#include <pthread.h>
#include <sys/time.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>
#include <stdio.h>
#include <unistd.h>
#include <stdatomic.h>

#include "stb_ds.h"
#include "cell.h"
#include "cell_internal.h"

#ifdef _WIN32
#include <windows.h>
#endif

typedef struct actor_node {
    cell_rt *actor;
    struct actor_node *next;
} actor_node;

typedef enum {
    TIMER_JS,
    TIMER_NATIVE_REMOVE
} timer_type;

typedef struct {
    uint64_t execute_at_ns;
    cell_rt *actor;
    uint32_t timer_id;
    timer_type type;
} timer_node;

static timer_node *timer_heap = NULL; 

// --- 3. The Global Engine State ---
static struct {
    pthread_mutex_t lock;       // Protects queue, shutdown flag, and timers
    pthread_cond_t  wake_cond;  // Wakes up workers
    pthread_cond_t  timer_cond; // Wakes up the timer thread
    pthread_cond_t  main_cond;  // Wakes up the main thread
    
    actor_node *head;           // Ready Queue Head
    actor_node *tail;           // Ready Queue Tail
    
    actor_node *main_head;      // Main Thread Queue Head
    actor_node *main_tail;      // Main Thread Queue Tail
    
    int shutting_down;          
    
    pthread_t *worker_threads;  
    int num_workers;
    pthread_t timer_thread;
} engine;

static pthread_mutex_t *actors_mutex;
static struct { char *key; cell_rt *value; } *actors = NULL;

#define lockless_shdel(NAME, KEY) pthread_mutex_lock(NAME##_mutex); shdel(NAME, KEY); pthread_mutex_unlock(NAME##_mutex);
#define lockless_shlen(NAME) ({ \
  pthread_mutex_lock(NAME##_mutex); \
  size_t _len = shlen(NAME); \
  pthread_mutex_unlock(NAME##_mutex); \
  _len; \
})
#define lockless_shgeti(NAME, KEY) ({ \
  pthread_mutex_lock(NAME##_mutex); \
  int _idx = shgeti(NAME, KEY); \
  pthread_mutex_unlock(NAME##_mutex); \
  _idx; \
})
#define lockless_shget(NAME, KEY) ({ \
  pthread_mutex_lock(NAME##_mutex); \
  cell_rt *_actor = shget(NAME, KEY); \
  pthread_mutex_unlock(NAME##_mutex); \
  _actor; \
})
#define lockless_shput_unique(NAME, KEY, VALUE) ({ \
  pthread_mutex_lock(NAME##_mutex); \
  int _exists = shgeti(NAME, KEY) != -1; \
  if (!_exists) shput(NAME, KEY, VALUE); \
  pthread_mutex_unlock(NAME##_mutex); \
  !_exists; \
})

// Forward declarations
uint32_t actor_remove_cb(cell_rt *actor, uint32_t id, uint32_t interval);
void actor_turn(cell_rt *actor);

void heap_push(uint64_t when, cell_rt *actor, uint32_t timer_id, timer_type type) {
    timer_node node = { .execute_at_ns = when, .actor = actor, .timer_id = timer_id, .type = type };
    arrput(timer_heap, node);
    
    // Bubble up
    int i = arrlen(timer_heap) - 1;
    while (i > 0) {
        int parent = (i - 1) / 2;
        if (timer_heap[i].execute_at_ns >= timer_heap[parent].execute_at_ns) break;
        
        timer_node tmp = timer_heap[i];
        timer_heap[i] = timer_heap[parent];
        timer_heap[parent] = tmp;
        i = parent;
    }
}

// Helper: Heap Pop
int heap_pop(timer_node *out) {
    if (arrlen(timer_heap) == 0) return 0;
    
