#ifndef _CORO_H_
#define _CORO_H_

#include <stdbool.h>

// Basic usage example:
//   Define a specific coroutine struct holding all your variables and return values (variables defined normally within the function will be reset):
//     typedef struct {
//     	Coro coro;
//     	int x_pos, y_pos;
//     } ExampleCoro;
//   
//   Define a specific coroutine function taking our custom type as a parameter:
//     void example(ExampleCoro *c)
//     CORO_BEGIN(&c->coro) // The coroutine initialization simply takes a reference to the core coroutine struct
//       // Draw the object for a total of 1s
//       CORO_BEGIN_REPEAT(1.0)
//         // Rapidly alternate between states A and B displaying each for 0.1s
//         CORO_BEGIN_REPEAT(0.1)
//           DrawThingA(c->x_pos, c->y_pos);
//         CORO_END_REPEAT()
//         CORO_BEGIN_REPEAT(0.1)
//           DrawThingB(c->x_pos, c->y_pos);
//         CORO_END_REPEAT()
//       CORO_END_REPEAT()
//       // Print a message
//       printf("Dying in 1s\n");
//       CORO_WAIT(1.0)
//       // Print another message after waiting for 1s
//       printf("XD\n");
//       // Done; c->done is now set to true and the coroutine will no longer run any code on subsequent calls
//     CORO_END()
//  
//   Initialization (zero value is ready-to-use):
//     ExampleCoro coro;
//     coro = (ExampleCoro){0};
//  
//   Each frame:
//     example(&coro)
//     coro.time += delta_time;

#ifndef CORO_MAX_DEPTH
#define CORO_MAX_DEPTH 8
#endif

#ifndef CORO_FATAL
#include <stdio.h>
#include <stdlib.h>
#define CORO_FATAL(...) { fprintf(stderr, "[FATAL] Coro: "__VA_ARGS__); abort(); }
#endif

#define CORO_BEGIN(_coro) \
  { \
  Coro *_coro_instance = _coro; \
  int _coro_goto_line = 0; \
  if (_coro_instance->done) \
    return; \
  if (_coro_instance->stack_size > 0 && !_coro_instance->stack[_coro_instance->stack_size-1].repeat) { \
    if (_coro_instance->time < _coro_instance->stack[_coro_instance->stack_size-1].timeout) \
      return; \
  } \
  if (_coro_instance->stack_size > 0) \
    _coro_goto_line = _coro_instance->stack[_coro_instance->stack_size-1].line; \
  switch (_coro_goto_line) { \
    case 0:
#define CORO_END() \
  if (_coro_instance->stack_size != 0) { CORO_FATAL("programmer error in %s:%d: CORO_END() called without closing all loops\n", __FILE__, __LINE__); } \
  _coro_instance->done = true; \
  }}
// Do nothing until the specified amount of time has passed
#define CORO_WAIT(_time) \
  if (_coro_instance->stack_size+1 > CORO_MAX_DEPTH) { CORO_FATAL("programmer error in %s:%d: maximum depth of %d exceeded\n", __FILE__, __LINE__, CORO_MAX_DEPTH); } \
  _coro_instance->stack_size++; \
  _coro_instance->stack[_coro_instance->stack_size-1].repeat = false; \
  _coro_instance->stack[_coro_instance->stack_size-1].timeout = _coro_instance->time + _time; \
  case __LINE__: _coro_instance->stack[_coro_instance->stack_size-1].line = __LINE__; \
  if (_coro_instance->time < _coro_instance->stack[_coro_instance->stack_size-1].timeout) \
    return; \
  else \
    _coro_instance->stack_size--;
// Repeat a piece of code each frame until the specified amount of time has passed
#define CORO_BEGIN_REPEAT(_time) \
  if (_coro_instance->stack_size+1 > CORO_MAX_DEPTH) { CORO_FATAL("programmer error in %s:%d: maximum depth of %d exceeded\n", __FILE__, __LINE__, CORO_MAX_DEPTH); } \
  _coro_instance->stack_size++; \
  _coro_instance->stack[_coro_instance->stack_size-1].repeat = true; \
  _coro_instance->stack[_coro_instance->stack_size-1].timeout = _coro_instance->time + _time; \
  case __LINE__: _coro_instance->stack[_coro_instance->stack_size-1].line = __LINE__;
#define CORO_END_REPEAT() \
  if (_coro_instance->stack_size == 0) { CORO_FATAL("programmer error in %s:%d: CORO_END_REPEAT() called without matching CORO_BEGIN_REPEAT()\n", __FILE__, __LINE__); } \
  if (_coro_instance->time < _coro_instance->stack[_coro_instance->stack_size-1].timeout) \
    return; \
  else \
    _coro_instance->stack_size--;

typedef struct {
  struct {
    unsigned int line; // line to return to for wait/repeat
    bool repeat;       // whether this is a repeat or simply a wait
    double timeout;    // when the repeat/wait is over
  } stack[CORO_MAX_DEPTH]; // stack for keeping track of waits and repeats
  unsigned int stack_size;
  double time; // current time; meaning and unit defined by user
  bool done;   // set to true when coroutine is finished executing
} Coro;

#endif /* !_CORO_H_ */