/*
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.apache.jena.sparql.engine.main ;

import java.util.ArrayList ;
import java.util.Iterator ;
import java.util.List ;
import java.util.Set ;

import org.apache.jena.atlas.iterator.Iter ;
import org.apache.jena.graph.Node ;
import org.apache.jena.query.ARQ ;
import org.apache.jena.query.QueryExecException ;
import org.apache.jena.query.SortCondition;
import org.apache.jena.sparql.ARQNotImplemented ;
import org.apache.jena.sparql.algebra.Op ;
import org.apache.jena.sparql.algebra.OpVars ;
import org.apache.jena.sparql.algebra.op.* ;
import org.apache.jena.sparql.core.BasicPattern ;
import org.apache.jena.sparql.core.Quad ;
import org.apache.jena.sparql.core.Var ;
import org.apache.jena.sparql.engine.ExecutionContext ;
import org.apache.jena.sparql.engine.QueryIterator ;
import org.apache.jena.sparql.engine.binding.Binding ;
import org.apache.jena.sparql.engine.iterator.* ;
import org.apache.jena.sparql.engine.join.Join ;
import org.apache.jena.sparql.engine.main.iterator.* ;
import org.apache.jena.sparql.expr.Expr ;
import org.apache.jena.sparql.expr.ExprList ;
import org.apache.jena.sparql.procedure.ProcEval ;
import org.apache.jena.sparql.procedure.Procedure ;

/**
 * Turn an Op expression into an execution of QueryIterators.
 * 
 * Does not consider optimizing the algebra expression (that should happen
 * elsewhere). BGPs are still subject to StageBuilding during iterator
 * execution.
 * 
 * During execution, when a substitution into an algebra expression
 * happens (in other words, a streaming operation, index-join-like), there is a
 * call into the executor each time so it does not just happen once before a
 * query starts.
 */

public class OpExecutor
{
    public static final OpExecutorFactory stdFactory = new OpExecutorFactory() {
        @Override
        public OpExecutor create(ExecutionContext execCxt) {
            return new OpExecutor(execCxt) ;
        }
    } ;

    private static OpExecutor createOpExecutor(ExecutionContext execCxt) {
        OpExecutorFactory factory = execCxt.getExecutor() ;
        if (factory == null)
            factory = stdFactory ;
        if (factory == null)
            return new OpExecutor(execCxt) ;
        return factory.create(execCxt) ;
    }

    // -------

    static QueryIterator execute(Op op, ExecutionContext execCxt) {
        return execute(op, createRootQueryIterator(execCxt), execCxt) ;
    }

    /** Public interface is via QC.execute. **/
    static QueryIterator execute(Op op, QueryIterator qIter, ExecutionContext execCxt) {
        OpExecutor exec = createOpExecutor(execCxt) ;
        QueryIterator q = exec.exec(op, qIter) ;
        return q ;
    }

    // -------- The object starts here --------

    protected ExecutionContext     execCxt ;
    protected ExecutionDispatch    dispatcher = null ;
    protected static final int     TOP_LEVEL  = 0 ;
    protected int                  level      = TOP_LEVEL - 1 ;
    private final boolean          hideBNodeVars ;
    protected final StageGenerator stageGenerator ;

    protected OpExecutor(ExecutionContext execCxt)
    {
        this.execCxt = execCxt ;
        this.dispatcher = new ExecutionDispatch(this) ;
        this.hideBNodeVars = execCxt.getContext().isTrue(ARQ.hideNonDistiguishedVariables) ;
        this.stageGenerator = StageBuilder.chooseStageGenerator(execCxt.getContext()) ;
    }

    // Public interface 
    public QueryIterator executeOp(Op op, QueryIterator input) {
        return exec(op, input) ;
    }
    
    // ---- The recursive step.
    protected QueryIterator exec(Op op, QueryIterator input) {
        level++ ;
        QueryIterator qIter = dispatcher.exec(op, input) ;
        // Intentionally not try/finally so exceptions leave some evidence
        // around.
        level-- ;
        return qIter ;
    }

    // ---- All the cases

    protected QueryIterator execute(OpBGP opBGP, QueryIterator input) {
        BasicPattern pattern = opBGP.getPattern() ;
        QueryIterator qIter = stageGenerator.execute(pattern, input, execCxt) ;
        if (hideBNodeVars)
            qIter = new QueryIterDistinguishedVars(qIter, execCxt) ;
        return qIter ;
    }

    protected QueryIterator execute(OpTriple opTriple, QueryIterator input) {
        return execute(opTriple.asBGP(), input) ;
    }

    protected QueryIterator execute(OpGraph opGraph, QueryIterator input) {
        QueryIterator qIter = specialcase(opGraph.getNode(), opGraph.getSubOp(), input) ;
        if (qIter != null)
            return qIter ;
        return new QueryIterGraph(input, opGraph, execCxt) ;
    }

    private QueryIterator specialcase(Node gn, Op subOp, QueryIterator input) {
        // This is a placeholder for code to specially handle explicitly named
        // default graph and union graph.

