package io.ebean.migration.runner;

import io.ebean.migration.MigrationConfig;
import io.ebean.migration.MigrationException;
import io.ebean.migration.MigrationVersion;
import io.ebean.migration.util.IOUtils;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import java.io.IOException;
import java.net.URL;
import java.sql.Connection;
import java.sql.DatabaseMetaData;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Timestamp;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.LinkedHashMap;
import java.util.List;
import java.util.Set;

import static io.ebean.migration.MigrationVersion.BOOTINIT_TYPE;

/**
 * Manages the migration table.
 */
public class MigrationTable {

  private static final Logger logger = LoggerFactory.getLogger(MigrationTable.class);

  private final Connection connection;
  private final boolean checkState;

  private final String catalog;
  private final String schema;
  private final String table;
  private final String sqlTable;
  private final String envUserName;
  private final String platformName;

  private final Timestamp runOn = new Timestamp(System.currentTimeMillis());

  private final ScriptTransform scriptTransform;

  private final String insertSql;
  private final String updateSql;
  private final String updateChecksumSql;
  private final String selectSql;

  private final LinkedHashMap<String, MigrationMetaRow> migrations;
  private final boolean skipChecksum;

  private final Set<String> patchInsertVersions;
  private final Set<String> patchResetChecksumVersions;

  private MigrationMetaRow lastMigration;
  private LocalMigrationResource priorVersion;

  private final List<LocalMigrationResource> checkMigrations = new ArrayList<>();

  /**
   * Version of a dbinit script. When set this means all migration version less than this are ignored.
   */
  private MigrationVersion dbInitVersion;

  /**
   * Construct with server, configuration and jdbc connection (DB admin user).
   */
  public MigrationTable(MigrationConfig config, Connection connection, boolean checkState) {

    this.connection = connection;
    this.checkState = checkState;
    this.migrations = new LinkedHashMap<>();

    this.catalog = null;
    this.patchResetChecksumVersions = config.getPatchResetChecksumOn();
    this.patchInsertVersions = config.getPatchInsertOn();
    this.skipChecksum = config.isSkipChecksum();
    this.schema = config.getDbSchema();
    this.table = config.getMetaTable();
    this.platformName = config.getPlatformName();
    this.sqlTable = sqlTable();
    this.selectSql = MigrationMetaRow.selectSql(sqlTable, platformName);
    this.insertSql = MigrationMetaRow.insertSql(sqlTable);
    this.updateSql = MigrationMetaRow.updateSql(sqlTable);
    this.updateChecksumSql = MigrationMetaRow.updateChecksumSql(sqlTable);
    this.scriptTransform = createScriptTransform(config);
    this.envUserName = System.getProperty("user.name");
  }

  private String sqlTable() {
    if (schema != null) {
      return schema + "." + table;
    } else {
      return table;
    }
  }

  private String sqlPrimaryKey() {
    return "pk_" + table;
  }

  /**
   * Return the number of migrations in the DB migration table.
   */
  public int size() {
    return migrations.size();
  }

  /**
   * Returns the versions that are already applied.
   */
  public Set<String> getVersions() {
    return migrations.keySet();
  }

  /**
   * Create the ScriptTransform for placeholder key/value replacement.
   */
  private ScriptTransform createScriptTransform(MigrationConfig config) {

    return ScriptTransform.build(config.getRunPlaceholders(), config.getRunPlaceholderMap());
  }

  /**
   * Create the table is it does not exist.
   * <p>
   * Also holds DB lock on migration table and loads existing migrations.
   * </p>
   */
  public void createIfNeededAndLock() throws SQLException, IOException {

    if (!tableExists(connection)) {
      createTable(connection);
    }

    // load existing migrations, hold DB lock on migration table
    try (PreparedStatement query = connection.prepareStatement(selectSql)) {
      try (ResultSet resultSet = query.executeQuery()) {
        while (resultSet.next()) {
          MigrationMetaRow metaRow = new MigrationMetaRow(resultSet);
          addMigration(metaRow.getVersion(), metaRow);
        }
      }
    }
  }

  private void createTable(Connection connection) throws IOException, SQLException {

    String tableScript = createTableDdl();
    MigrationScriptRunner run = new MigrationScriptRunner(connection);
    run.runScript(false, tableScript, "create migration table");
  }

  /**
   * Return the create table script.
   */
  String createTableDdl() throws IOException {
    String script = ScriptTransform.replace("${table}", sqlTable, getCreateTableScript());
    return ScriptTransform.replace("${pk_table}", sqlPrimaryKey(), script);
  }

