PowerBiResourceProvider.cs•9.64 kB
using Microsoft.Extensions.Caching.Memory;
using Microsoft.Extensions.Logging;
using Microsoft.Extensions.Options;
using pbi_local_mcp.Configuration;
using pbi_local_mcp.Core;
namespace pbi_local_mcp.Resources;
/// <summary>
/// Provides Power BI specific metadata and predefined DAX template resources to MCP clients.
/// Resources exposed (URIs):
/// - powerbi://server/info (basic connection/server metadata)
/// - powerbi://instances (discovered local Power BI Desktop instances - cached 5s)
/// - powerbi://schema/summary (lightweight model schema counts - internally cached in ITabularConnection)
/// - dax://templates/* (static DAX template descriptors)
/// </summary>
public sealed class PowerBiResourceProvider
{
// EventIds centralized in LogEvents
private readonly ITabularConnection _tabular;
private readonly IInstanceDiscovery? _instanceDiscovery;
private readonly ILogger<PowerBiResourceProvider> _logger;
private readonly IMemoryCache _cache;
private readonly ServerInfo _serverInfo;
private static readonly IReadOnlyDictionary<string, DaxTemplateDescriptor> _templates = BuildTemplates();
/// <summary>
/// Initializes a new instance of the <see cref="PowerBiResourceProvider"/> class.
/// </summary>
/// <param name="tabularConnection">Connection used to query the tabular model for metadata and schema information.</param>
/// <param name="logger">Logger instance for diagnostic messages.</param>
/// <param name="memoryCache">Memory cache used for short-lived resource caching.</param>
/// <param name="instanceDiscovery">Optional instance discovery service for enumerating local Power BI instances.</param>
/// <param name="config">Optional Power BI configuration options.</param>
public PowerBiResourceProvider(
ITabularConnection tabularConnection,
ILogger<PowerBiResourceProvider> logger,
IMemoryCache memoryCache,
IInstanceDiscovery? instanceDiscovery = null,
IOptions<PowerBiConfig>? config = null)
{
_tabular = tabularConnection ?? throw new ArgumentNullException(nameof(tabularConnection));
_logger = logger ?? throw new ArgumentNullException(nameof(logger));
_cache = memoryCache ?? throw new ArgumentNullException(nameof(memoryCache));
_instanceDiscovery = instanceDiscovery;
_serverInfo = new ServerInfo(
_tabular.Port,
_tabular.DatabaseId,
_tabular.StartupUtc,
_tabular.AssemblyVersion);
}
/// <summary>
/// Lists available resource descriptors exposed by this provider.
/// </summary>
public Task<IEnumerable<ResourceDescriptor>> ListResourcesAsync(CancellationToken ct = default)
{
_logger.LogDebug(LogEvents.ResourceRequest, "Listing resources");
var list = new List<ResourceDescriptor>
{
new("powerbi://server/info", "Power BI connection/server metadata"),
new("powerbi://instances", "Discovered local Power BI Desktop instances (cached 5s)"),
new("powerbi://schema/summary", "Lightweight model schema summary (tables/measures/columns)"),
};
list.AddRange(_templates.Keys.Select(k => new ResourceDescriptor(k, _templates[k].Description)));
return Task.FromResult<IEnumerable<ResourceDescriptor>>(list);
}
/// <summary>
/// Reads a specific resource by URI.
