# Epic 1: Implementation Summary

## Overview

Epic 1 implements the core kernel and infrastructure of the Go Platform, including database layer with Ent ORM, health monitoring, metrics, error handling, HTTP server, and OpenTelemetry tracing. This epic provides the foundation for all future modules and services.

## Completed Stories

### ✅ 1.1 Enhanced Dependency Injection Container
- Extended DI container with providers for all core services
- Database, health, metrics, error bus, and HTTP server providers
- Lifecycle management for all services
- `CoreModule()` exports all core services

### ✅ 1.2 Database Layer with Ent ORM
- Ent schema for User, Role, Permission, AuditLog entities
- Many-to-many relationships (User-Role, Role-Permission)
- Database client wrapper with connection pooling
- Automatic migrations on startup
- PostgreSQL support with connection management

### ✅ 1.3 Health Monitoring and Metrics System
- Health check registry with extensible checkers
- Database health checker
- Prometheus metrics with HTTP instrumentation
- `/healthz`, `/ready`, and `/metrics` endpoints

### ✅ 1.4 Error Handling and Error Bus
- Channel-based error bus with background consumer
- ErrorPublisher interface
- Panic recovery middleware
- Error context preservation

### ✅ 1.5 HTTP Server Foundation
- Gin-based HTTP server
- Comprehensive middleware stack:
  - Request ID generation
  - Structured logging
  - Panic recovery with error bus
  - Prometheus metrics
  - CORS support
- Core routes registration
- Graceful shutdown

### ✅ 1.6 OpenTelemetry Distributed Tracing
- Tracer initialization with stdout (dev) and OTLP (prod) exporters
- HTTP request instrumentation
- Trace ID correlation in logs
- Configurable tracing

## Prerequisites

Before verifying Epic 1, ensure you have:

1. **Docker and Docker Compose** installed
2. **PostgreSQL client** (optional, for direct database access)
3. **Go 1.24+** installed
4. **curl** or similar HTTP client for testing endpoints

## Setup Instructions

### 1. Start PostgreSQL Database

The project includes a `docker-compose.yml` file for easy database setup:

```bash
# Start PostgreSQL container
docker-compose up -d postgres

# Verify container is running
docker-compose ps

# Check database logs
docker-compose logs postgres
```

The database will be available at:
- **Host**: `localhost`
- **Port**: `5432`
- **Database**: `goplt`
- **User**: `goplt`
- **Password**: `goplt_password`

### 2. Configure Database Connection

Update `config/default.yaml` or set environment variable:

```bash
# Option 1: Edit config/default.yaml
# Set database.dsn to:
database:
  dsn: "postgres://goplt:goplt_password@localhost:5432/goplt?sslmode=disable"

# Option 2: Set environment variable
export DATABASE_DSN="postgres://goplt:goplt_password@localhost:5432/goplt?sslmode=disable"
```

### 3. Build and Run the Application

```bash
# Build the application
make build

# Or build directly
go build -o bin/platform ./cmd/platform

# Run the application
./bin/platform

# Or run directly
go run ./cmd/platform/main.go
```

The application will:
1. Load configuration
2. Initialize logger
3. Connect to database
4. Run migrations (create tables)
5. Start HTTP server on port 8080

## Verification Instructions

### 1. Verify Database Connection and Migrations

#### Option A: Using Application Logs

When you start the application, you should see:
- Database connection successful
- Migrations executed (tables created)

#### Option B: Using PostgreSQL Client

```bash
# Connect to database
docker exec -it goplt-postgres psql -U goplt -d goplt

# List tables (should see User, Role, Permission, AuditLog, etc.)
\dt

# Check a specific table structure
\d users
\d roles
\d permissions
\d audit_logs

# Exit psql
\q
```

#### Option C: Using SQL Query

```bash
# Execute SQL query
docker exec -it goplt-postgres psql -U goplt -d goplt -c "SELECT table_name FROM information_schema.tables WHERE table_schema = 'public';"

# Expected output should include:
# - users
# - roles
# - permissions
# - audit_logs
# - user_roles
# - role_permissions
```

### 2. Verify Health Endpoints

```bash
# Test liveness probe (should return 200)
curl http://localhost:8080/healthz

# Expected response:
# {"status":"healthy"}

# Test readiness probe (should return 200 if database is connected)
curl http://localhost:8080/ready

# Expected response:
# {"status":"healthy","components":[{"name":"database","status":"healthy"}]}

# If database is not connected, you'll see:
# {"status":"unhealthy","components":[{"name":"database","status":"unhealthy","error":"..."}]}
```

### 3. Verify Metrics Endpoint

```bash
# Get Prometheus metrics
curl http://localhost:8080/metrics

# Expected output should include:
# - http_request_duration_seconds
# - http_requests_total
# - http_errors_total
# - go_* (Go runtime metrics)
# - process_* (Process metrics)
```

