import org.apache.ibatis.executor.Executor;
import org.apache.ibatis.mapping.*;
import org.apache.ibatis.plugin.*;
import org.apache.ibatis.reflection.MetaObject;
import org.apache.ibatis.reflection.SystemMetaObject;
import org.apache.ibatis.session.ResultHandler;
import org.apache.ibatis.session.RowBounds;

import java.util.ArrayList;
import java.util.List;
import java.util.Properties;


/**
 * Mybatis - 通用分页拦截器v2.1
 *
 * @author liuzh/abel533/isea
 *         Created by liuzh on 14-4-15.
 *         Update by liuzh on 14-5-20.
 *         Update by liuzh on 14-5-21.
 */
@Intercepts(@Signature(type = Executor.class, method = "query", args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class}))
public class PageHelper implements Interceptor {
    private static final ThreadLocal<Page> localPage = new ThreadLocal<Page>();

    private static final List<ResultMapping> EMPTY_RESULTMAPPING = new ArrayList<ResultMapping>(0);

    /**
     * 开始分页
     *
     * @param pageNum
     * @param pageSize
     */
    public static void startPage(int pageNum, int pageSize) {
        startPage(pageNum, pageSize, true);
    }

    /**
     * 开始分页
     *
     * @param pageNum
     * @param pageSize
     */
    public static void startPage(int pageNum, int pageSize, boolean count) {
        localPage.set(new Page(pageNum, pageSize, count? Page.SQL_COUNT: Page.NO_SQL_COUNT));
    }

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        final Object[] args = invocation.getArgs();
        RowBounds rowBounds = (RowBounds)args[2];
        if (localPage.get() == null && rowBounds == RowBounds.DEFAULT) {
            return invocation.proceed();
        } else {
            MappedStatement ms = (MappedStatement) args[0];
            Object parameterObject = args[1];
            BoundSql boundSql = ms.getBoundSql(parameterObject);

            //分页信息
            Page page = localPage.get();
            //移除本地变量
            localPage.remove();

            if (page == null) {
                page = new Page(rowBounds);
            }
            MappedStatement qs = newMappedStatement(ms, new BoundSqlSqlSource(boundSql));
            //将参数中的MappedStatement替换为新的qs，防止并发异常
            args[0] = qs;
            MetaObject msObject = SystemMetaObject.forObject(qs);
            String sql = (String) msObject.getValue("sqlSource.boundSql.sql");
            //简单的通过total的值来判断是否进行count查询
            if (page.getTotal() > Page.NO_SQL_COUNT) {
                //求count - 重写sql
                msObject.setValue("sqlSource.boundSql.sql", getCountSql(sql));
                //查询总数
                Object result = invocation.proceed();
                int totalCount = Integer.parseInt(((List) result).get(0).toString());
                page.setTotal(totalCount);
                int totalPage = totalCount / page.getPageSize() + ((totalCount % page.getPageSize() == 0) ? 0 : 1);
                page.setPages(totalPage);
                //分页sql - 重写sql
                msObject.setValue("sqlSource.boundSql.sql", getPageSql(sql, page));
                //恢复类型
                msObject.setValue("resultMaps", ms.getResultMaps());
                //执行分页查询
                result = invocation.proceed();
                //得到处理结果
                page.addAll((List) result);
                //返回结果
                return page;
            } else {
                //分页sql - 重写sql
                msObject.setValue("sqlSource.boundSql.sql", getPageSql(sql, page));
                //恢复类型
                msObject.setValue("resultMaps", ms.getResultMaps());
                //返回结果
                return invocation.proceed();
            }
        }
    }

    /**
     * 获取总数sql - 如果要支持其他数据库，修改这里就可以
     * @param sql
     * @return
     */
    private String getCountSql(String sql) {
        return "select count(0) from (" + sql + ")";
    }

    /**
     * 获取分页sql - 如果要支持其他数据库，修改这里就可以
     * @param sql
     * @param page
     * @return
     */
    private String getPageSql(String sql, Page page) {
        StringBuilder pageSql = new StringBuilder(200);
        pageSql.append("select * from ( select temp.*, rownum row_id from ( ");
        pageSql.append(sql);
        pageSql.append(" ) temp where rownum <= ").append(page.getEndRow());
        pageSql.append(") where row_id > ").append(page.getStartRow());
        return pageSql.toString();
    }

    private class BoundSqlSqlSource implements SqlSource {
        BoundSql boundSql;

        public BoundSqlSqlSource(BoundSql boundSql) {
            this.boundSql = boundSql;
        }

        public BoundSql getBoundSql(Object parameterObject) {
            return boundSql;
        }
    }

    /**
     * 由于MappedStatement是一个全局共享的对象，因而需要复制一个对象来进行操作，防止并发访问导致错误
     *
     * @param ms
     * @param newSqlSource
     * @return
     */
    private MappedStatement newMappedStatement(MappedStatement ms, SqlSource newSqlSource) {
        MappedStatement.Builder builder = new MappedStatement.Builder(ms.getConfiguration(), ms.getId() + "_分页", newSqlSource, ms.getSqlCommandType());
        builder.resource(ms.getResource());
        builder.fetchSize(ms.getFetchSize());
        builder.statementType(ms.getStatementType());
        builder.keyGenerator(ms.getKeyGenerator());
        if (ms.getKeyProperties() != null && ms.getKeyProperties().length != 0) {
            StringBuffer keyProperties = new StringBuffer();
            for (String keyProperty : ms.getKeyProperties()) {
                keyProperties.append(keyProperty).append(",");
            }
            keyProperties.delete(keyProperties.length() - 1, keyProperties.length());
            builder.keyProperty(keyProperties.toString());
        }
        builder.timeout(ms.getTimeout());
        builder.parameterMap(ms.getParameterMap());
        //由于resultMaps第一次需要返回int类型的结果，所以这里需要生成一个resultMap - 防止并发错误
        List<ResultMap> resultMaps = new ArrayList<ResultMap>();
        ResultMap resultMap = new ResultMap.Builder(ms.getConfiguration(), ms.getId(), int.class, EMPTY_RESULTMAPPING).build();
        resultMaps.add(resultMap);
        builder.resultMaps(resultMaps);
        builder.resultSetType(ms.getResultSetType());
        builder.cache(ms.getCache());
        builder.flushCacheRequired(ms.isFlushCacheRequired());
        builder.useCache(ms.isUseCache());

        return builder.build();
    }

    /**
     * 只拦截Executor
     *
     * @param target
     * @return
     */
    @Override
    public Object plugin(Object target) {
        if (target instanceof Executor) {
            return Plugin.wrap(target, this);
        } else {
            return target;
        }
    }

    @Override
    public void setProperties(Properties properties) {

    }
}