import { readFileSync, readdirSync, statSync } from 'node:fs';
import { basename, dirname, extname, join, relative } from 'node:path';
import { fileURLToPath, pathToFileURL } from 'node:url';
import type { CanonicalizeContext, Importer, ImporterResult, Syntax } from 'sass';
import { findUrls } from './lexer';

/**
 * A preprocessed cache entry for the files and directories within a previously searched
 * directory when performing Sass import resolution.
 */
export interface DirectoryEntry {
  files: Set<string>;
  directories: Set<string>;
}

/**
 * A Sass Importer base class that provides the load logic to rebase all `url()` functions
 * within a stylesheet. The rebasing will ensure that the URLs in the output of the Sass compiler
 * reflect the final filesystem location of the output CSS file.
 *
 * This class provides the core of the rebasing functionality. To ensure that each file is processed
 * by this importer's load implementation, the Sass compiler requires the importer's canonicalize
 * function to return a non-null value with the resolved location of the requested stylesheet.
 * Concrete implementations of this class must provide this canonicalize functionality for rebasing
 * to be effective.
 */
abstract class UrlRebasingImporter implements Importer<'sync'> {
  /**
   * @param entryDirectory The directory of the entry stylesheet that was passed to the Sass compiler.
   * @param rebaseSourceMaps When provided, rebased files will have an intermediate sourcemap added to the Map
   * which can be used to generate a final sourcemap that contains original sources.
   */
  constructor(private entryDirectory: string) {}

  abstract canonicalize(url: string, options: { fromImport: boolean }): URL | null;

  load(canonicalUrl: URL): ImporterResult | null {
    const stylesheetPath = fileURLToPath(canonicalUrl);
    const stylesheetDirectory = dirname(stylesheetPath);
    let contents = readFileSync(stylesheetPath, 'utf-8');

    // Rebase any URLs that are found
    let updatedContents;
    for (const { start, end, value } of findUrls(contents)) {
      // Skip if value is empty or Webpack-specific prefix
      if (value.length === 0 || value[0] === '~' || value[0] === '^') {
        continue;
      }

      // Skip if root-relative, absolute or protocol relative url
      if (/^((?:\w+:)?\/\/|data:|chrome:|\/)/.test(value)) {
        continue;
      }

      // Skip if a fragment identifier but not a Sass interpolation
      if (value[0] === '#' && value[1] !== '{') {
        continue;
      }

      // Skip if value is value contains a function call
      if (/#\{.+\(.+\)\}/.test(value)) {
        continue;
      }

      // Sass variable usage either starts with a `$` or contains a namespace and a `.$`
      const valueNormalized = value[0] === '$' || /^\w+\.\$/.test(value) ? `#{${value}}` : value;
      const rebasedPath = relative(this.entryDirectory, stylesheetDirectory);

      // Normalize path separators and escape characters
      // https://developer.mozilla.org/en-US/docs/Web/CSS/url#syntax
      const rebasedUrl = rebasedPath.replace(/\\/g, '/').replace(/[()\s'"]/g, '\\$&');

      updatedContents ??= contents;
      updatedContents = contents.slice(0, start) + `"${rebasedUrl}||file:${valueNormalized}"` + contents.slice(end);
    }

    if (updatedContents) {
      contents = updatedContents;
    }

    let syntax: Syntax | undefined;
    switch (extname(stylesheetPath).toLowerCase()) {
      case '.css':
        syntax = 'css';
        break;
      case '.sass':
        syntax = 'indented';
        break;
      default:
        syntax = 'scss';
        break;
    }

    return {
      contents,
      syntax,
      sourceMapUrl: canonicalUrl,
    };
  }
}

/**
 * Provides the Sass importer logic to resolve relative stylesheet imports via both import and use rules
 * and also rebase any `url()` function usage within those stylesheets. The rebasing will ensure that
 * the URLs in the output of the Sass compiler reflect the final filesystem location of the output CSS file.
 */
export class RelativeUrlRebasingImporter extends UrlRebasingImporter {
  constructor(
    entryDirectory: string,
    private directoryCache = new Map<string, DirectoryEntry>(),
  ) {
    super(entryDirectory);
  }

  canonicalize(url: string, options: { fromImport: boolean }): URL | null {
    return this.resolveImport(url, options.fromImport, true);
  }

