/**
 * Two-tier rule store: persistent (operator/admin rules loaded from
 * rules.json, mutated by the prompt-rules tool) and external (in-memory
 * rules registered by other plugins via the __prismFacet cross-plugin
 * API). External rules are NOT saved to disk — they belong to the
 * registering plugin and are re-registered on every gateway start.
 *
 * Lookup precedence: persistent > external (operator wins over plugin
 * defaults so an explicit rules.json override is honored).
 */
import { readFileSync, writeFileSync } from "node:fs";

export type RuleStore = Record<string, string>; // "router:key" → prompt file path

const _G = globalThis as Record<string, unknown>;
const PERSISTENT_KEY = "_prismFacetRules";
const EXTERNAL_KEY = "_prismFacetExternalRules";
const RULES_PATH_KEY = "_prismFacetRulesPath";

function getPersistent(): RuleStore {
  if (!_G[PERSISTENT_KEY] || typeof _G[PERSISTENT_KEY] !== "object") {
    _G[PERSISTENT_KEY] = {};
  }
  return _G[PERSISTENT_KEY] as RuleStore;
}

function getExternal(): RuleStore {
  if (!_G[EXTERNAL_KEY] || typeof _G[EXTERNAL_KEY] !== "object") {
    _G[EXTERNAL_KEY] = {};
  }
  return _G[EXTERNAL_KEY] as RuleStore;
}

function getRulesPath(): string {
  return (_G[RULES_PATH_KEY] as string) || "";
}

function save(): void {
  const p = getRulesPath();
  if (!p) return;
  writeFileSync(p, JSON.stringify(getPersistent(), null, 2) + "\n", "utf8");
}

export function initRuleStore(filePath: string): void {
  _G[RULES_PATH_KEY] = filePath;
  try {
    const raw = readFileSync(filePath, "utf8");
    _G[PERSISTENT_KEY] = JSON.parse(raw) as RuleStore;
  } catch {
    _G[PERSISTENT_KEY] = {};
  }
}

/** Operator-facing addRule (writes through to rules.json on disk). */
export function addRule(router: string, key: string, promptFile: string): void {
  getPersistent()[`${router}:${key}`] = promptFile;
  save();
}

/** Cross-plugin API: register a rule that lives in memory only. */
export function addExternalRule(router: string, key: string, promptFile: string): void {
  getExternal()[`${router}:${key}`] = promptFile;
}

export function removeRule(router: string, key: string): boolean {
  const rules = getPersistent();
  const ruleKey = `${router}:${key}`;
  if (!(ruleKey in rules)) return false;
  delete rules[ruleKey];
  save();
  return true;
}

/** Lookup. Persistent (rules.json) overrides external (plugin defaults). */
export function getRule(router: string, key: string): string | undefined {
  const persistentValue = getPersistent()[`${router}:${key}`];
  if (persistentValue) return persistentValue;
  return getExternal()[`${router}:${key}`];
}

/** Merged view for the admin tool. Persistent overrides external. */
export function listRules(): Record<string, string> {
  return { ...getExternal(), ...getPersistent() };
}

/** Admin tool needs to know which tier a rule came from. */
export function listRulesTiered(): {
  persistent: RuleStore;
  external: RuleStore;
} {
  return { persistent: { ...getPersistent() }, external: { ...getExternal() } };
}