mixboard/Tests/Unit/KeychainMigrationTests.swift

import XCTest
@testable import MixBoard

// MARK: - Protocols for Dependency Injection
//
// ChadMusicCredentials must accept these protocols for testability.
// Production code uses KeychainService (conforming to KeyStoreProtocol)
// and UserDefaults (conforming to DefaultsStoreProtocol).

/// Abstraction over Keychain storage for the API key.
protocol KeyStoreProtocol {
    func save(_ key: String) throws
    func load() -> String?
    func delete()
}

/// Abstraction over UserDefaults for reading/removing the legacy API key.
protocol DefaultsStoreProtocol {
    func string(forKey key: String) -> String?
    func removeObject(forKey key: String)
}

// MARK: - In-Memory Mocks

final class InMemoryKeyStore: KeyStoreProtocol {
    var storedKey: String?
    var shouldThrowOnSave = false
    var saveCallCount = 0
    var deleteCallCount = 0

    func save(_ key: String) throws {
        saveCallCount += 1
        if shouldThrowOnSave {
            throw NSError(domain: "KeyStoreTest", code: -25293,
                          userInfo: [NSLocalizedDescriptionKey: "Keychain access denied (simulated)"])
        }
        storedKey = key
    }

    func load() -> String? {
        storedKey
    }

    func delete() {
        deleteCallCount += 1
        storedKey = nil
    }
}

final class InMemoryDefaultsStore: DefaultsStoreProtocol {
    var storage: [String: String] = [:]
    var removedKeys: [String] = []

    func string(forKey key: String) -> String? {
        storage[key]
    }

    func removeObject(forKey key: String) {
        removedKeys.append(key)
        storage.removeValue(forKey: key)
    }
}

// MARK: - ChadMusicCredentials Migration Tests
//
// These tests define the contract for ChadMusicCredentials.
// The implementation (fix-api-key-security task) must make all tests pass.
//
// ChadMusicCredentials must support initialization with injected stores:
//   ChadMusicCredentials(keyStore:defaultsStore:)
// so that tests can use in-memory mocks instead of real Keychain/UserDefaults.

@MainActor
final class KeychainMigrationTests: XCTestCase {

    private var keyStore: InMemoryKeyStore!
    private var defaultsStore: InMemoryDefaultsStore!

    override func setUp() {
        super.setUp()
        keyStore = InMemoryKeyStore()
        defaultsStore = InMemoryDefaultsStore()
    }

    // MARK: - Migration Logic

    /// Spec edge case: "Existing UserDefaults value, no Keychain → Migrate to Keychain, delete from UserDefaults"
    func testMigratesFromDefaultsToKeychain() {
        defaultsStore.storage["chadMusic.apiKey"] = "abc"
        // Keychain is empty (keyStore.storedKey == nil)

        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)
        let result = credentials.apiKey

        // Key migrated to Keychain
        XCTAssertEqual(result, "abc", "apiKey should return the migrated value")
        XCTAssertEqual(keyStore.storedKey, "abc", "Key should be saved to Keychain")
        // Plaintext removed from UserDefaults
        XCTAssertNil(defaultsStore.storage["chadMusic.apiKey"],
                     "UserDefaults key should be removed after migration")
        XCTAssertTrue(defaultsStore.removedKeys.contains("chadMusic.apiKey"),
                      "removeObject should have been called for the legacy key")
    }

    /// Spec edge case: "Both UserDefaults and Keychain have values → Keep Keychain value, delete UserDefaults copy"
    func testSkipsMigrationIfKeychainPopulated() {
        defaultsStore.storage["chadMusic.apiKey"] = "old-from-defaults"
        keyStore.storedKey = "new-from-keychain"

        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)
        let result = credentials.apiKey

        // Keychain value preserved, not overwritten
        XCTAssertEqual(result, "new-from-keychain",
                       "Should return existing Keychain value, not overwrite with UserDefaults")
        XCTAssertEqual(keyStore.storedKey, "new-from-keychain",
                       "Keychain value must not be overwritten")
        // UserDefaults plaintext still cleaned up
        XCTAssertNil(defaultsStore.storage["chadMusic.apiKey"],
                     "UserDefaults copy should be deleted even when Keychain already has a value")
        XCTAssertEqual(keyStore.saveCallCount, 0,
                       "Keychain save should NOT be called when Keychain already populated")
    }

    /// Spec edge case: "Fresh install (no UserDefaults, no Keychain) → apiKey returns nil"
    func testSkipsMigrationIfDefaultsEmpty() {
        // Both stores empty

        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)
        let result = credentials.apiKey

        XCTAssertNil(result, "apiKey should be nil when both stores are empty")
        XCTAssertNil(keyStore.storedKey, "Keychain should remain empty")
        XCTAssertEqual(keyStore.saveCallCount, 0, "No save should occur")
    }

