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//Copyright (C) 2013 LunarG, Inc.
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//
// Do sub tree walks for
// 1) inductive loop bodies to see if the inductive variable is modified
// 2) array-index expressions to see if they are "constant-index-expression"
//
// These are per Appendix A of ES 2.0:
//
// "Within the body of the loop, the loop index is not statically assigned to nor is it used as the
// argument to a function out or inout parameter."
//
// "The following are constant-index-expressions:
//  - Constant expressions
//  - Loop indices as defined in section 4
//  - Expressions composed of both of the above"
//
// N.B.: assuming the last rule excludes function calls
//

#include "ParseHelper.h"

namespace glslang {

//
// The inductive loop-body traverser.
//
// Just look at things that might modify the loop index.
//

class TInductiveTraverser : public TIntermTraverser {
public:
    TInductiveTraverser(int id, TSymbolTable& st) : loopId(id), symbolTable(st), bad(false)  { }
    int loopId;           // unique ID of the symbol that's the loop inductive variable
    TSymbolTable& symbolTable;
    bool bad;
    TSourceLoc badLoc;
};

// check binary operations for those modifying the loop index
bool InductiveBinary(bool /* preVisit */, TIntermBinary* node, TIntermTraverser* it)
{
    TInductiveTraverser* oit = static_cast<TInductiveTraverser*>(it);

    if (node->modifiesState() && node->getLeft()->getAsSymbolNode() && 
                                 node->getLeft()->getAsSymbolNode()->getId() == oit->loopId) {
        oit->bad = true;
        oit->badLoc = node->getLoc();
    }

    return true;
}

// check unary operations for those modifying the loop index
bool InductiveUnary(bool /* preVisit */, TIntermUnary* node, TIntermTraverser* it)
{
    TInductiveTraverser* oit = static_cast<TInductiveTraverser*>(it);

    if (node->modifiesState() && node->getOperand()->getAsSymbolNode() && 
                                 node->getOperand()->getAsSymbolNode()->getId() == oit->loopId) {
        oit->bad = true;
        oit->badLoc = node->getLoc();
    }

    return true;
}

// check function calls for arguments modifying the loop index
bool InductiveAggregate(bool /* preVisit */, TIntermAggregate* node, TIntermTraverser* it)
{
    TInductiveTraverser* oit = static_cast<TInductiveTraverser*>(it);

    if (node->getOp() == EOpFunctionCall) {
        // see if an out or inout argument is the loop index
        const TIntermSequence& args = node->getSequence();
        for (size_t i = 0; i < args.size(); ++i) {
            if (args[i]->getAsSymbolNode() && args[i]->getAsSymbolNode()->getId() == oit->loopId) {
                TSymbol* function = oit->symbolTable.find(node->getName());
                const TType* type = (*function->getAsFunction())[i].type;
                if (type->getQualifier().storage == EvqOut ||
                    type->getQualifier().storage == EvqInOut) {
                    oit->bad = true;
                    oit->badLoc = node->getLoc();
                }
            }
        }
    }

    return true;
}

//
// External function to call for loop check.
//
void TParseContext::inductiveLoopBodyCheck(TIntermNode* body, int loopId, TSymbolTable& symbolTable)
{
    TInductiveTraverser it(loopId, symbolTable);

    if (! body)
        return;

    it.visitAggregate = InductiveAggregate;
    it.visitBinary = InductiveBinary;
    it.visitUnary = InductiveUnary;

    body->traverse(&it);

    if (it.bad)
        error(it.badLoc, "inductive loop index modified", "limitations", "");
}

//
// The "constant-index-expression" tranverser.
//
// Just look at things that can form an index.  
//

class TIndexTraverser : public TIntermTraverser {
public:
    TIndexTraverser(const TIdSetType& ids) : inductiveLoopIds(ids), bad(false) { }
    const TIdSetType& inductiveLoopIds;
    bool bad;
    TSourceLoc badLoc;
};

// make sure symbols are inductive-loop indexes
void IndexSymbol(TIntermSymbol* symbol, TIntermTraverser* it)
{
    TIndexTraverser* oit = static_cast<TIndexTraverser*>(it);

    if (oit->inductiveLoopIds.find(symbol->getId()) == oit->inductiveLoopIds.end()) {
        oit->bad = true;
        oit->badLoc = symbol->getLoc();
    }
}

// check for function calls, assuming they are bad; spec. doesn't really say
bool IndexAggregate(bool /* preVisit */, TIntermAggregate* node, TIntermTraverser* it)
{
    TIndexTraverser* oit = static_cast<TIndexTraverser*>(it);

    if (node->getOp() == EOpFunctionCall) {
        oit->bad = true;
        oit->badLoc = node->getLoc();
    }

    return true;
}

//
// External function to call for loop check.
//
void TParseContext::constantIndexExpressionCheck(TIntermNode* index)
{
    TIndexTraverser it(inductiveLoopIds);

    it.visitSymbol = IndexSymbol;
    it.visitAggregate = IndexAggregate;

    index->traverse(&it);

    if (it.bad)
        error(it.badLoc, "Non-constant-index-expression", "limitations", "");
}

} // end namespace glslang