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Stop reading logs. Start watching them. MermaidTrace is a specialized logging tool that automatically generates Mermaid JS sequence diagrams from your code execution. It's perfect for visualizing complex business logic, microservice interactions, or asynchronous flows.

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<h1 align="center">MermaidTrace: Visualize Your Python Code Logic</h1>

 <img src="docs/images/logo.png" alt="MermaidTrace Logo" width="600">

Stop drowning in cryptic logs. One line of code to transform complex execution logic into clear Mermaid sequence diagrams.

🌐 Language: <a href="README.md">English</a> | <a href="README_CN.md">中文</a>

## 🏗️ Architecture

```mermaid
flowchart TB
    %% Style Definitions
    classDef userLayer fill:#e3f2fd,stroke:#1565c0,stroke-width:2px,color:#0d47a1,rx:5,ry:5
    classDef coreLayer fill:#fff3e0,stroke:#e65100,stroke-width:2px,color:#bf360c,rx:5,ry:5
    classDef ioLayer fill:#e8f5e9,stroke:#2e7d32,stroke-width:2px,color:#1b5e20,rx:5,ry:5
    classDef vizLayer fill:#f3e5f5,stroke:#7b1fa2,stroke-width:2px,color:#4a148c,rx:5,ry:5
    classDef storage fill:#eceff1,stroke:#455a64,stroke-width:2px,color:#263238,shape:cyl

subgraph User["👤 User Integration"]
        direction TB
        Decorator["@trace / @trace_class"]:::userLayer
        Middleware["FastAPI Middleware"]:::userLayer
        Callback["LangChain Callback"]:::userLayer
    end

subgraph Core["⚙️ Core Engine"]
 direction TB
 Context["ContextVars (Trace Context)"]:::coreLayer
 EventBus["Event Bus (LogContext)"]:::coreLayer
 Masker["Data Masking (Sanitizer)"]:::coreLayer
 end

subgraph IO["⚡ Async I/O Layer"]
 direction TB
 Queue["Async Queue (Non-blocking)"]:::ioLayer
 Writer["File Handler (Rotating/Timed)"]:::ioLayer
 end

Storage[(".mmd File")]:::storage

subgraph Viz["🌐 Visualization"]
 direction TB
 Watcher["Watchdog (File Monitor)"]:::vizLayer
 Server["FastAPI Server (SSE Support)"]:::vizLayer
 Browser["Web Browser (Mermaid.js + PanZoom)"]:::vizLayer
 end

%% Data Flow
    Decorator --> Context
    Middleware --> Context
    Callback --> Context
    Context --> EventBus
    EventBus --> Masker
    Masker --> Queue
    Queue --> Writer
    Writer --> Storage
    Storage -.-> Watcher
    Watcher --> Server
    Server == "SSE Push" ==> Browser

%% Link Styles
    linkStyle default stroke:#607d8b,stroke-width:2px
```

---

## ⚡️ Understand MermaidTrace in 5 Seconds

#### 1. Original Code (15+ lines)
```python
@trace(source="User", target="OrderSys")
def create_order(user_id, items):
    # Complex business logic
    if not check_inventory(items):
        return "Out of Stock"

# Nested logic calls
    price = calculate_price(items)
    discount = get_discount(user_id)
    final = price - discount

# External service interactions
    res = pay_service.process(final)
    if res.success:
        update_stock(items)
        send_notif(user_id)
        return "Success"
    return "Failed"
```

#### 2. Auto-Generated Sequence Diagram
```mermaid
sequenceDiagram
    autonumber
    User->>OrderSys: create_order(user_id, items)
    activate OrderSys
    OrderSys->>Inventory: check_inventory(items)
    Inventory-->>OrderSys: True
    OrderSys->>Pricing: calculate_price(items)
    Pricing-->>OrderSys: 100.0
    OrderSys->>UserDB: get_discount(user_id)
    UserDB-->>OrderSys: 5.0
    OrderSys->>PayService: process(95.0)
    activate PayService
    PayService-->>OrderSys: success
    deactivate PayService
    OrderSys->>Inventory: update_stock(items)
    OrderSys->>Notification: send_notif(user_id)
    OrderSys-->>User: "Success"
    deactivate OrderSys
```

---

## 🚀 Dynamic Demo & Online Tryout

### 🎬 Quick Demo

![MermaidTrace Master Preview](https://raw.githubusercontent.com/xt765/mermaid-trace/main/docs/images/master_preview.png)

*(Master Preview: Multi-file browsing, live-reload, and interactive pan/zoom)*

```mermaid
sequenceDiagram
    participant CLI as mermaid-trace CLI
    participant App as Python App
    participant Web as Live Preview

Note over CLI, Web: Enable Live Preview Mode
    CLI->>Web: Start HTTP Server (localhost:8000)
    App->>App: Run Logic (with @trace decorator)
    App->>App: Auto-update flow.mmd
    Web->>Web: File Change Detected (Hot Reload)
    Web-->>CLI: Render Latest Diagram
```
*(From adding decorators to browser live preview in 10 seconds)*

