/* coroutine_chan.h - Simple channel system for coroutine.{h,c}
 *
 * Copyright (C) 2024  Luke T. Shumaker <lukeshu@lukeshu.com>
 * SPDX-Licence-Identifier: AGPL-3.0-or-later
 */

/**
 * The cr_chan_* macros form a simple Go-like unbuffered channel
 * mechanism built on top of the cr_pause_and_yeild() and cr_unpause()
 * primitives.
 */
#ifndef _COROUTINE_CHAN_H_
#define _COROUTINE_CHAN_H_

#include <assert.h>

#include "coroutine.h"

/**
 * cr_chan_t(val_t) returns the type definition for a channel on
 * that transports values of type `val_t`.
 */
#define cr_chan_t(val_t) struct {   \
	bool ok_to_write;           \
	cid_t reader, *tail_reader; \
	val_t *reader_val;          \
                                    \
	bool ok_to_read;            \
	cid_t writer, *tail_writer; \
	val_t *writer_val;          \
	}

/* These "functions" are preprocessor macros instead of real C
 * functions so that the compiler can do type-checking instead of
 * having these functions take `void*`.  */

/**
 * ch_chan_send(*ch, val) sends `val` over `ch`.
 */
#define cr_chan_send(ch, _val) do {                                 \
		if ((ch)->ok_to_write) { /* non-blocking */         \
			*((ch)->reader_val) = (_val);               \
			(ch)->ok_to_write = false;                  \
			cr_unpause((ch)->reader);                   \
		} else { /* blocking */                             \
			cid_t next;                                 \
			if ((ch)->writer) {                         \
				*((ch)->tail_writer) = cr_getcid(); \
				(ch)->tail_writer = &next;          \
				cr_pause_and_yield();               \
			} else {                                    \
				(ch)->writer = cr_getcid();         \
				(ch)->tail_writer = &next;          \
			}                                           \
			assert((ch)->writer == cr_getcid());        \
			(ch)->writer_val = &(_val);                 \
			(ch)->ok_to_read = true;                    \
			cr_pause_and_yield();                       \
			assert((ch)->ok_to_read == false);          \
			if (next) {                                 \
				(ch)->writer = next;                \
				cr_unpause(next);                   \
			} else {                                    \
				(ch)->writer = 0;                   \
				(ch)->tail_writer = NULL;           \
			}                                           \
		}                                                   \
	} while (0)

/**
 * cr_chan_recv(ch, val_p) reads a value from ch into `*val_p`.
 */
#define cr_chan_recv(ch, _val_p) do {                               \
		if ((ch)->ok_to_read) { /* non-blocking */          \
			*(_val_p) = *((ch)->writer_val);            \
			(ch)->ok_to_read = false;                   \
			cr_unpause((ch)->writer;                    \
		} else { /* blocking */                             \
			cid_t next;                                 \
			if ((ch)->reader) {                         \
				*((ch)->tail_reader) = cr_getcid(); \
				(ch)->tail_reader = &next;          \
				cr_pause_and_yield();               \
			 } else {                                   \
				(ch)->reader = cr_getcid();         \
				(ch)->tail_reader = &next;          \
			}                                           \
			assert((ch)->reader == cr_getcid());        \
			(ch)->reader_val = (_val_p);                \
			(ch)->ok_to_write = true;                   \
			cr_pause_and_yield();                       \
			assert((ch)->ok_to_write == false);         \
			if (next) {                                 \
				(ch)->reader = next;                \
				cr_unpause(next);                   \
			} else {                                    \
				(ch)->reader = 0;                   \
				(ch)->tail_reader = NULL;           \
			}                                           \
		}                                                   \
	} while (0)

/**
 * cr_chan_can_send(ch) returns whether cr_chan_send(ch, val) would
 * run without blocking.
 */
#define cr_chan_can_send(ch) ((ch)->ok_to_write)

/**
 * cr_chan_can_recv(ch) returns whether cr_chan_recv(ch, &val) would
 * run without blocking.
 */
#define cr_chan_can_recv(ch) ((ch)->ok_to_read)

#endif /* _COROUTINE_CHAN_H_ */