ParryShell/parser.cpp at main · parthpathak1201/ParryShell · GitHub

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//
// Created by Parth Pathak on 17/05/26.
//

#include"parser.h"


#include<string>
#include<vector>

using string = std::string;
using vecS = std::vector<string>;

namespace {

constexprsize_tkMaxRawInputLength = 4096;
constexprsize_tkMaxTokens = 64;
constexprsize_tkMaxTokenLength = 1024;

vecS make_error(const string &message) {
return {"ERR", message};
}

boolis_var_start(constunsignedchar c) {
returnstd::isalpha(c) != 0 || c == '_';
}

boolis_var_char(constunsignedchar c) {
returnstd::isalnum(c) != 0 || c == '_';
}

boolhas_unquoted_syntax_error(const string &input, string &error_message) {
bool in_single = false;
bool in_double = false;
bool escape_next = false;
size_t pipe_count = 0;

for (size_t i = 0; i < input.size(); ++i) {
constchar c = input[i];

if (escape_next) {
 escape_next = false;
continue;
 }

if (c == '\\' && !in_single) {
 escape_next = true;
continue;
 }

if (c == '\'' && !in_double) {
 in_single = !in_single;
continue;
 }

if (c == '"' && !in_single) {
 in_double = !in_double;
continue;
 }

if (in_single || in_double) {
continue;
 }

if (c == '`') {
 error_message = "Error: Command chaining (&&, ||, ;) is not supported in ParryShell.";
returntrue;
 }

if (c == '$' && i + 1 < input.size() && input[i + 1] == '(') {
 error_message = "Error: Command chaining (&&, ||, ;) is not supported in ParryShell.";
returntrue;
 }

if (c == ';') {
 error_message = "Error: Command chaining (&&, ||, ;) is not supported in ParryShell.";
returntrue;
 }

if (c == '&' && i + 1 < input.size() && input[i + 1] == '&') {
 error_message = "Error: Command chaining (&&, ||, ;) is not supported in ParryShell.";
returntrue;
 }

if (c == '|' && i + 1 < input.size() && input[i + 1] == '|') {
 error_message = "Error: Command chaining (&&, ||, ;) is not supported in ParryShell.";
returntrue;
 }

if (c == '|') {
 ++pipe_count;
if (pipe_count > 1) {
 error_message = "Error: ParryShell supports only a single pipe.";
returntrue;
 }
 }
 }

returnfalse;
}

string expand_environment(const string &input) {
 string output;
 output.reserve(input.size());

bool in_single = false;
bool in_double = false;
bool escape_next = false;

for (size_t i = 0; i < input.size(); ++i) {
constchar c = input[i];

if (escape_next) {
 output.push_back(c);
 escape_next = false;
continue;
 }

if (c == '\\' && !in_single) {
 output.push_back(c);
 escape_next = true;
continue;
 }

if (c == '\'' && !in_double) {
 in_single = !in_single;
 output.push_back(c);
continue;
 }

if (c == '"' && !in_single) {
 in_double = !in_double;
 output.push_back(c);
continue;
 }

if (c == '$' && !in_single) {
if (i + 1 < input.size() && input[i + 1] == '{') {
size_t j = i + 2;
if (j < input.size() && is_var_start(static_cast<unsignedchar>(input[j]))) {
 ++j;
while (j < input.size() && is_var_char(static_cast<unsignedchar>(input[j]))) {
 ++j;
 }

if (j < input.size() && input[j] == '}') {
const string var_name = input.substr(i + 2, j - (i + 2));
constchar *value = std::getenv(var_name.c_str());
if (value) {
 output.append(value);
 } else {
 output.append(input.substr(i, j - i + 1));
 }
 i = j;
continue;
 }
 }
 } elseif (i + 1 < input.size() && is_var_start(static_cast<unsignedchar>(input[i + 1]))) {
size_t j = i + 2;
while (j < input.size() && is_var_char(static_cast<unsignedchar>(input[j]))) {
 ++j;
 }

