//
//  AnthropicOAuthService.swift
//  oAI
//
//  OAuth 2.0 PKCE flow for Anthropic Pro/Max subscription login
//
// SPDX-License-Identifier: AGPL-3.0-or-later
// Copyright (C) 2026 Rune Olsen
//
// This file is part of oAI.
//
// oAI is free software: you can redistribute it and/or modify
// it under the terms of the GNU Affero General Public License as
// published by the Free Software Foundation, either version 3 of the
// License, or (at your option) any later version.
//
// oAI is distributed in the hope that it will be useful, but WITHOUT
// ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
// or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General
// Public License for more details.
//
// You should have received a copy of the GNU Affero General Public
// License along with oAI. If not, see <https://www.gnu.org/licenses/>.


import Foundation
import CryptoKit
import Security

@Observable
class AnthropicOAuthService {
    static let shared = AnthropicOAuthService()

    // OAuth configuration (matches Claude Code CLI)
    private let clientId = "9d1c250a-e61b-44d9-88ed-5944d1962f5e"
    private let redirectURI = "https://console.anthropic.com/oauth/code/callback"
    private let scope = "org:create_api_key user:profile user:inference"
    private let tokenEndpoint = "https://console.anthropic.com/v1/oauth/token"

    // Keychain keys
    private enum Keys {
        static let accessToken = "com.oai.anthropic.oauth.accessToken"
        static let refreshToken = "com.oai.anthropic.oauth.refreshToken"
        static let expiresAt = "com.oai.anthropic.oauth.expiresAt"
    }

    // PKCE state for current flow
    private var currentVerifier: String?

    // Observable state
    var isAuthenticated: Bool { accessToken != nil }
    var isLoggingIn = false

    // MARK: - Token Access

    var accessToken: String? {
        getKeychainValue(for: Keys.accessToken)
    }

    private var refreshToken: String? {
        getKeychainValue(for: Keys.refreshToken)
    }

    private var expiresAt: Date? {
        guard let str = getKeychainValue(for: Keys.expiresAt),
              let interval = Double(str) else { return nil }
        return Date(timeIntervalSince1970: interval)
    }

    var isTokenExpired: Bool {
        guard let expires = expiresAt else { return true }
        return Date() >= expires
    }

    // MARK: - Step 1: Generate Authorization URL

    func generateAuthorizationURL() -> URL {
        let verifier = generateCodeVerifier()
        currentVerifier = verifier
        let challenge = generateCodeChallenge(from: verifier)

        var components = URLComponents(string: "https://claude.ai/oauth/authorize")!
        components.queryItems = [
            URLQueryItem(name: "code", value: "true"),
            URLQueryItem(name: "client_id", value: clientId),
            URLQueryItem(name: "response_type", value: "code"),
            URLQueryItem(name: "redirect_uri", value: redirectURI),
            URLQueryItem(name: "scope", value: scope),
            URLQueryItem(name: "code_challenge", value: challenge),
            URLQueryItem(name: "code_challenge_method", value: "S256"),
            URLQueryItem(name: "state", value: verifier),
        ]

        return components.url!
    }

    // MARK: - Step 2: Exchange Code for Tokens

    func exchangeCode(_ pastedCode: String) async throws {
        guard let verifier = currentVerifier else {
            throw OAuthError.noVerifier
        }

        // Code format: "auth_code#state"
        let parts = pastedCode.trimmingCharacters(in: .whitespacesAndNewlines).components(separatedBy: "#")
        let authCode: String
        let state: String

        if parts.count >= 2 {
            authCode = parts[0]
            state = parts.dropFirst().joined(separator: "#")
        } else {
            // If no # separator, treat entire string as the code
            authCode = pastedCode.trimmingCharacters(in: .whitespacesAndNewlines)
            state = verifier
        }

        Log.api.info("Exchanging OAuth code for tokens")

        let body: [String: String] = [
            "code": authCode,
            "state": state,
            "grant_type": "authorization_code",
            "client_id": clientId,
            "redirect_uri": redirectURI,
            "code_verifier": verifier,
        ]

        let tokenResponse = try await postTokenRequest(body)
        saveTokens(tokenResponse)
        currentVerifier = nil

        Log.api.info("OAuth login successful, token expires in \(tokenResponse.expiresIn)s")
    }

    // MARK: - Token Refresh

    func refreshAccessToken() async throws {
        guard let refresh = refreshToken else {
            throw OAuthError.noRefreshToken
        }

        Log.api.info("Refreshing OAuth access token")

        let body: [String: String] = [
            "grant_type": "refresh_token",
            "refresh_token": refresh,
            "client_id": clientId,
        ]

        let tokenResponse = try await postTokenRequest(body)
        saveTokens(tokenResponse)

