using NLog;
using SQLite;
using System;
using System.Collections.Generic;
using System.Globalization;
using System.Linq;
using System.Text.RegularExpressions;

namespace DBMerger
{
    public partial class Merger(SQLiteConnection dbConn, string oldDBName, string newDBName, Config config)
    {
        // C#'s iso date string has millionths of a second but the db stores
        // dates with only thousands of a second, so define our own format
        private const string JSDateTimeFormat = "yyyy'-'MM'-'dd'T'HH':'mm':'ss'.'fffzzz";

        private static readonly Logger logger = LogManager.GetCurrentClassLogger();
        private static readonly Regex userIDRegex = UserIDRegex();

        // This list of table names will be slowly emptied by specific
        // handlers until only unrecognied tables are left
        private List<string> unMergedTables;

        public void Merge()
        {
            logger.Info("Starting merge process...");

            logger.Debug("Creating transaction for databases");
            dbConn.BeginTransaction();
            try
            {
                MergeInternal();
            }
            catch
            {
                logger.Warn("Encoutered error! Rolling back changes to databases");
                dbConn.Rollback();

                throw;
            }

            logger.Debug("Committing changes to database");
            dbConn.Commit();

            logger.Info("Optimizing database size...");
            dbConn.Execute("VACUUM new_db;");
            logger.Info("Merge completed without any major issues!");
        }

        private void MergeInternal()
        {
            unMergedTables = dbConn.QueryScalars<string>($"SELECT name FROM {oldDBName}.sqlite_schema WHERE type='table';");

            // Holds sensitive information. Burn it with fire so no sensitive
            // data gets leaked
            unMergedTables.Remove("cookies");

            // Get any tables in the old db that arent in the new db
            logger.Info("Creating tables not present on new database that are present on old database...");
            var newDBTables = dbConn.QueryScalars<string>($"SELECT name FROM {newDBName}.sqlite_schema WHERE type='table';").ToHashSet();
            for (int i = 0; i < unMergedTables.Count; i++)
            {
                var table = unMergedTables[i];
                if (newDBTables.Contains(table) || table == "configs")
                {
                    continue;
                }
                unMergedTables.RemoveAt(i);
                if (table.StartsWith("sqlite_"))
                {
                    // Skip sqlite reserved tables
                    logger.Debug($"Skipping sqlite reserved table: {table}");
                    continue;
                }
                i--;

                // Then just tack them on
                // Get command to create the table
                logger.Info($"Adding table: {table}...");
                var createQuery = dbConn.ExecuteScalar<string>($"SELECT sql FROM {oldDBName}.sqlite_schema WHERE type='table' AND name=?;", table);

                // Insert name of new database into create table query
                createQuery = createQuery[..13] + newDBName + "." + createQuery[13..];
                logger.Debug($"Using command: {createQuery}");
                dbConn.Execute(createQuery);

                // Then add the rows
                logger.Debug("Addings rows to table");
                dbConn.Execute($"INSERT INTO {newDBName}.{table} SELECT * FROM {oldDBName}.{table};");
            }

            logger.Info("Merging memos into new database...");
            MergeMemos();

            logger.Info("Merging favorites into new database...");
            MergeFavorites();

            logger.Info("Merging avatar and world cache into new database...");
            MergeCaches();

            logger.Info("Merging gamelog into new database...");
            MergeGamelog();

            logger.Info("Merging user feed tables into new database...");
            MergeUsers();

            if (config.ImportConfig)
            {
                logger.Info("Importing config from old database...");
                ImportConfig();
            }
            else
            {
                unMergedTables.Remove("configs");
            }
            ResetDatabaseVersion();

            foreach (var table in unMergedTables)
            {
                logger.Warn("Found unmerged table: " + table);
            }
        }

        private void MergeMemos()
        {
            MergeTable(
                table => table.EndsWith("memos"),
                [0],
                (old, existing) =>
                {
                    if (existing == null)
                    {
                        logger.Trace("Inserting new memo");
                        return old;
                    }

                    logger.Trace("Replacing memo");

                    // Pick newer edited_at time
                    var oldDateTime = DateTime.Parse((string)old[1]);
                    var newDateTime = DateTime.Parse((string)existing[1]);
                    old[1] = oldDateTime > newDateTime ? oldDateTime : newDateTime;
                    old[1] = ((DateTime)old[1]).ToString(JSDateTimeFormat);

