/*
 * Copyright (C) 2016, 2017 "IoT.bzh"
 * Author José Bollo <jose.bollo@iot.bzh>
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#define _GNU_SOURCE

#include <stdlib.h>
#include <stdint.h>
#include <unistd.h>
#include <signal.h>
#include <time.h>
#include <sys/syscall.h>
#include <pthread.h>
#include <errno.h>
#include <assert.h>

#include <systemd/sd-event.h>

#include "jobs.h"
#include "sig-monitor.h"
#include "verbose.h"

#if 0
#define _alert_ "do you really want to remove monitoring?"
#define sig_monitor_init_timeouts()  ((void)0)
#define sig_monitor_clean_timeouts() ((void)0)
#define sig_monitor(to,cb,arg)       (cb(0,arg))
#endif

#define EVENT_TIMEOUT_TOP  	((uint64_t)-1)
#define EVENT_TIMEOUT_CHILD	((uint64_t)10000)

/** Internal shortcut for callback */
typedef void (*job_cb_t)(int, void*);

/** Description of a pending job */
struct job
{
	struct job *next;    /**< link to the next job enqueued */
	const void *group;   /**< group of the request */
	job_cb_t callback;   /**< processing callback */
	void *arg;           /**< argument */
	int timeout;         /**< timeout in second for processing the request */
	unsigned blocked: 1; /**< is an other request blocking this one ? */
	unsigned dropped: 1; /**< is removed ? */
};

/** Description of handled event loops */
struct events
{
	struct events *next;
	struct sd_event *event;
	uint64_t timeout;
	enum {
		Available,
		Modifiable,
		Locked
	} state;
};

/** Description of threads */
struct thread
{
	struct thread *next;   /**< next thread of the list */
	struct thread *upper;  /**< upper same thread */
	struct job *job;       /**< currently processed job */
	pthread_t tid;         /**< the thread id */
	unsigned stop: 1;      /**< stop requested */
	unsigned waits: 1;     /**< is waiting? */
};

/**
 * Description of synchonous callback
 */
struct sync
{
	struct thread thread;	/**< thread loop data */
	union {
		void (*callback)(int, void*);	/**< the synchronous callback */
		void (*enter)(int signum, void *closure, struct jobloop *jobloop);
				/**< the entering synchronous routine */
	};
	void *arg;		/**< the argument of the callback */
};


/* synchronisation of threads */
static pthread_mutex_t mutex = PTHREAD_MUTEX_INITIALIZER;
static pthread_cond_t  cond = PTHREAD_COND_INITIALIZER;

/* count allowed, started and waiting threads */
static int allowed = 0; /** allowed count of threads */
static int started = 0; /** started count of threads */
static int waiting = 0; /** waiting count of threads */
static int remains = 0; /** allowed count of waiting jobs */
static int nevents = 0; /** count of events */

/* list of threads */
static struct thread *threads;
static _Thread_local struct thread *current_thread;
static _Thread_local struct events *current_events;

/* queue of pending jobs */
static struct job *first_job;
static struct events *first_events;
static struct job *free_jobs;

/**
 * Create a new job with the given parameters
 * @param group    the group of the job
 * @param timeout  the timeout of the job (0 if none)
 * @param callback the function that achieves the job
 * @param arg      the argument of the callback
 * @return the created job unblock or NULL when no more memory
 */
static struct job *job_create(
		const void *group,
		int timeout,
		job_cb_t callback,
		void *arg)
{
	struct job *job;

	/* try recyle existing job */
	job = free_jobs;
	if (job)
		free_jobs = job->next;
	else {
		/* allocation  without blocking */
		pthread_mutex_unlock(&mutex);
		job = malloc(sizeof *job);
		pthread_mutex_lock(&mutex);
		if (!job) {
			errno = -ENOMEM;
			goto end;
		}
	}
	/* initialises the job */
	job->group = group;
	job->timeout = timeout;
	job->callback = callback;
	job->arg = arg;
	job->blocked = 0;
	job->dropped = 0;
end:
	return job;
}

/**
 * Adds 'job' at the end of the list of jobs, marking it
 * as blocked if an other job with the same group is pending.
 * @param job the job to add
 */
static void job_add(struct job *job)
{
	const void *group;
	struct job *ijob, **pjob;

