/**
 * @file smm.c
 *
 */
#include <stddef.h>
#include <errno.h>
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <stdbool.h>
#include <time.h>
#include <unistd.h>
#include <sys/mman.h>
#include <sys/stat.h>
#include <fcntl.h>
#include "smm.h"

#define MAX_NAME_ATTEMPTS (5)
#define PREFER_NUM_BUFFERS (3)

#define ROUND_UP(n, b) (((((n) ? (n) : 1) + (b) - 1) / (b)) * (b))
#define LLHEAD(type) \
struct { \
   struct type *first; \
   struct type *last; \
}

#define LLLINK(type) \
struct { \
   struct type *next; \
   struct type *prev; \
}

#define LL_FIRST(head) ((head)->first)
#define LL_LAST(head) ((head)->last)
#define LL_IS_EMPTY(head) (LL_FIRST(head) == NULL)
#define LL_NEXT(src, member) ((src)->member.next)
#define LL_PREV(src, member) ((src)->member.prev)

#define LL_INIT(head) do { \
   (head)->first = NULL; \
   (head)->last = NULL; \
} while (0)

#define LL_ENQUEUE(head, src, member) do { \
   (src)->member.next = NULL; \
   (src)->member.prev = (head)->last; \
   if ((head)->last == NULL) { \
      (head)->first = (src); \
   } else { \
      (head)->last->member.next = (src); \
   } \
   (head)->last = (src); \
} while (0)

#define LL_DEQUEUE(entry, head, member) do { \
   (entry) = LL_FIRST(head); \
   LL_REMOVE(head, entry, member); \
} while (0)

#define LL_INSERT_AFTER(head, dest, src, member) do { \
   (src)->member.prev = (dest); \
   (src)->member.next = (dest)->member.next; \
   if ((dest)->member.next != NULL) { \
      (dest)->member.next->member.prev = (src); \
   } else { \
      (head)->last = (src); \
   } \
   (dest)->member.next = (src); \
} while (0)

#define LL_REMOVE(head, src, member) do { \
   if ((src)->member.prev != NULL) { \
      (src)->member.prev->member.next = (src)->member.next; \
   } else { \
      (head)->first = (src)->member.next; \
   } \
   if ((src)->member.next != NULL) { \
      (src)->member.next->member.prev = (src)->member.prev; \
   } else { \
      (head)->last = (src)->member.prev; \
   } \
} while (0)

#define LL_FOREACH(entry, head, member) \
   for ((entry) = LL_FIRST(head); \
        (entry) != NULL; \
        (entry) = LL_NEXT(entry, member))

struct smm_pool {
   struct smm_pool_properties props;
   LLHEAD(smm_buffer) allocd;
   void *map;
   size_t map_size;
   bool map_outdated;
};

struct smm_buffer {
   struct smm_buffer_properties props;
   bool group_resized;
   LLLINK(smm_buffer) pool;
   LLLINK(smm_buffer) use;
   LLLINK(smm_buffer) age;
};

struct smm_group {
   struct smm_group_properties props;
   size_t size;
   unsigned char num_buffers;
   LLHEAD(smm_buffer) unused;
   LLHEAD(smm_buffer) inuse;
   LLHEAD(smm_buffer) history;
   LLLINK(smm_group) link;
};

static size_t calc_buffer_size(struct smm_buffer *buf);
static void purge_history(struct smm_buffer *buf);
static struct smm_buffer *get_from_pool(struct smm_group *grp);
static void return_to_pool(struct smm_buffer *buf);
static struct smm_pool *alloc_pool(void);
static void free_pool(struct smm_pool *pool);
static struct smm_buffer *alloc_buffer(struct smm_buffer *last, size_t offset);
static void free_buffer(struct smm_buffer *buf);

static struct {
   unsigned long page_sz;
   struct smm_events cbs;
   struct smm_pool *active;
   LLHEAD(smm_group) groups;
   struct {
      size_t active_used;
   } statistics;
} smm_instance;


void smm_init(struct smm_events *evs)
{
   memcpy(&smm_instance.cbs, evs, sizeof(struct smm_events));
   srand((unsigned int)clock());
   smm_instance.page_sz = (unsigned long)sysconf(_SC_PAGESIZE);
   LL_INIT(&smm_instance.groups);
}


void smm_deinit(void)
{
   struct smm_group *grp;

   /* Destroy all buffer groups */
   while (!LL_IS_EMPTY(&smm_instance.groups)) {
      LL_DEQUEUE(grp, &smm_instance.groups, link);
      smm_destroy(grp);
   }
}


void smm_setctx(void *ctx)
{
   smm_instance.cbs.ctx = ctx;
}


smm_group_t *smm_create(void)
{
   struct smm_group *grp;

