#include <stdlib.h>
#include <string.h>

#include "ant.h"
#include "ptr.h"
#include "errors.h"
#include "internal.h"
#include "runtime.h"
#include "sugar.h"

#include "gc/roots.h"
#include "silver/engine.h"
#include "modules/generator.h"
#include "modules/iterator.h"
#include "modules/symbol.h"

enum { GENERATOR_NATIVE_TAG = 0x47454e52u }; // GENR

typedef enum {
  GEN_SUSPENDED_START = 0,
  GEN_SUSPENDED_YIELD = 1,
  GEN_EXECUTING       = 2,
  GEN_COMPLETED       = 3,
} generator_state_t;

typedef struct generator_request {
  sv_resume_kind_t kind;
  ant_value_t value;
  ant_value_t promise;
  struct generator_request *next;
} generator_request_t;

typedef struct generator_data {
  coroutine_t *coro;
  generator_state_t state;
  generator_request_t *queue_head;
  generator_request_t *queue_tail;
  bool is_async;
} generator_data_t;

static ant_value_t generator_resume_kind(
  ant_t *js, ant_value_t gen, 
  ant_value_t resume_value, sv_resume_kind_t resume_kind
);

static ant_value_t generator_result(ant_t *js, bool done, ant_value_t value) {
  ant_value_t result = js_newobj(js);
  js_set(js, result, "value", value);
  js_set(js, result, "done", js_bool(done));
  return result;
}

static generator_data_t *generator_data(ant_value_t gen) {
  if (!js_check_native_tag(gen, GENERATOR_NATIVE_TAG)) return NULL;
  return (generator_data_t *)js_get_native_ptr(gen);
}

static generator_state_t generator_state(ant_value_t gen) {
  generator_data_t *data = generator_data(gen);
  return data ? data->state : GEN_COMPLETED;
}

static void generator_set_state(ant_value_t gen, generator_state_t state) {
  generator_data_t *data = generator_data(gen);
  if (data) data->state = state;
}

static bool generator_is_async(ant_value_t gen) {
  generator_data_t *data = generator_data(gen);
  return data && data->is_async;
}

static ant_value_t generator_async_wrap_result(ant_t *js, ant_value_t result) {
  ant_value_t promise = js_mkpromise(js);
  if (is_err(promise)) return promise;

  if (is_err(result)) {
    ant_value_t reject_value = js->thrown_exists ? js->thrown_value : result;
    js->thrown_exists = false;
    js->thrown_value = js_mkundef();
    js_reject_promise(js, promise, reject_value);
  } else js_resolve_promise(js, promise, result);

  return promise;
}

static generator_request_t *generator_dequeue_request(generator_data_t *data) {
  if (!data || !data->queue_head) return NULL;
  generator_request_t *req = data->queue_head;
  data->queue_head = req->next;
  if (!data->queue_head) data->queue_tail = NULL;
  req->next = NULL;
  return req;
}

static void generator_free_queue(generator_data_t *data) {
  if (!data) return;
  generator_request_t *req = data->queue_head;
  
  while (req) {
    generator_request_t *next = req->next;
    free(req);
    req = next;
  }
  
  data->queue_head = NULL;
  data->queue_tail = NULL;
}

static ant_value_t generator_enqueue_request(
  ant_t *js, ant_value_t gen, sv_resume_kind_t kind, ant_value_t value
) {
  generator_data_t *data = generator_data(gen);
  if (!data || !data->is_async) return js_mkerr_typed(js, JS_ERR_TYPE, "Generator is already executing");

  ant_value_t promise = js_mkpromise(js);
  if (is_err(promise)) return promise;

  generator_request_t *req = (generator_request_t *)calloc(1, sizeof(*req));
  if (!req) return js_mkerr(js, "out of memory for generator request");

