/*
  Parallel Programming - 2026/2027

  Implementation of a termination detection algorithm (Dijkstra-Scholten)
*/

#include <mpi.h>
#include <pthread.h>
#include <stdio.h>
#include <stdbool.h>
#include <unistd.h>

#include "global.h"
#include "control.h"
#include "util.h"

// Tag for control messages. Distinct from basic algorithm's tags.
#define CONTROL_SIGNAL 99

// Type for control messages (empty payload, just a signal)
typedef struct {
    int dummy;
} control_message_t;

// Node operational states
typedef enum {
    ACTIVE_STATE,
    PASSIVE_STATE
} node_state_t;

// --- SHARED LOCAL STATE ---
// Must be protected by mutex because basic_thread and control_thread access it concurrently
static pthread_mutex_t state_mutex = PTHREAD_MUTEX_INITIALIZER;
static node_state_t    state       = PASSIVE_STATE;
static int             parent      = -1; // -1 indicates null/no parent
static int             deficit     = 0;  // C_i counter (unacknowledged messages)
static bool            initiator = false;

// --- HELPER FUNCTION ---
// MUST BE DECLARED ABOVE THE OTHER FUNCTIONS!
// Evaluates if the node can detach from the tree. Caller must hold state_mutex.
static void try_resolve_tree(int my_id)
{
    if (state == PASSIVE_STATE && deficit == 0)
    {
        if (initiator) {
            // Root is passive and deficit is 0 -> Global Termination!
            return; 
        }

        if (parent != -1)
        {
            control_message_t sig = {0};
            // Send acknowledgment signal up the tree to our parent
            MPI_Send(&sig, sizeof(control_message_t), MPI_BYTE, parent, 
                     CONTROL_SIGNAL, MPI_COMM_WORLD);
            
            trace("%d: [CONTROL] Sent tree-signal to parent %d\n", my_id, parent);
            parent = -1; // Detach from tree
        }
    }
}

/*
  Main loop of the termination detection algorithm.
*/
void *detect_termination(void *_args)
{
    thread_args_t *args = _args;
    int id = args->id;
    initiator = args->initiator;
    
    // (Removed unused 'processes' variable to fix compiler warning)

    while (true)
    {
        pthread_mutex_lock(&state_mutex);
        
        // CHECK GLOBAL TERMINATION CONDITION
        if (initiator && state == PASSIVE_STATE && deficit == 0)
        {
            trace("%d: [CONTROL] GLOBAL TERMINATION DETECTED!\n", id);
            pthread_mutex_unlock(&state_mutex);
            break; // Breaks loop, tells main() to shut down
        }
        
        pthread_mutex_unlock(&state_mutex);

        // Check network for incoming child signals (non-blocking)
        int flag = 0;
        MPI_Status status;
        MPI_Iprobe(MPI_ANY_SOURCE, CONTROL_SIGNAL, MPI_COMM_WORLD, &flag, &status);

        if (flag)
        {
            control_message_t sig;
            MPI_Recv(&sig, sizeof(control_message_t), MPI_BYTE, status.MPI_SOURCE, 
                     CONTROL_SIGNAL, MPI_COMM_WORLD, MPI_STATUS_IGNORE);

            pthread_mutex_lock(&state_mutex);
            deficit--; // Rule D: A child finished its work and reported back
            trace("%d: [CONTROL] Got signal from %d (New Deficit: %d)\n", 
                  id, status.MPI_SOURCE, deficit);
            
            try_resolve_tree(id);
            pthread_mutex_unlock(&state_mutex);
        }
        else
        {
            // Sleep briefly to prevent pinning the CPU core at 100% usage
            usleep(1000); 
        }
    }

    return NULL;
}

/*
  Called at startup of the basic algorithm in process ID.
*/
void control_basic_start_hook(int id)
{
    pthread_mutex_lock(&state_mutex);
    state   = initiator ? ACTIVE_STATE : PASSIVE_STATE;
    parent  = -1;
    deficit = 0;
    pthread_mutex_unlock(&state_mutex);
}

/*
  Called when the basic algorithm process ID becomes passive.
*/
void control_become_passive_hook(int id)
{
    pthread_mutex_lock(&state_mutex);
    state = PASSIVE_STATE;
    try_resolve_tree(id); // Check if we can leave the tree right now
    pthread_mutex_unlock(&state_mutex);
}

/*
  Called when the basic algorithm process ID becomes active.
*/
void control_become_active_hook(int id)
{
    pthread_mutex_lock(&state_mutex);
    state = ACTIVE_STATE;
    pthread_mutex_unlock(&state_mutex);
}

/*
  Called when the basic algorithm process ID sends a basic message to
  process PEER.
*/
void control_basic_send_hook(int id, int peer)
{
    pthread_mutex_lock(&state_mutex);
    deficit++; // Rule A: Sent unacknowledged work
    pthread_mutex_unlock(&state_mutex);
}

/*
  Called when the basic algorithm process ID receives a basic message
  from process PEER.
*/
void control_basic_receive_hook(int id, int peer)
{
    pthread_mutex_lock(&state_mutex);
    
    if (parent == -1)
    {
        // Rule B (Case 1): Woken up from passive state
        state  = ACTIVE_STATE;
        parent = peer; // Adopt sender as parent in the tree
        trace("%d: [CONTROL] Joined tree under parent %d\n", id, parent);
    }
    else
    {
        // Rule B (Case 2): Already active! Reject parent change, immediately signal back
        control_message_t sig = {0};
        MPI_Send(&sig, sizeof(control_message_t), MPI_BYTE, peer, 
                 CONTROL_SIGNAL, MPI_COMM_WORLD);
        trace("%d: [CONTROL] Rejected parent %d (Already Active)\n", id, peer);
    }
    
    pthread_mutex_unlock(&state_mutex);
}