server.js

import express from 'express';
import { fal } from '@fal-ai/client';

// --- Multi-Key Configuration ---
// *** 使用 FAL_KEY 环境变量读取逗号分隔的密钥 ***
const rawFalKeys = process.env.FAL_KEY; // Expect comma-separated keys: key1,key2,key3 in FAL_KEY
const API_KEY = process.env.API_KEY; // Custom API Key for proxy auth remains the same

if (!rawFalKeys) {
    // *** 更新错误信息以引用 FAL_KEY ***
    console.error("Error: FAL_KEY environment variable is not set (should be comma-separated).");
    process.exit(1);
}

if (!API_KEY) {
    console.error("Error: API_KEY environment variable is not set.");
    process.exit(1);
}

// Parse and prepare the keys
let falKeys = rawFalKeys.split(',')
    .map(key => key.trim())
    .filter(key => key.length > 0)
    .map(key => ({
        key: key,
        failed: false,          // Track if the key is currently considered failed
        failedTimestamp: 0      // Timestamp when the key was marked as failed
    }));

if (falKeys.length === 0) {
    // *** 更新错误信息以引用 FAL_KEY ***
    console.error("Error: No valid keys found in FAL_KEY after processing the environment variable.");
    process.exit(1);
}

let currentKeyIndex = 0;
const failedKeyCooldown = 60 * 1000; // Cooldown period in milliseconds (e.g., 60 seconds) before retrying a failed key

// *** 更新日志信息以引用 FAL_KEY ***
console.log(`Loaded ${falKeys.length} FAL API Key(s) from FAL_KEY environment variable.`);
console.log(`Failed key cooldown period: ${failedKeyCooldown / 1000} seconds.`);

// NOTE: We will configure fal client per request now, so initial global config is removed.

// --- Key Management Functions ---

/**
 * Selects the next available FAL key using round-robin and skipping recently failed keys.
 * @returns {object | null} Key info object { key, failed, failedTimestamp } or null if all keys are failed.
 */
function getNextKey() {
    const totalKeys = falKeys.length;
    if (totalKeys === 0) return null;

    let attempts = 0;
    while (attempts < totalKeys) {
        const keyIndex = currentKeyIndex % totalKeys;
        const keyInfo = falKeys[keyIndex];
        // Increment index for the *next* call, ensuring round-robin
        currentKeyIndex = (currentKeyIndex + 1) % totalKeys;

        // Check if key is marked as failed and if cooldown has passed
        if (keyInfo.failed) {
            const now = Date.now();
            if (now - keyInfo.failedTimestamp < failedKeyCooldown) {
                // console.log(`Key index ${keyIndex} is in cooldown. Skipping.`);
                attempts++;
                continue; // Skip this key, it's still in cooldown
            } else {
                console.log(`Cooldown finished for key index ${keyIndex}. Resetting failure status.`);
                keyInfo.failed = false; // Cooldown expired, reset status
                keyInfo.failedTimestamp = 0;
            }
        }
        // console.log(`Selected key index: ${keyIndex}`);
        return keyInfo; // Return the valid key info object
    }

    console.warn("All FAL keys are currently marked as failed and in cooldown.");
    return null; // All keys are currently failed and within cooldown
}

/**
 * Marks a specific key as failed.
 * @param {object} keyInfo - The key info object to mark as failed.
 */
function markKeyFailed(keyInfo) {
    if (keyInfo && !keyInfo.failed) { // Only mark if not already marked
        keyInfo.failed = true;
        keyInfo.failedTimestamp = Date.now();
        const keyIndex = falKeys.findIndex(k => k.key === keyInfo.key);
        console.warn(`Marking key index ${keyIndex} (ending ...${keyInfo.key.slice(-4)}) as failed.`);
    }
}

/**
 * Determines if an error likely indicates an API key issue (auth, quota, etc.).
 * This needs refinement based on actual errors from fal.ai.
 * @param {Error} error - The error object caught from the fal client.
 * @returns {boolean} - True if the error suggests a key failure, false otherwise.
 */
function isKeyRelatedError(error) {
    const errorMessage = error?.message?.toLowerCase() || '';
    const errorStatus = error?.status; // Assuming the error object might have a status property

