/* Copyright (c) 2017 The Expat Maintainers
 * Copying is permitted under the MIT license.  See the file COPYING
 * for details.
 *
 * memcheck.c : debug allocators for the Expat test suite
 */

#include <stdio.h>
#include <stdlib.h>
#include "memcheck.h"


/* Structures to keep track of what has been allocated.  Speed isn't a
 * big issue for the tests this is required for, so we will use a
 * doubly-linked list to make deletion easier.
 */

typedef struct allocation_entry {
    struct allocation_entry * next;
    struct allocation_entry * prev;
    void * allocation;
    size_t num_bytes;
} AllocationEntry;

static AllocationEntry *alloc_head = NULL;
static AllocationEntry *alloc_tail = NULL;

static AllocationEntry *find_allocation(void *ptr);


/* Allocate some memory and keep track of it. */
void *
tracking_malloc(size_t size)
{
    AllocationEntry *entry = malloc(sizeof(AllocationEntry));

    if (entry == NULL) {
        printf("Allocator failure\n");
        return NULL;
    }
    entry->num_bytes = size;
    entry->allocation = malloc(size);
    if (entry->allocation == NULL) {
        free(entry);
        return NULL;
    }
    entry->next = NULL;

    /* Add to the list of allocations */
    if (alloc_head == NULL) {
        entry->prev = NULL;
        alloc_head = alloc_tail = entry;
    } else {
        entry->prev = alloc_tail;
        alloc_tail->next = entry;
        alloc_tail = entry;
    }

    return entry->allocation;
}

static AllocationEntry *
find_allocation(void *ptr)
{
    AllocationEntry *entry;

    for (entry = alloc_head; entry != NULL; entry = entry->next) {
        if (entry->allocation == ptr) {
            return entry;
        }
    }
    return NULL;
}

/* Free some memory and remove the tracking for it */
void
tracking_free(void *ptr)
{
    AllocationEntry *entry;

    if (ptr == NULL) {
        /* There won't be an entry for this */
        return;
    }

    entry = find_allocation(ptr);
    if (entry != NULL) {
        /* This is the relevant allocation.  Unlink it */
        if (entry->prev != NULL)
            entry->prev->next = entry->next;
        else
            alloc_head = entry->next;
        if (entry->next != NULL)
            entry->next->prev = entry->prev;
        else
            alloc_tail = entry->next;
        free(entry);
    } else {
        printf("Attempting to free unallocated memory at %p\n", ptr);
    }
    free(ptr);
}

/* Reallocate some memory and keep track of it */
void *
tracking_realloc(void *ptr, size_t size)
{
    AllocationEntry *entry;

    if (ptr == NULL) {
        /* By definition, this is equivalent to malloc(size) */
        return tracking_malloc(size);
    }
    if (size == 0) {
        /* By definition, this is equivalent to free(ptr) */
        tracking_free(ptr);
        return NULL;
    }

    /* Find the allocation entry for this memory */
    entry = find_allocation(ptr);
    if (entry == NULL) {
        printf("Attempting to realloc unallocated memory at %p\n", ptr);
        entry = malloc(sizeof(AllocationEntry));
        if (entry == NULL) {
            printf("Reallocator failure\n");
            return NULL;
        }
        entry->allocation = realloc(ptr, size);
        if (entry->allocation == NULL) {
            free(entry);
            return NULL;
        }

        /* Add to the list of allocations */
        entry->next = NULL;
        if (alloc_head == NULL) {
            entry->prev = NULL;
            alloc_head = alloc_tail = entry;
        } else {
            entry->prev = alloc_tail;
            alloc_tail->next = entry;
            alloc_tail = entry;
        }
    } else {
        entry->allocation = realloc(ptr, size);
        if (entry->allocation == NULL) {
            /* Realloc semantics say the original is still allocated */
            entry->allocation = ptr;
            return NULL;
        }
    }

    entry->num_bytes = size;
    return entry->allocation;
}

int
tracking_report(void)
{
    AllocationEntry *entry;

    if (alloc_head == NULL)
        return 1;

    /* Otherwise we have allocations that haven't been freed */
    for (entry = alloc_head; entry != NULL; entry = entry->next)
    {
        printf("Allocated %lu bytes at %p\n",
               entry->num_bytes, entry->allocation);
    }
    return 0;
}