#pragma once
/// \file heap_allocator.h
/// A buddy allocator for a memory heap

#include <stddef.h>
#include "kutil/spinlock.h"


/// Allocator for a given heap range
class heap_allocator
{
public:
    /// Default constructor creates a valid but empty heap.
    heap_allocator();

    /// Constructor. The given memory area must already have been reserved.
    /// \arg start  Starting address of the heap
    /// \arg size   Size of the heap in bytes
    heap_allocator(uintptr_t start, size_t size);

    /// Allocate memory from the area managed.
    /// \arg length  The amount of memory to allocate, in bytes
    /// \returns     A pointer to the allocated memory, or nullptr if
    ///              allocation failed.
    void * allocate(size_t length);

    /// Free a previous allocation.
    /// \arg p  A pointer previously retuned by allocate()
    void free(void *p);

    /// Minimum block size is (2^min_order). Must be at least 6.
    static const unsigned min_order = 6;

    /// Maximum block size is (2^max_order). Must be less than 64.
    static const unsigned max_order = 22;

protected:
    class mem_header;

    /// Ensure there is a block of a given order, recursively splitting
    /// \arg order   Order (2^N) of the block we want
    void ensure_block(unsigned order);

    /// Helper accessor for the list of blocks of a given order
    /// \arg order  Order (2^N) of the block we want
    /// \returns    A mutable reference to the head of the list
    mem_header *& get_free(unsigned order)  { return m_free[order - min_order]; }

    /// Helper to get a block of the given order, growing if necessary
    /// \arg order  Order (2^N) of the block we want
    /// \returns    A detached block of the given order
    mem_header * pop_free(unsigned order);

    uintptr_t m_start, m_end;
    size_t m_blocks;
    mem_header *m_free[max_order - min_order + 1];
    size_t m_allocated_size;

    kutil::spinlock m_lock;

    heap_allocator(const heap_allocator &) = delete;
};