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package org.opentripplanner.datastore.api;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.net.URI;
import java.text.SimpleDateFormat;
import org.apache.commons.io.IOUtils;
import org.opentripplanner.common.LoggingUtil;
import org.opentripplanner.datastore.OtpDataStore;

/**
 * A data source is generalized type to represent an file, database blob or unit that OTP read or
 * write to.
 * 
 * The data source instance contain metadata like {@code name}, {@code description}, {@code type}
 * and so on. To access (read from or write to) a datasource the methods {@link #asInputStream()}
 * and {@link #asOutputStream()} will open a connection to the underlying data source and make it
 * available for reading/writing.
 * 

 * Only metadata is retrieved before a stream is opened, making sure minimum data is transferred
 * before it is actually needed.
 * 

 * The data source metadata should be fetched once. The data is NOT updated even if the source
 * itself changes. If this happens it might cause the streaming to fail.
 * 

 * Concurrent modifications to underlying data-sources is not accounted for, and there is no need to
 * support that in the implementation of this class. This means that we assume all input- and
 * output-files in OTP are stable (not changed in any way) during the period OTP need to access
 * these files.
 */
public interface DataSource {
  /** Used for returning unknown file size and unknown last modified time */
  long UNKNOWN = -1;

  /**
   * @return the short name identifying the source within its scope (withing a {@link OtpDataStore}
   * or {@link CompositeDataSource}) Including the file extension.
   * 

   * Examples:
   * 

   * {@code build-config.json, gtfs.zip and stops.txt}
   */
  String name();

  /**
   * @return the full path (or description) to be used when describing this data source. This method
   * is mainly used for humans to identify the source in logs and error handling.
   */
  String path();

  /**
   * @return the URI of the datasource. The URI can be used to identify uniquely the data source.
   */
  URI uri();

  /**
   * The file type this data source is identified as.
   */
  FileType type();

  /**
   * @return size in bytes, if unknown returns {@code -1}
   */
  default long size() {
    return UNKNOWN;
  }

  /**
   * @return last modified timestamp in ms, if unknown returns {@code -1}
   */
  default long lastModified() {
    return UNKNOWN;
  }

  /**
   * @return true is it exist in the data store; hence calling {@link #asInputStream()} is safe.
   */
  default boolean exists() {
    return true;
  }

  /**
   * @return {@code true} if it is possible to write to data source. Also, return {@code true} if if
   * it is not easy to check. No guarantee is given and the {@link #asOutputStream()} may fail. This
   * method can be used to avoid consuming a lot of resource before writing to a datasource, if this
   * method return {@code false}.
   */
  default boolean isWritable() {
    return true;
  }

  /**
   * Connect to this data source and make it available as an input stream. The caller is responsible
   * to close the connection.
   * 

   * Note! This method might get called several times, and each time a new Stream should be
   * created.
   */
  default InputStream asInputStream() {
    throw new UnsupportedOperationException(
      "This datasource type " +
      getClass().getSimpleName() +
      " do not support READING. Can not read from: " +
      path()
    );
  }

  /**
   * Return the content as a byte array. The implementation may chose to implement this in a more
   * efficient way - not reading the input stream. Do not change the data returned.
   * 

   * Calling this method is the same as reading everything off the {@link #asInputStream()}.
   */
  default byte[] asBytes() {
    try {
      return IOUtils.toByteArray(asInputStream());
    } catch (IOException e) {
      throw new RuntimeException("Failed to read " + path() + ": " + e.getLocalizedMessage(), e);
    }
  }

  default OutputStream asOutputStream() {
    throw new UnsupportedOperationException(
      "This datasource type " +
      getClass().getSimpleName() +
      " do not support WRITING. Can not write to: " +
      path()
    );
  }

  /**
   * Return an info string like this:
   * 
   * {@code [icon] [filename]  [path]  [date time]  [file size]}
   */
  default String detailedInfo() {
    String info = String.format("%s %s  %s", type().icon(), name(), directory());
    if (lastModified() > 0) {
      SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
      info += "  " + sdf.format(lastModified());
    }
    if (size() > 0) {
      info += "  " + LoggingUtil.fileSizeToString(size());
    }
    return info;
  }

  /**
   * Return the directory that contains the file.
   */
  default String directory() {
    int endIndex = path().length() - (name().length() + 1);
    return endIndex <= 0 ? "" : path().substring(0, endIndex);
  }
}