        Log.api.info("OAuth token refreshed successfully")
    }

    /// Returns a valid access token, refreshing if needed
    func getValidAccessToken() async throws -> String {
        guard let token = accessToken else {
            throw OAuthError.notAuthenticated
        }

        if isTokenExpired {
            try await refreshAccessToken()
            guard let newToken = accessToken else {
                throw OAuthError.notAuthenticated
            }
            return newToken
        }

        return token
    }

    // MARK: - Logout

    func logout() {
        deleteKeychainValue(for: Keys.accessToken)
        deleteKeychainValue(for: Keys.refreshToken)
        deleteKeychainValue(for: Keys.expiresAt)
        currentVerifier = nil
        Log.api.info("OAuth logout complete")
    }

    // MARK: - PKCE Helpers

    private func generateCodeVerifier() -> String {
        var bytes = [UInt8](repeating: 0, count: 32)
        _ = SecRandomCopyBytes(kSecRandomDefault, bytes.count, &bytes)
        return Data(bytes).base64URLEncoded()
    }

    private func generateCodeChallenge(from verifier: String) -> String {
        let data = Data(verifier.utf8)
        let hash = SHA256.hash(data: data)
        return Data(hash).base64URLEncoded()
    }

    // MARK: - Token Request

    private func postTokenRequest(_ body: [String: String]) async throws -> TokenResponse {
        var request = URLRequest(url: URL(string: tokenEndpoint)!)
        request.httpMethod = "POST"
        request.addValue("application/json", forHTTPHeaderField: "Content-Type")
        request.httpBody = try JSONEncoder().encode(body)

        let (data, response) = try await URLSession.shared.data(for: request)

        guard let httpResponse = response as? HTTPURLResponse else {
            throw OAuthError.invalidResponse
        }

        guard httpResponse.statusCode == 200 else {
            let errorBody = String(data: data, encoding: .utf8) ?? "Unknown error"
            Log.api.error("OAuth token exchange failed HTTP \(httpResponse.statusCode): \(errorBody)")
            throw OAuthError.tokenExchangeFailed(httpResponse.statusCode, errorBody)
        }

        return try JSONDecoder().decode(TokenResponse.self, from: data)
    }

    // MARK: - Token Storage

    private func saveTokens(_ response: TokenResponse) {
        setKeychainValue(response.accessToken, for: Keys.accessToken)
        if let refresh = response.refreshToken {
            setKeychainValue(refresh, for: Keys.refreshToken)
        }
        let expiresAt = Date().addingTimeInterval(TimeInterval(response.expiresIn))
        setKeychainValue(String(expiresAt.timeIntervalSince1970), for: Keys.expiresAt)
    }

    // MARK: - Keychain Helpers

    private func getKeychainValue(for key: String) -> String? {
        let query: [String: Any] = [
            kSecClass as String: kSecClassGenericPassword,
            kSecAttrAccount as String: key,
            kSecReturnData as String: true,
            kSecMatchLimit as String: kSecMatchLimitOne,
        ]
        var ref: AnyObject?
        guard SecItemCopyMatching(query as CFDictionary, &ref) == errSecSuccess,
              let data = ref as? Data,
              let value = String(data: data, encoding: .utf8) else {
            return nil
        }
        return value
    }

    private func setKeychainValue(_ value: String, for key: String) {
        guard let data = value.data(using: .utf8) else { return }
        let query: [String: Any] = [
            kSecClass as String: kSecClassGenericPassword,
            kSecAttrAccount as String: key,
        ]
        let attrs: [String: Any] = [kSecValueData as String: data]
        let status = SecItemUpdate(query as CFDictionary, attrs as CFDictionary)
        if status == errSecItemNotFound {
            var newItem = query
            newItem[kSecValueData as String] = data
            SecItemAdd(newItem as CFDictionary, nil)
        }
    }

    private func deleteKeychainValue(for key: String) {
        let query: [String: Any] = [
            kSecClass as String: kSecClassGenericPassword,
            kSecAttrAccount as String: key,
        ]
        SecItemDelete(query as CFDictionary)
    }

    // MARK: - Types

    struct TokenResponse: Decodable {
        let accessToken: String
        let refreshToken: String?
        let expiresIn: Int

        enum CodingKeys: String, CodingKey {
            case accessToken = "access_token"
            case refreshToken = "refresh_token"
            case expiresIn = "expires_in"
        }
    }

    enum OAuthError: LocalizedError {
        case noVerifier
        case noRefreshToken
        case notAuthenticated
        case invalidResponse
        case tokenExchangeFailed(Int, String)

        var errorDescription: String? {
            switch self {
            case .noVerifier: return "No PKCE verifier — start the login flow first."
            case .noRefreshToken: return "No refresh token available. Please log in again."
            case .notAuthenticated: return "Not authenticated. Please log in."
            case .invalidResponse: return "Invalid response from Anthropic OAuth server."
            case .tokenExchangeFailed(let code, let body):
                return "Token exchange failed (HTTP \(code)): \(body)"
            }
        }
    }
}

// MARK: - Base64URL Encoding

private extension Data {
    func base64URLEncoded() -> String {
        base64EncodedString()
            .replacingOccurrences(of: "+", with: "-")
            .replacingOccurrences(of: "/", with: "_")
            .replacingOccurrences(of: "=", with: "")
    }
}