An example of using TCA FirestoreClient with Firestore ios sdk automatically bridged from Objective-C to Swift Concurrency.

FirestoreClient.swift

import Foundation
import ComposableArchitecture
import FirebaseFirestore
import FirebaseFirestoreSwift

// MARK: - FirestoreClient

struct FirestoreClient {
    enum Input {
        enum Create {
            struct Food {
                typealias ID = String

                let name: String
                let bestBeforeDate: Date
                let userID: ID
            }
        }
    }

    var createFood: (Input.Create.Food, CollectionReference) async throws -> FirestoreEntity.FoodID
}

extension FirestoreClient {
    static let liveValue = Self.live()

    static func live() -> Self {
        let firestore = Firestore.firestore()
        let foodStorageCollectionName = "/foodStorages"

        return Self(
            createFood: { food, collectionReference in
                // Objective-C completion handlers are automatically converted to async functions.
                // https://github.com/apple/swift-evolution/blob/main/proposals/0297-concurrency-objc.md
                let reference = try await collectionReference.addDocument(
                    data: try Firestore.Encoder().encode(
                        FirestoreEntity.Food(
                            name: food.name,
                            bestBeforeDate: food.bestBeforeDate
                        )
                    )
                )
                return reference.documentID
            }
        )
    }
}

// MARK: - For SwiftUI Preview

extension FirestoreClient {
    public static let noop = Self(
        createFood: { _, _ in try await Task.never()}
    )
}

// MARK: - For Dependencies

enum FirestoreClientKey: DependencyKey {
    static let liveValue = FirestoreClient.liveValue
    static let previewValue = FirestoreClient.noop
}

extension DependencyValues {
    var firestoreClient: FirestoreClient {
        get { self[FirestoreClientKey.self] }
        set { self[FirestoreClientKey.self] = newValue }
    }
}

// MARK: - FirestoreEntity

enum FirestoreEntity {}

extension FirestoreEntity {
    typealias FoodID = String

    struct Food: Equatable, Encodable, Decodable, Identifiable {
        @DocumentID var id: FoodID?
        @ServerTimestamp var createdDate: Timestamp?

        let name: String
        let bestBeforeDate: Date
    }
}

extension FirestoreEntity.Food {
    init(name: String, date: Date) {
        self.name = name
        self.bestBeforeDate = date
    }
}