/*
    * Copyright (C) 2016, 2021 Christian Halstrick <christian.halstrick@sap.com> and others
    *
    * 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;
  
  import static java.nio.charset.StandardCharsets.UTF_8;
  
  import java.io.BufferedInputStream;
  import java.io.BufferedReader;
  import java.io.ByteArrayInputStream;
  import java.io.IOException;
  import java.io.InputStream;
  import java.io.InputStreamReader;
  import java.io.OutputStream;
  import java.io.PrintStream;
  import java.io.UnsupportedEncodingException;
  import java.util.Locale;
  import java.util.Objects;
  
  import org.eclipse.jgit.annotations.Nullable;
  import org.eclipse.jgit.lfs.lib.AnyLongObjectId;
  import org.eclipse.jgit.lfs.lib.Constants;
  import org.eclipse.jgit.lfs.lib.LongObjectId;
  import org.eclipse.jgit.util.IO;
  
  /**
   * Represents an LFS pointer file
   *
   * @since 4.6
   */
  public class LfsPointer implements Comparable<LfsPointer> {
  	/**
  	 * The version of the LfsPointer file format
  	 */
  	public static final String VERSION = "https://git-lfs.github.com/spec/v1"; //$NON-NLS-1$
  
  	/**
  	 * The version of the LfsPointer file format using legacy URL
  	 * @since 4.7
  	 */
  	public static final String VERSION_LEGACY = "https://hawser.github.com/spec/v1"; //$NON-NLS-1$
  
  	/**
  	 * Don't inspect files that are larger than this threshold to avoid
  	 * excessive reading. No pointer file should be larger than this.
  	 * @since 4.11
  	 */
  	public static final int SIZE_THRESHOLD = 200;
  
  	/**
  	 * The name of the hash function as used in the pointer files. This will
  	 * evaluate to "sha256"
  	 */
  	public static final String HASH_FUNCTION_NAME = Constants.LONG_HASH_FUNCTION
  			.toLowerCase(Locale.ROOT).replace("-", ""); //$NON-NLS-1$ //$NON-NLS-2$
  
  	/**
  	 * {@link #SIZE_THRESHOLD} is too low; with lfs extensions a LFS pointer can
  	 * be larger. But 8kB should be more than enough.
  	 */
  	static final int FULL_SIZE_THRESHOLD = 8 * 1024;
  
  	private final AnyLongObjectId oid;
  
  	private final long size;
  
  	/**
  	 * <p>Constructor for LfsPointer.</p>
  	 *
  	 * @param oid
  	 *            the id of the content
  	 * @param size
  	 *            the size of the content
  	 */
  	public LfsPointer(AnyLongObjectId oid, long size) {
  		this.oid = oid;
  		this.size = size;
  	}
  
  	/**
  	 * <p>Getter for the field <code>oid</code>.</p>
  	 *
  	 * @return the id of the content
  	 */
  	public AnyLongObjectId getOid() {
  		return oid;
  	}
  
  	/**
  	 * <p>Getter for the field <code>size</code>.</p>
  	 *
  	 * @return the size of the content
  	 */
 	public long getSize() {
 		return size;
 	}
 
 	/**
 	 * Encode this object into the LFS format defined by {@link #VERSION}
 	 *
 	 * @param out
 	 *            the {@link java.io.OutputStream} into which the encoded data should be
 	 *            written
 	 */
 	public void encode(OutputStream out) {
 		try (PrintStream ps = new PrintStream(out, false,
 				UTF_8.name())) {
 			ps.print("version "); //$NON-NLS-1$
 			ps.print(VERSION + "\n"); //$NON-NLS-1$
 			ps.print("oid " + HASH_FUNCTION_NAME + ":"); //$NON-NLS-1$ //$NON-NLS-2$
 			ps.print(oid.name() + "\n"); //$NON-NLS-1$
 			ps.print("size "); //$NON-NLS-1$
 			ps.print(size + "\n"); //$NON-NLS-1$
 		} catch (UnsupportedEncodingException e) {
 			// should not happen, we are using a standard charset
 		}
 	}
 
 	/**
 	 * Try to parse the data provided by an InputStream to the format defined by
 	 * {@link #VERSION}. If the given stream supports mark and reset as
 	 * indicated by {@link InputStream#markSupported()}, its input position will
 	 * be reset if the stream content is not actually a LFS pointer (i.e., when
 	 * {@code null} is returned). If the stream content is an invalid LFS
 	 * pointer or the given stream does not support mark/reset, the input
 	 * position may not be reset.
 	 *
 	 * @param in
 	 *            the {@link java.io.InputStream} from where to read the data
 	 * @return an {@link org.eclipse.jgit.lfs.LfsPointer} or {@code null} if the
 	 *         stream was not parseable as LfsPointer
 	 * @throws java.io.IOException
 	 */
 	@Nullable
 	public static LfsPointer parseLfsPointer(InputStream in)
 			throws IOException {
 		if (in.markSupported()) {
 			return parse(in);
 		}
 		// Fallback; note that while parse() resets its input stream, that won't
 		// reset "in".
 		return parse(new BufferedInputStream(in));
 	}
 
