/*
    * Copyright (C) 2022, Matthias Fromme <mfromme@dspace.de>
    *
    * This program and the accompanying materials are made available under the
    * terms of the Eclipse Distribution License v. 1.0 which is available at
    * https://www.eclipse.org/org/documents/edl-v10.php.
    *
    * SPDX-License-Identifier: BSD-3-Clause
    */
  package org.eclipse.jgit.lfs.internal;
  
  import java.io.File;
  import java.io.IOException;
  
  import org.eclipse.jgit.annotations.Nullable;
  import org.eclipse.jgit.dircache.DirCacheEntry;
  import org.eclipse.jgit.errors.ConfigInvalidException;
  import org.eclipse.jgit.lfs.errors.LfsConfigInvalidException;
  import org.eclipse.jgit.lfs.lib.Constants;
  import org.eclipse.jgit.lib.BlobBasedConfig;
  import org.eclipse.jgit.lib.Config;
  import org.eclipse.jgit.lib.ObjectId;
  import org.eclipse.jgit.lib.Repository;
  import org.eclipse.jgit.revwalk.RevCommit;
  import org.eclipse.jgit.revwalk.RevTree;
  import org.eclipse.jgit.revwalk.RevWalk;
  import org.eclipse.jgit.storage.file.FileBasedConfig;
  import org.eclipse.jgit.treewalk.TreeWalk;
  
  import static org.eclipse.jgit.lib.Constants.HEAD;
  
  /**
   * Encapsulate access to the .lfsconfig.
   *
   * According to the document
   * https://github.com/git-lfs/git-lfs/blob/main/docs/man/git-lfs-config.5.ronn
   * the order to find the .lfsconfig file is:
   *
   * <pre>
   *   1. in the root of the working tree
   *   2. in the index
   *   3. in the HEAD, for bare repositories this is the only place
   *      that is searched
   * </pre>
   *
   * Values from the .lfsconfig are used only if not specified in another git
   * config file to allow local override without modifiction of a committed file.
   */
  public class LfsConfig {
  	private Repository db;
  	private Config delegate;
  
  	/**
  	 * Create a new instance of the LfsConfig.
  	 *
  	 * @param db
  	 *            the associated repo
  	 * @throws IOException
  	 */
  	public LfsConfig(Repository db) throws IOException {
  		this.db = db;
  		delegate = this.load();
  	}
  
  	/**
  	 * Read the .lfsconfig file from the repository
  	 *
  	 * @return The loaded lfs config or null if it does not exist
  	 *
  	 * @throws IOException
  	 */
  	private Config load() throws IOException {
  		Config result = null;
  
  		if (!db.isBare()) {
  			result = loadFromWorkingTree();
  			if (result == null) {
  				result = loadFromIndex();
  			}
  		}
  
  		if (result == null) {
  			result = loadFromHead();
  		}
  
  		if (result == null) {
  			result = emptyConfig();
  		}
  
  		return result;
  	}
  
  	/**
  	 * Try to read the lfs config from a file called .lfsconfig at the top level
  	 * of the working tree.
  	 *
  	 * @return the config, or <code>null</code>
  	 * @throws IOException
  	 */
 	@Nullable
 	private Config loadFromWorkingTree()
 			throws IOException {
 		File lfsConfig = db.getFS().resolve(db.getWorkTree(),
 				Constants.DOT_LFS_CONFIG);
 		if (lfsConfig.exists() && lfsConfig.isFile()) {
 			FileBasedConfig config = new FileBasedConfig(lfsConfig, db.getFS());
 			try {
 				config.load();
 				return config;
 			} catch (ConfigInvalidException e) {
 				throw new LfsConfigInvalidException(
 						LfsText.get().dotLfsConfigReadFailed, e);
 			}
 		}
 		return null;
 	}
 
 	/**
 	 * Try to read the lfs config from an entry called .lfsconfig contained in
 	 * the index.
 	 *
 	 * @return the config, or <code>null</code> if the entry does not exist
 	 * @throws IOException
 	 */
 	@Nullable
 	private Config loadFromIndex()
 			throws IOException {
 		try {
 			DirCacheEntry entry = db.readDirCache()
 					.getEntry(Constants.DOT_LFS_CONFIG);
 			if (entry != null) {
 				return new BlobBasedConfig(null, db, entry.getObjectId());
 			}
 		} catch (ConfigInvalidException e) {
 			throw new LfsConfigInvalidException(
 					LfsText.get().dotLfsConfigReadFailed, e);
 		}
 		return null;
 	}
 
 	/**
 	 * Try to read the lfs config from an entry called .lfsconfig contained in
 	 * the head revision.
 	 *
 	 * @return the config, or <code>null</code> if the file does not exist
 	 * @throws IOException
 	 */
 	@Nullable
 	private Config loadFromHead() throws IOException {
 		try (RevWalk revWalk = new RevWalk(db)) {
 			ObjectId headCommitId = db.resolve(HEAD);
 			if (headCommitId == null) {
 				return null;
 			}
 			RevCommit commit = revWalk.parseCommit(headCommitId);
 			RevTree tree = commit.getTree();
 			TreeWalk treewalk = TreeWalk.forPath(db, Constants.DOT_LFS_CONFIG,
 					tree);
 			if (treewalk != null) {
 				return new BlobBasedConfig(null, db, treewalk.getObjectId(0));
 			}
 		} catch (ConfigInvalidException e) {
 			throw new LfsConfigInvalidException(
 					LfsText.get().dotLfsConfigReadFailed, e);
 		}
 		return null;
 	}
 
 	/**
 	 * Create an empty config as fallback to avoid null pointer checks.
 	 *
 	 * @return an empty config
 	 */
 	private Config emptyConfig() {
 		return new Config();
 	}
 
 	/**
 	 * Get string value or null if not found.
 	 *
 	 * First tries to find the value in the git config files. If not found tries
 	 * to find data in .lfsconfig.
 	 *
 	 * @param section
 	 *            the section
 	 * @param subsection
 	 *            the subsection for the value
 	 * @param name
 	 *            the key name
 	 * @return a String value from the config, <code>null</code> if not found
 	 */
 	public String getString(final String section, final String subsection,
 			final String name) {
 		String result = db.getConfig().getString(section, subsection, name);
 		if (result == null) {
 			result = delegate.getString(section, subsection, name);
 		}
 		return result;
 	}
 }