/*
 * Copyright (c) Contributors, http://opensimulator.org/
 * See CONTRIBUTORS.TXT for a full list of copyright holders.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above copyright
 *       notice, this list of conditions and the following disclaimer in the
 *       documentation and/or other materials provided with the distribution.
 *     * Neither the name of the OpenSimulator Project nor the
 *       names of its contributors may be used to endorse or promote products
 *       derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE DEVELOPERS ``AS IS'' AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
 * WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
 * DISCLAIMED. IN NO EVENT SHALL THE CONTRIBUTORS BE LIABLE FOR ANY
 * DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
 * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
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 * ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
 * SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.Common;
using System.IO;
using System.Reflection;
using System.Text.RegularExpressions;
using log4net;

namespace OpenSim.Data
{
    /// <summary>
    ///
    /// The Migration theory is based on the ruby on rails concept.
    /// Each database driver is going to be allowed to have files in
    /// Resources that specify the database migrations.  They will be
    /// of the form:
    ///
    ///    001_Users.sql
    ///    002_Users.sql
    ///    003_Users.sql
    ///    001_Prims.sql
    ///    002_Prims.sql
    ///    ...etc...
    ///
    /// When a database driver starts up, it specifies a resource that
    /// needs to be brought up to the current revision.  For instance:
    ///
    ///    Migration um = new Migration(Assembly, DbConnection, "Users");
    ///    um.Upgrade();
    ///
    /// This works out which version Users is at, and applies all the
    /// revisions past it to it.  If there is no users table, all
    /// revisions are applied in order.  Consider each future
    /// migration to be an incremental roll forward of the tables in
    /// question.
    ///
    /// Assembly must be specifically passed in because otherwise you
    /// get the assembly that Migration.cs is part of, and what you
    /// really want is the assembly of your database class.
    ///
    /// </summary>

    public class Migration
    {
        private static readonly ILog m_log = LogManager.GetLogger(MethodBase.GetCurrentMethod().DeclaringType);

        private string _type;
        private DbConnection _conn;
        // private string _subtype;
        private Assembly _assem;
        private Regex _match;

        private static readonly string _migrations_create = "create table migrations(name varchar(100), version int)";
        // private static readonly string _migrations_init = "insert into migrations values('migrations', 1)";
        // private static readonly string _migrations_find = "select version from migrations where name='migrations'";


        public Migration(DbConnection conn, Assembly assem, string type)
        {
            _type = type;
            _conn = conn;
            _assem = assem;
            _match = new Regex(@"\.(\d\d\d)_" + _type + @"\.sql");
            Initialize();
        }

        public Migration(DbConnection conn, Assembly assem, string subtype, string type)
        {
            _type = type;
            _conn = conn;
            _assem = assem;
            _match = new Regex(subtype + @"\.(\d\d\d)_" + _type + @"\.sql");
            Initialize();
        }

        private void Initialize()
        {
            // clever, eh, we figure out which migrations version we are
            int migration_version = FindVersion(_conn, "migrations");

            if (migration_version > 0)
                return;

            // If not, create the migration tables
            DbCommand cmd = _conn.CreateCommand();
            cmd.CommandText = _migrations_create;
            cmd.ExecuteNonQuery();
            cmd.Dispose();

            InsertVersion("migrations", 1);
        }

        public void Update()
        {
            int version = 0;
            version = FindVersion(_conn, _type);

            SortedList<int, string> migrations = GetMigrationsAfter(version);
            if (migrations.Count < 1)
                return;

            // to prevent people from killing long migrations.
            m_log.InfoFormat("[MIGRATIONS] Upgrading {0} to latest revision.", _type);
            m_log.Info("[MIGRATIONS] NOTE: this may take a while, don't interupt this process!");

            DbCommand cmd = _conn.CreateCommand();
            foreach (KeyValuePair<int, string> kvp in migrations)
            {
                int newversion = kvp.Key;
                cmd.CommandText = kvp.Value;
                // we need to up the command timeout to infinite as we might be doing long migrations.
                cmd.CommandTimeout = 0;
                try
                {
                    cmd.ExecuteNonQuery();
                }
                catch (Exception e)
                {
                    m_log.Debug("[MIGRATIONS]: An error has occurred in the migration. This may mean you could see errors trying to run OpenSim. If you see database related errors, you will need to fix the issue manually. Continuing.");
                }

                if (version == 0)
                {
                    InsertVersion(_type, newversion);
                }
                else
                {
                    UpdateVersion(_type, newversion);
                }
                version = newversion;
                cmd.Dispose();
            }
        }

        // private int MaxVersion()
        // {
        //     int max = 0;
        //     string[] names = _assem.GetManifestResourceNames();

        //     foreach (string s in names)
        //     {
        //         Match m = _match.Match(s);
        //         if (m.Success)
        //         {
        //             int MigrationVersion = int.Parse(m.Groups[1].ToString());
        //             if (MigrationVersion > max)
        //                 max = MigrationVersion;
        //         }
        //     }
        //     return max;
        // }

        public int Version
        {
            get { return FindVersion(_conn, _type); }
            set {
                if (Version < 1)
                {
                    InsertVersion(_type, value);
                }
                else
                {
                    UpdateVersion(_type, value);
                }
            }
        }

        protected virtual int FindVersion(DbConnection conn, string type)
        {
            int version = 0;
            DbCommand cmd = conn.CreateCommand();
            try
            {
                cmd.CommandText = "select version from migrations where name='" + type +"' order by version desc";
                using (IDataReader reader = cmd.ExecuteReader())
                {
                    if (reader.Read())
                    {
                        version = Convert.ToInt32(reader["version"]);
                    }
                    reader.Close();
                }
            }
            catch
            {
                // Something went wrong, so we're version 0
            }
            cmd.Dispose();
            return version;
        }

        private void InsertVersion(string type, int version)
        {
            DbCommand cmd = _conn.CreateCommand();
            cmd.CommandText = "insert into migrations(name, version) values('" + type + "', " + version + ")";
            m_log.InfoFormat("[MIGRATIONS]: Creating {0} at version {1}", type, version);
            cmd.ExecuteNonQuery();
            cmd.Dispose();
        }

        private void UpdateVersion(string type, int version)
        {
            DbCommand cmd = _conn.CreateCommand();
            cmd.CommandText = "update migrations set version=" + version + " where name='" + type + "'";
            m_log.InfoFormat("[MIGRATIONS]: Updating {0} to version {1}", type, version);
            cmd.ExecuteNonQuery();
            cmd.Dispose();
        }

        // private SortedList<int, string> GetAllMigrations()
        // {
        //     return GetMigrationsAfter(0);
        // }

        private SortedList<int, string> GetMigrationsAfter(int after)
        {
            string[] names = _assem.GetManifestResourceNames();
            SortedList<int, string> migrations = new SortedList<int, string>();
            // because life is funny if we don't
            Array.Sort(names);

            foreach (string s in names)
            {
                Match m = _match.Match(s);
                if (m.Success)
                {
                    int version = int.Parse(m.Groups[1].ToString());
                    if (version > after) {
                        using (Stream resource = _assem.GetManifestResourceStream(s))
                        {
                            using (StreamReader resourceReader = new StreamReader(resource))
                            {
                                string resourceString = resourceReader.ReadToEnd();
                                migrations.Add(version, resourceString);
                            }
                        }
                    }
                }
            }

            if (migrations.Count < 1) {
                m_log.InfoFormat("[MIGRATIONS]: {0} up to date, no migrations to apply", _type);
            }
            return migrations;
        }
    }
}