/* Copyright (C) 2010 Tony Garnock-Jones. All rights reserved. */

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

#include <sys/time.h>

#include <ucontext.h>

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

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

#include <assert.h>

#ifdef __APPLE__
/* Bollocks. Looks like OS X chokes unless STACK_SIZE is a multiple of 32k. */
#define STACK_SIZE 32768
#elif linux
#define STACK_SIZE 32768
#else
#error Define STACK_SIZE for your platform. It should probably not be less than 32k?
#endif

Process *current_process = NULL;

static ucontext_t scheduler;
static ProcessQueue runlist = { 0, NULL, NULL };
static ProcessQueue deadlist = { 0, NULL, NULL };

static void zero_queue(ProcessQueue *pq) {
  pq->count = 0;
  pq->head = NULL;
  pq->tail = NULL;
}

static void enqueue(ProcessQueue *pq, Process *p) {
  p->link = NULL;
  if (pq->head == NULL) {
    pq->head = p;
  } else {
    pq->tail->link = p;
  }
  pq->tail = p;
  pq->count++;
}

static Process *dequeue(ProcessQueue *pq) {
  if (pq->head == NULL) {
    return NULL;
  } else {
    Process *p = pq->head;
    pq->head = p->link;
    if (pq->head == NULL) {
      pq->tail = NULL;
    }
    pq->count--;
    return p;
  }
}

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

static void schedule(void) {
  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();
}

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

void 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); /* what is a sane value here? 32k for mac... */
  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);
}

static void io_isr(struct bufferevent *bufev, IOHandle *h) {
  assert(h->p->state == PROCESS_WAITING);
  enqueue_runlist(h->p);
}

static void error_isr(struct bufferevent *bufev, short what, IOHandle *h) {
  h->error_direction = what & (EVBUFFER_READ | EVBUFFER_WRITE);
  h->error_kind = what & ~(EVBUFFER_READ | EVBUFFER_WRITE);
  if (h->p->state == PROCESS_WAITING) {
    enqueue_runlist(h->p);
  } else {
    warn("Um, not sure what to do here. Error what %d, fd %d, ioh %p process %p\n",
	 what,
	 bufev->ev_read.ev_fd,
	 h,
	 h->p);
  }
}

IOHandle *new_iohandle(int fd) {
  IOHandle *h = malloc(sizeof(*h));
  assert(current_process != NULL);
  h->p = current_process;
  h->fd = fd;
  h->io = bufferevent_new(fd,
			  (evbuffercb) io_isr,
			  (evbuffercb) io_isr,
			  (everrorcb) error_isr,
			  h);
  PCHECK(h->io, "bufferevent_new");
  h->error_direction = 0;
  h->error_kind = 0;
  return h;
}

void delete_iohandle(IOHandle *h) {
  bufferevent_free(h->io);
  free(h);
}

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

static void block_on_io(IOHandle *h, short event) {
  ICHECK(bufferevent_enable(h->io, event), "bufferevent_enable");
  assert(current_process == h->p);
  h->p->state = PROCESS_WAITING;
  schedule();
  ICHECK(bufferevent_disable(h->io, event), "bufferevent_disable");
}

cmsg_bytes_t iohandle_readwait(IOHandle *h, size_t at_least) {
  while (EVBUFFER_LENGTH(h->io->input) < at_least) {
    if (h->error_kind) {
      return EMPTY_BYTES;
    }
    block_on_io(h, EV_READ);
  }
  return (cmsg_bytes_t) {
    .len = EVBUFFER_LENGTH(h->io->input),
    .bytes = 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) {
  ICHECK(getcontext(&scheduler), "boot_harness getcontext");
  while (1) {
    while (runlist.count) {
      ProcessQueue work = runlist;
      zero_queue(&runlist);
      info("Processing %d jobs\n", work.count);
      while ((current_process = dequeue(&work)) != NULL) {
	ICHECK(swapcontext(&scheduler, &current_process->context), "boot_harness swapcontext");
	clean_dead_processes();
      }
      info("Polling for events\n");
      event_loop(EVLOOP_NONBLOCK);
    }
    info("Blocking for events\n");
    event_loop(EVLOOP_ONCE);
  }
}