  *req = (generator_request_t){
    .kind = kind,
    .value = value,
    .promise = promise,
    .next = NULL,
  };

  if (data->queue_tail) data->queue_tail->next = req;
  else data->queue_head = req;
  data->queue_tail = req;
  
  return promise;
}

static void generator_settle_request_promise(ant_t *js, ant_value_t promise, ant_value_t result) {
  if (is_err(result)) {
    ant_value_t reject_value = js->thrown_exists ? js->thrown_value : result;
    js->thrown_exists = false;
    js->thrown_value = js_mkundef();
    js_reject_promise(js, promise, reject_value);
  } else js_resolve_promise(js, promise, result);
}

static void generator_process_queue(ant_t *js, ant_value_t gen) {
  generator_data_t *data = generator_data(gen);
  if (!data || !data->is_async) return;

  GC_ROOT_SAVE(root_mark, js);
  GC_ROOT_PIN(js, gen);

  while (data->state != GEN_EXECUTING && data->queue_head) {
    generator_request_t *req = generator_dequeue_request(data);
    if (!req) break;
    
    GC_ROOT_PIN(js, req->value);
    GC_ROOT_PIN(js, req->promise);
    
    coroutine_t *coro = data->coro;
    if (coro) coro->async_promise = req->promise;
    
    ant_value_t result = generator_resume_kind(js, gen, req->value, req->kind);
    GC_ROOT_PIN(js, result);
    
    if (vtype(result) != T_PROMISE || result != req->promise) {
      generator_settle_request_promise(js, req->promise, result);
      js_maybe_drain_microtasks_after_async_settle(js);
    }
    
    free(req);
    data = generator_data(gen);
    if (!data) break;
  }

  GC_ROOT_RESTORE(js, root_mark);
}

static coroutine_t *generator_coro(ant_value_t gen) {
  generator_data_t *data = generator_data(gen);
  return data ? data->coro : NULL;
}

static void generator_clear_coro(ant_value_t gen, coroutine_t *coro) {
  generator_data_t *data = generator_data(gen);
  if (data && data->coro == coro) data->coro = NULL;
  if (coro) coroutine_unhold(coro, CORO_HOLD_GENERATOR);
}

coroutine_t *generator_get_coro_for_gc(ant_value_t gen) {
  return generator_coro(gen);
}

void generator_mark_for_gc(ant_t *js, ant_value_t gen) {
  generator_data_t *data = generator_data(gen);
  if (!data) return;
  for (generator_request_t *req = data->queue_head; req; req = req->next) {
    gc_mark_value(js, req->value);
    gc_mark_value(js, req->promise);
  }
}

static ant_value_t generator_find_owner_in_list(ant_object_t *head, coroutine_t *coro) {
  for (ant_object_t *obj = head; obj; obj = obj->next) {
    ant_value_t candidate = js_obj_from_ptr(obj);
    generator_data_t *data = generator_data(candidate);
    if (data && data->coro == coro) return candidate;
  }
  return js_mkundef();
}

static ant_value_t generator_find_owner(ant_t *js, coroutine_t *coro) {
  ant_value_t gen = generator_find_owner_in_list(js->objects, coro);
  if (vtype(gen) != T_UNDEF) return gen;
  gen = generator_find_owner_in_list(js->objects_old, coro);
  if (vtype(gen) != T_UNDEF) return gen;
  return generator_find_owner_in_list(js->permanent_objects, coro);
}

bool generator_resume_pending_request(ant_t *js, coroutine_t *coro, ant_value_t result) {
  if (!coro || coro->type != CORO_GENERATOR || vtype(coro->async_promise) != T_PROMISE) return false;

  ant_value_t gen = generator_find_owner(js, coro);
  generator_data_t *data = generator_data(gen);
  if (!data || !data->is_async) return false;

