chrono-node/src/common/parsers/AbstractParserWithWordBoundary.ts

A natural language date parser in Javascript

import { Parser, ParsingContext } from "../../chrono";
import { ParsingComponents, ParsingResult } from "../../results";
import { Component } from "../../types";

/**
 * A parser that checks for word boundary and applying the inner pattern and extraction.
 */
export abstract class AbstractParserWithWordBoundaryChecking implements Parser {
    abstract innerPattern(context: ParsingContext): RegExp;
    abstract innerExtract(
        context: ParsingContext,
        match: RegExpMatchArray
    ): ParsingComponents | ParsingResult | { [c in Component]?: number } | null;

    // Overrides this method if there is more efficient way to check for inner pattern change.
    innerPatternHasChange(context: ParsingContext, currentInnerPattern: RegExp): boolean {
        return this.innerPattern(context) !== currentInnerPattern;
    }

    patternLeftBoundary(): string {
        return `(\\W|^)`;
    }

    private cachedInnerPattern?: RegExp = null;
    private cachedPattern?: RegExp = null;

    pattern(context: ParsingContext): RegExp {
        if (this.cachedInnerPattern) {
            if (!this.innerPatternHasChange(context, this.cachedInnerPattern)) {
                return this.cachedPattern;
            }
        }
        this.cachedInnerPattern = this.innerPattern(context);
        this.cachedPattern = new RegExp(
            `${this.patternLeftBoundary()}${this.cachedInnerPattern.source}`,
            this.cachedInnerPattern.flags
        );
        return this.cachedPattern;
    }

    extract(context: ParsingContext, match: RegExpMatchArray) {
        const header = match[1] ?? "";
        match.index = match.index + header.length;
        match[0] = match[0].substring(header.length);
        for (let i = 2; i < match.length; i++) {
            match[i - 1] = match[i];
        }

        return this.innerExtract(context, match);
    }
}