//
//  GifListPresenter.swift

import Foundation


/*!
    GifListPresenters delegate
 */
protocol GifListPresenterDelegate: AnyObject {
    
    /// Called before making a call on an empty data
    func presenterWillStartLoadingForEmptyData()
    
    /// Called when inital data is loaded
    func presenterDidReceiveInitialData()
    
    /// Called when next page is loaded
    func presenterDidReceiveAdditionalData(at indexPaths: [IndexPath])

    
}

/*!
    Presenter that loads the trending page,
    if a search keyword is present, it uses that keyword to
    search the Giphy library
 */
class GifListPresenter {
    
    weak var delegate: GifListPresenterDelegate?

    /*!
        Last searched term
        On search term change, reset the pagination
     */
    private var lastSearchedTerm: String = "" {
        willSet {
            if newValue != lastSearchedTerm {
                pagination = GifListPagination()
            }
        }
    }
    
    /*!
        Last pagination object
     */
    private var pagination: GifListPagination = GifListPagination()
    
    /*!
        Array of objects to be shown
     */
    var gifsList: [GifObject] = []
    
    /*!
        Only one pagination request should be active
     */
    var isLoadingNewPage = false
    
    /*!
        If a search query is present, search data is fetched.
        If there is no search query, trending data is fetched.
     */
    func getData(query: String) {
        
        self.lastSearchedTerm = query
        
        if lastSearchedTerm.isEmpty {
            self.fetchTrendingData()
        } else {
            self.fetchSearchData(query: query)
        }
        
    }
    
    /// Trending data call
    private func fetchTrendingData() {
        
        self.prepareForFetch()
        
        GiphyApiManager.shared.getTrendingGifs(offset: pagination.nextOffset) { [weak self] result in
            
            switch result {
                
            case .success(let listResponse):
                self?.didReceiveSuccessfulListResponse(listResponse: listResponse)
                
            case .failure(let error):
                print(error)
            }
            
            self?.isLoadingNewPage = false

        }
        
    }
    
    /// Search data called
    private func fetchSearchData(query: String) {
        
        self.prepareForFetch()

        GiphyApiManager.shared.getSearchGifs(offset: pagination.nextOffset, query: query) { [weak self] result in
            
            switch result {
                
            case .success(let listResponse):
                self?.didReceiveSuccessfulListResponse(listResponse: listResponse)

            case .failure(let error):
                print(error)
            }

            self?.isLoadingNewPage = false
        }
        
    }
    
    /// Prepares self before making a call
    private func prepareForFetch() {
        

        if self.gifsList.count == 0 {
            self.delegate?.presenterWillStartLoadingForEmptyData()
        }

        GiphyApiManager.shared.cancelLastSearchableTask()
        
        if pagination.count + pagination.offset != 0 {
            isLoadingNewPage = true
        }

    }

    private func didReceiveSuccessfulListResponse(listResponse: GiphyListResponse) {
        
        let offset = listResponse.pagination.offset
        
        if (offset == 0) {
            self.gifsList = listResponse.data
            self.delegate?.presenterDidReceiveInitialData()
        } else {
            let indexPaths = (offset..<(offset + listResponse.data.count)).map({IndexPath(row: $0, section: 0)})
            self.gifsList += listResponse.data
            self.delegate?.presenterDidReceiveAdditionalData(at: indexPaths)
        }
        
        self.pagination = listResponse.pagination
        
    }

    
}