  GC_ROOT_SAVE(root_mark, js);
  GC_ROOT_PIN(js, gen);
  GC_ROOT_PIN(js, result);

  ant_value_t pending = coro->async_promise;
  GC_ROOT_PIN(js, pending);

  if (is_err(result)) {
    ant_value_t reject_value = js->thrown_exists ? js->thrown_value : result;
    js->thrown_exists = false;
    js->thrown_value = js_mkundef();
    
    GC_ROOT_PIN(js, reject_value);
    coro->async_promise = js_mkundef();
    generator_set_state(gen, GEN_COMPLETED);
    generator_clear_coro(gen, coro);
    
    js_reject_promise(js, pending, reject_value);
    js_maybe_drain_microtasks_after_async_settle(js);
    generator_process_queue(js, gen);
    GC_ROOT_RESTORE(js, root_mark);
    
    return true;
  }

  if (coro->sv_vm && coro->sv_vm->suspended) {
    if (vtype(coro->awaited_promise) != T_UNDEF) {
      generator_set_state(gen, GEN_EXECUTING);
      GC_ROOT_RESTORE(js, root_mark);
      return true;
    }

    ant_value_t out = generator_result(js, false, result);
    GC_ROOT_PIN(js, out);
    coro->async_promise = js_mkundef();
    generator_set_state(gen, GEN_SUSPENDED_YIELD);
    
    js_resolve_promise(js, pending, out);
    js_maybe_drain_microtasks_after_async_settle(js);
    generator_process_queue(js, gen);
    GC_ROOT_RESTORE(js, root_mark);
    
    return true;
  }

  ant_value_t out = generator_result(js, true, result);
  GC_ROOT_PIN(js, out);
  coro->async_promise = js_mkundef();
  
  generator_set_state(gen, GEN_COMPLETED);
  generator_clear_coro(gen, coro);
  
  js_resolve_promise(js, pending, out);
  js_maybe_drain_microtasks_after_async_settle(js);
  generator_process_queue(js, gen);
  GC_ROOT_RESTORE(js, root_mark);
  
  return true;
}

static void generator_finalize(ant_t *js, ant_object_t *obj) {
  ant_value_t gen = js_obj_from_ptr(obj);
  generator_data_t *data = (generator_data_t *)js_get_native_ptr(gen);
  
  if (!data) return;
  if (data->coro) generator_clear_coro(gen, data->coro);
  
  js_set_native_ptr(gen, NULL);
  js_set_native_tag(gen, 0);
  
  generator_free_queue(data);
  free(data);
}

static ant_value_t generator_resume_kind(
  ant_t *js, ant_value_t gen, ant_value_t resume_value, sv_resume_kind_t resume_kind
) {
  GC_ROOT_SAVE(root_mark, js);
  GC_ROOT_PIN(js, gen);
  GC_ROOT_PIN(js, resume_value);
  coroutine_t *coro = generator_coro(gen);
  
  if (!coro || !coro->sv_vm) {
    generator_set_state(gen, GEN_COMPLETED);
    if (resume_kind == SV_RESUME_THROW) {
      GC_ROOT_RESTORE(js, root_mark);
      return js_throw(js, resume_value);
    }
    
    ant_value_t out = generator_result(
      js, true, resume_kind == SV_RESUME_RETURN 
      ? resume_value : js_mkundef()
    );
    
    GC_ROOT_RESTORE(js, root_mark);
    return out;
  }

  generator_state_t state = generator_state(gen);
  if (state == GEN_EXECUTING) {
    ant_value_t queued = generator_enqueue_request(js, gen, resume_kind, resume_value);
    GC_ROOT_RESTORE(js, root_mark);
    return queued;
  }
    
  if (state == GEN_COMPLETED) {
    if (resume_kind == SV_RESUME_THROW) {
      GC_ROOT_RESTORE(js, root_mark);
      return js_throw(js, resume_value);
    }
    
    ant_value_t out = generator_result(
      js, true, resume_kind == SV_RESUME_RETURN
      ? resume_value : js_mkundef()
    );
    
