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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),        }    }}