markbaseengine/Sources/MarkBaseServer/SSE.swift

import Foundation

// ─────────────────────────────────────────────────────────────
// Server-Sent Events (SSE) Support
// ─────────────────────────────────────────────────────────────

/// SSE Event structure
public struct SSEEvent {
    public let id: String?
    public let event: String?
    public let data: String
    public let retry: Int?
    
    public init(id: String? = nil, event: String? = nil, data: String, retry: Int? = nil) {
        self.id = id
        self.event = event
        self.data = data
        self.retry = retry
    }
    
    /// Format as SSE string
    public func format() -> String {
        var output = ""
        
        if let id = id {
            output += "id: \(id)\n"
        }
        
        if let event = event {
            output += "event: \(event)\n"
        }
        
        if let retry = retry {
            output += "retry: \(retry)\n"
        }
        
        // Handle multi-line data
        let lines = data.split(separator: "\n")
        for line in lines {
            output += "data: \(line)\n"
        }
        
        output += "\n"
        return output
    }
}

/// SSE Stream Generator
public final class SSEStream {
    private var buffer = ""
    
    public init() {}
    
    /// Add event to stream
    public func add(event: SSEEvent) -> String {
        let formatted = event.format()
        buffer += formatted
        return formatted
    }
    
    /// Create chat completion chunk
    public static func chatChunk(
        id: String,
        model: String,
        content: String? = nil,
        role: String? = nil,
        finishReason: String? = nil
    ) -> SSEEvent {
        var delta: [String: String] = [:]
        if let role = role {
            delta["role"] = role
        }
        if let content = content {
            delta["content"] = content
        }
        
        let chunk: [String: Any] = [
            "id": id,
            "object": "chat.completion.chunk",
            "created": Int(Date().timeIntervalSince1970),
            "model": model,
            "choices": [
                [
                    "index": 0,
                    "delta": delta,
                    "finish_reason": finishReason as Any
                ]
            ]
        ]
        
        guard let jsonData = try? JSONSerialization.data(withJSONObject: chunk),
              let jsonString = String(data: jsonData, encoding: .utf8) else {
            return SSEEvent(data: "")
        }
        
        return SSEEvent(data: jsonString)
    }
    
    /// Create text completion chunk
    public static func textChunk(
        id: String,
        model: String,
        text: String,
        finishReason: String? = nil
    ) -> SSEEvent {
        let chunk: [String: Any] = [
            "id": id,
            "object": "text_completion",
            "created": Int(Date().timeIntervalSince1970),
            "model": model,
            "choices": [
                [
                    "index": 0,
                    "text": text,
                    "finish_reason": finishReason as Any
                ]
            ]
        ]
        
        guard let jsonData = try? JSONSerialization.data(withJSONObject: chunk),
              let jsonString = String(data: jsonData, encoding: .utf8) else {
            return SSEEvent(data: "")
        }
        
        return SSEEvent(data: jsonString)
    }
    
    /// Create [DONE] event
    public static func done() -> SSEEvent {
        SSEEvent(data: "[DONE]")
    }
    
    /// Create error event
    public static func error(message: String) -> SSEEvent {
        let error: [String: Any] = [
            "error": [
                "message": message,
                "type": "invalid_request_error",
                "code": nil
            ]
        ]
        
        guard let jsonData = try? JSONSerialization.data(withJSONObject: error),
              let jsonString = String(data: jsonData, encoding: .utf8) else {
            return SSEEvent(data: "")
        }
        
        return SSEEvent(event: "error", data: jsonString)
    }
}