  /**
   * Return the create table script.
   */
  private String getCreateTableScript() throws IOException {
    // supply a script to override the default table create script
    String script = readResource("migration-support/create-table.sql");
    if (script == null && platformName != null && !platformName.isEmpty()) {
      // look for platform specific create table
      script = readResource("migration-support/" + platformName + "-create-table.sql");
    }
    if (script == null) {
      // no, just use the default script
      script = readResource("migration-support/default-create-table.sql");
    }
    return script;
  }

  private String readResource(String location) throws IOException {

    Enumeration<URL> resources = getClassLoader().getResources(location);
    if (resources.hasMoreElements()) {
      URL url = resources.nextElement();
      return IOUtils.readUtf8(url);
    }
    return null;
  }

  private ClassLoader getClassLoader() {
    return Thread.currentThread().getContextClassLoader();
  }

  /**
   * Return true if the table exists.
   */
  private boolean tableExists(Connection connection) throws SQLException {

    String migTable = table;

    DatabaseMetaData metaData = connection.getMetaData();
    if (metaData.storesUpperCaseIdentifiers()) {
      migTable = migTable.toUpperCase();
    }
    String checkCatalog = (catalog != null) ? catalog : connection.getCatalog();
    String checkSchema = (schema != null) ? schema : connection.getSchema();
    try (ResultSet tables = metaData.getTables(checkCatalog, checkSchema, migTable, null)) {
      return tables.next();
    }
  }

  /**
   * Return true if the migration ran successfully and false if the migration failed.
   */
  private boolean shouldRun(LocalMigrationResource localVersion, LocalMigrationResource prior) throws SQLException {

    if (prior != null && !localVersion.isRepeatable()) {
      if (!migrationExists(prior)) {
        logger.error("Migration {} requires prior migration {} which has not been run", localVersion.getVersion(), prior.getVersion());
        return false;
      }
    }

    MigrationMetaRow existing = migrations.get(localVersion.key());
    if (!runMigration(localVersion, existing)) {
      return false;
    }

    // migration was run successfully ...
    priorVersion = localVersion;
    connection.commit();
    return true;
  }

  /**
   * Run the migration script.
   *
   * @param local    The local migration resource
   * @param existing The information for this migration existing in the table
   * @return True if the migrations should continue
   */
  private boolean runMigration(LocalMigrationResource local, MigrationMetaRow existing) throws SQLException {

    String script = null;
    int checksum;
    if (local instanceof LocalDdlMigrationResource) {
      script = convertScript(local.getContent());
      checksum = Checksum.calculate(script);
    } else {
      checksum = ((LocalJdbcMigrationResource) local).getChecksum();
    }

    if (existing == null && patchInsertMigration(local, checksum)) {
      return true;
    }
    if (existing != null && skipMigration(checksum, local, existing)) {
      return true;
    }
    executeMigration(local, script, checksum, existing);
    return true;
  }

  /**
   * Return true if we 'patch history' inserting a DB migration without running it.
   */
  private boolean patchInsertMigration(LocalMigrationResource local, int checksum) throws SQLException {
    if (patchInsertVersions != null && patchInsertVersions.contains(local.key())) {
      logger.info("patch migration - insert into history {}", local.getLocation());
      if (!checkState) {
        insertIntoHistory(local, checksum, 0);
      }
      return true;
    }
    return false;
  }

  /**
   * Return true if the migration should be skipped.
   */
  boolean skipMigration(int checksum, LocalMigrationResource local, MigrationMetaRow existing) throws SQLException {

    boolean matchChecksum = (existing.getChecksum() == checksum);
    if (matchChecksum) {
      logger.trace("... skip unchanged migration {}", local.getLocation());
      return true;

    } else if (patchResetChecksum(existing, checksum)) {
      logger.info("patch migration - reset checksum on {}", local.getLocation());
      return true;

    } else if (local.isRepeatable() || skipChecksum) {
      // re-run the migration
      return false;
    } else {
      throw new MigrationException("Checksum mismatch on migration " + local.getLocation());
    }
  }

  /**
   * Return true if the checksum is reset on the existing migration.
   */
  private boolean patchResetChecksum(MigrationMetaRow existing, int newChecksum) throws SQLException {

    if (isResetOnVersion(existing.getVersion())) {
      if (!checkState) {
        existing.resetChecksum(newChecksum, connection, updateChecksumSql);
      }
      return true;
    } else {
      return false;
    }
  }

  private boolean isResetOnVersion(String version) {
    return patchResetChecksumVersions != null && patchResetChecksumVersions.contains(version);
  }

