@maplibre/maplibre-gl-style-spec/src/validate/validate_projectiondefinition.ts

a specification for maplibre styles

import {ValidationError} from '../error/validation_error';
import {ProjectionDefinitionT, PropertyValueSpecification} from '../types.g';
import {getType} from '../util/get_type';

export function validateProjectionDefinition(options) {
    const key = options.key;
    let value = options.value;
    value = value instanceof String ? value.valueOf() : value;

    const type = getType(value);

    if (
        type === 'array' &&
        !isProjectionDefinitionValue(value) &&
        !isPropertyValueSpecification(value)
    ) {
        return [
            new ValidationError(
                key,
                value,
                `projection expected, invalid array ${JSON.stringify(value)} found`
            )
        ];
    } else if (!['array', 'string'].includes(type)) {
        return [
            new ValidationError(key, value, `projection expected, invalid type "${type}" found`)
        ];
    }

    return [];
}

function isPropertyValueSpecification(
    value: unknown
): value is PropertyValueSpecification<ProjectionDefinitionT> {
    if (['interpolate', 'step', 'literal'].includes(value[0])) {
        return true;
    }
    return false;
}

function isProjectionDefinitionValue(value: unknown): value is ProjectionDefinitionT {
    return (
        Array.isArray(value) &&
        value.length === 3 &&
        typeof value[0] === 'string' &&
        typeof value[1] === 'string' &&
        typeof value[2] === 'number'
    );
}