    /// Spec edge case: "Empty string in UserDefaults → Treated as 'not set' — no migration"
    func testSkipsMigrationIfDefaultsHasEmptyString() {
        defaultsStore.storage["chadMusic.apiKey"] = ""

        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)
        let result = credentials.apiKey

        XCTAssertNil(result, "Empty string should be treated as nil")
        XCTAssertNil(keyStore.storedKey, "Empty string should not be migrated to Keychain")
        XCTAssertEqual(keyStore.saveCallCount, 0, "No save should occur for empty string")
    }

    /// Spec edge case: "Keychain access denied → Leave UserDefaults in place, no crash"
    func testFallbackWhenKeychainDenied() {
        defaultsStore.storage["chadMusic.apiKey"] = "abc"
        keyStore.shouldThrowOnSave = true

        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)

        // Should not crash — graceful fallback
        let result = credentials.apiKey

        // UserDefaults value preserved (migration failed)
        XCTAssertEqual(defaultsStore.storage["chadMusic.apiKey"], "abc",
                       "UserDefaults should keep the key when Keychain save fails")
        // apiKey should still be accessible (either from failed Keychain or fallback)
        // The exact behavior depends on implementation: it may return nil from Keychain
        // or fall back to UserDefaults. Either way, no crash.
        // The key point: the app doesn't crash and the plaintext isn't lost.
        XCTAssertFalse(defaultsStore.removedKeys.contains("chadMusic.apiKey"),
                       "UserDefaults key must NOT be removed if Keychain save failed")
    }

    /// Migration runs only once per instance — second access doesn't re-migrate.
    func testMigrationRunsOnlyOnce() {
        defaultsStore.storage["chadMusic.apiKey"] = "abc"

        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)

        // First access triggers migration
        _ = credentials.apiKey
        XCTAssertEqual(keyStore.saveCallCount, 1, "First access should trigger one save")

        // Manually put something back in defaults (simulating external write)
        defaultsStore.storage["chadMusic.apiKey"] = "should-not-migrate"

        // Second access should NOT re-migrate
        _ = credentials.apiKey
        XCTAssertEqual(keyStore.saveCallCount, 1,
                       "Second access should not trigger another migration")
        XCTAssertEqual(keyStore.storedKey, "abc",
                       "Keychain should still have the original migrated value")
    }

    // MARK: - Save / Load / Delete

    /// Spec: "Call save('xyz') → load() returns 'xyz'"
    func testSaveWritesToKeychain() throws {
        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)

        try credentials.save("xyz")

        XCTAssertEqual(keyStore.storedKey, "xyz", "save() should write to the key store")
        XCTAssertEqual(credentials.apiKey, "xyz", "apiKey should return the saved value")
    }

    /// Spec: "Save then delete → load() returns nil"
    func testDeleteRemovesKey() throws {
        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)

        try credentials.save("to-delete")
        XCTAssertNotNil(credentials.apiKey)

        credentials.delete()

        XCTAssertNil(keyStore.storedKey, "delete() should remove the key from the store")
        XCTAssertNil(credentials.apiKey, "apiKey should return nil after deletion")
    }

    /// Spec: "Keychain has '' → apiKey returns nil (empty treated as nil)"
    func testApiKeyNilWhenKeychainHasEmptyString() {
        keyStore.storedKey = ""

        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)
        let result = credentials.apiKey

        XCTAssertNil(result, "Empty string in Keychain should be treated as nil")
    }

    /// Save overwrites existing value.
    func testSaveOverwritesExistingKey() throws {
        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)

        try credentials.save("first")
        XCTAssertEqual(credentials.apiKey, "first")

        try credentials.save("second")
        XCTAssertEqual(credentials.apiKey, "second")
        XCTAssertEqual(keyStore.storedKey, "second")
    }

    /// Save propagates Keychain errors.
    func testSaveThrowsOnKeychainError() {
        keyStore.shouldThrowOnSave = true
        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)

        XCTAssertThrowsError(try credentials.save("fail")) { error in
            XCTAssertNotNil(error.localizedDescription)
        }
    }

    /// Unicode API keys are handled correctly.
    func testSaveAndLoadUnicodeKey() throws {
        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)
        let key = "api-key-with-ünîcödé-чëрт"

        try credentials.save(key)
        XCTAssertEqual(credentials.apiKey, key)
    }

    // MARK: - isConfigured helper (if exposed)

    /// ChadMusicCredentials should expose whether a key is set.
    func testHasKeyWhenSet() throws {
        let credentials = ChadMusicCredentials(keyStore: keyStore, defaultsStore: defaultsStore)
        XCTAssertFalse(credentials.hasKey, "hasKey should be false when no key is stored")

        try credentials.save("some-key")
        XCTAssertTrue(credentials.hasKey, "hasKey should be true after saving a key")

        credentials.delete()
        XCTAssertFalse(credentials.hasKey, "hasKey should be false after deletion")
    }
}