#include "shadermanager.hpp"

#include <fstream>
#include <algorithm>
#include <sstream>
#include <regex>
#include <filesystem>

#include <osg/Program>

#include <components/debug/debuglog.hpp>
#include <components/misc/strings/algorithm.hpp>
#include <components/misc/strings/format.hpp>
#include <components/settings/settings.hpp>

namespace Shader
{

    ShaderManager::ShaderManager()
    {
    }

    void ShaderManager::setShaderPath(const std::string &path)
    {
        mPath = path;
    }

    bool addLineDirectivesAfterConditionalBlocks(std::string& source)
    {
        for (size_t position = 0; position < source.length(); )
        {
            size_t foundPos = source.find("#endif", position);
            foundPos = std::min(foundPos, source.find("#elif", position));
            foundPos = std::min(foundPos, source.find("#else", position));

            if (foundPos == std::string::npos)
                break;

            foundPos = source.find_first_of("\n\r", foundPos);
            foundPos = source.find_first_not_of("\n\r", foundPos);

            if (foundPos == std::string::npos)
                break;

            size_t lineDirectivePosition = source.rfind("#line", foundPos);
            int lineNumber;
            if (lineDirectivePosition != std::string::npos)
            {
                size_t lineNumberStart = lineDirectivePosition + std::string("#line ").length();
                size_t lineNumberEnd = source.find_first_not_of("0123456789", lineNumberStart);
                std::string lineNumberString = source.substr(lineNumberStart, lineNumberEnd - lineNumberStart);
                lineNumber = std::stoi(lineNumberString) - 1;
            }
            else
            {
                lineDirectivePosition = 0;
                lineNumber = 1;
            }
            lineNumber += std::count(source.begin() + lineDirectivePosition, source.begin() + foundPos, '\n');

            source.replace(foundPos, 0, "#line " + std::to_string(lineNumber) + "\n");

            position = foundPos;
        }

        return true;
    }

    // Recursively replaces include statements with the actual source of the included files.
    // Adjusts #line statements accordingly and detects cyclic includes.
    // includingFiles is the set of files that include this file directly or indirectly, and is intentionally not a reference to allow automatic cleanup.
    static bool parseIncludes(const std::filesystem::path& shaderPath, std::string& source, const std::string& fileName, int& fileNumber, std::set<std::filesystem::path> includingFiles)
    {
        // An include is cyclic if it is being included by itself
        if (includingFiles.insert(shaderPath/fileName).second == false)
        {
            Log(Debug::Error) << "Shader " << fileName << " error: Detected cyclic #includes";
            return false;
        }

        Misc::StringUtils::replaceAll(source, "\r\n", "\n");

        size_t foundPos = 0;
        while ((foundPos = source.find("#include")) != std::string::npos)
        {
            size_t start = source.find('"', foundPos);
            if (start == std::string::npos || start == source.size() - 1)
            {
                Log(Debug::Error) << "Shader " << fileName << " error: Invalid #include";
                return false;
            }
            size_t end = source.find('"', start + 1);
            if (end == std::string::npos)
            {
                Log(Debug::Error) << "Shader " << fileName << " error: Invalid #include";
                return false;
            }
            std::string includeFilename = source.substr(start + 1, end - (start + 1));
            std::filesystem::path includePath = shaderPath / includeFilename;

            // Determine the line number that will be used for the #line directive following the included source
            size_t lineDirectivePosition = source.rfind("#line", foundPos);
            int lineNumber;
            if (lineDirectivePosition != std::string::npos)
            {
                size_t lineNumberStart = lineDirectivePosition + std::string("#line ").length();
                size_t lineNumberEnd = source.find_first_not_of("0123456789", lineNumberStart);
                std::string lineNumberString = source.substr(lineNumberStart, lineNumberEnd - lineNumberStart);
                lineNumber = std::stoi(lineNumberString) - 1;
            }
            else
            {
                lineDirectivePosition = 0;
                lineNumber = 0;
            }
            lineNumber += std::count(source.begin() + lineDirectivePosition, source.begin() + foundPos, '\n');