   /* Allocate and intialize a new buffer group */
   grp = malloc(sizeof(struct smm_group));
   if (grp != NULL) {
      grp->size = smm_instance.page_sz;
      grp->num_buffers = 0;
      LL_INIT(&grp->unused);
      LL_INIT(&grp->inuse);
      LL_INIT(&grp->history);

      /* Add to instance groups queue */
      LL_ENQUEUE(&smm_instance.groups, grp, link);
   }

   return grp;
}


void smm_resize(smm_group_t *grp, size_t sz)
{
   struct smm_buffer *buf;
   struct smm_group *rgrp = grp;

   /* Round allocation size up to a sysconf(_SC_PAGE_SIZE) boundary */
   rgrp->size = ROUND_UP(sz, smm_instance.page_sz);

   /* Return all unused buffers to pool (to be re-allocated at the new size) */
   while (!LL_IS_EMPTY(&rgrp->unused)) {
      LL_DEQUEUE(buf, &rgrp->unused, use);
      return_to_pool(buf);
   }

   /* Mark all buffers in use to be freed to pool when possible */
   LL_FOREACH(buf, &rgrp->inuse, use) {
      buf->group_resized = true;
      purge_history(buf);
   }
}


void smm_destroy(smm_group_t *grp)
{
   struct smm_buffer *buf;
   struct smm_group *dgrp = grp;

   /* Return unused buffers */
   while (!LL_IS_EMPTY(&dgrp->unused)) {
      LL_DEQUEUE(buf, &dgrp->unused, use);
      return_to_pool(buf);
   }

   /* Return buffers that are still in use (ideally this queue should be empty
    * at this time)
    */
   while (!LL_IS_EMPTY(&dgrp->inuse)) {
      LL_DEQUEUE(buf, &dgrp->inuse, use);
      return_to_pool(buf);
   }

   /* Remove from instance groups queue */
   LL_REMOVE(&smm_instance.groups, dgrp, link);
   free(dgrp);
}


smm_buffer_t *smm_acquire(smm_group_t *grp)
{
   struct smm_buffer *buf;
   struct smm_group *agrp = grp;

   if (LL_IS_EMPTY(&agrp->unused)) {
      /* No unused buffer available, so get a new one from pool */
      buf = get_from_pool(agrp);
   } else {
      /* Otherwise, reuse an unused buffer */
      LL_DEQUEUE(buf, &agrp->unused, use);
   }

   if (buf != NULL) {
      /* Add buffer to in-use queue */
      LL_ENQUEUE(&agrp->inuse, buf, use);

      /* Emit 'init buffer' event */
      if (smm_instance.cbs.init_buffer != NULL) {
         if (smm_instance.cbs.init_buffer(smm_instance.cbs.ctx, &buf->props)) {
            smm_release(buf);
            buf = NULL;
         }
      }

      if (buf != NULL) {
         /* Remove from history */
         purge_history(buf);

         /* Add to history a-new */
         LL_ENQUEUE(&agrp->history, buf, age);
      }
   }

   return buf;
}


void *smm_map(smm_buffer_t *buf)
{
   struct smm_buffer *mbuf = buf;
   struct smm_pool *pool = mbuf->props.pool;
   void *map = pool->map;

   if (pool->map_outdated) {
      /* Update mapping to current pool size */
      if (pool->map != NULL) {
         munmap(pool->map, pool->map_size);
      }

      map = mmap(NULL,
                 pool->props.size,
                 PROT_READ | PROT_WRITE,
                 MAP_SHARED,
                 pool->props.fd,
                 0);

      if (map == MAP_FAILED) {
         map = NULL;
         pool->map = NULL;
      } else {
         pool->map = map;
         pool->map_size = pool->props.size;
         pool->map_outdated = false;
      }
   }

   /* Calculate buffer mapping (from offset in pool) */
   if (map != NULL) {
      map = (((char *)map) + mbuf->props.offset);
   }

   return map;
}


void smm_release(smm_buffer_t *buf)
{
   struct smm_buffer *rbuf = buf;
   struct smm_group *grp = rbuf->props.group;

   /* Remove from in-use queue */
   LL_REMOVE(&grp->inuse, rbuf, use);

   if (rbuf->group_resized) {
      /* Buffer group was resized while this buffer was in-use, thus it must be
       * returned to it's pool
       */
      rbuf->group_resized = false;
      return_to_pool(rbuf);
   } else {
      /* Move to unused queue */
      LL_ENQUEUE(&grp->unused, rbuf, use);

