# System Architecture

This document breaks down how the system is designed and why certain architectural decisions were made.

## High Level Architecture

```
[ASCII diagram showing major components and how they connect]

Example:
┌─────────────┐
│   Client    │
└──────┬──────┘
       │
       ▼
┌─────────────┐
│  Component  │
└──────┬──────┘
       │
       ▼
┌─────────────┐
│   Storage   │
└─────────────┘
```

### Component Breakdown

**[Component 1]**
- Purpose: [What this component does]
- Responsibilities: [Specific tasks it handles]
- Interfaces: [How other components interact with it]

**[Component 2]**
- Purpose: [What this component does]
- Responsibilities: [Specific tasks it handles]
- Interfaces: [How other components interact with it]

**[Component 3]**
- Purpose: [What this component does]
- Responsibilities: [Specific tasks it handles]
- Interfaces: [How other components interact with it]

## Data Flow

### [Primary Use Case Flow]

Step by step walkthrough of what happens when [primary operation]:

```
1. [Action] → [Component]
   [What happens, what data is passed]

2. [Component] → [Next component]
   [Processing that occurs, transformations]

3. [Next component] → [Result]
   [Final output or state change]
```

Example with code references:
```
1. User sends request → API endpoint (src/routes/endpoint.py:42)
   Validates input, extracts credentials

2. API → Service layer (src/services/auth.py:108)
   Business logic runs, queries database

3. Service → Response (src/routes/endpoint.py:67)
   Formats result, returns to user
```

### [Secondary Use Case Flow]

[Repeat for other major operations]

## Design Patterns

### [Pattern 1 Used in Project]

**What it is:**
[Brief explanation of the pattern]

**Where we use it:**
[Specific files or components that implement this pattern]

**Why we chose it:**
[Advantages for this specific use case, alternatives considered]

**Trade-offs:**
- Pros: [What you gain]
- Cons: [What you give up]

Example implementation:
```[language]
[Code snippet showing the pattern in action from the actual project]
```

### [Pattern 2]

[Same structure]

## Layer Separation

[If applicable - explain the layer architecture]

```
┌────────────────────────────────────┐
│    Layer 1: [Name]                 │
│    - [Responsibility]              │
│    - [What it doesn't do]          │
└────────────────────────────────────┘
           ↓
┌────────────────────────────────────┐
│    Layer 2: [Name]                 │
│    - [Responsibility]              │
│    - [What it doesn't do]          │
└────────────────────────────────────┘
           ↓
┌────────────────────────────────────┐
│    Layer 3: [Name]                 │
│    - [Responsibility]              │
│    - [What it doesn't do]          │
└────────────────────────────────────┘
```

### Why Layers?

[Explain the benefits of this separation]
- [Benefit 1]
- [Benefit 2]
- [Benefit 3]

### What Lives Where

**[Layer 1]:**
- Files: [Which files belong to this layer]
- Imports: [Can import from which other layers]
- Forbidden: [What this layer should never do]

**[Layer 2]:**
[Same structure]

**[Layer 3]:**
[Same structure]

## Data Models

### [Model 1]

```[language]
[Actual data structure from the project]
```

**Fields explained:**
- `[field_name]`: [What this stores, why it's needed, any constraints]
- `[field_name]`: [Explanation]
- `[field_name]`: [Explanation]

**Relationships:**
- [How this model connects to others]
- [Why these relationships exist]

### [Model 2]

[Same structure for each major data model]

## Security Architecture

### Threat Model

What we're protecting against:
1. **[Threat 1]** - [Specific attack scenario]
2. **[Threat 2]** - [Specific attack scenario]
3. **[Threat 3]** - [Specific attack scenario]

What we're NOT protecting against (out of scope):
- [Thing 1] - [Why this is out of scope]
- [Thing 2] - [Reason]

### Defense Layers

[Explain how security is implemented at different levels]

```
Layer 1: [Defense mechanism]
    ↓
Layer 2: [Defense mechanism]
    ↓
Layer 3: [Defense mechanism]
```

**Why multiple layers?**
[Explain defense in depth for this specific project]

## Storage Strategy

### [Storage Type 1]

**What we store:**
- [Data type 1]
- [Data type 2]

**Why this storage:**
[Explain choice - performance, durability, cost, etc]

**Schema design:**
```
[Show key structure or table design]
```

### [Storage Type 2]

[If using multiple storage backends]

## Configuration

### Environment Variables

```bash
[VARIABLE_NAME]  # [What it configures, default value, why you'd change it]
[VARIABLE_NAME]  # [Explanation]
```

### Configuration Strategy

[Explain how config is managed - files, env vars, secrets, etc]

**Development:**
[How config works in dev]

**Production:**
[How config works in prod, security considerations]

## Performance Considerations

### Bottlenecks

Where this system gets slow under load:
1. **[Bottleneck 1]** - [Why this happens, when it matters]
2. **[Bottleneck 2]** - [Explanation]

### Optimizations

What we did to make it faster:
- **[Optimization 1]**: [What we changed, impact it had]
- **[Optimization 2]**: [Details]

### Scalability

**Vertical scaling:**
[How to scale up - more CPU/RAM]
[Where limits are]

**Horizontal scaling:**
[How to scale out - more instances]
[What needs to change to support this]

## Design Decisions

### [Major Decision 1]

**What we chose:**
[The approach taken]

**Alternatives considered:**
- [Option A] - Rejected because [reason]
- [Option B] - Rejected because [reason]

**Trade-offs:**
[What we gained and what we gave up with this choice]

### [Major Decision 2]

[Same structure for each significant architectural choice]

## Deployment Architecture

[If applicable - how this runs in production]

```
[Diagram showing deployment topology]
```

**Components:**
- [Service 1]: [What it runs, how many instances, why]
- [Service 2]: [Details]

**Infrastructure:**
- [Database/cache/etc]: [How it's deployed]

## Error Handling Strategy

### Error Types

1. **[Error category 1]** - [What causes this, how we handle it]
2. **[Error category 2]** - [Details]

### Recovery Mechanisms

[How the system recovers from failures]

**[Failure scenario 1]:**
- Detection: [How we know it happened]
- Response: [What the system does]
- Recovery: [How to get back to normal]

## Extensibility

### Where to Add Features

Want to add [type of feature]? Here's where it goes:

1. [Step 1 with file references]
2. [Step 2]
3. [Step 3]

### Plugin Architecture

[If applicable - how the system can be extended without modifying core code]

## Limitations

Current architectural limitations:
1. **[Limitation 1]** - [What you can't do, why not, how to fix it]
2. **[Limitation 2]** - [Details]

These are not bugs, they're conscious trade-offs. Fixing them would require [what changes].

## Comparison to Similar Systems

### [Similar tool/approach 1]

How we're different:
- [Difference 1]
- [Difference 2]

Why we made different choices:
[Reasoning specific to this use case]

### [Similar tool/approach 2]

[Same structure]

## Evolution

### Version 1.0 Design

[If relevant - how the architecture has changed]

Initial design was [approach]. We changed to current design because [reason].

### Future Improvements

Planned architectural changes:
1. **[Improvement 1]** - [Why we want this, what it enables]
2. **[Improvement 2]** - [Details]

## Key Files Reference

Quick map of where to find things:

- `[file/directory]` - [What's implemented here]
- `[file/directory]` - [Purpose]
- `[file/directory]` - [What to look at]

## Next Steps

Now that you understand the architecture:
1. Read [03-IMPLEMENTATION.md](./03-IMPLEMENTATION.md) for code walkthrough
2. Try modifying [specific component] to understand [concept]