//
//  ContentViewController.swift
//  TagTunes
//
//  Created by Kim Wittenburg on 21.01.16.
//  Copyright © 2016 Kim Wittenburg. All rights reserved.
//

import Cocoa
import SearchAPI

/// A `ContentViewController` displays a set of `TagTunesItem`s. It is
/// responsible for allowing the user to associate `TagTunesTrack`s with
/// `TagTunesEntityItem`s.
///
/// The expected structure of the content view controller is a tree structure in
/// the following form:
///
/// 1. At the root level there are `TagTunesGroupItem`s (groups) and
///    `TagTunesEntityItem`s (entities).
/// 2. Groups can contain other entities (children).
/// 3. Entities can have tracks associated with them. A track should not be
///    associated with multiple entities.
public class ContentViewController: NSViewController {

    override public func viewDidLoad() {
        super.viewDidLoad()
        
        NSNotificationCenter.defaultCenter().addObserver(self, selector: #selector(ContentViewController.itemDidChangeState(_:)), name: TagTunesGroupItem.StateChangedNotificationName, object: nil)
    }
    
    /// Called when the `TagTunesGroupItem.StateChangedNotification` is posted.
    private dynamic func itemDidChangeState(notification: NSNotification) {
        if let item = notification.object as? TagTunesItem {
            updateItem(item)
        }
    }
    
    deinit {
        NSNotificationCenter.defaultCenter().removeObserver(self)
    }

    /// Returns all selected items. This property should remove duplicate items
    /// from the selection following these three rules:
    ///
    /// 1. If an entity is selected (and thus contained in the returned array)
    ///    none of its `associatedTracks` should be contained in the returned
    ///    array.
    /// 2. If a group is selected none of its children should be contained in the
    ///    returned array.
    /// 3. If a track is selected and (1) and (2) do not appy it should be
    ///    contained in the returned array.
    ///
    /// This value is not cached. If you need to access this multiple times in a
    /// row, you should consider caching it yourself in a local variable. The
    /// order in which the selected objects occur in the returned array may be
    /// different from the order in which they are displayed.
    ///
    /// This method must be implemented by subclasses.
    public var selectedItems: [AnyObject] {
        fatalError("Must override property selectedItems")
    }

    /// Returns the item the user clicked on. This property should be used
    /// instead of the `selectedItems` for any context menu related actions. This
    /// property should behave the same way that `selectedItems` does.
    ///
    /// This method must be implemented by subclasses.
    public var clickedItems: [AnyObject] {
        fatalError("Must override property clickedItem")
    }

    /// Returns the item that represents the specified `entity`. If no such item
    /// exists in the content view controller `nil` is returned.
    ///
    /// This method must be implemented by subclasses.
    public func itemForEntity(entity: SearchAPIEntity) -> TagTunesItem? {
        fatalError("Must override itemForEntity(_:)")
    }

    /// Adds the specified `item` to the view controller. This should insert the
    /// `item` at the root level of the controller. If the controller already
    /// contains an item that represents the same entity as the specified `item`
    /// this method should do nothing.
    ///
    /// This method must be implemented by subclasses.
    public func addItem(item: TagTunesItem) {
        fatalError("Must override addItem(_:)")
    }
    
    /// Updates the specified `item`. This method should be called if the
    /// properties of the `item` changed in any way and the view should be
    /// notified about it. If the `item` has not previously been added to the
    /// view controller this method should do nothing.
    ///
    /// This method must be implemented by subclasses.
    public func updateItem(item: TagTunesItem) {
        fatalError("Must override updateItem(_:)")
    }
    
    /// Updates all items. If many items in the view controller changed it may be
    /// more efficient to use this method instead of `updateItem(_:)`.
    ///
    /// This method must be implemented by subclasses.
    public func updateAllItems() {
        fatalError("Must override updateAllItems()")
    }

    /// Removes the selected items from the view controller. By default the
    /// implementation just calls `removeItems(selectedItems` but subclasses may
    /// override this method to optimize the behavior.
    public func removeSelectedItems() {
        removeItems(selectedItems)
    }
    
    /// Removes the specified items from the view controller and updates the view
    /// accordingly.
    ///
    /// This method must be implemented by subclasses.
    public func removeItems(items: [AnyObject]) {
        fatalError("Must override removeItems(_:)")
    }
    
}