diff --git a/.envrc b/.envrc
new file mode 100644
index 0000000..82b2b9e
--- /dev/null
+++ b/.envrc
@@ -0,0 +1,9 @@
+#!/usr/bin/env bash
+# the shebang is ignored, but nice for editors
+
+if type -P lorri &>/dev/null; then
+  eval "$(lorri direnv)"
+else
+  echo 'while direnv evaluated .envrc, could not find the command "lorri" [https://github.com/nix-community/lorri]'
+  use nix
+fi
diff --git a/Cargo.lock b/Cargo.lock
index 8a761a6..e66d302 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -2,6 +2,15 @@
 # It is not intended for manual editing.
 version = 3
 
+[[package]]
+name = "aho-corasick"
+version = "1.1.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "8e60d3430d3a69478ad0993f19238d2df97c507009a52b3c10addcd7f6bcb916"
+dependencies = [
+ "memchr",
+]
+
 [[package]]
 name = "android-tzdata"
 version = "0.1.1"
@@ -17,12 +26,73 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "anstream"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0ca84f3628370c59db74ee214b3263d58f9aadd9b4fe7e711fd87dc452b7f163"
+dependencies = [
+ "anstyle",
+ "anstyle-parse",
+ "anstyle-query",
+ "anstyle-wincon",
+ "colorchoice",
+ "is-terminal",
+ "utf8parse",
+]
+
+[[package]]
+name = "anstyle"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3a30da5c5f2d5e72842e00bcb57657162cdabef0931f40e2deb9b4140440cecd"
+
+[[package]]
+name = "anstyle-parse"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "938874ff5980b03a87c5524b3ae5b59cf99b1d6bc836848df7bc5ada9643c333"
+dependencies = [
+ "utf8parse",
+]
+
+[[package]]
+name = "anstyle-query"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5ca11d4be1bab0c8bc8734a9aa7bf4ee8316d462a08c6ac5052f888fef5b494b"
+dependencies = [
+ "windows-sys",
+]
+
+[[package]]
+name = "anstyle-wincon"
+version = "1.0.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "180abfa45703aebe0093f79badacc01b8fd4ea2e35118747e5811127f926e188"
+dependencies = [
+ "anstyle",
+ "windows-sys",
+]
+
+[[package]]
+name = "anyhow"
+version = "1.0.72"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3b13c32d80ecc7ab747b80c3784bce54ee8a7a0cc4fbda9bf4cda2cf6fe90854"
+
 [[package]]
 name = "autocfg"
 version = "1.1.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "d468802bab17cbc0cc575e9b053f41e72aa36bfa6b7f55e3529ffa43161b97fa"
 
+[[package]]
+name = "bitflags"
+version = "2.3.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "630be753d4e58660abd17930c71b647fe46c27ea6b63cc59e1e3851406972e42"
+
 [[package]]
 name = "bumpalo"
 version = "3.13.0"
@@ -56,12 +126,92 @@ dependencies = [
  "winapi",
 ]
 
+[[package]]
+name = "clap"
+version = "4.3.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "1640e5cc7fb47dbb8338fd471b105e7ed6c3cb2aeb00c2e067127ffd3764a05d"
+dependencies = [
+ "clap_builder",
+ "clap_derive",
+ "once_cell",
+]
+
+[[package]]
+name = "clap_builder"
+version = "4.3.11"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "98c59138d527eeaf9b53f35a77fcc1fad9d883116070c63d5de1c7dc7b00c72b"
+dependencies = [
+ "anstream",
+ "anstyle",
+ "clap_lex",
+ "strsim",
+]
+
+[[package]]
+name = "clap_derive"
+version = "4.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b8cd2b2a819ad6eec39e8f1d6b53001af1e5469f8c177579cdaeb313115b825f"
+dependencies = [
+ "heck",
+ "proc-macro2",
+ "quote",
+ "syn",
+]
+
+[[package]]
+name = "clap_lex"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2da6da31387c7e4ef160ffab6d5e7f00c42626fe39aea70a7b0f1773f7dd6c1b"
+
+[[package]]
+name = "colorchoice"
+version = "1.0.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "acbf1af155f9b9ef647e42cdc158db4b64a1b61f743629225fde6f3e0be2a7c7"
+
 [[package]]
 name = "core-foundation-sys"
 version = "0.8.4"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "e496a50fda8aacccc86d7529e2c1e0892dbd0f898a6b5645b5561b89c3210efa"
 
