#include <string.h>
#include <stdlib.h>
#include <errno.h>
#include <sys/ksys.h>
#include "_mem.h"

// Macro to align a value to a specified alignment.
// Ensures that the allocated memory is aligned to a certain boundary (e.g., 16 bytes).
#define __mem_align(value, align) ((value + align - 1) & ~(align - 1))

void* malloc(size_t size)
{
    // Handle zero-size allocation.
    if (size == 0) {
        return NULL;
    }

    // Align the size to 16 bytes.
    size = __mem_align(size, 16);

    struct mem_node* current_node = __mem_node; // Start at the head of the linked list.
    struct mem_node* new_node = NULL;           // Pointer to the new node that will be created.

    // Iterate through the linked list of memory nodes.
    while (current_node != NULL) {
        // Check if the current node has enough free space for the requested size.
        if (size + sizeof(struct mem_node) <= current_node->free) {

            // Calculate the used memory in current node
            const size_t s = GET_MEM_NODE_USED_MEM(current_node);

            // Create a new memory node after the current node's used space.
            new_node = (struct mem_node*)(GET_MEM_NODE_PTR(current_node) + s);

            // Set the size of the new node.
            new_node->size = current_node->free - sizeof(struct mem_node);

            // Update current node's size
            current_node->size = s;

            // Mark current node as used.
            current_node->free = 0;

            break; // Found a suitable node, exit the loop.
        }
        current_node = current_node->next; // Move to the next node in the list.
    }

    // If no suitable node was found in the existing list:
    if (new_node == NULL) {
        // Calculate the size of the new block, including the mem_block header, mem_node header and alignment.
        const size_t s = __mem_align(size + sizeof(struct mem_block) + sizeof(struct mem_node), ALLOC_BLOCK_SIZE);

        // Allocate a new block of memory using the ksys_alloc function (presumably a kernel-level allocation function).
        struct mem_block* block = (struct mem_block*)_ksys_alloc(s);

        // Check if the allocation was successful.
        if (block == NULL) {
            __errno = ENOMEM; // Set the error number to indicate memory allocation failure.
            return NULL;      // Return NULL to indicate allocation failure.
        }

        // Create a new memory node after the mem_block header.
        new_node = (struct mem_node*)(block + sizeof(struct mem_block));

        // Set the size of the new node.
        new_node->size = s - sizeof(struct mem_block) - sizeof(struct mem_node);
    }

    // Set the free space in the new node.
    new_node->free = new_node->size - size;

    // Set the last pointer of the new node to the current node.
    new_node->last = current_node;

    // Link the new node into the linked list.
    if (current_node != NULL) {
        // Set the next pointer of the current node to the new node.
        new_node->next = current_node->next;

        // Update the last pointer of the next node, if it exists.
        if (current_node->next != NULL) {
            current_node->next->last = new_node;
        }
        current_node->next = new_node;
    } else {
        // If the current node is NULL, the new node is the first node in the list.
        new_node->next = NULL;
    }

    // If the linked list was empty, set the head to the new node.
    if (__mem_node == NULL) {
        __mem_node = new_node;
    }

    // Return a pointer to the user data area of the new node.
    return GET_MEM_NODE_PTR(new_node);
}

#undef __mem_align