import { WORKS_SQUARE_CONFIG } from '../api/works-config';
import { proxyAwareFetch, runWithDeadline } from '../utils/proxy-fetch';

const MAX_CATALOG_BYTES = 1_310_720;
const MAX_CATALOG_VERSION = 64;
const MAX_PLUGIN_ID = 48;
const MAX_CAPABILITY_ID = 64;
const MAX_OPERATION_ID = 64;
const MAX_NOTICE = 160;
const DEFAULT_POLICY_REQUEST_TIMEOUT_MS = 10_000;
const PLUGIN_ID_PATTERN = /^[a-z][a-z0-9.-]{0,47}$/u;
const CAPABILITY_ID_PATTERN = /^[a-z][a-z0-9.-]{0,63}$/u;
const OPERATION_ID_PATTERN = /^[a-z][a-z0-9._-]{0,63}$/u;
const TOKEN_POINT_AMOUNT_PATTERN = /^(?:0|[1-9]\d*)(?:\.\d{1,2})?$/u;

type UnknownRecord = Record<string, unknown>;
type FetchImplementation = (input: string | URL, init?: RequestInit) => Promise<Response>;

export interface PluginPricingVersion {
  version: number;
  version_id: string;
  effective_at: string;
}

export type PluginBillingPolicy =
  | {
      mode: 'included';
      entitlement_scope: null;
      notice: string;
    }
  | {
      mode: 'external_account';
      notice: string;
    }
  | {
      mode: 'platform_metered';
      entitlement_scope: string;
      notice: string;
      unit_name: string;
      unit_size: number;
      rate_points: string;
      minimum_charge_points: string;
      rounding_mode: 'ceil';
    }
  | {
      mode: 'platform_metered';
      status: 'billing_unavailable';
      entitlement_scope: string;
      notice: string;
    };

export interface PluginCatalogOperation {
  operation: string;
  billing: PluginBillingPolicy;
}

export interface PluginCatalogCapability {
  capability_id: string;
  operations: PluginCatalogOperation[];
}

export interface PluginCatalogPlugin {
  plugin_id: string;
  supported_contract_versions: number[];
  status: 'active';
  capabilities: PluginCatalogCapability[];
}

export interface PluginCatalog {
  schema_version: 1;
  catalog_version: string;
  pricing_version: PluginPricingVersion | null;
  plugins: PluginCatalogPlugin[];
}

export type PluginPolicyAvailability = 'unavailable' | 'current' | 'stale';

export interface PluginPolicyClientState {
  status: PluginPolicyAvailability;
  catalog: PluginCatalog | null;
  revision: number;
  lastVerifiedAt: number | null;
  errorCode?: 'plugin_backend_unavailable';
}

export interface PluginPolicyClientOptions {
  fetchImpl?: FetchImplementation;
  apiBaseUrl?: string;
  now?: () => number;
  requestTimeoutMs?: number;
}

export class PluginPolicyCatalogError extends Error {
  readonly code = 'plugin_policy_invalid' as const;

  constructor(message = 'Plugin policy catalog is invalid') {
    super(message);
    this.name = 'PluginPolicyCatalogError';
  }
}

function isRecord(value: unknown): value is UnknownRecord {
  return value !== null && typeof value === 'object' && !Array.isArray(value);
}

function exactKeys(
  value: UnknownRecord,
  required: readonly string[],
  optional: readonly string[] = [],
): void {
  const allowed = new Set([...required, ...optional]);
  const keys = Object.keys(value);
  if (keys.some((key) => !allowed.has(key))
    || required.some((key) => !Object.prototype.hasOwnProperty.call(value, key))) {
    throw new PluginPolicyCatalogError('Plugin policy catalog contains unexpected fields');
  }
}

function text(value: unknown, maximum: number, field: string): string {
  if (typeof value !== 'string' || value.length === 0 || value.length > maximum) {
    throw new PluginPolicyCatalogError(`${field} is invalid`);
  }
  return value;
}

function identifier(
  value: unknown,
  maximum: number,
  pattern: RegExp,
  field: string,
): string {
  const result = text(value, maximum, field);
  if (!pattern.test(result)) throw new PluginPolicyCatalogError(`${field} has invalid shape`);
  return result;
}