                    // Don't concatenate memos if they're the exact same or
                    // the new memo ends with the old one (suggesting import
                    // has already been run)
                    old[2] = existing[2] == old[2] || ((string)existing[2]).EndsWith((string)old[2])
                        ? existing[2] : old[2] + "\n" + existing[2];

                    return old;
                }
            );
        }

        private void MergeFavorites()
        {
            MergeTable(
                table => table.StartsWith("favorite_"),
                [2, 3],
                (old, existing) =>
                {
                    if (existing == null)
                    {
                        logger.Trace("Inserting new favorite");
                        // Let sqlite generate new pk
                        old[0] = null;
                        return old;
                    }

                    logger.Trace("Replacing favorite");

                    // Favorites are the same, so just pick the older create
                    // time and add it
                    var oldDateTime = DateTime.Parse((string)old[1]);
                    var newDateTime = DateTime.Parse((string)existing[1]);
                    var updatedDateTime = oldDateTime < newDateTime ? oldDateTime : newDateTime;
                    existing[1] = updatedDateTime;

                    return existing;
                }
            );
        }

        private void MergeCaches()
        {
            MergeTable(
                table => table.StartsWith("cache_"),
                [0],
                (old, existing) =>
                {
                    if (existing == null)
                    {
                        logger.Trace("Inserting new cache entry");
                        return old;
                    }

                    logger.Trace("Replacing cache entry");

                    // old and existing have the same pk, so pick the newer
                    // cache entry
                    var oldDateTime = DateTime.Parse((string)old[1]);
                    var newDateTime = DateTime.Parse((string)existing[1]);

                    return oldDateTime > newDateTime ? old : existing;
                }
            );
        }

        private void MergeGamelog()
        {
            // While this could be handled throw a single query, I would like to
            // log anything determined to be a duplicate in case this doens't
            // work
            MergeTable(
                table => table.StartsWith("gamelog_") && table != "gamelog_join_leave",
                // These tables can be merged just fine by checking the created
                // date and first col of information because we just need to
                // know if 2 rows are the same
                [1, 2],
                // Literally just place back in what's already there
                // created_at times should be pretty consistent, so we can trust
                // that no duplicates will be created
                (old, existing) =>
                {
                    if (existing != null)
                    {
                        logger.Trace("Determined these rows to be the same: ");
                        logger.Trace(string.Join(", ", old));
                        logger.Trace(string.Join(", ", existing));
                    }
                    old[0] = null;
                    // Return existing over old so we know that pk is unique
                    return existing ?? old;
                },
                table => SortTable(dbConn, newDBName, table, 1)
            );

            MergeTable(
                table => table == "gamelog_join_leave",
                [1, 3],
                (old, existing) =>
                {
                    if (existing != null)
                    {
                        logger.Trace("Determined these rows to be the same: ");
                        logger.Trace(string.Join(", ", old));
                        logger.Trace(string.Join(", ", existing));
                    }
                    old[0] = null;
                    return existing ?? old;
                },
                table => SortTable(dbConn, newDBName, table, 1)
            );
        }

        private void MergeUsers()
        {
            MergeTable(
                table => userIDRegex.IsMatch(table) &&
                         (table.EndsWith("_notifications") || table.EndsWith("_moderation")),
                [0],
                (old, existing) =>
                {
                    if (existing == null)
                    {
                        logger.Trace("Inserting new feed entry");
                        return old;
                    }

                    logger.Trace("Replacing feed entry");

                    // old and existing have the same pk, so pick the newer
                    // cache entry
                    var oldDateTime = DateTime.Parse((string)old[1]);
                    var newDateTime = DateTime.Parse((string)existing[1]);

                    return oldDateTime > newDateTime ? old : existing;
                }
            );

            MergeTable(
                table => userIDRegex.IsMatch(table) && table.EndsWith("_avatar_history"),
                [0],
                (old, existing) =>
                {
                    if (existing == null)
                    {
                        logger.Trace("Inserting new avatar feed entry");
                        return old;
                    }

                    logger.Trace("Replacing avatar feed entry");

                    // old and existing have the same pk, so pick the newer
                    // cache entry
                    var oldDateTime = DateTime.Parse((string)old[1]);
                    var newDateTime = DateTime.Parse((string)existing[1]);

