#include "../include/Conf.hpp"
#include "../include/FileUtil.hpp"
#include "../external/utf8/unchecked.h"
#include <stdexcept>

using namespace std;
using u8string = utf8::unchecked::iterator<char*>;

namespace sibs
{
    u32 min(u32 a, u32 b) { return a < b ? a : b; }

    class UnexpectedTokenException : public std::runtime_error
    {
    public:
        UnexpectedTokenException(const string &errMsg) : runtime_error(errMsg)
        {

        }
    };

    enum class Token
    {
        NONE,
        END_OF_FILE,
        IDENTIFIER,
        OPEN_BRACKET,
        CLOSING_BRACKET,
        EQUALS,
        STRING
    };

    const char *getTokenName(Token token)
    {
        switch(token)
        {
            case Token::NONE:               return "NONE";
            case Token::END_OF_FILE:        return "<EOF>";
            case Token::IDENTIFIER:         return "identifier";
            case Token::OPEN_BRACKET:       return "[";
            case Token::CLOSING_BRACKET:    return "]";
            case Token::EQUALS:             return "=";
            case Token::STRING:             return "string";
            default:                        return "Unknown";
        }
    }

    class Tokenizer
    {
    public:
        Tokenizer(const char *_code) :
            currentToken(Token::NONE),
            code((char*)_code)
        {

        }

        Token nextToken()
        {
            u32 c = *code;
            while(isWhitespace(c))
            {
                ++code;
                c = *code;
            }

            if(isAlpha(c) || c == '_')
            {
                char *startOfIdentifier = code.base();
                ++code;
                c = *code;
                while(isAlpha(c) || c == '_' || isDigit(c))
                {
                    ++code;
                    c = *code;
                }
                char *endOfIdentifier = code.base();

                identifier = StringView(startOfIdentifier, endOfIdentifier - startOfIdentifier);
                return Token::IDENTIFIER;
            }
            else if(c == '[')
            {
                ++code;
                return Token::OPEN_BRACKET;
            }
            else if(c == ']')
            {
                ++code;
                return Token::CLOSING_BRACKET;
            }
            else if(c == '=')
            {
                ++code;
                return Token::EQUALS;
            }
            else if(c == '"')
            {
                u32 escapeCount = 0;

                ++code;
                char *startOfStr = code.base();
                while(escapeCount > 0 || *code != '"')
                {
                    c = *code;
                    if(c == '\0')
                        return Token::END_OF_FILE;
                    else if(c == '\\')
                        ++escapeCount;
                    else
                        escapeCount = min(0, escapeCount - 1);
                    ++code;
                }

                str = StringView(startOfStr, code.base() - startOfStr);
                ++code;
                return Token::STRING;
            }
            else if(c == '\0')
            {
                return Token::END_OF_FILE;
            }
            else
            {
                string errMsg = "Unexpected token: ";
                errMsg += (char)c;
                throw UnexpectedTokenException(errMsg);
            }
        }

        StringView getIdentifier() const { return identifier; }
        StringView getString() const { return str; }
    private:
        bool isWhitespace(u32 c)
        {
            return c == ' ' || c == '\t' || c == '\n' || c == '\r';
        }

        bool isAlpha(u32 c)
        {
            return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z');
        }

        bool isDigit(u32 c)
        {
            return c >= '0' && c <= '9';
        }
    private:
        Token currentToken;
        u8string code;

        union
        {
            StringView identifier;
            StringView str;
        };
    };

    class ParserException : public std::runtime_error
    {
    public:
        ParserException(const string &errMsg) : runtime_error(errMsg)
        {

        }
    };

    class Parser
    {
    public:
        static Result<bool> parse(const char *code, const ConfigCallback &callback)
        {
            try
            {
                Parser parser(code, (ConfigCallback*)&callback);
                parser.parse();
                return Result<bool>::Ok(true);
            }
            catch (const UnexpectedTokenException &e)
            {
                return Result<bool>::Err(e.what());
            }
            catch (const ParserException &e)
            {
                return Result<bool>::Err(e.what());
            }
        }
    private:
        Parser(const char *code, ConfigCallback *_callback) :
            tokenizer(code),
            callback(_callback),
            objectDefined(false)
        {