function positiveInteger(value: unknown, field: string): number {
  if (!Number.isSafeInteger(value) || (value as number) < 1) {
    throw new PluginPolicyCatalogError(`${field} must be a positive integer`);
  }
  return value as number;
}

function unique(values: readonly string[], field: string): void {
  if (new Set(values).size !== values.length) {
    throw new PluginPolicyCatalogError(`${field} contains duplicates`);
  }
}

function timestamp(value: unknown, field: string): string {
  const result = text(value, 64, field);
  if (!result.endsWith('Z') || Number.isNaN(Date.parse(result))) {
    throw new PluginPolicyCatalogError(`${field} is invalid`);
  }
  return result;
}

function publicAmount(value: unknown, field: string): string {
  const result = text(value, 32, field);
  if (!TOKEN_POINT_AMOUNT_PATTERN.test(result)) {
    throw new PluginPolicyCatalogError(`${field} is invalid`);
  }
  return result;
}

function parsePricingVersion(value: unknown): PluginPricingVersion | null {
  if (value === null) return null;
  if (!isRecord(value)) throw new PluginPolicyCatalogError('pricing_version is invalid');
  exactKeys(value, ['version', 'version_id', 'effective_at']);
  return {
    version: positiveInteger(value.version, 'pricing_version.version'),
    version_id: text(value.version_id, 36, 'pricing_version.version_id'),
    effective_at: timestamp(value.effective_at, 'pricing_version.effective_at'),
  };
}

function parseBilling(value: unknown): PluginBillingPolicy {
  if (!isRecord(value)) throw new PluginPolicyCatalogError('billing is invalid');
  if (value.mode === 'included') {
    exactKeys(value, ['mode', 'entitlement_scope', 'notice']);
    if (value.entitlement_scope !== null) {
      throw new PluginPolicyCatalogError('included entitlement_scope must be null');
    }
    return {
      mode: 'included',
      entitlement_scope: null,
      notice: text(value.notice, MAX_NOTICE, 'billing.notice'),
    };
  }
  if (value.mode === 'external_account') {
    exactKeys(value, ['mode', 'notice']);
    return {
      mode: 'external_account',
      notice: text(value.notice, MAX_NOTICE, 'billing.notice'),
    };
  }
  if (value.mode !== 'platform_metered') {
    throw new PluginPolicyCatalogError('billing.mode is invalid');
  }
  if (value.status === 'billing_unavailable') {
    exactKeys(value, ['mode', 'status', 'entitlement_scope', 'notice']);
    return {
      mode: 'platform_metered',
      status: 'billing_unavailable',
      entitlement_scope: identifier(
        value.entitlement_scope,
        64,
        OPERATION_ID_PATTERN,
        'billing.entitlement_scope',
      ),
      notice: text(value.notice, MAX_NOTICE, 'billing.notice'),
    };
  }
  exactKeys(value, [
    'mode',
    'entitlement_scope',
    'notice',
    'unit_name',
    'unit_size',
    'rate_points',
    'minimum_charge_points',
    'rounding_mode',
  ]);
  if (value.rounding_mode !== 'ceil') {
    throw new PluginPolicyCatalogError('billing.rounding_mode is invalid');
  }
  return {
    mode: 'platform_metered',
    entitlement_scope: identifier(
      value.entitlement_scope,
      64,
      OPERATION_ID_PATTERN,
      'billing.entitlement_scope',
    ),
    notice: text(value.notice, MAX_NOTICE, 'billing.notice'),
    unit_name: text(value.unit_name, 80, 'billing.unit_name'),
    unit_size: positiveInteger(value.unit_size, 'billing.unit_size'),
    rate_points: publicAmount(value.rate_points, 'billing.rate_points'),
    minimum_charge_points: publicAmount(
      value.minimum_charge_points,
      'billing.minimum_charge_points',
    ),
    rounding_mode: 'ceil',
  };
}

function parseOperation(value: unknown): PluginCatalogOperation {
  if (!isRecord(value)) throw new PluginPolicyCatalogError('operation is invalid');
  exactKeys(value, ['operation', 'billing']);
  return {
    operation: identifier(value.operation, MAX_OPERATION_ID, OPERATION_ID_PATTERN, 'operation'),
    billing: parseBilling(value.billing),
  };
}

