import type { Schema, VariableDeclarations } from "../types.js";
import resolveSchema from "./resolveSchema.js";

/**
 * Loads a schema and recursively resolves all extended schemas.
 * Merges rules from parent schemas with child schemas, where child
 * rules override parent rules with the same name. The `variables` block
 * is merged by key (child variables override inherited ones) rather than
 * replaced wholesale. Special properties like $schema and name are
 * preserved from the child schema.
 *
 * @param schemaArg - Schema identifier (built-in name, file path, or URL)
 * @returns Promise that resolves to the fully merged schema with all extensions resolved
 * @throws Will throw an error if any schema in the inheritance chain cannot be loaded
 *
 * @example
 * ```typescript
 * // Load a schema that extends other schemas
 * const schema = await loadFullSchema("package-react");
 * // Returns merged schema with rules from base, base-package, and package-react
 * ```
 */
export default async function loadFullSchema(
  schemaArg: string,
): Promise<Schema> {
  const schema = await resolveSchema(schemaArg);
  if (schema.extends) {
    const baseSchemas = await Promise.all(schema.extends.map(loadFullSchema));
    const baseRules: Record<string, unknown> = {};
    for (const s of baseSchemas) {
      const { extends: _, ...rules } = s;
      Object.assign(baseRules, rules);
    }
    const { $schema, name, extends: _, ...rules } = schema;
    const merged = Object.assign({}, baseRules, rules, {
      $schema,
      name,
    }) as Schema;

    // `variables` must merge by key (child overrides parent) rather than be
    // wholesale-replaced by Object.assign, so a child ruleset can add or refine
    // variables without dropping ones inherited from a parent ruleset.
    const baseVariables = baseRules.variables as
      | VariableDeclarations
      | undefined;
    if (baseVariables && schema.variables) {
      merged.variables = { ...baseVariables, ...schema.variables };
    }

    return merged;
  }
  return schema;
}