/**
 * ActionExecutionPolicy — pure rules for `canExecute`.
 *
 * Order: consent → idempotency → capability → rate-limit.
 * Failure of any step returns `ActionExecutionRefused` with a typed reason.
 * This is the invariant core of the Action spine (CLAUDE.md #2, #3, #5, #7).
 */
import type {
  Action,
  AdapterCapability,
  ActionExecutionRefused,
} from "@courtmitra/contracts";
import { consentHashMatches } from "./consent-hash.js";

// ---------------------------------------------------------------------------
// Refusal result
// ---------------------------------------------------------------------------

export interface ExecutionRefusal {
  refused: true;
  reason: string;
  code: ActionExecutionRefused["code"];
}

export interface ExecutionAllowance {
  refused: false;
}

export type CanExecuteResult = ExecutionRefusal | ExecutionAllowance;

// ---------------------------------------------------------------------------
// Adapter capability check
// ---------------------------------------------------------------------------

function adapterForAction(action: Action): string | null {
  const t = action.actionType;
  if (t === "send_email" || t === "takedown") return "resend_email";
  if (t === "post_social") return "social_publisher";
  // All other types (generate_packet, manual_packet, prepare_portal,
  // submit_portal, inform_user, etc.) are local/user-driven — no adapter needed.
  return null;
}

function capabilityIsAvailable(cap: AdapterCapability): boolean {
  return cap.status === "available" || cap.status === "dev_only";
}

const executedProofStates = new Set<Action["proofState"]>([
  "sent_by_email",
  "sent_via_channel",
  "posted_to_social",
  "user_confirmed_external_submission",
  "receipt_verified",
]);

// ---------------------------------------------------------------------------
// Public gate — pure function, zero side-effects
// ---------------------------------------------------------------------------

/**
 * Evaluate whether an action may be executed.
 *
 * @param action — the Action row to execute.
 * @param consentGrant — the consent grant (null if not yet granted).
 * @param outgoingPreview — the ConsentPreview computed from the EXACT outgoing payload.
 * @param allCapabilities — full capability registry (adapter list).
 * @returns `{ refused: false }` or `{ refused: true, reason, code }`.
 */
export function canExecute(
  action: Action,
  consentGrant: { actionPreviewHash: string } | null,
  outgoingPreview: Parameters<typeof consentHashMatches>[1],
  allCapabilities: AdapterCapability[],
): CanExecuteResult {
  // 1. Consent must exist
  if (!consentGrant) {
    return {
      refused: true,
      reason: "Consent has not been granted for this action.",
      code: "consent_not_found",
    };
  }

  // 2. Consent hash must match the outgoing payload (CLAUDE.md #5)
  if (!consentHashMatches(consentGrant.actionPreviewHash, outgoingPreview)) {
    return {
      refused: true,
      reason:
        "The action draft has changed since consent was given — re-approval required.",
      code: "consent_hash_mismatch",
    };
  }

  // 3. Action must be in an executable status.
  //    A preview is not executable until consent has explicitly moved it to approved.
  //    "executing" is allowed for worker retries after the attempt row is recorded.
  const executableStatuses = new Set(["approved", "executing"]);
  if (!executableStatuses.has(action.status)) {
    return {
      refused: true,
      reason: `Action status is "${action.status}", not "approved" or "executing".`,
      code: "action_not_approved",
    };
  }

  // 4. Idempotency key must not already have been used (caller checks DB)
  if (action.status === "succeeded" || executedProofStates.has(action.proofState)) {
    return {
      refused: true,
      reason: "This action has already been executed (idempotency key consumed).",
      code: "idempotency_key_used",
    };
  }

  // 5. Adapter capability must be available
  const adapterName = adapterForAction(action);
  if (adapterName) {
    const matching = allCapabilities.find((c) => c.adapter === adapterName);
    if (!matching || !capabilityIsAvailable(matching)) {
      return {
        refused: true,
        reason: matching
          ? `Adapter "${adapterName}" is not available (status: ${matching.status}). ${matching.reason ?? ""}`
          : `No adapter found for "${adapterName}".`,
        code: "adapter_capability_blocked",
      };
    }
  }

  return { refused: false };
}