//----------------------------------------------------------------------------//
//                           GNU GPL OS/K                                     //
//                                                                            //
//  Desc:       Process scheduler                                             //
//                                                                            //
//                                                                            //
//  Copyright © 2018-2019 The OS/K Team                                       //
//                                                                            //
//  This file is part of OS/K.                                                //
//                                                                            //
//  OS/K is free software: you can redistribute it and/or modify              //
//  it under the terms of the GNU General Public License as published by      //
//  the Free Software Foundation, either version 3 of the License, or         //
//  any later version.                                                        //
//                                                                            //
//  OS/K is distributed in the hope that it will be useful,                   //
//  but WITHOUT ANY WARRANTY//without even the implied warranty of            //
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the             //
//  GNU General Public License for more details.                              //
//                                                                            //
//  You should have received a copy of the GNU General Public License         //
//  along with OS/K.  If not, see <https://www.gnu.org/licenses/>.            //
//----------------------------------------------------------------------------//

#include <extras/list.h>
#include <kernel/proc.h>
#include <kernel/sched.h>

#ifndef _KALEID_KERNEL

#include <stdio.h>

//
// For test purpose only
//
int       procslen = 10;
Process_t procs[] = {
    { 0, 0, 0, 12, 12, STATE_RUNNABLE, DEF_PROC_TSLICE, DEF_PROC_TSLICE, NULL, NULL, NULL   },
    { 1, 2, 2, 16, 16, STATE_RUNNABLE, DEF_PROC_TSLICE, DEF_PROC_TSLICE, NULL, NULL, NULL   },
    { 2, 3, 3, 31, 31, STATE_RUNNABLE, DEF_PROC_TSLICE, DEF_PROC_TSLICE, NULL, NULL, NULL   },
    { 3, 2, 2, 1,  1,  STATE_RUNNABLE, DEF_PROC_TSLICE, DEF_PROC_TSLICE, NULL, NULL, NULL   },
    { 4, 3, 3, 5,  5,  STATE_RUNNABLE, DEF_PROC_TSLICE, DEF_PROC_TSLICE, NULL, NULL, NULL   },
    { 5, 0, 0, 30, 30, STATE_RUNNABLE, DEF_PROC_TSLICE, DEF_PROC_TSLICE, NULL, NULL, NULL   },
    { 6, 1, 1, 19, 19, STATE_RUNNABLE, DEF_PROC_TSLICE, DEF_PROC_TSLICE, NULL, NULL, NULL   },
    { 7, 1, 1, 0,  0,  STATE_RUNNABLE, DEF_PROC_TSLICE, DEF_PROC_TSLICE, NULL, NULL, NULL   },
    { 8, 3, 3, 12, 12, STATE_RUNNABLE, DEF_PROC_TSLICE, DEF_PROC_TSLICE, NULL, NULL, NULL   },
    { 9, 2, 2, 21, 21, STATE_RUNNABLE, DEF_PROC_TSLICE, DEF_PROC_TSLICE, NULL, NULL, NULL   },
};

#endif

//
// Set current process
// TODO Select thread, context switch
//
static void SetCurProc(Process_t *proc)
{
    _SetCurProc(proc);
    if (GetCurProc() != NULL) {
        GetCurProc()->procState = STATE_RUNNING;
    }
}

//
// (Un)Lock priority class list heads
//

static inline
void SchedLock(void) {
#ifdef _KALEID_KERNEL
    DisableIRQs();
#endif
}

static inline
void SchedUnlock(void) {
#ifdef _KALEID_KERNEL
    EnableIRQs();
#endif
}

//
// The four priority classes of OS/2
//
CREATE_PER_CPU(TimeCritProcs, ListHead_t *);
CREATE_PER_CPU(ServPrioProcs, ListHead_t *);
CREATE_PER_CPU(ReglPrioProcs, ListHead_t *);
CREATE_PER_CPU(IdlePrioProcs, ListHead_t *);

const char *PrioClassesNames[] = {
    "Time-critical class",
    "Server priority class",
    "Regular priority class",
    "Idle priority class",
};