    // Check for common indicators of key issues
    if (errorStatus === 401 || errorStatus === 403 || // Unauthorized, Forbidden
        errorMessage.includes('authentication failed') ||
        errorMessage.includes('invalid api key') ||
        errorMessage.includes('permission denied')) {
        return true;
    }
    if (errorStatus === 429 || // Too Many Requests (Rate Limit / Quota)
        errorMessage.includes('rate limit exceeded') ||
        errorMessage.includes('quota exceeded')) {
        return true;
    }
    // Add more specific error messages or codes from fal.ai if known
    // console.log("Error does not appear to be key-related:", error); // Debugging
    return false;
}

// --- Express App Setup ---
const app = express();
app.use(express.json({ limit: '50mb' }));
app.use(express.urlencoded({ extended: true, limit: '50mb' }));

const PORT = process.env.PORT || 3000;

// API Key 鉴权中间件 (Remains the same, checks custom API_KEY)
const apiKeyAuth = (req, res, next) => {
    const authHeader = req.headers['authorization'];

    if (!authHeader) {
        console.warn('Unauthorized: No Authorization header provided');
        return res.status(401).json({ error: 'Unauthorized: No API Key provided' });
    }

    const authParts = authHeader.split(' ');
    if (authParts.length !== 2 || authParts[0].toLowerCase() !== 'bearer') {
        console.warn('Unauthorized: Invalid Authorization header format');
        return res.status(401).json({ error: 'Unauthorized: Invalid Authorization header format' });
    }

    const providedKey = authParts[1];
    if (providedKey !== API_KEY) {
        console.warn('Unauthorized: Invalid API Key');
        return res.status(401).json({ error: 'Unauthorized: Invalid API Key' });
    }

    next();
};

app.use(['/v1/models', '/v1/chat/completions'], apiKeyAuth);

// === 全局定义限制 === (Remains the same)
const PROMPT_LIMIT = 4800;
const SYSTEM_PROMPT_LIMIT = 4800;
// === 限制定义结束 ===

// 定义 fal-ai/any-llm 支持的模型列表 (Remains the same)
const FAL_SUPPORTED_MODELS = [
    "anthropic/claude-3.7-sonnet",
    "anthropic/claude-3.5-sonnet",
    "anthropic/claude-3-5-haiku",
    "anthropic/claude-3-haiku",
    "google/gemini-pro-1.5",
    "google/gemini-flash-1.5",
    "google/gemini-flash-1.5-8b",
    "google/gemini-2.0-flash-001",
    "meta-llama/llama-3.2-1b-instruct",
    "meta-llama/llama-3.2-3b-instruct",
    "meta-llama/llama-3.1-8b-instruct",
    "meta-llama/llama-3.1-70b-instruct",
    "openai/gpt-4o-mini",
    "openai/gpt-4o",
    "deepseek/deepseek-r1",
    "meta-llama/llama-4-maverick",
    "meta-llama/llama-4-scout"
];

// Helper function to get owner from model ID (Remains the same)
const getOwner = (modelId) => {
    if (modelId && modelId.includes('/')) {
        return modelId.split('/')[0];
    }
    return 'fal-ai';
};

// GET /v1/models endpoint (Remains the same)
app.get('/v1/models', (req, res) => {
    console.log("Received request for GET /v1/models");
    try {
        const modelsData = FAL_SUPPORTED_MODELS.map(modelId => ({
            id: modelId, object: "model", created: 1700000000, owned_by: getOwner(modelId)
        }));
        res.json({ object: "list", data: modelsData });
        console.log("Successfully returned model list.");
    } catch (error) {
        console.error("Error processing GET /v1/models:", error);
        res.status(500).json({ error: "Failed to retrieve model list." });
    }
});

// === convertMessagesToFalPrompt 函数 (Remains the same) ===
function convertMessagesToFalPrompt(messages) {
    let fixed_system_prompt_content = "";
    const conversation_message_blocks = [];
    // console.log(`Original messages count: ${messages.length}`); // Less verbose logging

    // 1. 分离 System 消息，格式化 User/Assistant 消息
    for (const message of messages) {
        let content = (message.content === null || message.content === undefined) ? "" : String(message.content);
        switch (message.role) {
            case 'system':
                fixed_system_prompt_content += `System: ${content}\n\n`;
                break;
            case 'user':
                conversation_message_blocks.push(`Human: ${content}\n\n`);
                break;
            case 'assistant':
                conversation_message_blocks.push(`Assistant: ${content}\n\n`);
                break;
            default:
                console.warn(`Unsupported role: ${message.role}`);
                continue;
        }
    }

