Gemini/BrowserCore/NavigationManager.swift

//
//  NavigationManager.swift
//  Gemini
//
//  Created by Shadowfacts on 7/14/20.
//

import Foundation
import Combine

public protocol NavigationManagerDelegate: AnyObject {
    func loadNonGeminiURL(_ url: URL)
}

public class NavigationManager: NSObject, ObservableObject, Codable {
    
    public weak var delegate: NavigationManagerDelegate?
    
    @Published public var currentURL: URL
    @Published public var backStack = [HistoryEntry]()
    @Published public var forwardStack = [HistoryEntry]()
    
    public let navigationOperation = PassthroughSubject<Operation, Never>()
    
    public var displayURL: String {
        var components = URLComponents(url: currentURL, resolvingAgainstBaseURL: false)!
        if components.port == 1965 {
            components.port = nil
        }
        return components.string!
    }
    
    private var currentHistoryEntry: HistoryEntry
    
    public init(url: URL) {
        self.currentURL = url
        self.currentHistoryEntry = HistoryEntry(url: url, title: nil)
    }
    
    public required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        self.currentHistoryEntry = try container.decode(HistoryEntry.self, forKey: .currentHistoryEntry)
        self.currentURL = self.currentHistoryEntry.url
        self.backStack = try container.decode([HistoryEntry].self, forKey: .backStack)
        self.forwardStack = try container.decode([HistoryEntry].self, forKey: .forwardStack)
    }
    
    public func encode(to encoder: Encoder) throws {
        var container = encoder.container(keyedBy: CodingKeys.self)
        try container.encode(currentHistoryEntry, forKey: .currentHistoryEntry)
        try container.encode(backStack, forKey: .backStack)
        try container.encode(forwardStack, forKey: .forwardStack)
    }
    
    public func setTitleForCurrentURL(_ title: String?) {
        currentHistoryEntry.title = title
    }
    
    public func changeURL(_ url: URL) {
        var components = URLComponents(url: url, resolvingAgainstBaseURL: false)!
        if let scheme = url.scheme {
            if scheme != "gemini" {
                delegate?.loadNonGeminiURL(url)
                return
            }
        } else {
            components.scheme = "gemini"
        }
        
        // Foundation parses bare hosts (e.g. `example.com`) as having no host and a path of `example.com`
        if components.host == nil {
            components.host = components.path
            components.path = "/"
        }
        
        // Some Gemini servers break on empty paths
        if components.path.isEmpty {
            components.path = "/"
        }
        
        let url = components.url!
        
        backStack.append(currentHistoryEntry)
        currentURL = url
        currentHistoryEntry = HistoryEntry(url: url, title: nil)
        forwardStack = []
        
        navigationOperation.send(.go)
    }
    
    @objc public func reload() {
        let url = currentURL
        currentURL = url
        navigationOperation.send(.reload)
    }
    
    @objc public func goBack() {
        back(count: 1)
    }
    
    public func back(count: Int) {
        guard count <= backStack.count else { return }
        var removed = backStack.suffix(count)
        backStack.removeLast(count)
        forwardStack.insert(currentHistoryEntry, at: 0)
        currentHistoryEntry = removed.removeFirst()
        currentURL = currentHistoryEntry.url
        forwardStack.insert(contentsOf: removed, at: 0)
        
        navigationOperation.send(.backward(count: count))
    }
    
    @objc public func goForward() {
        forward(count: 1)
    }
    
    public func forward(count: Int) {
        guard count <= forwardStack.count else { return }
        var removed = forwardStack.prefix(count)
        forwardStack.removeFirst(count)
        backStack.append(currentHistoryEntry)
        currentHistoryEntry = removed.removeLast()
        currentURL = currentHistoryEntry.url
        backStack.append(contentsOf: removed)
        
        navigationOperation.send(.forward(count: count))
    }
    
}

extension NavigationManager {
    enum CodingKeys: String, CodingKey {
        case currentHistoryEntry
        case backStack
        case forwardStack
    }
}

public extension NavigationManager {
    enum Operation {
        case go, reload, forward(count: Int), backward(count: Int)
    }
}

public extension NavigationManager {
    struct HistoryEntry: Codable {
        public let url: URL
        public internal(set) var title: String?
    }
}