my-mistral-project/
├── src/
│   ├── mistral/
│   │   ├── client.ts           # Singleton client wrapper
│   │   ├── config.ts           # Environment configuration
│   │   ├── types.ts            # TypeScript types
│   │   ├── errors.ts           # Custom error classes
│   │   ├── prompts/            # Prompt templates
│   │   │   ├── system.ts       # System prompts
│   │   │   └── templates.ts    # Reusable templates
│   │   └── handlers/
│   │       ├── chat.ts         # Chat completion handlers
│   │       ├── embeddings.ts   # Embedding handlers
│   │       └── tools.ts        # Function calling handlers
│   ├── services/
│   │   └── ai/
│   │       ├── index.ts        # Service facade
│   │       ├── chat.ts         # Chat service
│   │       ├── rag.ts          # RAG implementation
│   │       └── cache.ts        # Caching layer
│   ├── api/
│   │   └── chat/
│   │       ├── route.ts        # API endpoint
│   │       └── stream.ts       # Streaming endpoint
│   └── jobs/
│       └── ai/
│           └── batch.ts        # Background processing
├── tests/
│   ├── unit/
│   │   └── mistral/
│   └── integration/
│       └── mistral/
├── config/
│   ├── mistral.development.json
│   ├── mistral.staging.json
│   └── mistral.production.json
└── docs/
    └── mistral/
        ├── SETUP.md
        └── RUNBOOK.md

┌─────────────────────────────────────────┐
│             API Layer                    │
│   (Routes, Controllers, Middleware)      │
├─────────────────────────────────────────┤
│           Service Layer                  │
│  (Business Logic, Orchestration)         │
├─────────────────────────────────────────┤
│          Mistral Layer                   │
│   (Client, Prompts, Error Handling)      │
├─────────────────────────────────────────┤
│         Infrastructure Layer             │
│    (Cache, Queue, Monitoring)            │
└─────────────────────────────────────────┘

// src/mistral/client.ts
import Mistral from '@mistralai/mistralai';
import { getMistralConfig } from './config';

let instance: Mistral | null = null;

export function getMistralClient(): Mistral {
  if (!instance) {
    const config = getMistralConfig();
    instance = new Mistral({
      apiKey: config.apiKey,
      timeout: config.timeout,
    });
  }
  return instance;
}

export function resetMistralClient(): void {
  instance = null;
}

// src/mistral/config.ts
import { z } from 'zod';

const configSchema = z.object({
  apiKey: z.string().min(1),
  model: z.string().default('mistral-small-latest'),
  timeout: z.number().default(30000),
  maxRetries: z.number().default(3),
  cache: z.object({
    enabled: z.boolean().default(true),
    ttlSeconds: z.number().default(300),
  }).default({}),
});

export type MistralConfig = z.infer<typeof configSchema>;

export function getMistralConfig(): MistralConfig {
  const env = process.env.NODE_ENV || 'development';

  const baseConfig = {
    apiKey: process.env.MISTRAL_API_KEY,
    model: process.env.MISTRAL_MODEL,
    timeout: parseInt(process.env.MISTRAL_TIMEOUT || '30000'),
    maxRetries: parseInt(process.env.MISTRAL_MAX_RETRIES || '3'),
  };

  return configSchema.parse(baseConfig);
}

// src/mistral/errors.ts
export class MistralServiceError extends Error {
  constructor(
    message: string,
    public readonly code: string,
    public readonly status?: number,
    public readonly retryable: boolean = false,
    public readonly originalError?: Error
  ) {
    super(message);
    this.name = 'MistralServiceError';
  }
}

export function wrapMistralError(error: unknown): MistralServiceError {
  if (error instanceof MistralServiceError) return error;

  const err = error as any;

  // Rate limit
  if (err.status === 429) {
    return new MistralServiceError(
      'Rate limit exceeded',
      'RATE_LIMIT',
      429,
      true,
      err
    );
  }

  // Auth error
  if (err.status === 401) {
    return new MistralServiceError(
      'Authentication failed',
      'AUTH_ERROR',
      401,
      false,
      err
    );
  }

  // Server error
  if (err.status >= 500) {
    return new MistralServiceError(
      'Mistral service error',
      'SERVICE_ERROR',
      err.status,
      true,
      err
    );
  }

  return new MistralServiceError(
    err.message || 'Unknown error',
    'UNKNOWN',
    err.status,
    false,
    err
  );
}