	/* prepare to add */
	group = job->group;
	job->next = NULL;

	/* search end and blockers */
	pjob = &first_job;
	ijob = first_job;
	while (ijob) {
		if (group && ijob->group == group)
			job->blocked = 1;
		pjob = &ijob->next;
		ijob = ijob->next;
	}

	/* queue the jobs */
	*pjob = job;
}

/**
 * Get the next job to process or NULL if none.
 * @return the first job that isn't blocked or NULL
 */
static inline struct job *job_get()
{
	struct job *job = first_job;
	while (job && job->blocked)
		job = job->next;
	return job;
}

/**
 * Get the next events to process or NULL if none.
 * @return the first events that isn't running or NULL
 */
static inline struct events *events_get()
{
	struct events *events = first_events;
	while (events && events->state != Available)
		events = events->next;
	return events;
}

/**
 * Releases the processed 'job': removes it
 * from the list of jobs and unblock the first
 * pending job of the same group if any.
 * @param job the job to release
 */
static inline void job_release(struct job *job)
{
	struct job *ijob, **pjob;
	const void *group;

	/* first unqueue the job */
	pjob = &first_job;
	ijob = first_job;
	while (ijob != job) {
		pjob = &ijob->next;
		ijob = ijob->next;
	}
	*pjob = job->next;

	/* then unblock jobs of the same group */
	group = job->group;
	if (group) {
		ijob = job->next;
		while (ijob && ijob->group != group)
			ijob = ijob->next;
		if (ijob)
			ijob->blocked = 0;
	}

	/* recycle the job */
	job->next = free_jobs;
	free_jobs = job;
}

/**
 * Monitored cancel callback for a job.
 * This function is called by the monitor
 * to cancel the job when the safe environment
 * is set.
 * @param signum 0 on normal flow or the number
 *               of the signal that interrupted the normal
 *               flow, isn't used
 * @param arg    the job to run
 */
static void job_cancel(int signum, void *arg)
{
	struct job *job = arg;
	job->callback(SIGABRT, job->arg);
}

/**
 * Monitored normal callback for events.
 * This function is called by the monitor
 * to run the event loop when the safe environment
 * is set.
 * @param signum 0 on normal flow or the number
 *               of the signal that interrupted the normal
 *               flow
 * @param arg     the events to run
 */
static void events_call(int signum, void *arg)
{
	int rc;
	struct sd_event *se;
	struct events *events = arg;

	if (!signum) {
		se = events->event;
		rc = sd_event_prepare(se);
		if (rc < 0) {
			errno = -rc;
			ERROR("sd_event_prepare returned an error (state: %d): %m", sd_event_get_state(events->event));
		} else {
			if (rc == 0) {
				rc = sd_event_wait(se, events->timeout);
				if (rc < 0) {
					errno = -rc;
					ERROR("sd_event_wait returned an error (state: %d): %m", sd_event_get_state(events->event));
				}
			}

			if (rc > 0) {
				rc = sd_event_dispatch(se);
				if (rc < 0) {
					errno = -rc;
					ERROR("sd_event_dispatch returned an error (state: %d): %m", sd_event_get_state(events->event));
				}
			}
		}
	}
}

/**
 * Main processing loop of threads processing jobs.
 * The loop must be called with the mutex locked
 * and it returns with the mutex locked.
 * @param me the description of the thread to use
 * TODO: how are timeout handled when reentering?
 */
static void thread_run(volatile struct thread *me)
{
	struct thread **prv;
	struct job *job;
	struct events *events;
	uint64_t evto;

	/* initialize description of itself and link it in the list */
	me->tid = pthread_self();
	me->stop = 0;
	me->waits = 0;
	me->upper = current_thread;
	if (current_thread) {
		evto = EVENT_TIMEOUT_CHILD;
	} else {
		started++;
		sig_monitor_init_timeouts();
		evto = EVENT_TIMEOUT_TOP;
	}
	me->next = threads;
	threads = (struct thread*)me;
	current_thread = (struct thread*)me;

	/* loop until stopped */
	while (!me->stop) {
		/* get a job */
		job = job_get(first_job);
		if (job) {
			/* prepare running the job */
			remains++; /* increases count of job that can wait */
			job->blocked = 1; /* mark job as blocked */
			me->job = job; /* record the job (only for terminate) */

