use alloc::borrow::ToOwned;
use alloc::vec::Vec;

use syscall::{Error, EINTR};
use syscall::flag::{O_CLOEXEC, O_RDONLY};

use redox_exec::*;

pub fn main() -> ! {
    let initfs_length;

    let envs = {
        let mut env = [0_u8; 4096];

        let fd = FdGuard::new(syscall::open("sys:env", O_RDONLY).expect("bootstrap: failed to open env"));
        let bytes_read = syscall::read(*fd, &mut env).expect("bootstrap: failed to read env");

        if bytes_read >= env.len() {
            // TODO: Handle this, we can allocate as much as we want in theory.
            panic!("env is too large");
        }
        let env = &mut env[..bytes_read];

        let raw_iter = || env.split(|c| *c == b'\n').filter(|var| !var.is_empty());

        let mut initfs_length_opt = None;

        for var in raw_iter() {
            let equal_sign = var.iter().position(|c| *c == b'=').expect("malformed environment variable");
            let name = &var[..equal_sign];
            let value = &var[equal_sign + 1..];

            match name {
                b"INITFS_LENGTH" => initfs_length_opt = core::str::from_utf8(value).ok().and_then(|s| usize::from_str_radix(s, 16).ok()),

                _ => continue,
            }
        }
        initfs_length = initfs_length_opt.expect("missing INITFS_LENGTH");

        let iter = || raw_iter().filter(|var| !var.starts_with(b"INITFS_"));

        iter().map(|var| var.to_owned()).collect::<Vec<_>>()
    };

    extern {
        // The linker script will define this as the location of the initfs header.
        static __initfs_header: u8;
    }

    unsafe {
        // Creating a reference to NULL is UB. Mask the UB for now using black_box.
        // FIXME use a raw pointer and inline asm for reading instead for the initfs header.
        spawn_initfs(core::ptr::addr_of!(__initfs_header), initfs_length);
    }
    const CWD: &[u8] = b"/scheme/initfs";
    let extrainfo = redox_exec::ExtraInfo {
        cwd: Some(CWD),
    };

    let path = "/scheme/initfs/bin/init";
    let total_args_envs_auxvpointee_size = path.len() + 1 + envs.len() + envs.iter().map(|v| v.len()).sum::<usize>() + CWD.len() + 1;

    let image_file = FdGuard::new(syscall::open(path, O_RDONLY).expect("failed to open init"));
    let open_via_dup = FdGuard::new(syscall::open("thisproc:current/open_via_dup", 0).expect("failed to open open_via_dup"));
    let memory = FdGuard::new(syscall::open("memory:", 0).expect("failed to open memory"));

    fexec_impl(image_file, open_via_dup, &memory, path.as_bytes(), [path], envs.iter(), total_args_envs_auxvpointee_size, &extrainfo, None).expect("failed to execute init");

    unreachable!()
}

unsafe fn spawn_initfs(initfs_start: *const u8, initfs_length: usize) {
    let read = syscall::open("pipe:", O_CLOEXEC).expect("failed to open sync read pipe");

    // The write pipe will not inherit O_CLOEXEC, but is closed by the daemon later.
    let write = syscall::dup(read, b"write").expect("failed to open sync write pipe");

    match redox_exec::fork_impl() {
        Err(err) => {
            panic!("Failed to fork in order to start initfs daemon: {}", err);
        }
        // Continue serving the scheme as the child.
        Ok(0) => {
            let _ = syscall::close(read);
        }
        // Return in order to execute init, as the parent.
        Ok(_) => {
            let _ = syscall::close(write);
            loop {
                match syscall::read(read, &mut [0]) {
                    Err(Error { errno: EINTR }) => continue,
                    _ => break,
                }
            }

            return;
        }
    }
    crate::initfs::run(core::slice::from_raw_parts(initfs_start, initfs_length), write);
}