        if (Quad.isDefaultGraph(gn)) {
            ExecutionContext cxt2 = new ExecutionContext(execCxt, execCxt.getDataset().getDefaultGraph()) ;
            return execute(subOp, input, cxt2) ;
        }

        // Bad news -- if ( Lib.equals(gn, Quad.tripleInQuad) ) {}
        return null ;
    }

    protected QueryIterator execute(OpQuad opQuad, QueryIterator input) {
        return execute(opQuad.asQuadPattern(), input) ;
    }

    protected QueryIterator execute(OpQuadPattern quadPattern, QueryIterator input) {
        // Convert to BGP forms to execute in this graph-centric engine.
        if (quadPattern.isDefaultGraph() && execCxt.getActiveGraph() == execCxt.getDataset().getDefaultGraph()) {
            // Note we tested that the containing graph was the dataset's
            // default graph.
            // Easy case.
            OpBGP opBGP = new OpBGP(quadPattern.getBasicPattern()) ;
            return execute(opBGP, input) ;
        }
        // Not default graph - (graph .... )
        OpBGP opBGP = new OpBGP(quadPattern.getBasicPattern()) ;
        OpGraph op = new OpGraph(quadPattern.getGraphNode(), opBGP) ;
        return execute(op, input) ;
    }
    
    protected QueryIterator execute(OpQuadBlock quadBlock, QueryIterator input) {
        Op op = quadBlock.convertOp() ;
        return exec(op, input) ;
    }

    protected QueryIterator execute(OpPath opPath, QueryIterator input) {
        return new QueryIterPath(opPath.getTriplePath(), input, execCxt) ;
    }

    protected QueryIterator execute(OpProcedure opProc, QueryIterator input) {
        Procedure procedure = ProcEval.build(opProc, execCxt) ;
        QueryIterator qIter = exec(opProc.getSubOp(), input) ;
        // Delay until query starts executing.
        return new QueryIterProcedure(qIter, procedure, execCxt) ;
    }

    protected QueryIterator execute(OpPropFunc opPropFunc, QueryIterator input) {
        Procedure procedure = ProcEval.build(opPropFunc.getProperty(), opPropFunc.getSubjectArgs(),
                                             opPropFunc.getObjectArgs(), execCxt) ;
        QueryIterator qIter = exec(opPropFunc.getSubOp(), input) ;
        return new QueryIterProcedure(qIter, procedure, execCxt) ;
    }

    protected QueryIterator execute(OpJoin opJoin, QueryIterator input) {
        // Need to clone input into left and right.
        // Do by evaling for each input case, the left and right and concat'ing
        // the results.

        if (false) {
            // If needed, applies to OpDiff and OpLeftJoin as well.
            List<Binding> a = all(input) ;
            QueryIterator qIter1 = new QueryIterPlainWrapper(a.iterator(), execCxt) ;
            QueryIterator qIter2 = new QueryIterPlainWrapper(a.iterator(), execCxt) ;

            QueryIterator left = exec(opJoin.getLeft(), qIter1) ;
            QueryIterator right = exec(opJoin.getRight(), qIter2) ;
            QueryIterator qIter = Join.join(left, right, execCxt) ;
            return qIter ;
        }
        QueryIterator left = exec(opJoin.getLeft(), input) ;
        QueryIterator right = exec(opJoin.getRight(), root()) ;
        // Join key.
        QueryIterator qIter = Join.join(left, right, execCxt) ;
        return qIter ;
    }

    // Pass iterator from one step directly into the next.
    protected QueryIterator execute(OpSequence opSequence, QueryIterator input) {
        QueryIterator qIter = input ;
        for (Iterator<Op> iter = opSequence.iterator(); iter.hasNext();) {
            Op sub = iter.next() ;
            qIter = exec(sub, qIter) ;
        }
        return qIter ;
    }

    protected QueryIterator execute(OpLeftJoin opLeftJoin, QueryIterator input) {
        QueryIterator left = exec(opLeftJoin.getLeft(), input) ;
        QueryIterator right = exec(opLeftJoin.getRight(), root()) ;
        QueryIterator qIter = Join.leftJoin(left, right, opLeftJoin.getExprs(), execCxt) ;
        return qIter ;
    }

    protected QueryIterator execute(OpConditional opCondition, QueryIterator input) {
        QueryIterator left = exec(opCondition.getLeft(), input) ;
        QueryIterator qIter = new QueryIterOptionalIndex(left, opCondition.getRight(), execCxt) ;
        return qIter ;
    }

    protected QueryIterator execute(OpDiff opDiff, QueryIterator input) {
        QueryIterator left = exec(opDiff.getLeft(), input) ;
        QueryIterator right = exec(opDiff.getRight(), root()) ;
        return new QueryIterDiff(left, right, execCxt) ;
    }

    protected QueryIterator execute(OpMinus opMinus, QueryIterator input) {
        Op lhsOp = opMinus.getLeft() ;
        Op rhsOp = opMinus.getRight() ;