        }

        void parse()
        {
            while(true)
            {
                Token token = tokenizer.nextToken();
                switch(token)
                {
                    case Token::IDENTIFIER:
                    {
                        parseConfigField();
                        break;
                    }
                    case Token::OPEN_BRACKET:
                    {
                        parseConfigObject();
                        break;
                    }
                    case Token::END_OF_FILE:
                    {
                        callback->finished();
                        return;
                    }
                    default:
                    {
                        string errMsg = "Expected identifier or object, got: ";
                        errMsg += getTokenName(token);
                        throw ParserException(errMsg);
                    }
                }
            }
        }

        void parseConfigField()
        {
            StringView fieldName = tokenizer.getIdentifier();
            if (!objectDefined)
            {
                string errMsg = "An object has to be the first element defined in a config file";
                throw ParserException(errMsg);
            }

            Token token = tokenizer.nextToken();
            if(token == Token::EQUALS)
            {
                parseConfigFieldRhs(fieldName);
            }
            else
            {
                string errMsg = "Expected '=' after identifier, got: ";
                errMsg += getTokenName(token);
                throw ParserException(errMsg);
            }
        }

        void parseConfigFieldRhs(StringView fieldName)
        {
            Token token = tokenizer.nextToken();
            if(token == Token::STRING)
            {
                callback->processField(fieldName, tokenizer.getString());
            }
            else if(token == Token::OPEN_BRACKET)
            {
                token = tokenizer.nextToken();
                if(token == Token::STRING)
                {
                    StringView str = tokenizer.getString();
                    token = tokenizer.nextToken();
                    if(token == Token::CLOSING_BRACKET)
                    {
                        vector<StringView> values;
                        values.push_back(str);
                        callback->processField(fieldName, values);
                    }
                    else
                    {
                        string errMsg = "Expected ']' to close value list, got: ";
                        errMsg += getTokenName(token);
                        throw ParserException(errMsg);
                    }
                }
                else
                {
                    string errMsg = "Expected string value inside list in field definition, got: ";
                    errMsg += getTokenName(token);
                    throw ParserException(errMsg);
                }
            }
            else
            {
                string errMsg = "Expected string on right-hand side of field '";
                errMsg += string(fieldName.data, fieldName.size);
                errMsg += "', got: ";
                errMsg += getTokenName(token);
                throw ParserException(errMsg);
            }
        }

        void parseConfigObject()
        {
            Token token = tokenizer.nextToken();
            if(token == Token::IDENTIFIER)
            {
                StringView objectName = tokenizer.getIdentifier();
                token = tokenizer.nextToken();
                if(token == Token::CLOSING_BRACKET)
                {
                    objectDefined = true;
                    callback->processObject(objectName);
                }
                else
                {
                    string errMsg = "Expected ']' after identifier to close object definition, got: ";
                    errMsg += getTokenName(token);
                    throw ParserException(errMsg);
                }
            }
            else
            {
                string errMsg = "Expected identifier after '[', got: ";
                errMsg += getTokenName(token);
                throw ParserException(errMsg);
            }
        }
    private:
        Tokenizer tokenizer;
        ConfigCallback *callback;
        bool objectDefined;
    };

    Result<bool> Config::readFromFile(const char *filepath, const ConfigCallback &callback)
    {
        Result<StringView> fileContentResult = getFileContent(filepath);
        if(fileContentResult.isErr())
            return Result<bool>::Err(fileContentResult.getErrMsg());

        const char *code = fileContentResult.unwrap().data;
        if(!utf8::is_valid(code, code + fileContentResult.unwrap().size))
            return Result<bool>::Err("File is not in valid utf8 format");

        if(fileContentResult.unwrap().size >= 3 && utf8::is_bom(code))
            code += 3;

        return Parser::parse(code, callback);
    }
}