import {CRSWorldCoordinateHelper, identityCrs, type CRS} from '../geo/projection/crs.ts';
import {warnOnce} from '../util/util.ts';

/**
 * @experimental
 * Builds the converter for a coordinate reference system from its definition string, the way `proj4(definition)`
 * does: `forward` takes lng/lat to CRS coordinates and `inverse` takes them back. A worker script sets one with
 * `self.setProjectionHandler`, loaded through {@link importScriptInWorkers}, so that GeoJSON sources follow a
 * registered projection that has a `definition`.
 */
export type ProjectionHandler = (definition: string) => CRS['projection'];

let projectionHandler: ProjectionHandler | null = null;

/**
 * The converters the projection handler has built, by the string it built each from, so that data loaded again in the
 * same projection does not make it parse the string again.
 */
const projections = new Map<string, CRS['projection']>();

/**
 * @internal
 * Sets the worker's projection handler; a later call replaces it, and `null` removes it.
 */
export function setProjectionHandler(handler: ProjectionHandler | null): void {
    projectionHandler = handler;
    projections.clear();
}

/**
 * @internal
 * The world coordinate helper a worker builds for a registered projection the main thread describes: from the
 * definition string through the projection handler, or the built-in identity CRS when there is none. `undefined`,
 * with a warning, when a definition string comes with no handler set.
 */
export function createWorkerCRSHelper(crs: Pick<CRS, 'name' | 'definition' | 'tileMatrixSet'>): CRSWorldCoordinateHelper | undefined {
    if (!crs.definition) return new CRSWorldCoordinateHelper(identityCrs);
    if (!projectionHandler) {
        warnOnce('GeoJSON sources are drawn in the wrong place: no projection handler is set in the workers, see `setProjectionHandler` in the custom CRS guide.');
        return undefined;
    }
    if (!projections.has(crs.definition)) projections.set(crs.definition, projectionHandler(crs.definition));
    return new CRSWorldCoordinateHelper({name: crs.name, definition: crs.definition, projection: projections.get(crs.definition), tileMatrixSet: crs.tileMatrixSet});
}