refactor: Modified ArenaPointer

ArenaPointer now contains a reference to the original arena and an
offset instad of a raw address. Change was made to avoid invalidating
addresses and keeping a more consise system. arena_unwrap_pointer was
also included as a helper function.

src/arena.c

@@ -5,6 +5,8 @@
 #include <stdlib.h>
 #include <string.h>
 
+
+
 ArenaResult arena_init(size_t capacity) {
     if (capacity < 1) {
         return (ArenaResult) {.is_valid = false, .err = ARENA_INVALID_SIZE};
@@ -41,7 +43,6 @@ ArenaPointer arena_alloc(Arena *arena, size_t size, size_t alignment) {
         return (ArenaPointer) {.is_valid = false, .err = padding.err};
     }
 
-
     if (arena->offset + padding.val >= arena->capacity) {
         return (ArenaPointer) {.is_valid = false, .err = ARENA_OUT_OF_SPACE};
     }
@@ -53,7 +54,7 @@ ArenaPointer arena_alloc(Arena *arena, size_t size, size_t alignment) {
     size_t aligned_offset = arena->offset + padding.val;
 
     arena->offset = aligned_offset + size;
-    return (ArenaPointer) {.is_valid = true, .address = arena->buffer + aligned_offset};
+    return (ArenaPointer) {.is_valid = true, .offset = aligned_offset, .arena = arena};
 }
 
 ArenaErr arena_ensure_capacity(Arena *arena, size_t size, size_t alignment) {
@@ -104,7 +105,7 @@ ArenaPointer arena_push(Arena *arena, void *data, size_t size, size_t alignment)
     }
     
     memcpy(
-        pointer.address,
+        arena_unwrap_pointer(pointer),
         data,
         size);
 
@@ -126,6 +127,8 @@ ArenaErr arena_realloc(Arena *arena, size_t new_capacity) {
     return ARENA_OK;
 }
 
+
+
 SizeResult get_arena_align_padding(Arena *arena, size_t alignment) {
     if (arena == NULL) {
         return (SizeResult) {.is_valid = false, .err = ARENA_NULL_ARG};
@@ -141,6 +144,13 @@ SizeResult get_arena_align_padding(Arena *arena, size_t alignment) {
     return (SizeResult) {.is_valid = true, .err = aligned - current_address};
 }
 
+void *arena_unwrap_pointer(ArenaPointer p) {
+    if (!p.is_valid) {
+        return NULL;
+    }
+    return p.arena->buffer + p.offset;
+}
+
 bool mul_size_t_safe(size_t a, size_t b, size_t *out) {
     if (out == NULL) {
         return true;