global const SizeU default_reserve_size   = gib(4);
global const SizeU default_alignment      = 8;
global const SizeU additional_commit_size = mib(1);
function SizeU align_up(SizeU size, SizeU align);

function void
memory_copy(void *dst, void *src, SizeU size){
  U8 *d = (U8*)dst;
  U8 *s = (U8*)src;
  for(SizeU i = 0; i < size; i++){
    d[i] = s[i];
  }
}

function void
memory_zero(void *p, SizeU size){
  U8 *pp = (U8 *)p;
  for(SizeU i = 0; i < size; i++)
    pp[i] = 0;
}

function int 
max_int(int a, int b){
  if(a>b) return a;
  return b;
}

function void
arena_init(Arena *a){
  a->memory = os_reserve(default_reserve_size);
  a->alignment = default_alignment;
}

function void *
arena_push_size(Arena *a, SizeU size){
  SizeU generous_size = size;
  if(a->memory.commit+generous_size>a->memory.commit){
    if(a->memory.reserve == 0){
      arena_init(a);
    }
    os_commit(&a->memory, generous_size+additional_commit_size);
  }
  
  a->len = align_up(a->len, a->alignment);
  void *result = (U8*)a->memory.data + a->len;
  a->len += size;
  
  memory_zero(result, size);
  return result;
}

function void *
arena_push_copy(Arena *a, void *pointer, SizeU size){
  void *result = arena_push_size(a, size);
  memory_copy(result, pointer, size);
  return result;
}

function SizeU
clamp_top_sizeu(SizeU val, SizeU max){
  if(val>max)return max;
  return val;
}

function void
arena_pop_pos(Arena *arena, SizeU pos){
  pos = clamp_top_sizeu(pos, arena->len);
  arena->len = pos;
}

function Arena_Checkpoint
arena_checkpoint(Arena *arena){
  Arena_Checkpoint result = {arena, arena->len};
  return result;
}

function void
arena_restore(Arena_Checkpoint checkpoint){
  arena_pop_pos(checkpoint.arena, checkpoint.pos);
}

function String
arena_push_string_copy(Arena *arena, String string){
  U8 *copy = arena_push_array(arena, U8, string.len+1);
  memory_copy(copy, string.str, string.len);
  copy[string.len] = 0;
  return (String){copy, string.len};
}

function String
string_fmtv(Arena *arena, const char *str, va_list args1) {
  va_list args2;
  va_copy(args2, args1);
  S64 len = vsnprintf(0, 0, str, args2);
  va_end(args2);
  
  char *result = (char *)arena_push_size(arena, len + 1);
  vsnprintf(result, len + 1, str, args1);
  if (arena->len > 0)
    arena->len -= 1;
  
  String res = {(U8 *)result, len};
  return res;
}

#define STRING_FMT(arena, str, result) \
va_list args1; \
va_start(args1, str); \
String result = string_fmtv(arena, str, args1); \
va_end(args1)

function String 
string_fmt(Arena *arena, const char *str, ...) {
  STRING_FMT(arena, str, result);
  return result;
}

function void
string_listf(Arena *arena, String_List *list, const char *str, ...){
  STRING_FMT(arena, str, string);
  String_Node *node = arena_push_struct(arena, String_Node);
  node->string = string;
  SLLQueuePush(list->first, list->last, node);
  list->char_count += node->string.len;
  list->node_count += 1;
}

function String
string_list_flatten(Arena *arena, String_List *list){
  String result = {(U8 *)arena_push_size(arena, list->char_count + 1)};
  for(String_Node *node = list->first; node; node=node->next){
    memory_copy(result.str+result.len, node->str, node->len);
    result.len += node->len;
  }
  return result;
}