@maplibre/maplibre-gl-style-spec/src/expression/definitions/index_of.ts

a specification for maplibre styles

import {
    BooleanType,
    StringType,
    ValueType,
    NullType,
    typeToString,
    NumberType,
    isValidType,
    isValidNativeType
} from '../types';
import {RuntimeError} from '../runtime_error';
import {typeOf} from '../values';

import type {Expression} from '../expression';
import type {ParsingContext} from '../parsing_context';
import type {EvaluationContext} from '../evaluation_context';
import type {Type} from '../types';

export class IndexOf implements Expression {
    type: Type;
    needle: Expression;
    haystack: Expression;
    fromIndex: Expression;

    constructor(needle: Expression, haystack: Expression, fromIndex?: Expression) {
        this.type = NumberType;
        this.needle = needle;
        this.haystack = haystack;
        this.fromIndex = fromIndex;
    }

    static parse(args: ReadonlyArray<unknown>, context: ParsingContext): Expression {
        if (args.length <= 2 || args.length >= 5) {
            return context.error(
                `Expected 2 or 3 arguments, but found ${args.length - 1} instead.`
            ) as null;
        }

        const needle = context.parse(args[1], 1, ValueType);

        const haystack = context.parse(args[2], 2, ValueType);

        if (!needle || !haystack) return null;
        if (!isValidType(needle.type, [BooleanType, StringType, NumberType, NullType, ValueType])) {
            return context.error(
                `Expected first argument to be of type boolean, string, number or null, but found ${typeToString(needle.type)} instead`
            ) as null;
        }

        if (args.length === 4) {
            const fromIndex = context.parse(args[3], 3, NumberType);
            if (!fromIndex) return null;
            return new IndexOf(needle, haystack, fromIndex);
        } else {
            return new IndexOf(needle, haystack);
        }
    }

    evaluate(ctx: EvaluationContext) {
        const needle = this.needle.evaluate(ctx) as any;
        const haystack = this.haystack.evaluate(ctx) as any;

        if (!isValidNativeType(needle, ['boolean', 'string', 'number', 'null'])) {
            throw new RuntimeError(
                `Expected first argument to be of type boolean, string, number or null, but found ${typeToString(typeOf(needle))} instead.`
            );
        }

        let fromIndex;
        if (this.fromIndex) {
            fromIndex = this.fromIndex.evaluate(ctx) as number;
        }

        if (isValidNativeType(haystack, ['string'])) {
            const rawIndex = haystack.indexOf(needle, fromIndex);
            if (rawIndex === -1) {
                return -1;
            } else {
                // The index may be affected by surrogate pairs, so get the length of the preceding substring.
                return [...haystack.slice(0, rawIndex)].length;
            }
        } else if (isValidNativeType(haystack, ['array'])) {
            return haystack.indexOf(needle, fromIndex);
        } else {
            throw new RuntimeError(
                `Expected second argument to be of type array or string, but found ${typeToString(typeOf(haystack))} instead.`
            );
        }
    }

    eachChild(fn: (_: Expression) => void) {
        fn(this.needle);
        fn(this.haystack);
        if (this.fromIndex) {
            fn(this.fromIndex);
        }
    }

    outputDefined() {
        return false;
    }
}