//
//  Recents.swift
//  Reader
//
//  Created by Shadowfacts on 6/19/22.
//

import WidgetKit
import SwiftUI
import Persistence

struct RecentsProvider: IntentTimelineProvider {
    func placeholder(in context: Context) -> RecentsEntry {
        RecentsEntry(items: [], configuration: ConfigurationIntent())
    }

    func getSnapshot(for configuration: ConfigurationIntent, in context: Context, completion: @escaping (RecentsEntry) -> ()) {
        let entry = RecentsEntry(items: getItems(), configuration: configuration)
        completion(entry)
    }

    func getTimeline(for configuration: ConfigurationIntent, in context: Context, completion: @escaping (Timeline<RecentsEntry>) -> ()) {
        // TODO: get account from configuration intent
        
        let entry = RecentsEntry(items: getItems(), configuration: configuration)
        let refreshDate = Calendar.current.date(byAdding: .hour, value: 1, to: Date())!
        let timeline = Timeline(entries: [entry], policy: .after(refreshDate))
        completion(timeline)
    }
    
    private func getItems() -> [WidgetData.Item] {
        guard let account = LocalData.mostRecentAccount() else {
            return []
        }
        return WidgetData.load(account: account).recentItems
    }
    
}

struct RecentsEntry: TimelineEntry {
    let date = Date()
    
    let items: [WidgetData.Item]
    let configuration: ConfigurationIntent
}

struct RecentsEntryView: View {
    let entry: RecentsEntry
    
    @Environment(\.widgetFamily) var family

    var body: some View {
        if entry.items.isEmpty {
        } else {
            switch family {
            case .systemSmall:
                SquareItemView(item: entry.items[0])
                    .padding()
                
            case .systemMedium, .systemLarge:
                VStack {
                    ForEach(Array(entry.items.prefix(family.maxItemCount).enumerated()), id: \.element.id) { (index, item) in
                        if index != 0 {
                            Divider()
                        }
                        ItemListEntryView(item: item)
                        Spacer(minLength: 4)
                    }
                }
                .padding()
                
            case .systemExtraLarge:
                if #available(iOS 16.0, *) {
                    VStack {
                        ForEach(Array(stride(from: 0, to: min(entry.items.count, family.maxItemCount), by: 2)), id: \.self) { idx in
                            HStack {
                                ItemListEntryView(item: entry.items[idx])
                                if idx + 1 < entry.items.count {
                                    Divider()
                                    ItemListEntryView(item: entry.items[idx + 1])
                                }
                            }
                            if idx + 2 < entry.items.count {
                                Spacer()
                                Divider()
                            }
                        }
                    }
                    .padding()
                } else {
                    Text("Requires iOS 16")
                }
                
            default:
                fatalError("unreachable")
            }
        }
    }
}

private extension WidgetFamily {
    var maxItemCount: Int {
        switch self {
        case .systemSmall:
            return 1
        case .systemMedium:
            return 2
        case .systemLarge:
            return 4
        case .systemExtraLarge:
            return 8
        default:
            return 0
        }
    }
}

private var feedFont = Font.subheadline.weight(.medium).italic()
private var titleUIFont: UIFont {
    // TODO: this should use the compressed SF Pro variant, but there's no API to get at it
    let descriptor = UIFontDescriptor.preferredFontDescriptor(withTextStyle: .headline).withSymbolicTraits(.traitCondensed)!
    return UIFont(descriptor: descriptor, size: 0)
}
private var titleFont = Font(titleUIFont).leading(.tight)

struct SquareItemView: View {
    let item: WidgetData.Item
    
    var body: some View {
        VStack(alignment: .leading) {
            HStack {
                Text(verbatim: item.feedTitle ?? "")
                    .font(feedFont)
                    .foregroundColor(.red)
                // force the vstack to be as wide as possible
                Spacer(minLength: 0)
            }
            Text(verbatim: item.title ?? "")
                .font(titleFont)
            if let published = item.published {
                Text(published, format: .relative(presentation: .numeric, unitsStyle: .narrow))
                    .font(.caption)
            }
            Spacer(minLength: 0)
        }
        .widgetURL(item.launchURL)
    }
}

struct ItemListEntryView: View {
    let item: WidgetData.Item
    
    var body: some View {
        Link(destination: item.launchURL) {
            VStack(alignment: .leading) {
                HStack {
                    Text(verbatim: item.feedTitle ?? "")
                        .font(feedFont)
                        .foregroundColor(.red)
                    Spacer()
                    if let published = item.published {
                        Text(published, format: .relative(presentation: .numeric, unitsStyle: .narrow))
                            .font(.caption)
                    }
                }
                Text(verbatim: item.title ?? "")
                    .font(titleFont)
                    .lineLimit(3)
                Spacer(minLength: 0)
            }
        }
    }
}

struct Recents_Previews: PreviewProvider {
    static let item1 = WidgetData.Item(
        id: "1",
        feedTitle: "Daring Fireball",
        title: "There's a Privacy Angle on Apple's Decision to Finance Apple Pay Layer On Its Own",
        published: Calendar.current.date(byAdding: .hour, value: -1, to: Date())!
    )
    static let item2 = WidgetData.Item(
        id: "2",
        feedTitle: "Ars Technica",
        title: "Senate bill would ban data brokers from selling location and health data",
        published: Calendar.current.date(byAdding: .hour, value: -2, to: Date())!
    )
    
    static var previews: some View {
//        RecentsEntryView(entry: RecentsEntry(items: [item1], configuration: ConfigurationIntent()))
//            .previewContext(WidgetPreviewContext(family: .systemSmall))
        
        RecentsEntryView(entry: RecentsEntry(items: [item1, item2], configuration: ConfigurationIntent()))
            .previewContext(WidgetPreviewContext(family: .systemMedium))
    }
}