package runtime

@(private)
byte_slice :: #force_inline proc "contextless" (data: rawptr, len: int) -> []byte {
	return transmute([]u8)Raw_Slice{data=data, len=max(len, 0)}
}


DEFAULT_TEMP_ALLOCATOR_BACKING_SIZE: int : #config(DEFAULT_TEMP_ALLOCATOR_BACKING_SIZE, 1<<22)


Default_Temp_Allocator :: struct {
	data:               []byte,
	curr_offset:        int,
	prev_allocation:    rawptr,
	backup_allocator:   Allocator,
	leaked_allocations: [dynamic][]byte,
}

default_temp_allocator_init :: proc(s: ^Default_Temp_Allocator, size: int, backup_allocator := context.allocator) {
	s.data = make_aligned([]byte, size, 2*align_of(rawptr), backup_allocator)
	s.curr_offset = 0
	s.prev_allocation = nil
	s.backup_allocator = backup_allocator
	s.leaked_allocations.allocator = backup_allocator
}

default_temp_allocator_destroy :: proc(s: ^Default_Temp_Allocator) {
	if s == nil {
		return
	}
	for ptr in s.leaked_allocations {
		free(raw_data(ptr), s.backup_allocator)
	}
	delete(s.leaked_allocations)
	delete(s.data, s.backup_allocator)
	s^ = {}
}

@(private)
default_temp_allocator_alloc :: proc(s: ^Default_Temp_Allocator, size, alignment: int, loc := #caller_location) -> ([]byte, Allocator_Error) {
	size := size
	size = align_forward_int(size, alignment)

	switch {
	case s.curr_offset+size <= len(s.data):
		start := uintptr(raw_data(s.data))
		ptr := start + uintptr(s.curr_offset)
		ptr = align_forward_uintptr(ptr, uintptr(alignment))
		mem_zero(rawptr(ptr), size)

		s.prev_allocation = rawptr(ptr)
		offset := int(ptr - start)
		s.curr_offset = offset + size
		return byte_slice(rawptr(ptr), size), .None

	case size <= len(s.data):
		start := uintptr(raw_data(s.data))
		ptr := align_forward_uintptr(start, uintptr(alignment))
		mem_zero(rawptr(ptr), size)

		s.prev_allocation = rawptr(ptr)
		offset := int(ptr - start)
		s.curr_offset = offset + size
		return byte_slice(rawptr(ptr), size), .None
	}
	a := s.backup_allocator
	if a.procedure == nil {
		a = context.allocator
		s.backup_allocator = a
	}

	data, err := mem_alloc_bytes(size, alignment, a, loc)
	if err != nil {
		return data, err
	}
	if s.leaked_allocations == nil {
		s.leaked_allocations = make([dynamic][]byte, a)
	}
	append(&s.leaked_allocations, data)

	// TODO(bill): Should leaks be notified about?
	if logger := context.logger; logger.lowest_level <= .Warning {
		if logger.procedure != nil {
			logger.procedure(logger.data, .Warning, "default temp allocator resorted to backup_allocator" , logger.options, loc)
		}
	}

	return data, .None
}

@(private)
default_temp_allocator_free :: proc(s: ^Default_Temp_Allocator, old_memory: rawptr, loc := #caller_location) -> Allocator_Error {
	if old_memory == nil {
		return .None
	}

	start := uintptr(raw_data(s.data))
	end := start + uintptr(len(s.data))
	old_ptr := uintptr(old_memory)

	if s.prev_allocation == old_memory {
		s.curr_offset = int(uintptr(s.prev_allocation) - start)
		s.prev_allocation = nil
		return .None
	}

	if start <= old_ptr && old_ptr < end {
		// NOTE(bill): Cannot free this pointer but it is valid
		return .None
	}

	if len(s.leaked_allocations) != 0 {
		for data, i in s.leaked_allocations {
			ptr := raw_data(data)
			if ptr == old_memory {
				free(ptr, s.backup_allocator)
				ordered_remove(&s.leaked_allocations, i)
				return .None
			}
		}
	}
	return .Invalid_Pointer
	// panic("invalid pointer passed to default_temp_allocator");
}

@(private)
default_temp_allocator_free_all :: proc(s: ^Default_Temp_Allocator, loc := #caller_location) {
	s.curr_offset = 0
	s.prev_allocation = nil
	for data in s.leaked_allocations {
		free(raw_data(data), s.backup_allocator)
	}
	clear(&s.leaked_allocations)
}

@(private)
default_temp_allocator_resize :: proc(s: ^Default_Temp_Allocator, old_memory: rawptr, old_size, size, alignment: int, loc := #caller_location) -> ([]byte, Allocator_Error) {
	begin := uintptr(raw_data(s.data))
	end := begin + uintptr(len(s.data))
	old_ptr := uintptr(old_memory)
	if old_memory == s.prev_allocation && old_ptr & uintptr(alignment)-1 == 0 {
		if old_ptr+uintptr(size) < end {
			s.curr_offset = int(old_ptr-begin)+size
			return byte_slice(old_memory, size), .None
		}
	}
	data, err := default_temp_allocator_alloc(s, size, alignment, loc)
	if err == .None {
		copy(data, byte_slice(old_memory, old_size))
		err = default_temp_allocator_free(s, old_memory, loc)
	}
	return data, err
}

default_temp_allocator_proc :: proc(allocator_data: rawptr, mode: Allocator_Mode,
                                    size, alignment: int,
                                    old_memory: rawptr, old_size: int, loc := #caller_location) -> (data: []byte, err: Allocator_Error) {

	s := (^Default_Temp_Allocator)(allocator_data)

	if s.data == nil {
		default_temp_allocator_init(s, DEFAULT_TEMP_ALLOCATOR_BACKING_SIZE, default_allocator())
	}

	switch mode {
	case .Alloc:
		data, err = default_temp_allocator_alloc(s, size, alignment, loc)
	case .Free:
		err = default_temp_allocator_free(s, old_memory, loc)

	case .Free_All:
		default_temp_allocator_free_all(s, loc)

	case .Resize:
		data, err = default_temp_allocator_resize(s, old_memory, old_size, size, alignment, loc)

	case .Query_Features:
		set := (^Allocator_Mode_Set)(old_memory)
		if set != nil {
			set^ = {.Alloc, .Free, .Free_All, .Resize, .Query_Features}
		}

	case .Query_Info:
		// Nothing to give
	}

	return
}

default_temp_allocator :: proc(allocator: ^Default_Temp_Allocator) -> Allocator {
	return Allocator{
		procedure = default_temp_allocator_proc,
		data = allocator,
	}
}
