//! # The Redox OS Kernel, version 2
//!
//! The Redox OS Kernel is a microkernel that supports `x86_64` systems and
//! provides Unix-like syscalls for primarily Rust applications

// Useful for adding comments about different branches
#![allow(clippy::if_same_then_else)]
// Useful in the syscall function
#![allow(clippy::many_single_char_names)]
// Used for context::context
#![allow(clippy::module_inception)]
// Not implementing default is sometimes useful in the case something has significant cost
// to allocate. If you implement default, it can be allocated without evidence using the
// ..Default::default() syntax. Not fun in kernel space
#![allow(clippy::new_without_default)]
// Used to make it nicer to return errors, for example, .ok_or(Error::new(ESRCH))
#![allow(clippy::or_fun_call)]
// This is needed in some cases, like for syscall
#![allow(clippy::too_many_arguments)]
// There is no harm in this being done
#![allow(clippy::useless_format)]

// TODO: address ocurrances and then deny
#![warn(clippy::not_unsafe_ptr_arg_deref)]
// TODO: address ocurrances and then deny
#![warn(clippy::cast_ptr_alignment)]
// Indexing a slice can cause panics and that is something we always want to avoid
// in kernel code. Use .get and return an error instead
// TODO: address ocurrances and then deny
#![warn(clippy::indexing_slicing)]
// Overflows are very, very bad in kernel code as it may provide an attack vector for
// userspace applications, and it is only checked in debug builds
// TODO: address ocurrances and then deny
#![warn(clippy::integer_arithmetic)]
// Avoid panicking in the kernel without information about the panic. Use expect
// TODO: address ocurrances and then deny
#![warn(clippy::result_unwrap_used)]

// This is usually a serious issue - a missing import of a define where it is interpreted
// as a catch-all variable in a match, for example
#![deny(unreachable_patterns)]
// Ensure that all must_use results are used
#![deny(unused_must_use)]

#![feature(allocator_api)]
#![feature(asm)] // TODO: Relax requirements of most asm invocations
#![cfg_attr(target_arch = "aarch64", feature(llvm_asm))] // TODO: Rewrite using asm!
#![feature(concat_idents)]
#![feature(const_fn)]
#![feature(core_intrinsics)]
#![feature(global_asm)]
#![feature(integer_atomics)]
#![feature(lang_items)]
#![feature(naked_functions)]
#![feature(ptr_internals)]
#![feature(thread_local)]
#![no_std]

#[cfg(target_arch = "x86_64")]
pub extern crate x86;

#[macro_use]
extern crate alloc;

#[macro_use]
extern crate bitflags;
#[macro_use]
extern crate bitfield;
extern crate goblin;
extern crate linked_list_allocator;
extern crate rustc_demangle;
extern crate spin;
#[cfg(feature = "slab")]
extern crate slab_allocator;

use alloc::vec::Vec;
use core::sync::atomic::{AtomicUsize, Ordering};

use crate::scheme::{FileHandle, SchemeNamespace};

pub use crate::consts::*;

#[macro_use]
/// Shared data structures
pub mod common;

/// Architecture-dependent stuff
#[macro_use]
pub mod arch;
pub use crate::arch::*;

use crate::log::info;

/// Heap allocators
pub mod allocator;

/// ACPI table parsing
#[cfg(feature = "acpi")]
mod acpi;

/// Context management
pub mod context;

/// Architecture-independent devices
pub mod devices;

/// ELF file parsing
#[cfg(not(feature="doc"))]
pub mod elf;

/// Event handling
pub mod event;

/// External functions
pub mod externs;

/// Logging
pub mod log;

/// Memory management
pub mod memory;

/// Panic
#[cfg(not(any(feature="doc", test)))]
pub mod panic;

/// Process tracing
pub mod ptrace;

/// Schemes, filesystem handlers
pub mod scheme;

/// Synchronization primitives
pub mod sync;

/// Syscall handlers
pub mod syscall;

/// Time
pub mod time;

/// Tests
#[cfg(test)]
pub mod tests;

#[global_allocator]
static ALLOCATOR: allocator::Allocator = allocator::Allocator;

/// A unique number that identifies the current CPU - used for scheduling
#[thread_local]
static CPU_ID: AtomicUsize = AtomicUsize::new(0);

/// Get the current CPU's scheduling ID
#[inline(always)]
pub fn cpu_id() -> usize {
    CPU_ID.load(Ordering::Relaxed)
}

/// The count of all CPUs that can have work scheduled
static CPU_COUNT : AtomicUsize = AtomicUsize::new(0);

