src/frontend/app/maps/styleloader.ts


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import type { StyleSpecification } from "react-map-gl/maplibre";

export async function loadStyle(
  styleName: string,
  colorScheme: string,
): Promise<StyleSpecification> {
  const stylePath = `/maps/styles/${styleName}-${colorScheme}.json`;
  const resp = await fetch(stylePath);

  if (!resp.ok) {
    throw new Error(`Failed to load style: ${stylePath}`);
  }

  const style = await resp.json();

  const baseUrl = window.location.origin;
  const spritePath = style.sprite;

  // Handle both string and array cases for spritePath
  if (Array.isArray(spritePath)) {
    // For array format, update each sprite object's URL to be absolute
    style.sprite = spritePath.map((spriteObj) => {
      const isAbsoluteUrl =
        spriteObj.url.startsWith("http://") ||
        spriteObj.url.startsWith("https://");
      if (isAbsoluteUrl) {
        return spriteObj;
      }

      return {
        ...spriteObj,
        url: `${baseUrl}${spriteObj.url}`,
      };
    });
  } else if (typeof spritePath === "string") {
    if (
      !spritePath.startsWith("http://") &&
      !spritePath.startsWith("https://")
    ) {
      style.sprite = `${baseUrl}${spritePath}`;
    }
  }

  // Detect on each source if it the 'tiles' URLs are relative and convert them to absolute URLs
  for (const sourceKey in style.sources) {
    const source = style.sources[sourceKey];
    for (const tileKey in source.tiles) {
      const tileUrl = source.tiles[tileKey];
      const isAbsoluteUrl =
        tileUrl.startsWith("http://") || tileUrl.startsWith("https://");
      if (!isAbsoluteUrl) {
        source.tiles[tileKey] = `${baseUrl}${tileUrl}`;
      }
    }
  }

  return style as StyleSpecification;
}