/* Copyright 2010, 2011, 2012 Tony Garnock-Jones <tonygarnockjones@gmail.com>.
 *
 * This file is part of Hop.
 *
 * Hop is free software: you can redistribute it and/or modify it
 * under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 3 of the License, or
 * (at your option) any later version.
 *
 * Hop is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public
 * License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with Hop.  If not, see <http://www.gnu.org/licenses/>.
 */
#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <stddef.h>
#include <errno.h>

#include <sys/time.h>

#include <ucontext.h>

typedef unsigned char u_char;
#include <event.h>

#include "cmsg_private.h"
#include "harness.h"
#include "dataq.h"

#include <assert.h>

/* What is a sane value for STACK_SIZE? */
#ifdef __APPLE__
/* Bollocks. Looks like OS X chokes unless STACK_SIZE is a multiple of 32k. */
# include <AvailabilityMacros.h>
# if !defined(MAC_OS_X_VERSION_10_6) || MAC_OS_X_VERSION_MAX_ALLOWED < MAC_OS_X_VERSION_10_6
/* Hmm, and looks like 10.5 has more aggressive stack requirements than 10.6. */
#  define STACK_SIZE 65536
# else
#  define STACK_SIZE 32768
# endif
#elif linux
# define STACK_SIZE 32768
#else
# error Define STACK_SIZE for your platform. It should probably not be less than 32k?
#endif

/* TODO: reuse stacks (via a freelist) */
/* TODO: investigate avoiding syscall in swapcontext, setcontext etc. */

IOHandle *stdin_h = NULL;
IOHandle *stdout_h = NULL;
IOHandle *stderr_h = NULL;

static volatile int harness_running = 1;
Process *current_process = NULL;

#define EMPTY_PROCESS_QUEUE EMPTY_QUEUE(Process, link)

static ucontext_t scheduler;
static queue_t runlist = EMPTY_PROCESS_QUEUE;
static queue_t deadlist = EMPTY_PROCESS_QUEUE;

static void enqueue_runlist(Process *p) {
  p->state = PROCESS_RUNNING;
  enqueue(&runlist, p);
}

static void schedule(void) {
  //info("schedule %p\n", current_process);
  if (current_process == NULL) {
    ICHECK(setcontext(&scheduler), "schedule setcontext");
  } else {
    ICHECK(swapcontext(&current_process->context, &scheduler), "schedule swapcontext");
  }
}

void yield(void) {
  enqueue_runlist(current_process);
  schedule();
}

void killproc(void) {
  assert(current_process->state == PROCESS_RUNNING);
  current_process->state = PROCESS_DEAD;
  enqueue(&deadlist, current_process);
  current_process = NULL;
  schedule();
}

void suspend(void) {
  assert(current_process->state == PROCESS_RUNNING);
  current_process->state = PROCESS_WAITING;
  schedule();
}

int resume(Process *p) {
  if (p->state == PROCESS_WAITING) {
    enqueue_runlist(p);
    return 0;
  } else {
    return -1;
  }
}

static void driver(void (*f)(void *), void *arg) {
  f(arg);
  killproc();
}

Process *spawn(void (*f)(void *), void *arg) {
  Process *p = calloc(1, sizeof(*p));
  PCHECK(p, "spawn calloc");

  p->state = PROCESS_DEAD;

  p->stack_base = malloc(STACK_SIZE);
  PCHECK(p->stack_base, "stack pointer malloc");

  ICHECK(getcontext(&p->context), "spawn getcontext");
  p->context.uc_link = NULL;
  p->context.uc_stack.ss_sp = p->stack_base;
  p->context.uc_stack.ss_size = STACK_SIZE;
  p->context.uc_stack.ss_flags = 0;
  makecontext(&p->context, (void (*)(void)) driver, 2, f, arg);

  p->link = NULL;

  enqueue_runlist(p);

  return p;
}

typedef struct nap_context_t_ {
  Process *p;
  int timeout_fired;
} nap_context_t;

void nap_isr(int fd, short what, void *arg) {
  nap_context_t *context = arg;
  //info("nap_isr %p\n", p);
  if ((context->p->state == PROCESS_WAITING) && (context->p->wait_flags & EV_TIMEOUT)) {
    context->timeout_fired = 1;
    enqueue_runlist(context->p);
  }
}

int nap(long millis) {
  struct event ev;
  struct timeval tv;
  nap_context_t context;
  assert(current_process != NULL);
  assert(current_process->state == PROCESS_RUNNING);
  context.p = current_process;
  context.timeout_fired = 0;
  tv.tv_sec = millis / 1000;
  tv.tv_usec = (millis % 1000) * 1000;
  evtimer_set(&ev, nap_isr, &context);
  ICHECK(evtimer_add(&ev, &tv), "evtimer_add");
  current_process->state = PROCESS_WAITING;
  current_process->wait_flags |= EV_TIMEOUT;
  schedule();
  current_process->wait_flags &= ~EV_TIMEOUT;
  evtimer_del(&ev);
  return context.timeout_fired;
}

