//
//  Copyright (c) 2018 Touch Instinct
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import RxSwift
import RxCocoa

/// Class that maps data model field to String and vise-versa.
public final class DataModelFieldBinding<T> {

    public typealias GetFieldClosure = (T) -> String?
    public typealias MergeFieldClosure = (T, String?) -> T

    private let modelRelay: BehaviorRelay<T>
    private let modelDriver: Driver<T>
    private let getFieldClosure: DataModelFieldBinding<T>.GetFieldClosure
    private let mergeFieldClosure: DataModelFieldBinding<T>.MergeFieldClosure

    /// Memberwise initializer.
    ///
    /// - Parameters:
    ///   - modelRelay: BehaviourRelay that contains data model.
    ///   - modelDriver: Driver that emits new data models.
    ///   - getFieldClosure: Closure for getting field string reprerentation from data model.
    ///   - mergeFieldClosure: Closure for merging new field value into data model.
    public init(modelRelay: BehaviorRelay<T>,
                modelDriver: Driver<T>,
                getFieldClosure: @escaping GetFieldClosure,
                mergeFieldClosure: @escaping MergeFieldClosure) {

        self.modelRelay = modelRelay
        self.modelDriver = modelDriver
        self.getFieldClosure = getFieldClosure
        self.mergeFieldClosure = mergeFieldClosure
    }

    /// Method that merges new field values with data model.
    ///
    /// - Parameter textDriver: Driver that emits new text values.
    /// - Returns: Disposable object that can be used to unsubscribe the observer from the behaviour relay.
    public func mergeStringToModel(from textDriver: Driver<String?>) -> Disposable {
        return textDriver.map { [modelRelay, mergeFieldClosure] in
            mergeFieldClosure(modelRelay.value, $0)
        }
        .drive(modelRelay)
    }

    /// A Driver that will emit current field value.
    public var fieldDriver: Driver<String?> {
        return modelDriver.map(getFieldClosure)
    }

}

public extension DataModelFieldBinding {

    /// Convenience initializer without modelDriver, which will be obtained from modelRelay.
    ///
    /// - Parameters:
    ///   - modelRelay: BehaviourRelay that contains data model.
    ///   - getFieldClosure: Closure for getting field string reprerentation from data model.
    ///   - mergeFieldClosure: Closure for merging new field value into data model.
    convenience init(modelRelay: BehaviorRelay<T>,
                     getFieldClosure: @escaping GetFieldClosure,
                     mergeFieldClosure: @escaping MergeFieldClosure) {

        self.init(modelRelay: modelRelay,
                  modelDriver: modelRelay.asDriver(),
                  getFieldClosure: getFieldClosure,
                  mergeFieldClosure: mergeFieldClosure)
    }

}

public extension DataModelFieldBinding where T == String? {

    /// Convenience initializer for data model of string.
    ///
    /// - Parameter modelRelay: BehaviourRelay that contains data model.
    convenience init(modelRelay: BehaviorRelay<T>) {
        self.init(modelRelay: modelRelay,
                  modelDriver: modelRelay.asDriver(),
                  getFieldClosure: { $0 },
                  mergeFieldClosure: { $1 })
    }

}

public extension BehaviorRelay {

    /// Creates DataModelFieldBinding configured with given closures and behaviour relay itself.
    ///
    /// - Parameters:
    ///   - getFieldClosure: Closure for getting field string reprerentation from data model.
    ///   - mergeFieldClosure: Closure for merging new field value into data model.
    /// - Returns: DataModelFieldBinding instance.
    func fieldBinding(getFieldClosure: @escaping DataModelFieldBinding<E>.GetFieldClosure,
                      mergeFieldClosure: @escaping DataModelFieldBinding<E>.MergeFieldClosure) -> DataModelFieldBinding<E> {

        return DataModelFieldBinding(modelRelay: self,
                                     getFieldClosure: getFieldClosure,
                                     mergeFieldClosure: mergeFieldClosure)
    }

}

public extension BehaviorRelay where Element == String? {

    /// Creates DataModelFieldBinding configured with behaviour relay itself.
    ///
    /// - Returns: DataModelFieldBinding instance.
    func fieldBinding() -> DataModelFieldBinding<E> {
        return DataModelFieldBinding(modelRelay: self)
    }

}