batchApc

fn batchApc(
    apc_context: ?*anyopaque,
    iosb: *windows.IO_STATUS_BLOCK,
    _: windows.ULONG,
) align(apc_align) callconv(.winapi) void {
    const b: *Io.Batch = @ptrCast(@alignCast(apc_context));
    const operation_userdata: *WindowsBatchOperationUserdata = @fieldParentPtr("iosb", iosb);
    const erased_userdata = operation_userdata.toErased();
    const pending: *Io.Operation.Storage.Pending = @fieldParentPtr("userdata", erased_userdata);
    switch (pending.node.prev) {
        .none => b.pending.head = pending.node.next,
        else => |prev_index| b.storage[prev_index.toIndex()].pending.node.next = pending.node.next,
    }
    switch (pending.node.next) {
        .none => b.pending.tail = pending.node.prev,
        else => |next_index| b.storage[next_index.toIndex()].pending.node.prev = pending.node.prev,
    }
    const storage: *Io.Operation.Storage = @fieldParentPtr("pending", pending);
    const index: Io.Operation.OptionalIndex = .fromIndex(storage - b.storage.ptr);
    switch (iosb.u.Status) {
        .CANCELLED => {
            const tail_index = b.unused.tail;
            switch (tail_index) {
                .none => b.unused.head = index,
                else => b.storage[tail_index.toIndex()].unused.next = index,
            }
            storage.* = .{ .unused = .{ .prev = tail_index, .next = .none } };
            b.unused.tail = index;
        },
        else => {
            switch (b.completed.tail) {
                .none => b.completed.head = index,
                else => |tail_index| b.storage[tail_index.toIndex()].completion.node.next = index,
            }
            b.completed.tail = index;
            const result: Io.Operation.Result = switch (pending.tag) {
                .file_read_streaming => .{ .file_read_streaming = ntReadFileResult(iosb) },
                .file_write_streaming => .{ .file_write_streaming = ntWriteFileResult(iosb) },
                .device_io_control => .{ .device_io_control = iosb.* },
                .net_receive => unreachable,
                .net_send => unreachable,
                .net_read => unreachable,
                .net_write => unreachable,
            };
            storage.* = .{ .completion = .{ .node = .{ .next = .none }, .result = result } };
        },
    }
}