#include "slang-ir-vk-invert-y.h"
#include "slang-ir.h"
#include "slang-ir-insts.h"

namespace Slang
{

static IRInst* _invertYOfVector(IRBuilder& builder, IRInst* originalVector)
{
    auto vectorType = as<IRVectorType>(originalVector->getDataType());
    SLANG_ASSERT(vectorType);
    UInt elementIndexY = 1;
    auto originalY = builder.emitSwizzle(vectorType->getElementType(), originalVector, 1, &elementIndexY);
    auto negY = builder.emitNeg(originalY->getDataType(), originalY);
    auto newVal = builder.emitSwizzleSet(originalVector->getDataType(), originalVector, negY, 1, &elementIndexY);
    return newVal;
}
// Find outputs to SV_Position and invert the y coordinates of it right before the write.
void invertYOfPositionOutput(IRModule* module)
{
    for (auto globalInst : module->getGlobalInsts())
    {
        if (globalInst->findDecoration<IRGLPositionOutputDecoration>())
        {
            // Find all loads and stores to it.
            IRBuilder builder(module);
            traverseUses(globalInst, [&](IRUse* use)
                {
                    if (auto store = as<IRStore>(use->getUser()))
                    {
                        if (store->getPtr() != globalInst)
                            return;

                        builder.setInsertBefore(store);
                        auto originalVal = store->getVal();
                        auto invertedVal = _invertYOfVector(builder, originalVal);
                        builder.replaceOperand(&store->val, invertedVal);
                    }
                    else if (auto load = as<IRLoad>(use->getUser()))
                    {
                        // Since we negate the y coordinate before writing
                        // to gl_Position, we also need to negate the value after reading from it.
                        builder.setInsertAfter(load);
                        // Store existing uses of the load that we are going to replace with inverted val later.
                        List<IRUse*> oldUses;
                        for (auto loadUse = load->firstUse; loadUse; loadUse = loadUse->nextUse)
                            oldUses.add(loadUse);
                        // Get the inverted vector.
                        auto invertedVal = _invertYOfVector(builder, load);
                        // Replace original uses with the invertex vector.
                        for (auto loadUse : oldUses)
                            builder.replaceOperand(loadUse, invertedVal);
                    }
                });
        }
    }
}

}