CodableDatastore

dependencies: [
    .package(
        url: "https://github.com/mochidev/CodableDatastore.git", 
        .upToNextMinor(from: "0.3.4")
    ),
],
...
targets: [
    .target(
        name: "MyPackage",
        dependencies: [
            "CodableDatastore",
        ]
    )
]

import Foundation
import CodableDatastore

struct BookStore: DatastoreFormat {
    // These are both required, and used by the initializer for `Datastore` below.
    static let defaultKey: DatastoreKey = "BooksStore"
    static let currentVersion: Version = .current

    // A required description of your current and past versions you support
    // decoding. Note that the current version should always have a sensible
    // value, as it will get encoded to the persistence. 
    // Either `Int`s or `String`s are supported.
    enum Version: String {
        case v1 = "2024-04-01"
        case current = "2024-04-09"
    }

    // A required "pointer" to the latest representation of your type.
    typealias Instance = Book
    // Optional if the Instance above is Identifiable, but required otherwise.
    // typealias Identifier = UUID

    // The first version we shipped with and need to support.
    struct BookV1: Codable, Identifiable {
        var id: UUID
        var title: String
        var author: String
    }

    // The current version we use in the app.
    struct Book: Codable, Identifiable {
        var id: UUID
        var title: SortableTitle
        var authors: [AuthorID]
        var isbn: ISBN
    }

    // A non-required helper for instanciating a datastore. Note many
    // parameters are inferred, since `DatastoreFormat` declares a specialized
    // `Self.Datastore` with all the generic parameters filled out.
    // `CodableDatastore` comes with initializers for JSON and Property list
    // stores, though completely custom coders can easily be supported by using
    // the default initializers on `Datastore`.
    static func datastore(for persistence: DiskPersistence<ReadWrite>) -> Self.Datastore {
        .JSONStore(
            persistence: persistence,
            // This is where all the migrations for different versions are
            // defined; Simply decode the type you know if stored for a given 
            // version, and convert it to the modern type you use in the app.
            // Conversions are typically only done at read time.
            migrations: [
                .v1: { data, decoder in try Book(decoder.decode(BookV1.self, from: data)) },
                .current: { data, decoder in try decoder.decode(Book.self, from: data) }
            ]
        )
    }
    
    // Declare your indexes here by declaring stored properties in one of the
    // provided `Index` types. The keypaths refer to the main Instance for the
    // format you declared. Both stored and computed keypaths are supported.
    // Indexes are automatically re-computed whenever the names or types of
    // these declarations change, though the key path itself can change silently.
    // Note: Manual migrations of these is not currently supported but is planned.
    let title = Index(\.title)
    let author = ManyToManyIndex(\.authors)
    // A one to one index where every isbn points to exactly one book.
    // Note the index is marked with `@Direct`, which optimizes reads by isbn by
    // trading off the additional storage space needed to store full copies of
    // the `Book` struct in that index.
    @Direct var isbn = OneToOneIndex(\.isbn)
}

// A convenience alias for the rest of the app to use.
typealias Book = BookStore.Book

// Declare any necessary conversions to make old stored instances continue working.
extension Book {
    init(_ bookV1: BookStore.BookV1) {
        self.init(
            id: id,
            title: SortableTitle(title),
            authors: [AuthorID(authors)],
            isbn: ISBN.generate()
        )
    }
}

import Foundation
import CodableDatastore

actor LibraryPersistence {
    // Keep these around so we can access them as necessary
    let persistence: DiskPersistence<ReadWrite>
    
    let bookDatastore: BookStore.Datastore
    let authorDatastore: AuthorStore.Datastore
    let shelfDatastore: ShelfStore.Datastore

    init() async throws {
        // Initialize the persistence to Application Support, or pass in a readWriteURL
        persistence = try DiskPersistence.defaultStore()
        // Make sure we can write and access it
        try await persistence.createPersistenceIfNecessary()
        
        // Initialize the datastores so we can refer back to them
        bookDatastore = BookStore.datastore(for: persistence)
        authorDatastore = AuthorStore.datastore(for: persistence)
        shelfDatastore = ShelfStore.datastore(for: persistence)
        
        // Warm the datastores to re-build any indexes changed suring development.
        // This is an excellend opportunity to show migration UI if the process takes longer than a second.
        try await bookDatastore.warm { progress in
            switch progress {
            case .evaluating:
                // Always called
                print("Checking Books…") 
            case .working(let current, let total):
                // Only called if migrating. Signal some UI and log the values.
                // `current` is 0-based.
                print("  → Migrating \(current+1)/\(total) Books…")
            case .complete(let total):
                // Always called
                print("  ✓ Finished checking \(total) Books!") 
            }
        }
        try await authorDatastore.warm()
        try await shelfDatastore.warm()
    }
}

let bookByID = try await bookDatastore.load(bookID)
let bookByISBN = try await bookDatastore.load(isbn, from: \.isbn)

for try await book in bookDatastore.load("A"..<"B", from: \.title) {
    print("Book that starts with A: \(book.title)")
}

guard let dimitri = authorDatastore.load("Dimitri Bouniol", from: \.fullname).first(where: { _ in true })
else { throw NotFoundError() }
for try await book in bookDatastore.load(dimitri.id, from: \.author) {
    print("Book written by Dimitri: \(book.title)")
}

let allShelves = try await shelfDatastore.load(...).reduce(into: []) { $0.append($1) }

let oldValue = try await bookDatastore.persist(newBook)
let oldValue = try await bookDatastore.delete(oldBookID)
let oldOptionalValue = try await bookDatastore.deleteIfPresent(oldBookID)

// Passing an Identifiable instance also works:
let oldValue = try await bookDatastore.delete(oldBook)

try await persistence.perform {
    try await authorDatastore.persist(newAuthor)
    for newBook in newBooks {
        guard let shelf = try await shelfDatastore.load(newBook.genre, from: \.genre)
        else { throw ShelfNotFoundError() }
        
        newBook.shelfID = shelf
        try await authorDatastore.persist(newBook)
    }
}