import SwiftUI
import OSLog

struct LogScreen: View {

    @State private var entries: [OSLogEntryLog] = []
    @State private var previousOccurenceDate: Date?

    private var store: OSLogStore!

    init() {
        do { store = try OSLogStore(scope: .currentProcessIdentifier) } catch { }
    }

    var body: some View {
        VStack {
            ScrollView(.vertical) {
                LazyVStack {
                    ForEach(entries, id: \.self) { log in
                        Text(log.composedMessage)
                    }
                }
            }
        }
        .toolbar {
            ToolbarItem(placement: .topBarTrailing) {
                Button {
                    loadLogEntries()
                } label: {
                    Image(systemName: "arrow.triangle.2.circlepath")
                }
            }
            ToolbarItem(placement: .topBarTrailing) {
                Button {
                    Logger.default.info("NEW LOG")
                } label: {
                    Image(systemName: "plus.circle")
                }
            }
        }
    }

    private func loadLogEntries() {
        DispatchQueue.global().async {
            do {
                let position = {
                    defer { previousOccurenceDate = Date.now }

                    if let previousOccurenceDate {
                        return store.position(date: previousOccurenceDate)
                    } else {
                        return store.position(timeIntervalSinceLatestBoot: 0)
                    }
                }()
                let newEntries: [OSLogEntryLog] = try store
                    .getEntries(at: position)
                    .compactMap { $0 as? OSLogEntryLog }
                self.entries.append(contentsOf: newEntries)
            } catch {
                Logger.default.critical("Cannot extract logs from OSLogStore: \(error)")
            }
        }
    }
}