/*
 * Copyright 2004-2014 H2 Group. Multiple-Licensed under the MPL 2.0,
 * and the EPL 1.0 (http://h2database.com/html/license.html).
 * Initial Developer: H2 Group
 */
package org.h2.command.dml;

import java.util.ArrayList;
import java.util.HashSet;

import org.h2.api.ErrorCode;
import org.h2.command.Prepared;
import org.h2.engine.Database;
import org.h2.engine.Session;
import org.h2.expression.Alias;
import org.h2.expression.Expression;
import org.h2.expression.ExpressionColumn;
import org.h2.expression.ExpressionVisitor;
import org.h2.expression.Parameter;
import org.h2.expression.ValueExpression;
import org.h2.message.DbException;
import org.h2.result.LocalResult;
import org.h2.result.ResultTarget;
import org.h2.result.SortOrder;
import org.h2.table.ColumnResolver;
import org.h2.table.Table;
import org.h2.table.TableFilter;
import org.h2.util.New;
import org.h2.value.Value;
import org.h2.value.ValueInt;
import org.h2.value.ValueNull;

/**
 * Represents a SELECT statement (simple, or union).
 */
public abstract class Query extends Prepared {

    /**
     * The limit expression as specified in the LIMIT or TOP clause.
     */
    protected Expression limitExpr;

    /**
     * The offset expression as specified in the LIMIT .. OFFSET clause.
     */
    protected Expression offsetExpr;

    /**
     * The sample size expression as specified in the SAMPLE_SIZE clause.
     */
    protected Expression sampleSizeExpr;

    /**
     * Whether the result must only contain distinct rows.
     */
    protected boolean distinct;

    /**
     * Whether the result needs to support random access.
     */
    protected boolean randomAccessResult;

    private boolean noCache;
    private int lastLimit;
    private long lastEvaluated;
    private LocalResult lastResult;
    private Value[] lastParameters;
    private boolean cacheableChecked;

    Query(Session session) {
        super(session);
    }

    /**
     * Execute the query without checking the cache. If a target is specified,
     * the results are written to it, and the method returns null. If no target
     * is specified, a new LocalResult is created and returned.
     *
     * @param limit the limit as specified in the JDBC method call
     * @param target the target to write results to
     * @return the result
     */
    protected abstract LocalResult queryWithoutCache(int limit,
            ResultTarget target);

    /**
     * Initialize the query.
     */
    public abstract void init();

    /**
     * The the list of select expressions.
     * This may include invisible expressions such as order by expressions.
     *
     * @return the list of expressions
     */
    public abstract ArrayList<Expression> getExpressions();

    /**
     * Calculate the cost to execute this query.
     *
     * @return the cost
     */
    public abstract double getCost();

    /**
     * Calculate the cost when used as a subquery.
     * This method returns a value between 10 and 1000000,
     * to ensure adding other values can't result in an integer overflow.
     *
     * @return the estimated cost as an integer
     */
    public int getCostAsExpression() {
        // ensure the cost is not larger than 1 million,
        // so that adding other values can't overflow
        return (int) Math.min(1000000.0, 10.0 + 10.0 * getCost());
    }

    /**
     * Get all tables that are involved in this query.
     *
     * @return the set of tables
     */
    public abstract HashSet<Table> getTables();

    /**
     * Set the order by list.
     *
     * @param order the order by list
     */
    public abstract void setOrder(ArrayList<SelectOrderBy> order);

    /**
     * Set the 'for update' flag.
     *
     * @param forUpdate the new setting
     */
    public abstract void setForUpdate(boolean forUpdate);

    /**
     * Get the column count of this query.
     *
     * @return the column count
     */
    public abstract int getColumnCount();

    /**
     * Map the columns to the given column resolver.
     *
     * @param resolver
     *            the resolver
     * @param level
     *            the subquery level (0 is the top level query, 1 is the first
     *            subquery level)
     */
    public abstract void mapColumns(ColumnResolver resolver, int level);

    /**
     * Change the evaluatable flag. This is used when building the execution
     * plan.
     *
     * @param tableFilter the table filter
     * @param b the new value
     */
    public abstract void setEvaluatable(TableFilter tableFilter, boolean b);

    /**
     * Add a condition to the query. This is used for views.
     *
     * @param param the parameter
     * @param columnId the column index (0 meaning the first column)
     * @param comparisonType the comparison type
     */
    public abstract void addGlobalCondition(Parameter param, int columnId,
            int comparisonType);

    /**
     * Check whether adding condition to the query is allowed. This is not
     * allowed for views that have an order by and a limit, as it would affect
     * the returned results.
     *
     * @return true if adding global conditions is allowed
     */
    public abstract boolean allowGlobalConditions();

    /**
     * Check if this expression and all sub-expressions can fulfill a criteria.
     * If any part returns false, the result is false.
     *
     * @param visitor the visitor
     * @return if the criteria can be fulfilled
     */
    public abstract boolean isEverything(ExpressionVisitor visitor);

    /**
     * Update all aggregate function values.
     *
     * @param s the session
     */
    public abstract void updateAggregate(Session s);