/// Get the number of CPUs currently active
#[inline(always)]
pub fn cpu_count() -> usize {
    CPU_COUNT.load(Ordering::Relaxed)
}

static mut INIT_ENV: &[u8] = &[];

/// Initialize userspace by running the initfs:bin/init process
/// This function will also set the CWD to initfs:bin and open debug: as stdio
pub extern fn userspace_init() {
    let path = "initfs:/bin/init";
    let env = unsafe { INIT_ENV };

    if let Err(err) = syscall::chdir("initfs:") {
        info!("Failed to enter initfs ({}).", err);
        info!("Perhaps the kernel was compiled with an incorrect INITFS_FOLDER \
               environment variable value?");
        panic!("Unexpected error while trying to enter initfs:.");
    }

    assert_eq!(syscall::open("debug:", syscall::flag::O_RDONLY).map(FileHandle::into), Ok(0));
    assert_eq!(syscall::open("debug:", syscall::flag::O_WRONLY).map(FileHandle::into), Ok(1));
    assert_eq!(syscall::open("debug:", syscall::flag::O_WRONLY).map(FileHandle::into), Ok(2));

    let fd = syscall::open(path, syscall::flag::O_RDONLY).expect("failed to open init");

    let mut args = Vec::new();
    args.push(path.as_bytes().to_vec().into_boxed_slice());

    let mut vars = Vec::new();
    for var in env.split(|b| *b == b'\n') {
        if ! var.is_empty() {
            vars.push(var.to_vec().into_boxed_slice());
        }
    }

    syscall::fexec_kernel(fd, args.into_boxed_slice(), vars.into_boxed_slice(), None, None).expect("failed to execute init");

    panic!("init returned");
}

/// This is the kernel entry point for the primary CPU. The arch crate is responsible for calling this
pub fn kmain(cpus: usize, env: &'static [u8]) -> ! {
    CPU_ID.store(0, Ordering::SeqCst);
    CPU_COUNT.store(cpus, Ordering::SeqCst);
    unsafe { INIT_ENV = env };

    //Initialize the first context, stored in kernel/src/context/mod.rs
    context::init();

    let pid = syscall::getpid();
    info!("BSP: {:?} {}", pid, cpus);
    info!("Env: {:?}", ::core::str::from_utf8(env));

    match context::contexts_mut().spawn(userspace_init) {
        Ok(context_lock) => {
            let mut context = context_lock.write();
            context.rns = SchemeNamespace::from(1);
            context.ens = SchemeNamespace::from(1);
            context.status = context::Status::Runnable;
        },
        Err(err) => {
            panic!("failed to spawn userspace_init: {:?}", err);
        }
    }

    loop {
        unsafe {
            interrupt::disable();
            if context::switch() {
                interrupt::enable_and_nop();
            } else {
                // Enable interrupts, then halt CPU (to save power) until the next interrupt is actually fired.
                interrupt::enable_and_halt();
            }
        }
    }
}

/// This is the main kernel entry point for secondary CPUs
#[allow(unreachable_code, unused_variables)]
pub fn kmain_ap(id: usize) -> ! {
    CPU_ID.store(id, Ordering::SeqCst);

    if cfg!(feature = "multi_core") {
        context::init();

        let pid = syscall::getpid();
        info!("AP {}: {:?}", id, pid);

        loop {
            unsafe {
                interrupt::disable();
                if context::switch() {
                    interrupt::enable_and_nop();
                } else {
                    // Enable interrupts, then halt CPU (to save power) until the next interrupt is actually fired.
                    interrupt::enable_and_halt();
                }
            }
        }
    } else {
        info!("AP {}: Disabled", id);

        loop {
            unsafe {
                interrupt::disable();
                interrupt::halt();
            }
        }
    }
}

/// Allow exception handlers to send signal to arch-independant kernel
#[no_mangle]
pub extern fn ksignal(signal: usize) {
    info!("SIGNAL {}, CPU {}, PID {:?}", signal, cpu_id(), context::context_id());
    {
        let contexts = context::contexts();
        if let Some(context_lock) = contexts.current() {
            let context = context_lock.read();
            info!("NAME {}", *context.name.read());
        }
    }

    // Try running kill(getpid(), signal), but fallback to exiting
    syscall::getpid()
        .and_then(|pid| syscall::kill(pid, signal).map(|_| ()))
        .unwrap_or_else(|_| {
            syscall::exit(signal & 0x7F);
        });
}