static void awaken_waiters(IOHandle *h, short mask) {
  Process *prev = NULL;
  Process *p;
  Process *next;
  for (p = h->waiters; p != NULL; p = next) {
    next = p->link;
    assert(p->state == PROCESS_WAITING);
    if ((p->wait_flags & mask) != 0) {
      if (prev == NULL) {
	h->waiters = next;
      } else {
	prev->link = next;
      }
      enqueue_runlist(p);
    } else {
      prev = p;
    }
  }
}

static void input_isr(struct bufferevent *bufev, IOHandle *h) {
  awaken_waiters(h, EV_READ);
}

static void output_isr(struct bufferevent *bufev, IOHandle *h) {
  awaken_waiters(h, EV_WRITE);
}

static void error_isr(struct bufferevent *bufev, short what, IOHandle *h) {
  unsigned short kind = what & ~(EVBUFFER_READ | EVBUFFER_WRITE);
  int saved_errno = errno;
  info("error_isr 0x%04X fd %d\n", what, h->fd);
  h->error_direction = what & (EVBUFFER_READ | EVBUFFER_WRITE);
  if (kind == EVBUFFER_EOF) {
    h->eof = 1;
  } else {
    h->error_kind = kind;
    h->error_errno = saved_errno;
  }
  awaken_waiters(h, EV_READ | EV_WRITE);
}

IOHandle *new_iohandle(int fd) {
  IOHandle *h = malloc(sizeof(*h));
  h->waiters = NULL;
  h->fd = fd;
  h->io = bufferevent_new(fd,
			  (evbuffercb) input_isr,
			  (evbuffercb) output_isr,
			  (everrorcb) error_isr,
			  h);
  PCHECK(h->io, "bufferevent_new");
  bufferevent_setwatermark(h->io, EV_READ, 0, 256 * 1024);
  h->eof = 0;
  iohandle_clear_error(h);
  return h;
}

void delete_iohandle(IOHandle *h) {
  if (h->waiters) {
    warn("Deleting IOHandle %p with fd %d: processes are blocked on this handle!\n",
	 h,
	 h->fd);
  }
  bufferevent_free(h->io);
  free(h);
}

void iohandle_clear_error(IOHandle *h) {
  h->error_direction = 0;
  h->error_kind = 0;
  h->error_errno = 0;
}

static void block_on_io(IOHandle *h, short event) {
  assert(current_process->link == NULL);
  current_process->link = h->waiters;
  h->waiters = current_process;
  current_process->state = PROCESS_WAITING;
  current_process->wait_flags |= event;
  schedule();
  current_process->wait_flags &= ~event;
}

cmsg_bytes_t iohandle_readwait(IOHandle *h, size_t at_least) {
  while (EVBUFFER_LENGTH(h->io->input) < at_least) {
    if (h->eof || h->error_kind) {
      return EMPTY_BYTES;
    }
    ICHECK(bufferevent_enable(h->io, EV_READ), "bufferevent_enable");
    block_on_io(h, EV_READ);
    ICHECK(bufferevent_disable(h->io, EV_READ), "bufferevent_disable");
  }
  return CMSG_BYTES(EVBUFFER_LENGTH(h->io->input), EVBUFFER_DATA(h->io->input));
}

void iohandle_drain(IOHandle *h, size_t count) {
  evbuffer_drain(h->io->input, count);
}

void iohandle_write(IOHandle *h, cmsg_bytes_t buf) {
  ICHECK(bufferevent_write(h->io, buf.bytes, buf.len), "bufferevent_write");
}

int iohandle_flush(IOHandle *h) {
  while (EVBUFFER_LENGTH(h->io->output) > 0) {
    if (h->error_kind) {
      return -1;
    }
    block_on_io(h, EV_WRITE);
  }
  return 0;
}

void iohandle_settimeout(IOHandle *h, int timeout_read, int timeout_write) {
  bufferevent_settimeout(h->io, timeout_read, timeout_write);
}

static void clean_dead_processes(void) {
  Process *deadp;
  while ((deadp = dequeue(&deadlist)) != NULL) {
    free(deadp->stack_base);
    free(deadp);
  }
}

void boot_harness(void) {
  stdin_h = new_iohandle(0);
  stdout_h = new_iohandle(1);
  stderr_h = new_iohandle(2);

  ICHECK(getcontext(&scheduler), "boot_harness getcontext");

  while (1) {
    while (runlist.count) {
      queue_t work = runlist;
      runlist = EMPTY_PROCESS_QUEUE;
      //info("Processing %d jobs\n", work.count);
      while ((current_process = dequeue(&work)) != NULL) {
	//info("entering %p\n", current_process);
	ICHECK(swapcontext(&scheduler, &current_process->context), "boot_harness swapcontext");
	clean_dead_processes();
      }
      //info("Polling for events\n");
      event_loop(EVLOOP_NONBLOCK);
    }
    if (!harness_running) break;
    //info("Blocking for events\n");
    event_loop(EVLOOP_ONCE);
  }

  info("Shutting down.\n");

  delete_iohandle(stdin_h);
  delete_iohandle(stdout_h);
  delete_iohandle(stderr_h);
}

void interrupt_harness(void) {
  info("Interrupting harness\n");
  harness_running = 0;
}