namespace Parser {
    String* standard_in;
    String* parser_file;
    int parser_line;
    int parser_col;

    proc eat_comment_line(char* text, int* index_in_text) -> void {
        // safety check if we are actually starting a comment here
        if (text[*index_in_text] != ';')
            return;

        // eat the comment line
        do {
            ++(*index_in_text);
            ++parser_col;
        } while (text[(*index_in_text)] != '\n' &&
                 text[(*index_in_text)] != '\r' &&
                 text[(*index_in_text)] != '\0');
    }

    proc step_char(char* text, int* index_in_text, int steps = 1) {
        for (int i = 0; i < steps; ++i) {
            if (text[(*index_in_text)] == '\n') {
                ++parser_line;
                parser_col = 0;
            }
            ++parser_col;
            ++(*index_in_text);
        }
    }

    proc eat_whitespace(char* text, int* index_in_text) -> void {
        // skip whitespaces
        while (text[(*index_in_text)] == ' '  ||
               text[(*index_in_text)] == '\t' ||
               text[(*index_in_text)] == '\n' ||
               text[(*index_in_text)] == '\r')
        {
            step_char(text, index_in_text);
        }
    }

    proc eat_until_code(char* text, int* index_in_text) -> void {
        profile_this();
        int position_before;
        do {
            position_before = *index_in_text;
            eat_comment_line(text, index_in_text);
            eat_whitespace(text, index_in_text);
        } while (position_before != *index_in_text);
    }

    proc step_char_and_eat_until_code(char* text, int* index_in_text) {
        step_char(text, index_in_text);
        eat_until_code(text, index_in_text);
    }

    proc parse_fancy_delimiter(char* text, int* index_in_text, char l_delimiter, char r_delimiter, Lisp_Object* first_elem) -> Lisp_Object* {
        profile_this();
        if (text[*index_in_text] != l_delimiter) {
            create_parsing_error("a fancy cannot be parsed here");
            return nullptr;
        }

        Lisp_Object* ret;
        Lisp_Object* head;
        try ret = Memory::create_lisp_object_pair(first_elem, Memory::nil);
        head = ret;

        step_char(text, index_in_text);

        eat_until_code(text, index_in_text);
        while (text[*index_in_text] != r_delimiter) {
            Lisp_Object* element;
            try element = parse_expression(text, index_in_text);
            try head->value.pair.rest = Memory::create_lisp_object_pair(element, Memory::nil);
            head = head->value.pair.rest;
            eat_until_code(text, index_in_text);
        }

        step_char(text, index_in_text);

        return ret;
    }

    proc get_atom_text_length(char* text, int* index_in_text) -> int {
        int atom_length = 0;
        while (text[*index_in_text+atom_length] != ' '  &&
               text[*index_in_text+atom_length] != ')'  &&
               text[*index_in_text+atom_length] != '('  &&
               text[*index_in_text+atom_length] != '['  &&
               text[*index_in_text+atom_length] != ']'  &&
               text[*index_in_text+atom_length] != '{'  &&
               text[*index_in_text+atom_length] != '}'  &&
               text[*index_in_text+atom_length] != '\0' &&
               text[*index_in_text+atom_length] != '\n' &&
               text[*index_in_text+atom_length] != '\r' &&
               text[*index_in_text+atom_length] != '\t')
        {
            ++atom_length;
        }
        return atom_length;
    }

    proc parse_number(char* text, int* index_in_text) -> Lisp_Object* {
        Lisp_Object* ret;
        try ret = Memory::create_lisp_object(0.0);

        sscanf(text+*index_in_text, "%lf", &ret->value.number);

        int atom_length = get_atom_text_length(text, index_in_text);
        step_char(text, index_in_text, atom_length);

        return ret;
    }

    proc parse_symbol_or_keyword(char* text, int* index_in_text) -> Lisp_Object* {
        bool keyword = false;
        if (text[*index_in_text] == ':') {
            keyword = true;
            step_char(text, index_in_text);
        }

        int atom_length = get_atom_text_length(text, index_in_text);
        char orig = text[*index_in_text+atom_length];
        text[*index_in_text+atom_length] = '\0';