+[[package]]
+name = "errno"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4bcfec3a70f97c962c307b2d2c56e358cf1d00b558d74262b5f929ee8cc7e73a"
+dependencies = [
+ "errno-dragonfly",
+ "libc",
+ "windows-sys",
+]
+
+[[package]]
+name = "errno-dragonfly"
+version = "0.1.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "aa68f1b12764fab894d2755d2518754e71b4fd80ecfb822714a1206c2aab39bf"
+dependencies = [
+ "cc",
+ "libc",
+]
+
+[[package]]
+name = "heck"
+version = "0.4.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "95505c38b4572b2d910cecb0281560f54b440a19336cbbcb27bf6ce6adc6f5a8"
+
+[[package]]
+name = "hermit-abi"
+version = "0.3.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "443144c8cdadd93ebf52ddb4056d257f5b52c04d3c804e657d19eb73fc33668b"
+
 [[package]]
 name = "iana-time-zone"
 version = "0.1.57"
@@ -85,6 +235,17 @@ dependencies = [
  "cc",
 ]
 
+[[package]]
+name = "is-terminal"
+version = "0.4.9"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cb0889898416213fab133e1d33a0e5858a48177452750691bde3666d0fdbaf8b"
+dependencies = [
+ "hermit-abi",
+ "rustix",
+ "windows-sys",
+]
+
 [[package]]
 name = "js-sys"
 version = "0.3.64"
@@ -100,12 +261,24 @@ version = "0.2.147"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b4668fb0ea861c1df094127ac5f1da3409a82116a4ba74fca2e58ef927159bb3"
 
+[[package]]
+name = "linux-raw-sys"
+version = "0.4.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09fc20d2ca12cb9f044c93e3bd6d32d523e6e2ec3db4f7b2939cd99026ecd3f0"
+
 [[package]]
 name = "log"
 version = "0.4.19"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b06a4cde4c0f271a446782e3eff8de789548ce57dbc8eca9292c27f4a42004b4"
 
+[[package]]
+name = "memchr"
+version = "2.7.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "78ca9ab1a0babb1e7d5695e3530886289c18cf2f87ec19a575a0abdce112e3a3"
+
 [[package]]
 name = "num-traits"
 version = "0.2.15"
@@ -139,6 +312,54 @@ dependencies = [
  "proc-macro2",
 ]
 
+[[package]]
+name = "regex"
+version = "1.11.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "b544ef1b4eac5dc2db33ea63606ae9ffcfac26c1416a2806ae0bf5f56b201191"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-automata",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-automata"
+version = "0.4.8"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "368758f23274712b504848e9d5a6f010445cc8b87a7cdb4d7cbee666c1288da3"
+dependencies = [
+ "aho-corasick",
+ "memchr",
+ "regex-syntax",
+]
+
+[[package]]
+name = "regex-syntax"
+version = "0.8.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2b15c43186be67a4fd63bee50d0303afffcef381492ebe2c5d87f324e1b8815c"
+
+[[package]]
+name = "rustix"
+version = "0.38.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "ac5ffa1efe7548069688cd7028f32591853cd7b5b756d41bcffd2353e4fc75b4"
+dependencies = [
+ "bitflags",
+ "errno",
+ "libc",
+ "linux-raw-sys",
+ "windows-sys",
+]
+
+[[package]]
+name = "strsim"
+version = "0.10.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "73473c0e59e6d5812c5dfe2a064a6444949f089e20eec9a2e5506596494e4623"
+
 [[package]]
 name = "syn"
 version = "2.0.23"
@@ -163,9 +384,12 @@ dependencies = [
 
 [[package]]
 name = "time-track"
-version = "0.1.0"
+version = "2.1.4"
 dependencies = [
+ "anyhow",
  "chrono",
+ "clap",
+ "regex",
 ]
 
