CollectionViewBinder.swift

import UIKit
import Foundation
import ReactiveCocoa
import Result
import Dwifft

/**
 Encapsulates information about collection view nib/cell registration.

 - Nib:   UINib.
 - Class: UICollectionViewCell class.
 */
private enum RegisteredType {
    case Nib(UINib)
    case Class(AnyClass)
}

/// CollectionViewBinder is a ReactiveCocoa helper class for simplifying using `UICollectionView`s with ReactiveCocoa.
/// Using the binder lets the view configuration for collection view cells move to the view and out of the view controller.
final class CollectionViewBinder<T: Equatable>: NSObject, UICollectionViewDataSource, UICollectionViewDelegate {

        /// `UICollectionViewDelegate` object.
    weak var delegate: UICollectionViewDelegate? {
        get { return self.collectionView?.delegate }
        set { self.collectionView?.delegate = newValue }
    }

        /// `CollectionBinderDataSource` object.
    weak var dataSource: CollectionBinderDataSource? {
        willSet {
            if let _ = newValue {
                reloadData()
            }
        }
    }

        /// `UICollectionView` associated with the binder.
    private(set) weak var collectionView: UICollectionView?

        /// Signal that emits the data
    private var dataSignal: SignalProducer<[[T]], NoError>
        /// Signal that emits the supplementary data
    private var supplementarySignal: SignalProducer<[String: [T]], NoError>?

        /// Mutable data property
    private let data = MutableProperty<[[T]]>([])
        /// Mutable supplementary data property
    private let supplementaryData: MutableProperty<[String: [T]]> = MutableProperty<[String: [T]]>([:])


    // MARK: - Registration Information

        /// All the cells registered with the binder.
    private var cells: [String: RegisteredType] = [:]
        /// All the supplementary views registered with the binder.
    private var supplementaries: [String: (String, RegisteredType)] = [:]
        /// All the decoration views registered with the binder.z
    private var decorations: [String: RegisteredType] = [:]

    /**
     Create a binding helper.

     - parameter collectionView:      Collection view object to bind data to.
     - parameter dataSignal:          SignalProducer that emits changes to the underlying data.
     - parameter supplementarySignal: SignalProducer that emits changes to the data the represents headers, footers, etc.
     */
    init(collectionView: UICollectionView, dataSignal: SignalProducer<[[T]], NoError>, supplementarySignal: SignalProducer<[String: [T]], NoError>?) {
        self.collectionView = collectionView
        self.dataSignal = dataSignal
        self.supplementarySignal = supplementarySignal

        super.init()
        self.data <~ self.dataSignal
        self.supplementaryData <~ self.supplementarySignal ?? SignalProducer.empty
        self.collectionView?.dataSource = self

        self.data.producer.on(next: { print($0.count) }).on(next: { _ in self.reloadData() }).takeUntil(self.willDeallocSignal()).start()
    } 

    // MARK: - UICollectionViewDataSource

    func numberOfSectionsInCollectionView(collectionView: UICollectionView) -> Int {
        guard let _ = self.dataSource where !self.cells.isEmpty else {
            return 0
        }
        return self.data.value.count
    }


    func collectionView(collectionView: UICollectionView, numberOfItemsInSection section: Int) -> Int {
        guard let _ = self.dataSource where !self.cells.isEmpty && section < self.data.value.count else {
            return 0
        }
        return self.data.value[section].count
    }

    func collectionView(collectionView: UICollectionView, cellForItemAtIndexPath indexPath: NSIndexPath) -> UICollectionViewCell {
        guard let dataSource = self.dataSource else {
            return UICollectionViewCell()
        }
        let model = self.data.value[indexPath.section][indexPath.item]
        if let reuseIdentifier = dataSource.collectionView(collectionView, reuseIdentifierForItemAtIndexPath: indexPath) {
            let cell = collectionView.dequeueReusableCellWithReuseIdentifier(reuseIdentifier, forIndexPath: indexPath)
            if cell is ReactiveView {
                (cell as! ReactiveView).bindViewModel(model)
            }
            return cell
        }
        return UICollectionViewCell()
    }

    func collectionView(collectionView: UICollectionView, viewForSupplementaryElementOfKind kind: String, atIndexPath indexPath: NSIndexPath) -> UICollectionReusableView {

        if let model = self.supplementaryData.value[kind]?[indexPath.section],
            reuseIdentifier = self.dataSource?.collectionView(collectionView, reuseIdentifierForSupplementaryViewOfKind: kind, atIndexPath: indexPath) {
            let view = collectionView.dequeueReusableSupplementaryViewOfKind(kind, withReuseIdentifier: reuseIdentifier, forIndexPath: indexPath)
            if view is ReactiveView {
                (view as! ReactiveView).bindViewModel(model)
            }
            return view
        }
        return UICollectionReusableView()
    }
}

// MARK: - Registering Views
extension CollectionViewBinder {

    /**
     Register a nib for a cell reuse identifier.

