feat(osdb): basic read loop

src/build.rs

@@ -0,0 +1,9 @@
+use std::process::Command;
+fn main() {
+    let output = Command::new("git")
+        .args(&["rev-parse", "HEAD"])
+        .output()
+        .unwrap();
+    let git_hash = String::from_utf8(output.stdout).unwrap();
+    println!("cargo:rustc-env=GIT_HASH={}", git_hash);
+}

src/main.rs

@@ -1,3 +1,73 @@
-fn main() {
-    println!("Hello, world!");
+enum MetaCommand {
+    Exit,
+}
+
+enum MetaCommandParseError {
+    Unrecognized { cmd: String },
+}
+
+impl std::fmt::Display for MetaCommandParseError {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        match self {
+            MetaCommandParseError::Unrecognized { cmd } => {
+                write!(f, "unrecognized meta-command {cmd:?}")
+            }
+        }
+    }
+}
+
+impl std::str::FromStr for MetaCommand {
+    type Err = MetaCommandParseError;
+
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        match s.trim() {
+            ".exit" => Ok(MetaCommand::Exit),
+            cmd => Err(MetaCommandParseError::Unrecognized {
+                cmd: cmd.to_string(),
+            }),
+        }
+    }
+}
+
+fn main() {
+    startup_msg();
+    while let Some(input) = read_input() {
+        match input.parse() {
+            Ok(cmd) => match cmd {
+                MetaCommand::Exit => {
+                    println!("Good-bye");
+                    break;
+                }
+            },
+            Err(err) => eprintln!("{err}"),
+        }
+    }
+}
+
+fn startup_msg() {
+    let name = env!("CARGO_PKG_NAME");
+    let version = env!("CARGO_PKG_VERSION");
+    let authors = env!("CARGO_PKG_AUTHORS");
+
+    println!("{name} v{version} started.",);
+    println!("Copyright 2024 {authors}. All rights reserved.")
+}
+
+fn read_input() -> Option<String> {
+    use std::io::{BufRead, Write};
+
+    print!("osdb > ");
+    std::io::stdout().flush().expect("failed to flush stdout");
+
+    let mut input = String::new();
+    let len = std::io::stdin()
+        .lock()
+        .read_line(&mut input)
+        .expect("failed to read input from stdin");
+
+    if len == 0 {
+        None
+    } else {
+        Some(input)
+    }
 }