                    // Make sure to combine time values if they exist
                    if (existing.Length < 2)
                    {
                        return oldDateTime > newDateTime ? old : existing;
                    }

                    var oldAvatarTime = old.Length >= 3 && old[2] != null ? (int)old[2] : 0;
                    var newAvatarTime = existing[2] != null ? (int)existing[2] : 0;

                    if (oldDateTime <= newDateTime)
                    {
                        old.CopyTo(existing, 0);
                    }
                    existing[2] = oldAvatarTime + newAvatarTime;

                    logger.Trace(
                        "Combined avatar time: {} + {} = {}", 
                        oldAvatarTime, newAvatarTime, oldAvatarTime + newAvatarTime
                    );

                    return existing;
                }
            );

            var overlappingTables = new List<string>();
            DateTime? oldestInNewTables = null;
            DateTime? newestInOldTables = null;
            for (int i = 0; i < unMergedTables.Count; i++)
            {
                // All other feed tables shouldve been merged, so just by
                // matching user we should get all the rest of the user tables
                string table = unMergedTables[i];
                if (!userIDRegex.IsMatch(table))
                {
                    continue;
                }
                unMergedTables.RemoveAt(i);
                i--;

                // Skip friend log current for obvious reasons
                // Skip notes and mutual friends since they aren't time based
                if (table.EndsWith("_friend_log_current") || table.EndsWith("_notes") ||
                    table.EndsWith("_mutual_graph_friends") || table.EndsWith("_mutual_graph_links"))
                {
                    continue;
                }

                logger.Debug($"Merging table `{table}` into new database");

                List<string> colNames = GetTableColumnNames(dbConn, oldDBName, table);

                // Find min value of new db table and max value of old db table
                var oldestInNew = dbConn.ExecuteScalar<string>($"SELECT MIN({colNames[1]}) FROM {newDBName}.{table};");
                DateTime? oldestInNewDT = oldestInNew != null ? DateTime.Parse(oldestInNew) : null;
                var newestInOld = dbConn.ExecuteScalar<string>($"SELECT MAX({colNames[1]}) FROM {oldDBName}.{table};");
                DateTime? newestInOldDT = newestInOld != null ? DateTime.Parse(newestInOld) : null;

                // If either tables are empty or the oldest value in the new
                // table is still newer than the newest value in the old
                // (the tables don't overlap in time at all)
                if (newestInOldDT == null || oldestInNewDT == null || oldestInNewDT > newestInOldDT)
                {
                    logger.Debug($"User tables {table} has no overlap");
                    // Then we can just combine them since there is no data
                    // overlap
                    var columnsClause = string.Join(", ", colNames.Skip(1));
                    dbConn.Execute(
                        $"INSERT INTO {newDBName}.{table}({columnsClause})" +
                            $"SELECT {columnsClause} FROM {oldDBName}.{table};"
                    );
                    SortTable(dbConn, newDBName, table, 1);
                }
                else
                {
                    // I don't think people will actually care to choose a date
                    // for every single overlapping database
                    // Although it could easily be argued that people would want
                    // per user overlap control
                    logger.Debug($"User tables {table} has overlap");
                    if (oldestInNewTables == null || oldestInNewDT < oldestInNewTables)
                    {
                        oldestInNewTables = oldestInNewDT;
                    }
                    if (newestInOldTables == null || newestInOldDT > newestInOldTables)
                    {
                        newestInOldTables = newestInOldDT;
                    }
                    overlappingTables.Add(table);
                }
            }

            if (overlappingTables.Count > 0)
            {
                // The datetimes should not be null here since there are
                // overlapping tables
                MergeUsersOverlap(overlappingTables, oldestInNewTables.Value, newestInOldTables.Value);
            }
        }

        private void MergeUsersOverlap(List<string> tables, DateTime oldestInNew, DateTime newestInOld)
        {
            PrintOverlapWarning(tables, oldestInNew, newestInOld);

            string userInput = null;
            bool datetimeParsed;
            DateTime cutoffTime;
            do
            {
                if (userInput != null)
                {
                    logger.Error("Unrecognized input: " + userInput);
                }

                userInput = Console.ReadLine();
                datetimeParsed = DateTime.TryParseExact(
                    userInput, "yyyy-MM-dd HH:mm:ss", CultureInfo.InvariantCulture, DateTimeStyles.None, out cutoffTime
                );
            }
            while (userInput != "keep old" && userInput != "keep new" && !datetimeParsed);

            // If user wants to keep new one then do nothing
            if (userInput == "keep new")
            {
                logger.Info("Keeping new");
                return;
            }
            if (userInput == "keep old")
            {
                logger.Info("Keeping old");