     - parameter nib:        Nib object.
     - parameter identifier: Reuse identifier to register the specified nib with.
     */
    func registerNib(nib: UINib, forCellReuseIdentifier identifier: String) {
        self.cells[identifier] = .Nib(nib)
        self.collectionView?.registerNib(nib, forCellWithReuseIdentifier: identifier)
    }

    /**
     Register a class for a cell reuse identifier.

     - parameter aClass:     Class object.
     - parameter identifier: Reuse identifier to register the specified class with.
     */
    func registerClass(aClass: AnyClass, forCellReuseIdentifier identifier: String) {
        self.cells[identifier] = .Class(aClass)
        self.collectionView?.registerClass(aClass, forCellWithReuseIdentifier: identifier)
    }

    /**
     Register a nib for a supplementary reuse identifier.

     - parameter nib:        Nib object.
     - parameter kind:       Supplementary element kind.
     - parameter identifier: Reuse identifier to register the specified nib with.
     */
    func registerNib(nib: UINib, forSupplementaryViewOfKind kind: String, withReuseIdentifier identifier: String) {
        self.supplementaries[kind] = (identifier, .Nib(nib))
        self.collectionView?.registerNib(nib, forSupplementaryViewOfKind: kind, withReuseIdentifier: identifier)
    }

    /**
     Register a class for a supplementary reuse identifier.

     - parameter aClass:     Class object.
     - parameter kind:       Supplementary element kind.
     - parameter identifier: Reuse identifier to register the specified class with.
     */
    func registerClass(aClass: AnyClass, forSupplementaryViewOfKind kind: String, withReuseIdentifier identifier: String) {
        self.supplementaries[kind] = (identifier, .Class(aClass))
        self.collectionView?.registerClass(aClass, forSupplementaryViewOfKind: kind, withReuseIdentifier: identifier)
    }

    /**
     Register a nib for a decoration kind.

     - parameter nib:         Nib object.
     - parameter elementKind: Decoration identifier.
     */
    func registerNib(nib: UINib, forDecorationViewOfKind elementKind: String) {
        self.decorations[elementKind] = .Nib(nib)
        self.collectionView?.collectionViewLayout.registerNib(nib, forDecorationViewOfKind: elementKind)
    }

    /**
     Register a class for a decoration kind.

     - parameter aClass:      Class object.
     - parameter elementKind: Decoration identifier.
     */
    func registerClass(aClass: AnyClass, forDecorationViewOfKind elementKind: String) {
        self.decorations[elementKind] = .Class(aClass)
        self.collectionView?.collectionViewLayout.registerClass(aClass, forDecorationViewOfKind: elementKind)
    }

}

// MARK: - Reloading
extension CollectionViewBinder {
    /**
     Reload the binder.
     */
    func reloadData() {
        dispatch_async(dispatch_get_main_queue(), { [weak self] in
            self?.collectionView?.reloadData()
        })
    }

    /**
     Reload the specified sections.

     - parameter indexes: Index set of sections to reload.
     */
    func reloadSections(indexes: NSIndexSet) {
        dispatch_async(dispatch_get_main_queue(), { [weak self] in
            self?.collectionView?.reloadSections(indexes)
        })
    }

    /**
     Reload all the items at the specified index paths.

     - parameter indexPaths: List of index paths to reload.
     */
    func reloadItemsAtIndexPaths(indexPaths: [NSIndexPath]) {
        dispatch_async(dispatch_get_main_queue(), { [weak self] in
            self?.collectionView?.reloadItemsAtIndexPaths(indexPaths)
        })
    }

    /**
     Reload the input views.
     */
    func reloadInputViews() {
        dispatch_async(dispatch_get_main_queue(), { [weak self] in
            self?.collectionView?.reloadInputViews()
        })
    }
}