using DbTools.Model;
using System.Data;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DbTools {
    public class Delta {
        public string Db1Sql { get; set; }
        public string Db2Sql { get; set; }

        public string BuildDelta(IDbConnection currentDb, IDbConnection newDb, bool removeUnusedTables = false, bool removeUnusedColumns = false, bool removeUnusedTriggers = true, bool removeUnusedIndexes = true) {
            Database db1 = new Database(currentDb, true);
            Database db2 = new Database(newDb, true);

            Db1Sql = db1.ToSql();
            Db2Sql = db2.ToSql();
            return BuildDelta(db1, db2, removeUnusedTables, removeUnusedColumns, removeUnusedTriggers, removeUnusedIndexes);
        }

        public string BuildDelta(string currentDbSql, string newDbSql, bool removeUnusedTables = false, bool removeUnusedColumns = false, bool removeUnusedTriggers = true, bool removeUnusedIndexes = true) {
            Database db1 = new Database(currentDbSql);
            Database db2 = new Database(newDbSql);
            return BuildDelta(db1, db2, removeUnusedTables, removeUnusedColumns, removeUnusedTriggers, removeUnusedIndexes);
        }

        public string BuildDelta(IDbConnection currentDb, string newDbSql, bool removeUnusedTables = false, bool removeUnusedColumns = false, bool removeUnusedTriggers = true, bool removeUnusedIndexes = true) {
            Database db1 = new Database(currentDb);
            Database db2 = new Database(newDbSql);
            return BuildDelta(db1, db2, removeUnusedTables, removeUnusedColumns, removeUnusedTriggers, removeUnusedIndexes);
        }

        public string BuildDelta(string currentDbSql, IDbConnection newDb, bool removeUnusedTables = false, bool removeUnusedColumns = false, bool removeUnusedTriggers = true, bool removeUnusedIndexes = true) {
            Database db1 = new Database(currentDbSql);
            Database db2 = new Database(newDb);
            return BuildDelta(db1, db2, removeUnusedTables, removeUnusedColumns, removeUnusedTriggers, removeUnusedIndexes);
        }

        public async Task<bool> ApplyDeltaAsync(IDbConnection cn, string sql) {
            return await Task.Run(() => {
                return ApplyDelta(cn, sql);
            });
        }

        public bool ApplyDelta(IDbConnection cn, string sql) {
            bool success = false;
            using (var cmd = cn.CreateCommand()) {
                cmd.CommandText = sql;
                success = cmd.ExecuteNonQuery() > 0;
            }
            return success;
        }

        private string BuildDelta(Database db1, Database db2, bool removeUnusedTables, bool removeUnusedColumns, bool removeUnusedTriggers, bool removeUnusedIndexes) {
            StringBuilder sb = new StringBuilder();

            // Remove tables that are not in db2 if requested
            if (removeUnusedTables) {
                var unusedTables = db1.Tables.GetTables().Where(t1 => !db2.ContainsTable(t1.TableName)).ToArray();
                if (unusedTables.Length > 0) {
                    sb.AppendLine("-- DROP UNUSED TABLES --");
                    foreach (var table in unusedTables) {
                        sb.AppendLine(table.GenerateDropTable());
                    }
                    sb.AppendLine();
                }
            }

            foreach (var table2 in db2.Tables.GetTables()) {
                var table1 = db1.Tables[table2.TableName];
                if (table1 == null) {
                    sb.AppendLine(table2.FullSql());
                } else {
                    // Remove unused triggers if requested
                    if (removeUnusedTriggers) {
                        var unusedTriggers = table1.Triggers.Keys.Where(t1 => !table2.Triggers.ContainsKey(t1)).ToArray();
                        if (unusedTriggers.Length > 0) {
                            sb.AppendLine("-- DROP UNUSED TRIGGERS " + table2.TableName + " --");
                            foreach (var trigger in unusedTriggers) {
                                sb.AppendLine($"DROP TRIGGER IF EXISTS {trigger};");
                            }
                            sb.AppendLine();
                        }
                    }

                    // Remove unused indexes if requested
                    if (removeUnusedIndexes) {
                        var unusedIndexes = table1.Indexes.Keys.Where(i1 => !table2.Indexes.ContainsKey(i1)).ToArray();
                        if (unusedIndexes.Length > 0) {
                            sb.AppendLine("-- DROP UNUSED INDEXES IN TABLE " + table2.TableName + " --");
                            foreach (var index in unusedIndexes) {
                                sb.AppendLine($"DROP INDEX IF EXISTS {index};");
                            }
                            sb.AppendLine();
                        }
                    }

                    // Add missing columns
                    var commonColumns = table1.GetCommonColumns(table2);
                    var onlyInTable2 = table2.Columns.GetColumnNames().Where(c => !commonColumns.Contains(c)).ToArray();
                    var onlyInTable1 = table1.Columns.GetColumnNames().Where(c => !commonColumns.Contains(c)).ToArray();
                    if (removeUnusedColumns && onlyInTable1.Length > 0) {
                        // We have columns in table1 that are not in table2 and we want to remove them,
                        // so we need to recreate the table
                        sb.AppendLine("-- UNUSED COLUMNS EXIST IN TABLE " + table2.TableName + " --");
                        string sql = table2.GenerateTableMigration(table1);
                        sb.AppendLine(sql);
                    }
                    if (onlyInTable2.Length > 0) {
                        // We have columns in table2 that are not in table1, so we can just add them
                        sb.AppendLine($"-- ALTER TABLE {table2.TableName} --");
                        foreach (var colName in onlyInTable2) {
                            var col = table2.Columns[colName];
                            sb.AppendLine($"ALTER TABLE {table2.TableName} ADD COLUMN {col};");
                        }
                        sb.AppendLine($"-- END ALTER TABLE {table2.TableName} --");
                        sb.AppendLine();
                    }
                }
            }
            return sb.ToString();
        }

    }
}