//
// Copyright 2026 Element Creations Ltd.
//
// SPDX-License-Identifier: AGPL-3.0-only OR LicenseRef-Element-Commercial.
// Please see LICENSE files in the repository root for full details.
//

import Foundation

// sourcery: AutoMockable
protocol HealthChatOpenIDTokenProviderProtocol {
    /// A valid OpenID access token, from cache when possible.
    func validToken() async -> Result<String, HealthChatAPIError>
    
    /// Drops the cached token, e.g. after the API rejected it.
    func invalidateToken()
}

final class HealthChatOpenIDTokenProvider: HealthChatOpenIDTokenProviderProtocol {
    private let clientProxy: ClientProxyProtocol
    private let dateProvider: () -> Date
    
    /// Tokens this close to expiry are refreshed early, matching the web client's buffer.
    private static let expiryBuffer: TimeInterval = 60
    
    private var cachedToken: (token: String, expiry: Date)?
    
    init(clientProxy: ClientProxyProtocol, dateProvider: @escaping () -> Date = Date.init) {
        self.clientProxy = clientProxy
        self.dateProvider = dateProvider
    }
    
    func validToken() async -> Result<String, HealthChatAPIError> {
        if let cachedToken, dateProvider().addingTimeInterval(Self.expiryBuffer) < cachedToken.expiry {
            return .success(cachedToken.token)
        }
        
        switch await clientProxy.requestOpenIDToken() {
        case .success(let token):
            cachedToken = (token.accessToken, dateProvider().addingTimeInterval(token.expiresIn))
            return .success(token.accessToken)
        case .failure:
            return .failure(.tokenAcquisitionFailed)
        }
    }
    
    func invalidateToken() {
        cachedToken = nil
    }
}