# Hydra Browser Architecture

This document explains the Hydra Browser architecture for a developer who knows Python but is new to frontend and Electron. It focuses on how the app is structured, how data flows, and how the main features work.

## 1. What This App Is

Hydra is a **desktop app** (Electron) that renders **web pages inside a canvas of linked windows**. Each window is a React Flow node. Links can open new windows and form a graph of browsing paths.

Key ideas:
- **Electron** runs a desktop window using Chromium.
- The **renderer** is a React app (frontend UI).
- A **local proxy server** fetches web pages and injects scripts to intercept clicks.
- **Zustand store** holds all app state (nodes, edges, UI state).

## 2. High-Level Architecture

```mermaid
flowchart LR
  subgraph Electron App
    Main[Main Process
src/main/index.js]
    Renderer[Renderer Process
React UI]
  end

  Renderer -->|HTTP| Proxy[Local Proxy Server
src/server/proxy.js]
  Renderer <-->|IPC| Main
  Proxy -->|Fetch| Internet[Websites]
```

### Roles
- **Main Process**: bootstraps Electron and starts the proxy server.
- **Renderer**: React UI + state. Renders the canvas and windows.
- **Proxy Server**: fetches web content, injects scripts, returns HTML to iframes.

## 3. Key Modules

### 3.1 Main Process (Electron)
**File:** `src/main/index.js`

Responsibilities:
- Create the Electron window.
- Start the local proxy server (port 3001).
- Provide IPC handlers for file-based session save/load.

### 3.2 Proxy Server
**File:** `src/server/proxy.js`

Responsibilities:
- Fetch remote pages (via Axios).
- Inject a script into HTML to:
  - intercept clicks
  - intercept form submissions
  - intercept programmatic navigations
  - send `postMessage` events back to the renderer
  - provide page text for summaries/chat

### 3.3 Renderer
**Root:** `src/renderer`

Key pieces:
- `components/ReactFlowCanvas.tsx`: canvas and node types
- `components/BrowserWindowNode.tsx`: web window node
- `components/NoteWindowNode.tsx`: notes
- `components/SummaryWindowNode.tsx`: AI summary output
- `components/ChatWindowNode.tsx`: AI chat window
- `store/hydraStore.ts`: Zustand store (all app state)

## 4. Data Flow: Opening a Page

```mermaid
sequenceDiagram
  participant UI as BrowserWindowNode
  participant Store as Hydra Store
  participant Proxy as Proxy Server
  participant Web as Website

  UI->>Store: addBrowserWindow(url)
  Store->>UI: node created (BrowserWindowNode)
  UI->>Proxy: GET /fetch?url=...
  Proxy->>Web: fetch page
  Web->>Proxy: HTML response
  Proxy->>Proxy: inject link interception script
  Proxy->>UI: HTML (blob URL)
  UI->>UI: iframe loads blob
```

## 5. How Link Expansion Works

When the injected script sees a link click or navigation, it sends:

```js
window.parent.postMessage({
  type: 'HYDRA_LINK_CLICK',
  url: 'https://example.com',
  openInNewWindow: true|false
}, '*')
```

The renderer listens for these messages and either:
- opens a new node and connects it with an edge, or
- navigates within the same node

```mermaid
flowchart TD
  Click[User clicks link] --> Script[Injected script]
  Script -->|postMessage| Renderer
  Renderer -->|openInNewWindow| StoreAdd[addBrowserWindow]
  Renderer -->|same window| StoreNav[navigateBrowserWindow]
```

## 6. State Management (Zustand)

**File:** `src/renderer/store/hydraStore.ts`

The store keeps:
- **nodes**: all windows on the canvas
- **edges**: relationships between windows
- **theme**: dark/light
- **AI settings**: provider, API key, model
- **session info**: file path + name

### Example: Creating a Browser Window Node

```ts
addBrowserWindow(url, parentId?)
```
- Creates a new React Flow node
- Optionally creates an edge from the parent
- Re-layouts the graph so windows align

## 7. Layout Engine

**File:** `src/renderer/store/hydraStore.ts`

A custom layout function positions nodes:
- Root nodes are stacked vertically
- Children appear to the right of their parent
- Subtrees never overlap

```mermaid
graph LR
  A[Root 1] --> B[Child 1]
  A --> C[Child 2]
  D[Root 2] --> E[Child]
```

## 8. Node Types

| Type | Purpose | File |
|------|---------|------|
| browserWindow | Render a web page | `BrowserWindowNode.tsx` |
| noteWindow | Editable note | `NoteWindowNode.tsx` |
| summaryWindow | AI summary output | `SummaryWindowNode.tsx` |
| chatWindow | AI chat UI | `ChatWindowNode.tsx` |

## 9. AI Features

### 9.1 Summaries
- Renderer requests page text via `postMessage`.
- Sends request to `/summarize` on the proxy.
- Proxy calls OpenAI/Anthropic API.
- Summary text displayed in a Summary node.

```mermaid
sequenceDiagram
  participant UI as BrowserWindowNode
  participant Proxy as Proxy Server
  participant LLM as AI Provider

  UI->>Proxy: POST /summarize {text, url}
  Proxy->>LLM: summarize
  LLM->>Proxy: summary
  Proxy->>UI: summary
```

### 9.2 Chat
- Chat node sends messages to `/chat` on proxy.
- Proxy adds context text and calls LLM API.

## 10. Session Files (File-Based)

Sessions are saved to disk using file dialogs. No in-app storage.

- **Save**: user chooses a `.hydra` file.
- **Load**: user selects a `.hydra` file.

Flow:
```mermaid
flowchart LR
  UI -->|IPC| Main
  Main -->|showSaveDialog/openDialog| OS
  OS --> Main
  Main -->|read/write file| FileSystem
```

## 11. Important Constraints

- Some sites block iframes (`X-Frame-Options`, `CSP frame-ancestors`).
- JavaScript-driven navigation can bypass the proxy if not intercepted.
- Removing `allow-same-origin` increases safety but prevents direct DOM access.

## 12. Mental Model (Python Developer Friendly)

Think of it as:
- **Electron Main** = Python `if __name__ == '__main__':` boot process
- **Renderer** = GUI app logic (like a web app)
- **Proxy Server** = a local Flask server that fetches and rewrites HTML
- **Zustand Store** = a global state dictionary
- **React Flow** = a canvas + graph UI library

## 13. Where to Start Reading

Recommended order:
1. `src/main/index.js` – app bootstrap
2. `src/server/proxy.js` – page fetching and injection
3. `src/renderer/store/hydraStore.ts` – core data model
4. `src/renderer/components/ReactFlowCanvas.tsx` – node registration
5. `src/renderer/components/BrowserWindowNode.tsx` – core window node

---

If you want a deeper walkthrough of any module, ask and I’ll expand that section.