  /**
   * Attempts to resolve a provided URL to a stylesheet file using the Sass compiler's resolution algorithm.
   * Based on https://github.com/sass/dart-sass/blob/44d6bb6ac72fe6b93f5bfec371a1fffb18e6b76d/lib/src/importer/utils.dart
   * @param url The file protocol URL to resolve.
   * @param fromImport If true, URL was from an import rule; otherwise from a use rule.
   * @param checkDirectory If true, try checking for a directory with the base name containing an index file.
   * @returns A full resolved URL of the stylesheet file or `null` if not found.
   */
  private resolveImport(url: string, fromImport: boolean, checkDirectory: boolean): URL | null {
    let stylesheetPath;
    try {
      stylesheetPath = fileURLToPath(url);
    } catch {
      // Only file protocol URLs are supported by this importer
      return null;
    }

    const directory = dirname(stylesheetPath);
    const extension = extname(stylesheetPath);
    const hasStyleExtension = extension === '.scss' || extension === '.sass' || extension === '.css';
    // Remove the style extension if present to allow adding the `.import` suffix
    const filename = basename(stylesheetPath, hasStyleExtension ? extension : undefined);

    const importPotentials = new Set<string>();
    const defaultPotentials = new Set<string>();

    if (hasStyleExtension) {
      if (fromImport) {
        importPotentials.add(filename + '.import' + extension);
        importPotentials.add('_' + filename + '.import' + extension);
      }
      defaultPotentials.add(filename + extension);
      defaultPotentials.add('_' + filename + extension);
    } else {
      if (fromImport) {
        importPotentials.add(filename + '.import.scss');
        importPotentials.add(filename + '.import.sass');
        importPotentials.add(filename + '.import.css');
        importPotentials.add('_' + filename + '.import.scss');
        importPotentials.add('_' + filename + '.import.sass');
        importPotentials.add('_' + filename + '.import.css');
      }
      defaultPotentials.add(filename + '.scss');
      defaultPotentials.add(filename + '.sass');
      defaultPotentials.add(filename + '.css');
      defaultPotentials.add('_' + filename + '.scss');
      defaultPotentials.add('_' + filename + '.sass');
      defaultPotentials.add('_' + filename + '.css');
    }

    let foundDefaults;
    let foundImports;
    let hasPotentialIndex = false;

    let cachedEntries = this.directoryCache.get(directory);
    if (cachedEntries) {
      // If there is a preprocessed cache of the directory, perform an intersection of the potentials
      // and the directory files.
      const { files, directories } = cachedEntries;
      foundDefaults = [...defaultPotentials].filter(potential => files.has(potential));
      foundImports = [...importPotentials].filter(potential => files.has(potential));
      hasPotentialIndex = checkDirectory && !hasStyleExtension && directories.has(filename);
    } else {
      // If no preprocessed cache exists, get the entries from the file system and, while searching,
      // generate the cache for later requests.
      let entries;
      try {
        entries = readdirSync(directory, { withFileTypes: true });
      } catch (error) {
        // If the containing directory does not exist return null to indicate it cannot be resolved
        if (error.code === 'ENOENT') {
          return null;
        }

        throw new Error(`Error reading directory ["${directory}"] while resolving Sass import`, {
          cause: error,
        });
      }

      foundDefaults = [];
      foundImports = [];
      cachedEntries = { files: new Set<string>(), directories: new Set<string>() };
      for (const entry of entries) {
        let isDirectory: boolean;
        let isFile: boolean;

        if (entry.isSymbolicLink()) {
          const stats = statSync(join(directory, entry.name));
          isDirectory = stats.isDirectory();
          isFile = stats.isFile();
        } else {
          isDirectory = entry.isDirectory();
          isFile = entry.isFile();
        }

        if (isDirectory) {
          cachedEntries.directories.add(entry.name);

