add RelayLog class

Signed-off-by: Bryan Montz <bryanmontz@me.com>
Signed-off-by: William Casarin <jb55@jb55.com>

damus/Nostr/RelayLog.swift

@@ -0,0 +1,143 @@
+//
+//  RelayLog.swift
+//  damus
+//
+//  Created by Bryan Montz on 6/1/23.
+//
+
+import Combine
+import Foundation
+import UIKit
+
+/// Stores a running list of events and state changes related to a relay, so that users
+/// will have information to help developers debug issues.
+final class RelayLog: ObservableObject {
+    private static let line_limit = 250
+    private let relay_url: URL?
+    private lazy var formatter: DateFormatter = {
+        let formatter = DateFormatter()
+        formatter.dateStyle = .short
+        formatter.timeStyle = .medium
+        return formatter
+    }()
+    
+    private(set) var lines = [String]()
+    
+    private var notification_token: AnyCancellable?
+    
+    /// Creates a RelayLog
+    /// - Parameter relay_url: the relay url the log represents. Pass nil for the url to create
+    /// a RelayLog that does nothing. This is required to allow RelayLog to be used as a StateObject,
+    /// because they cannot be Optional.
+    init(_ relay_url: URL? = nil) {
+        self.relay_url = relay_url
+        
+        setUp()
+    }
+    
+    private var log_files_directory: URL {
+        FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask).first!.appendingPathComponent("RelayLogs", isDirectory: true)
+    }
+    
+    private var log_file_url: URL? {
+        guard let file_name = relay_url?.absoluteString.data(using: .utf8) else {
+            return nil
+        }
+        return log_files_directory.appendingPathComponent(file_name.base64EncodedString())
+    }
+    
+    /// Sets up the log file and prepares to listen to app state changes
+    private func setUp() {
+        guard let log_file_url else {
+            return
+        }
+        
+        try? FileManager.default.createDirectory(at: log_files_directory, withIntermediateDirectories: false)
+        
+        if !FileManager.default.fileExists(atPath: log_file_url.path) {
+            // create the log file if it doesn't exist yet
+            FileManager.default.createFile(atPath: log_file_url.path, contents: nil)
+        } else {
+            // otherwise load it into memory
+            readFromDisk()
+        }
+        
+        let willResignPublisher = NotificationCenter.default.publisher(for: UIApplication.willResignActiveNotification)
+        let willTerminatePublisher = NotificationCenter.default.publisher(for: UIApplication.willTerminateNotification)
+        notification_token = Publishers.Merge(willResignPublisher, willTerminatePublisher)
+            .sink { [weak self] _ in
+                self?.writeToDisk()
+            }
+    }
+    
+    /// The current contents of the log
+    var contents: String? {
+        guard !lines.isEmpty else {
+            return nil
+        }
+        return lines.joined(separator: "\n")
+    }
+    
+    /// Adds content to the log
+    /// - Parameter content: what to add to the log. The date and time are prepended to the content.
+    func add(_ content: String) {
+        let line = "\(formatter.string(from: .now)) - \(content)"
+        lines.insert(line, at: 0)
+        truncateLines()
+        
+        Task {
+            await publishChanges()
+        }
+    }
+    
+    /// Tells views that our log has been updated
+    @MainActor private func publishChanges() {
+        objectWillChange.send()
+    }
+    
+    private func truncateLines() {
+        lines = Array(lines.prefix(RelayLog.line_limit))
+    }
+    
+    /// Reads the contents of the log file from disk into memory
+    private func readFromDisk() {
+        guard let log_file_url else {
+            return
+        }
+        
+        do {
+            let handle = try FileHandle(forReadingFrom: log_file_url)
+            let data = try handle.readToEnd()
+            try handle.close()
+            
+            guard let data, let content = String(data: data, encoding: .utf8) else {
+                return
+            }
+            
+            lines = content.components(separatedBy: "\n")
+            
+            truncateLines()
+        } catch {
+            print("⚠️ Warning: RelayLog failed to read from \(log_file_url)")
+        }
+    }
+    
+    /// Writes the contents of the lines in memory to disk
+    private func writeToDisk() {
+        guard let log_file_url, let relay_url,
+              !lines.isEmpty,
+              let content = lines.joined(separator: "\n").data(using: .utf8) else {
+            return
+        }
+        
+        do {
+            let handle = try FileHandle(forWritingTo: log_file_url)
+            
+            try handle.truncate(atOffset: 0)
+            try handle.write(contentsOf: content)
+            try handle.close()
+        } catch {
+            print("⚠️ Warning: RelayLog(\(relay_url)) failed to write to file: \(error)")
+        }
+    }
+}