//
// Get priority class list head
//
static ListHead_t *GetPrioClassHead(int prioClass)
{
    switch (prioClass) {
        case TIME_CRIT_PROC: return GetTimeCritProcs();
        case SERV_PRIO_PROC: return GetServPrioProcs();
        case REGL_PRIO_PROC: return GetReglPrioProcs();
        case IDLE_PRIO_PROC: return GetIdlePrioProcs();
        default: KalAssert(FALSE && "Unknown priority class");
    }

    return NULL;
}

//
// Determine which process is going to run first
// Return NULL for "equal" processes
//
static Process_t *CompareProcs(Process_t *proc1, Process_t *proc2)
{
    KalAssert(proc1 && proc2);

    if (proc1->prioClass < proc2->prioClass) return proc1;
    if (proc1->prioClass > proc2->prioClass) return proc2;

    if (proc1->prioLevel > proc2->prioLevel) return proc1;
    if (proc1->prioLevel < proc2->prioLevel) return proc2;

    return NULL; // same class and level
}

//
// Add process to schedule lists (unlocked)
//
static void SchedThisProcUnlocked(Process_t *proc)
{
    KalAssert(proc && proc->procState == STATE_RUNNABLE && !proc->schedNode);

    bool found = false;
    ListNode_t *iterNode = NULL;
    ListNode_t *procNode = CreateNode(proc);
    ListHead_t *head = GetPrioClassHead(proc->prioClass);

    KalAssert(procNode && head);

    proc->schedNode = procNode;

    // Find a process with lesser priority
    for (iterNode = head->first; iterNode; iterNode = iterNode->next) {
        if (proc->prioLevel > GetNodeData(iterNode, Process_t *)->prioLevel) {
            // Detect double insertions
            KalAssert(proc->pid != GetNodeData(iterNode, Process_t *)->pid);

            // Add process to schedule
            AddNodeBefore(head, iterNode, procNode);
            found = true;
            break;
        }
    }

    // Didn't find any process with lesser priority
    if (found == false) {
        AppendNode(head, procNode);
    }
}

//
// Add process to schedule lists
//
void SchedThisProc(Process_t *proc)
{
    SchedLock();

    SchedThisProcUnlocked(proc);

    SchedUnlock();
}

//
// Selects process to schedule next
//
// WARNING
//      Does not call SchedLock()/SchedUnlock()
//
static Process_t *SelectSchedNext(void)
{
    if (GetTimeCritProcs()->length > 0) return GetNodeData(GetTimeCritProcs()->first, Process_t *);
    if (GetServPrioProcs()->length > 0) return GetNodeData(GetServPrioProcs()->first, Process_t *);
    if (GetReglPrioProcs()->length > 0) return GetNodeData(GetReglPrioProcs()->first, Process_t *);
    if (GetIdlePrioProcs()->length > 0) return GetNodeData(GetIdlePrioProcs()->first, Process_t *);

    return NULL;
}

//
// Remove running process from schedule lists
// and schedule next runnable process
//
void BlockCurProc(void)
{
    KalAssert(GetCurProc() && GetCurProc()->procState == STATE_RUNNING);

    ListNode_t *procNode = GetCurProc()->schedNode;

    KalAssert(procNode && "Blocking non-scheduled process");

    GetCurProc()->procState = STATE_BLOCKED;
    RemoveNode(procNode->head, procNode);

    GetCurProc()->schedNode = NULL;
    SetCurProc(SelectSchedNext());
}

static void ReSchedCurProc(void)
{
    KalAssert(GetCurProc() && GetCurProc()->procState == STATE_RUNNING);
    KalAssert(GetCurProc()->schedNode);

    // Restore default attributes, cancelling boosts
    GetCurProc()->prioClass = GetCurProc()->defPrioClass;
    GetCurProc()->prioLevel = GetCurProc()->defPrioLevel;
    GetCurProc()->timeSlice = GetCurProc()->defTimeSlice;
    GetCurProc()->procState = STATE_RUNNABLE;

    // Remove from list
    RemoveNode(GetCurProc()->schedNode->head, GetCurProc()->schedNode);
    GetCurProc()->schedNode = NULL;

    // Schedule again, with default attributes now
    SchedThisProcUnlocked(GetCurProc());
}

//
// Should we schedule another process?
// Called at each tick
//
void SchedOnTick(void)
{
    SchedLock();

    Process_t *procNext, *winner, *previous = GetCurProc();

    // We're either idle or running something
    KalAssert(GetCurProc() == NULL || GetCurProc()->procState == STATE_RUNNING);

    // Have the current process spent its timeslice?
    // (To be handled in CPU decisions function)
    if (GetCurProc() != NULL) {
        if (GetCurProc()->timeSlice <= 1) {
            // Re-schedule
            ReSchedCurProc();

