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// Copyright (c) 2019 Stefan Lankes, RWTH Aachen University
//
// Licensed under the Apache License, Version 2.0, <LICENSE-APACHE or
// http://apache.org/licenses/LICENSE-2.0> or the MIT license <LICENSE-MIT or
// http://opensource.org/licenses/MIT>, at your option. This file may not be
// copied, modified, or distributed except according to those terms.

// The implementation is inspired by Andrew D. Birrell's paper
// "Implementing Condition Variables with Semaphores"

use alloc::boxed::Box;
use core::mem;
use core::sync::atomic::{AtomicIsize, Ordering};
use synch::semaphore::Semaphore;

struct CondQueue {
	counter: AtomicIsize,
	sem1: Semaphore,
	sem2: Semaphore,
}

impl CondQueue {
	pub fn new() -> Self {
		CondQueue {
			counter: AtomicIsize::new(0),
			sem1: Semaphore::new(0),
			sem2: Semaphore::new(0),
		}
	}
}

unsafe fn __sys_destroy_queue(ptr: usize) -> i32 {
	let id = ptr as *mut usize;
	if id.is_null() {
		debug!("sys_wait: ivalid address to condition variable");
		return -1;
	}

	if *id != 0 {
		let cond = Box::from_raw((*id) as *mut CondQueue);
		mem::drop(cond);
	}

	0
}

#[no_mangle]
pub unsafe fn sys_destroy_queue(ptr: usize) -> i32 {
	kernel_function!(__sys_destroy_queue(ptr))
}

unsafe fn __sys_notify(ptr: usize, count: i32) -> i32 {
	let id = ptr as *const usize;

	if id.is_null() {
		// invalid argument
		debug!("sys_notify: invalid address to condition variable");
		return -1;
	}

	if *id == 0 {
		debug!("sys_notify: invalid reference to condition variable");
		return -1;
	}

	let cond = &mut *((*id) as *mut CondQueue);

	if count < 0 {
		// Wake up all task that has been waiting for this condition variable
		while cond.counter.load(Ordering::SeqCst) > 0 {
			cond.counter.fetch_sub(1, Ordering::SeqCst);
			cond.sem1.release();
			cond.sem2.acquire(None);
		}
	} else {
		for _ in 0..count {
			cond.counter.fetch_sub(1, Ordering::SeqCst);
			cond.sem1.release();
			cond.sem2.acquire(None);
		}
	}

	0
}

#[no_mangle]
pub unsafe fn sys_notify(ptr: usize, count: i32) -> i32 {
	kernel_function!(__sys_notify(ptr, count))
}

unsafe fn __sys_init_queue(ptr: usize) -> i32 {
	let id = ptr as *mut usize;
	if id.is_null() {
		debug!("sys_init_queue: ivalid address to condition variable");
		return -1;
	}

	if *id == 0 {
		debug!("Create condition variable queue");
		let queue = Box::new(CondQueue::new());
		*id = Box::into_raw(queue) as usize;
	}

	0
}

#[no_mangle]
pub unsafe fn sys_init_queue(ptr: usize) -> i32 {
	kernel_function!(__sys_init_queue(ptr))
}

unsafe fn __sys_add_queue(ptr: usize, timeout_ns: i64) -> i32 {
	let id = ptr as *mut usize;
	if id.is_null() {
		debug!("sys_add_queue: invalid address to condition variable");
		return -1;
	}

	if *id == 0 {
		debug!("Create condition variable queue");
		let queue = Box::new(CondQueue::new());
		*id = Box::into_raw(queue) as usize;
	}

	if timeout_ns <= 0 {
		let cond = &mut *((*id) as *mut CondQueue);
		cond.counter.fetch_add(1, Ordering::SeqCst);

		0
	} else {
		error!("Conditional variables with timeout is currently not supported");

		-1
	}
}

#[no_mangle]
pub unsafe fn sys_add_queue(ptr: usize, timeout_ns: i64) -> i32 {
	kernel_function!(__sys_add_queue(ptr, timeout_ns))
}

unsafe fn __sys_wait(ptr: usize) -> i32 {
	let id = ptr as *mut usize;
	if id.is_null() {
		debug!("sys_wait: invalid address to condition variable");
		return -1;
	}

	if *id == 0 {
		error!("sys_wait: Unable to determine condition variable");
		return -1;
	}

	let cond = &mut *((*id) as *mut CondQueue);
	cond.sem1.acquire(None);
	cond.sem2.release();

	0
}

#[no_mangle]
pub unsafe fn sys_wait(ptr: usize) -> i32 {
	kernel_function!(__sys_wait(ptr))
}