Tusker/Tusker/Filterer.swift

//
//  Filterer.swift
//  Tusker
//
//  Created by Shadowfacts on 12/3/22.
//  Copyright © 2022 Shadowfacts. All rights reserved.
//

import Foundation
import Pachyderm
import Combine

class FilterState {
    static var unknown: FilterState { FilterState(state: .unknown) }
    
    private var state: State
    
    var isWarning: Bool {
        switch state {
        case .known(.warn(_)):
            return true
        default:
            return false
        }
    }
    
    private init(state: State) {
        self.state = state
    }
    
    // Use a closure for the status in case the result is cached and we don't need to look it up
    @MainActor
    func resolveFor(status: () -> StatusMO, resolver: Filterer) -> Filterer.Result {
        switch state {
        case .unknown:
            let result = resolver.resolve(status: status())
            state = .known(result)
            return result
        case .known(let result):
            return result
        }
    }
    
    func setResult(_ result: Filterer.Result) {
        self.state = .known(result)
    }
    
    private enum State {
        case unknown
        case known(Filterer.Result)
    }
}

@MainActor
class Filterer {
    let mastodonController: MastodonController
    let context: FilterV1.Context
    
    private let htmlConverter = HTMLConverter()
    private var needsSetupFilters = true
    private var matchers = [(NSRegularExpression, Result)]()
    private var filtersChanged: AnyCancellable?
    private var filterObservers = Set<AnyCancellable>()
    
    init(mastodonController: MastodonController, context: FilterV1.Context) {
        self.mastodonController = mastodonController
        self.context = context
        
        filtersChanged = mastodonController.$filters
            .sink { [unowned self] _ in
                self.needsSetupFilters = true
            }
    }
    
    private func setupFilters(filters: [FilterMO]) {
        print("setting up filters")
        matchers = []
        filterObservers = []
        for filter in filters where filter.contexts.contains(context) {
            guard let matcher = filter.createMatcher() else {
                continue
            }
            matchers.append(matcher)
            
            filter.objectWillChange
                .sink { [unowned self] _ in
                    self.needsSetupFilters = true
                }
                .store(in: &filterObservers)
        }
        needsSetupFilters = false
    }
    
    func resolve(status: StatusMO) -> Result {
        if needsSetupFilters {
            setupFilters(filters: mastodonController.filters)
        }
        if matchers.isEmpty {
            return .allow
        }
        lazy var text = htmlConverter.convert(status.content).string
        for (regex, result) in matchers {
            if (!status.spoilerText.isEmpty && regex.numberOfMatches(in: status.spoilerText, range: NSRange(location: 0, length: status.spoilerText.utf16.count)) > 0)
                || regex.numberOfMatches(in: text, range: NSRange(location: 0, length: text.utf16.count)) > 0 {
                return result
            }
        }
        return .allow
    }
    
    enum Result {
        case allow
        case hide
        case warn(String)
    }
}

private extension FilterMO {
    func createMatcher() -> (NSRegularExpression,  Filterer.Result)? {
        guard keywords.count > 0 else {
            return nil
        }
        
        // TODO: it would be cool to use the Regex builder stuff for this, but it's iOS 16 only
        var pattern = ""
        
        var isFirst = true
        for keyword in keywordMOs {
            if isFirst {
                isFirst = false
            } else {
                pattern += "|"
            }
            pattern += "("
            if keyword.wholeWord {
                pattern += "\\b"
            }
            pattern += NSRegularExpression.escapedPattern(for: keyword.keyword)
            if keyword.wholeWord {
                pattern += "\\b"
            }
            pattern += ")"
        }
        
        guard let regex = try? NSRegularExpression(pattern: pattern, options: [.useUnicodeWordBoundaries, .caseInsensitive]) else {
            return nil
        }
        
        let result: Filterer.Result
        switch filterAction {
        case .hide:
            result = .hide
        case .warn:
            result = .warn(titleOrKeyword)
        }
        
        return (regex, result)
    }
}