using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace FireBirdUtil.SqlUtils
{
	public class SqlUtil
	{
		/// <summary>
		/// 判断表是否存在的SQL语句
		/// <para>执行该sql语句后，结果为1时，表示表存在；否则不存在（小于1）</para>
		/// </summary>
		/// <param name="tableName">表名</param>
		public static string GetJudgeTableExistSql(string tableName)//查询结果为1时，表示表存在；否则不存在（小于1）
		{
			return "select count(*) from rdb$relations where rdb$relation_name='" + tableName.ToUpper() + "' AND RDB$VIEW_SOURCE IS NULL";
		}

		/// <summary>
		/// 创建表的SQL语句
		/// </summary>
		/// <param name="tableName">表名</param>
		/// <param name="tableParams">所有字段的参数。如：uid int,uname varchar(20)</param>
		public static string GetCreateTableSql(string tableName, string tableParams)
		{
			return "create table " + tableName + " (" + tableParams + ")";//tableParams如:“uid int,uname varchar(20)”
		}

		/// <summary>
		/// 插入一条数据的SQL语句
		/// </summary>
		/// <param name="tableName">表名</param>
		/// <param name="fieldsValues">一条数据的信息:Key为字段，Value为字段对应的值</param>
		public static string GetInsertSql(string tableName, IDictionary<string, object> fieldsValues)
		{
			string insertSql = "insert into {0} ({1}) values ({2})";
			insertSql = string.Format(insertSql, tableName, string.Join(", ", fieldsValues.Keys), "'" + string.Join("', '", fieldsValues.Values) + "'");
			return insertSql;
		}

		/// <summary>
		/// 删除表
		/// </summary>
		/// <param name="tableName">表名</param>
		public static string GetDropSql(string tableName)//TODO:未测试
		{
			return "drop table " + tableName;
		}

		/// <summary>
		/// 删除表的所有数据
		/// </summary>
		/// <param name="tableName">表名</param>
		public static string GetDeleteSql(string tableName)
		{
			return "delete from " + tableName;
		}

		/// <summary>
		/// 删除符合条件的数据
		/// </summary>
		/// <param name="tableName">表名</param>
		/// <param name="conditions">以where打头的条件</param>
		public static string GetDeleteSql(string tableName, string conditions)
		{
			return "delete from " + tableName + " " + conditions;
		}
		//delete from table1 where id=1 or id=2
		//delete from table1 where id in (3,4,5)
		//delete from table1 where age is null
		//delete from table1 where age is null and id<10

		/// <summary>
		/// 将符合条件的数据行的指定字段的值更新//不能处理将一个字段的值赋给另一个字段
		/// </summary>
		/// <param name="newValues">新值：Key为字段名，Value为新值</param>
		/// <param name="conditions">以where打头的条件</param>
		public static string GetUpdateSql(string tableName, Dictionary<string, object> newValues, string conditions)
		{
			List<string> setValueString = new List<string>();
			foreach (var item in newValues) {
				setValueString.Add(item.Key + "=" + UpdateValueToString(item.Value));
			}
			return "update " + tableName + " set " + string.Join(", ", setValueString) + " " + conditions;
		}

		private static string UpdateValueToString(object obj)
		{
			return "'" + obj.ToString() + "'";
		}

		/// <summary>
		/// 获取自增变量名。说明：长度是有限制的，好像最长是31个字符
		/// </summary>
		/// <param name="tableName">表名</param>
		internal static string GetGeneratorName(string tableName)
		{
			return tableName + "_gen";
		}

		/// <summary>
		/// 创建自增变量的SQL语句
		/// </summary>
		/// <param name="tableName">表名</param>
		public static string GetSql_AddGenerator(string tableName)
		{
			return "create generator " + GetGeneratorName(tableName);
		}

		/// <summary>
		/// 删除自增变量
		/// </summary>
		/// <param name="tableName">表名</param>
		public static string GetSql_DropGenerator(string tableName)
		{
			return "drop generator " + GetGeneratorName(tableName);
		}

		/// <summary>
		/// 查找指定自增变量的数量（用于判断是否存在指定自增变量）
		/// </summary>
		/// <param name="tableName">表名</param>
		public static string GetSql_SelectGeneratorCount(string tableName)
		{
			return string.Format("select count(*) from rdb$generators where rdb$generator_name='{0}'", GetGeneratorName(tableName).ToUpper());
		}

		/// <summary>
		/// 创建字段自增功能的SQL语句（通过添加触发器实现）
		/// <para>字段类型不是数字类型时，还有强制转换类型</para>
		/// </summary>
		/// <param name="tableName">表名</param>
		/// <param name="fieldName">字段名</param>
		/// <param name="AutoIncreasedFieldTypeIfNotNum">强制转换后的类型。为空则不转换</param>
		public static string GetSql_AddAutoIncreaseTrigger(string tableName, string fieldName, string AutoIncreasedFieldTypeIfNotNum)
		{//TODO:未测试AutoIncreasedFieldTypeIfNotNum不为空的情况
			string generatorName = GetGeneratorName(tableName);
			string triggerName = tableName + "_increaseID";
			string newValue = string.Format("gen_id({0}, 1)", generatorName);
			if (!string.IsNullOrEmpty(AutoIncreasedFieldTypeIfNotNum))
				newValue = string.Format("cast({0} as {1})", newValue, AutoIncreasedFieldTypeIfNotNum);
			string sql = @"
create trigger {1} for {2} active before insert
as
begin
  if ((new.{3} is null) or (new.{3} = 0)) then
  begin
	  new.{3} = {4};
  end
end
";//TODO:需不需要判读是否为0？
			return string.Format(sql, generatorName, triggerName, tableName, fieldName, newValue);
		}
	}
}