/*
 * 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
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 * 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(DbConnection, Assembly, "Users");
    ///    um.Update();
    ///
    /// 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);

        protected string _type;
        protected DbConnection _conn;
        protected Assembly _assem;

        private Regex _match_old;
        private Regex _match_new;

        /// <summary>Have the parameterless constructor just so we can specify it as a generic parameter with the new() constraint.
        /// Currently this is only used in the tests. A Migration instance created this way must be then
        /// initialized with Initialize(). Regular creation should be through the parameterized constructors. 
        /// </summary>
        public Migration()
        { 
        }

        public Migration(DbConnection conn, Assembly assem, string subtype, string type)
        {
            Initialize(conn, assem, type, subtype);
        }

        public Migration(DbConnection conn, Assembly assem, string type) 
        {
            Initialize(conn, assem, type, "");
        }

        /// <summary>Must be called after creating with the parameterless constructor.
        /// NOTE that the Migration class now doesn't access database in any way during initialization.
        /// Specifically, it won't check if the [migrations] table exists. Such checks are done later:
        /// automatically on Update(), or you can explicitly call InitMigrationsTable().
        /// </summary>
        /// <param name="conn"></param>
        /// <param name="assem"></param>
        /// <param name="subtype"></param>
        /// <param name="type"></param>
        public void Initialize (DbConnection conn, Assembly assem, string type, string subtype)
        {
            _type = type;
            _conn = conn;
            _assem = assem;
            _match_old = new Regex(subtype + @"\.(\d\d\d)_" + _type + @"\.sql");
            string s = String.IsNullOrEmpty(subtype) ? _type : _type + @"\." + subtype;
            _match_new = new Regex(@"\." + s + @"\.migrations(?:\.(?<ver>\d+)$|.*)");
        }

        public void InitMigrationsTable()
        {
            // NOTE: normally when the [migrations] table is created, the version record for 'migrations' is
            // added immediately. However, if for some reason the table is there but empty, we want to handle that as well.
            int ver = FindVersion(_conn, "migrations");
            if (ver <= 0)   // -1 = no table, 0 = no version record
            {
                if( ver < 0 )
                    ExecuteScript("create table migrations(name varchar(100), version int)");
                InsertVersion("migrations", 1);
            }
        }

        /// <summary>Executes a script, possibly in a database-specific way.
        /// It can be redefined for a specific DBMS, if necessary. Specifically,
        /// to avoid problems with proc definitions in MySQL, we must use
        /// MySqlScript class instead of just DbCommand. We don't want to bring
        /// MySQL references here, so instead define a MySQLMigration class
        /// in OpenSim.Data.MySQL
        /// </summary>
        /// <param name="conn"></param>
        /// <param name="script">Array of strings, one-per-batch (often just one)</param>
        protected virtual void ExecuteScript(DbConnection conn, string[] script)
        {
            using (DbCommand cmd = conn.CreateCommand())
            {
                cmd.CommandTimeout = 0;
                foreach (string sql in script)
                {
                    cmd.CommandText = sql;
                    try
                    {
                        cmd.ExecuteNonQuery();
                    }
                    catch(Exception e)
                    {
                        throw new Exception(e.Message + " in SQL: " + sql);
                    }
                }
            }
        }

        protected void ExecuteScript(DbConnection conn, string sql)
        {
            ExecuteScript(conn, new string[]{sql});
        }

        protected void ExecuteScript(string sql)
        {
            ExecuteScript(_conn, sql);
        }

        protected void ExecuteScript(string[] script)
        {
            ExecuteScript(_conn, script);
        }

        public void Update()
        {
            InitMigrationsTable();

            int 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 {1}.", _type, migrations.Keys[migrations.Count - 1]);
            m_log.Info("[MIGRATIONS]: NOTE - this may take a while, don't interrupt this process!");

            foreach (KeyValuePair<int, string[]> kvp in migrations)
            {
                int newversion = kvp.Key;
                // we need to up the command timeout to infinite as we might be doing long migrations.

                /* [AlexRa 01-May-10]: We can't always just run any SQL in a single batch (= ExecuteNonQuery()). Things like 
                 * stored proc definitions might have to be sent to the server each in a separate batch.
                 * This is certainly so for MS SQL; not sure how the MySQL connector sorts out the mess
                 * with 'delimiter @@'/'delimiter ;' around procs.  So each "script" this code executes now is not
                 * a single string, but an array of strings, executed separately.
                */
                try
                {
                    ExecuteScript(kvp.Value);
                }
                catch (Exception e)
                {
                    m_log.DebugFormat("[MIGRATIONS]: Cmd was {0}", e.Message.Replace("\n", " "));
                    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.");
                    ExecuteScript("ROLLBACK;");
                }

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

        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;
            using (DbCommand cmd = conn.CreateCommand())
            {
                try
                {
                    cmd.CommandText = "select version from migrations where name='" + type + "' order by version desc";
                    using (DbDataReader reader = cmd.ExecuteReader())
                    {
                        if (reader.Read())
                        {
                            version = Convert.ToInt32(reader["version"]);
                        }
                        reader.Close();
                    }
                }
                catch
                {
                    // Something went wrong (probably no table), so we're at version -1
                    version = -1;
                }
            }
            return version;
        }

        private void InsertVersion(string type, int version)
        {
            m_log.InfoFormat("[MIGRATIONS]: Creating {0} at version {1}", type, version);
            ExecuteScript("insert into migrations(name, version) values('" + type + "', " + version + ")");
        }