        String* str_keyword;
        Lisp_Object* ret;
        try str_keyword = Memory::create_string("", atom_length);
        strcpy(&str_keyword->data, text+*index_in_text);

        if (keyword) {
            try ret = Memory::get_keyword(str_keyword);
        } else {
            try ret = Memory::get_symbol(str_keyword);
        }


        text[*index_in_text+atom_length] = orig;
        step_char(text, index_in_text, atom_length);

        return ret;
    }

    proc parse_string(char* text, int* index_in_text) -> Lisp_Object* {
        // the first character is the '"'
        step_char(text, index_in_text);

        // now we are at the first letter, if this is the closing '"' then
        // it's easy
        if (text[*index_in_text] == '"') {
            Lisp_Object* ret;
            try ret = Memory::create_lisp_object(Memory::create_string("", 0));
            // inject_scl(ret);

            // plus one because we want to go after the quotes
            step_char(text, index_in_text);

            return ret;
        }

        // okay so the first letter was not actually closing the string...
        int string_length = 0;
        bool escaping = false;
        while (escaping || text[*index_in_text+string_length] != '"') {
            if (escaping) {
                escaping = false;
            }
            else
                if (text[*index_in_text+string_length] == '\\')
                    escaping = true;

            ++string_length;
        }

        // we found the end of the string
        text[*index_in_text+string_length] = '\0';

        // NOTE(Felix): Tactic: Through unescaping the string will
        // only get shorter, so we replace it inplace and later jump
        // to the original end of the string.
        int new_len;
        try new_len = unescape_string(text+(*index_in_text));

        String* string = Memory::create_string("", new_len);

        strcpy(&string->data, text+(*index_in_text));
        // printf("------ %s\n", &string->data);

        text[*index_in_text+string_length] = '"';

        // plus one because we want to go after the quotes
        step_char(text, index_in_text, string_length+1);

        Lisp_Object* ret;
        try ret = Memory::create_lisp_object(string);

        // inject_scl(ret);
        return ret;
    }

    proc parse_atom(char* text, int* index_in_text) -> Lisp_Object* {
        profile_this();
        Lisp_Object* ret;
        // numbers
        if ((text[*index_in_text] <= 57 &&   // if number
             text[*index_in_text] >= 48)
            ||
            ((text[*index_in_text] == '+' || // or if sign and then number
              text[*index_in_text] == '-')
             &&
             (text[*index_in_text +1] <= 57 &&
              text[*index_in_text +1] >= 48))
            ||
            ((text[*index_in_text] == '.')  // or if . and then number
             &&
             (text[*index_in_text +1] <= 57 &&
              text[*index_in_text +1] >= 48)))
        {
            try ret = parse_number(text, index_in_text);
        }

        else if (text[*index_in_text] == '"')
            try ret = parse_string(text, index_in_text);
        else
            try ret = parse_symbol_or_keyword(text, index_in_text);

        return ret;
    }



    proc parse_list(char* text, int* index_in_text) -> Lisp_Object* {
        profile_this();
        if (text[*index_in_text] != '(') {
            create_parsing_error("a list cannot be parsed here");
            return nullptr;
        }
        step_char_and_eat_until_code(text, index_in_text);

        if (text[*index_in_text] == ')') {
            step_char(text, index_in_text);
            return Memory::nil;
        }

        Lisp_Object* first_elem;
        Lisp_Object* ret;
        Lisp_Object* head;


        try first_elem = parse_expression(text, index_in_text);
        try ret = Memory::create_lisp_object_pair(first_elem, Memory::nil);
        head = ret;

        eat_until_code(text, index_in_text);
        while (text[*index_in_text] != ')') {
            Lisp_Object* element;

            if (text[*index_in_text+0] == '.' &&
                text[*index_in_text+1] == ' ')
            {
                step_char(text, index_in_text, 2);
                try element = parse_expression(text, index_in_text);
                head->value.pair.rest = element;

                eat_until_code(text, index_in_text);
                if (text[*index_in_text] != ')') {
                    create_parsing_error("expected the list to end after the dotted end.");
                    return nullptr;
                }
                step_char(text, index_in_text);
                return ret;
            }

            try element = parse_expression(text, index_in_text);
            try head->value.pair.rest = Memory::create_lisp_object_pair(element, Memory::nil);
            head = head->value.pair.rest;
            eat_until_code(text, index_in_text);
        }
        step_char(text, index_in_text);
        return ret;
    }

    proc maybe_expand_short_form(char* text, int* index_in_text) -> Lisp_Object* {
        profile_this();
        Lisp_Object* vector_sym           = Memory::get_symbol("vector");
        Lisp_Object* hash_map_sym         = Memory::get_symbol("hash-map");