        QueryIterator left = exec(lhsOp, input) ;
        QueryIterator right = exec(rhsOp, root()) ;

        Set<Var> commonVars = OpVars.visibleVars(lhsOp) ;
        commonVars.retainAll(OpVars.visibleVars(rhsOp)) ;

        return QueryIterMinus.create(left, right, commonVars, execCxt) ;
    }

    protected QueryIterator execute(OpDisjunction opDisjunction, QueryIterator input) {
        QueryIterator cIter = new QueryIterUnion(input, opDisjunction.getElements(), execCxt) ;
        return cIter ;
    }

    protected QueryIterator execute(OpUnion opUnion, QueryIterator input) {
        List<Op> x = flattenUnion(opUnion) ;
        QueryIterator cIter = new QueryIterUnion(input, x, execCxt) ;
        return cIter ;
    }

    // Based on code from Olaf Hartig.
    protected List<Op> flattenUnion(OpUnion opUnion) {
        List<Op> x = new ArrayList<>() ;
        flattenUnion(x, opUnion) ;
        return x ;
    }

    protected void flattenUnion(List<Op> acc, OpUnion opUnion) {
        if (opUnion.getLeft() instanceof OpUnion)
            flattenUnion(acc, (OpUnion)opUnion.getLeft()) ;
        else
            acc.add(opUnion.getLeft()) ;

        if (opUnion.getRight() instanceof OpUnion)
            flattenUnion(acc, (OpUnion)opUnion.getRight()) ;
        else
            acc.add(opUnion.getRight()) ;
    }

    protected QueryIterator execute(OpFilter opFilter, QueryIterator input) {
        ExprList exprs = opFilter.getExprs() ;

        Op base = opFilter.getSubOp() ;
        QueryIterator qIter = exec(base, input) ;

        for (Expr expr : exprs)
            qIter = new QueryIterFilterExpr(qIter, expr, execCxt) ;
        return qIter ;
    }

    protected QueryIterator execute(OpService opService, QueryIterator input) {
        return new QueryIterService(input, opService, execCxt) ;
    }

    // Quad form, "GRAPH ?g {}" Flip back to OpGraph.
    // Normally quad stores override this.
    protected QueryIterator execute(OpDatasetNames dsNames, QueryIterator input) {
        if (false) {
            OpGraph op = new OpGraph(dsNames.getGraphNode(), new OpBGP()) ;
            return execute(op, input) ;
        }
        throw new ARQNotImplemented("execute/OpDatasetNames") ;
    }

    protected QueryIterator execute(OpTable opTable, QueryIterator input) {
        if (opTable.isJoinIdentity())
            return input ;
        if (input.isJoinIdentity() ) {
            input.close() ;
            return opTable.getTable().iterator(execCxt);
        }
        QueryIterator qIterT = opTable.getTable().iterator(execCxt) ;
        QueryIterator qIter = Join.join(input, qIterT, execCxt) ;
        return qIter ;
    }

    protected QueryIterator execute(OpExt opExt, QueryIterator input) {
        try {
            QueryIterator qIter = opExt.eval(input, execCxt) ;
            if (qIter != null)
                return qIter ;
        } catch (UnsupportedOperationException ex) {}
        // null or UnsupportedOperationException
        throw new QueryExecException("Encountered unsupported OpExt: " + opExt.getName()) ;
    }

    protected QueryIterator execute(OpLabel opLabel, QueryIterator input) {
        if (!opLabel.hasSubOp())
            return input ;

        return exec(opLabel.getSubOp(), input) ;
    }

    protected QueryIterator execute(OpNull opNull, QueryIterator input) {
        // Loose the input.
        input.close() ;
        return QueryIterNullIterator.create(execCxt) ;
    }

    protected QueryIterator execute(OpList opList, QueryIterator input) {
        return exec(opList.getSubOp(), input) ;
    }

    protected QueryIterator execute(OpOrder opOrder, QueryIterator input) {
        QueryIterator qIter = exec(opOrder.getSubOp(), input) ;
        qIter = new QueryIterSort(qIter, opOrder.getConditions(), execCxt) ;
        return qIter ;
    }