            // Include the file recursively
            std::ifstream includeFstream;
            includeFstream.open(includePath);
            if (includeFstream.fail())
            {
                Log(Debug::Error) << "Shader " << fileName << " error: Failed to open include " << includePath.string();
                return false;
            }
            int includedFileNumber = fileNumber++;

            std::stringstream buffer;
            buffer << includeFstream.rdbuf();
            std::string stringRepresentation = buffer.str();
            if (!addLineDirectivesAfterConditionalBlocks(stringRepresentation)
                || !parseIncludes(shaderPath, stringRepresentation, includeFilename, fileNumber, includingFiles))
            {
                Log(Debug::Error) << "In file included from " << fileName << "." << lineNumber;
                return false;
            }

            std::stringstream toInsert;
            toInsert << "#line 0 " << includedFileNumber << "\n" << stringRepresentation << "\n#line " << lineNumber << " 0\n";

            source.replace(foundPos, (end - foundPos + 1), toInsert.str());
        }
        return true;
    }

    bool parseForeachDirective(std::string& source, const std::string& templateName, size_t foundPos)
    {
        size_t iterNameStart = foundPos + strlen("$foreach") + 1;
        size_t iterNameEnd = source.find_first_of(" \n\r()[].;,", iterNameStart);
        if (iterNameEnd == std::string::npos)
        {
            Log(Debug::Error) << "Shader " << templateName << " error: Unexpected EOF";
            return false;
        }
        std::string iteratorName = "$" + source.substr(iterNameStart, iterNameEnd - iterNameStart);

        size_t listStart = iterNameEnd + 1;
        size_t listEnd = source.find_first_of("\n\r", listStart);
        if (listEnd == std::string::npos)
        {
            Log(Debug::Error) << "Shader " << templateName << " error: Unexpected EOF";
            return false;
        }
        std::string list = source.substr(listStart, listEnd - listStart);
        std::vector<std::string> listElements;
        if (list != "")
            Misc::StringUtils::split(list, listElements, ",");

        size_t contentStart = source.find_first_not_of("\n\r", listEnd);
        size_t contentEnd = source.find("$endforeach", contentStart);
        if (contentEnd == std::string::npos)
        {
            Log(Debug::Error) << "Shader " << templateName << " error: Unexpected EOF";
            return false;
        }
        std::string content = source.substr(contentStart, contentEnd - contentStart);

        size_t overallEnd = contentEnd + std::string("$endforeach").length();

        size_t lineDirectivePosition = source.rfind("#line", overallEnd);
        int lineNumber;
        if (lineDirectivePosition != std::string::npos)
        {
            size_t lineNumberStart = lineDirectivePosition + std::string("#line ").length();
            size_t lineNumberEnd = source.find_first_not_of("0123456789", lineNumberStart);
            std::string lineNumberString = source.substr(lineNumberStart, lineNumberEnd - lineNumberStart);
            lineNumber = std::stoi(lineNumberString);
        }
        else
        {
            lineDirectivePosition = 0;
            lineNumber = 2;
        }
        lineNumber += std::count(source.begin() + lineDirectivePosition, source.begin() + overallEnd, '\n');

        std::string replacement;
        for (std::vector<std::string>::const_iterator element = listElements.cbegin(); element != listElements.cend(); element++)
        {
            std::string contentInstance = content;
            size_t foundIterator;
            while ((foundIterator = contentInstance.find(iteratorName)) != std::string::npos)
                contentInstance.replace(foundIterator, iteratorName.length(), *element);
            replacement += contentInstance;
        }
        replacement += "\n#line " + std::to_string(lineNumber);
        source.replace(foundPos, overallEnd - foundPos, replacement);
        return true;
    }