        Lisp_Object* quote_sym            = Memory::get_symbol("quote");
        Lisp_Object* quasiquote_sym       = Memory::get_symbol("quasiquote");
        Lisp_Object* unquote_sym          = Memory::get_symbol("unquote");
        Lisp_Object* unquote_splicing_sym = Memory::get_symbol("unquote-splicing");

        Lisp_Object* ret = nullptr;
        Lisp_Object* expr;

        switch (text[*index_in_text]) {
        case '\'': {
            // quote
            step_char_and_eat_until_code(text, index_in_text);
            try expr = parse_expression(text, index_in_text);
            try ret = Memory::create_lisp_object_pair(expr, Memory::nil);
            try ret = Memory::create_lisp_object_pair(quote_sym, ret);
        } break;
        case '`': {
            // quasiquote
            step_char_and_eat_until_code(text, index_in_text);
            try expr = parse_expression(text, index_in_text);
            try ret = Memory::create_lisp_object_pair(expr, Memory::nil);
            try ret = Memory::create_lisp_object_pair(quasiquote_sym, ret);
        } break;
        case ',': {
            step_char_and_eat_until_code(text, index_in_text);
            if (text[*index_in_text] == '@') {
                // unquote-splicing
                step_char_and_eat_until_code(text, index_in_text);
                try expr = parse_expression(text, index_in_text);
                try ret = Memory::create_lisp_object_pair(expr, Memory::nil);
                try ret = Memory::create_lisp_object_pair(unquote_splicing_sym, ret);
            } else {
                // unquote
                try expr = parse_expression(text, index_in_text);
                try ret = Memory::create_lisp_object_pair(expr, Memory::nil);
                try ret = Memory::create_lisp_object_pair(unquote_sym, ret);
            }
        } break;
        case '[': {
            // vector
            try ret = parse_fancy_delimiter(text, index_in_text, '[', ']', vector_sym);
        } break;
        case '{': {
            // hashmap
            try ret = parse_fancy_delimiter(text, index_in_text, '{', '}', hash_map_sym);
        } break;
        default: break;
        }

        return ret;
    }

    proc parse_expression(char* text, int* index_in_text) -> Lisp_Object* {
        profile_this();
        Lisp_Object* ret;
        eat_until_code(text, index_in_text);
        try ret = maybe_expand_short_form(text, index_in_text);
        if (ret)
            return ret;

        if (text[*index_in_text] == '(') {
            try ret = parse_list(text, index_in_text);
        } else {
            try ret = parse_atom(text, index_in_text);
        }

        return ret;
    }

    proc parse_single_expression(wchar_t* text) -> Lisp_Object* {
        char* res = wchar_to_char(text);
        defer {free(res);};
        return parse_single_expression(res);
    }

    proc parse_single_expression(char* text) -> Lisp_Object* {
        parser_file = standard_in;
        parser_line = 1;
        parser_col = 1;

        int index_in_text = 0;
        Lisp_Object* ret;
        try ret = parse_expression(text, &index_in_text);
        return ret;
    }


    proc parse_program(String* file_name, char* text) -> Array_List<Lisp_Object*>* {
        profile_this();
        parser_file = file_name;
        parser_line = 1;
        parser_col = 0;

        Array_List<Lisp_Object*>* program = new Array_List<Lisp_Object*>;

        int index_in_text = 0;
        Lisp_Object* parsed;

        eat_until_code(text, &index_in_text);
        while (text[index_in_text] != '\0') {
            try parsed = parse_expression(text, &index_in_text);
            program->append(parsed);
            eat_until_code(text, &index_in_text);
        }
        return program;
    }

}