    /**
     * Call the before triggers on all tables.
     */
    public abstract void fireBeforeSelectTriggers();

    /**
     * Set the distinct flag.
     *
     * @param b the new value
     */
    public void setDistinct(boolean b) {
        distinct = b;
    }

    public boolean isDistinct() {
        return distinct;
    }

    /**
     * Whether results need to support random access.
     *
     * @param b the new value
     */
    public void setRandomAccessResult(boolean b) {
        randomAccessResult = b;
    }

    @Override
    public boolean isQuery() {
        return true;
    }

    @Override
    public boolean isTransactional() {
        return true;
    }

    /**
     * Disable caching of result sets.
     */
    public void disableCache() {
        this.noCache = true;
    }

    private boolean sameResultAsLast(Session s, Value[] params,
            Value[] lastParams, long lastEval) {
        if (!cacheableChecked) {
            long max = getMaxDataModificationId();
            noCache = max == Long.MAX_VALUE;
            cacheableChecked = true;
        }
        if (noCache) {
            return false;
        }
        Database db = s.getDatabase();
        for (int i = 0; i < params.length; i++) {
            Value a = lastParams[i], b = params[i];
            if (a.getType() != b.getType() || !db.areEqual(a, b)) {
                return false;
            }
        }
        if (!isEverything(ExpressionVisitor.DETERMINISTIC_VISITOR) ||
                !isEverything(ExpressionVisitor.INDEPENDENT_VISITOR)) {
            return false;
        }
        if (db.getModificationDataId() > lastEval &&
                getMaxDataModificationId() > lastEval) {
            return false;
        }
        return true;
    }

    public final Value[] getParameterValues() {
        ArrayList<Parameter> list = getParameters();
        if (list == null) {
            list = New.arrayList();
        }
        int size = list.size();
        Value[] params = new Value[size];
        for (int i = 0; i < size; i++) {
            Value v = list.get(i).getParamValue();
            params[i] = v;
        }
        return params;
    }

    @Override
    public LocalResult query(int maxrows) {
        return query(maxrows, null);
    }

    /**
     * Execute the query, writing the result to the target result.
     *
     * @param limit the maximum number of rows to return
     * @param target the target result (null will return the result)
     * @return the result set (if the target is not set).
     */
    LocalResult query(int limit, ResultTarget target) {
        fireBeforeSelectTriggers();
        if (noCache || !session.getDatabase().getOptimizeReuseResults()) {
            return queryWithoutCache(limit, target);
        }
        Value[] params = getParameterValues();
        long now = session.getDatabase().getModificationDataId();
        if (isEverything(ExpressionVisitor.DETERMINISTIC_VISITOR)) {
            if (lastResult != null && !lastResult.isClosed() &&
                    limit == lastLimit) {
                if (sameResultAsLast(session, params, lastParameters,
                        lastEvaluated)) {
                    lastResult = lastResult.createShallowCopy(session);
                    if (lastResult != null) {
                        lastResult.reset();
                        return lastResult;
                    }
                }
            }
        }
        lastParameters = params;
        closeLastResult();
        LocalResult r = queryWithoutCache(limit, target);
        lastResult = r;
        this.lastEvaluated = now;
        lastLimit = limit;
        return r;
    }

    private void closeLastResult() {
        if (lastResult != null) {
            lastResult.close();
        }
    }

