add ProfileDatabase class to read and write profiles to disk

damus/Nostr/ProfileDatabase.swift

@@ -0,0 +1,110 @@
+//
+//  ProfileDatabase.swift
+//  damus
+//
+//  Created by Bryan Montz on 4/30/23.
+//
+
+import Foundation
+import CoreData
+
+enum ProfileDatabaseError: Error {
+    case missing_context
+    case outdated_input
+}
+
+final class ProfileDatabase {
+    
+    private let entity_name = "PersistedProfile"
+    private var persistent_container: NSPersistentContainer?
+    private var background_context: NSManagedObjectContext?
+    
+    init() {
+        set_up()
+    }
+    
+    private var profile_cache_url: URL {
+        (FileManager.default.urls(for: .cachesDirectory, in: .userDomainMask).first?.appendingPathComponent("profiles"))!
+    }
+    
+    private var persistent_store_description: NSPersistentStoreDescription {
+        let description = NSPersistentStoreDescription(url: profile_cache_url)
+        description.type = NSSQLiteStoreType
+        description.setOption(true as NSNumber, forKey: NSMigratePersistentStoresAutomaticallyOption)
+        description.setOption(true as NSNumber, forKey: NSInferMappingModelAutomaticallyOption)
+        description.setOption(true as NSNumber, forKey: NSSQLiteManualVacuumOption)
+        return description
+    }
+    
+    private var object_model: NSManagedObjectModel? {
+        guard let url = Bundle.main.url(forResource: "Damus", withExtension: "momd") else {
+            return nil
+        }
+        return NSManagedObjectModel(contentsOf: url)
+    }
+    
+    private func set_up() {
+        guard let object_model else {
+            print("⚠️ Warning: ProfileDatabase failed to load its object model")
+            return
+        }
+        
+        persistent_container = NSPersistentContainer(name: "Damus", managedObjectModel: object_model)
+        persistent_container?.persistentStoreDescriptions = [persistent_store_description]
+        persistent_container?.loadPersistentStores { _, error in
+            if let error {
+                print("WARNING: ProfileDatabase failed to load: \(error)")
+            }
+        }
+        
+        persistent_container?.viewContext.automaticallyMergesChangesFromParent = true
+        persistent_container?.viewContext.mergePolicy = NSMergePolicy(merge: .mergeByPropertyObjectTrumpMergePolicyType)
+        
+        background_context = persistent_container?.newBackgroundContext()
+        background_context?.mergePolicy = NSMergePolicy(merge: .mergeByPropertyObjectTrumpMergePolicyType)
+    }
+    
+    private func get_persisted(id: String) -> PersistedProfile? {
+        let request = NSFetchRequest<PersistedProfile>(entityName: entity_name)
+        request.predicate = NSPredicate(format: "id == %@", id)
+        request.fetchLimit = 1
+        return try? persistent_container?.viewContext.fetch(request).first
+    }
+    
+    // MARK: - Public
+    
+    /// Updates or inserts a new Profile into the local database. Rejects profiles whose update date
+    /// is older than one we already have. Database writes occur on a background context for best performance.
+    /// - Parameters:
+    ///   - id: Profile id (pubkey)
+    ///   - profile: Profile object to be stored
+    ///   - last_update: Date that the Profile was updated
+    func upsert(id: String, profile: Profile, last_update: Date) throws {
+        guard let context = background_context else {
+            throw ProfileDatabaseError.missing_context
+        }
+        
+        var persisted_profile: PersistedProfile?
+        if let profile = get_persisted(id: id) {
+            if let existing_last_update = profile.last_update, last_update < existing_last_update {
+                throw ProfileDatabaseError.outdated_input
+            } else {
+                persisted_profile = profile
+            }
+        } else {
+            persisted_profile = NSEntityDescription.insertNewObject(forEntityName: entity_name, into: context) as? PersistedProfile
+            persisted_profile?.id = id
+        }
+        persisted_profile?.copyValues(from: profile)
+        persisted_profile?.last_update = last_update
+        
+        try context.save()
+    }
+    
+    func get(id: String) -> Profile? {
+        guard let profile = get_persisted(id: id) else {
+            return nil
+        }
+        return Profile(persisted_profile: profile)
+    }
+}