import { createRule, isNullType } from '@typespec/compiler'

export const noNullableRule = createRule({
  name: 'no-nullable',
  description: 'Use `?` for optional properties.',
  severity: 'warning',
  messages: {
    default:
      "Don't use `| null`. If you meant to have an optional property, use `?`. (e.g. `myProp?: string`)",
  },
  create(context) {
    return {
      modelProperty: (property) => {
        if (property.type.kind !== 'Union') {
          return
        }

        if (
          !property.node?.optional &&
          [...property.type.variants.values()].some((x) => isNullType(x.type))
        ) {
          context.reportDiagnostic({
            target: property,
          })
        }
      },
    }
  },
})