import CryptoKit
import Foundation

enum ImitationAssessorError: LocalizedError {
    case invalidHash
    case cannotReadRecording

    var errorDescription: String? {
        switch self {
        case .invalidHash:
            return "视频 id 必须是 64 位 SHA-256 十六进制字符串"
        case .cannotReadRecording:
            return "无法读取录音文件"
        }
    }
}

enum ImitationAssessor {
    /// 分块计算文件的 SHA-256（与安卓端一致，适合大视频文件）。
    static func sha256Hex(of fileURL: URL) throws -> String {
        let handle: FileHandle
        do {
            handle = try FileHandle(forReadingFrom: fileURL)
        } catch {
            throw ImitationAssessorError.cannotReadRecording
        }
        defer { try? handle.close() }
        var hasher = SHA256()
        while true {
            guard let data = try? handle.read(upToCount: 1 << 20), !data.isEmpty else {
                break
            }
            hasher.update(data: data)
        }
        return hasher.finalize().map { String(format: "%02x", $0) }.joined()
    }

    /// 复制到缓存目录的同时计算 SHA-256（单次读取完成两件事）。
    static func copyAndHash(from source: URL, to destination: URL) throws -> String {
        let input: FileHandle
        do {
            input = try FileHandle(forReadingFrom: source)
        } catch {
            throw ImitationAssessorError.cannotReadRecording
        }
        defer { try? input.close() }
        try? FileManager.default.removeItem(at: destination)
        FileManager.default.createFile(atPath: destination.path, contents: nil)
        let output = try FileHandle(forWritingTo: destination)
        defer { try? output.close() }
        var hasher = SHA256()
        while true {
            guard let data = try input.read(upToCount: 1 << 20), !data.isEmpty else {
                break
            }
            hasher.update(data: data)
            try output.write(contentsOf: data)
        }
        try output.synchronize()
        return hasher.finalize().map { String(format: "%02x", $0) }.joined()
    }

    /// 上传一句录音到服务端 MOSS 评测接口（multipart/form-data，与安卓端字段一致）。
    static func assess(request: ImitationAssessmentRequest) async throws -> ImitationAssessmentResult {
        let hash = request.mediaId.lowercased()
        guard hash.range(of: AppConfig.sha256Pattern, options: .regularExpression) != nil else {
            throw ImitationAssessorError.invalidHash
        }
        let path = "api/v1/videos/\(hash)/sentences/\(request.sentence.index)/assessments"
        let boundary = "----OralTrainer-\(UUID().uuidString)"
        var body = Data()
        appendField(&body, boundary: boundary, name: "language", value: request.locale ?? request.sentence.language ?? "")
        let recordingData: Data
        do {
            recordingData = try Data(contentsOf: request.recordingURL)
        } catch {
            throw ImitationAssessorError.cannotReadRecording
        }
        let filename = request.recordingURL.lastPathComponent
        let mimeType = request.recordingURL.pathExtension.lowercased() == "wav" ? "audio/wav" : "audio/m4a"
        appendFile(&body, boundary: boundary, name: "audio", filename: filename, mimeType: mimeType, data: recordingData)
        body.append(Data("--\(boundary)--\r\n".utf8))

        let result = try await HTTPClient.execute(
            baseURL: AppConfig.serverBaseURL,
            path: path,
            method: "POST",
            timeout: AppConfig.assessmentTimeout,
            headers: [
                "Accept": "application/json",
                "Content-Type": "multipart/form-data; boundary=\(boundary)",
                "X-Client-Key": AppConfig.assessmentAPIKey,
            ],
            body: body
        )
        guard (200...299).contains(result.statusCode) else {
            let responseBody = String(data: result.body, encoding: .utf8) ?? ""
            throw HTTPClientError.badStatus(result.statusCode, responseBody)
        }
        return try JSONDecoder().decode(ImitationAssessmentResult.self, from: result.body)
    }

    private static func appendField(_ body: inout Data, boundary: String, name: String, value: String) {
        body.append(Data("--\(boundary)\r\n".utf8))
        body.append(Data("Content-Disposition: form-data; name=\"\(name)\"\r\n\r\n".utf8))
        body.append(Data(value.utf8))
        body.append(Data("\r\n".utf8))
    }

    private static func appendFile(
        _ body: inout Data,
        boundary: String,
        name: String,
        filename: String,
        mimeType: String,
        data: Data
    ) {
        body.append(Data("--\(boundary)\r\n".utf8))
        body.append(Data("Content-Disposition: form-data; name=\"\(name)\"; filename=\"\(filename)\"\r\n".utf8))
        body.append(Data("Content-Type: \(mimeType)\r\n\r\n".utf8))
        body.append(data)
        body.append(Data("\r\n".utf8))
    }
}