//
//  GenericTableViewDataSource.swift
//  Instant
//
//  Created by Javier Soto on 3/15/16.
//  Copyright © 2016 Fabric. All rights reserved.
//

import UIKit
import ReactiveCocoa
import func FabricAPI.debugAssertMainThread
import enum Result.NoError

final class GenericTableViewDataSource<ObservableTableViewData: PropertyType, SectionType: TableSectionType, RowType: TableRowType where SectionType.AssociatedTableRowType == RowType, SectionType: Equatable, RowType: Equatable>: NSObject, UITableViewDataSource {
    typealias ConfigureRow = (row: RowType, indexPath: NSIndexPath) -> UITableViewCell
    private unowned let tableView: UITableView
    private let tableViewData: ObservableTableViewData
    private let updateAnimations: TableUpdateOperationAnimations?
    private let computeSections: ObservableTableViewData.Value -> [SectionType]
    private let configureRow: ConfigureRow

    private var sectionsMutableProperty = MutableProperty<[SectionType]>([])
    var sections: AnyProperty<[SectionType]>

    private var tableViewUpdatesObserver: Observer<(), NoError>
    var tableViewUpdatesProducer: SignalProducer<(), NoError>

    init(tableView: UITableView, tableViewData: ObservableTableViewData, updateAnimations: TableUpdateOperationAnimations? = TableUpdateOperation.defaultAnimations, computeSections: ObservableTableViewData.Value -> [SectionType], configureRow: ConfigureRow) {
        self.tableView = tableView
        self.tableViewData = tableViewData
        self.updateAnimations = updateAnimations
        self.computeSections = computeSections
        self.configureRow = configureRow

        self.sections = AnyProperty(self.sectionsMutableProperty)

        (self.tableViewUpdatesProducer, self.tableViewUpdatesObserver) = SignalProducer<(), NoError>.buffer(0)

        super.init()

        self.sectionsMutableProperty <~ self.tableViewData.producer
            .map(computeSections)

        self.sectionsMutableProperty.producer
            .combinePrevious([])
            .startWithNext { [unowned self] oldValue, sections in
                debugAssertMainThread()
                
                if let updateAnimations = self.updateAnimations {
                    let operations = TableSectionDataDiffing.tableOperationsToUpdateFromSections(sections: oldValue, toSections: sections)

                    self.tableView.applyTableOperations(operations, withAnimations: updateAnimations) { [weak self] in
                        self?.tableViewUpdatesObserver.sendNext(())
                    }
                }
                else {
                    self.tableView.reloadData()

                    self.tableViewUpdatesObserver.sendNext(())
                }
        }
    }

    func indexPathsOfRowsPassingTest(test: RowType -> Bool) -> [NSIndexPath] {
        return self.sections.value.enumerate().flatMap { sectionIndex, element in
            element.rows
                .enumerate()
                .filter { test($0.element) }
                .map { NSIndexPath(forRow: $0.index, inSection: sectionIndex) }
        }
    }

    func rowAtIndexPath(indexPath: NSIndexPath) -> RowType {
        return self.sections.value[indexPath.section].rows[indexPath.row]
    }

    func tableView(tableView: UITableView, titleForHeaderInSection section: Int) -> String? {
        return self.sections.value[section].title
    }

    func numberOfSectionsInTableView(tableView: UITableView) -> Int {
        return self.sections.value.count
    }

    @objc func tableView(tableView: UITableView, numberOfRowsInSection section: Int) -> Int {
        return self.sections.value[section].rows.count
    }

    @objc func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell {
        return self.configureRow(row: self.rowAtIndexPath(indexPath), indexPath: indexPath)
    }
}