//
//  DKImageGroupDataManager.swift
//  DKImagePickerController
//
//  Created by ZhangAo on 15/12/16.
//  Copyright © 2015年 ZhangAo. All rights reserved.
//

import Photos

@objc
protocol DKImageGroupDataManagerObserver {

    @objc optional func groupDidUpdate(groupId: String)
    @objc optional func groupDidRemove(groupId: String)
    @objc optional func group(groupId: String, didRemoveAssets assets: [DKAsset])
    @objc optional func group(groupId: String, didInsertAssets assets: [DKAsset])
    @objc optional func groupDidUpdateComplete(groupId: String)
    @objc optional func groupsDidInsert(groupIds: [String])
}

/*
 Configuration options for a DKImageGroupDataManager. When a manager is created,
 a copy of the configuration object is made - you cannot modify the configuration
 of a manager after it has been created.
 */
@objc
public class DKImageGroupDataManagerConfiguration: NSObject, NSCopying {
    
    /// The types of PHAssetCollection to display in the picker.
    public var assetGroupTypes: [PHAssetCollectionSubtype] = [
        .smartAlbumUserLibrary,
        .smartAlbumVideos,
        .smartAlbumFavorites,
        .albumRegular
    ]
    
    /// A predicate that specifies which properties to select results by and that also specifies any constraints on selection.
    public var groupFetchPredicate: NSPredicate? = nil
    
    /// Options that specify a filter predicate and sort order for the fetched assets, or nil to use default options.
    @objc public var assetFetchOptions: PHFetchOptions?
    
    /// Limits the maximum number of objects displayed on the UI, a value of 0 means no limit.  Defaults to 0.
    @objc public var fetchLimit = 0
    
    public required override init() {
        super.init()
    }
    
    public func copy(with zone: NSZone? = nil) -> Any {
        let copy = type(of: self).init()
        copy.assetGroupTypes = self.assetGroupTypes
        copy.assetFetchOptions = self.assetFetchOptions
        copy.fetchLimit = self.fetchLimit
        copy.groupFetchPredicate = self.groupFetchPredicate
        
        return copy
    }
    
}

/////////////////////////////////////////////////////////////////////////////////////

/*
 Create and manage a collection of DKAssetGroup.
 */
@objc
open class DKImageGroupDataManager: DKImageBaseManager, PHPhotoLibraryChangeObserver {

    public var groupIds: [String]?
    private var groups: [String : DKAssetGroup]?
    private var assets = [String: DKAsset]()
    
    private let configuration: DKImageGroupDataManagerConfiguration
    
    public init(configuration: DKImageGroupDataManagerConfiguration) {
        self.configuration = configuration.copy() as! DKImageGroupDataManagerConfiguration 

        super.init()
    }
    
    deinit {
        PHPhotoLibrary.shared().unregisterChangeObserver(self)
    }

    open func invalidate() {
        self.groupIds?.removeAll()
        self.groups?.removeAll()
        self.assets.removeAll()

        PHPhotoLibrary.shared().unregisterChangeObserver(self)
    }

    open func fetchGroups(_ completeBlock: @escaping (_ groups: [String]?, _ error: NSError?) -> Void) {
        let assetGroupTypes = self.configuration.assetGroupTypes
        
        DispatchQueue.global(qos: .userInteractive).async { [weak self] in
            guard let strongSelf = self else { return }
            
            guard strongSelf.groups == nil else {
                DispatchQueue.main.async {
                    completeBlock(strongSelf.groupIds, nil)
                }
                return
            }
            
            var groups: [String : DKAssetGroup] = [:]
            var groupIds: [String] = []
            
            strongSelf.fetchGroups(assetGroupTypes: assetGroupTypes,
                                   groupFetchPredicate: self?.configuration.groupFetchPredicate,
                                   block: { (collection) in
                                    let assetGroup = strongSelf.makeDKAssetGroup(with: collection)
                                    groups[assetGroup.groupId] = assetGroup
                                    groupIds.append(assetGroup.groupId)
                                    
