module dlib.alloc;

import dlib.aliases;
import dlib.math;
import dlib.platform;
import dlib.util;

import std.stdio;
import core.stdc.string : memset;
import core.memory;

const DEFAULT_ALIGNMENT = (void *).sizeof * 2;

struct ArenaPool
{
	u8* mem;
	u64 pos;
}

struct Arena
{
	SLList!(ArenaPool) pools;
	u64                pool_length;
	u64                length;
};

T*
MAlloc(T)()
{
	void* mem = MemAlloc(T.sizeof);
	return cast(T*)mem;
}

T[]
MAllocArray(T)(u64 count)
{
	void* mem = MemAlloc(T.sizeof * count);
	return (cast(T*)mem)[0 .. count];
}

void
MFree(T)(T* ptr)
{
	MemFree(ptr, T.sizeof);
}

void
MFreeArray(T)(T[] slice)
{
	MemFree(slice.ptr, cast(u64)slice.length * T.sizeof);
}

T*
Alloc(T)()
{
	void* mem = pureMalloc(T.sizeof);
	memset(mem, 0, T.sizeof);
	return (cast(T*)mem);
}

T[]
AllocArray(T)(u64 count)
{
	void* mem = pureMalloc(T.sizeof * count);
	memset(mem, 0, T.sizeof * count);
	return (cast(T*)mem)[0 .. count];
}

Arena 
CreateArena(u64 size)
{
	Arena arena = { 
		length: size,
		pool_length: size - Node!(ArenaPool).sizeof,
	};

	AddArenaPool(&arena);

	return arena;
};

void
AddArenaPool(Arena* arena)
{
	u8* mem = cast(u8*)MemAlloc(arena.length);

	Node!(ArenaPool)* node = cast(Node!(ArenaPool)*)mem;

	node.value.mem = (cast(u8*)mem) + Node!(ArenaPool).sizeof;
	node.value.pos = 0;

	assert(node.value.mem != null, "Unable to allocate memory for arena");

	PushFront(&arena.pools, node, null);
}

T[]
AllocArray(T)(Arena* arena, u64 count)
{
	void* mem = AllocAlign(arena, T.sizeof * count, DEFAULT_ALIGNMENT);
	memset(mem, 0, T.sizeof * count);
	return (cast(T*)mem)[0 .. count];
}

T* 
Alloc(T)(Arena* arena)
{
	void* mem = AllocAlign(arena, T.sizeof, DEFAULT_ALIGNMENT);
	memset(mem, 0, T.sizeof);
	return cast(T*)mem;
};

void* 
AllocAlign(Arena* arena, u64 size, u64 alignment)
{
	assert(size <= arena.pool_length, "Unable to allocate memory within arena size");

	void* ptr = null;

	uintptr mem_pos, current, offset;
	Node!(ArenaPool)* node = arena.pools.first;
	while (true)
	{
		if (node == null)
		{
			AddArenaPool(arena);
			node = arena.pools.first;
		}

		mem_pos = cast(uintptr)node.value.mem;
		current = mem_pos + node.value.pos;
		offset = AlignPow2(current, alignment) - mem_pos;

		if (offset+size <= arena.pool_length)
		{
			break;
		}

		node = node.next;
	}
	
	ptr = &node.value.mem[offset];
	node.value.pos = offset+size;

	return ptr;
};

void
Reset(Arena* arena)
{
	Node!(ArenaPool)* node = arena.pools.first;
	while (node != null)
	{
		node.value.pos = 0;
		node = node.next;
	}
}

void
Free(Arena* arena)
{
	Node!(ArenaPool)* node = arena.pools.first;
	while (node != null)
	{
		MemFree(node.value.mem, arena.length);
		node = node.next;
	}
}

void
FreeArray(T)(T[] arr)
{
	pureFree(arr.ptr);
}

void Free(T)(T* ptr)
{
	pureFree(ptr);
}