import WidgetKit
import SwiftUI

struct HabitTimelineEntry: TimelineEntry {
    let date: Date
    let snapshot: WidgetSnapshot
}

struct Provider: TimelineProvider {
    func placeholder(in context: Context) -> HabitTimelineEntry {
        HabitTimelineEntry(date: .now, snapshot: .empty)
    }

    func getSnapshot(in context: Context, completion: @escaping (HabitTimelineEntry) -> Void) {
        completion(HabitTimelineEntry(date: .now, snapshot: SharedStore.load()))
    }

    func getTimeline(in context: Context, completion: @escaping (Timeline<HabitTimelineEntry>) -> Void) {
        let entry = HabitTimelineEntry(date: .now, snapshot: SharedStore.load())
        // Reset "today" at the next midnight.
        let nextMidnight = Calendar.current.startOfDay(for: .now.addingTimeInterval(86_400))
        completion(Timeline(entries: [entry], policy: .after(nextMidnight)))
    }
}

struct HabitTrackerWidgetEntryView: View {
    var entry: Provider.Entry
    @Environment(\.widgetFamily) private var family

    private var items: [WidgetSnapshot.Item] { entry.snapshot.items }
    private var doneCount: Int { items.filter(\.isDoneToday).count }

    var body: some View {
        if items.isEmpty {
            emptyState
        } else {
            switch family {
            case .systemSmall:
                smallView
            default:
                mediumView
            }
        }
    }

    private var emptyState: some View {
        VStack(spacing: 6) {
            Image(systemName: "checklist")
                .font(.title)
                .foregroundStyle(.secondary)
            Text("Keine Gewohnheiten")
                .font(.caption)
                .foregroundStyle(.secondary)
        }
    }

    private var header: some View {
        HStack {
            Text("Heute")
                .font(.caption.bold())
                .foregroundStyle(.secondary)
            Spacer()
            Text("\(doneCount)/\(items.count)")
                .font(.caption.bold())
                .foregroundStyle(.secondary)
        }
    }

    private var smallView: some View {
        VStack(alignment: .leading, spacing: 8) {
            header
            Spacer(minLength: 0)
            Text("\(doneCount)")
                .font(.system(size: 44, weight: .bold))
                + Text(" / \(items.count)")
                .font(.title3.weight(.semibold))
                .foregroundColor(.secondary)
            Text(doneCount == items.count ? "Alles erledigt 🎉" : "erledigt")
                .font(.caption)
                .foregroundStyle(.secondary)
        }
    }

    private var mediumView: some View {
        VStack(alignment: .leading, spacing: 8) {
            header
            ForEach(items.prefix(3)) { item in
                HStack(spacing: 10) {
                    Image(systemName: item.symbolName)
                        .foregroundStyle(Color(hex: item.colorHex))
                        .frame(width: 22)
                    Text(item.name)
                        .font(.subheadline)
                        .lineLimit(1)
                    Spacer()
                    Image(systemName: item.isDoneToday ? "checkmark.circle.fill" : "circle")
                        .foregroundStyle(item.isDoneToday ? Color(hex: item.colorHex) : .secondary)
                }
            }
            if items.count > 3 {
                Text("+ \(items.count - 3) weitere")
                    .font(.caption2)
                    .foregroundStyle(.secondary)
            }
        }
    }
}

struct HabitTrackerWidget: Widget {
    let kind = "HabitTrackerWidget"

    var body: some WidgetConfiguration {
        StaticConfiguration(kind: kind, provider: Provider()) { entry in
            HabitTrackerWidgetEntryView(entry: entry)
                .containerBackground(.fill.tertiary, for: .widget)
        }
        .configurationDisplayName("Gewohnheiten")
        .description("Dein Fortschritt von heute.")
        .supportedFamilies([.systemSmall, .systemMedium])
    }
}