////////////////////////////////////////////////////////////
//~ Arena types

#define ArenaHeaderSize 256
#define ArenaBlockSize  16384

Struct(ThreadLocalArenaCtx)
{
  Arena *perm;
  Arena *scratch[2];
};

////////////////////////////////////////////////////////////
//~ Arena management

Arena *AcquireArena(u64 reserve);
void ReleaseArena(Arena *arena);

void CopyArena(Arena *dst, Arena *src);
void ShrinkArena(Arena *arena);
void SetArenaReadonly(Arena *arena);
void SetArenaReadWrite(Arena *arena);
void *ResetArena(Arena *arena);

////////////////////////////////////////////////////////////
//~ Push / pop

#define PushStructs(a, type, n)         ((type *)PushBytes((a), (sizeof(type) * (n)), alignof(type)))
#define PushStruct(a, type)             PushStructs((a), type, 1)

#define PushStructsNoZero(a, type, n)   ((type *)PushBytesNoZero((a), (sizeof(type) * (n)), alignof(type)))
#define PushStructNoZero(a, type)       PushStructsNoZero((a), type, 1)

#define PopStructs(a, type, dst, n)     PopBytes((a), sizeof(type) * (n), dst)
#define PopStruct(a, type, dst)         PopStructs((a), type, (dst), 1)

#define PopStructsNoCopy(a, type, n)    PopBytesNoCopy((a), sizeof(type) * (n))
#define PopStructNoCopy(a, type)        PopStructsNoCopy((a), type, 1)

#define ArenaFirst(arena, type) ((type *)ArenaFirst_((arena), alignof(type)))
#define ArenaNext(arena, type)  ((type *)ArenaNext_((arena), alignof(type)))
#define ArenaCount(arena, type) ((arena)->pos / sizeof(type))

void *PushBytesNoZero(Arena *arena, u64 size, u64 align);
void *PushBytes(Arena *arena, u64 size, u64 align);
void *PushAlign(Arena *arena, u64 align);

void PopTo(Arena *arena, u64 pos);
void PopBytesNoCopy(Arena *arena, u64 size);
void PopBytes(Arena *arena, u64 size, void *copy_dst);

void *ArenaNext_(Arena *arena, u64 align);
void *ArenaFirst_(Arena *arena, u64 align);

////////////////////////////////////////////////////////////
//~ Thread arena helpers

TempArena BeginTempArena(Arena *arena);
void EndTempArena(TempArena temp);

#define PermArena() (Base_tl.arenas.perm)

////////////////////////////////////////////////////////////
//~ Scratch arena helpers

TempArena BeginScratch(Arena *potential_conflict);
TempArena BeginScratchNoConflict_(void);
void EndScratch(TempArena scratch_temp);

// This macro declares an unused "arena" variable that will produce a shadowing
// warning variable is present (due to shadowing). This is for catching obvious
// cases of `BeginScratchNoConflict` getting called when an `arena` variable
// already exists in the caller's scope.
#define BeginScratchNoConflict() \
  BeginScratchNoConflict_();     \
  do {                           \
    u8 arena = 0;                \
  } while (0)