			/* run the job */
			pthread_mutex_unlock(&mutex);
			sig_monitor(job->timeout, job->callback, job->arg);
			pthread_mutex_lock(&mutex);

			/* release event if any */
			events = current_events;
			if (events && events->state == Modifiable) {
				current_events = NULL;
				events->state = Available;
			}

			/* release the run job */
			job_release(job);
		} else {
			/* no job, check events */
			events = current_events;
			if (!events)
				events = events_get();
			else if (events->state == Locked) {
				events = 0;
				WARNING("Loosing an event loop because reentering");
			}
			if (events) {
				/* run the events */
				events->state = Locked;
				events->timeout = evto;
				current_events = events;
				pthread_mutex_unlock(&mutex);
				sig_monitor(0, events_call, events);
				pthread_mutex_lock(&mutex);
				current_events = NULL;
				events->state = Available;
			} else {
				/* no job and not events */
				waiting++;
				me->waits = 1;
				pthread_cond_wait(&cond, &mutex);
				me->waits = 0;
				waiting--;
			}
		}
	}

	/* unlink the current thread and cleanup */
	prv = &threads;
	while (*prv != me)
		prv = &(*prv)->next;
	*prv = me->next;
	current_thread = me->upper;
	if (!current_thread) {
		sig_monitor_clean_timeouts();
		started--;
	}
}

/**
 * Entry point for created threads.
 * @param data not used
 * @return NULL
 */
static void *thread_main(void *data)
{
	struct thread me;

	pthread_mutex_lock(&mutex);
	thread_run(&me);
	pthread_mutex_unlock(&mutex);
	return NULL;
}

/**
 * Starts a new thread
 * @return 0 in case of success or -1 in case of error
 */
static int start_one_thread()
{
	pthread_t tid;
	int rc;

	rc = pthread_create(&tid, NULL, thread_main, NULL);
	if (rc != 0) {
		/* errno = rc; */
		WARNING("not able to start thread: %m");
		rc = -1;
	}
	return rc;
}

/**
 * Queues a new asynchronous job represented by 'callback' and 'arg'
 * for the 'group' and the 'timeout'.
 * Jobs are queued FIFO and are possibly executed in parallel
 * concurrently except for job of the same group that are
 * executed sequentially in FIFO order.
 * @param group    The group of the job or NULL when no group.
 * @param timeout  The maximum execution time in seconds of the job
 *                 or 0 for unlimited time.
 * @param callback The function to execute for achieving the job.
 *                 Its first parameter is either 0 on normal flow
 *                 or the signal number that broke the normal flow.
 *                 The remaining parameter is the parameter 'arg1'
 *                 given here.
 * @param arg      The second argument for 'callback'
 * @return 0 in case of success or -1 in case of error
 */
int jobs_queue(
		const void *group,
		int timeout,
		void (*callback)(int, void*),
		void *arg)
{
	const char *info;
	struct job *job;
	int rc;

	pthread_mutex_lock(&mutex);

	/* allocates the job */
	job = job_create(group, timeout, callback, arg);
	if (!job) {
		errno = ENOMEM;
		info = "out of memory";
		goto error;
	}

	/* check availability */
	if (remains == 0) {
		errno = EBUSY;
		info = "too many jobs";
		goto error2;
	}

	/* start a thread if needed */
	if (waiting == 0 && started < allowed) {
		/* all threads are busy and a new can be started */
		rc = start_one_thread();
		if (rc < 0 && started == 0) {
			info = "can't start first thread";
			goto error2;
		}
	}

	/* queues the job */
	remains--;
	job_add(job);

	/* signal an existing job */
	pthread_cond_signal(&cond);
	pthread_mutex_unlock(&mutex);
	return 0;

error2:
	job->next = free_jobs;
	free_jobs = job;
error:
	ERROR("can't process job with threads: %s, %m", info);
	pthread_mutex_unlock(&mutex);
	return -1;
}

/**
 * Internal helper function for 'jobs_enter'.
 * @see jobs_enter, jobs_leave
 */
static void enter_cb(int signum, void *closure)
{
	struct sync *sync = closure;
	sync->enter(signum, sync->arg, (void*)&sync->thread);
}