    GC_ROOT_RESTORE(js, root_mark);
    return out;
  }
  
  if (state == GEN_SUSPENDED_START && resume_kind == SV_RESUME_THROW) {
    generator_set_state(gen, GEN_COMPLETED);
    generator_clear_coro(gen, coro);
    GC_ROOT_RESTORE(js, root_mark);
    return js_throw(js, resume_value);
  }
  
  if (state == GEN_SUSPENDED_START && resume_kind == SV_RESUME_RETURN) {
    generator_set_state(gen, GEN_COMPLETED);
    generator_clear_coro(gen, coro);
    ant_value_t out = generator_result(js, true, resume_value);
    GC_ROOT_RESTORE(js, root_mark);
    return out;
  }

  generator_set_state(gen, GEN_EXECUTING);
  coroutine_t *saved_active = js->active_async_coro;
  
  coro->active_parent = saved_active;
  coro->active_prev = NULL;
  
  if (saved_active) saved_active->active_prev = coro;
  js->active_async_coro = coro;
  coroutine_hold(coro, CORO_HOLD_ACTIVE);

  ant_value_t result;
  if (state == GEN_SUSPENDED_START) {
    sv_closure_t *closure = (vtype(coro->async_func) == T_FUNC) ? js_func_closure(coro->async_func) : NULL;
    if (!closure || !closure->func) result = js_mkerr(js, "invalid generator function");
    else result = sv_execute_closure_entry(
      coro->sv_vm, closure, coro->async_func,
      coro->super_val, coro->this_val, coro->args, coro->nargs, NULL
    );
  } else {
    coro->sv_vm->suspended_resume_value = resume_value;
    coro->sv_vm->suspended_resume_is_error = (resume_kind == SV_RESUME_THROW);
    coro->sv_vm->suspended_resume_kind = resume_kind;
    coro->sv_vm->suspended_resume_pending = true;
    result = sv_resume_suspended(coro->sv_vm);
  }
  
  GC_ROOT_PIN(js, result);
  js->active_async_coro = saved_active;
  if (saved_active) saved_active->active_prev = NULL;
  
  coro->active_parent = NULL;
  coro->active_prev = NULL;
  coroutine_unhold(coro, CORO_HOLD_ACTIVE);

  if (is_err(result)) {
    generator_set_state(gen, GEN_COMPLETED);
    generator_clear_coro(gen, coro);
    GC_ROOT_RESTORE(js, root_mark);
    return result;
  }

  if (coro->sv_vm && coro->sv_vm->suspended) {
    if (generator_is_async(gen) && vtype(coro->awaited_promise) != T_UNDEF) {
      generator_set_state(gen, GEN_EXECUTING);
      if (vtype(coro->async_promise) != T_PROMISE) {
        coro->async_promise = js_mkpromise(js);
        GC_ROOT_PIN(js, coro->async_promise);
      }
      
      ant_value_t out = coro->async_promise;
      GC_ROOT_RESTORE(js, root_mark);
      return out;
    }
    
    generator_set_state(gen, GEN_SUSPENDED_YIELD);
    ant_value_t out = generator_result(js, false, result);
    GC_ROOT_RESTORE(js, root_mark);
    
    return out;
  }

  generator_set_state(gen, GEN_COMPLETED);
  generator_clear_coro(gen, coro);
  
  ant_value_t out = generator_result(js, true, result);
  GC_ROOT_RESTORE(js, root_mark);
  
  return out;
}

static ant_value_t generator_resume(ant_t *js, ant_value_t gen, ant_value_t resume_value) {
  return generator_resume_kind(js, gen, resume_value, SV_RESUME_NEXT);
}

static ant_value_t generator_next(ant_t *js, ant_value_t *args, int nargs) {
  ant_value_t gen = js->this_val;
  if (vtype(gen) != T_GENERATOR)
    return js_mkerr_typed(js, JS_ERR_TYPE, "Generator.prototype.next called on incompatible receiver");
    
