# Stream Configuration

Per-stream configuration for fine-grained control over retention, dead letter queues, lifecycle, performance, and access control.

## Overview

Stream configuration allows you to customize behavior on a per-stream basis, enabling:
- **Retention Policies** - Time, size, and count-based retention per stream
- **Dead Letter Queues** - Error handling and retry logic
- **Lifecycle Management** - Automatic archival and deletion
- **Performance Tuning** - Batch sizes, compression, indexing
- **Access Control** - Stream-level permissions and rate limits

**Key Features:**

- ✅ **Per-Stream Settings** - Override global configuration per stream
- ✅ **Retention Control** - MaxAge, MaxSizeBytes, MaxEventCount
- ✅ **DLQ Configuration** - Automatic retry and dead letter handling
- ✅ **Auto-Archival** - Move old events to cold storage
- ✅ **Performance Options** - Batching, compression, indexing
- ✅ **Access Control** - Stream-level permissions
- ✅ **Tag-Based Filtering** - Organize streams by tags

## Quick Start

```csharp
using Svrnty.CQRS.Events.Abstractions;
using Svrnty.CQRS.Events.PostgreSQL;

var builder = WebApplication.CreateBuilder(args);

// Register stream configuration
builder.Services.AddPostgresStreamConfiguration();

var app = builder.Build();

// Configure stream
var configStore = app.Services.GetRequiredService<IStreamConfigurationStore>();

await configStore.SetConfigurationAsync(new StreamConfiguration
{
    StreamName = "orders",
    Retention = new RetentionConfiguration
    {
        MaxAge = TimeSpan.FromDays(90),
        MaxEventCount = 1000000
    },
    DeadLetterQueue = new DeadLetterQueueConfiguration
    {
        Enabled = true,
        MaxDeliveryAttempts = 5
    }
});

app.Run();
```

## Configuration Components

### Retention Configuration

Control event retention per stream:

```csharp
var retention = new RetentionConfiguration
{
    MaxAge = TimeSpan.FromDays(30),           // Keep 30 days
    MaxSizeBytes = 10L * 1024 * 1024 * 1024,  // 10 GB limit
    MaxEventCount = 1000000,                  // Keep last 1M events
    EnablePartitioning = true,                // Partition by time
    PartitionInterval = PartitionInterval.Daily
};
```

[Learn more about Retention Configuration →](retention-config.md)

### Dead Letter Queue Configuration

Handle failed events automatically:

```csharp
var dlq = new DeadLetterQueueConfiguration
{
    Enabled = true,
    DeadLetterStreamName = "orders-dlq",      // Custom DLQ stream
    MaxDeliveryAttempts = 5,                  // Retry 5 times
    RetryDelay = TimeSpan.FromMinutes(5),     // Wait 5 min between retries
    EnableExponentialBackoff = true           // Exponential retry delays
};
```

[Learn more about Dead Letter Queues →](dead-letter-queues.md)

### Lifecycle Configuration

Automate archival and cleanup:

```csharp
var lifecycle = new LifecycleConfiguration
{
    AutoCreate = true,                        // Create stream on first append
    AutoArchive = true,                       // Enable archival
    ArchiveAfter = TimeSpan.FromDays(365),    // Archive after 1 year
    ArchiveLocation = "s3://archive/orders",  // S3 bucket
    AutoDelete = true,                        // Delete after archive
    DeleteAfter = TimeSpan.FromDays(400)      // Delete 400 days old
};
```

[Learn more about Lifecycle Configuration →](lifecycle-config.md)

### Performance Configuration

Optimize stream performance:

```csharp
var performance = new PerformanceConfiguration
{
    BatchSize = 1000,                         // Read 1000 events per query
    EnableCompression = true,                 // Compress event data
    CompressionAlgorithm = "gzip",
    EnableIndexing = true,                    // Index metadata fields
    IndexedFields = new List<string> { "userId", "tenantId" },
    CacheSize = 10000                         // Cache last 10k events
};
```

[Learn more about Performance Configuration →](performance-config.md)

### Access Control Configuration

Control stream access:

```csharp
var accessControl = new AccessControlConfiguration
{
    PublicRead = false,                       // Require authentication
    PublicWrite = false,
    AllowedReaders = new List<string> { "admin", "order-service" },
    AllowedWriters = new List<string> { "order-service" },
    MaxConsumerGroups = 10,                   // Limit consumer groups
    MaxEventsPerSecond = 10000                // Rate limit writes
};
```

[Learn more about Access Control →](access-control.md)