    bool parseLinkDirective(std::string& source, std::string& linkTarget, const std::string& templateName, size_t foundPos)
    {
        size_t endPos = foundPos + 5;
        size_t lineEnd = source.find_first_of('\n', endPos);
        // If lineEnd = npos, this is the last line, so no need to check
        std::string linkStatement = source.substr(endPos, lineEnd - endPos);
        std::regex linkRegex(
            R"r(\s*"([^"]+)"\s*)r" // Find any quoted string as the link name -> match[1]
            R"r((if\s+)r" // Begin optional condition -> match[2]
                R"r((!)?\s*)r" // Optional ! -> match[3]
                R"r(([_a-zA-Z0-9]+)?)r" // The condition -> match[4]
            R"r()?\s*)r" // End optional condition -> match[2]
        );
        std::smatch linkMatch;
        bool hasCondition = false;
        std::string linkConditionExpression;
        if (std::regex_match(linkStatement, linkMatch, linkRegex))
        {
            linkTarget = linkMatch[1].str();
            hasCondition = !linkMatch[2].str().empty();
            linkConditionExpression = linkMatch[4].str();
        }
        else
        {
            Log(Debug::Error) << "Shader " << templateName << " error: Expected a shader filename to link";
            return false;
        }
        if (linkTarget.empty())
        {
            Log(Debug::Error) << "Shader " << templateName << " error: Empty link name";
            return false;
        }

        if (hasCondition)
        {
            bool condition = !(linkConditionExpression.empty() || linkConditionExpression == "0");
            if (linkMatch[3].str() == "!")
                condition = !condition;
            
            if (!condition)
                linkTarget.clear();
        }

        source.replace(foundPos, lineEnd - foundPos, "");
        return true;
    }

    bool parseDirectives(std::string& source, std::vector<std::string>& linkedShaderTemplateNames, const ShaderManager::DefineMap& defines, const ShaderManager::DefineMap& globalDefines, const std::string& templateName)
    {
        const char escapeCharacter = '$';
        size_t foundPos = 0;

        while ((foundPos = source.find(escapeCharacter, foundPos)) != std::string::npos)
        {
            size_t endPos = source.find_first_of(" \n\r()[].;,", foundPos);
            if (endPos == std::string::npos)
            {
                Log(Debug::Error) << "Shader " << templateName << " error: Unexpected EOF";
                return false;
            }
            std::string directive = source.substr(foundPos + 1, endPos - (foundPos + 1));
            if (directive == "foreach")
            {
                if (!parseForeachDirective(source, templateName, foundPos))
                    return false;
            }
            else if (directive == "link")
            {
                std::string linkTarget;
                if (!parseLinkDirective(source, linkTarget, templateName, foundPos))
                    return false;
                if (!linkTarget.empty() && linkTarget != templateName)
                    linkedShaderTemplateNames.push_back(linkTarget);
            }
            else
            {
                Log(Debug::Error) << "Shader " << templateName << " error: Unknown shader directive: $" << directive;
                return false;
            }
        }

        return true;
    }

    bool parseDefines(std::string& source, const ShaderManager::DefineMap& defines,
        const ShaderManager::DefineMap& globalDefines, const std::string& templateName)
    {
        const char escapeCharacter = '@';
        size_t foundPos = 0;
        std::vector<std::string> forIterators;
        while ((foundPos = source.find(escapeCharacter)) != std::string::npos)
        {
            size_t endPos = source.find_first_of(" \n\r()[].;,", foundPos);
            if (endPos == std::string::npos)
            {
                Log(Debug::Error) << "Shader " << templateName << " error: Unexpected EOF";
                return false;
            }
            std::string define = source.substr(foundPos+1, endPos - (foundPos+1));
            ShaderManager::DefineMap::const_iterator defineFound = defines.find(define);
            ShaderManager::DefineMap::const_iterator globalDefineFound = globalDefines.find(define);
            if (define == "foreach")
            {
                source.replace(foundPos, 1, "$");
                size_t iterNameStart = endPos + 1;
                size_t iterNameEnd = source.find_first_of(" \n\r()[].;,", iterNameStart);
                if (iterNameEnd == std::string::npos)
                {
                    Log(Debug::Error) << "Shader " << templateName << " error: Unexpected EOF";
                    return false;
                }
                forIterators.push_back(source.substr(iterNameStart, iterNameEnd - iterNameStart));
            }
            else if (define == "endforeach")
            {
                source.replace(foundPos, 1, "$");
                if (forIterators.empty())
                {
                    Log(Debug::Error) << "Shader " << templateName << " error: endforeach without foreach";
                    return false;
                }
                else
                    forIterators.pop_back();
            }
            else if (define == "link")
            {
                source.replace(foundPos, 1, "$");
            }
            else if (std::find(forIterators.begin(), forIterators.end(), define) != forIterators.end())
            {
                source.replace(foundPos, 1, "$");
            }
            else if (defineFound != defines.end())
            {
                source.replace(foundPos, endPos - foundPos, defineFound->second);
            }
            else if (globalDefineFound != globalDefines.end())
            {
                source.replace(foundPos, endPos - foundPos, globalDefineFound->second);
            }
            else
            {
                Log(Debug::Error) << "Shader " << templateName << " error: Undefined " << define;
                return false;
            }
        }
        return true;
    }