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

        private delegate void FlushProc();

        /// <summary>Scans for migration resources in either old-style "scattered" (one file per version)
        /// or new-style "integrated" format (single file with ":VERSION nnn" sections). 
        /// In the new-style migrations it also recognizes ':GO' separators for parts of the SQL script
        /// that must be sent to the server separately.  The old-style migrations are loaded each in one piece
        /// and don't support the ':GO' feature.
        /// </summary>
        /// <param name="after">The version we are currently at. Scan for any higher versions</param>
        /// <returns>A list of string arrays, representing the scripts.</returns>
        private SortedList<int, string[]> GetMigrationsAfter(int after)
        {
            SortedList<int, string[]> migrations = new SortedList<int, string[]>();

            string[] names = _assem.GetManifestResourceNames();
            if( names.Length == 0 )     // should never happen
                return migrations;

            Array.Sort(names);  // we want all the migrations ordered

            int nLastVerFound = 0;
            Match m = null;
            string sFile = Array.FindLast(names, nm => { m = _match_new.Match(nm); return m.Success; });  // ; nm.StartsWith(sPrefix, StringComparison.InvariantCultureIgnoreCase

            if( (m != null) && !String.IsNullOrEmpty(sFile) )
            {
                /* The filename should be '<StoreName>.migrations[.NNN]' where NNN
                 * is the last version number defined in the file. If the '.NNN' part is recognized, the code can skip
                 * the file without looking inside if we have a higher version already. Without the suffix we read 
                 * the file anyway and use the version numbers inside.  Any unrecognized suffix (such as '.sql')
                 * is valid but ignored.
                 * 
                 *  NOTE that we expect only one 'merged' migration file. If there are several, we take the last one. 
                 *  If you are numbering them, leave only the latest one in the project or at least make sure they numbered 
                 *  to come up in the correct order (e.g. 'SomeStore.migrations.001' rather than 'SomeStore.migrations.1')
                 */

                if (m.Groups.Count > 1 && int.TryParse(m.Groups[1].Value, out nLastVerFound))
                {
                    if( nLastVerFound <= after )
                        goto scan_old_style;
                }

                System.Text.StringBuilder sb = new System.Text.StringBuilder(4096);
                int nVersion = -1;

                List<string> script = new List<string>();

                FlushProc flush = delegate()
                {
                    if (sb.Length > 0)     // last SQL stmt to script list
                    {
                        script.Add(sb.ToString());
                        sb.Length = 0;
                    }

                    if ( (nVersion > 0) && (nVersion > after) && (script.Count > 0) && !migrations.ContainsKey(nVersion))   // script to the versioned script list
                    {
                        migrations[nVersion] = script.ToArray();
                    }
                    script.Clear();
                };

                using (Stream resource = _assem.GetManifestResourceStream(sFile))
                using (StreamReader resourceReader = new StreamReader(resource))
                {
                    int nLineNo = 0;
                    while (!resourceReader.EndOfStream)
                    {
                        string sLine = resourceReader.ReadLine();
                        nLineNo++;

                        if( String.IsNullOrEmpty(sLine) || sLine.StartsWith("#") )  // ignore a comment or empty line
                            continue;

                        if (sLine.Trim().Equals(":GO", StringComparison.InvariantCultureIgnoreCase))
                        {
                            if (sb.Length == 0) continue;
                            if (nVersion > after) 
                                script.Add(sb.ToString());
                            sb.Length = 0;
                            continue;
                        }

                        if (sLine.StartsWith(":VERSION ", StringComparison.InvariantCultureIgnoreCase))  // ":VERSION nnn"
                        {
                            flush();

                            int n = sLine.IndexOf('#');     // Comment is allowed in version sections, ignored
                            if (n >= 0)
                                sLine = sLine.Substring(0, n);

                            if (!int.TryParse(sLine.Substring(9).Trim(), out nVersion))
                            {
                                m_log.ErrorFormat("[MIGRATIONS]: invalid version marker at {0}: line {1}. Migration failed!", sFile, nLineNo);
                                break;
                            }
                        }
                        else
                        {
                            sb.AppendLine(sLine);
                        }
                    }
                    flush();

                    // If there are scattered migration files as well, only look for those with higher version numbers.
                    if (after < nVersion)
                        after = nVersion;
                }
            }

scan_old_style:
            // scan "old style" migration pieces anyway, ignore any versions already filled from the single file
            foreach (string s in names)
            {
                m = _match_old.Match(s);
                if (m.Success)
                {
                    int version = int.Parse(m.Groups[1].ToString());
                    if ( (version > after) && !migrations.ContainsKey(version) )
                    {
                        using (Stream resource = _assem.GetManifestResourceStream(s))
                        {
                            using (StreamReader resourceReader = new StreamReader(resource))
                            {
                                string sql = resourceReader.ReadToEnd();
                                migrations.Add(version, new string[]{sql});
                            }
                        }
                    }
                }
            }
            
            if (migrations.Count < 1) 
            {
                m_log.InfoFormat("[MIGRATIONS]: {0} up to date, no migrations to apply", _type);
            }
            return migrations;
        }
    }
}