                                    // Filter the reloads to avoid frequetly reloadData() calling in collectionView
                                    if !groupIds.isEmpty && collection.assetCollectionSubtype == .smartAlbumUserLibrary {
                                        strongSelf.updatePartial(groups: groups, groupIds: groupIds, completeBlock: completeBlock)
                                    }
            })
            PHPhotoLibrary.shared().register(strongSelf)
            if !groupIds.isEmpty {
                strongSelf.updatePartial(groups: groups, groupIds: groupIds, completeBlock: completeBlock)
            }
        }
    }

    open func fetchGroup(with groupId: String) -> DKAssetGroup? {
        return self.groups?[groupId]
    }

    open func fetchGroupThumbnail(with groupId: String,
                                  size: CGSize,
                                  options: PHImageRequestOptions,
                                  completeBlock: @escaping (_ image: UIImage?, _ info: [AnyHashable: Any]?) -> Void)
    {
        guard let group = self.fetchGroup(with: groupId) else {
            assertionFailure("Expect group")
            completeBlock(nil, nil)
            return
        }
        if group.totalCount == 0 {
            completeBlock(nil, nil)
            return
        }

        guard let lastResult = group.fetchResult?.lastObject else {
            assertionFailure("Expect latestAsset")
            completeBlock(nil, nil)
            return
        }

        let latestAsset = DKAsset(originalAsset: lastResult)
        latestAsset.fetchImage(with: size, options: options, completeBlock: completeBlock)
    }

    open func fetchAsset(_ group: DKAssetGroup, index: Int) -> DKAsset? {
        guard let phAsset = fetchPHAsset(group, index: index) else {
            assertionFailure("Expect phAsset")
            return nil
        }

        if let asset = assets[phAsset.localIdentifier] {
            return asset
        }

        let asset = DKAsset(originalAsset: phAsset)
        assets[phAsset.localIdentifier] = asset
        return asset
    }
    
    open func fetchPHAsset(_ group: DKAssetGroup, index: Int) -> PHAsset? {
        guard let fetchResult = group.fetchResult else {
            assertionFailure("Expect fetchResult")
            return nil
        }
        let idx = fetchResult.count - 1 - index
        guard idx >= 0 && fetchResult.count > idx else {
            assertionFailure("idx out of range:\(idx) fetchResult count:\(fetchResult.count)")
            return nil
        }
        return fetchResult[idx]
    }
    
    open func makeDKAssetGroup(with collection: PHAssetCollection) -> DKAssetGroup {
        let assetGroup = DKAssetGroup(groupId: collection.localIdentifier)

        self.updateGroup(assetGroup, collection: collection)

        let fetchResult = PHAsset.fetchAssets(in: collection,
                                              options: self.configuration.assetFetchOptions)
        self.updateGroup(assetGroup, fetchResult: fetchResult)

        return assetGroup
    }
    
    open func collectionType(for subtype: PHAssetCollectionSubtype) -> PHAssetCollectionType {
        return subtype.rawValue < PHAssetCollectionSubtype.smartAlbumGeneric.rawValue ? .album : .smartAlbum
    }
    
    open func fetchGroups(assetGroupTypes: [PHAssetCollectionSubtype],
                          groupFetchPredicate: NSPredicate? = nil,
                          block: @escaping (PHAssetCollection) -> Void) {
        for (_, groupType) in assetGroupTypes.enumerated() {
            let fetchResult = PHAssetCollection.fetchAssetCollections(with: self.collectionType(for: groupType),
                                                                      subtype: groupType,
                                                                      options: nil)
            fetchResult.enumerateObjects({ (collection, index, stop) in
                if let groupFetchPredicate = groupFetchPredicate {
                    if groupFetchPredicate.evaluate(with: collection) {
                        block(collection)
                    }
                } else {
                    block(collection)
                }
            })
        }
    }
    