    osg::ref_ptr<osg::Shader> ShaderManager::getShader(const std::string &templateName, const ShaderManager::DefineMap &defines, osg::Shader::Type shaderType)
    {
        std::unique_lock<std::mutex> lock(mMutex);

        // read the template if we haven't already
        TemplateMap::iterator templateIt = mShaderTemplates.find(templateName);
        if (templateIt == mShaderTemplates.end())
        {
            std::filesystem::path path = (std::filesystem::path(mPath) / templateName);
            std::ifstream stream;
            stream.open(path);
            if (stream.fail())
            {
                Log(Debug::Error) << "Failed to open " << path.string();
                return nullptr;
            }
            std::stringstream buffer;
            buffer << stream.rdbuf();

            // parse includes
            int fileNumber = 1;
            std::string source = buffer.str();
            if (!addLineDirectivesAfterConditionalBlocks(source)
                || !parseIncludes(std::filesystem::path(mPath), source, templateName, fileNumber, {}))
                return nullptr;

            templateIt = mShaderTemplates.insert(std::make_pair(templateName, source)).first;
        }

        ShaderMap::iterator shaderIt = mShaders.find(std::make_pair(templateName, defines));
        if (shaderIt == mShaders.end())
        {
            std::string shaderSource = templateIt->second;
            std::vector<std::string> linkedShaderNames;
            if (!createSourceFromTemplate(shaderSource, linkedShaderNames, templateName, defines))
            {
                // Add to the cache anyway to avoid logging the same error over and over.
                mShaders.insert(std::make_pair(std::make_pair(templateName, defines), nullptr));
                return nullptr;
            }

            osg::ref_ptr<osg::Shader> shader (new osg::Shader(shaderType));
            shader->setShaderSource(shaderSource);
            // Assign a unique prefix to allow the SharedStateManager to compare shaders efficiently.
            // Append shader source filename for debugging.
            static unsigned int counter = 0;
            shader->setName(Misc::StringUtils::format("%u %s", counter++, templateName));

            lock.unlock();
            getLinkedShaders(shader, linkedShaderNames, defines);
            lock.lock();

            shaderIt = mShaders.insert(std::make_pair(std::make_pair(templateName, defines), shader)).first;
        }
        return shaderIt->second;
    }

    osg::ref_ptr<osg::Program> ShaderManager::getProgram(osg::ref_ptr<osg::Shader> vertexShader, osg::ref_ptr<osg::Shader> fragmentShader, const osg::Program* programTemplate)
    {
        std::lock_guard<std::mutex> lock(mMutex);
        ProgramMap::iterator found = mPrograms.find(std::make_pair(vertexShader, fragmentShader));
        if (found == mPrograms.end())
        {
            if (!programTemplate) programTemplate = mProgramTemplate;
            osg::ref_ptr<osg::Program> program = programTemplate ? cloneProgram(programTemplate) : osg::ref_ptr<osg::Program>(new osg::Program);
            program->addShader(vertexShader);
            program->addShader(fragmentShader);
            addLinkedShaders(vertexShader, program);
            addLinkedShaders(fragmentShader, program);

            found = mPrograms.insert(std::make_pair(std::make_pair(vertexShader, fragmentShader), program)).first;
        }
        return found->second;
    }

    osg::ref_ptr<osg::Program> ShaderManager::cloneProgram(const osg::Program* src)
    {
        osg::ref_ptr<osg::Program> program = static_cast<osg::Program*>(src->clone(osg::CopyOp::SHALLOW_COPY));
        for (auto& [name, idx] : src->getUniformBlockBindingList())
            program->addBindUniformBlock(name, idx);
        return program;
    }