      /* Try to limit total number of buffers to preferred number */
      while ((grp->num_buffers > PREFER_NUM_BUFFERS) &&
             (!LL_IS_EMPTY(&grp->unused))) {
         LL_DEQUEUE(rbuf, &grp->unused, use);
         return_to_pool(rbuf);
      }
   }
}


smm_buffer_t *smm_latest(smm_group_t *grp)
{
   struct smm_group *lgrp = grp;

   return LL_LAST(&lgrp->history);
}


smm_buffer_t *smm_next(smm_buffer_t *buf)
{
   struct smm_buffer *ibuf;
   struct smm_buffer *nbuf = buf;
   struct smm_group *grp = nbuf->props.group;

   LL_FOREACH(ibuf, &grp->history, age) {
      if (ibuf == nbuf) {
         ibuf = LL_NEXT(ibuf, age);
         break;
      }
   }

   return ibuf;
}

void purge_history(struct smm_buffer *buf)
{
   struct smm_buffer *ibuf;
   struct smm_group *grp = buf->props.group;

   /* Remove from history (and any older) */
   LL_FOREACH(ibuf, &grp->history, age) {
      if (ibuf == buf) {
         do {
            LL_DEQUEUE(ibuf, &grp->history, age);
         } while (ibuf != buf);
         break;
      }
   }
}


size_t calc_buffer_size(struct smm_buffer *buf)
{
   size_t buf_sz;
   struct smm_pool *buf_pool = buf->props.pool;

   if (buf == LL_LAST(&buf_pool->allocd)) {
      buf_sz = (buf_pool->props.size - buf->props.offset);
   } else {
      buf_sz = (LL_NEXT(buf, pool)->props.offset - buf->props.offset);
   }

   return buf_sz;
}


struct smm_buffer *get_from_pool(struct smm_group *grp)
{
   int ret;
   size_t buf_sz;
   struct smm_buffer *buf;
   struct smm_buffer *last = NULL;

   /* TODO: Determine when to allocate a new active pool (i.e. memory shrink) */

   if (smm_instance.active == NULL) {
      /* Allocate a new active pool */
      smm_instance.active = alloc_pool();
      smm_instance.statistics.active_used = 0;
   }

   if (smm_instance.active == NULL) {
      buf = NULL;
   } else {
      /* Search for a free buffer large enough for allocation */
      LL_FOREACH(buf, &smm_instance.active->allocd, pool) {
         last = buf;
         if (buf->props.group == NULL) {
            buf_sz = calc_buffer_size(buf);
            if (buf_sz == grp->size) {
               break;
            } else if (buf_sz > grp->size) {
               if ((buf != LL_LAST(&smm_instance.active->allocd)) &&
                   (LL_NEXT(buf, pool)->props.group == NULL)) {
                  /* Pull back next buffer to use unallocated size */
                  LL_NEXT(buf, pool)->props.offset -= (buf_sz - grp->size);
               } else {
                  /* Allocate another buffer to hold unallocated size */
                  alloc_buffer(buf, buf->props.offset + grp->size);
               }

               break;
            }
         }
      }

      if (buf == NULL) {
         /* No buffer found to meet allocation size, expand pool */
         if ((last != NULL) &&
             (last->props.group == NULL)) {
            /* Use last free buffer */
            buf_sz = (grp->size - buf_sz);
         } else {
            /* Allocate new buffer */
            buf_sz = grp->size;
            if (last == NULL) {
               buf = alloc_buffer(NULL, 0);
            } else {
               buf = alloc_buffer(last, smm_instance.active->props.size);
            }
            last = buf;
         }

         if (last != NULL) {
            /* Expand pool backing memory */
            ret = ftruncate(smm_instance.active->props.fd,
                            smm_instance.active->props.size + buf_sz);
            if (ret) {
               if (buf != NULL) {
                  free_buffer(buf);
                  buf = NULL;
               }
            } else {
               smm_instance.active->props.size += buf_sz;
               smm_instance.active->map_outdated = true;
               buf = last;

               if (!(smm_instance.active->props.size - buf_sz)) {
                  /* Emit 'new pool' event */
                  if ((smm_instance.cbs.new_pool != NULL) &&
                      (smm_instance.cbs.new_pool(smm_instance.cbs.ctx,
                                                &smm_instance.active->props))) {
                     free_buffer(buf);
                     free_pool(smm_instance.active);
                     smm_instance.active = NULL;
                     buf = NULL;
                  }
               } else {
                  /* Emit 'expand pool' event */
                  if (smm_instance.cbs.expand_pool != NULL) {
                     smm_instance.cbs.expand_pool(smm_instance.cbs.ctx,
                                                  &smm_instance.active->props);
                  }
               }
            }
         }
      }
   }

   if (buf != NULL) {
      /* Set buffer group */
      memcpy((void *)&buf->props.group, &grp, sizeof(struct smm_group *));

