// PK resolver — pre-pass over the loaded metadata to build a name → PK info map.
// codegen uses this when emitting FK columns (per design §13 #2).

import type { MetaRoot } from "@metaobjectsdev/metadata";
import {
  FIELD_SUBTYPE_LONG,
  IDENTITY_ATTR_FIELDS,
  IDENTITY_ATTR_GENERATION,
} from "@metaobjectsdev/metadata";

export interface PkInfo {
  /** Field name within the entity (e.g., "id"). */
  fieldName: string;
  /** Field subType (e.g., "long", "string", "int"). */
  fieldSubType: string;
  /** Generation strategy: 'increment' | 'uuid' | 'assigned' (or undefined). */
  generation?: string;
}

/**
 * Walk the loaded metadata root, find each object's primary identity,
 * resolve the referenced field's subType, and build a name → PkInfo map.
 *
 * Used by FK column emission: when Post.authorId references User, codegen
 * looks up User's PK info to choose the matching FK column type.
 */
export function buildPkMap(root: MetaRoot): Map<string, PkInfo> {
  const result = new Map<string, PkInfo>();
  for (const obj of root.objects()) {
    // primaryIdentity() resolves the primary identity across the super-chain.
    const primary = obj.primaryIdentity();
    if (!primary) continue;
    // attr() (effective) not ownAttr() — @fields/@generation can be inherited when the
    // identity node-level `extends` a base identity without restating them (#56).
    const fields = primary.attr(IDENTITY_ATTR_FIELDS);
    if (!Array.isArray(fields) && typeof fields !== "string") continue;
    const fieldsList = Array.isArray(fields) ? fields : [fields];
    if (fieldsList.length === 0) continue;
    const pkFieldName = String(fieldsList[0]);
    // findField() resolves the field across the super-chain (handles extends:).
    const pkField = obj.findField(pkFieldName);
    const fieldSubType = pkField?.subType ?? FIELD_SUBTYPE_LONG; // sane default
    const generation = primary.attr(IDENTITY_ATTR_GENERATION);
    const info: PkInfo = { fieldName: pkFieldName, fieldSubType };
    if (typeof generation === "string") info.generation = generation;
    result.set(obj.name, info);
  }
  return result;
}