basic functionality works

.gitignore

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+target

Cargo.lock

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+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 4
+
+[[package]]
+name = "getopts"
+version = "0.2.21"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "14dbbfd5c71d70241ecf9e6f13737f7b5ce823821063188d7e46c41d371eebd5"
+dependencies = [
+ "unicode-width",
+]
+
+[[package]]
+name = "proc-macro2"
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+dependencies = [
+ "unicode-ident",
+]
+
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+ "proc-macro2",
+]
+
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+dependencies = [
+ "proc-macro2",
+ "quote",
+ "unicode-ident",
+]
+
+[[package]]
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+ "thiserror-impl",
+]
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+dependencies = [
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "timars"
+version = "0.1.0"
+dependencies = [
+ "getopts",
+ "thiserror",
+]
+
+[[package]]
+name = "unicode-ident"
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Cargo.toml

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+[package]
+name = "timars"
+version = "0.1.0"
+edition = "2024"
+publish = false
+authors = ["Christoph J. Scherr <software@cscherr.de>"]
+license = "MIT"
+readme = "README.md"
+homepage = "https://git.cscherr.de/PlexSheep/rs-base"
+repository = "https://git.cscherr.de/PlexSheep/rs-base"
+
+
+[dependencies]
+getopts = "0.2.21"
+thiserror = "2.0.12"

README.md

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 # timars
 
+Timars is two things at once: It lets you calculate time between two clock times, 
+and it lets you hide some secret beneath an intended binary exploitation.
+

src/main.rs

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+use std::fmt::Display;
+use std::ops::Sub;
+use std::str::FromStr;
+
+use getopts::Options;
+use thiserror::Error;
+
+const FLAG: &str = "FlÂG{E1nb38V9a3V5e86HzlY27UFAErIP5mA34kES9fbu}";
+
+fn options() -> Options {
+    let mut opts = Options::new();
+
+    opts.reqopt(
+        "f",
+        "from",
+        "calculate time starting from this time",
+        "HH:MM",
+    );
+    opts.reqopt("t", "to", "calculate time until this time", "HH:MM");
+
+    opts.optflag("h", "help", "print this help menu");
+
+    opts
+}
+
+struct Timestamp {
+    hour: i8,
+    minute: i8,
+}
+
+#[derive(Error, Debug)]
+enum TimestampParseError {
+    #[error("Too many or too few separators ':'")]
+    BadAmountOfSeparators,
+    #[error("Time numbers t must fullfill 0 < t < 60 (was {0})")]
+    InvalidTimeNumber(i8),
+    #[error(transparent)]
+    ParseInt(#[from] std::num::ParseIntError),
+}
+
+impl Sub for Timestamp {
+    type Output = Self;
+
+    fn sub(self, rhs: Self) -> Self::Output {
+        if self.minute >= rhs.minute {
+            Timestamp {
+                hour: self.hour - rhs.hour,
+                minute: self.minute - rhs.minute,
+            }
+        } else {
+            Timestamp {
+                hour: self.hour - rhs.hour - 1,
+                minute: 60 + self.minute - rhs.minute,
+            }
+        }
+    }
+}
+
+impl Display for Timestamp {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{:02}:{:02}", self.hour, self.minute)
+    }
+}
+
+impl FromStr for Timestamp {
+    fn from_str(s: &str) -> Result<Self, Self::Err> {
+        let parts: Vec<&str> = s.split(":").collect();
+        if parts.len() != 2 {
+            return Err(TimestampParseError::BadAmountOfSeparators);
+        }
+
+        let hour: i8 = parts[0].parse()?;
+        let minute: i8 = parts[1].parse()?;
+
+        if hour > 59 {
+            return Err(TimestampParseError::InvalidTimeNumber(hour));
+        }
+        if minute > 59 {
+            return Err(TimestampParseError::InvalidTimeNumber(minute));
+        }
+
+        let t = Timestamp { hour, minute };
+        Ok(t)
+    }
+
+    type Err = TimestampParseError;
+}
+
+fn main() {
+    let args: Vec<String> = std::env::args().collect();
+    let program = args[0].clone();
+    let opts = options();
+    let matches = match opts.parse(&args[1..]) {
+        Ok(m) => m,
+        Err(f) => usage(&program, &opts),
+    };
+    let from_time: Timestamp = match matches.opt_str("from").expect("thats required").parse() {
+        Ok(t) => t,
+        Err(e) => {
+            eprintln!("{e}");
+            usage(&program, &opts)
+        }
+    };
+    let to_time: Timestamp = match matches.opt_str("to").expect("thats required").parse() {
+        Ok(t) => t,
+        Err(e) => {
+            eprintln!("{e}");
+            usage(&program, &opts)
+        }
+    };
+
+    println!("from\t\t: {from_time}");
+    println!("to\t\t: {to_time}");
+    println!("difference\t: {}", to_time - from_time)
+}
+
+fn usage(program: &str, opts: &Options) -> ! {
+    let brief = format!("Usage: {} FILE [options]", program);
+    print!("{}", opts.usage(&brief));
+    std::process::exit(1)
+}