function parseCapability(value: unknown): PluginCatalogCapability {
  if (!isRecord(value)) throw new PluginPolicyCatalogError('capability is invalid');
  exactKeys(value, ['capability_id', 'operations']);
  if (!Array.isArray(value.operations) || value.operations.length < 1 || value.operations.length > 256) {
    throw new PluginPolicyCatalogError('capability.operations is invalid');
  }
  const operations = value.operations.map(parseOperation);
  unique(operations.map(({ operation }) => operation), 'capability.operations');
  return {
    capability_id: identifier(
      value.capability_id,
      MAX_CAPABILITY_ID,
      CAPABILITY_ID_PATTERN,
      'capability_id',
    ),
    operations,
  };
}

function parsePlugin(value: unknown): PluginCatalogPlugin {
  if (!isRecord(value)) throw new PluginPolicyCatalogError('plugin is invalid');
  exactKeys(value, ['plugin_id', 'supported_contract_versions', 'status', 'capabilities']);
  if (value.status !== 'active') throw new PluginPolicyCatalogError('plugin.status is invalid');
  if (!Array.isArray(value.supported_contract_versions)
    || value.supported_contract_versions.length < 1
    || value.supported_contract_versions.length > 32) {
    throw new PluginPolicyCatalogError('supported_contract_versions is invalid');
  }
  const supportedContractVersions = value.supported_contract_versions.map((item) => (
    positiveInteger(item, 'supported_contract_versions')
  ));
  if (new Set(supportedContractVersions).size !== supportedContractVersions.length) {
    throw new PluginPolicyCatalogError('supported_contract_versions contains duplicates');
  }
  if (!Array.isArray(value.capabilities) || value.capabilities.length < 1 || value.capabilities.length > 128) {
    throw new PluginPolicyCatalogError('plugin.capabilities is invalid');
  }
  const capabilities = value.capabilities.map(parseCapability);
  unique(capabilities.map(({ capability_id }) => capability_id), 'plugin.capabilities');
  return {
    plugin_id: identifier(value.plugin_id, MAX_PLUGIN_ID, PLUGIN_ID_PATTERN, 'plugin_id'),
    supported_contract_versions: supportedContractVersions,
    status: 'active',
    capabilities,
  };
}

/** Parse the exact public server catalog; unknown fields are rejected. */
export function parsePluginCatalog(value: unknown): PluginCatalog {
  if (!isRecord(value)) throw new PluginPolicyCatalogError();
  exactKeys(value, ['schema_version', 'catalog_version', 'pricing_version', 'plugins']);
  if (value.schema_version !== 1) throw new PluginPolicyCatalogError('schema_version must equal 1');
  if (!Array.isArray(value.plugins) || value.plugins.length > 128) {
    throw new PluginPolicyCatalogError('plugins is invalid');
  }
  const plugins = value.plugins.map(parsePlugin);
  unique(plugins.map(({ plugin_id }) => plugin_id), 'plugins');
  return Object.freeze({
    schema_version: 1 as const,
    catalog_version: text(value.catalog_version, MAX_CATALOG_VERSION, 'catalog_version'),
    pricing_version: parsePricingVersion(value.pricing_version),
    plugins,
  });
}

async function readBoundedText(response: Response): Promise<string> {
  const declaredLength = response.headers.get('content-length');
  if (declaredLength && /^\d+$/u.test(declaredLength)
    && Number(declaredLength) > MAX_CATALOG_BYTES) {
    await response.body?.cancel().catch(() => undefined);
    throw new PluginPolicyCatalogError('catalog response is too large');
  }
  if (!response.body) {
    const textValue = await response.text();
    if (Buffer.byteLength(textValue, 'utf8') > MAX_CATALOG_BYTES) {
      throw new PluginPolicyCatalogError('catalog response is too large');
    }
    return textValue;
  }
  const reader = response.body.getReader();
  const chunks: Uint8Array[] = [];
  let size = 0;
  try {
    while (true) {
      const { done, value } = await reader.read();
      if (done) break;
      if (!value) continue;
      size += value.byteLength;
      if (size > MAX_CATALOG_BYTES) {
        await reader.cancel().catch(() => undefined);
        throw new PluginPolicyCatalogError('catalog response is too large');
      }
      chunks.push(value);
    }
  } finally {
    reader.releaseLock();
  }
  return Buffer.concat(chunks.map((chunk) => Buffer.from(chunk))).toString('utf8');
}