                // For old we just delete all rows from new and reinsert rows
                // from old
                foreach (var table in tables)
                {
                    logger.Debug($"Deleting all rows in new database's {table}");
                    dbConn.Execute($"DELETE FROM {newDBName}.{table}");

                    logger.Debug($"Adding rows from old database's {table}");
                    dbConn.Execute($"INSERT INTO {newDBName}.{table} SELECT * FROM {oldDBName}.{table};");

                    SortTable(dbConn, newDBName, table, 1);
                }
                return;
            }

            // Else we do the cutoff
            var cutoffStr = cutoffTime.ToString(JSDateTimeFormat);
            logger.Info("Merging at date: " + cutoffTime.ToString("yyyy-MM-dd HH:mm:ss"));
            foreach (var table in tables)
            {
                // Get column names from old db in case newdb has columns
                // old db doesn't
                var colNames = GetTableColumnNames(dbConn, oldDBName, table);

                // Cutoff data in new db thats older than cutoff
                logger.Debug($"Deleting rows in new database's {table} older than cutoff");
                dbConn.Execute($"DELETE FROM {newDBName}.{table} WHERE {colNames[1]}<?;", cutoffStr);

                // Insert old rows in to the new db
                logger.Debug($"Adding rows from old database's {table} older than cutoff");
                var columnsClause = string.Join(", ", colNames.Skip(1));
                dbConn.Execute(
                    $"INSERT INTO {newDBName}.{table}({columnsClause})" +
                        $"SELECT {columnsClause} FROM {oldDBName}.{table} " +
                            $"WHERE {colNames[1]}<?;", cutoffStr
                );

                SortTable(dbConn, newDBName, table, 1);
            }
        }

        private void PrintOverlapWarning(List<string> tables, DateTime oldestInNew, DateTime newestInOld)
        {
            var overlap = newestInOld - oldestInNew;
            var overlapString = $"{overlap.Days} days, {overlap.Hours} hours";

            logger.Warn(new string('=', 100));
            logger.Warn("WARNING:".PadLeft(46));
            logger.Warn("The merger has is unable to automatically merge the following USER FEED tables:");
            foreach (var table in tables)
            {
                logger.Warn(table);
            }
            logger.Warn("");
            logger.Warn("This is because these USER FEED tables contain overlap that can't be resolved:");
            logger.Warn("old database".PadRight(64, '-') + "|");
            logger.Warn(("|" + " new database".PadLeft(64, '-')).PadLeft(100));
            logger.Warn($"overlap ({overlapString})".PadRight(35) + "|" + new string('-', 28) + "|");
            logger.Warn("cutoff (^)".PadLeft(49));
            logger.Warn("");
            logger.Warn("Please choose a cutoff date and time. Data in the old USER FEED tables after this date");
            logger.Warn("will be discarded, and data in the new USER FEED tables before this date will be discarded as well.");
            logger.Warn("The remaining data will then be spliced together.");
            logger.Warn("Your input should be in this format: `YYYY-MM-DD HH:MM:SS`");
            logger.Warn("");
            logger.Warn("Alternatively, you can enter `keep new` to discard the old data or `keep old` to discard new data.");
            logger.Warn("");
            logger.Warn("Again, this only affects USER FEED tables, all other tables are merged properly.");
            logger.Warn("To read more about this process please check the VRCX wiki: <woops>");
            logger.Warn(new string('=', 100));
        }

        private void ImportConfig()
        {
            unMergedTables.Remove("configs");

            // Skip saved credentials to avoid accidentally exposing sensitive
            // information somehow
            dbConn.Execute(
                $"INSERT OR REPLACE INTO {newDBName}.configs " +
                    $"SELECT * FROM {oldDBName}.configs " +
                        $"WHERE key!=?;", "config:savedcredentials"
            );
        }

        private void ResetDatabaseVersion()
        {
            // Tell VRCX to add in any missing fields that the merger may have
            // missed, just as a precaution
            dbConn.Execute(
                $"INSERT OR REPLACE INTO {newDBName}.configs VALUES (?, 0)",
                "config:vrcx_databaseversion"
            );
        }