    ShaderManager::DefineMap ShaderManager::getGlobalDefines()
    {
        return DefineMap(mGlobalDefines);
    }

    void ShaderManager::setGlobalDefines(DefineMap & globalDefines)
    {
        mGlobalDefines = globalDefines;
        for (const auto& [key, shader]: mShaders)
        {
            std::string templateId = key.first;
            ShaderManager::DefineMap defines = key.second;
            if (shader == nullptr)
                // I'm not sure how to handle a shader that was already broken as there's no way to get a potential replacement to the nodes that need it.
                continue;
            std::string shaderSource = mShaderTemplates[templateId];
            std::vector<std::string> linkedShaderNames;
            if (!createSourceFromTemplate(shaderSource, linkedShaderNames, templateId, defines))
                // We just broke the shader and there's no way to force existing objects back to fixed-function mode as we would when creating the shader.
                // If we put a nullptr in the shader map, we just lose the ability to put a working one in later.
                continue;
            shader->setShaderSource(shaderSource);

            getLinkedShaders(shader, linkedShaderNames, defines);
        }
    }

    void ShaderManager::releaseGLObjects(osg::State *state)
    {
        std::lock_guard<std::mutex> lock(mMutex);
        for (const auto& [_, shader] : mShaders)
        {
            if (shader != nullptr)
                shader->releaseGLObjects(state);
        }
        for (const auto& [_, program] : mPrograms)
            program->releaseGLObjects(state);
    }

    bool ShaderManager::createSourceFromTemplate(std::string& source, std::vector<std::string>& linkedShaderTemplateNames, const std::string& templateName, const ShaderManager::DefineMap& defines)
    {
        if (!parseDefines(source, defines, mGlobalDefines, templateName))
            return false;
        if (!parseDirectives(source, linkedShaderTemplateNames, defines, mGlobalDefines, templateName))
            return false;
        return true;
    }

    void ShaderManager::getLinkedShaders(osg::ref_ptr<osg::Shader> shader, const std::vector<std::string>& linkedShaderNames, const DefineMap& defines)
    {
        mLinkedShaders.erase(shader);
        if (linkedShaderNames.empty())
            return;

        for (auto& linkedShaderName : linkedShaderNames)
        {
            auto linkedShader = getShader(linkedShaderName, defines, shader->getType());
            if (linkedShader)
                mLinkedShaders[shader].emplace_back(linkedShader);
        }
    }

    void ShaderManager::addLinkedShaders(osg::ref_ptr<osg::Shader> shader, osg::ref_ptr<osg::Program> program)
    {
        auto linkedIt = mLinkedShaders.find(shader);
        if (linkedIt != mLinkedShaders.end())
            for (const auto& linkedShader : linkedIt->second)
                program->addShader(linkedShader);
    }

    int ShaderManager::reserveGlobalTextureUnits(Slot slot)
    {
        int unit = mReservedTextureUnitsBySlot[static_cast<int>(slot)];
        if (unit >= 0)
            return unit;

        {
            // Texture units from `8 - numberOfShadowMaps` to `8` are used for shadows, so we skip them here.
            // TODO: Maybe instead of fixed texture units use `reserveGlobalTextureUnits` for shadows as well.
            static const int numberOfShadowMaps = Settings::Manager::getBool("enable shadows", "Shadows") ?
                                                  std::clamp(Settings::Manager::getInt("number of shadow maps", "Shadows"), 1, 8) :
                                                  0;
            if (getAvailableTextureUnits() >= 8 && getAvailableTextureUnits() - 1 < 8)
                mReservedTextureUnits = mMaxTextureUnits - (8 - numberOfShadowMaps);
        }

        if (getAvailableTextureUnits() < 2)
            throw std::runtime_error("Can't reserve texture unit; no available units");
        mReservedTextureUnits++;

        unit = mMaxTextureUnits - mReservedTextureUnits;

        mReservedTextureUnitsBySlot[static_cast<int>(slot)] = unit;

        return unit;
    }

}