negate-stage.ts
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negate-stage.ts
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	import type { MatchBody } from "./query-stage.js";

	export default function negate_match(stage: MatchBody) {
	const negated_stage: MatchBody = {};
	for (const key in stage) {
	if (key === "$or") {
	negated_stage.$nor = stage.$or;
	} else if (key === "$nor") {
	negated_stage.$or = stage.$nor;
	} else if (key === "$and") {
	negated_stage.$or = stage.$and?.map((expression: MatchBody) =>
	negate_match(expression)
	);
	} else {
	if ((stage[key] as MatchBody).$not) {
	negated_stage[key] = (stage[key] as MatchBody)
	.$not as MatchBody;
	} else if (typeof stage[key] == "boolean") {
	// in this case, the behavior for true and false is not symmetrical.
	// We treat "unset" values as false. - see if.test.ts
	if (stage[key]) {
	// negating a 'true' value - so we're matching both false and unset
	negated_stage[key] = { $ne: true };
	} else {
	// negating a 'false' value - so we're matching only true
	negated_stage[key] = true;
	}
	} else if (typeof stage[key] !== "object") {
	negated_stage[key] = { $not: { $eq: stage[key] } };
	} else {
	negated_stage[key] = { $not: stage[key] };
	}
	}
	}
	return negated_stage;
	}