// src/services/ai/chat.ts
import { getMistralClient } from '../../mistral/client';
import { wrapMistralError } from '../../mistral/errors';
import { withRetry } from '../../utils/retry';
import { cache } from './cache';

export interface ChatOptions {
  model?: string;
  temperature?: number;
  maxTokens?: number;
  useCache?: boolean;
}

export class ChatService {
  async complete(
    messages: Array<{ role: string; content: string }>,
    options: ChatOptions = {}
  ): Promise<string> {
    const client = getMistralClient();
    const model = options.model || 'mistral-small-latest';

    // Check cache for deterministic requests
    if (options.useCache && options.temperature === 0) {
      const cached = await cache.get(messages, model);
      if (cached) return cached;
    }

    try {
      const response = await withRetry(() =>
        client.chat.complete({
          model,
          messages,
          temperature: options.temperature,
          maxTokens: options.maxTokens,
        })
      );

      const content = response.choices?.[0]?.message?.content ?? '';

      // Cache deterministic responses
      if (options.useCache && options.temperature === 0) {
        await cache.set(messages, model, content);
      }

      return content;
    } catch (error) {
      throw wrapMistralError(error);
    }
  }

  async *stream(
    messages: Array<{ role: string; content: string }>,
    options: ChatOptions = {}
  ): AsyncGenerator<string> {
    const client = getMistralClient();
    const model = options.model || 'mistral-small-latest';

    try {
      const stream = await client.chat.stream({
        model,
        messages,
        temperature: options.temperature,
        maxTokens: options.maxTokens,
      });

      for await (const event of stream) {
        const content = event.data?.choices?.[0]?.delta?.content;
        if (content) yield content;
      }
    } catch (error) {
      throw wrapMistralError(error);
    }
  }
}

export const chatService = new ChatService();

// src/mistral/health.ts
import { getMistralClient } from './client';

export interface HealthStatus {
  status: 'healthy' | 'degraded' | 'unhealthy';
  latencyMs: number;
  error?: string;
}

export async function checkMistralHealth(): Promise<HealthStatus> {
  const client = getMistralClient();
  const start = Date.now();

  try {
    await client.models.list();
    return {
      status: 'healthy',
      latencyMs: Date.now() - start,
    };
  } catch (error: any) {
    return {
      status: 'unhealthy',
      latencyMs: Date.now() - start,
      error: error.message,
    };
  }
}

// src/mistral/prompts/templates.ts
export interface PromptTemplate {
  system: string;
  user: (vars: Record<string, string>) => string;
}

export const templates: Record<string, PromptTemplate> = {
  summarize: {
    system: 'You are a helpful assistant that creates concise summaries.',
    user: ({ text, maxWords }) =>
      `Summarize the following text in ${maxWords || '100'} words or less:\n\n${text}`,
  },

  classify: {
    system: 'You are a classifier. Respond with only the category name.',
    user: ({ text, categories }) =>
      `Classify the following text into one of these categories: ${categories}\n\nText: ${text}`,
  },

  codeReview: {
    system: 'You are an expert code reviewer. Be concise and actionable.',
    user: ({ code, language }) =>
      `Review this ${language} code and suggest improvements:\n\n\`\`\`${language}\n${code}\n\`\`\``,
  },
};

export function buildPrompt(
  templateName: keyof typeof templates,
  vars: Record<string, string>
): Array<{ role: string; content: string }> {
  const template = templates[templateName];
  return [
    { role: 'system', content: template.system },
    { role: 'user', content: template.user(vars) },
  ];
}

User Request
     │
     ▼
┌─────────────┐
│   API       │
│   Gateway   │
└──────┬──────┘
       │
       ▼
┌─────────────┐    ┌─────────────┐
│   Service   │───▶│   Cache     │
│   Layer     │    │   (Redis)   │
└──────┬──────┘    └─────────────┘
       │
       ▼
┌─────────────┐
│   Mistral   │
│   Client    │
└──────┬──────┘
       │
       ▼
┌─────────────┐
│  Mistral    │
│   API       │
└─────────────┘

mkdir -p src/mistral/{handlers,prompts}
mkdir -p src/services/ai
mkdir -p src/api/chat
mkdir -p tests/{unit,integration}/mistral
mkdir -p config docs/mistral