    *out = timer_heap[0];
    timer_node last = arrpop(timer_heap);
    
    if (arrlen(timer_heap) > 0) {
        timer_heap[0] = last;
        // Bubble down
        int i = 0;
        int n = arrlen(timer_heap);
        while (1) {
            int left = 2 * i + 1;
            int right = 2 * i + 2;
            int smallest = i;
            
            if (left < n && timer_heap[left].execute_at_ns < timer_heap[smallest].execute_at_ns)
                smallest = left;
            if (right < n && timer_heap[right].execute_at_ns < timer_heap[smallest].execute_at_ns)
                smallest = right;
            
            if (smallest == i) break;
            
            timer_node tmp = timer_heap[i];
            timer_heap[i] = timer_heap[smallest];
            timer_heap[smallest] = tmp;
            i = smallest;
        }
    }
    return 1;
}

void *timer_thread_func(void *arg) {
  while (1) {
    pthread_mutex_lock(&engine.lock);
    
    if (engine.shutting_down) {
      pthread_mutex_unlock(&engine.lock);
      return NULL;
    }

    if (arrlen(timer_heap) == 0) {
      pthread_cond_wait(&engine.timer_cond, &engine.lock);
    } else {
      uint64_t now = cell_ns();
      if (timer_heap[0].execute_at_ns <= now) {
        // --- TIMER FIRED ---
        timer_node t;
        heap_pop(&t);
        pthread_mutex_unlock(&engine.lock);

        if (t.type == TIMER_NATIVE_REMOVE) {
          actor_remove_cb(t.actor, t.timer_id, 0);
        } else {
          pthread_mutex_lock(t.actor->msg_mutex); 
          int idx = hmgeti(t.actor->timers, t.timer_id);
          if (idx != -1) {
            JSValue cb = t.actor->timers[idx].value;
            hmdel(t.actor->timers, t.timer_id);
            actor_clock(t.actor, cb);
            JS_FreeValue(t.actor->context, cb);
          }
          pthread_mutex_unlock(t.actor->msg_mutex);
        }
        
        continue; 
      } else {
        // --- WAIT FOR DEADLINE ---
        struct timespec ts;
        uint64_t wait_ns = timer_heap[0].execute_at_ns - now;
        
        // Convert relative wait time to absolute CLOCK_REALTIME
        struct timespec now_real;
        clock_gettime(CLOCK_REALTIME, &now_real);
        
        uint64_t deadline_real_ns = (uint64_t)now_real.tv_sec * 1000000000ULL + 
                                     (uint64_t)now_real.tv_nsec + wait_ns;
        ts.tv_sec = deadline_real_ns / 1000000000ULL;
        ts.tv_nsec = deadline_real_ns % 1000000000ULL;
        
        pthread_cond_timedwait(&engine.timer_cond, &engine.lock, &ts);
      }
    }
    pthread_mutex_unlock(&engine.lock);
  }
  return NULL;
}

void *actor_runner(void *arg) {
    while (1) {
        pthread_mutex_lock(&engine.lock);
        
        // Wait while queue is empty AND not shutting down
        while (engine.head == NULL && !engine.shutting_down) {
            pthread_cond_wait(&engine.wake_cond, &engine.lock);
        }

        if (engine.shutting_down && engine.head == NULL) {
            pthread_mutex_unlock(&engine.lock);
            break; // Exit thread
        }

        // Pop from Linked List
        actor_node *node = engine.head;
        engine.head = node->next;
        if (engine.head == NULL) engine.tail = NULL;
        
        pthread_mutex_unlock(&engine.lock);

        if (node) {
            actor_turn(node->actor);
            free(node);
        }
    }
    return NULL;
}

void actor_initialize(void) {
    pthread_mutex_init(&engine.lock, NULL);
    pthread_cond_init(&engine.wake_cond, NULL);
    pthread_cond_init(&engine.timer_cond, NULL);
    pthread_cond_init(&engine.main_cond, NULL);
    
    engine.shutting_down = 0;
    engine.head = NULL;
    engine.tail = NULL;
    engine.main_head = NULL;
    engine.main_tail = NULL;
    
    actors_mutex = malloc(sizeof(pthread_mutex_t));
    pthread_mutex_init(actors_mutex, NULL);
    
    // Start Timer Thread
    pthread_create(&engine.timer_thread, NULL, timer_thread_func, NULL);

    // Start Workers
#ifdef _WIN32
    SYSTEM_INFO sysinfo;
    GetSystemInfo(&sysinfo);
    long n = sysinfo.dwNumberOfProcessors;
#else
    long n = sysconf(_SC_NPROCESSORS_ONLN);
#endif
    engine.num_workers = (int)n;
    engine.worker_threads = malloc(sizeof(pthread_t) * n);
    for (int i=0; i < n; i++) {
        pthread_create(&engine.worker_threads[i], NULL, actor_runner, NULL);
    }
}

void actor_free(cell_rt *actor)
{
  lockless_shdel(actors, actor->id);