const string var_name = input.substr(i + 1, j - (i + 1));
constchar *value = std::getenv(var_name.c_str());
if (value) {
 output.append(value);
 } else {
 output.append(input.substr(i, j - i));
 }
 i = j - 1;
continue;
 }
 }

 output.push_back(c);
 }

return output;
}

boolmaybe_emit_operator(const string &input, size_t &i, string &current, vecS &tokens, bool &token_started) {
auto flush_current = [&]() {
if (token_started) {
 tokens.push_back(current);
 current.clear();
 token_started = false;
 }
 };

if (i >= input.size()) {
returnfalse;
 }

constchar c = input[i];

if (c == '2' && token_started == false) {
if (i + 3 < input.size() && input.compare(i, 4, "2>&1") == 0) {
flush_current();
 tokens.emplace_back("2>&1");
 i += 3;
returntrue;
 }

if (i + 2 < input.size() && input.compare(i, 3, "2>>") == 0) {
flush_current();
 tokens.emplace_back("2>>");
 i += 2;
returntrue;
 }

if (i + 1 < input.size() && input.compare(i, 2, "2>") == 0) {
flush_current();
 tokens.emplace_back("2>");
 ++i;
returntrue;
 }
 }

if (c == '>' || c == '<' || c == '|' || c == '&') {
flush_current();

if (c == '>' && i + 1 < input.size() && input[i + 1] == '>') {
 tokens.emplace_back(">>");
 ++i;
 } else {
 tokens.emplace_back(string(1, c));
 }

returntrue;
 }

returnfalse;
}

vecS tokenize(const string &input) {
 vecS tokens;
 string current;
bool in_single = false;
bool in_double = false;
bool escape_next = false;
bool token_started = false;

auto flush_current = [&]() {
if (token_started) {
 tokens.push_back(current);
 current.clear();
 token_started = false;
 }
 };

for (size_t i = 0; i < input.size(); ++i) {
constchar c = input[i];

if (escape_next) {
 current.push_back(c);
 token_started = true;
 escape_next = false;
continue;
 }

if (!in_single && c == '\\') {
 escape_next = true;
 token_started = true;
continue;
 }

if (!in_double && c == '\'') {
 in_single = !in_single;
 token_started = true;
continue;
 }

if (!in_single && c == '"') {
 in_double = !in_double;
 token_started = true;
continue;
 }

if (!in_single && !in_double && std::isspace(static_cast<unsignedchar>(c)) != 0) {
flush_current();
continue;
 }

if (!in_single && !in_double) {
if (c == '~' && !token_started) {
constchar *home = std::getenv("HOME");
 current.append(home ? home : "~");
 token_started = true;
continue;
 }

size_t op_index = i;
if (maybe_emit_operator(input, op_index, current, tokens, token_started)) {
 i = op_index;
continue;
 }
 }

 current.push_back(c);
 token_started = true;
 }

if (escape_next) {
 current.push_back('\\');
 token_started = true;
 }

flush_current();
return tokens;
}

boolvalidate_tokens(const vecS &tokens, string &error_message) {
if (tokens.size() > kMaxTokens) {
 error_message = "Error: Too many arguments. Maximum 64 allowed.";
returnfalse;
 }

for (constauto &token : tokens) {
if (token.size() > kMaxTokenLength) {
 error_message = "Error: Argument too long. Maximum 1024 characters per argument.";
returnfalse;
 }
 }

returntrue;
}

} // namespace

vecS parse_(const string& command) {
if (command.size() > kMaxRawInputLength) {
returnmake_error("Error: Command too long. Maximum 4096 characters.");
 }

const string expanded = expand_environment(command);

 string syntax_error;
if (has_unquoted_syntax_error(expanded, syntax_error)) {
returnmake_error(syntax_error);
 }

 vecS tokens = tokenize(expanded);

if (tokens.empty()) {
return tokens;
 }

if (!validate_tokens(tokens, syntax_error)) {
returnmake_error(syntax_error);
 }

return tokens;
}