  /**
   * Run a migration script as new migration or update on existing repeatable migration.
   */
  private void executeMigration(LocalMigrationResource local, String script, int checksum, MigrationMetaRow existing) throws SQLException {

    if (checkState) {
      checkMigrations.add(local);
      // simulate the migration being run such that following migrations also match
      addMigration(local.key(), createMetaRow(local, checksum, 1));
      return;
    }

    logger.debug("run migration {}", local.getLocation());

    long start = System.currentTimeMillis();
    if (local instanceof LocalDdlMigrationResource) {
      MigrationScriptRunner run = new MigrationScriptRunner(connection);
      run.runScript(false, script, "run migration version: " + local.getVersion());
    } else {
      ((LocalJdbcMigrationResource) local).getMigration().migrate(connection);
    }
    long exeMillis = System.currentTimeMillis() - start;

    if (existing != null) {
      existing.rerun(checksum, exeMillis, envUserName, runOn);
      existing.executeUpdate(connection, updateSql);

    } else {
      insertIntoHistory(local, checksum, exeMillis);
    }
  }

  private void insertIntoHistory(LocalMigrationResource local, int checksum, long exeMillis) throws SQLException {
    MigrationMetaRow metaRow = createMetaRow(local, checksum, exeMillis);
    metaRow.executeInsert(connection, insertSql);
    addMigration(local.key(), metaRow);
  }

  /**
   * Create the MigrationMetaRow for this migration.
   */
  private MigrationMetaRow createMetaRow(LocalMigrationResource migration, int checksum, long exeMillis) {

    int nextId = 1;
    if (lastMigration != null) {
      nextId = lastMigration.getId() + 1;
    }

    String type = migration.getType();
    String runVersion = migration.key();
    String comment = migration.getComment();

    return new MigrationMetaRow(nextId, type, runVersion, comment, checksum, envUserName, runOn, exeMillis);
  }

  /**
   * Return true if the migration exists.
   */
  private boolean migrationExists(LocalMigrationResource priorVersion) {
    return migrations.containsKey(priorVersion.key());
  }

  /**
   * Apply the placeholder key/value replacement on the script.
   */
  private String convertScript(String script) {
    return scriptTransform.transform(script);
  }

  /**
   * Register the successfully executed migration (to allow dependant scripts to run).
   */
  private void addMigration(String key, MigrationMetaRow metaRow) {
    lastMigration = metaRow;
    if (metaRow.getVersion() == null) {
      throw new IllegalStateException("No runVersion in db migration table row? " + metaRow);
    }
    migrations.put(key, metaRow);
    if (BOOTINIT_TYPE.equals(metaRow.getType())) {
      dbInitVersion = MigrationVersion.parse(metaRow.getVersion());
    }
  }

  /**
   * Return true if there are no migrations.
   */
  public boolean isEmpty() {
    return migrations.isEmpty();
  }

  /**
   * Run all the migrations in order as needed.
   *
   * @return the migrations that have been run (collected if checkstate is true).
   */
  public List<LocalMigrationResource> runAll(List<LocalMigrationResource> localVersions) throws SQLException {
    for (LocalMigrationResource localVersion : localVersions) {
      if (!localVersion.isRepeatable() && dbInitVersion != null && dbInitVersion.compareTo(localVersion.getVersion()) >= 0) {
        logger.debug("migration skipped by dbInitVersion {}", dbInitVersion);
      } else if (!shouldRun(localVersion, priorVersion)) {
        break;
      }
    }
    return checkMigrations;
  }

  /**
   * Run using an init migration.
   *
   * @return the migrations that have been run (collected if checkstate is true).
   */
  public List<LocalMigrationResource> runInit(LocalMigrationResource initVersion, List<LocalMigrationResource> localVersions) throws SQLException {

    runRepeatableInit(localVersions);

    initVersion.setInitType();
    if (!shouldRun(initVersion, null)) {
      throw new IllegalStateException("Expected to run init migration but it didn't?");
    }

    // run any migrations greater that the init migration
    for (LocalMigrationResource localVersion : localVersions) {
      if (localVersion.compareTo(initVersion) > 0 && !shouldRun(localVersion, priorVersion)) {
        break;
      }
    }
    return checkMigrations;
  }

  private void runRepeatableInit(List<LocalMigrationResource> localVersions) throws SQLException {
    for (LocalMigrationResource localVersion : localVersions) {
      if (!localVersion.isRepeatableInit() || !shouldRun(localVersion, priorVersion)) {
        break;
      }
    }
  }

}