            // See next 'if' statement
            _SetCurProc(NULL);
        }

        // Otherwise, make it lose a tick
        else {
            GetCurProc()->timeSlice--;
        }
    }

    // Are we idle, or scheduling next process?
    if (GetCurProc() == NULL) {
        SetCurProc(SelectSchedNext());
        goto leave;
    }

    // Is preemption on and a re-schedule is needed?
    if (GetPreemptCount() == PREEMPT_ON && GetReSchedFlag()) {

        // Is there a higher priority process that is runnable?
        procNext = SelectSchedNext();
        winner = CompareProcs(GetCurProc(), procNext);

        // Yes, procNext should preempt current process
        if (winner == procNext) {
            // Re-schedule
            ReSchedCurProc();

            // Switch to procNext
            SetCurProc(procNext);
        }
    }

    // Current process won't be preempted and has time remaining
leave:
    SchedUnlock();

    if (GetCurProc() != NULL && GetCurProc() != previous) {
        // XXX context switch
    }
}

//
// Initialize scheduler
//
void InitSched(void)
{
    int pid;

    SchedLock();

    _SetTimeCritProcs(CreateListHead());
    _SetServPrioProcs(CreateListHead());
    _SetReglPrioProcs(CreateListHead());
    _SetIdlePrioProcs(CreateListHead());

#ifndef _KALEID_KERNEL
    for (pid = 0; pid < procslen; pid++) {
        if (procs[pid].procState == STATE_RUNNABLE) {
            SchedThisProcUnlocked(&procs[pid]);
        }
    }
#endif

    SchedUnlock();
}

//
// Shutdown scheduler
//
void FiniSched(void)
{
    KalAssert(GetIdlePrioProcs() && GetReglPrioProcs() && GetServPrioProcs() && GetTimeCritProcs());

    SchedLock();

    while (GetIdlePrioProcs()->length > 0) RemoveNode(GetIdlePrioProcs(), GetIdlePrioProcs()->first);
    while (GetReglPrioProcs()->length > 0) RemoveNode(GetReglPrioProcs(), GetReglPrioProcs()->first);
    while (GetServPrioProcs()->length > 0) RemoveNode(GetServPrioProcs(), GetServPrioProcs()->first);
    while (GetTimeCritProcs()->length > 0) RemoveNode(GetTimeCritProcs(), GetTimeCritProcs()->first);

    DestroyListHead(GetIdlePrioProcs()); _SetIdlePrioProcs(NULL);
    DestroyListHead(GetReglPrioProcs()); _SetReglPrioProcs(NULL);
    DestroyListHead(GetServPrioProcs()); _SetServPrioProcs(NULL);
    DestroyListHead(GetTimeCritProcs()); _SetTimeCritProcs(NULL);

    SchedUnlock();
}

#ifndef _KALEID_KERNEL

#define PrintProc(proc) printf("{ %d, '%s', %d , %lu}\n", (proc)->pid, \
                                 PrioClassesNames[(proc)->prioClass], (proc)->prioLevel, (proc)->timeSlice);

//
// Print out process list
//
void PrintList(ListHead_t *head)
{
    KalAssert(head);

    Process_t *proc;
    ListNode_t *node = head->first;

    printf("len: %lu\n", head->length);

    while (node) {
        proc = GetNodeData(node, Process_t *);

        PrintProc(proc);

        node = node->next;
    }

    puts("");
}

int main(void)
{
    InitSched();

    puts("---------------");

    puts("Time Critical:");
    PrintList(GetTimeCritProcs());

    puts("Server:");
    PrintList(GetServPrioProcs());

    puts("Regular:");
    PrintList(GetReglPrioProcs());

    puts("Idle:");
    PrintList(GetIdlePrioProcs());

    puts("---------------");

    getchar();

    int tick = 0;

    while (tick < 120) {
        if (tick > 0 && tick != 50 && tick % 10 == 0) {
            puts("Blocking current process");
            BlockCurProc();
        }

        if (tick == 50) {
            procs[0].procState = STATE_RUNNABLE;
            SchedThisProc(&procs[0]);
        }

        printf("Tick %d - Running: ", tick);

        if (GetCurProc() == NULL) {
            puts("IDLE");
        }

        else {
            PrintProc(GetCurProc());
        }

        SchedOnTick();

        if (tick == 50) // already done
            puts("Re-scheduling process 0");

        tick++;
    }

    FiniSched();

    return 0;
}

#endif