You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: lib.rs
    path of file: ./repos/feather/feather/old/core/inventory/src
    
    the code of the file until where you have to start completion: //! An implementation of inventory handling.
//!
//! # Key types
//! * `Area`: an area in an inventory, e.g. hotbar, storage, crafting
//! * `Inventory`: stores the items inside an inventory, associated
//! with their respective areas
//! * `Window`: handles mapping from protocol inventory indices
//! to internal indices used for `Inventory`.

use feather_items::ItemStack;
use maplit::btreemap;
use parking_lot::{RwLock, RwLockWriteGuard};
use std::collections::BTreeMap;
use std::iter::repeat_with;
use thiserror::Error;

mod window;

use once_cell::sync::Lazy;
use smallvec::{Array, SmallVec};
use std::cmp::min;
pub use window::{constants as player_constants, Error as WindowError, Window, WindowAccessor};

static COLLECT_SEARCH_ORDER: Lazy<Vec<(Area, usize)>> = Lazy::new(|| {
    let mut result = vec![];
    // TODO: move to constants
    for x in 0..9 {
        result.push((Area::Hotbar, x));
    }

    for x in 0..27 {
        result.push((Area::Main, x));
    }

    result
});

/// An area inside an inventory, used to differentiat
    
    pub fn collect_item(&self, mut item: ItemStack) -> (SmallVec<[SlotIndex; 2]>, u8) {
        let mut affected_slots = SmallVec::new();

        // First, look for slots already having the type.
        for (area, slot) in COLLECT_SEARCH_ORDER.iter() {
            if let Some(slot_item) = self.item_at(*area, *slot).expect("index out of bounds") {
                if slot_item.eq_ignore_amount(item) {
                    self.add_to_stack(
                        &mut item,
                        slot_item,
                        SlotIndex {
                            area: *area,
                            slot: *slot,
                        },
                        &mut affected_slots,
                    );

                    if item.amount == 0 {
                        return (affected_slots, 0);
                    }
                }
            }
        }

        for (area, slot) in COLLECT_SEARCH_ORDER.iter() {
            let slot_item = self.item_at(*area, *slot).unwrap();
            if slot_item.is_none() {
                let fake = item.of_amount(0);
                self.add_to_stack(
                    &mut item,
                    fake,
                    SlotIndex {
                        area: *area,
                        slot: *slot,
                    },
                    &mut affected_slots,
                );
                if item.amount == 0 {
                    return (affected_slots, 0);
                }
            }

            if let Some(slot_item) = slot_item {
                if slot_item.eq_ignore_amount(item) {
                    self.add_to_stack(
                        &mut item,
                        slot_item,
                        SlotIndex {
                            area: *area,
                            slot: *slot,
                        },
                        &mut affected_slots,
                    );

                    if item.amount == 0 {
                        return (affected_slots, 0);
                    }
                }
            }
        }

        (affected_slots, item.amount)
    }