Implemented .bfuck file reading

src/lex.cpp

@@ -0,0 +1,47 @@
+#include "lex.hpp"
+
+#include <iostream>
+#include <fstream>
+#include <algorithm>
+
+bool lex_brainfuck_file(const std::string &path, std::string &tokens) {
+    if (!tokens.empty()) {
+        std::cout << "Result string \"tokens\" has to be empty!" << std::endl;
+        return false;
+    }
+
+    std::ifstream input_stream;
+    input_stream.open(path, std::ios::in);
+    if (!input_stream.is_open()) {
+        std::cout << "Failed to open file \"" << path << "\"" << std::endl;
+        return false;
+    }
+
+    std::string line;
+    while (std::getline(input_stream, line)) {
+        tokens += line;
+    }
+
+    if (!input_stream.eof() && input_stream.fail()) {
+        std::cout << "Error reading from file \"" << path << "\"" << std::endl;
+        input_stream.close();
+        return false;
+    }
+    input_stream.close();
+
+    if (!token_string_valid(tokens)) {
+        std::cout << "Program is invalid!" << std::endl;
+        return false;
+    }
+
+    std::cout << "Lexed BrainFuck program:\n" << tokens << std::endl;
+    return true;
+}
+
+bool token_string_valid(const std::string_view tokens) {
+    std::string valid_tokens = "><+-.,[]";
+
+    return std::ranges::all_of(tokens.begin(), tokens.end(), [&valid_tokens](const char c){
+        return valid_tokens.find(c) != std::string::npos;
+    });
+}