import type { AnalysisProviderSelector } from "../../contracts/providerSelection.js";
import type { AnalysisProfileCommitment } from "../../domain/analysisProfile.js";
import type { BinaryTarget } from "../../domain/binaryTargetTypes.js";
import { AnalysisCapabilityUnavailableError } from "../../domain/analysisErrorCore.js";
import { ProviderSelectionError } from "../../domain/providerSelectionError.js";
import type { AnalysisError } from "../../domain/analysisErrorBase.js";
import { err, ok, type Result } from "../../domain/result.js";
import type {
  AnalysisClient,
  AnalysisClientContext,
  AnalysisProvider,
  CapabilityDescriptor,
  ProviderIdentity,
} from "../AnalysisProvider.js";
import {
  AnalysisProviderRegistry,
  type AnalysisProviderBinding,
  type AnalysisProviderCandidateStatus,
  type AnalysisProviderSelection,
} from "./AnalysisProviderRegistry.js";
import { CompositeProvider } from "./CompositeProvider.js";

/** Immutable operation routes and binding metadata for one target transition. */
export interface SessionProviderRoute {
  readonly identity: ProviderIdentity;
  readonly capabilities: ReadonlyMap<string, CapabilityDescriptor>;
  readonly profile: AnalysisProfileCommitment | null;
  readonly binding: AnalysisProviderBinding | null;
  readonly selection: AnalysisProviderSelection | undefined;
  createClient(
    target: BinaryTarget,
    context: AnalysisClientContext,
  ): AnalysisClient;
}

/** Resolve one registry-selected deep provider and disjoint auxiliary families. */
export class SessionProviderRouter {
  private constructor(
    private readonly registry: AnalysisProviderRegistry,
    private readonly auxiliaryProviders: readonly AnalysisProvider[],
    private readonly route: SessionProviderRoute,
  ) {}

  /** Create selection-aware routing while keeping auxiliary families disjoint. */
  static selectable(
    registry: AnalysisProviderRegistry,
    auxiliaryProviders: readonly AnalysisProvider[],
  ): SessionProviderRouter {
    const identities = [
      ...registry.identities(),
      ...auxiliaryProviders.map((provider) => provider.identity()),
    ];
    assertUniqueProviderIds(identities);
    const auxiliaryOperations = assertDisjoint(auxiliaryProviders);
    for (const operation of registry.declaredOperations())
      if (auxiliaryOperations.has(operation))
        throw new TypeError(
          `Deep and auxiliary providers both declare operation ${operation}`,
        );
    const initialRoute = selectableRoute(auxiliaryProviders, undefined);
    return new SessionProviderRouter(
      registry,
      [...auxiliaryProviders],
      initialRoute,
    );
  }

  /** Target-free routes and discovery metadata. */
  initialRoute(): SessionProviderRoute {
    return this.route;
  }

  /** Resolve target routes before any provider client is created. */
  async resolve(
    target: BinaryTarget,
    providerId?: AnalysisProviderSelector,
    signal?: AbortSignal,
  ): Promise<Result<SessionProviderRoute, AnalysisError>> {
    const resolutionOptions = signal === undefined ? undefined : { signal };
    const selected = await this.registry.select(
      target,
      providerId,
      resolutionOptions,
    );
    return selected.ok
      ? ok(selectableRoute(this.auxiliaryProviders, selected.value))
      : selected;
  }

  /** Candidate status authoritative for the active or target-free route. */
  candidateStatuses(
    route: SessionProviderRoute,
  ): readonly AnalysisProviderCandidateStatus[] {
    return route.selection?.candidates ?? this.registry.candidates();
  }

  /** Produce exact candidate rejections for an intentionally unbound route. */
  unboundOperationError(
    operation: string,
    route: SessionProviderRoute,
  ): ProviderSelectionError | undefined {
    if (
      route.binding !== null ||
      route.selection === undefined ||
      !this.registry.declaredOperations().includes(operation)
    )
      return undefined;
    return this.registry.unboundOperationError(operation, route.selection);
  }
}

const selectableRoute = (
  auxiliaryProviders: readonly AnalysisProvider[],
  selection: AnalysisProviderSelection | undefined,
): SessionProviderRoute => {
  const binding = selection?.binding ?? null;
  const providers = [
    ...auxiliaryProviders,
    ...(binding === null ? [] : [binding.provider]),
  ];
  const provider =
    binding === null && providers.length === 1
      ? providers[0]
      : providers.length === 0
        ? undefined
        : new CompositeProvider(providers);
  const identity = provider?.identity() ?? emptyProviderIdentity();
  // The binding attributes deep-provider capabilities to the resolved version.
  const capabilities = capabilityMap([
    ...auxiliaryProviders.flatMap((auxiliary) => auxiliary.capabilities()),
    ...(binding?.capabilities ?? []),
  ]);
  return {
    identity,
    capabilities,
    profile: binding?.profile ?? null,
    binding,
    selection,
    createClient: (target, context) =>
      provider?.createClient(target, binding?.profile, context) ??
      emptyClient(identity),
  };
};

const emptyClient = (identity: ProviderIdentity): AnalysisClient => ({
  execute: (operation) =>
    operation === "health"
      ? Promise.resolve(
          ok({
            result: null,
            rawResult: null,
            provider: identity,
            limitations: [],
            locations: [],
            subject: null,
          }),
        )
      : Promise.resolve(
          err(
            new AnalysisCapabilityUnavailableError(
              identity.id,
              operation,
              "operation is not declared by this provider set",
            ),
          ),
        ),
  close: () => Promise.resolve(ok(null)),
});

const emptyProviderIdentity = (): ProviderIdentity => ({
  id: "composite:none",
  name: "REA composite analysis provider",
  version: null,
});

const capabilityMap = (
  capabilities: readonly CapabilityDescriptor[],
): ReadonlyMap<string, CapabilityDescriptor> =>
  new Map(capabilities.map((descriptor) => [descriptor.operation, descriptor]));

const assertDisjoint = (
  providers: readonly AnalysisProvider[],
): ReadonlySet<string> => {
  const routes = new Set<string>();
  for (const provider of providers)
    for (const { operation } of provider.capabilities()) {
      if (routes.has(operation))
        throw new TypeError(
          `Multiple auxiliary providers declare operation ${operation}`,
        );
      routes.add(operation);
    }
  return routes;
};

const assertUniqueProviderIds = (
  identities: readonly ProviderIdentity[],
): void => {
  const ids = new Set<string>();
  for (const identity of identities) {
    if (ids.has(identity.id))
      throw new TypeError(`Duplicate configured provider ID: ${identity.id}`);
    ids.add(identity.id);
  }
};