/* 
 * Copyright 2010 Stefan Lankes, Chair for Operating Systems,
 *                               RWTH Aachen University
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 *
 * This file is part of MetalSVM. 
 */

#include <metalsvm/stdio.h>
#include <metalsvm/stdlib.h>
#include <metalsvm/string.h>
#include <metalsvm/mmu.h>
#include <metalsvm/tasks.h>
#include <metalsvm/processor.h>
#include <metalsvm/spinlocks.h>

task_t* current_task = NULL;
static task_t task_table[MAX_TASKS];
static spinlock_t table_lock = SPINLOCK_INIT;

int multitasking_init(void) {
	memset(task_table, 0, sizeof(task_t)*MAX_TASKS);
	task_table[0].id = 0;
	task_table[0].mm.usage = 0;
	task_table[0].stack = NULL;
	task_table[0].stack_size = 8192;
	task_table[0].status = TASK_RUNNING;
	current_task = task_table;
	return 0;
}

static void wakeup_blocked_tasks(void* result)
{
	unsigned int i;

	spinlock_lock_irqsave(&table_lock);

	/* wake up blocked tasks */
	for(i=0; i<MAX_TASKS; i++) {
		if (current_task->blocked_tasks[i] && (task_table[i].status == TASK_BLOCKED)) {
			task_table[i].return_value = result;
			task_table[i].status = TASK_READY;
		}
		current_task->blocked_tasks[i] = 0;
	}

	spinlock_unlock_irqsave(&table_lock);
}

void NORETURN leave_task(void) {
	void* result = NULL;

	get_return_value(result);

	kprintf("Terminate task: %u, return value = %p\n", current_task->id, result);	

	wakeup_blocked_tasks(result);
	current_task->status = TASK_FINISHED;
	schedule();

	kputs("Kernel panic: scheduler found no valid task\n");
	while(1) {
		NOP8;
	}
}

void NORETURN abort(void) {
	void* result = (void*) -1;

	kprintf("Abort task: %u\n", current_task->id);

	wakeup_blocked_tasks(result);
	current_task->status = TASK_FINISHED;
	schedule();

	kputs("Kernel panic: scheduler found no valid task\n");
	while(1) {
		NOP8;
	}
}

int create_kernel_task(tid_t* id, entry_point_t ep, void* arg, size_t stack_size)
{
	int ret = -1;
	unsigned int i;

	if (BUILTIN_EXPECT(!ep, 0))
		return -1;

	if (!stack_size)
		stack_size = DEFAULT_STACK_SIZE;

	spinlock_lock_irqsave(&table_lock);

	for(i=0; i<MAX_TASKS; i++) {
		if (task_table[i].status == TASK_INVALID) {
			if (task_table[i].stack)
				kfree(task_table[i].stack, task_table[i].stack_size);
			if (task_table[i].mm.usage) {
				kprintf("Task %d has a memory leax (%d byte)\n", task_table[i].id, task_table[i].mm.usage);
				task_table[i].mm.usage = 0;
			}
			task_table[i].stack = create_stack(task_table+i, stack_size);
			if (!task_table[i].stack)
				break;
			task_table[i].stack_size = stack_size;
			task_table[i].top = task_table[i].stack + stack_size - sizeof(size_t);
			task_table[i].ip = 0;
			task_table[i].id = i;
			memset(task_table[i].blocked_tasks, 0x00, sizeof(unsigned char)*MAX_TASKS);
			task_table[i].return_value = NULL;
			task_table[i].status = TASK_READY;
		
			if (id)
				*id = i;	

			ret = create_default_frame(task_table+i, ep, arg);
			break;
		}
	}

	spinlock_unlock_irqsave(&table_lock);

	return ret;
}

int join_kernel_task(tid_t id, void** result) 
{
	spinlock_lock_irqsave(&table_lock);

	/* 
	 * idle tasks are not allowed to wait for another task 
	 * they should always run...
	 */
	if (BUILTIN_EXPECT(current_task->status == TASK_IDLE, 0))
		goto join_out;

	/* a task is not able to wait for itself */
	if (BUILTIN_EXPECT(current_task->id == id, 0))
		goto join_out;

	/* invalid id */
	if (BUILTIN_EXPECT(id >= MAX_TASKS, 0))
		goto join_out;

	/* task already finished */
	if (BUILTIN_EXPECT(task_table[id].status == TASK_INVALID, 0))
		goto join_out;

	/* task already finished */
	if (BUILTIN_EXPECT(task_table[id].status == TASK_FINISHED, 0))
                goto join_out;

	task_table[id].blocked_tasks[current_task->id] = 1;
	current_task->status = TASK_BLOCKED;

	spinlock_unlock_irqsave(&table_lock);
	schedule();

	if (result) {
		*result = current_task->return_value;
		current_task->return_value = NULL;
	}

	return 0;

join_out: 
	spinlock_unlock_irqsave(&table_lock);
	return -1;
}

int wakeup_task(tid_t id)
{
	int ret = -1;

	spinlock_lock_irqsave(&table_lock);

	if (task_table[id].status != TASK_BLOCKED) {
		kprintf("Task %u is already unblocked\n", id);
		goto wakeup_out;
	}

	task_table[id].status = TASK_READY;
	ret = 0;

wakeup_out:
	spinlock_unlock_irqsave(&table_lock);
	return ret;
}

task_t* get_new_task(void) 
{
	task_t* ret;
	unsigned int i, new_id;

	spinlock_lock(&table_lock);

	/* signalize that this task could be reuse */
	if (current_task->status == TASK_FINISHED)
		current_task->status = TASK_INVALID; 

	for(i=1; i <= MAX_TASKS; i++) {
		new_id  = (current_task->id + i) % MAX_TASKS;

		if (task_table[new_id].status == TASK_READY) {
			if (current_task->status == TASK_RUNNING)
				current_task->status = TASK_READY;
			task_table[new_id].status = TASK_RUNNING;
	
			ret = task_table+new_id;
			goto get_task_out;
		}
	}

	if (current_task->status == TASK_RUNNING) {
		ret = current_task;
		goto get_task_out;
	 }

	/* 
	 * we switch to the idle task (id=0), if the current task terminates 
	 * and no other is ready
	 */
	ret = task_table+0;

get_task_out:
	spinlock_unlock(&table_lock);
	return ret;
}