index.ts

import {existsSync} from 'fs';
import {join as joinPaths} from 'path';

interface NetlifyUtils {
	cache: {
		restore: (path: string, options?: Partial<{cwd: string}>) => Promise<boolean>;
		save: (path: string, options?: Partial<{digests: string[]; cwd: string; ttl: number}>) => Promise<boolean>;
	};
	build: {
		failBuild: (message: string) => unknown;
		failPlugin: (message: string) => unknown;
		cancelBuild: (message: string) => unknown;
	};
	status: {
		/** @see https://docs.netlify.com/configure-builds/build-plugins/create-plugins/#logging */
		show: (status: {title?: string; summary: string; text?: string}) => unknown;
	};
}

interface NetlifyInputs {
	// The TOML config uses snakecase for readability and because it's convention
	custom_build_dir_name: string;
	build_dir_path: string;
}

interface NetlifyOpts {
	utils: NetlifyUtils;
	netlifyConfig: {build: {base: string}};
	inputs: NetlifyInputs;
}

function generateAbsolutePaths(options: Pick<NetlifyOpts, 'inputs'>): {
	absolute: {
		/** The absolute path to the build folder for Next.js. */
		buildDir: string;
		/** The absolute path to the build manifest Next.js uses. */
		manifest: string;
	};
	/** The name of the build directory. */
	buildDirName: string;
} {
	/** The name of the build folder. `.next`, unless specially configured. */
	const buildDirName = options.inputs.custom_build_dir_name;
	/** The directory the build folder is in. Defaults to current directory, although some larger repositories might keep this in a `frontend` folder. */
	const buildDirPathFromProject = options.inputs.build_dir_path;

	/** The absolute path to the build folder for Next.js. */
	const absoluteBuildDirPath = joinPaths(buildDirPathFromProject, buildDirName, 'cache');
	/** The absolute path to the build manifest Next.js uses. */
	// I don't actually know if this build manifest has any relation to the cache folder
	const manifestPath = joinPaths(absoluteBuildDirPath, '..', 'build-manifest.json');

	return {
		absolute: {
			buildDir: absoluteBuildDirPath,
			manifest: manifestPath,
		},
		buildDirName,
	};
}

module.exports = {
	// Restore file/directory cached in previous builds.
	// Does not do anything if:
	//  - the file/directory already exists locally
	//  - the file/directory has not been cached yet
	async onPreBuild({utils, inputs}: NetlifyOpts) {
		const paths = generateAbsolutePaths({inputs});
		const success = await utils.cache.restore(paths.absolute.buildDir);

		console.log(`${paths.absolute.buildDir} ${existsSync(paths.absolute.buildDir) ? 'exists' : 'does not exist'} on disk`);

		if (success) {
			const message = `Restored the cached ${paths.buildDirName} folder at the location ${paths.absolute.buildDir}`;

			console.log(message);
			utils.status.show({summary: `Restored the ${paths.buildDirName} folder`, text: message});
		} else {
			console.error(`Couldn't restore the cache for the ${paths.buildDirName} folder at the location ${paths.absolute.buildDir}`);
		}
	},
	// Cache file/directory for future builds.
	// Does not do anything if:
	//  - the file/directory does not exist locally
	//  - the file/directory is already cached and its contents has not changed
	//    If this is a directory, this includes children's contents
	// Note that this will cache after the build, even if it fails, which fcould be unwanted behavior
	async onPostBuild({utils, inputs}: NetlifyOpts) {
		const paths = generateAbsolutePaths({inputs});

		console.log(`${paths.absolute.buildDir} ${existsSync(paths.absolute.buildDir) ? 'exists' : 'does not exist'} on disk`);

		const success = await utils.cache.save(paths.absolute.buildDir, {
			digests: [paths.absolute.manifest],
		});

		if (success) {
			const message = `Cached the ${paths.buildDirName} folder at the location ${paths.absolute.buildDir}`;

			console.log(message);
			utils.status.show({summary: `Saved the ${paths.buildDirName} folder`, text: message});
		} else {
			console.error(`Couldn't cache the ${paths.buildDirName} folder at the location ${paths.absolute.buildDir}`);
		}
	},
};