/// </summary>
/// <param name="uri">Resource URI.</param>
/// <param name="ct">Cancellation token.</param>
public async Task<object> ReadResourceAsync(string uri, CancellationToken ct = default)
{
_logger.LogDebug(LogEvents.ResourceRequest, "ReadResource start Uri={Uri}", uri);
try
{
return uri switch
{
"powerbi://server/info" => _serverInfo,
"powerbi://instances" => await GetInstancesAsync(ct).ConfigureAwait(false),
"powerbi://schema/summary" => await _tabular.GetSchemaSummaryAsync(ct).ConfigureAwait(false),
_ when _templates.ContainsKey(uri) => _templates[uri],
_ => throw new Exception($"[ResourceProvider] Unknown resource URI: {uri}")
};
}
catch (OperationCanceledException)
{
throw;
}
catch (Exception ex)
{
_logger.LogError(LogEvents.ResourceError, ex, "Failed reading resource {Uri}", uri);
throw new Exception($"[ResourceProvider] Failed to read resource '{uri}': {ex.Message}", ex);
}
}
private async Task<IEnumerable<InstanceInfo>> GetInstancesAsync(CancellationToken ct)
{
if (_instanceDiscovery == null)
{
return Array.Empty<InstanceInfo>();
}
const string cacheKey = "PowerBiResourceProvider.Instances";
if (_cache.TryGetValue(cacheKey, out IEnumerable<InstanceInfo> cached))
{
return cached;
}
_logger.LogDebug(LogEvents.CacheMiss, "Instance list cache miss");
var instances = await _instanceDiscovery.DiscoverInstances().ConfigureAwait(false);
_cache.Set(cacheKey, instances, new MemoryCacheEntryOptions
{
AbsoluteExpirationRelativeToNow = TimeSpan.FromSeconds(5)
});
return instances;
}
// ----- Static template catalog -----
private static IReadOnlyDictionary<string, DaxTemplateDescriptor> BuildTemplates()
{
var dict = new Dictionary<string, DaxTemplateDescriptor>(StringComparer.OrdinalIgnoreCase);
dict["dax://templates/topn"] = new DaxTemplateDescriptor(
"dax://templates/topn",
"Top N template",
"Return top N rows ordered by an expression",
"EVALUATE TOPN(@N, @Table, @OrderExpression)",
"EVALUATE TOPN(10, 'Sales', [Total Sales])",
new[]
{
new DaxTemplateParameter("N","Number of rows to return", true, "10"),
new DaxTemplateParameter("Table","Source table reference", true, "'Sales'"),
new DaxTemplateParameter("OrderExpression","Ordering expression (descending)", true, "[Total Sales]")
});
dict["dax://templates/distinct"] = new DaxTemplateDescriptor(
"dax://templates/distinct",
"Distinct values template",
"Return distinct values from a column",
"EVALUATE DISTINCT(SELECTCOLUMNS(@Table, \"Value\", @Column))",
"EVALUATE DISTINCT(SELECTCOLUMNS('Customers', \"Value\", 'Customers'[Country]))",
new[]
{
new DaxTemplateParameter("Table","Source table", true, "'Customers'"),
new DaxTemplateParameter("Column","Column reference", true, "'Customers'[Country]")
});
dict["dax://templates/calculate"] = new DaxTemplateDescriptor(
"dax://templates/calculate",
"CALCULATE with filter",
"Apply a filter to an expression using CALCULATE",
"EVALUATE ROW(\"Value\", CALCULATE(@Expression, @Filter))",
"EVALUATE ROW(\"Value\", CALCULATE([Total Sales], 'Calendar'[Year]=2024))",
new[]
{
new DaxTemplateParameter("Expression","Base measure or expression", true, "[Total Sales]"),
new DaxTemplateParameter("Filter","Filter predicate", true, "'Calendar'[Year]=2024")
});
dict["dax://templates/filter"] = new DaxTemplateDescriptor(
"dax://templates/filter",
"FILTER wrapper",
"Filter a table expression with a predicate",
"EVALUATE FILTER(@Table, @Predicate)",
"EVALUATE FILTER('Sales', [Total Sales] > 1000)",
new[]
{
new DaxTemplateParameter("Table","Table expression", true, "'Sales'"),
new DaxTemplateParameter("Predicate","Filter predicate", true, "[Total Sales] > 1000")
});
dict["dax://templates/summarize"] = new DaxTemplateDescriptor(
"dax://templates/summarize",
"Summarize template",
"Summarize a table by grouping columns and aggregating measures",
"EVALUATE SUMMARIZE(@Table, @GroupByColumns, \"Value\", @MeasureExpression)",
"EVALUATE SUMMARIZE('Sales', 'Sales'[Region], \"Value\", [Total Sales])",
new[]
{
new DaxTemplateParameter("Table","Base table", true, "'Sales'"),
new DaxTemplateParameter("GroupByColumns","Grouping columns (comma-separated)", true, "'Sales'[Region]"),
new DaxTemplateParameter("MeasureExpression","Aggregation measure/expression", true, "[Total Sales]")
});
return dict;
}
// ----- Records -----
/// <summary>Descriptor for a resource URI.</summary>
public record ResourceDescriptor(string Uri, string Description);
/// <summary>Power BI server / connection metadata.</summary>
public record ServerInfo(int Port, string? DatabaseId, DateTime StartupUtc, Version AssemblyVersion);
/// <summary>Template parameter descriptor.</summary>
public record DaxTemplateParameter(string Name, string Description, bool Required, string? DefaultValue);
/// <summary>DAX template descriptor.</summary>
public record DaxTemplateDescriptor(
string Uri,
string Name,
string Description,
string Template,
string Sample,
IReadOnlyList<DaxTemplateParameter> Parameters);
}