/**
 * Internal helper function for 'jobs_call'.
 * @see jobs_call
 */
static void call_cb(int signum, void *closure)
{
	struct sync *sync = closure;
	sync->callback(signum, sync->arg);
	jobs_leave((void*)&sync->thread);
}

/**
 * Internal helper for synchronous jobs. It enters
 * a new thread loop for evaluating the given job
 * as recorded by the couple 'sync_cb' and 'sync'.
 * @see jobs_call, jobs_enter, jobs_leave
 */
static int do_sync(
		const void *group,
		int timeout,
		void (*sync_cb)(int signum, void *closure),
		struct sync *sync
)
{
	struct job *job;

	pthread_mutex_lock(&mutex);

	/* allocates the job */
	job = job_create(group, timeout, sync_cb, sync);
	if (!job) {
		ERROR("out of memory");
		errno = ENOMEM;
		pthread_mutex_unlock(&mutex);
		return -1;
	}

	/* queues the job */
	job_add(job);

	/* run until stopped */
	thread_run(&sync->thread);
	pthread_mutex_unlock(&mutex);
	return 0;
}

/**
 * Enter a synchronisation point: activates the job given by 'callback'
 * and 'closure' using 'group' and 'timeout' to control sequencing and
 * execution time.
 * @param group the group for sequencing jobs
 * @param timeout the time in seconds allocated to the job
 * @param callback the callback that will handle the job.
 *                 it receives 3 parameters: 'signum' that will be 0
 *                 on normal flow or the catched signal number in case
 *                 of interrupted flow, the context 'closure' as given and
 *                 a 'jobloop' reference that must be used when the job is
 *                 terminated to unlock the current execution flow.
 * @param arg the argument to the callback
 * @return 0 on success or -1 in case of error
 */
int jobs_enter(
		const void *group,
		int timeout,
		void (*callback)(int signum, void *closure, struct jobloop *jobloop),
		void *closure
)
{
	struct sync sync;

	sync.enter = callback;
	sync.arg = closure;
	return do_sync(group, timeout, enter_cb, &sync);
}

/**
 * Unlocks the execution flow designed by 'jobloop'.
 * @param jobloop indication of the flow to unlock
 * @return 0 in case of success of -1 on error
 */
int jobs_leave(struct jobloop *jobloop)
{
	struct thread *t;

	pthread_mutex_lock(&mutex);
	t = threads;
	while (t && t != (struct thread*)jobloop)
		t = t->next;
	if (!t) {
		errno = EINVAL;
	} else {
		t->stop = 1;
		if (t->waits)
			pthread_cond_broadcast(&cond);
	}
	pthread_mutex_unlock(&mutex);
	return -!t;
}

/**
 * Calls synchronously the job represented by 'callback' and 'arg1'
 * for the 'group' and the 'timeout' and waits for its completion.
 * @param group    The group of the job or NULL when no group.
 * @param timeout  The maximum execution time in seconds of the job
 *                 or 0 for unlimited time.
 * @param callback The function to execute for achieving the job.
 *                 Its first parameter is either 0 on normal flow
 *                 or the signal number that broke the normal flow.
 *                 The remaining parameter is the parameter 'arg1'
 *                 given here.
 * @param arg      The second argument for 'callback'
 * @return 0 in case of success or -1 in case of error
 */
int jobs_call(
		const void *group,
		int timeout,
		void (*callback)(int, void*),
		void *arg)
{
	struct sync sync;

	sync.callback = callback;
	sync.arg = arg;

	return do_sync(group, timeout, call_cb, &sync);
}

/**
 * Gets a sd_event item for the current thread.
 * @return a sd_event or NULL in case of error
 */
struct sd_event *jobs_get_sd_event()
{
	struct events *events;
	int rc;

	pthread_mutex_lock(&mutex);