### 4. Verify HTTP Server Functionality

```bash
# Make a request to trigger logging and metrics
curl -v http://localhost:8080/healthz

# Check application logs for:
# - Request ID in logs
# - Structured JSON logs
# - Request method, path, status, duration
```

### 5. Verify Error Handling

To test panic recovery and error bus:

```bash
# The error bus will capture any panics automatically
# Check logs for error bus messages when errors occur
```

### 6. Verify OpenTelemetry Tracing

#### Development Mode (stdout)

When `tracing.enabled: true` and `environment: development`, traces are exported to stdout:

```bash
# Start the application and make requests
curl http://localhost:8080/healthz

# Check application stdout for trace output
# Should see JSON trace spans with:
# - Trace ID
# - Span ID
# - Operation name
# - Attributes (method, path, status, etc.)
```

#### Verify Trace ID in Logs

```bash
# Make a request
curl http://localhost:8080/healthz

# Check application logs for trace_id and span_id fields
# Example log entry:
# {"level":"info","msg":"HTTP request","method":"GET","path":"/healthz","status":200,"trace_id":"...","span_id":"..."}
```

### 7. Verify Database Operations

#### Test Database Write

You can test database operations by creating a simple test script or using the database client directly. For now, verify that migrations worked (see Verification 1).

#### Test Database Health Check

```bash
# The /ready endpoint includes database health check
curl http://localhost:8080/ready

# If healthy, you'll see database component status: "healthy"
```

## Testing Database Specifically

### Direct Database Testing

1. **Connect to Database**:
```bash
docker exec -it goplt-postgres psql -U goplt -d goplt
```

2. **Verify Tables Exist**:
```sql
SELECT table_name 
FROM information_schema.tables 
WHERE table_schema = 'public' 
ORDER BY table_name;
```

3. **Check Table Structures**:
```sql
-- Check users table
\d users

-- Check relationships
\d user_roles
\d role_permissions
```

4. **Test Insert Operation** (manual test):
```sql
-- Note: Ent generates UUIDs, so we'd need to use the Ent client
-- This is just to verify the schema is correct
-- Actual inserts should be done through the application/Ent client
```

### Using Application to Test Database

The database is automatically tested through:
1. **Migrations**: Run on startup - if they succeed, schema is correct
2. **Health Check**: `/ready` endpoint tests database connectivity
3. **Connection Pool**: Database client manages connections automatically

## Docker Compose Commands

```bash
# Start database
docker-compose up -d postgres

# Stop database
docker-compose stop postgres

# Stop and remove containers
docker-compose down

# Stop and remove containers + volumes (WARNING: deletes data)
docker-compose down -v

# View database logs
docker-compose logs -f postgres

# Access database shell
docker exec -it goplt-postgres psql -U goplt -d goplt

# Check database health
docker-compose ps
```

## Common Issues and Solutions

### Issue: Database connection fails

**Symptoms**: Application fails to start, error about database connection

**Solutions**:
1. Ensure PostgreSQL container is running: `docker-compose ps`
2. Check database DSN in config: `postgres://goplt:goplt_password@localhost:5432/goplt?sslmode=disable`
3. Verify port 5432 is not in use: `lsof -i :5432`
4. Check database logs: `docker-compose logs postgres`

### Issue: Migrations fail

**Symptoms**: Error during startup about migrations

**Solutions**:
1. Ensure database is accessible
2. Check database user has proper permissions
3. Verify Ent schema is correct: `go generate ./internal/ent`
4. Check for existing tables that might conflict

### Issue: Health check fails

**Symptoms**: `/ready` endpoint returns unhealthy

**Solutions**:
1. Verify database connection
2. Check database health: `docker-compose ps`
3. Review application logs for specific error

### Issue: Metrics not appearing

**Symptoms**: `/metrics` endpoint is empty or missing metrics

**Solutions**:
1. Make some HTTP requests first (metrics are collected per request)
2. Verify Prometheus registry is initialized
3. Check middleware is registered correctly

### Issue: Traces not appearing

**Symptoms**: No trace output in logs

**Solutions**:
1. Verify `tracing.enabled: true` in config
2. Check environment is set correctly (development = stdout, production = OTLP)
3. Make HTTP requests to generate traces

## Expected Application Output

When running successfully, you should see logs like:

```json
{"level":"info","msg":"Application starting","component":"bootstrap"}
{"level":"info","msg":"Database migrations completed"}
{"level":"info","msg":"HTTP server listening","addr":"0.0.0.0:8080"}
```

When making requests:
```json
{"level":"info","msg":"HTTP request","method":"GET","path":"/healthz","status":200,"duration_ms":5,"request_id":"...","trace_id":"...","span_id":"..."}
```

## Next Steps

After verifying Epic 1:
1. All core infrastructure is in place
2. Database is ready for Epic 2 (Authentication & Authorization)
3. HTTP server is ready for API endpoints
4. Observability is ready for production monitoring

Proceed to [Epic 2](../epic2/README.md) to implement authentication and authorization features.