 	@Nullable
 	private static LfsPointer parse(InputStream in)
 			throws IOException {
 		if (!in.markSupported()) {
 			// No translation; internal error
 			throw new IllegalArgumentException(
 					"LFS pointer parsing needs InputStream.markSupported() == true"); //$NON-NLS-1$
 		}
 		// Try reading only a short block first.
 		in.mark(SIZE_THRESHOLD);
 		byte[] preamble = new byte[SIZE_THRESHOLD];
 		int length = IO.readFully(in, preamble, 0);
 		if (length < preamble.length || in.read() < 0) {
 			// We have the whole file. Try to parse a pointer from it.
 			try (BufferedReader r = new BufferedReader(new InputStreamReader(
 					new ByteArrayInputStream(preamble, 0, length), UTF_8))) {
 				LfsPointer ptr = parse(r);
 				if (ptr == null) {
 					in.reset();
 				}
 				return ptr;
 			}
 		}
 		// Longer than SIZE_THRESHOLD: expect "version" to be the first line.
 		boolean hasVersion = checkVersion(preamble);
 		in.reset();
 		if (!hasVersion) {
 			return null;
 		}
 		in.mark(FULL_SIZE_THRESHOLD);
 		byte[] fullPointer = new byte[FULL_SIZE_THRESHOLD];
 		length = IO.readFully(in, fullPointer, 0);
 		if (length == fullPointer.length && in.read() >= 0) {
 			in.reset();
 			return null; // Too long.
 		}
 		try (BufferedReader r = new BufferedReader(new InputStreamReader(
 				new ByteArrayInputStream(fullPointer, 0, length), UTF_8))) {
 			LfsPointer ptr = parse(r);
 			if (ptr == null) {
 				in.reset();
 			}
 			return ptr;
 		}
 	}
 
 	private static LfsPointer parse(BufferedReader r) throws IOException {
 		boolean versionLine = false;
 		LongObjectId id = null;
 		long sz = -1;
 		// This parsing is a bit too general if we go by the spec at
 		// https://github.com/git-lfs/git-lfs/blob/master/docs/spec.md
 		// Comment lines are not mentioned in the spec, the "version" line
 		// MUST be the first, and keys are ordered alphabetically.
 		for (String s = r.readLine(); s != null; s = r.readLine()) {
 			if (s.startsWith("#") || s.length() == 0) { //$NON-NLS-1$
 				continue;
 			} else if (s.startsWith("version")) { //$NON-NLS-1$
 				if (versionLine || !checkVersionLine(s)) {
 					return null; // Not a LFS pointer
 				}
 				versionLine = true;
 			} else {
 				try {
 					if (s.startsWith("oid sha256:")) { //$NON-NLS-1$
 						if (id != null) {
 							return null; // Not a LFS pointer
 						}
 						id = LongObjectId.fromString(s.substring(11).trim());
 					} else if (s.startsWith("size")) { //$NON-NLS-1$
 						if (sz > 0 || s.length() < 5 || s.charAt(4) != ' ') {
 							return null; // Not a LFS pointer
 						}
 						sz = Long.parseLong(s.substring(5).trim());
 					}
 				} catch (RuntimeException e) {
 					// We could not parse the line. If we have a version
 					// already, this is a corrupt LFS pointer. Otherwise it
 					// is just not an LFS pointer.
 					if (versionLine) {
 						throw e;
 					}
 					return null;
 				}
 			}
 			if (versionLine && id != null && sz > -1) {
 				return new LfsPointer(id, sz);
 			}
 		}
 		return null;
 	}
 
 	private static boolean checkVersion(byte[] data) {
 		// According to the spec at
 		// https://github.com/git-lfs/git-lfs/blob/master/docs/spec.md
 		// it MUST always be the first line.
 		try (BufferedReader r = new BufferedReader(
 				new InputStreamReader(new ByteArrayInputStream(data), UTF_8))) {
 			String s = r.readLine();
 			if (s != null && s.startsWith("version")) { //$NON-NLS-1$
 				return checkVersionLine(s);
 			}
 		} catch (IOException e) {
 			// Doesn't occur, we're reading from a byte array!
 		}
 		return false;
 	}
 
 	private static boolean checkVersionLine(String s) {
 		if (s.length() < 8 || s.charAt(7) != ' ') {
 			return false; // Not a valid LFS pointer version line
 		}
 		String rest = s.substring(8).trim();
 		return VERSION.equals(rest) || VERSION_LEGACY.equals(rest);
 	}
 
 	/** {@inheritDoc} */
 	@Override
 	public String toString() {
 		return "LfsPointer: oid=" + oid.name() + ", size=" //$NON-NLS-1$ //$NON-NLS-2$
 				+ size;
 	}
 
 	/**
 	 * @since 4.11
 	 */
 	@Override
 	public int compareTo(LfsPointer o) {
 		int x = getOid().compareTo(o.getOid());
 		if (x != 0) {
 			return x;
 		}
 
 		return Long.compare(getSize(), o.getSize());
 	}
 
 	@Override
 	public int hashCode() {
 		return Objects.hash(getOid()) * 31 + Long.hashCode(getSize());
 	}
 
 	@Override
 	public boolean equals(Object obj) {
 		if (this == obj) {
 			return true;
 		}
 		if (obj == null || getClass() != obj.getClass()) {
 			return false;
 		}
 		LfsPointer other = (LfsPointer) obj;
 		return Objects.equals(getOid(), other.getOid())
 				&& getSize() == other.getSize();
 	}
 }