    // 2. 截断合并后的 system 消息（如果超长）
    if (fixed_system_prompt_content.length > SYSTEM_PROMPT_LIMIT) {
        const originalLength = fixed_system_prompt_content.length;
        fixed_system_prompt_content = fixed_system_prompt_content.substring(0, SYSTEM_PROMPT_LIMIT);
        console.warn(`Combined system messages truncated from ${originalLength} to ${SYSTEM_PROMPT_LIMIT}`);
    }
    fixed_system_prompt_content = fixed_system_prompt_content.trim();


    // 3. 计算 system_prompt 中留给对话历史的剩余空间
    let space_occupied_by_fixed_system = 0;
    if (fixed_system_prompt_content.length > 0) {
         space_occupied_by_fixed_system = fixed_system_prompt_content.length + 4; // 预留 \n\n...\n\n 的长度
    }
     const remaining_system_limit = Math.max(0, SYSTEM_PROMPT_LIMIT - space_occupied_by_fixed_system);
    // console.log(`Trimmed fixed system prompt length: ${fixed_system_prompt_content.length}. Approx remaining system history limit: ${remaining_system_limit}`);


    // 4. 反向填充 User/Assistant 对话历史
    const prompt_history_blocks = [];
    const system_prompt_history_blocks = [];
    let current_prompt_length = 0;
    let current_system_history_length = 0;
    let promptFull = false;
    let systemHistoryFull = (remaining_system_limit <= 0);

    // console.log(`Processing ${conversation_message_blocks.length} user/assistant messages for recency filling.`);
    for (let i = conversation_message_blocks.length - 1; i >= 0; i--) {
        const message_block = conversation_message_blocks[i];
        const block_length = message_block.length;

        if (promptFull && systemHistoryFull) {
            // console.log(`Both prompt and system history slots full. Omitting older messages from index ${i}.`);
            break;
        }

        // 优先尝试放入 prompt
        if (!promptFull) {
            if (current_prompt_length + block_length <= PROMPT_LIMIT) {
                prompt_history_blocks.unshift(message_block);
                current_prompt_length += block_length;
                continue;
            } else {
                promptFull = true;
                // console.log(`Prompt limit (${PROMPT_LIMIT}) reached. Trying system history slot.`);
            }
        }

        // 如果 prompt 满了，尝试放入 system_prompt 的剩余空间
        if (!systemHistoryFull) {
            if (current_system_history_length + block_length <= remaining_system_limit) {
                 system_prompt_history_blocks.unshift(message_block);
                 current_system_history_length += block_length;
                 continue;
            } else {
                 systemHistoryFull = true;
                 // console.log(`System history limit (${remaining_system_limit}) reached.`);
            }
        }
    }

    // 5. *** 组合最终的 prompt 和 system_prompt (包含分隔符逻辑) ***
    const system_prompt_history_content = system_prompt_history_blocks.join('').trim();
    const final_prompt = prompt_history_blocks.join('').trim();

    // 定义分隔符
    const SEPARATOR = "\n\n-------下面是比较早之前的对话内容-----\n\n";

    let final_system_prompt = "";

    const hasFixedSystem = fixed_system_prompt_content.length > 0;
    const hasSystemHistory = system_prompt_history_content.length > 0;

    if (hasFixedSystem && hasSystemHistory) {
        final_system_prompt = fixed_system_prompt_content + SEPARATOR + system_prompt_history_content;
        // console.log("Combining fixed system prompt and history with separator.");
    } else if (hasFixedSystem) {
        final_system_prompt = fixed_system_prompt_content;
        // console.log("Using only fixed system prompt.");
    } else if (hasSystemHistory) {
        final_system_prompt = system_prompt_history_content;
        // console.log("Using only history in system prompt slot.");
    }

    // 6. 返回结果
    const result = {
        system_prompt: final_system_prompt,
        prompt: final_prompt
    };

    console.log(`Final system_prompt length: ${result.system_prompt.length}, Final prompt length: ${result.prompt.length}`);

    return result;
}
// === convertMessagesToFalPrompt 函数结束 ===


/**
 * Wraps the fal.ai API call with retry logic using available keys.
 * @param {'stream' | 'subscribe'} operation - The fal operation to perform.
 * @param {string} functionId - The fal function ID (e.g., "fal-ai/any-llm").
 * @param {object} params - The parameters for the fal function call (input, logs, etc.).
 * @returns {Promise<any>} - The result from the successful fal call (stream or subscription result).
 * @throws {Error} - Throws an error if all keys fail or a non-key-related error occurs.
 */
async function tryFalCallWithFailover(operation, functionId, params) {
    const maxRetries = falKeys.length; // Try each key at most once per request cycle
    let lastError = null;