    /**
     * Initialize the order by list. This call may extend the expressions list.
     *
     * @param session the session
     * @param expressions the select list expressions
     * @param expressionSQL the select list SQL snippets
     * @param orderList the order by list
     * @param visible the number of visible columns in the select list
     * @param mustBeInResult all order by expressions must be in the select list
     * @param filters the table filters
     */
    static void initOrder(Session session,
            ArrayList<Expression> expressions,
            ArrayList<String> expressionSQL,
            ArrayList<SelectOrderBy> orderList,
            int visible,
            boolean mustBeInResult,
            ArrayList<TableFilter> filters) {
        Database db = session.getDatabase();
        for (SelectOrderBy o : orderList) {
            Expression e = o.expression;
            if (e == null) {
                continue;
            }
            // special case: SELECT 1 AS A FROM DUAL ORDER BY A
            // (oracle supports it, but only in order by, not in group by and
            // not in having):
            // SELECT 1 AS A FROM DUAL ORDER BY -A
            boolean isAlias = false;
            int idx = expressions.size();
            if (e instanceof ExpressionColumn) {
                // order by expression
                ExpressionColumn exprCol = (ExpressionColumn) e;
                String tableAlias = exprCol.getOriginalTableAliasName();
                String col = exprCol.getOriginalColumnName();
                for (int j = 0; j < visible; j++) {
                    boolean found = false;
                    Expression ec = expressions.get(j);
                    if (ec instanceof ExpressionColumn) {
                        // select expression
                        ExpressionColumn c = (ExpressionColumn) ec;
                        found = db.equalsIdentifiers(col, c.getColumnName());
                        if (found && tableAlias != null) {
                            String ca = c.getOriginalTableAliasName();
                            if (ca == null) {
                                found = false;
                                if (filters != null) {
                                    // select id from test order by test.id
                                    for (int i = 0, size = filters.size(); i < size; i++) {
                                        TableFilter f = filters.get(i);
                                        if (db.equalsIdentifiers(f.getTableAlias(), tableAlias)) {
                                            found = true;
                                            break;
                                        }
                                    }
                                }
                            } else {
                                found = db.equalsIdentifiers(ca, tableAlias);
                            }
                        }
                    } else if (!(ec instanceof Alias)) {
                        continue;
                    } else if (tableAlias == null && db.equalsIdentifiers(col, ec.getAlias())) {
                        found = true;
                    } else {
                        Expression ec2 = ec.getNonAliasExpression();
                        if (ec2 instanceof ExpressionColumn) {
                            ExpressionColumn c2 = (ExpressionColumn) ec2;
                            String ta = exprCol.getSQL();
                            String tb = c2.getSQL();
                            String s2 = c2.getColumnName();
                            found = db.equalsIdentifiers(col, s2);
                            if (!db.equalsIdentifiers(ta, tb)) {
                                found = false;
                            }
                        }
                    }
                    if (found) {
                        idx = j;
                        isAlias = true;
                        break;
                    }
                }
            } else {
                String s = e.getSQL();
                if (expressionSQL != null) {
                    for (int j = 0, size = expressionSQL.size(); j < size; j++) {
                        String s2 = expressionSQL.get(j);
                        if (db.equalsIdentifiers(s2, s)) {
                            idx = j;
                            isAlias = true;
                            break;
                        }
                    }
                }
            }
            if (!isAlias) {
                if (mustBeInResult) {
                    throw DbException.get(ErrorCode.ORDER_BY_NOT_IN_RESULT,
                            e.getSQL());
                }
                expressions.add(e);
                String sql = e.getSQL();
                expressionSQL.add(sql);
            }
            o.columnIndexExpr = ValueExpression.get(ValueInt.get(idx + 1));
            Expression expr = expressions.get(idx).getNonAliasExpression();
            o.expression = expr;
        }
    }

    /**
     * Create a {@link SortOrder} object given the list of {@link SelectOrderBy}
     * objects. The expression list is extended if necessary.
     *
     * @param orderList a list of {@link SelectOrderBy} elements
     * @param expressionCount the number of columns in the query
     * @return the {@link SortOrder} object
     */
    public SortOrder prepareOrder(ArrayList<SelectOrderBy> orderList,
            int expressionCount) {
        int size = orderList.size();
        int[] index = new int[size];
        int[] sortType = new int[size];
        for (int i = 0; i < size; i++) {
            SelectOrderBy o = orderList.get(i);
            int idx;
            boolean reverse = false;
            Expression expr = o.columnIndexExpr;
            Value v = expr.getValue(null);
            if (v == ValueNull.INSTANCE) {
                // parameter not yet set - order by first column
                idx = 0;
            } else {
                idx = v.getInt();
                if (idx < 0) {
                    reverse = true;
                    idx = -idx;
                }
                idx -= 1;
                if (idx < 0 || idx >= expressionCount) {
                    throw DbException.get(ErrorCode.ORDER_BY_NOT_IN_RESULT, "" + (idx + 1));
                }
            }
            index[i] = idx;
            boolean desc = o.descending;
            if (reverse) {
                desc = !desc;
            }
            int type = desc ? SortOrder.DESCENDING : SortOrder.ASCENDING;
            if (o.nullsFirst) {
                type += SortOrder.NULLS_FIRST;
            } else if (o.nullsLast) {
                type += SortOrder.NULLS_LAST;
            }
            sortType[i] = type;
        }
        return new SortOrder(session.getDatabase(), index, sortType, orderList);
    }

    public void setOffset(Expression offset) {
        this.offsetExpr = offset;
    }

    public Expression getOffset() {
        return offsetExpr;
    }

    public void setLimit(Expression limit) {
        this.limitExpr = limit;
    }

    public Expression getLimit() {
        return limitExpr;
    }

    /**
     * Add a parameter to the parameter list.
     *
     * @param param the parameter to add
     */
    void addParameter(Parameter param) {
        if (parameters == null) {
            parameters = New.arrayList();
        }
        parameters.add(param);
    }

    public void setSampleSize(Expression sampleSize) {
        this.sampleSizeExpr = sampleSize;
    }

    /**
     * Get the sample size, if set.
     *
     * @param session the session
     * @return the sample size
     */
    int getSampleSizeValue(Session session) {
        if (sampleSizeExpr == null) {
            return 0;
        }
        Value v = sampleSizeExpr.optimize(session).getValue(session);
        if (v == ValueNull.INSTANCE) {
            return 0;
        }
        return v.getInt();
    }

    public final long getMaxDataModificationId() {
        ExpressionVisitor visitor = ExpressionVisitor.getMaxModificationIdVisitor();
        isEverything(visitor);
        return visitor.getMaxDataModificationId();
    }

}
