import { Schema } from '../schema';
import { literalToString } from '../utils';

/**
 * Create a 'defaults' schema.
 *
 * During mapping or unmapping, if the value is null or undefined, the schema
 * defaults to the 'defaultValue' specified in the schema.
 */
export function defaults<M, U, V extends M & U>(
  schema: Schema<M, U>,
  defaultValue: V
): Schema<M, U> {
  return {
    type: () => `Defaults<${schema.type()},${literalToString(defaultValue)}>`,
    validateBeforeMap: (v, ctxt) =>
      shouldDefault(v, defaultValue) ? [] : schema.validateBeforeMap(v, ctxt),
    validateBeforeUnmap: (v, ctxt) =>
      shouldDefault(v, defaultValue) ? [] : schema.validateBeforeUnmap(v, ctxt),
    map: (v, ctxt) =>
      shouldDefault(v, defaultValue) ? defaultValue : schema.map(v, ctxt),
    unmap: (v, ctxt) =>
      shouldDefault(v, defaultValue) ? defaultValue : schema.unmap(v, ctxt),
    validateBeforeMapXml: (v, ctxt) =>
      shouldDefault(v, defaultValue)
        ? []
        : schema.validateBeforeMapXml(v, ctxt),
    mapXml: (v, ctxt) =>
      shouldDefault(v, defaultValue) ? defaultValue : schema.mapXml(v, ctxt),
    unmapXml: (v, ctxt) =>
      shouldDefault(v, defaultValue) ? defaultValue : schema.unmapXml(v, ctxt),
  };
}

function shouldDefault<T, V extends T>(value: T, defaultValue: V) {
  return value === null || value === undefined || value === defaultValue;
}