  ant_value_t resume_value = nargs > 0 ? args[0] : js_mkundef();
  ant_value_t result = generator_resume(js, gen, resume_value);
  
  if (generator_is_async(gen) && vtype(result) == T_PROMISE) return result;
  return generator_is_async(gen) ? generator_async_wrap_result(js, result) : result;
}

static ant_value_t generator_return(ant_t *js, ant_value_t *args, int nargs) {
  ant_value_t gen = js->this_val;
  if (vtype(gen) != T_GENERATOR)
    return js_mkerr_typed(js, JS_ERR_TYPE, "Generator.prototype.return called on incompatible receiver");

  generator_state_t state = generator_state(gen);
  if (state == GEN_EXECUTING && !generator_is_async(gen))
    return js_mkerr_typed(js, JS_ERR_TYPE, "Generator is already executing");
    
  ant_value_t value = nargs > 0 ? args[0] : js_mkundef();
  ant_value_t result = generator_resume_kind(js, gen, value, SV_RESUME_RETURN);
  
  if (generator_is_async(gen) && vtype(result) == T_PROMISE) return result;
  return generator_is_async(gen) ? generator_async_wrap_result(js, result) : result;
}

static ant_value_t generator_throw(ant_t *js, ant_value_t *args, int nargs) {
  ant_value_t gen = js->this_val;
  if (vtype(gen) != T_GENERATOR)
    return js_mkerr_typed(js, JS_ERR_TYPE, "Generator.prototype.throw called on incompatible receiver");
    
  generator_state_t state = generator_state(gen);
  if (state == GEN_EXECUTING && !generator_is_async(gen))
    return js_mkerr_typed(js, JS_ERR_TYPE, "Generator is already executing");
    
  ant_value_t value = nargs > 0 ? args[0] : js_mkundef();
  ant_value_t result = generator_resume_kind(js, gen, value, SV_RESUME_THROW);
  
  if (generator_is_async(gen) && vtype(result) == T_PROMISE) return result;
  return generator_is_async(gen) ? generator_async_wrap_result(js, result) : result;
}

static ant_value_t generator_async_dispose(ant_t *js, ant_value_t *args, int nargs) {
  ant_value_t gen = js->this_val;
  if (vtype(gen) != T_GENERATOR || !generator_is_async(gen)) return js_mkerr_typed(
    js, JS_ERR_TYPE,
    "AsyncGenerator.prototype[Symbol.asyncDispose] called on incompatible receiver"
  );

  return generator_return(js, NULL, 0);
}

void init_generator_module(void) {
  ant_t *js = rt->js;
  ant_value_t proto = js_mkobj(js);
  
  js->sym.generator_proto = proto;
  js_set_proto_init(proto, js->sym.iterator_proto);
  
  js_set(js, proto, "next", js_mkfun(generator_next));
  js_set(js, proto, "return", js_mkfun(generator_return));
  js_set(js, proto, "throw", js_mkfun(generator_throw));
  js_set_sym(js, proto, get_toStringTag_sym(), js_mkstr(js, "Generator", 9));

  ant_value_t async_proto = js_mkobj(js);
  js->sym.async_generator_proto = async_proto;
  js_set_proto_init(async_proto, js->sym.async_iterator_proto);
  js_set(js, async_proto, "next", js_mkfun(generator_next));
  js_set(js, async_proto, "return", js_mkfun(generator_return));
  js_set(js, async_proto, "throw", js_mkfun(generator_throw));
  js_set_sym(js, async_proto, get_toStringTag_sym(), js_mkstr(js, "AsyncGenerator", 14));
  js_set_sym(js, async_proto, get_asyncDispose_sym(), js_mkfun(generator_async_dispose));

