! {
    rustbelt::test_panic_handler(info)
}