	/* search events on stack */
	events = current_events;
	if (!events) {
		/* search an available events */
		events = events_get();
		if (!events) {
			/* not found, check if creation possible */
			if (nevents >= allowed) {
				ERROR("not possible to add a new event");
				events = NULL;
			} else {
				events = malloc(sizeof *events);
				if (events && (rc = sd_event_new(&events->event)) >= 0) {
					if (nevents < started || start_one_thread() >= 0) {
						events->state = Available;
						events->next = first_events;
						first_events = events;
					} else {
						ERROR("can't start thread for events");
						sd_event_unref(events->event);
						free(events);
						events = NULL;
					}
				} else {
					if (!events) {
						ERROR("out of memory");
						errno = ENOMEM;
					} else {
						free(events);
						ERROR("creation of sd_event failed: %m");
						events = NULL;
						errno = -rc;
					}
				}
			}
		}
		if (events) {
			events->state = Modifiable;
			if (!current_thread)
				WARNING("event returned for unknown thread!");
			current_events = events;
		}
	}
	pthread_mutex_unlock(&mutex);
	return events ? events->event : NULL;
}

/**
 * Enter the jobs processing loop.
 * @param allowed_count Maximum count of thread for jobs including this one
 * @param start_count   Count of thread to start now, must be lower.
 * @param waiter_count  Maximum count of jobs that can be waiting.
 * @param start         The start routine to activate (can't be NULL)
 * @return 0 in case of success or -1 in case of error.
 */
int jobs_start(int allowed_count, int start_count, int waiter_count, void (*start)(int signum))
{
	int rc, launched;
	struct thread me;
	struct job *job;

	assert(allowed_count >= 1);
	assert(start_count >= 0);
	assert(waiter_count > 0);
	assert(start_count <= allowed_count);

	rc = -1;
	pthread_mutex_lock(&mutex);

	/* check whether already running */
	if (current_thread || allowed) {
		ERROR("thread already started");
		errno = EINVAL;
		goto error;
	}

	/* start */
	if (sig_monitor_init() < 0) {
		ERROR("failed to initialise signal handlers");
		goto error;
	}

	/* records the allowed count */
	allowed = allowed_count;
	started = 0;
	waiting = 0;
	remains = waiter_count;

	/* start at least one thread */
	launched = 0;
	while ((launched + 1) < start_count) {
		if (start_one_thread() != 0) {
			ERROR("Not all threads can be started");
			goto error;
		}
		launched++;
	}

	/* queue the start job */
	job = job_create(NULL, 0, (job_cb_t)start, NULL);
	if (!job) {
		ERROR("out of memory");
		errno = ENOMEM;
		goto error;
	}
	job_add(job);
	remains--;

	/* run until end */
	thread_run(&me);
	rc = 0;
error:
	pthread_mutex_unlock(&mutex);
	return rc;
}

/**
 * Terminate all the threads and cancel all pending jobs.
 */
void jobs_terminate()
{
	struct job *job, *head, *tail;
	pthread_t me, *others;
	struct thread *t;
	int count;

	/* how am i? */
	me = pthread_self();

	/* request all threads to stop */
	pthread_mutex_lock(&mutex);
	allowed = 0;

	/* count the number of threads */
	count = 0;
	t = threads;
	while (t) {
		if (!t->upper && !pthread_equal(t->tid, me))
			count++;
		t = t->next;
	}

	/* fill the array of threads */
	others = alloca(count * sizeof *others);
	count = 0;
	t = threads;
	while (t) {
		if (!t->upper && !pthread_equal(t->tid, me))
			others[count++] = t->tid;
		t = t->next;
	}

	/* stops the threads */
	t = threads;
	while (t) {
		t->stop = 1;
		t = t->next;
	}

	/* wait the threads */
	pthread_cond_broadcast(&cond);
	pthread_mutex_unlock(&mutex);
	while (count)
		pthread_join(others[--count], NULL);
	pthread_mutex_lock(&mutex);

	/* cancel pending jobs of other threads */
	remains = 0;
	head = first_job;
	first_job = NULL;
	tail = NULL;
	while (head) {
		/* unlink the job */
		job = head;
		head = job->next;

		/* search if job is stacked for current */
		t = current_thread;
		while (t && t->job != job)
			t = t->upper;
		if (t) {
			/* yes, relink it at end */
			if (tail)
				tail->next = job;
			else
				first_job = job;
			tail = job;
			job->next = NULL;
		} else {
			/* no cancel the job */
			pthread_mutex_unlock(&mutex);
			sig_monitor(0, job_cancel, job);
			free(job);
			pthread_mutex_lock(&mutex);
		}
	}
	pthread_mutex_unlock(&mutex);
}