Adds the `@cast` smart tag to Postgraphile v5

cast-type-plugin.ts

declare global {
	namespace GraphileBuild {
		interface ScopeObjectFieldsField {
			castMap?: Map<string, string>;
		}
		interface ScopeObjectFieldsFieldArgsArg {
			castMap?: Map<string, string>;
		}
	}
}

const CAST_RE = /\s+as\s+/;

/**
 * Allows generic casting from one GraphQL type to another in function arguments
 * 
 * ```sql
 * create or replace public.my_function (arg_a varchar, arg_b varchar);
 * 
 * comment on public.my_function is E'
 * @cast arg_a as IncludeArchivedOption
 * @cast arg_b as SomeOtherType
 * ';
 * ```
 */
const CastType: GraphileConfig.Plugin = {
	name: 'CastType',
	version: '1.0.0',
	schema: {
		hooks: {
			GraphQLObjectType_fields_field (field, build, context) {
				const resource = context.scope?.pgFieldResource;
				const raw = resource?.extensions?.tags?.cast;
				if (!raw) return field;

				const castTags = Array.isArray(raw) ? raw : [raw];
				const castMap = new Map<string, string>();

				for (const tag of castTags) {
					const [k, v] = String(tag).split(CAST_RE);
					const i = resource.parameters!.findIndex((p: any) => p.name === k);
					if (i === -1) continue;

					const inflected = build.inflection.argument({
						resource,
						param: resource.parameters![i],
						index: i,
					});

					castMap.set(inflected, v);
				}

				if (castMap.size) context.scope.castMap = castMap;

				return field;
			},
			GraphQLObjectType_fields_field_args_arg (arg, build, context) {
				const castMap: Map<string, string> | undefined = context.scope.castMap;
				if (!castMap) return arg;

				const targetType = castMap.get(context.scope.argName);
				if (targetType) arg.type = build.getInputTypeByName(targetType);

				return arg;
			},
		},
	},
};

export default CastType;