 [[package]]
@@ -174,6 +398,12 @@ version = "1.0.10"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "22049a19f4a68748a168c0fc439f9516686aa045927ff767eca0a85101fb6e73"
 
+[[package]]
+name = "utf8parse"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "711b9620af191e0cdc7468a8d14e709c3dcdb115b36f838e601583af800a370a"
+
 [[package]]
 name = "wasi"
 version = "0.10.0+wasi-snapshot-preview1"
@@ -265,6 +495,15 @@ dependencies = [
  "windows-targets",
 ]
 
+[[package]]
+name = "windows-sys"
+version = "0.48.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "677d2418bec65e3338edb076e806bc1ec15693c5d0104683f2efe857f61056a9"
+dependencies = [
+ "windows-targets",
+]
+
 [[package]]
 name = "windows-targets"
 version = "0.48.1"
diff --git a/Cargo.toml b/Cargo.toml
index d0ed88f..74de412 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,9 +1,12 @@
 [package]
 name = "time-track"
-version = "0.1.0"
+version = "2.1.4"
 edition = "2021"
 
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+anyhow = "1.0.72"
 chrono = "0.4.26"
+clap = { version = "4.3.11", features = ["derive"] }
+regex = "1.11.1"
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..bbcf4bc
--- /dev/null
+++ b/README.md
@@ -0,0 +1,22 @@
+# time-track
+
+A simple CLI tool for tracking how much time you have left to work. I find myself stressing about whether I'm hitting 8 real hours, so this little tool helps me avoid wasting
+time calculating when my work day will end.
+
+Simply enter times, one per line and send an EOF character when you're done. The first lines opens a span of work and the next line closes it so that you can build up working
+time be clocking in and out. Finally, you can send additional arguments to the program to configure how long you intend to work (the default is 8 hours).
+
+```
+❯ time-track
+Working for 8 hours
+Input times one per line. Send an EOF character to finish inputting...
+8:30
+9:30
+11:15
+12:30
+13:16
+18:20
+19:30
+20:11 # Send an EOF
+Exactly done
+```
diff --git a/shell.nix b/shell.nix
new file mode 100644
index 0000000..157b677
--- /dev/null
+++ b/shell.nix
@@ -0,0 +1,8 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+pkgs.mkShell {
+  buildInputs = [
+    pkgs.rustc
+    pkgs.cargo
+  ] ++ [ pkgs.libiconv pkgs.darwin.apple_sdk.frameworks.CoreServices ];
+}
diff --git a/src/args.rs b/src/args.rs
new file mode 100644
index 0000000..e24e8c3
--- /dev/null
+++ b/src/args.rs
@@ -0,0 +1,19 @@
+use clap::Parser;
+
+/// A simple program to track time spans and calculate remaining hours to work
+#[derive(Parser, Debug)]
+#[command(author, version, about, long_about = None)]
+pub struct Args {
+    /// How many hours you intend to work (sums with `minutes`)
+    /// Usually defaults to 8 hours, but if discount is set then it defaults to 0
+    #[arg(long)]
+    pub hours: Option<i64>,
+
+    /// How many minutes you intend to work (sums with `hours`)
+    #[arg(long, default_value_t = 0)]
+    pub minutes: i64,
+
+    /// If true, the the hours and minutes fields are treated as subtracting from 8 hours
+    #[arg(long, default_value_t = false)]
+    pub discount: bool,
+}
diff --git a/src/main.rs b/src/main.rs
index 3ed32dd..19dc159 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -1,35 +1,65 @@
-use std::io::{stdin, Read};
-use chrono::{NaiveTime, Duration};
+use std::io::{self, BufRead};
+use chrono::{DateTime, Local};
 
-fn read_times() -> Vec<String> {
-    println!("Write all times separated by newlines and finish with CTRL+D\n");
-    let mut times = String::new();
-    stdin().read_to_string(&mut times).expect("An error occurred reading a line");
-    times.split("\n")
-         .map(|s| { s.trim().to_string() })
-         .collect()
-}
+use clap::Parser;
+use anyhow::{anyhow, Result};
+mod args;
+mod time;
 
