Add provider credential store abstractions

Sources/CodexBarCore/Credentials/CredentialStore.swift

@@ -0,0 +1,101 @@
+import Foundation
+
+public struct ProviderCredentialKey: Hashable, Sendable {
+    public let provider: UsageProvider
+
+    public init(provider: UsageProvider) {
+        self.provider = provider
+    }
+}
+
+public protocol ProviderCredentialStore: Sendable {
+    func apiKey(for key: ProviderCredentialKey) -> String?
+}
+
+public struct EnvironmentProviderCredentialStore: ProviderCredentialStore {
+    private let env: [String: String]
+
+    public init(env: [String: String] = ProcessInfo.processInfo.environment) {
+        self.env = env
+    }
+
+    public func apiKey(for key: ProviderCredentialKey) -> String? {
+        let names = Self.environmentNames(for: key.provider)
+        for name in names {
+            if let value = self.env[name]?.trimmingCharacters(in: .whitespacesAndNewlines), !value.isEmpty {
+                return value
+            }
+        }
+        return nil
+    }
+
+    private static func environmentNames(for provider: UsageProvider) -> [String] {
+        switch provider {
+        case .zai:
+            [ZaiSettingsReader.apiTokenKey]
+        case .copilot:
+            ["COPILOT_API_TOKEN"]
+        case .minimax:
+            [MiniMaxAPISettingsReader.apiTokenKey]
+        case .kimik2:
+            KimiK2SettingsReader.apiKeyEnvironmentKeys
+        case .synthetic:
+            [SyntheticSettingsReader.apiKeyKey]
+        case .warp:
+            WarpSettingsReader.apiKeyEnvironmentKeys
+        default:
+            []
+        }
+    }
+}
+
+public struct FileProviderCredentialStore: ProviderCredentialStore {
+    public let fileURL: URL
+    private let fileManager: FileManager
+    private let decoder: JSONDecoder
+
+    public init(
+        fileURL: URL = Self.defaultURL(),
+        fileManager: FileManager = .default,
+        decoder: JSONDecoder = JSONDecoder())
+    {
+        self.fileURL = fileURL
+        self.fileManager = fileManager
+        self.decoder = decoder
+    }
+
+    public func apiKey(for key: ProviderCredentialKey) -> String? {
+        guard let map = self.loadMap() else { return nil }
+        guard let value = map[key.provider.rawValue]?.trimmingCharacters(in: .whitespacesAndNewlines) else { return nil }
+        return value.isEmpty ? nil : value
+    }
+
+    public static func defaultURL(home: URL = FileManager.default.homeDirectoryForCurrentUser) -> URL {
+        home
+            .appendingPathComponent(".codexbar", isDirectory: true)
+            .appendingPathComponent("credentials.json")
+    }
+
+    private func loadMap() -> [String: String]? {
+        guard self.fileManager.fileExists(atPath: self.fileURL.path) else { return nil }
+        guard let data = try? Data(contentsOf: self.fileURL) else { return nil }
+        return try? self.decoder.decode([String: String].self, from: data)
+    }
+}
+
+public struct CompositeProviderCredentialStore: ProviderCredentialStore {
+    private let stores: [any ProviderCredentialStore]
+
+    public init(stores: [any ProviderCredentialStore]) {
+        self.stores = stores
+    }
+
+    public func apiKey(for key: ProviderCredentialKey) -> String? {
+        for store in self.stores {
+            if let value = store.apiKey(for: key), !value.isEmpty {
+                return value
+            }
+        }
+        return nil
+    }
+}