//
//  ContentView.swift
//  Gemini
//
//  Created by Shadowfacts on 7/12/20.
//

import SwiftUI
import GeminiFormat
import GeminiRenderer
import GeminiProtocol

public struct BrowserView: View {
    let navigator: NavigationManager
    let scrollingEnabled: Bool
    @State var task: GeminiDataTask?
    @State var state: ViewState = .loading
    
    public init(navigator: NavigationManager, scrollingEnabled: Bool = true) {
        self.navigator = navigator
        self.scrollingEnabled = scrollingEnabled
    }
    
    public var body: some View {
        mainView
            .onReceive(navigator.$currentURL, perform: self.urlChanged)
    }
    
    @ViewBuilder
    private var mainView: some View {
        VStack {
            switch state {
            case .loading:
                Spacer()
                loadingView
                    .onAppear(perform: self.loadDocument)
                Spacer()
            case let .error(message):
                Text("An error occurred")
                    .font(.headline)
                Text(message)
                    .lineLimit(nil)
            case let .document(doc):
                DocumentView(document: doc, scrollingEnabled: scrollingEnabled, changeURL: navigator.changeURL)
                Spacer()
            }
        }
    }
    
    @ViewBuilder
    private var loadingView: some View {
        if #available(macOS 10.16, iOS 14.0, *) {
            ProgressView("Loading...")
        } else {
            Text("Loading...")
        }
    }
    
    private func loadDocument() {
        let url = navigator.currentURL
        task = try! GeminiDataTask(url: url, completion: { (response) in
            self.task = nil
            switch response {
            case let .failure(error):
                state = .error(error.localizedDescription)
            case let .success(response):
                if response.status.isRedirect {
                    if let redirect = URL(string: response.meta) {
                        navigator.changeURL(redirect)
                        loadDocument()
                    } else {
                        state = .error("Invalid redirect URL: '\(response.meta)'")
                    }
                } else if response.status.isSuccess,
                          let text = response.bodyText {
                    state = .document(GeminiParser.parse(text: text, baseURL: url))
                } else {
                    state = .error("Unknown error: \(response.header)")
                }
            }
        })
        task!.resume()
    }
    
    private func urlChanged(_ newValue: URL) {
        if case .loading = state {
            task?.cancel()
            loadDocument()
        } else {
            state = .loading
        }
    }
}

extension BrowserView {
    enum ViewState {
        case loading
        case document(Document)
        case error(String)
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        BrowserView(navigator: NavigationManager(url: URL(string: "gemini://localhost/overview.gmi")!))
    }
}