import { canonicalJson } from "./comparisonSemantics.js";
import type { FunctionSnapshot } from "./functionDossierEvidence.js";
import { isAutoName, sorted } from "./functionComparisonNormalization.js";
import {
  referenceFactsCompatible,
  type ReferenceCompatibilityRow,
} from "./functionReferenceCompatibility.js";
import { nativeAddressInputSchema } from "./native/nativeAddress.js";

type Reference = FunctionSnapshot["dossier"]["outgoing_references"][number];
type KnownKind = Omit<
  Extract<Reference["kind"], { available: true }>,
  "available" | "provenance"
>;
type Endpoint =
  | { readonly kind: "address"; readonly address: string }
  | {
      readonly kind: "name";
      readonly name: string;
      readonly ambiguous: boolean;
    }
  | {
      readonly kind: "unknown";
      readonly reason: "unparsed_address" | "missing_name" | "generated_name";
      readonly reported_address: string;
      readonly reported_name: string | null;
    };

interface ReferenceFact {
  readonly direction: "in" | "out";
  readonly source: Endpoint;
  readonly target: Endpoint;
  readonly kind: KnownKind | null;
}

type ReferenceComparison = {
  readonly leftCount: number;
  readonly rightCount: number;
  readonly limitations: readonly string[];
} & (
  | { readonly status: "unknown" }
  | {
      readonly status: "changed" | "unchanged";
      readonly left: readonly ReferenceFact[];
      readonly right: readonly ReferenceFact[];
    }
);

/** Names observed at different procedure entries do not uniquely identify an overload. */
const ambiguousProcedureNames = (
  snapshots: readonly FunctionSnapshot[],
): Set<string> => {
  const ambiguous = new Set<string>();
  for (const snapshot of snapshots) {
    const entries = new Map<string, string>();
    const observe = (procedure: Reference["source_procedure"]): void => {
      if (procedure === null) return;
      const address = nativeAddressInputSchema.safeParse(procedure.address);
      if (!address.success) {
        ambiguous.add(procedure.name);
        return;
      }
      const previous = entries.get(procedure.name);
      if (previous !== undefined && previous !== address.data)
        ambiguous.add(procedure.name);
      entries.set(procedure.name, address.data);
    };
    observe(snapshot.dossier.procedure);
    for (const edge of snapshot.dossier.incoming_references) {
      observe(edge.source_procedure);
      observe(edge.target_procedure);
    }
    for (const edge of snapshot.dossier.outgoing_references) {
      observe(edge.source_procedure);
      observe(edge.target_procedure);
    }
  }
  return ambiguous;
};

const endpoint = (
  procedure: Reference["source_procedure"],
  address: string,
  sameArtifact: boolean,
  ambiguousNames: ReadonlySet<string>,
): Endpoint => {
  if (sameArtifact) {
    const parsed = nativeAddressInputSchema.safeParse(address);
    if (parsed.success) return { kind: "address", address: parsed.data };
    return {
      kind: "unknown",
      reason: "unparsed_address",
      reported_address: address,
      reported_name: procedure?.name ?? null,
    };
  }
  if (
    procedure === null ||
    procedure.name.length === 0 ||
    isAutoName(procedure.name)
  )
    return {
      kind: "unknown",
      reason:
        procedure !== null && isAutoName(procedure.name)
          ? "generated_name"
          : "missing_name",
      reported_address: address,
      reported_name: procedure?.name ?? null,
    };
  return {
    kind: "name",
    name: procedure.name,
    ambiguous: ambiguousNames.has(procedure.name),
  };
};

const project = (
  snapshot: FunctionSnapshot,
  sameArtifact: boolean,
  ambiguousNames: ReadonlySet<string>,
): ReferenceFact[] => {
  const facts: ReferenceFact[] = [];
  const collect = (
    references: readonly Reference[],
    direction: "in" | "out",
  ): void => {
    for (const edge of references) {
      let kind: KnownKind | null = null;
      if (edge.kind.available) {
        const {
          available: _available,
          provenance: _provenance,
          ...known
        } = edge.kind;
        kind = known;
      }
      facts.push({
        direction,
        source: endpoint(
          edge.source_procedure,
          edge.source_address,
          sameArtifact,
          ambiguousNames,
        ),
        target: endpoint(
          edge.target_procedure,
          edge.target_address,
          sameArtifact,
          ambiguousNames,
        ),
        kind,
      });
    }
  };
  collect(snapshot.dossier.incoming_references, "in");
  collect(snapshot.dossier.outgoing_references, "out");
  return facts;
};

/** Ambiguity blocks equality, but a known label can still contradict another label. */
const endpointKey = (value: Endpoint): string | null => {
  if (value.kind === "unknown") return null;
  return canonicalJson(
    value.kind === "address"
      ? { address: value.address }
      : { name: value.name },
  );
};

const constraints = (
  facts: readonly ReferenceFact[],
): ReferenceCompatibilityRow[] =>
  facts.map((fact) => ({
    direction: fact.direction,
    source: endpointKey(fact.source),
    target: endpointKey(fact.target),
    kind: fact.kind === null ? null : canonicalJson(fact.kind),
  }));

/** Compare parsed endpoint and kind facts without replacing partial knowledge with absence. */
export const compareFunctionReferences = (
  left: FunctionSnapshot,
  right: FunctionSnapshot,
): ReferenceComparison => {
  const sameArtifact =
    left.subject.digest.sha256 === right.subject.digest.sha256;
  const ambiguousNames = sameArtifact
    ? new Set<string>()
    : ambiguousProcedureNames([left, right]);
  const leftFacts = project(left, sameArtifact, ambiguousNames);
  const rightFacts = project(right, sameArtifact, ambiguousNames);
  let unknownIdentity = false;
  let ambiguousIdentity = false;
  let unknownKinds = false;
  for (const facts of [leftFacts, rightFacts]) {
    for (const fact of facts) {
      unknownKinds ||= fact.kind === null;
      for (const value of [fact.source, fact.target]) {
        unknownIdentity ||= value.kind === "unknown";
        ambiguousIdentity ||= value.kind === "name" && value.ambiguous;
      }
    }
  }
  const limitations: string[] = [];
  if (unknownIdentity)
    limitations.push(
      sameArtifact
        ? "Reference endpoint coordinates could not be parsed, so their identity remains unknown."
        : "Unnamed reference endpoints and generated procedure names have no stable identity across different artifacts.",
    );
  if (ambiguousIdentity)
    limitations.push(
      "A reference name does not uniquely identify an observed procedure entry, so matching names do not establish equal endpoints.",
    );
  if (unknownKinds)
    limitations.push(
      "At least one provider did not expose reference kinds, so compatible endpoints do not prove equal edge semantics.",
    );
  const context = {
    leftCount: leftFacts.length,
    rightCount: rightFacts.length,
    limitations,
  };
  if (
    !referenceFactsCompatible(constraints(leftFacts), constraints(rightFacts))
  )
    return {
      ...context,
      status: "changed",
      left: sorted(leftFacts),
      right: sorted(rightFacts),
      limitations: [
        "Known reference facts cannot be paired without contradicting an endpoint or reference kind.",
        ...limitations,
      ],
    };
  if (unknownIdentity || ambiguousIdentity || unknownKinds)
    return { ...context, status: "unknown" };
  return {
    ...context,
    status: "unchanged",
    left: sorted(leftFacts),
    right: sorted(rightFacts),
  };
};