        /// <summary>
        /// A method that automates various processes of merging.
        /// 
        /// It first finds a table that matches the `tableMatcher` predicate,
        /// then removes it from `unMergedTables`.
        /// Then it loops over every row in the old database table, checking if
        /// the row exists in the new table. It does this by checking if the
        /// column indices passed into `colIndicesToMatch` are the same.
        /// Then for each row, it calls `rowTransformer`, passing in the old 
        /// rows and existing new rows. `rowTransformer` should return the row 
        /// to insert into the new database or null.
        /// </summary>
        /// <param name="tableMatcher">A predicate to check if a table is one to edit</param>
        /// <param name="colIndicesToMatch">The column indices to match to see if old and new rows are the same</param>
        /// <param name="rowTransformer">An func called on every row</param>
        /// <param name="finalizer">An action called once all rows have been iterated</param>
        private void MergeTable(
            Predicate<string> tableMatcher,
            int[] colIndicesToMatch,
            Func<object[], object[], object[]> rowTransformer,
            Action<string> finalizer = null
        ) {
            for (int i = 0; i < unMergedTables.Count; i++)
            {
                // Find table that we want to merge
                string table = unMergedTables[i];
                if (!tableMatcher(table))
                {
                    continue;
                }
                unMergedTables.RemoveAt(i);
                i--;

                logger.Debug($"Merging table `{table}` into new database");

                // Prepare queries
                var colNames = GetTableColumnNames(dbConn, newDBName, table);

                var valuesClause = string.Join(',', new string('?', colNames.Count).ToCharArray());
                var insertQuery = $"INSERT INTO {newDBName}.{table} VALUES ({valuesClause});";

                var whereClause = string.Join(" AND ", colIndicesToMatch.Select(i => colNames[i] + "=?"));
                var existsQuery = $"DELETE FROM {newDBName}.{table} WHERE {whereClause} RETURNING *;";

                // Loop over every row on table in old database
                var rowsCommand = dbConn.CreateCommand($"SELECT * FROM {oldDBName}.{table};");
                foreach (object[] oldRow in rowsCommand.ExecuteQueryScalars(dbConn))
                {
                    // Find existing row (if it exists at all) and remove it
                    object[] colsToMatch = colIndicesToMatch.Select(i => oldRow[i]).ToArray();
                    var existingRow = dbConn.QueryScalars(existsQuery, colsToMatch).FirstOrDefault();

                    // Insert new row in place of the existing row
                    var newRow = rowTransformer(oldRow, existingRow);
                    if (newRow.Length < colNames.Count)
                    {
                        // Row count may not match between old and new db, so
                        // just add null data
                        var temp = new object[colNames.Count];
                        newRow.CopyTo(temp, 0);
                        newRow = temp;
                    }
                    dbConn.Execute(insertQuery, newRow);
                }

                finalizer?.Invoke(table);
            }
        }

        private static List<string> GetTableColumnNames(SQLiteConnection conn, string db, string table)
            => conn.QueryScalars<string>($"SELECT name FROM pragma_table_info(?, ?);", table, db);

        private static void SortTable(SQLiteConnection conn, string db, string table, int sortCol, bool isDesc = false)
        {
            logger.Debug($"Sorting table {db}.{table}");

            // Just to ensure name is unique
            var time = DateTime.Now.Ticks;
            var newTableName = table + time.ToString();
            logger.Debug($"Creating new table: " + newTableName);

            // Split create query into words
            var createQuery = conn.ExecuteScalar<string>($"SELECT sql FROM {db}.sqlite_schema WHERE type='table' AND name=?;", table);
            var words = createQuery.Split(' ');
            // Third word is table name
            words[2] = db + "." + newTableName;
            createQuery = string.Join(' ', words);

            logger.Debug("Creating table with command: " + createQuery);
            conn.Execute(createQuery);

            logger.Debug("Adding rows...");
            var colNames = GetTableColumnNames(conn, db, table);
            // Skip pks so they get reassigned
            var selectClause = string.Join(',', colNames.Skip(1));
            conn.Execute(
                $"INSERT INTO {db}.{newTableName} ({selectClause}) " +
                    $"SELECT {selectClause} FROM {db}.{table} " +
                        $"ORDER BY {colNames[sortCol]} {(isDesc ? "DESC" : "ASC")};"
            );

            logger.Debug("Dropping old and renaming");
            conn.Execute($"DROP TABLE {db}.{table}");
            conn.Execute($"ALTER TABLE {db}.{newTableName} RENAME TO {table}");
        }

        [GeneratedRegex("^([A-Za-z0-9]{10}|usr[0-9A-Fa-f]{32})")]
        private static partial Regex UserIDRegex();
    }
}