/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hbase.test.util.warc;

import java.io.ByteArrayOutputStream;
import java.io.DataInput;
import java.io.DataOutput;
import java.io.IOException;
import java.util.LinkedHashMap;
import java.util.Map;
import java.util.regex.Pattern;

/**
 * Immutable implementation of a record in a WARC file. You create a {@link WARCRecord} by parsing
 * it out of a {@link DataInput} stream. The file format is documented in the [ISO
 * Standard](http://bibnum.bnf.fr/warc/WARC_ISO_28500_version1_latestdraft.pdf). In a nutshell, it's
 * a textual format consisting of lines delimited by `\r\n`. Each record has the following
 * structure: 1. A line indicating the WARC version number, such as `WARC/1.0`. 2. Several header
 * lines (in key-value format, similar to HTTP or email headers), giving information about the
 * record. The header is terminated by an empty line. 3. A body consisting of raw bytes (the number
 * of bytes is indicated in one of the headers). 4. A final separator of `\r\n\r\n` before the next
 * record starts. There are various different types of records, as documented on
 * {@link Header#getRecordType()}.
 */
public class WARCRecord {

  public static final String WARC_VERSION = "WARC/1.0";
  private static final Pattern VERSION_PATTERN = Pattern.compile("WARC/[0-9\\.]+");
  private static final Pattern CONTINUATION_PATTERN = Pattern.compile("^[\\t ]+.*");
  private static final String CRLF = "\r\n";
  private static final byte[] CRLF_BYTES = { 13, 10 };

  private final Header header;
  private final byte[] content;

  /**
   * Creates a new WARCRecord by parsing it out of a {@link DataInput} stream.
   * @param in The input source from which one record will be read.
   */
  public WARCRecord(DataInput in) throws IOException {
    header = readHeader(in);
    content = new byte[header.getContentLength()];
    in.readFully(content);
    readSeparator(in);
  }

  private static Header readHeader(DataInput in) throws IOException {
    String versionLine = readLine(in);
    if (!VERSION_PATTERN.matcher(versionLine).matches()) {
      throw new IllegalStateException("Expected WARC version, but got: " + versionLine);
    }

    LinkedHashMap<String, String> headers = new LinkedHashMap<String, String>();
    String line, fieldName = null;

    do {
      line = readLine(in);
      if (fieldName != null && CONTINUATION_PATTERN.matcher(line).matches()) {
        headers.put(fieldName, headers.get(fieldName) + line);
      } else if (!line.isEmpty()) {
        String[] field = line.split(":", 2);
        if (field.length < 2) {
          throw new IllegalStateException("Malformed header line: " + line);
        }
        fieldName = field[0].trim();
        headers.put(fieldName, field[1].trim());
      }
    } while (!line.isEmpty());

    return new Header(headers);
  }

  private static String readLine(DataInput in) throws IOException {
    ByteArrayOutputStream out = new ByteArrayOutputStream();
    boolean seenCR = false, seenCRLF = false;
    while (!seenCRLF) {
      byte b = in.readByte();
      if (!seenCR && b == 13) {
        seenCR = true;
      } else if (seenCR && b == 10) {
        seenCRLF = true;
      } else {
        seenCR = false;
        out.write(b);
      }
    }
    return out.toString("UTF-8");
  }

  private static void readSeparator(DataInput in) throws IOException {
    byte[] sep = new byte[4];
    in.readFully(sep);
    if (sep[0] != 13 || sep[1] != 10 || sep[2] != 13 || sep[3] != 10) {
      throw new IllegalStateException(
        String.format("Expected final separator CR LF CR LF, but got: %d %d %d %d", sep[0], sep[1],
          sep[2], sep[3]));
    }
  }

  /**
   * Returns the parsed header structure of the WARC record.
   */
  public Header getHeader() {
    return header;
  }

  /**
   * Returns the body of the record, as an unparsed raw array of bytes. The content of the body
   * depends on the type of record (see {@link Header#getRecordType()}). For example, in the case of
   * a `response` type header, the body consists of the full HTTP response returned by the server
   * (HTTP headers followed by the body).
   */
  public byte[] getContent() {
    return content;
  }