## Complete Configuration Example

```csharp
using Svrnty.CQRS.Events.Abstractions;

// High-volume production stream
var orderConfig = new StreamConfiguration
{
    StreamName = "orders",
    Description = "Production order events",
    Tags = new List<string> { "production", "critical", "orders" },

    Retention = new RetentionConfiguration
    {
        MaxAge = TimeSpan.FromDays(90),
        MaxSizeBytes = 50L * 1024 * 1024 * 1024,  // 50 GB
        MaxEventCount = 10000000,
        EnablePartitioning = true,
        PartitionInterval = PartitionInterval.Daily
    },

    DeadLetterQueue = new DeadLetterQueueConfiguration
    {
        Enabled = true,
        DeadLetterStreamName = "orders-dlq",
        MaxDeliveryAttempts = 5,
        RetryDelay = TimeSpan.FromMinutes(5),
        EnableExponentialBackoff = true
    },

    Lifecycle = new LifecycleConfiguration
    {
        AutoCreate = true,
        AutoArchive = true,
        ArchiveAfter = TimeSpan.FromDays(90),
        ArchiveLocation = "s3://prod-archive/orders",
        AutoDelete = false  // Keep in archive indefinitely
    },

    Performance = new PerformanceConfiguration
    {
        BatchSize = 1000,
        EnableCompression = true,
        CompressionAlgorithm = "gzip",
        EnableIndexing = true,
        IndexedFields = new List<string> { "userId", "orderId", "tenantId" },
        CacheSize = 100000
    },

    AccessControl = new AccessControlConfiguration
    {
        PublicRead = false,
        PublicWrite = false,
        AllowedReaders = new List<string> { "admin", "order-service", "analytics-service" },
        AllowedWriters = new List<string> { "order-service" },
        MaxConsumerGroups = 20,
        MaxEventsPerSecond = 50000
    }
};

await configStore.SetConfigurationAsync(orderConfig);
```

## Getting Effective Configuration

Merge stream-specific and global settings:

```csharp
var configProvider = serviceProvider.GetRequiredService<IStreamConfigurationProvider>();

// Get effective configuration (stream-specific merged with defaults)
var effectiveConfig = await configProvider.GetEffectiveConfigurationAsync("orders");

Console.WriteLine($"Retention: {effectiveConfig.Retention.MaxAge}");
Console.WriteLine($"DLQ Enabled: {effectiveConfig.DeadLetterQueue.Enabled}");
Console.WriteLine($"Batch Size: {effectiveConfig.Performance.BatchSize}");
```

## Configuration Precedence

Configuration is resolved in this order:

1. **Stream-Specific Configuration** - Highest priority
2. **Global Configuration** - Fallback for missing values
3. **Framework Defaults** - Built-in defaults

```csharp
// Example: Stream-specific overrides global
// Global: MaxAge = 30 days
// Stream "orders": MaxAge = 90 days
// Effective for "orders": MaxAge = 90 days

// Global: BatchSize = 100
// Stream "orders": BatchSize not set
// Effective for "orders": BatchSize = 100 (from global)
```

## Managing Configuration

### Set Configuration

```csharp
var config = new StreamConfiguration
{
    StreamName = "analytics",
    Retention = new RetentionConfiguration { MaxAge = TimeSpan.FromDays(7) }
};

await configStore.SetConfigurationAsync(config);
```

### Get Configuration

```csharp
var config = await configStore.GetConfigurationAsync("analytics");

if (config == null)
{
    Console.WriteLine("No configuration found, using defaults");
}
```

### Update Configuration

```csharp
var config = await configStore.GetConfigurationAsync("analytics");

if (config != null)
{
    config.Retention.MaxAge = TimeSpan.FromDays(14);  // Update retention
    await configStore.SetConfigurationAsync(config);
}
```

### Delete Configuration

```csharp
await configStore.DeleteConfigurationAsync("analytics");
// Stream will now use global configuration
```

## Configuration by Environment

Different settings for dev vs production:

```csharp
var environment = builder.Environment.EnvironmentName;

var retention = environment == "Production"
    ? new RetentionConfiguration { MaxAge = TimeSpan.FromDays(90) }
    : new RetentionConfiguration { MaxAge = TimeSpan.FromDays(7) };

var config = new StreamConfiguration
{
    StreamName = "orders",
    Retention = retention
};

await configStore.SetConfigurationAsync(config);
```

## Multi-Tenant Configuration

Per-tenant stream configuration:

```csharp
// Tenant A - high retention
await configStore.SetConfigurationAsync(new StreamConfiguration
{
    StreamName = "tenant-a-orders",
    Retention = new RetentionConfiguration { MaxAge = TimeSpan.FromDays(365) },
    Tags = new List<string> { "tenant-a", "premium" }
});

// Tenant B - standard retention
await configStore.SetConfigurationAsync(new StreamConfiguration
{
    StreamName = "tenant-b-orders",
    Retention = new RetentionConfiguration { MaxAge = TimeSpan.FromDays(90) },
    Tags = new List<string> { "tenant-b", "standard" }
});
```

## Querying by Tags

```csharp
// Find all production streams
var prodStreams = await configStore.GetStreamsByTagAsync("production");

foreach (var config in prodStreams)
{
    Console.WriteLine($"Production stream: {config.StreamName}");
}
```

## Best Practices

### ✅ DO

- Use tags to organize streams
- Set retention appropriate for data type
- Enable DLQ for critical streams
- Configure archival for compliance
- Use compression for large events
- Index fields used in queries
- Limit consumer groups per stream
- Test configuration in development first

### ❌ DON'T

- Don't use the same configuration for all streams
- Don't set retention too short for audit logs
- Don't disable DLQ for critical streams
- Don't forget to configure archival location
- Don't over-index (impacts write performance)
- Don't allow unlimited consumer groups
- Don't forget environment-specific settings

## See Also

- [Retention Configuration](retention-config.md)
- [Dead Letter Queues](dead-letter-queues.md)
- [Lifecycle Configuration](lifecycle-config.md)
- [Performance Configuration](performance-config.md)
- [Access Control](access-control.md)
- [Retention Policies](../retention-policies/README.md)
- [Event Streaming Overview](../README.md)