import Foundation

enum SentenceBoundaryAPIError: LocalizedError {
    case invalidHash
    case hashMismatch

    var errorDescription: String? {
        switch self {
        case .invalidHash:
            return "video_hash 必须是 64 位 SHA-256 十六进制字符串"
        case .hashMismatch:
            return "服务端返回的句边界哈希与请求不一致"
        }
    }
}

enum SentenceBoundaryAPI {
    static func fetch(videoHash: String) async throws -> SentenceBoundaryDocument {
        let hash = videoHash.lowercased()
        guard hash.range(of: AppConfig.sha256Pattern, options: .regularExpression) != nil else {
            throw SentenceBoundaryAPIError.invalidHash
        }
        var headers: [String: String] = [:]
        if !AppConfig.authToken.isEmpty {
            headers["Authorization"] = "Bearer \(AppConfig.authToken)"
        }
        let result = try await HTTPClient.getJSON(
            SentenceBoundaryDocument.self,
            baseURL: AppConfig.serverBaseURL,
            path: "api/v1/videos/\(hash)/sentence-boundaries",
            timeout: AppConfig.readTimeout,
            additionalHeaders: headers
        )
        guard result.value.videoHash.lowercased() == hash else {
            throw SentenceBoundaryAPIError.hashMismatch
        }
        return result.value
    }
}

struct SentenceExplanationResponse: Decodable {
    let explanation: String

    private enum CodingKeys: String, CodingKey {
        case explanation
    }
}

extension SentenceBoundaryAPI {
    static func explain(
        _ sentence: SentenceBoundary,
        courseTitle: String
    ) async throws -> String {
        var body: [String: Any] = [
            "sentence_text": sentence.text ?? "",
            "course_title": courseTitle,
            "sentence_index": sentence.index,
        ]
        if let language = sentence.language {
            body["language"] = language
        }
        var headers: [String: String] = ["Content-Type": "application/json"]
        if !AppConfig.authToken.isEmpty {
            headers["Authorization"] = "Bearer \(AppConfig.authToken)"
        }
        let result = try await HTTPClient.execute(
            baseURL: AppConfig.serverBaseURL,
            path: "api/v1/sentences/explain",
            method: "POST",
            timeout: AppConfig.readTimeout,
            headers: headers,
            body: try JSONSerialization.data(withJSONObject: body)
        )
        guard (200...299).contains(result.statusCode) else {
            let detail = String(data: result.body, encoding: .utf8) ?? ""
            throw HTTPClientError.badStatus(result.statusCode, detail)
        }
        return try JSONDecoder()
            .decode(SentenceExplanationResponse.self, from: result.body)
            .explanation
    }
}