import Foundation
import Postbox
import SwiftSignalKit

private final class ManagedMessageHistoryHolesState {
    private var holeDisposables: [MessageHistoryHolesViewEntry: Disposable] = [:]
    
    func clearDisposables() -> [Disposable] {
        let disposables = Array(self.holeDisposables.values)
        self.holeDisposables.removeAll()
        return disposables
    }
    
    func update(entries: Set<MessageHistoryHolesViewEntry>) -> (removed: [Disposable], added: [MessageHistoryHolesViewEntry: MetaDisposable]) {
        var removed: [Disposable] = []
        var added: [MessageHistoryHolesViewEntry: MetaDisposable] = [:]
        
        for (entry, disposable) in self.holeDisposables {
            if !entries.contains(entry) {
                removed.append(disposable)
                self.holeDisposables.removeValue(forKey: entry)
            }
        }
        
        for entry in entries {
            if self.holeDisposables[entry] == nil {
                let disposable = MetaDisposable()
                self.holeDisposables[entry] = disposable
                added[entry] = disposable
            }
        }
        
        return (removed, added)
    }
}

func managedMessageHistoryHoles(network: Network, postbox: Postbox) -> Signal<Void, NoError> {
    return Signal { _ in
        let state = Atomic(value: ManagedMessageHistoryHolesState())
        
        let disposable = postbox.messageHistoryHolesView().start(next: { view in
            let (removed, added) = state.with { state -> (removed: [Disposable], added: [MessageHistoryHolesViewEntry: MetaDisposable]) in
                var entries = Set<MessageHistoryHolesViewEntry>()
                for (_, entrySet) in view.entries {
                    for entry in entrySet {
                        entries.insert(entry)
                    }
                }
                return state.update(entries: entries)
            }
            
            for disposable in removed {
                disposable.dispose()
            }
            
            for (entry, disposable) in added {
                disposable.set(fetchMessageHistoryHole(network: network, postbox: postbox, hole: entry.hole, direction: entry.direction, tagMask: entry.tags).start())
            }
        })
        
        return ActionDisposable {
            disposable.dispose()
            for disposable in state.with({ state -> [Disposable] in
                state.clearDisposables()
            }) {
                disposable.dispose()
            }
        }
    }
}