    protected QueryIterator execute(OpTopN opTop, QueryIterator input) {
        QueryIterator qIter = null ;
        // We could also do (reduced) here as well.
        // but it's detected in TransformTopN and turned into (distinct)
        // there so that code catches that already.
        // We leave this to do the strict case of (top (distinct ...))
        if (opTop.getSubOp() instanceof OpDistinct) {
            OpDistinct opDistinct = (OpDistinct)opTop.getSubOp() ;
            qIter = exec(opDistinct.getSubOp(), input) ;
            qIter = new QueryIterTopN(qIter, opTop.getConditions(), opTop.getLimit(), true, execCxt) ;
        } else {
            qIter = exec(opTop.getSubOp(), input) ;
            qIter = new QueryIterTopN(qIter, opTop.getConditions(), opTop.getLimit(), false, execCxt) ;
        }
        return qIter ;
    }

    protected QueryIterator execute(OpProject opProject, QueryIterator input) {
        // This may be under a (graph) in which case we need to operate
        // on the active graph.

        // More intelligent QueryIterProject needed.

        if (input instanceof QueryIterRoot) {
            QueryIterator qIter = exec(opProject.getSubOp(), input) ;
            qIter = new QueryIterProject(qIter, opProject.getVars(), execCxt) ;
            return qIter ;
        }
        // Nested projected : need to ensure the input is seen.
        QueryIterator qIter = new QueryIterProjectMerge(opProject, input, this, execCxt) ;
        return qIter ;
    }

    protected QueryIterator execute(OpSlice opSlice, QueryIterator input) {
        QueryIterator qIter = exec(opSlice.getSubOp(), input) ;
        qIter = new QueryIterSlice(qIter, opSlice.getStart(), opSlice.getLength(), execCxt) ;
        return qIter ;
    }

    protected QueryIterator execute(OpGroup opGroup, QueryIterator input) {
        QueryIterator qIter = exec(opGroup.getSubOp(), input) ;
        qIter = new QueryIterGroup(qIter, opGroup.getGroupVars(), opGroup.getAggregators(), execCxt) ;
        return qIter ;
    }

    protected QueryIterator execute(OpDistinct opDistinct, QueryIterator input) {
        QueryIterator qIter = exec(opDistinct.getSubOp(), input) ;
        List<SortCondition> conditions = null;
        if ( opDistinct.getSubOp() instanceof OpOrder ) {
            // For DISTINCT-ORDER, and if DISTINCT spills
            // then we need to take account of the ORDER.
            // The normal (non-spill case) already preserves the input order,
            // passing through the first occurence. It is only if a spill happens that
            // we need to ensure the spill buckets respect sort order. 
            OpOrder subOrder = (OpOrder)opDistinct.getSubOp();
            conditions = subOrder.getConditions();
        }
        
        qIter = new QueryIterDistinct(qIter, conditions, execCxt) ;
        return qIter ;
    }

    protected QueryIterator execute(OpReduced opReduced, QueryIterator input) {
        QueryIterator qIter = exec(opReduced.getSubOp(), input) ;
        qIter = new QueryIterReduced(qIter, execCxt) ;
        return qIter ;
    }

    protected QueryIterator execute(OpAssign opAssign, QueryIterator input) {
        QueryIterator qIter = exec(opAssign.getSubOp(), input) ;
        qIter = new QueryIterAssign(qIter, opAssign.getVarExprList(), execCxt, false) ;
        return qIter ;
    }

    protected QueryIterator execute(OpExtend opExtend, QueryIterator input) {
        // We know (parse time checking) the variable is unused so far in
        // the query so we can use QueryIterAssign knowing that it behaves
        // the same as extend. The boolean should only be a check.
        QueryIterator qIter = exec(opExtend.getSubOp(), input) ;
        qIter = new QueryIterAssign(qIter, opExtend.getVarExprList(), execCxt, true) ;
        return qIter ;
    }

    public static QueryIterator createRootQueryIterator(ExecutionContext execCxt) {
        return QueryIterRoot.create(execCxt) ;
    }

    protected QueryIterator root() {
        return createRootQueryIterator(execCxt) ;
    }

    // Use this to debug evaluation
    // Example:
    // input = debug(input) ;
    private QueryIterator debug(String marker, QueryIterator input) {
        List<Binding> x = all(input) ;
        for (Binding b : x) {
            System.out.print(marker) ;
            System.out.print(": ") ;
            System.out.println(b) ;
        }

        return new QueryIterPlainWrapper(x.iterator(), execCxt) ;
    }

    private static List<Binding> all(QueryIterator input) {
        return Iter.toList(input) ;
    }
}
