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

a specification for maplibre styles

import {ResolvedImageType, StringType} from '../types';
import {ResolvedImage} from '../types/resolved_image';

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

export class ImageExpression implements Expression {
    type: Type;
    input: Expression;

    constructor(input: Expression) {
        this.type = ResolvedImageType;
        this.input = input;
    }

    static parse(args: ReadonlyArray<unknown>, context: ParsingContext): Expression {
        if (args.length !== 2) {
            return context.error('Expected two arguments.') as null;
        }

        const name = context.parse(args[1], 1, StringType);
        if (!name) return context.error('No image name provided.') as null;

        return new ImageExpression(name);
    }

    evaluate(ctx: EvaluationContext) {
        const evaluatedImageName = this.input.evaluate(ctx);

        const value = ResolvedImage.fromString(evaluatedImageName);
        if (value && ctx.availableImages)
            value.available = ctx.availableImages.indexOf(evaluatedImageName) > -1;

        return value;
    }

    eachChild(fn: (_: Expression) => void) {
        fn(this.input);
    }

    outputDefined() {
        // The output of image is determined by the list of available images in the evaluation context
        return false;
    }
}