  // Do not go forward with actor destruction until the actor is completely free
  pthread_mutex_lock(actor->msg_mutex);
  pthread_mutex_lock(actor->mutex);

  JSContext *js = actor->context;
  
  JS_FreeValue(js, actor->idx_buffer);
  JS_FreeValue(js, actor->message_handle);
  JS_FreeValue(js, actor->on_exception);
  JS_FreeValue(js, actor->unneeded);
  JS_FreeValue(js, actor->actor_sym);
  
  for (int i = 0; i < hmlen(actor->timers); i++) {
    JS_FreeValue(js, actor->timers[i].value);
  }
  
  hmfree(actor->timers);
  
  /* Free all letters in the queue */
  for (int i = 0; i < arrlen(actor->letters); i++) {
    if (actor->letters[i].type == LETTER_BLOB) {
      blob_destroy(actor->letters[i].blob_data);
    } else if (actor->letters[i].type == LETTER_CALLBACK) {
      JS_FreeValue(js, actor->letters[i].callback);
    }
  }
  
  arrfree(actor->letters);
  
  JSRuntime *rt = JS_GetRuntime(js);
  JS_SetInterruptHandler(rt, NULL, NULL);  
  JS_FreeContext(js);
  JS_FreeRuntime(rt);
  free(actor->id);
  
  pthread_mutex_unlock(actor->mutex);
  pthread_mutex_destroy(actor->mutex);
  free(actor->mutex);
  pthread_mutex_unlock(actor->msg_mutex);
  pthread_mutex_destroy(actor->msg_mutex);
  free(actor->msg_mutex);
  
  free(actor);

  int actor_count = lockless_shlen(actors);
  if (actor_count == 0) exit(0);
}

void exit_handler(void) {
    pthread_mutex_lock(&engine.lock);
    engine.shutting_down = 1;
    pthread_cond_broadcast(&engine.wake_cond);  
    pthread_cond_broadcast(&engine.timer_cond); 
    pthread_cond_broadcast(&engine.main_cond);
    pthread_mutex_unlock(&engine.lock);

    pthread_join(engine.timer_thread, NULL);

    for (int i=0; i < engine.num_workers; i++) {
        pthread_join(engine.worker_threads[i], NULL);
    }
    
    free(engine.worker_threads);
    pthread_mutex_destroy(&engine.lock);
    pthread_cond_destroy(&engine.wake_cond);
    pthread_cond_destroy(&engine.timer_cond);
    pthread_cond_destroy(&engine.main_cond);
    
    pthread_mutex_destroy(actors_mutex);
    free(actors_mutex);
    
    arrfree(timer_heap);
    
    exit(0);
}

int actor_exists(const char *id)
{
  int idx = lockless_shgeti(actors, id);
  return idx != -1;
}

void set_actor_state(cell_rt *actor)
{
  if (actor->disrupt) {
    actor_free(actor);
    return;
  }
  pthread_mutex_lock(actor->msg_mutex);
  
  switch(actor->state) {
    case ACTOR_RUNNING:
    case ACTOR_READY:
    if (actor->ar)
      actor->ar = 0;
    break;
      
    case ACTOR_IDLE:
      if (arrlen(actor->letters)) {
        actor->state = ACTOR_READY;
        actor->ar = 0;
        
        actor_node *n = malloc(sizeof(actor_node));
        n->actor = actor;
        n->next = NULL;

        pthread_mutex_lock(&engine.lock);
        if (actor->main_thread_only) {
            if (engine.main_tail) {
                engine.main_tail->next = n;
            } else {
                engine.main_head = n;
            }
            engine.main_tail = n;
            pthread_cond_signal(&engine.main_cond);
        } else {
            if (engine.tail) {
                engine.tail->next = n;
            } else {
                engine.head = n;
            }
            engine.tail = n;
            pthread_cond_signal(&engine.wake_cond);
        }
        pthread_mutex_unlock(&engine.lock);

