import { ProviderSelectionError } from "../domain/errors.js";
import { err, ok } from "../domain/result.js";
import type { BinaryTarget } from "../domain/binaryTarget.js";
import type {
  AnalysisClient,
  AnalysisProvider,
  CapabilityDescriptor,
  ProviderIdentity,
} from "./AnalysisProvider.js";

const compositeIdentity = (
  providers: readonly AnalysisProvider[],
): ProviderIdentity => ({
  id: `composite:${providers
    .map((provider) => provider.identity().id)
    .sort()
    .join("+")}`,
  name: "REA composite analysis provider",
  version: null,
});

/** Deterministically route disjoint operations without eagerly starting children. */
export class CompositeProvider implements AnalysisProvider {
  readonly #identity: ProviderIdentity;
  readonly #capabilities: readonly CapabilityDescriptor[];
  readonly #providerByOperation: ReadonlyMap<string, AnalysisProvider>;

  constructor(readonly providers: readonly AnalysisProvider[]) {
    if (providers.length === 0)
      throw new RangeError("CompositeProvider requires at least one provider");
    this.#identity = Object.freeze(compositeIdentity(providers));
    const routes = new Map<string, AnalysisProvider>();
    const capabilities: CapabilityDescriptor[] = [];
    for (const provider of providers) {
      for (const descriptor of provider.capabilities()) {
        if (routes.has(descriptor.operation))
          throw new TypeError(
            `Multiple providers declare operation ${descriptor.operation}`,
          );
        routes.set(descriptor.operation, provider);
        capabilities.push(descriptor);
      }
    }
    this.#providerByOperation = routes;
    this.#capabilities = Object.freeze(
      capabilities.sort(
        (left, right) =>
          left.operation.localeCompare(right.operation) ||
          left.provider.id.localeCompare(right.provider.id),
      ),
    );
  }

  identity(): ProviderIdentity {
    return this.#identity;
  }

  capabilities(): readonly CapabilityDescriptor[] {
    return this.#capabilities;
  }

  createClient(target: BinaryTarget): AnalysisClient {
    const clients = new Map<AnalysisProvider, AnalysisClient>();
    const clientFor = (provider: AnalysisProvider): AnalysisClient => {
      const existing = clients.get(provider);
      if (existing !== undefined) return existing;
      const created = provider.createClient(target);
      clients.set(provider, created);
      return created;
    };
    return {
      execute: (operation, parameters, options) => {
        if (operation === "health")
          return Promise.resolve(
            ok({
              result: null,
              rawResult: null,
              provider: this.#identity,
              limitations: [],
              locations: [],
              subject: null,
            }),
          );
        const provider = this.#providerByOperation.get(operation);
        return provider === undefined
          ? Promise.resolve(err(new ProviderSelectionError(operation)))
          : clientFor(provider).execute(operation, parameters, options);
      },
      close: async () => {
        await Promise.allSettled(
          [...clients.values()].map(async (client) => client.close()),
        );
      },
    };
  }
}