PS1 variable support, ~ expansion and pretty pwd

- if arsh has a PS1 env var, it will use it to display prompt. It
supports esc sequences, \u, \w
- if '~' is used, it will be expanded to $HOME env var value
- if PS1 env var uses \w, and $PWD is somewhere inside $HOME, then it
will show '~' in prompt instead of a long path
- arsh sets $SHELL env var on startup

main.c

@@ -9,13 +9,21 @@
 #include <ctype.h>
 
 constexpr size_t max_length = 1024;
-constexpr size_t max_env_var_lenght = 256;
+constexpr size_t max_env_var_length = 256;
 const char* token_separators = " \t\n\r";
+char* esc = "\x1B";
+
+char* default_prompt = "arsh> ";
 
 static sigjmp_buf restart_jmp_buf;
 static constexpr int restart_value = 69;
 static volatile sig_atomic_t jump_active = 0;
 
+size_t min_size_t(size_t a, size_t b)
+{
+  return a > b ? b : a;
+}
+
 void sigint_handler(int signo)
 {
   if(!jump_active)
@@ -168,6 +176,7 @@ static void append_str(char** buf, size_t* len, size_t* cap, const char* s)
 
 struct pipeline* parse_pipeline(char *str);
 int execute_pipeline(struct pipeline* pl, int capture, char** out);
+char* get_home();
 
 static char* run_subcommand(const char* cmd)
 {
@@ -223,6 +232,13 @@ char* parse_token(char** input)
       continue;
     }
     
+    if (!in_single && *p == '~')
+    {
+      p++;
+      append_str(&buf, &len, &cap, get_home());
+      continue;
+    }
+
     if (!in_single && *p == '\\')
     {
       p++;
@@ -288,7 +304,7 @@ char* parse_token(char** input)
       if (*p == '{')
       {
         p++;
-        char name[max_env_var_lenght];
+        char name[max_env_var_length];
         int i = 0;
         while (*p && *p != '}')
           name[i++] = *p++;
@@ -299,7 +315,7 @@ char* parse_token(char** input)
         continue;
       }
 
-      char name[max_env_var_lenght];
+      char name[max_env_var_length];
       int i = 0;
       while (*p && (isalnum(*p) || *p == '_'))
         name[i++] = *p++;
@@ -519,7 +535,13 @@ pid_t run_with_redir(struct command* command, int n_pipes, int (*pipes)[2])
 
 int cd(char* path)
 {
-  return chdir(path);
+  int result = chdir(path);
+  char cwd[max_length];
+  if (getcwd(cwd, sizeof(cwd)) != NULL)
+  {
+    setenv("PWD", cwd, 1);
+  }
+  return result;
 }
 
 int execute_pipeline(struct pipeline* pl, int capture, char** out)
@@ -618,10 +640,155 @@ int execute_pipeline(struct pipeline* pl, int capture, char** out)
     return WEXITSTATUS(status);
 }
 
