export type GateStepExpectation =
  | Readonly<{ kind: "pass" }>
  | Readonly<{
      kind: "fail";
      expectedExitCode: number;
      expectedDiagnosticId: string;
    }>;

export type GateProcessResult = Readonly<{
  status: number | null;
  signal: string | null;
  stdout: string;
  stderr: string;
  error?: Readonly<{ code?: string }>;
}>;

export type GateStepClassification =
  | Readonly<{
      kind: "EXPECTED_PASS" | "EXPECTED_FAILURE";
      expectationMet: true;
    }>
  | Readonly<{
      kind: "UNEXPECTED_EXIT";
      expectationMet: false;
    }>
  | Readonly<{
      kind: "UNEXPECTED_DIAGNOSTIC";
      expectationMet: false;
    }>
  | Readonly<{
      kind: "INFRASTRUCTURE_FAILURE";
      expectationMet: false;
      detail: string;
    }>;

/** A negative fixture passes only with its registered exit and diagnostic. */
export function classifyGateStepResult(
  expectation: GateStepExpectation,
  result: GateProcessResult,
): GateStepClassification {
  const errorCode = result.error?.code;
  const spawnFailed = result.error !== undefined;
  if (spawnFailed || result.signal || result.status === null) {
    return Object.freeze({
      kind: "INFRASTRUCTURE_FAILURE" as const,
      expectationMet: false as const,
      detail:
        errorCode ??
        result.signal ??
        (spawnFailed ? "SPAWN_ERROR" : "NO_EXIT_STATUS"),
    });
  }
  if (expectation.kind === "pass" && result.status === 0) {
    return Object.freeze({
      kind: "EXPECTED_PASS" as const,
      expectationMet: true as const,
    });
  }
  if (expectation.kind === "fail") {
    if (result.status !== expectation.expectedExitCode) {
      return Object.freeze({
        kind: "UNEXPECTED_EXIT" as const,
        expectationMet: false as const,
      });
    }
    const diagnosticOutput = `${result.stdout}\n${result.stderr}`;
    if (!diagnosticOutput.includes(expectation.expectedDiagnosticId)) {
      return Object.freeze({
        kind: "UNEXPECTED_DIAGNOSTIC" as const,
        expectationMet: false as const,
      });
    }
    return Object.freeze({
      kind: "EXPECTED_FAILURE" as const,
      expectationMet: true as const,
    });
  }
  return Object.freeze({
    kind: "UNEXPECTED_EXIT" as const,
    expectationMet: false as const,
  });
}