async function readCatalog(response: Response): Promise<PluginCatalog> {
  let source: string;
  try {
    source = await readBoundedText(response);
  } catch (error) {
    if (error instanceof PluginPolicyCatalogError) throw error;
    throw new PluginPolicyCatalogError();
  }
  let payload: unknown;
  try {
    payload = JSON.parse(source) as unknown;
  } catch {
    throw new PluginPolicyCatalogError();
  }
  return parsePluginCatalog(payload);
}

function cloneState(state: PluginPolicyClientState): PluginPolicyClientState {
  return {
    ...state,
    catalog: state.catalog ? structuredClone(state.catalog) : null,
  };
}

/**
 * Narrow HTTP adapter for the unauthenticated, user-independent policy catalog.
 * Only the last successfully parsed catalog is retained after a refresh error;
 * it is visibly stale and never becomes a source of billing authority.
 */
export class PluginPolicyClient {
  private readonly fetchImpl: FetchImplementation;
  private readonly apiBaseUrl: string;
  private readonly now: () => number;
  private readonly requestTimeoutMs: number;
  private state: PluginPolicyClientState = {
    status: 'unavailable',
    catalog: null,
    revision: 0,
    lastVerifiedAt: null,
  };
  private refreshFlight: Promise<PluginPolicyClientState> | null = null;

  constructor(options: PluginPolicyClientOptions = {}) {
    this.fetchImpl = options.fetchImpl ?? proxyAwareFetch;
    this.apiBaseUrl = (options.apiBaseUrl ?? WORKS_SQUARE_CONFIG.apiBaseUrl).replace(/\/+$/u, '');
    this.now = options.now ?? (() => Date.now());
    this.requestTimeoutMs = options.requestTimeoutMs ?? DEFAULT_POLICY_REQUEST_TIMEOUT_MS;
  }

  getState(): PluginPolicyClientState {
    return cloneState(this.state);
  }

  getStatus(): PluginPolicyAvailability {
    return this.state.status;
  }

  get catalog(): PluginCatalog | null {
    return this.state.catalog ? structuredClone(this.state.catalog) : null;
  }

  refresh(): Promise<PluginPolicyClientState> {
    if (this.refreshFlight) return this.refreshFlight;
    const flight = this.fetchCatalog()
      .then((catalog) => {
        this.state = {
          status: 'current',
          catalog,
          revision: this.state.revision + 1,
          lastVerifiedAt: this.now(),
        };
        return this.getState();
      })
      .catch(() => {
        this.state = {
          ...this.state,
          status: this.state.catalog ? 'stale' : 'unavailable',
          errorCode: 'plugin_backend_unavailable',
        };
        return this.getState();
      })
      .finally(() => {
        if (this.refreshFlight === flight) this.refreshFlight = null;
      });
    this.refreshFlight = flight;
    return flight;
  }

  refreshCatalog(): Promise<PluginPolicyClientState> {
    return this.refresh();
  }

  private async fetchCatalog(): Promise<PluginCatalog> {
    try {
      return await runWithDeadline(async (signal) => {
        const response = await this.fetchImpl(
          `${this.apiBaseUrl}/api/plugins/v1/catalog`,
          {
            method: 'GET',
            headers: { Accept: 'application/json' },
            redirect: 'manual',
            signal,
          },
        );
        if (!response.ok) {
          await response.body?.cancel().catch(() => undefined);
          throw new PluginPolicyCatalogError('catalog request failed');
        }
        return await readCatalog(response);
      }, this.requestTimeoutMs);
    } catch {
      throw new PluginPolicyCatalogError('catalog request failed');
    }
  }
}

export const parsePluginPolicyCatalog = parsePluginCatalog;