+char username_buf[max_env_var_length] = {0};
+char* get_user()
+{
+  char* result = getenv("USER");
+  if(!result)
+  {
+    return "UNKNOWN";
+  }
+  size_t length = min_size_t(sizeof(username_buf), strlen(result) + 1);
+  memcpy(username_buf, result, length);
+  return username_buf;
+}
+
+char home_buf[max_length] = {0};
+char* get_home()
+{
+  char* result = getenv("HOME");
+  if(!result)
+  {
+    return "UNKNOWN_HOME_PATH";
+  }
+  size_t length = min_size_t(sizeof(home_buf), strlen(result) + 1);
+  memcpy(home_buf, result, length);
+  return home_buf;
+}
+
+char pwd_buf[max_length] = {0};
+char* get_pwd()
+{
+  char* result = getenv("PWD");
+  if(!result)
+  {
+    return "UNKNOWN";
+  }
+  size_t length = min_size_t(sizeof(pwd_buf), strlen(result) + 1);
+  memcpy(pwd_buf, result, length);
+  return pwd_buf;
+}
+
+char* prettify_pwd(char* pwd)
+{
+  if (!pwd)
+  {
+    fprintf(stderr, "Internal Error: pwd can't be null");
+    exit(1);
+  }
+  char* home = get_home();
+  size_t home_len = strlen(home);
+  size_t pwd_len = strlen(pwd);
+  if(pwd_len < home_len)
+  {
+    return pwd;
+  }
+  if(memcmp(home, pwd, home_len) == 0)
+  {
+    char* ret = ccalloc(sizeof(char), pwd_len - home_len + 1 + 1);
+    parser_allocated(ret);
+    ret[0] = '~';
+    memcpy(ret + 1, pwd + home_len, pwd_len - home_len);
+    ret[pwd_len - home_len + 1] = '\0';
+    return ret;
+  }
+  return pwd;
+}
+
+char prompt_buf[max_length] = {0};
+char* generate_ps1_prompt()
+{
+  char env_buf[max_env_var_length] = {0};
+  char* ps1 = getenv("PS1");
+  if(!ps1)
+  {
+    return default_prompt;
+  }
+  size_t ps1_len = min_size_t(sizeof(env_buf), strlen(ps1) + 1) - 1;
+  if(ps1_len == 0)
+  {
+    return default_prompt;
+  }
+  memcpy(env_buf, ps1, ps1_len);
+  env_buf[ps1_len + 1] = '\0';
+  if(ps1_len < 2)
+  {
+    memcpy(prompt_buf, env_buf, ps1_len + 1);
+    return prompt_buf;
+  }
+  size_t i = 1, j = 0;
+  size_t start = 0;
+  while(env_buf[i] != '\0' && j < sizeof(prompt_buf))
+  {
+    if(env_buf[i - 1] != '\\')
+    {
+      i++;
+      continue;
+    }
+    char* data = 0;
+    switch (env_buf[i])
+    {
+      case 'u':
+	data = get_user();
+	break;
+      case 'w':
+	data = prettify_pwd(get_pwd());
+	break;
+      case 'e':
+	data = esc;
+	break;
+      case ']':
+      case '[':
+	data = "";
+	break;
+      default:
+	i++;
+	continue;
+    }
+    if(!data)
+    {
+      i++;
+      continue;
+    }
+    size_t len = strlen(data);
+    if(j + i - 1 - start + len >= sizeof(prompt_buf))
+    {
+      fprintf(stderr, "Out of memory(1) for prompt: %d >= %d", j + i - start + len, sizeof(prompt_buf));
+      break;
+    }
+    size_t start_len = min_size_t(sizeof(prompt_buf) - j, i - start - 1);
+    memcpy(prompt_buf + j, env_buf + start, start_len);
+    j += start_len;
+    if(j + len >= sizeof(prompt_buf))
+    {
+      fprintf(stderr, "Out of memory(2) for prompt: %d >= %d", j + len, sizeof(prompt_buf));
+      break;
+    }
+    memcpy(prompt_buf + j, data, len);
+    i += 1; start = i; j += len;
+  }
+  size_t start_len = min_size_t(sizeof(prompt_buf) - j, i - start);
+  memcpy(prompt_buf + j, env_buf + start, start_len);
+  j += start_len;
+  prompt_buf[j] = '\0';
+  return prompt_buf;
+}
+
 int main(int argc, const char* argv[])
 {
+  setenv("SHELL", argv[0], 1);
   FILE* stream = stdin;
-  char* prompt = "arsh> ";
+  char* prompt = generate_ps1_prompt();
   const bool spawn_command = argc >= 2 && strcmp(argv[1], "-c") == 0;
   if(spawn_command)
   {
@@ -674,5 +841,10 @@ int main(int argc, const char* argv[])
     execute_pipeline(pipeline, 0, NULL);
 
     parser_free();
+
+    if(prompt)
+    {
+      prompt = generate_ps1_prompt();
+    }
   }
 }