From 79e4546664b3c44a3f42ab6f34b33c0c485b27c8 Mon Sep 17 00:00:00 2001
From: Maxwell Jeffress <max@maxwellj.xyz>
Date: Wed, 15 Jan 2025 13:46:21 +1100
Subject: [PATCH] Add source code

---
 src/main.cpp | 131 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 131 insertions(+)
 create mode 100644 src/main.cpp

diff --git a/src/main.cpp b/src/main.cpp
new file mode 100644
index 0000000..df45e8a
--- /dev/null
+++ b/src/main.cpp
@@ -0,0 +1,131 @@
+#include <iostream>
+#include <string>
+#include <vector>
+
+#include <filesystem>
+#include <unistd.h>
+#include <sys/wait.h>
+#include <cstring>
+
+using namespace std;
+
+vector<string> builtInFunctions = {"exit", "cd"};
+
+void log(string input) {
+    cout << input << endl;
+}
+
+string prompt() {
+    string input;
+    cout << filesystem::current_path() << " > ";
+    getline(cin, input);
+    return input;
+}
+
+string findExecutable(string executable) {
+    for (int i = 0; i < builtInFunctions.size(); i++) {
+        if (builtInFunctions[i] == executable) {
+            return executable;
+        }
+    }
+    if (filesystem::exists(executable)) {
+        if (executable[0] != '/') {
+            return "./" + executable;
+        }
+        return executable;
+    }
+    string output;
+    vector<string> path = {"/bin", "/usr/bin", "/usr/local/bin"};
+    for (int i = 0; i < path.size(); i++) {
+        output = path[i] + "/" + executable;
+        if (filesystem::exists(output)) {
+            return output;
+        } else {
+            output.clear();
+        }
+    }
+    return output;
+}
+
+vector<string> tokenise(string input) {
+    vector<string> output;
+    string currentArg;
+    for (int i = 0; i < input.size(); i++) {
+        if (input[i] == ' ' && !currentArg.empty()) {
+            output.push_back(currentArg);
+            currentArg.clear();
+        } else {
+            currentArg += input[i];
+        }
+    }
+    if (!currentArg.empty()) {
+        output.push_back(currentArg);
+    }
+    
+    string executableLocation = findExecutable(output[0]);
+    if (!executableLocation.empty()) {
+        output[0] = executableLocation;
+    } else {
+        log("Couldn't find an executable in the path");
+        output.clear();
+    }
+
+    return output;
+}
+
+int runProcess(vector<string> args) {
+    pid_t pid = fork();
+    if (pid == -1) {
+        cerr << "Fork failed!" << endl;
+        return -1;
+    }
+    if (pid == 0) {
+        vector<char*> cargs;
+        cargs.push_back(const_cast<char*>(args[0].c_str()));        
+        for (int i = 1; i < args.size(); i++) {
+            cargs.push_back(const_cast<char*>(args[i].c_str()));        
+        }
+        cargs.push_back(nullptr);
+        execvp(args[0].c_str(), cargs.data());
+        
+        cerr << "Execution failed with error " << strerror(errno) << endl;
+        _exit(1);
+    }
+    int status;
+    waitpid(pid, &status, 0);
+
+    if (WIFEXITED(status)) {
+        return WEXITSTATUS(status);
+    }
+    return -1;
+}
+
+int main(int argc, char *argv[]) {
+    bool continueLoop = true;
+    while (continueLoop) {
+        string input = prompt();
+        if (input == "") {
+            break;
+        }
+        vector<string> tokens = tokenise(input);
+        auto path = filesystem::current_path();
+        if (tokens[0] == "exit") {
+            exit(0);
+        } else if (tokens[0] == "cd") {
+            if (tokens.size() == 1) {
+                log("cd requires an argument");
+            } else {
+                filesystem::current_path(tokens[1]);
+            }
+            continue;
+        }
+        if (tokens.empty()) {
+            continue;
+        }
+        int returnCode = runProcess(tokens);
+        if (returnCode != 0) {
+            log("Process failed with error code " + to_string(returnCode));
+        }
+    }
+    return 0;
+}