package xarr

import "base:builtin"
import "base:intrinsics"

BASE_CHUNK_SIZE :: uint(64)
BASE_CHUNK_SIZE_LOG2 :: intrinsics.constant_log2(BASE_CHUNK_SIZE)
BASE_CHUNK_SHIFT :: BASE_CHUNK_SIZE_LOG2 - 1
NUM_CHUNKS :: 30

Xarr :: struct($T: typeid, $SOA := false) {
	chunks:                ([NUM_CHUNKS]#soa[]T when SOA else [NUM_CHUNKS][^]T),
	len:                   int,
	allocated_chunks_mask: u32,
}

UINT_BITS :: size_of(uint) * 8

msb :: #force_inline proc "contextless" (#any_int idx: uint) -> i8 {
	return i8(UINT_BITS - intrinsics.count_leading_zeros(idx)) - 1
}

chunk_by_index :: #force_inline proc "contextless" (#any_int idx: uint) -> (chunk: i8) {
	return max(msb(idx) - BASE_CHUNK_SHIFT, 0)
}

chunk_size :: #force_inline proc "contextless" (chunk_idx: i8) -> uint {
	return BASE_CHUNK_SIZE << u32(max(chunk_idx - 1, 0))
}

get_chunk_slice_scalar :: #force_inline proc "contextless" (
	a: $T/Xarr($E, false),
	chunk_idx: i8,
) -> []E {
	return a.chunks[chunk_idx][:chunk_size(chunk_idx)]
}

get_chunk_slice_soa :: #force_inline proc "contextless" (
	a: $T/Xarr($E, true),
	chunk_idx: i8,
) -> #soa[]E {
	return a.chunks[chunk_idx]
}

get_chunk_slice :: proc {
	get_chunk_slice_scalar,
	get_chunk_slice_soa,
}

capacity_from_allocated_mask :: #force_inline proc(allocated_mask: uint) -> uint {
	return(
		(allocated_mask >> 1) << BASE_CHUNK_SIZE_LOG2 +
		(allocated_mask & 1) << BASE_CHUNK_SIZE_LOG2 \
	)
}

capacity :: #force_inline proc(a: $T/Xarr($E, $SOA)) -> u32 {
	allocated_mask := a.allocated_chunks_mask
	return capacity_from_allocated_mask(allocated_mask)
}

reserve :: proc(a: $T/^Xarr($E, $SOA), cap: int, allocator := context.allocator) {
	allocated_mask := a.allocated_chunks_mask

	current_chunk := msb(allocated_mask)
	required_chunks := chunk_by_index(max(cap - 1, 0)) + 1

	for i := current_chunk + 1; i < required_chunks; i += 1 {
		when SOA {
			chunk_slice := make_soa_slice(#soa[]E, chunk_size(i), allocator)
			a.chunks[i] = chunk_slice
		} else {
			chunk_slice := make([]E, chunk_size(i), allocator)
			a.chunks[i] = raw_data(chunk_slice)
		}
		a.allocated_chunks_mask |= u32(1) << u8(i)
	}
}

append :: proc(a: $T/^Xarr($E, $SOA), elems: ..E, allocator := context.allocator) {
	if len(elems) == 0 {
		return
	}

	reserve(a, a.len + len(elems))
	set_elems_assume_allocated(a, elems)
	a.len += len(elems)
}

translate_index :: #force_inline proc(
	#any_int idx: int,
) -> (
	chunk_idx: i8,
	idx_within_chunk: uint,
) {
	assert(idx >= 0)

	chunk_idx = chunk_by_index(idx)
	idx_within_chunk = uint(idx) & (chunk_size(chunk_idx) - 1)

	return
}

@(private = "file")
set_elems_assume_allocated :: proc(a: $T/^Xarr($E, $SOA), elems: []E) {
	for &e, i in elems {
		idx := a.len + i
		chunk_idx, idx_within_chunk := translate_index(idx)
		assert(a.chunks[chunk_idx] != nil)

		a.chunks[chunk_idx][idx_within_chunk] = e
	}
}

set :: proc(a: $T/Xarr($E, $SOA), #any_int idx: int, val: E) {
	assert(idx >= 0 && idx < a.len)
	chunk_idx, idx_within_chunk := translate_index(idx)
	return get_chunk_slice(a, chunk_idx)[idx_within_chunk]
}

get :: proc(a: $T/Xarr($E, $SOA), #any_int idx: int) -> E {
	assert(idx >= 0 && idx < a.len)

	chunk_idx, idx_within_chunk := translate_index(idx)
	return get_chunk_slice(a, chunk_idx)[idx_within_chunk]
}

get_ptr :: proc(a: $T/Xarr($E, $SOA), #any_int idx: int) -> ^E {
	assert(idx >= 0 && idx < a.len)

	chunk_idx, idx_within_chunk := translate_index(idx)
	return &get_chunk_slice(a, chunk_idx)[idx_within_chunk]
}

unordered_remove :: proc(a: $T/^Xarr($E, $SOA), #any_int idx: int) {
	assert(idx >= 0 && idx < a.len)

	get_ptr(a^, idx)^ = get(a^, a.len - 1)
	a.len -= 1
}

clear :: proc "contextless" (a: $T/^Xarr($E, $SOA)) {
	a.len = 0
}

delete :: proc(a: $T/^Xarr($E, $SOA), allocator := context.allocator) {
	for i in 0 ..< len(a.chunks) {
		builtin.delete(get_chunk_slice(a^, i8(i)), allocator)
	}

	a^ = Xarr(E, SOA){}
}

Iterator :: struct($E: typeid, $SOA: bool) {
	xarr: ^Xarr(E, SOA),
	idx:  int,
}

iterator :: proc(a: $T/^Xarr($E, $SOA), start_idx := 0) -> Iterator(E, SOA) {
	return Iterator(E, SOA){xarr = a, idx = start_idx}
}

iterator_next :: proc(it: ^Iterator($E, $SOA)) -> (e: ^E, idx: int, ok: bool) {
	if it.idx >= it.xarr.len {
		return nil, it.idx, false
	}

	e = get_ptr(it.xarr^, it.idx)
	idx = it.idx
	ok = true

	it.idx += 1
	return
}