      } else if (!arrlen(actor->letters) && !hmlen(actor->timers)) {
          // Schedule remove timer
          static uint32_t global_timer_id = 1;
          uint32_t id = global_timer_id++;
          actor->ar = id;
          
          uint64_t now = cell_ns();
          uint64_t execute_at = now + (uint64_t)(actor->ar_secs * 1e9);

          pthread_mutex_lock(&engine.lock);
          heap_push(execute_at, actor, id, TIMER_NATIVE_REMOVE);
          if (timer_heap[0].timer_id == id) {
              pthread_cond_signal(&engine.timer_cond);
          }
          pthread_mutex_unlock(&engine.lock);
      }
      break;
  }

  pthread_mutex_unlock(actor->msg_mutex);
}

uint32_t actor_remove_cb(cell_rt *actor, uint32_t id, uint32_t interval)
{
  pthread_mutex_lock(actor->mutex);
  // Check if this timer is still valid (match actor->ar)
  if (actor->ar != id && id != 0) { // id 0 means force (optional)
      pthread_mutex_unlock(actor->mutex);
      return 0;
  }
  
  actor->disrupt = 1;
  
  if (!JS_IsNull(actor->unneeded)) {
    JSValue ret = JS_Call(actor->context, actor->unneeded, JS_NULL, 0, NULL);
    uncaught_exception(actor->context, ret);
  }

  int should_free = (actor->state == ACTOR_IDLE);
  pthread_mutex_unlock(actor->mutex);
  
  if (should_free) actor_free(actor);
  return 0;
}

void actor_unneeded(cell_rt *actor, JSValue fn, double seconds)
{
  if (actor->disrupt) return;
  JS_FreeValue(actor->context, actor->unneeded);
  
  if (!JS_IsFunction(fn)) {
    actor->unneeded = JS_NULL;
    goto END;
  }
  
  actor->unneeded = JS_DupValue(actor->context, fn);
  actor->ar_secs = seconds;
  
  END:
  if (actor->ar)
    actor->ar = 0;
  set_actor_state(actor);
}

cell_rt *get_actor(char *id)
{
  int idx = lockless_shgeti(actors, id);
  if (idx == -1) {
    return NULL;
  }

  return lockless_shget(actors, id);
}

void actor_loop()
{
  while (!engine.shutting_down) { // Direct read safe enough here or use lock
    pthread_mutex_lock(&engine.lock);
    while (engine.main_head == NULL && !engine.shutting_down) {
      pthread_cond_wait(&engine.main_cond, &engine.lock);
    }
    
    if (engine.shutting_down && engine.main_head == NULL) {
        pthread_mutex_unlock(&engine.lock);
        break;
    }

    actor_node *node = engine.main_head;
    engine.main_head = node->next;
    if (engine.main_head == NULL) engine.main_tail = NULL;
    
    pthread_mutex_unlock(&engine.lock);

    if (node) {
        actor_turn(node->actor);
        free(node);
    }
  }
}

cell_rt *create_actor(void *wota)
{
  cell_rt *actor = calloc(sizeof(*actor), 1);
#ifdef HAVE_MIMALLOC
  actor->heap = mi_heap_new();
#endif
  actor->init_wota = wota;
  actor->idx_buffer = JS_NULL;
  actor->message_handle = JS_NULL;
  actor->unneeded = JS_NULL;
  actor->on_exception = JS_NULL;
  actor->actor_sym = JS_NULL;

  arrsetcap(actor->letters, 5);

  actor->mutex = malloc(sizeof(pthread_mutex_t));
  pthread_mutexattr_t attr;
  pthread_mutexattr_init(&attr);
  pthread_mutexattr_settype(&attr, PTHREAD_MUTEX_RECURSIVE);
  pthread_mutex_init(actor->mutex, &attr);
  actor->msg_mutex = malloc(sizeof(pthread_mutex_t));
  pthread_mutex_init(actor->msg_mutex, &attr); // msg_mutex can be recursive too to be safe
  pthread_mutexattr_destroy(&attr);
  