          // Record if the name should be checked as a directory with an index file
          if (checkDirectory && !hasStyleExtension && entry.name === filename) {
            hasPotentialIndex = true;
          }
        }

        if (!isFile) {
          continue;
        }

        cachedEntries.files.add(entry.name);

        if (importPotentials.has(entry.name)) {
          foundImports.push(entry.name);
        }

        if (defaultPotentials.has(entry.name)) {
          foundDefaults.push(entry.name);
        }
      }

      this.directoryCache.set(directory, cachedEntries);
    }

    // `foundImports` will only contain elements if `options.fromImport` is true
    const result = this.checkFound(foundImports) ?? this.checkFound(foundDefaults);
    if (result !== null) {
      return pathToFileURL(join(directory, result));
    }

    if (hasPotentialIndex) {
      // Check for index files using filename as a directory
      return this.resolveImport(url + '/index', fromImport, false);
    }

    return null;
  }

  /**
   * Checks an array of potential stylesheet files to determine if there is a valid
   * stylesheet file. More than one discovered file may indicate an error.
   * @param found An array of discovered stylesheet files.
   * @returns A fully resolved path for a stylesheet file or `null` if not found.
   * @throws If there are ambiguous files discovered.
   */
  private checkFound(found: string[]): string | null {
    if (found.length === 0) {
      // Not found
      return null;
    }

    // More than one found file may be an error
    if (found.length > 1) {
      // Presence of CSS files alongside a Sass file does not cause an error
      const foundWithoutCss = found.filter(element => extname(element) !== '.css');
      // If the length is zero then there are two or more css files
      // If the length is more than one than there are two or more sass/scss files
      if (foundWithoutCss.length !== 1) {
        throw new Error('Ambiguous import detected.');
      }

      // Return the non-CSS file (sass/scss files have priority)
      // https://github.com/sass/dart-sass/blob/44d6bb6ac72fe6b93f5bfec371a1fffb18e6b76d/lib/src/importer/utils.dart#L44-L47
      return foundWithoutCss[0];
    }

    return found[0];
  }
}

/**
 * Provides the Sass importer logic to resolve module (npm package) stylesheet imports via both import and
 * use rules and also rebase any `url()` function usage within those stylesheets. The rebasing will ensure that
 * the URLs in the output of the Sass compiler reflect the final filesystem location of the output CSS file.
 */
export class ModuleUrlRebasingImporter extends RelativeUrlRebasingImporter {
  constructor(
    entryDirectory: string,
    directoryCache: Map<string, DirectoryEntry>,
    private finder: (specifier: string, options: CanonicalizeContext) => URL | null,
  ) {
    super(entryDirectory, directoryCache);
  }

  override canonicalize(url: string, options: CanonicalizeContext): URL | null {
    if (url.startsWith('file://')) {
      return super.canonicalize(url, options);
    }

    let result = this.finder(url, options);
    result &&= super.canonicalize(result.href, options);

    return result;
  }
}

/**
 * Provides the Sass importer logic to resolve load paths located stylesheet imports via both import and
 * use rules and also rebase any `url()` function usage within those stylesheets. The rebasing will ensure that
 * the URLs in the output of the Sass compiler reflect the final filesystem location of the output CSS file.
 */
export class LoadPathsUrlRebasingImporter extends RelativeUrlRebasingImporter {
  constructor(
    entryDirectory: string,
    directoryCache: Map<string, DirectoryEntry>,
    private loadPaths: Iterable<string>,
  ) {
    super(entryDirectory, directoryCache);
  }

  override canonicalize(url: string, options: { fromImport: boolean }): URL | null {
    if (url.startsWith('file://')) {
      return super.canonicalize(url, options);
    }

    let result = null;
    for (const loadPath of this.loadPaths) {
      result = super.canonicalize(pathToFileURL(join(loadPath, url)).href, options);
      if (result !== null) {
        break;
      }
    }

    return result;
  }
}

/**
 * Workaround for Sass not calling instance methods with `this`.
 * The `canonicalize` and `load` methods will be bound to the class instance.
 * @param importer A Sass importer to bind.
 * @returns The bound Sass importer.
 */
export function sassBindWorkaround<T extends Importer>(importer: T): T {
  importer.canonicalize = importer.canonicalize.bind(importer);
  importer.load = importer.load.bind(importer);

  return importer;
}