      /* Emit 'new buffer' event */
      if (smm_instance.cbs.new_buffer != NULL) {
         if (smm_instance.cbs.new_buffer(smm_instance.cbs.ctx, &buf->props)) {
            grp = NULL;
            memcpy((void *)&buf->props.group, &grp, sizeof(struct smm_group *));
            buf = NULL;
         }
      }

      if (buf != NULL) {
         /* Update active pool usage statistic */
         smm_instance.statistics.active_used += grp->size;
         grp->num_buffers++;
      }
   }

   return buf;
}


void return_to_pool(struct smm_buffer *buf)
{
   struct smm_group *grp = buf->props.group;
   struct smm_pool *pool = buf->props.pool;

   /* Emit 'free buffer' event */
   if (smm_instance.cbs.free_buffer != NULL) {
      smm_instance.cbs.free_buffer(smm_instance.cbs.ctx, &buf->props);
   }

   /* Buffer is no longer part of history */
   purge_history(buf);

   /* Buffer is no longer part of group */
   grp->num_buffers--;
   grp = NULL;
   memcpy((void *)&buf->props.group, &grp, sizeof(struct smm_group *));

   /* Update active pool usage statistic */
   if (smm_instance.active == pool) {
      smm_instance.statistics.active_used -= calc_buffer_size(buf);
   }

   /* Coalesce with ungrouped buffers beside this one */
   if ((buf != LL_LAST(&pool->allocd)) &&
       (LL_NEXT(buf, pool)->props.group == NULL)) {
      free_buffer(LL_NEXT(buf, pool));
   }
   if ((buf != LL_FIRST(&pool->allocd)) &&
       (LL_PREV(buf, pool)->props.group == NULL)) {
      buf = LL_PREV(buf, pool);
      pool = buf->props.pool;
      free_buffer(LL_NEXT(buf, pool));
   }

   /* Free buffer (and pool), if only remaining buffer in pool */
   if ((buf == LL_FIRST(&pool->allocd)) &&
       (buf == LL_LAST(&pool->allocd))) {
      free_buffer(buf);

      /* Emit 'free pool' event */
      if (smm_instance.cbs.free_pool != NULL) {
         smm_instance.cbs.free_pool(smm_instance.cbs.ctx, &pool->props);
      }

      free_pool(pool);
      if (smm_instance.active == pool) {
         smm_instance.active = NULL;
      }
   }
}


struct smm_pool *alloc_pool(void)
{
   struct smm_pool *pool;
   char name[] = ("/" SMM_FD_NAME "-XXXXX");
   unsigned char attempts = 0;
   bool opened = false;

   pool = malloc(sizeof(struct smm_pool));
   if (pool != NULL) {
      do {
         /* A randomized pool name should help reduce collisions */
         sprintf(name + sizeof(SMM_FD_NAME) + 1, "%05X", rand() & 0xFFFF);
         pool->props.fd = shm_open(name,
                                   O_RDWR | O_CREAT | O_EXCL,
                                   S_IRUSR | S_IWUSR);
         if (pool->props.fd >= 0) {
            shm_unlink(name);
            pool->props.size = 0;
            pool->map = NULL;
            pool->map_size = 0;
            pool->map_outdated = false;
            LL_INIT(&pool->allocd);
            opened = true;
            break;
         } else {
            if (errno != EEXIST) {
               break;
            }
            attempts++;
         }
      } while (attempts < MAX_NAME_ATTEMPTS);

      if (!opened) {
         free(pool);
         pool = NULL;
      }
   }

   return pool;
}


void free_pool(struct smm_pool *pool)
{
   if (pool->map != NULL) {
      munmap(pool->map, pool->map_size);
   }

   close(pool->props.fd);
   free(pool);
}


struct smm_buffer *alloc_buffer(struct smm_buffer *last, size_t offset)
{
   struct smm_buffer *buf;
   struct smm_buffer_properties initial_props = {
      {NULL},
      NULL,
      smm_instance.active,
      offset
   };

   /* Allocate and intialize a new buffer (including linking in to pool) */
   buf = malloc(sizeof(struct smm_buffer));
   if (buf != NULL) {
      memcpy(&buf->props, &initial_props, sizeof(struct smm_buffer_properties));
      buf->group_resized = false;

      if (last == NULL) {
         LL_ENQUEUE(&smm_instance.active->allocd, buf, pool);
      } else {
         LL_INSERT_AFTER(&smm_instance.active->allocd, last, buf, pool);
      }
   }

   return buf;
}


void free_buffer(struct smm_buffer *buf)
{
   struct smm_pool *buf_pool = buf->props.pool;

   /* Remove from pool */
   LL_REMOVE(&buf_pool->allocd, buf, pool);
   free(buf);
}
