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restrictive-index.ts
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restrictive-index.ts
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import { _IIndex, IValue, IndexExpression, _Transaction, IndexKey, _Explainer, _IndexExplanation, IndexOp, _ISelection, Stats } from '../interfaces-private.ts';
export class RestrictiveIndex<T> implements _IIndex<T> {
constructor(private base: _IIndex<T>, readonly filter: _ISelection<T>) {
}
private match(raw: T, t: _Transaction) {
return this.filter.hasItem(raw, t);
}
get expressions(): IndexExpression[] {
return this.base.expressions;
}
stats(t: _Transaction, key?: IndexKey): Stats | null {
// cannot comput without iterating
return null;
}
iterateKeys() {
// cannot comput without iterating
// (we know underlying keys, but we dont know which have items that match our filter)
return null;
}
eqFirst(rawKey: IndexKey, t: _Transaction) {
for (const i of this.base.enumerate({
key: rawKey,
t: t,
type: 'eq',
})) {
if (this.match(i, t)) {
return i;
}
}
return null;
}
entropy(t: IndexOp): number {
return this.base.entropy(t);
}
*enumerate(op: IndexOp): Iterable<T> {
for (const i of this.base.enumerate(op)) {
if (this.match(i, op.t)) {
yield i;
}
}
}
explain(e: _Explainer): _IndexExplanation {
return {
_: 'indexRestriction',
lookup: this.base.explain(e),
for: this.filter.explain(e),
// criteria: this.restrict.explain(e),
}
}
}