  /**
   * Writes this record to a {@link DataOutput} stream. The output may, in some edge cases, be not
   * byte-for-byte identical to what was parsed from a {@link DataInput}. However it has the same
   * meaning and should not lose any information.
   * @param out The output stream to which this record should be appended.
   */
  public void write(DataOutput out) throws IOException {
    header.write(out);
    out.write(CRLF_BYTES);
    out.write(content);
    out.write(CRLF_BYTES);
    out.write(CRLF_BYTES);
  }

  /**
   * Returns a human-readable string representation of the record.
   */
  @Override
  public String toString() {
    return header.toString();
  }

  /**
   * Contains the parsed headers of a {@link WARCRecord}. Each record contains a number of headers
   * in key-value format, where some header keys are standardised, but nonstandard ones can be
   * added. The documentation of the methods in this class is excerpted from the [WARC 1.0
   * specification](http://bibnum.bnf.fr/warc/WARC_ISO_28500_version1_latestdraft.pdf). Please see
   * the specification for more detail.
   */
  public final static class Header {
    private final Map<String, String> fields;

    private Header(Map<String, String> fields) {
      this.fields = fields;
    }

    /**
     * Returns the type of WARC record (the value of the `WARC-Type` header field). WARC 1.0 defines
     * the following record types: (for full definitions, see the
     * [spec](http://bibnum.bnf.fr/warc/WARC_ISO_28500_version1_latestdraft.pdf)) * `warcinfo`:
     * Describes the records that follow it, up through end of file, end of input, or until next
     * `warcinfo` record. Typically, this appears once and at the beginning of a WARC file. For a
     * web archive, it often contains information about the web crawl which generated the following
     * records. The format of this descriptive record block may vary, though the use of the
     * `"application/warc-fields"` content-type is recommended. (...) * `response`: The record
     * should contain a complete scheme-specific response, including network protocol information
     * where possible. For a target-URI of the `http` or `https` schemes, a `response` record block
     * should contain the full HTTP response received over the network, including headers. That is,
     * it contains the 'Response' message defined by section 6 of HTTP/1.1 (RFC2616). The WARC
     * record's Content-Type field should contain the value defined by HTTP/1.1,
     * `"application/http;msgtype=response"`. The payload of the record is defined as its
     * 'entity-body' (per RFC2616), with any transfer-encoding removed. * `resource`: The record
     * contains a resource, without full protocol response information. For example: a file directly
     * retrieved from a locally accessible repository or the result of a networked retrieval where
     * the protocol information has been discarded. For a target-URI of the `http` or `https`
     * schemes, a `resource` record block shall contain the returned 'entity-body' (per RFC2616,
     * with any transfer-encodings removed), possibly truncated. * `request`: The record holds the
     * details of a complete scheme-specific request, including network protocol information where
     * possible. For a target-URI of the `http` or `https` schemes, a `request` record block should
     * contain the full HTTP request sent over the network, including headers. That is, it contains
     * the 'Request' message defined by section 5 of HTTP/1.1 (RFC2616). The WARC record's
     * Content-Type field should contain the value defined by HTTP/1.1,
     * `"application/http;msgtype=request"`. The payload of a `request` record with a target-URI of
     * scheme `http` or `https` is defined as its 'entity-body' (per RFC2616), with any
     * transfer-encoding removed. * `metadata`: The record contains content created in order to
     * further describe, explain, or accompany a harvested resource, in ways not covered by other
     * record types. A `metadata` record will almost always refer to another record of another type,
     * with that other record holding original harvested or transformed content. The format of the
     * metadata record block may vary. The `"application/warc-fields"` format may be used. *
     * `revisit`: The record describes the revisitation of content already archived, and might
     * include only an abbreviated content body which has to be interpreted relative to a previous
     * record. Most typically, a `revisit` record is used instead of a `response` or `resource`
     * record to indicate that the content visited was either a complete or substantial duplicate of
     * material previously archived. A `revisit` record shall contain a WARC-Profile field which
     * determines the interpretation of the record's fields and record block. Please see the
     * specification for details. * `conversion`: The record shall contain an alternative version of
     * another record's content that was created as the result of an archival process. Typically,
     * this is used to hold content transformations that maintain viability of content after widely
     * available rendering tools for the originally stored format disappear. As needed, the original
     * content may be migrated (transformed) to a more viable format in order to keep the
     * information usable with current tools while minimizing loss of information. * `continuation`:
     * Record blocks from `continuation` records must be appended to corresponding prior record
     * blocks (eg. from other WARC files) to create the logically complete full-sized original
     * record. That is, `continuation` records are used when a record that would otherwise cause a
     * WARC file size to exceed a desired limit is broken into segments. A continuation record shall
     * contain the named fields `WARC-Segment-Origin-ID` and `WARC-Segment-Number`, and the last
     * `continuation` record of a series shall contain a `WARC-Segment-Total-Length` field. Please
     * see the specification for details. * Other record types may be added in future, so this list
     * is not exclusive.
     * @return The record's `WARC-Type` header field, as a string.
     */
    public String getRecordType() {
      return fields.get("WARC-Type");
    }

