/**
 * @license
 * Copyright 2025 Google LLC
 * SPDX-License-Identifier: Apache-2.0
 */

import * as fs from 'node:fs';
import * as path from 'node:path';
import ignore from 'ignore';

export interface GitIgnoreFilter {
  isIgnored(filePath: string): boolean;
}

export class GitIgnoreParser implements GitIgnoreFilter {
  private projectRoot: string;
  private cache: Map<string, string[]> = new Map();
  private globalPatterns: string[] | undefined;

  constructor(projectRoot: string) {
    this.projectRoot = path.resolve(projectRoot);
  }

  private loadPatternsForFile(patternsFilePath: string): string[] {
    let content: string;
    try {
      content = fs.readFileSync(patternsFilePath, 'utf-8');
    } catch (_error) {
      return [];
    }

    const isExcludeFile = patternsFilePath.endsWith(
      path.join('.git', 'info', 'exclude'),
    );

    const relativeBaseDir = isExcludeFile
      ? '.'
      : path.dirname(path.relative(this.projectRoot, patternsFilePath));

    return content
      .split('\n')
      .map((p) => p.trim())
      .filter((p) => p !== '' && !p.startsWith('#'))
      .map((p) => {
        const isNegative = p.startsWith('!');
        if (isNegative) {
          p = p.substring(1);
        }

        const isAnchoredInFile = p.startsWith('/');
        if (isAnchoredInFile) {
          p = p.substring(1);
        }

        // An empty pattern can result from a negated pattern like `!`,
        // which we can ignore.
        if (p === '') {
          return '';
        }

        let newPattern = p;
        if (relativeBaseDir && relativeBaseDir !== '.') {
          // Only in nested .gitignore files, the patterns need to be modified according to:
          // - If `a/b/.gitignore` defines `/c` then it needs to be changed to `/a/b/c`
          // - If `a/b/.gitignore` defines `c` then it needs to be changed to `/a/b/**/c`
          // - If `a/b/.gitignore` defines `c/d` then it needs to be changed to `/a/b/c/d`

          if (!isAnchoredInFile && !p.includes('/')) {
            // If no slash and not anchored in file, it matches files in any
            // subdirectory.
            newPattern = path.join('**', p);
          }

          // Prepend the .gitignore file's directory.
          newPattern = path.join(relativeBaseDir, newPattern);

          // Anchor the pattern to a nested gitignore directory.
          if (!newPattern.startsWith('/')) {
            newPattern = '/' + newPattern;
          }
        }

        // Anchor the pattern if originally anchored
        if (isAnchoredInFile && !newPattern.startsWith('/')) {
          newPattern = '/' + newPattern;
        }

        if (isNegative) {
          newPattern = '!' + newPattern;
        }

        // Even in windows, Ignore expects forward slashes.
        newPattern = newPattern.replace(/\\/g, '/');

        return newPattern;
      })
      .filter((p) => p !== '');
  }

  isIgnored(filePath: string): boolean {
    if (!filePath || typeof filePath !== 'string') {
      return false;
    }

    const absoluteFilePath = path.resolve(this.projectRoot, filePath);
    if (!absoluteFilePath.startsWith(this.projectRoot)) {
      return false;
    }

    try {
      const resolved = path.resolve(this.projectRoot, filePath);
      const relativePath = path.relative(this.projectRoot, resolved);

      if (relativePath === '' || relativePath.startsWith('..')) {
        return false;
      }

      // Even in windows, Ignore expects forward slashes.
      const normalizedPath = relativePath.replace(/\\/g, '/');

      if (normalizedPath.startsWith('/') || normalizedPath === '') {
        return false;
      }

      const ig = ignore();

      // Always ignore .git directory
      ig.add('.git');

      // Load global patterns from .git/info/exclude on first call
      if (this.globalPatterns === undefined) {
        const excludeFile = path.join(
          this.projectRoot,
          '.git',
          'info',
          'exclude',
        );
        this.globalPatterns = fs.existsSync(excludeFile)
          ? this.loadPatternsForFile(excludeFile)
          : [];
      }
      ig.add(this.globalPatterns);

      const pathParts = relativePath.split(path.sep);

      const dirsToVisit = [this.projectRoot];
      let currentAbsDir = this.projectRoot;
      // Collect all directories in the path
      for (let i = 0; i < pathParts.length - 1; i++) {
        currentAbsDir = path.join(currentAbsDir, pathParts[i]);
        dirsToVisit.push(currentAbsDir);
      }

      for (const dir of dirsToVisit) {
        const relativeDir = path.relative(this.projectRoot, dir);
        if (relativeDir) {
          const normalizedRelativeDir = relativeDir.replace(/\\/g, '/');
          if (ig.ignores(normalizedRelativeDir)) {
            // This directory is ignored by an ancestor's .gitignore.
            // According to git behavior, we don't need to process this
            // directory's .gitignore, as nothing inside it can be
            // un-ignored.
            break;
          }
        }

        if (this.cache.has(dir)) {
          const patterns = this.cache.get(dir);
          if (patterns) {
            ig.add(patterns);
          }
        } else {
          const gitignorePath = path.join(dir, '.gitignore');
          if (fs.existsSync(gitignorePath)) {
            const patterns = this.loadPatternsForFile(gitignorePath);
            this.cache.set(dir, patterns);
            ig.add(patterns);
          } else {
            this.cache.set(dir, []); // Cache miss
          }
        }
      }

      return ig.ignores(normalizedPath);
    } catch (_error) {
      return false;
    }
  }
}