#include <pthread.h>
#include <semaphore.h>
#include <stdbool.h>
#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>

#define THINKING    0           /*philosopher is thinking*/
#define HUNGRY      1           /*philosopher is trying to get forks*/
#define EATING      2           /*philosopher is eating*/


typedef struct PhilosopherData {
    int eatingCount;
    int position;
    sem_t semaphore;
    int state;
    pthread_t thread;
} PhilosopherData;

bool AllPhilosophersFull(PhilosopherData PhilosopherList[], int numPhilosophers);
void Down(sem_t* semaphore);
void Eat(PhilosopherData* philosopherSelected);
int GetPhilosopherCount(char* argv);
void* Philosopher(void* philosopherPassed);
void PhilosopherInit(int philosopherTotal);
void PhilosopherListInit(PhilosopherData PhilosopherList[], int philosopherTotal);
void PutForks(PhilosopherData* philosopherSelected);
void TakeForks(PhilosopherData* philosopherSelected);
bool PhilosopherCanEat(PhilosopherData PhilosopherList[], int selectedPosition, int philosopherTotal);
void Think(PhilosopherData* philosopherSelected);
void Up(sem_t* semaphore);

int main(int argc, char* argv[]) 
{
    if (argc < 2)
        printf("Too few arguments, exiting...\n");
    if (argc > 2)
        printf("Too many arguments, exiting...\n");
    if (argc == 2)
    {
        int philosopherTotal;
        philosopherTotal = GetPhilosopherCount(argv[1]);
        PhilosopherInit(philosopherTotal);    
    }
    return 0;
}

//  Takes in array of times each philosopher has eaten
//  If all philosophers have ate twice, then returns true
//  Otherwise, if a philosopher has not eaten twice, returns false
bool AllPhilosophersFull(PhilosopherData PhilosopherList[], int numPhilosophers)
{
    for (int i = 0; i < numPhilosophers; i++)
        if (PhilosopherList[i].eatingCount < 2)
            return false;
    return true;
}

//  Philosopher enters critical section.
void Down(sem_t* semaphore)
{
    sem_wait(semaphore);
    printf("A semaphore was put into waiting...\n");
}

//  Sets philosopher to eating state and increments eating count.
void Eat(PhilosopherData* philosopherSelected)
{
    printf("Philosopher %d is eating...\n", philosopherSelected->position);
    philosopherSelected->state = EATING;
    ++philosopherSelected->eatingCount;
}

//  Converts char* to number.
int GetPhilosopherCount(char* argv)
{
    int philosopherTotal;
    sscanf(argv, "%d", &philosopherTotal);
    return philosopherTotal;
}

//  Main function that each thread runs.
void* Philosopher(void* philosopherPassed)
{
    PhilosopherData *philosopherSelected = (PhilosopherData*) philosopherPassed;
    while (true)
    {
        Think(philosopherSelected);                /*philosopher is thinking*/
        TakeForks(philosopherSelected);          /*acquire two forks or block*/
        Eat(philosopherSelected);                  /*yum-yum, spaghetti*/
        PutForks(philosopherSelected);           /*put both forks back on table*/
    }
}

//  Handles all philosopher threads, finishes when all philosophers are full.
void PhilosopherInit(int philosopherTotal)
{
    PhilosopherData PhilosopherList[philosopherTotal];
    PhilosopherListInit(PhilosopherList, philosopherTotal);
    while (!AllPhilosophersFull(PhilosopherList, philosopherTotal))
    {
        for (int i = 0; i < philosopherTotal; i++)
        {
            if (PhilosopherCanEat(PhilosopherList, i, philosopherTotal))
            {
                Up(&(PhilosopherList[i].semaphore));
            }
        }
    }
}

//  Initializes full list of philosophers.
void PhilosopherListInit(PhilosopherData PhilosopherList[], int philosopherTotal)
{
    for (int i = 0; i < philosopherTotal; i++)
    {
        PhilosopherList[i].position = i;
        PhilosopherList[i].eatingCount = 0;
        sem_init(&PhilosopherList[i].semaphore, 0, 1);
        pthread_create(&PhilosopherList[i].thread, NULL, &Philosopher, &PhilosopherList[i]);
        pthread_join(PhilosopherList[i].thread, NULL);
    }
}

//  Philosopher puts forks down.
void PutForks(PhilosopherData* philosopherSelected)
{
    printf("Philosopher %d is putting forks down...\n", philosopherSelected->position);
}

//  Philosopher takes the forks on the left and right.
void TakeForks(PhilosopherData* philosopherSelected)
{
    printf("Philosopher %d is taking forks...\n", philosopherSelected->position);
    Down(&philosopherSelected->semaphore);
}

//  If philosopher is hungry and forks are free, then returns true.
//  Else, philosopher returns false.
//  Left philosopher math: (i+N-1)%N    Right philosopher math: (i+1)%N
bool PhilosopherCanEat(PhilosopherData PhilosopherList[], int selectedPosition, int philosopherTotal)
{
    if (PhilosopherList[selectedPosition].state != HUNGRY)
        return false;
    int leftPhilosopher = (selectedPosition + (philosopherTotal-1)) % philosopherTotal;
    int rightPhilosopher = (selectedPosition + 1) % philosopherTotal;
    if (PhilosopherList[leftPhilosopher].state == EATING)
        return false;
    if (PhilosopherList[rightPhilosopher].state == EATING)
        return false;
    return true;
}

//  Philosopher begins thinking
void Think(PhilosopherData* philosopherSelected)
{
    philosopherSelected->state = THINKING;
    printf("Philosopher %d is thinking...\n", philosopherSelected->position);
}

//  Philosopher exits critical section
void Up(sem_t* semaphore)
{
    sem_post(semaphore);
    printf("A semaphore was released...\n");
}