schemaValidator

/**
 * @typedef {string | number} PathSegment
 *
 * @typedef {{
 *   path: PathSegment[],
 *   message: string,
 * }} ValidationError
 *
 * @typedef {{
 *   success: true,
 *   data: unknown,
 * } | {
 *   success: false,
 *   errors: ValidationError[],
 * }} ParseResult
 *
 * @typedef {{
 *   safeParse(value: unknown): ParseResult,
 * }} Schema
 */

/**
 * @type {{
 *   string(): Schema,
 *   number(): Schema,
 *   boolean(): Schema,
 *   object(shape: Record<string, Schema>): Schema,
 * }}
 */
const v = {
  string() {
    return createPrimitiveSchema('string', 'Expected string');
  },
  number() {
    return createPrimitiveSchema('number', 'Expected number');
  },
  boolean() {
    return createPrimitiveSchema('boolean', 'Expected boolean');
  },
  object(shape) {
    return {
      safeParse(value) {
        if (value === null || typeof value !== 'object' || Array.isArray(value)) {
          return {
            success: false,
            errors: [{path: [], message: 'Expected object'}]
          };
        }

        const errors = [];
        for (const key of Object.keys(shape)) {
          if (value[key] === undefined) {
            errors.push({
              path: [key],
              message: 'Required'
            });
            continue;
          }
          const result = shape[key].safeParse(value[key]);
          if (!result.success) {
            errors.push({
              path: [key],
              message: result.errors[0].message
            });
          }
        }
        if (errors.length > 0) {
          return {
            success: false,
            errors,
          };
        }
        return {
          success: true,
          data: {...value}
        };
      }
    }
  },
};

function createPrimitiveSchema(type, message) {
  return {
    safeParse(value) {
      if (typeof value === type) {
        return {
          success: true,
          data: value;
        };
      }
      return {
        success: false,
        errors: [{path: [], message}]
      }
    }
  }
}

export default v;

/**
const User = v.object({
  name: v.string(),
  age: v.number(),
  admin: v.boolean(),
});

User.safeParse({
  name: 'Alice',
  age: 30,
  admin: false,
  team: 'Core',
});
// {
//   success: true,
//   data: {
//     name: 'Alice',
//     age: 30,
//     admin: false,
//     team: 'Core',
//   },
// }

 */