    /**
     * A 14-digit UTC timestamp formatted according to YYYY-MM-DDThh:mm:ssZ, described in the W3C
     * profile of ISO8601. The timestamp shall represent the instant that data capture for record
     * creation began. Multiple records written as part of a single capture event shall use the same
     * WARC-Date, even though the times of their writing will not be exactly synchronized.
     * @return The record's `WARC-Date` header field, as a string.
     */
    public String getDateString() {
      return fields.get("WARC-Date");
    }

    /**
     * An identifier assigned to the current record that is globally unique for its period of
     * intended use. No identifier scheme is mandated by this specification, but each record-id
     * shall be a legal URI and clearly indicate a documented and registered scheme to which it
     * conforms (e.g., via a URI scheme prefix such as `http:` or `urn:`).
     * @return The record's `WARC-Record-ID` header field, as a string.
     */
    public String getRecordID() {
      return fields.get("WARC-Record-ID");
    }

    /**
     * The MIME type (RFC2045) of the information contained in the record's block. For example, in
     * HTTP request and response records, this would be `application/http` as per section 19.1 of
     * RFC2616 (or `application/http; msgtype=request` and `application/http; msgtype=response`
     * respectively). In particular, the content-type is *not* the value of the HTTP Content-Type
     * header in an HTTP response, but a MIME type to describe the full archived HTTP message (hence
     * `application/http` if the block contains request or response headers).
     * @return The record's `Content-Type` header field, as a string.
     */
    public String getContentType() {
      return fields.get("Content-Type");
    }

    /**
     * The original URI whose capture gave rise to the information content in this record. In the
     * context of web harvesting, this is the URI that was the target of a crawler's retrieval
     * request. For a `revisit` record, it is the URI that was the target of a retrieval request.
     * Indirectly, such as for a `metadata`, or `conversion` record, it is a copy of the
     * `WARC-Target-URI` appearing in the original record to which the newer record pertains. The
     * URI in this value shall be properly escaped according to RFC3986, and written with no
     * internal whitespace.
     * @return The record's `WARC-Target-URI` header field, as a string.
     */
    public String getTargetURI() {
      return fields.get("WARC-Target-URI");
    }

    /**
     * The number of bytes in the body of the record, similar to RFC2616.
     * @return The record's `Content-Length` header field, parsed into an int.
     */
    public int getContentLength() {
      String lengthStr = fields.get("Content-Length");
      if (lengthStr == null) {
        throw new IllegalStateException("Missing Content-Length header");
      }
      try {
        return Integer.parseInt(lengthStr);
      } catch (NumberFormatException e) {
        throw new IllegalStateException("Malformed Content-Length header: " + lengthStr);
      }
    }

    /**
     * Returns the value of a selected header field, or null if there is no header with that field
     * name.
     * @param field The name of the header to return (case-sensitive).
     * @return The value associated with that field name, or null if not present.
     */
    public String getField(String field) {
      return fields.get(field);
    }

    /**
     * Appends this header to a {@link DataOutput} stream, in WARC/1.0 format.
     * @param out The data output to which the header should be written.
     */
    public void write(DataOutput out) throws IOException {
      out.write(toString().getBytes("UTF-8"));
    }

    /**
     * Formats this header in WARC/1.0 format, consisting of a version line followed by
     * colon-delimited key-value pairs, and `\r\n` line endings.
     */
    @Override
    public String toString() {
      StringBuilder buf = new StringBuilder();
      buf.append(WARC_VERSION);
      buf.append(CRLF);
      for (Map.Entry<String, String> field : fields.entrySet()) {
        buf.append(field.getKey());
        buf.append(": ");
        buf.append(field.getValue());
        buf.append(CRLF);
      }
      return buf.toString();
    }
  }

}