dotnet add package Azure.ResourceManager.CosmosDB
dotnet add package Azure.Identity

AZURE_SUBSCRIPTION_ID=<your-subscription-id>
# For service principal auth (optional)
AZURE_TENANT_ID=<tenant-id>
AZURE_CLIENT_ID=<client-id>
AZURE_CLIENT_SECRET=<client-secret>

using Azure.Identity;
using Azure.ResourceManager;
using Azure.ResourceManager.CosmosDB;

// Always use DefaultAzureCredential
var credential = new DefaultAzureCredential();
var armClient = new ArmClient(credential);

// Get subscription
var subscriptionId = Environment.GetEnvironmentVariable("AZURE_SUBSCRIPTION_ID");
var subscription = armClient.GetSubscriptionResource(
    new ResourceIdentifier($"/subscriptions/{subscriptionId}"));

ArmClient
└── SubscriptionResource
    └── ResourceGroupResource
        └── CosmosDBAccountResource
            ├── CosmosDBSqlDatabaseResource
            │   └── CosmosDBSqlContainerResource
            │       ├── CosmosDBSqlStoredProcedureResource
            │       ├── CosmosDBSqlTriggerResource
            │       └── CosmosDBSqlUserDefinedFunctionResource
            ├── CassandraKeyspaceResource
            ├── GremlinDatabaseResource
            ├── MongoDBDatabaseResource
            └── CosmosDBTableResource

using Azure.ResourceManager.CosmosDB;
using Azure.ResourceManager.CosmosDB.Models;

// Get resource group
var resourceGroup = await subscription
    .GetResourceGroupAsync("my-resource-group");

// Define account
var accountData = new CosmosDBAccountCreateOrUpdateContent(
    location: AzureLocation.EastUS,
    locations: new[]
    {
        new CosmosDBAccountLocation
        {
            LocationName = AzureLocation.EastUS,
            FailoverPriority = 0,
            IsZoneRedundant = false
        }
    })
{
    Kind = CosmosDBAccountKind.GlobalDocumentDB,
    ConsistencyPolicy = new ConsistencyPolicy(DefaultConsistencyLevel.Session),
    EnableAutomaticFailover = true
};

// Create account (long-running operation)
var accountCollection = resourceGroup.Value.GetCosmosDBAccounts();
var operation = await accountCollection.CreateOrUpdateAsync(
    WaitUntil.Completed,
    "my-cosmos-account",
    accountData);

CosmosDBAccountResource account = operation.Value;

var databaseData = new CosmosDBSqlDatabaseCreateOrUpdateContent(
    new CosmosDBSqlDatabaseResourceInfo("my-database"));

var databaseCollection = account.GetCosmosDBSqlDatabases();
var dbOperation = await databaseCollection.CreateOrUpdateAsync(
    WaitUntil.Completed,
    "my-database",
    databaseData);

CosmosDBSqlDatabaseResource database = dbOperation.Value;

var containerData = new CosmosDBSqlContainerCreateOrUpdateContent(
    new CosmosDBSqlContainerResourceInfo("my-container")
    {
        PartitionKey = new CosmosDBContainerPartitionKey
        {
            Paths = { "/partitionKey" },
            Kind = CosmosDBPartitionKind.Hash
        },
        IndexingPolicy = new CosmosDBIndexingPolicy
        {
            Automatic = true,
            IndexingMode = CosmosDBIndexingMode.Consistent
        },
        DefaultTtl = 86400 // 24 hours
    });

var containerCollection = database.GetCosmosDBSqlContainers();
var containerOperation = await containerCollection.CreateOrUpdateAsync(
    WaitUntil.Completed,
    "my-container",
    containerData);

CosmosDBSqlContainerResource container = containerOperation.Value;

// Manual throughput
var throughputData = new ThroughputSettingsUpdateData(
    new ThroughputSettingsResourceInfo
    {
        Throughput = 400
    });

// Autoscale throughput
var autoscaleData = new ThroughputSettingsUpdateData(
    new ThroughputSettingsResourceInfo
    {
        AutoscaleSettings = new AutoscaleSettingsResourceInfo
        {
            MaxThroughput = 4000
        }
    });

// Apply to database
await database.CreateOrUpdateCosmosDBSqlDatabaseThroughputAsync(
    WaitUntil.Completed,
    throughputData);

// Get keys
var keys = await account.GetKeysAsync();
Console.WriteLine($"Primary Key: {keys.Value.PrimaryMasterKey}");

// Get connection strings
var connectionStrings = await account.GetConnectionStringsAsync();
foreach (var cs in connectionStrings.Value.ConnectionStrings)
{
    Console.WriteLine($"{cs.Description}: {cs.ConnectionString}");
}

using Azure;

try
{
    var operation = await accountCollection.CreateOrUpdateAsync(
        WaitUntil.Completed, accountName, accountData);
}
catch (RequestFailedException ex) when (ex.Status == 409)
{
    Console.WriteLine("Account already exists");
}
catch (RequestFailedException ex)
{
    Console.WriteLine($"ARM Error: {ex.Status} - {ex.ErrorCode}: {ex.Message}");
}