    for (let i = 0; i < maxRetries; i++) {
        const keyInfo = getNextKey();
        if (!keyInfo) {
            throw new Error(lastError ? `All FAL keys failed. Last error: ${lastError.message}` : "All FAL keys are currently unavailable (failed or in cooldown).");
        }

        const currentFalKey = keyInfo.key;
        console.log(`Attempt ${i + 1}/${maxRetries}: Using key ending in ...${currentFalKey.slice(-4)}`);

        try {
            // --- Configure fal client with the selected key for this attempt ---
            // WARNING: This global config change might have concurrency issues in high-load scenarios
            // if the fal client library doesn't isolate requests properly.
            fal.config({ credentials: currentFalKey });

            if (operation === 'stream') {
                const streamResult = await fal.stream(functionId, params);
                console.log(`Successfully initiated stream with key ending in ...${currentFalKey.slice(-4)}`);
                return streamResult;
            } else { // 'subscribe' (non-stream)
                const result = await fal.subscribe(functionId, params);
                console.log(`Successfully completed subscribe request with key ending in ...${currentFalKey.slice(-4)}`);

                if (result && result.error) {
                     console.warn(`Fal-ai returned an application error (non-stream) with key ...${currentFalKey.slice(-4)}: ${JSON.stringify(result.error)}`);
                }
                return result;
            }
        } catch (error) {
            console.error(`Error using key ending in ...${currentFalKey.slice(-4)}:`, error.message || error);
            lastError = error;

            if (isKeyRelatedError(error)) {
                markKeyFailed(keyInfo);
                console.log(`Key marked as failed. Trying next key if available...`);
            } else {
                console.error("Non-key related error occurred. Aborting retries.");
                throw error;
            }
        }
    }

    console.error("All FAL keys failed after attempting each one.");
    throw new Error(lastError ? `All FAL keys failed. Last error: ${lastError.message}` : "All FAL API keys failed.");
}


// POST /v1/chat/completions endpoint (Modified to use tryFalCallWithFailover)
app.post('/v1/chat/completions', async (req, res) => {
    const { model, messages, stream = false, reasoning = false, ...restOpenAIParams } = req.body;

    console.log(`Received chat completion request for model: ${model}, stream: ${stream}`);

    if (!FAL_SUPPORTED_MODELS.includes(model)) {
         console.warn(`Warning: Requested model '${model}' is not in the explicitly supported list.`);
    }
    if (!model || !messages || !Array.isArray(messages) || messages.length === 0) {
        console.error("Invalid request parameters:", { model, messages: Array.isArray(messages) ? messages.length : typeof messages });
        return res.status(400).json({ error: 'Missing or invalid parameters: model and messages array are required.' });
    }

    try {
        const { prompt, system_prompt } = convertMessagesToFalPrompt(messages);

        const falInput = {
            model: model,
            prompt: prompt,
            ...(system_prompt && { system_prompt: system_prompt }),
            reasoning: !!reasoning,
        };

        console.log("Prepared Fal Input (lengths):", { system_prompt: system_prompt?.length, prompt: prompt?.length });

        if (stream) {
            res.setHeader('Content-Type', 'text/event-stream; charset=utf-8');
            res.setHeader('Cache-Control', 'no-cache');
            res.setHeader('Connection', 'keep-alive');
            res.setHeader('Access-Control-Allow-Origin', '*');
            res.flushHeaders();

            let previousOutput = '';
            let falStream;

            try {
                 falStream = await tryFalCallWithFailover('stream', "fal-ai/any-llm", { input: falInput });

                 for await (const event of falStream) {
                    const currentOutput = (event && typeof event.output === 'string') ? event.output : '';
                    const isPartial = (event && typeof event.partial === 'boolean') ? event.partial : true;
                    const errorInfo = (event && event.error) ? event.error : null;

                    if (errorInfo) {
                        console.error("Error received *during* fal stream:", errorInfo);
                        const errorChunk = { id: `chatcmpl-${Date.now()}-error`, object: "chat.completion.chunk", created: Math.floor(Date.now() / 1000), model: model, choices: [{ index: 0, delta: {}, finish_reason: "error", message: { role: 'assistant', content: `Fal Stream Error: ${JSON.stringify(errorInfo)}` } }] };
                        res.write(`data: ${JSON.stringify(errorChunk)}\n\n`);
                        break;
                    }

