using Grpc.Core;
using Microsoft.Extensions.Options;
using ZB.MOM.WW.GalaxyRepository.Grpc;
using ZB.MOM.WW.MxGateway.Server.Configuration;
using ZB.MOM.WW.MxGateway.Server.Security.Authentication;

namespace ZB.MOM.WW.MxGateway.Server.Security.Authorization;

/// <summary>Scopes Galaxy browse results to the calling API key's BrowseSubtrees constraint.</summary>
/// <remarks>
/// Distinguishes two states the earlier code collapsed into one: "authenticated, no
/// BrowseSubtrees constraint" (legitimately unscoped — the common case) and "no ambient identity
/// at all" (the interceptor-ordering invariant below is broken). The second used to resolve to the
/// full hierarchy silently, which made a scoping bypass invisible; it now denies loudly.
/// </remarks>
/// <param name="identityAccessor">Accessor for the ambient per-call API-key identity.</param>
/// <param name="options">Gateway options supplying <c>MxGateway:Authentication:Mode</c>.</param>
/// <param name="logger">Logger used to name the broken invariant when identity is absent.</param>
public sealed class GatewayBrowseScopeProvider(
    IGatewayRequestIdentityAccessor identityAccessor,
    IOptions<GatewayOptions> options,
    ILogger<GatewayBrowseScopeProvider> logger)
    : IGalaxyBrowseScopeProvider
{
    /// <summary>Resolves the Galaxy browse subtrees the calling API key is scoped to, from the ambient request identity.</summary>
    /// <param name="context">The gRPC server call context for the in-flight browse request.</param>
    /// <returns>The caller's configured browse subtrees, or <see langword="null"/>/empty when the caller is unscoped (full hierarchy).</returns>
    /// <exception cref="RpcException">
    /// <see cref="StatusCode.PermissionDenied"/> when API-key authentication is enabled but no
    /// ambient identity is present — the invariant described below has been broken and the
    /// request's scope cannot be established.
    /// </exception>
    public IReadOnlyList<string>? ResolveBrowseSubtrees(ServerCallContext context)
    {
        // Invariant: the caller identity is the ambient one pushed by
        // GatewayGrpcAuthorizationInterceptor earlier in this same call. That interceptor is
        // registered globally and therefore runs before the library's galaxy service, so
        // Current is populated for any authenticated galaxy RPC. Do not reorder the interceptor
        // without revisiting this.
        ApiKeyIdentity? identity = identityAccessor.Current;
        if (identity is not null)
        {
            return identity.EffectiveConstraints.BrowseSubtrees;
        }

        // Mode=Disabled is the one configuration in which identity-absent is expected rather than
        // broken: nothing authenticates, so no key and no constraints exist to scope by, and the
        // deployment has already accepted an unauthenticated gRPC surface. Empty BrowseSubtrees is
        // what the library reads as "no scoping".
        if (options.Value.Authentication.Mode == AuthenticationMode.Disabled)
        {
            return ApiKeyConstraints.Empty.BrowseSubtrees;
        }

        // Authentication is on, so an identity MUST have been pushed before the galaxy service ran.
        // Failing open here would hand a browse-scoped key the full hierarchy with nothing logged
        // and nothing failing — a constraint-narrowing control's absence is invisible in normal
        // operation. Deny instead, and name the invariant so the misconfiguration is diagnosable
        // from one log line rather than from a scoping audit nobody thought to run.
        logger.LogWarning(
            "Galaxy browse scope could not be resolved for {Method}: no ambient API-key identity "
            + "while Authentication:Mode is {Mode}. GatewayGrpcAuthorizationInterceptor must run "
            + "before the Galaxy service on every call; the request is denied rather than served "
            + "unscoped.",
            context.Method,
            options.Value.Authentication.Mode);

        throw new RpcException(new Status(
            StatusCode.PermissionDenied,
            "Browse scope could not be established for this request."));
    }
}