### 🛠️ Try Online (Google Colab)

No local setup required. Experience core features in your browser:

[![Open In Colab](https://img.shields.io/badge/Colab-Open%20in%20Colab-blue?style=flat&logo=google-colab&logoColor=white)](https://colab.research.google.com/github/xt765/mermaid-trace/blob/main/examples/MermaidTrace_Demo.ipynb)

---

## 🎯 Why MermaidTrace? (Use Cases)

### 1. Master "Legacy" Codebases
**Pain**: Taking over a complex, undocumented legacy project with tangled function calls.
**Solution**: Add `@trace_class` or `@trace` to entry points and run the code once.
**Value**: Instantly generate a complete execution path map to understand the architecture.

### 2. Automated Technical Docs
**Pain**: Manual sequence diagrams are time-consuming and quickly become outdated.
**Solution**: Integrate MermaidTrace during development.
**Value**: Diagrams stay 100% in sync with your code logic automatically.

### 3. Debug Complex Recursion & Concurrency
**Pain**: Nested calls or async tasks produce interleaved logs that are impossible to read.
**Solution**: Use built-in async support and intelligent collapsing.
**Value**: Visualize recursion depth and concurrency flow to pinpoint logic bottlenecks.

---

## 🚀 Quick Start in 3 Steps

### 1. Install
```bash
pip install mermaid-trace
```

### 2. Add Decorators
```python
from mermaid_trace import trace, configure_flow

# Configure output file
configure_flow("my_flow.mmd")

@trace(source="User", target="AuthService")
def login(username):
    return verify_db(username)

@trace(source="AuthService", target="DB")
def verify_db(username):
    return True

login("admin")
```

### 3. View Diagram

Run the built-in CLI tool to preview in real-time (with hot-reload):

```bash
# Preview a single file (Auto-reload, Pan/Zoom supported)
mermaid-trace serve my_flow.mmd

# Preview a directory (File browser, Multi-file switching)
mermaid-trace serve .
```

### 🔗 LangChain Integration
Visualize LLM chains, agents, and RAG retrieval with a single handler:
```python
from mermaid_trace.integrations.langchain import MermaidTraceCallbackHandler

handler = MermaidTraceCallbackHandler(host_name="MyAIApp")
# Pass to any LangChain object
chain.invoke({"input": "..."}, config={"callbacks": [handler]})
```

---

## ✨ Key Features

- **Decorator-Driven**: Simply add `@trace` or `@trace_interaction` to functions.
- **Auto-Instrumentation**: Use `@trace_class` to trace a whole class at once.
- **Data Privacy**: Automatic **Data Masking** for sensitive fields (passwords, tokens).
- **Performance Control**: Configurable **Sampling Rate** for high-throughput systems.
- **Distributed Tracing**: Support for **W3C Trace Context**, **B3**, and custom headers to link microservices.
- **Third-Party Patching**: Use `patch_object` to trace calls inside external libraries.
- **Async Support**: Seamlessly works with `asyncio` coroutines and concurrency.
- **Enhanced Web UI**: Interactive preview server with file browsing, auto-reload, and pan/zoom support.
- **Intelligent Collapsing**: Automatically collapses repetitive calls and identifies loops.
- **FastAPI Integration**: Middleware for zero-config HTTP request tracing with header propagation.
- **LangChain Integration**: Callback Handler for LLM chains and agent visualization.
- **Detailed Exceptions**: Captures full stack traces for errors, displayed in the diagram.

---

## 📚 Documentation

### Core Documentation

[User Guide](docs/en/USER_GUIDE.md) · [API Reference](docs/en/API.md) · [Contributing Guidelines](docs/en/CONTRIBUTING.md) · [Changelog](docs/en/CHANGELOG.md) · [License](LICENSE)

### Code Comment Documents

| Category | Links |
| :--- | :--- |
| **Core Modules** | [Context](docs/en/code_comments/src/mermaid_trace/core/context.md) · [Decorators](docs/en/code_comments/src/mermaid_trace/core/decorators.md) · [Events](docs/en/code_comments/src/mermaid_trace/core/events.md) · [Formatter](docs/en/code_comments/src/mermaid_trace/core/formatter.md) |
| **Handlers** | [Async Handler](docs/en/code_comments/src/mermaid_trace/handlers/async_handler.md) · [Mermaid Handler](docs/en/code_comments/src/mermaid_trace/handlers/mermaid_handler.md) |
| **Integrations** | [FastAPI](docs/en/code_comments/src/mermaid_trace/integrations/fastapi.md) |
| **Others** | [init](docs/en/code_comments/src/mermaid_trace/__init__.md) · [CLI](docs/en/code_comments/src/mermaid_trace/cli.md) |

---

## 🤝 Contributing

We welcome contributions! Please see [CONTRIBUTING.md](docs/en/CONTRIBUTING.md) for details.

---

## 📄 License

MIT

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