    open func updatePartial(groups: [String : DKAssetGroup],
                            groupIds: [String],
                            completeBlock: @escaping (_ groups: [String]?, _ error: NSError?) -> Void) {
        self.groups = groups
        self.groupIds = groupIds
        DispatchQueue.main.async {
            completeBlock(groupIds, nil)
        }
    }

    open func updateGroup(_ group: DKAssetGroup, collection: PHAssetCollection) {
        group.groupName = collection.localizedTitle
        group.originalCollection = collection
    }

    open func updateGroup(_ group: DKAssetGroup, fetchResult: PHFetchResult<PHAsset>) {
        group.fetchResult = fetchResult
        group.displayCount = self.configuration.fetchLimit
    }

    // MARK: - PHPhotoLibraryChangeObserver methods

    open func photoLibraryDidChange(_ changeInstance: PHChange) {
        guard let groups = self.groups?.values else { return  }
        
        for group in groups {
            if let originalCollection = group.originalCollection,
                let changeDetails = changeInstance.changeDetails(for: originalCollection)
            {
                if changeDetails.objectWasDeleted {
                    self.groups?[group.groupId] = nil
                    notify(with: #selector(DKImageGroupDataManagerObserver.groupDidRemove(groupId:)),
                           object: group.groupId as AnyObject?)
                    continue
                }

                if let objectAfterChanges = changeDetails.objectAfterChanges {
                    if let groups = self.groups, let group = groups[group.groupId] {
                        updateGroup(group, collection: objectAfterChanges)
                    } else {
                        assertionFailure("Expect group with id:\(group.groupId)")
                    }
                    notify(with: #selector(DKImageGroupDataManagerObserver.groupDidUpdate(groupId:)),
                           object: group.groupId as AnyObject?)
                }
            }

            if let fetchResult = group.fetchResult, let changeDetails = changeInstance.changeDetails(for: fetchResult) {
                let removedAssets = changeDetails.removedObjects.map{ DKAsset(originalAsset: $0) }
                if removedAssets.count > 0 {
                    self.notify(with: #selector(DKImageGroupDataManagerObserver.group(groupId:didRemoveAssets:)),
                                object: group.groupId as AnyObject?,
                                objectTwo: removedAssets as AnyObject?)
                }
                self.updateGroup(group, fetchResult: changeDetails.fetchResultAfterChanges)

                let insertedAssets = changeDetails.insertedObjects.map{ DKAsset(originalAsset: $0) }
                if insertedAssets.count > 0  {
                    self.notify(with: #selector(DKImageGroupDataManagerObserver.group(groupId:didInsertAssets:)),
                                object: group.groupId as AnyObject?,
                                objectTwo: insertedAssets as AnyObject?)
                }
                
                self.notify(with: #selector(DKImageGroupDataManagerObserver.groupDidUpdateComplete(groupId:)),
                            object: group.groupId as AnyObject?)
            }
        }
        
        let assetGroupTypes = self.configuration.assetGroupTypes
        var insertedGroupIds: [String] = []
        
        self.fetchGroups(assetGroupTypes: assetGroupTypes, groupFetchPredicate: self.configuration.groupFetchPredicate) { [weak self] collection in
            if let groups = self?.groups,
                groups[collection.localIdentifier] == nil,
                let assetGroup = self?.makeDKAssetGroup(with: collection)
            {
                self?.groups?[assetGroup.groupId] = assetGroup
                self?.groupIds?.append(assetGroup.groupId)
                
                insertedGroupIds.append(assetGroup.groupId)
            }
        }
        
        if (insertedGroupIds.count > 0) {
            self.notify(with: #selector(DKImageGroupDataManagerObserver.groupsDidInsert(groupIds:)),
                        object: insertedGroupIds as AnyObject)
        }
    }
}