  /* Lock actor->mutex while initializing JS runtime. */
  pthread_mutex_lock(actor->mutex);
  script_startup(actor);
  set_actor_state(actor);
  pthread_mutex_unlock(actor->mutex);  

  return actor;
}

const char *register_actor(const char *id, cell_rt *actor, int mainthread, double ar)
{
  actor->main_thread_only = mainthread;
  actor->id = strdup(id);
  actor->ar_secs = ar;
  int added = lockless_shput_unique(actors, id, actor);
  if (!added) {
    free(actor->id);
    return "Actor with given ID already exists.";
  }
  return NULL;
}

int actor_interrupt_cb(JSRuntime *rt, cell_rt *crt)
{
  return engine.shutting_down || crt->disrupt;
}

const char *send_message(const char *id, void *msg)
{
  cell_rt *target = get_actor(id);
  if (!target) {
    blob_destroy((blob *)msg);
    return "Could not get actor from id.";
  }
  
  letter l;
  l.type = LETTER_BLOB;
  l.blob_data = (blob *)msg;
  
  pthread_mutex_lock(target->msg_mutex);
  arrput(target->letters, l);
  pthread_mutex_unlock(target->msg_mutex);

  if (target->ar)
    target->ar = 0;
  
  set_actor_state(target);
  
  return NULL;
}

void actor_turn(cell_rt *actor)
{
  pthread_mutex_lock(actor->mutex);

  actor->state = ACTOR_RUNNING;

  if (actor->trace_hook)
    actor->trace_hook(actor->name, CELL_HOOK_ENTER);

  TAKETURN:

  pthread_mutex_lock(actor->msg_mutex);
  JSValue result;
  if (!arrlen(actor->letters)) {
    pthread_mutex_unlock(actor->msg_mutex);
    goto ENDTURN;
  }
  letter l = actor->letters[0];
  arrdel(actor->letters, 0); // O(N) but we kept array as requested
  pthread_mutex_unlock(actor->msg_mutex);
  
  if (l.type == LETTER_BLOB) { 
    // Create a JS blob from the C blob
    size_t size = blob_length(l.blob_data) / 8; // Convert bits to bytes
    JSValue arg = js_new_blob_stoned_copy(actor->context, (void*)blob_data(l.blob_data), size);
    blob_destroy(l.blob_data);
    result = JS_Call(actor->context, actor->message_handle, JS_NULL, 1, &arg);
    uncaught_exception(actor->context, result);
    JS_FreeValue(actor->context, arg);
  } else if (l.type == LETTER_CALLBACK) {
    result = JS_Call(actor->context, l.callback, JS_NULL, 0, NULL);
    uncaught_exception(actor->context, result);
    JS_FreeValue(actor->context, l.callback);
  }
  
  if (actor->disrupt) goto ENDTURN;

  ENDTURN:
  actor->state = ACTOR_IDLE;

  if (actor->trace_hook)
    actor->trace_hook(actor->name, CELL_HOOK_EXIT);
  
  set_actor_state(actor);
  
  pthread_mutex_unlock(actor->mutex);
}

void actor_clock(cell_rt *actor, JSValue fn)
{
  letter l;
  l.type = LETTER_CALLBACK;
  l.callback = JS_DupValue(actor->context, fn);
  pthread_mutex_lock(actor->msg_mutex);
  arrput(actor->letters, l);
  pthread_mutex_unlock(actor->msg_mutex);
  set_actor_state(actor);
}

uint32_t actor_delay(cell_rt *actor, JSValue fn, double seconds)
{
  pthread_mutex_lock(actor->msg_mutex); 
  
  static uint32_t global_timer_id = 1;
  uint32_t id = global_timer_id++;
  
  JSValue cb = JS_DupValue(actor->context, fn);
  hmput(actor->timers, id, cb);
  
  uint64_t now = cell_ns();
  uint64_t execute_at = now + (uint64_t)(seconds * 1e9);

  pthread_mutex_lock(&engine.lock);
  heap_push(execute_at, actor, id, TIMER_JS);
  if (timer_heap[0].timer_id == id) {
      pthread_cond_signal(&engine.timer_cond);
  }
  pthread_mutex_unlock(&engine.lock);

  pthread_mutex_unlock(actor->msg_mutex);
  return id;
}

JSValue actor_remove_timer(cell_rt *actor, uint32_t timer_id)
{
  JSValue cb = JS_NULL;
  pthread_mutex_lock(actor->msg_mutex);
  int id = hmgeti(actor->timers, timer_id);
  if (id != -1) {
    cb = actor->timers[id].value;
    hmdel(actor->timers, timer_id);
  }
  pthread_mutex_unlock(actor->msg_mutex);
  // Note: We don't remove from heap, it will misfire safely
  return cb;
}