/*
 * SPDX-License-Identifier: GPL-2.0-only
 * Copyright (C) 2026 KolibriOS team
 * Author: Yarin Egor<y.yarin@inbox.ru>
 */

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

static struct mem_node* __new_mem_node_from_exist(struct mem_node* current_node, size_t size, bool* from_empty_node)
{
    struct mem_node* new_node = NULL;
    // Check if the current node has enough free space for the requested size.
    if (size + sizeof(struct mem_node) <= current_node->free) {

        *from_empty_node = MEM_NODE_IS_FREE(current_node);
        if (*from_empty_node) {
            new_node = current_node;
        } else {
            // 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);

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

            // Set the size of the new node.
            // for new node give all free space in current node
            new_node->size = current_node->free - sizeof(struct mem_node);

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

void* malloc(size_t size)
{
    char b[32];

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

    // Align the size to 8 bytes.
    size = __mem_default_align(size);

    struct mem_node* current_node = __mem_node;
    struct mem_node* new_node = NULL; // Pointer to the new node that will be created.
    bool from_empty_node = false;

    if (__last_biggest_mem_node != NULL)
        new_node = __new_mem_node_from_exist(__last_biggest_mem_node, size, &from_empty_node); // try find free space in last created node

    // if cant find in __last_biggest_mem_node
    if (new_node == NULL) {
        // Iterate through the linked list of memory nodes.
        while (current_node != NULL) {
            new_node = __new_mem_node_from_exist(current_node, size, &from_empty_node);
            if (new_node)
                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.
        }

        block->size = s;

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

    if (!from_empty_node) {
        // 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;
    }

    if (__last_biggest_mem_node == NULL || new_node->free > __last_biggest_mem_node->free) {
        __last_biggest_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