import type { ViteUserConfig } from 'astro';
import MagicString from 'magic-string';

// https://vite.dev/guide/api-plugin#hook-filters
const pluginTransformIdIncludeFilter = /\.astro$/;
const pluginTransformIdExcludeFilter = /@astrojs\/starlight\/components\/StarlightPage\.astro$/;
const pluginTransformCodeFilter = 'StarlightPage.astro';

const starlightPageImportSource = '@astrojs/starlight/components/StarlightPage.astro';

/**
 * Vite plugin that ensures the StarlightPage component is always imported first when imported in
 * an Astro file.
 *
 * This is necessary to ensure a predictable CSS layer order which is defined by the `<Page />`
 * imported by the `<StarlightPage />` component. If a user imports any other component using
 * cascade layers before the `<StarlightPage />` component, it will result in undesired layers
 * being created before we explicitly set the expected layer order.
 */
export function vitePluginStarlightCssLayerOrder(): VitePlugin {
	return {
		name: 'vite-plugin-starlight-css-layer-order',
		enforce: 'pre',
		transform: {
			filter: {
				id: { include: pluginTransformIdIncludeFilter, exclude: pluginTransformIdExcludeFilter },
				code: pluginTransformCodeFilter,
			},
			handler(code, id) {
				let ast: ReturnType<typeof this.parse>;

				try {
					ast = this.parse(code);
				} catch {
					return;
				}

				let hasStarlightPageImport = false;

				for (const node of ast.body) {
					if (node.type !== 'ImportDeclaration') continue;
					if (node.source.value !== starlightPageImportSource) continue;

					const importDefaultSpecifier = node.specifiers.find(
						(specifier) => specifier.type === 'ImportDefaultSpecifier'
					);
					if (!importDefaultSpecifier) continue;

					hasStarlightPageImport = true;
					break;
				}

				if (!hasStarlightPageImport) return;

				// Format path to unix style path.
				const filename = id.replace(/\\/g, '/');
				const ms = new MagicString(code, { filename });
				ms.prepend(`import "${starlightPageImportSource}";\n`);

				return {
					code: ms.toString(),
					map: ms.generateMap({ hires: 'boundary' }),
				};
			},
		},
	};
}

type VitePlugin = NonNullable<ViteUserConfig['plugins']>[number];