                    let deltaContent = '';
                    if (currentOutput.startsWith(previousOutput)) {
                        deltaContent = currentOutput.substring(previousOutput.length);
                    } else if (currentOutput.length > 0) {
                        console.warn("Fal stream output mismatch detected. Sending full current output as delta.", { previousLength: previousOutput.length, currentLength: currentOutput.length });
                        deltaContent = currentOutput;
                        previousOutput = '';
                    }
                    previousOutput = currentOutput;

                    if (deltaContent || !isPartial) {
                        const openAIChunk = { id: `chatcmpl-${Date.now()}`, object: "chat.completion.chunk", created: Math.floor(Date.now() / 1000), model: model, choices: [{ index: 0, delta: { content: deltaContent }, finish_reason: isPartial === false ? "stop" : null }] };
                        res.write(`data: ${JSON.stringify(openAIChunk)}\n\n`);
                    }
                 }
                 res.write(`data: [DONE]\n\n`);
                 res.end();
                 console.log("Stream finished successfully.");

            } catch (streamError) {
                console.error('Error during stream processing:', streamError);
                if (!res.writableEnded) {
                     try {
                         const errorDetails = (streamError instanceof Error) ? streamError.message : JSON.stringify(streamError);
                         const finalErrorChunk = { error: { message: "Stream failed", type: "proxy_error", details: errorDetails } };
                         res.write(`data: ${JSON.stringify(finalErrorChunk)}\n\n`);
                         res.write(`data: [DONE]\n\n`);
                         res.end();
                     } catch (finalError) {
                         console.error('Error sending final stream error message to client:', finalError);
                         if (!res.writableEnded) { res.end(); }
                     }
                 }
            }

        } else { // Non-stream
             console.log("Executing non-stream request with failover...");
             const result = await tryFalCallWithFailover('subscribe', "fal-ai/any-llm", { input: falInput, logs: true });

             console.log("Received non-stream result from fal-ai via failover wrapper.");

             if (result && result.error) {
                 console.error("Fal-ai returned an application error in non-stream mode (after successful API call):", result.error);
                 return res.status(500).json({
                      object: "error",
                      message: `Fal-ai application error: ${JSON.stringify(result.error)}`,
                      type: "fal_ai_error",
                      param: null,
                      code: result.error.code || null
                 });
             }

             const openAIResponse = {
                 id: `chatcmpl-${result?.requestId || Date.now()}`,
                 object: "chat.completion",
                 created: Math.floor(Date.now() / 1000),
                 model: model,
                 choices: [{
                     index: 0,
                     message: {
                         role: "assistant",
                         content: result?.output || ""
                     },
                     finish_reason: "stop"
                 }],
                 usage: {
                     prompt_tokens: null,
                     completion_tokens: null,
                     total_tokens: null
                 },
                 system_fingerprint: null,
                 ...(result?.reasoning && { fal_reasoning: result.reasoning }),
             };
             res.json(openAIResponse);
             console.log("Returned non-stream response successfully.");
        }

    } catch (error) {
        console.error('Unhandled error in /v1/chat/completions:', error);
        if (!res.headersSent) {
            const errorMessage = (error instanceof Error) ? error.message : JSON.stringify(error);
            const errorType = error.message?.includes("All FAL keys failed") ? "api_key_error" : "proxy_internal_error";
            res.status(500).json({
                 error: {
                     message: `Internal Server Error in Proxy: ${errorMessage}`,
                     type: errorType,
                     details: error.stack // Optional: include stack in dev/debug mode
                 }
            });
        } else if (!res.writableEnded) {
             console.error("Headers already sent, attempting to end response after error.");
             res.end();
        }
    }
});

// --- Server Start ---
app.listen(PORT, () => {
    console.log(`===========================================================`);
    console.log(` Fal OpenAI Proxy Server (Multi-Key Failover)`);
    console.log(` Listening on port: ${PORT}`);
    // *** 更新日志信息以引用 FAL_KEY ***
    console.log(` Loaded ${falKeys.length} FAL API Key(s) from FAL_KEY.`);
    console.log(` API Key Auth Enabled: ${API_KEY ? 'Yes' : 'No'}`);
    console.log(` Limits: System Prompt=${SYSTEM_PROMPT_LIMIT}, Prompt=${PROMPT_LIMIT}`);
    console.log(` Chat Completions: POST http://localhost:${PORT}/v1/chat/completions`);
    console.log(` Models Endpoint: GET http://localhost:${PORT}/v1/models`);
    console.log(`===========================================================`);
});

// Root path response
app.get('/', (req, res) => {
    res.send('Fal OpenAI Proxy (Multi-Key Failover) is running.');
});