  ant_value_t async_generator_func_proto = js_get_slot(js_glob(js), SLOT_ASYNC_GENERATOR_PROTO);
  if (is_object_type(async_generator_func_proto)) {
    js_set(js, async_generator_func_proto, "prototype", async_proto);
    js_set_descriptor(js, js_as_obj(async_generator_func_proto), "prototype", 9, JS_DESC_C);
    js_set(js, async_proto, "constructor", async_generator_func_proto);
    js_set_descriptor(js, async_proto, "constructor", 11, JS_DESC_C);
  }
  
  init_async_iterator_helpers();
}

ant_value_t sv_call_generator_closure_dispatch(
  sv_vm_t *caller_vm, ant_t *js, sv_closure_t *closure,
  ant_value_t callee_func, ant_value_t super_val,
  ant_value_t this_val, ant_value_t *args, int argc
) {
  if (!closure || !closure->func) return js_mkerr(js, "invalid generator function");

  sv_vm_t *gen_vm = sv_vm_create(js, SV_VM_ASYNC);
  if (!gen_vm) return js_mkerr(js, "out of memory for generator VM");

  coroutine_t *coro = (coroutine_t *)CORO_MALLOC(sizeof(coroutine_t));
  if (!coro) {
    sv_vm_destroy(gen_vm);
    return js_mkerr(js, "out of memory for generator");
  }

  ant_value_t *copied_args = NULL;
  if (argc > 0 && args) {
    copied_args = (ant_value_t *)CORO_MALLOC(sizeof(ant_value_t) * (size_t)argc);
    if (!copied_args) {
      sv_vm_destroy(gen_vm);
      CORO_FREE(coro);
      return js_mkerr(js, "out of memory for generator args");
    }
    memcpy(copied_args, args, sizeof(ant_value_t) * (size_t)argc);
  }

  ant_value_t gen = js_mkgenerator(js);
  if (is_err(gen)) {
    if (copied_args) CORO_FREE(copied_args);
    sv_vm_destroy(gen_vm);
    CORO_FREE(coro);
    return gen;
  }

  generator_data_t *data = (generator_data_t *)calloc(1, sizeof(*data));
  if (!data) {
    if (copied_args) CORO_FREE(copied_args);
    sv_vm_destroy(gen_vm);
    CORO_FREE(coro);
    return js_mkerr(js, "out of memory for generator data");
  }

  *coro = (coroutine_t){
    .js = js,
    .type = CORO_GENERATOR,
    .this_val = this_val,
    .super_val = super_val,
    .new_target = js->new_target,
    .awaited_promise = js_mkundef(),
    .result = js_mkundef(),
    .async_func = callee_func,
    .args = copied_args,
    .nargs = argc,
    .active_parent = NULL,
    .is_settled = false,
    .is_error = false,
    .is_done = false,
    .resume_point = 0,
    .yield_value = js_mkundef(),
    .async_promise = js_mkundef(),
    .next = NULL,
    .mco = NULL,
    .owner_vm = gen_vm,
    .sv_vm = gen_vm,
    .mco_started = false,
    .is_ready = false,
    .did_suspend = false,
    .refcount = 1,
    .hold_bits = 0,
    .await_registered = false,
    .destroy_requested = false,
  };

  *data = (generator_data_t){
    .coro = coro,
    .state = GEN_SUSPENDED_START,
    .is_async = closure->func->is_async,
  };
  coroutine_hold(coro, CORO_HOLD_GENERATOR);
  coroutine_release(coro);

  js_set_native_ptr(gen, data);
  js_set_native_tag(gen, GENERATOR_NATIVE_TAG);
  js_set_finalizer(gen, generator_finalize);

  ant_value_t instance_proto = js_get(js, callee_func, "prototype");
  if (is_object_type(instance_proto)) js_set_proto_wb(js, gen, instance_proto);
  else if (data->is_async && is_object_type(js->sym.async_generator_proto))
    js_set_proto_wb(js, gen, js->sym.async_generator_proto);

  return gen;
}