-fn parse_time(time_str: &str) -> NaiveTime {
-    NaiveTime::parse_from_str(time_str, "%H:%M")
-        .expect(&format!("Failed to parse time from {time_str}"))
-}
+use args::Args;
 
-fn main() {
-    let times = read_times();
-    let mut durations = vec![];
-    for i in (0..times.len() - 1).step_by(2) {
-        let first = parse_time(times.get(i).unwrap());
-        let mut second = parse_time(times.get(i + 1).unwrap());
-        if second < first {
-            second = second + Duration::hours(12);
+fn main() -> Result<()> {
+    let args = Args::parse();
+    let stdin = io::stdin();
+    let hours = args.hours.unwrap_or(
+        if args.discount {
+            0
+        } else {
+            8
         }
-        durations.push(second - first);
+    );
+
+    let target_minutes = if args.discount {
+        (8 * 60) - ((hours * 60) + args.minutes)
+    } else {
+         hours * 60 + args.minutes
+    };
+    let (hrs, mins) = time::to_hrs_minutes(target_minutes);
+    println!("Working for {}", time::show_time(hrs, mins));
+    println!("Input times one per line. Send an EOF character to finish inputting...");
+    let mut lines: Vec<String> = vec![];
+    for line in stdin.lock().lines() {
+        lines.push(line.expect("Issues when reading from stdin"));
     }
 
-    let total_minutes: i64  = durations.iter().map(|d| { d.num_minutes() }).sum();
-    let minutes = total_minutes % 60;
-    let hours = total_minutes / 60;
+    // This is immeidately going to be turned back into a DateTime, which the doc says is fine
+    #[allow(deprecated)]
+    let midnight = Local::now().date().and_hms_opt(0, 0, 0).ok_or(anyhow!("Expected midnight to exist"))?;
+    let times = time::from_stream(&midnight, lines.iter())?;
 
-    println!("You have been working for {hours} hour(s) and {minutes} minute(s)");
+    let mut total_minutes: i64 = 0;
+    let mut first: Option<DateTime<Local>> = None;
+    let mut last: Option<DateTime<Local>> = None;
+    for time in times {
+        match first {
+            None => {
+                first = Some(time);
+            },
+            Some(prev) => {
+                total_minutes += (time - prev).num_minutes();
+                first = None;
+                last = Some(time);
+            }
+        }
+    }
+
+    if let Some(remaining) = first {
+        let now = Local::now();
+        let now_str = now.format("%-I:%M %p");
+        println!("Ended with unclosed span... assuming ending now: {}", now_str);
+        total_minutes += (now - remaining).num_minutes();
+    }
+
+    println!("{}", time::get_charaterized_time_remaining(total_minutes, target_minutes, last.unwrap_or_else(|| Local::now())));
+    Ok(())
 }
diff --git a/src/time.rs b/src/time.rs
new file mode 100644
index 0000000..2b31d50
--- /dev/null
+++ b/src/time.rs
@@ -0,0 +1,89 @@
+use chrono::{Duration, Local, DateTime};
+use anyhow::{Result, anyhow};
+use std::iter::Iterator;
+use regex::Regex;
+
+fn parse_datetime(reference_date: &DateTime<Local>, s: &str) -> Result<DateTime<Local>> {
+    let re = Regex::new(r"^\s*([12]?\d):([012345]\d)\s*$")?;
+    let (_, [hrs, mins]) = re.captures(s).ok_or(anyhow!(format!("Failed to parse \"{s}\" as a time")))?.extract();
+    let mins: u32 = mins.parse()?;
+    let mut hrs: u32 = hrs.parse()?;
+    let mut date = *reference_date;
+
+    if hrs > 23 {
+        let num_days = hrs / 24;
+        date = *reference_date + Duration::days(num_days.into());
+        hrs = hrs % 24;
+    }
+    #[allow(deprecated)]
+    Ok(date.date().and_hms_opt(hrs, mins, 0).ok_or(anyhow!(format!("{}:{:0>2} not a real time", hrs, mins)))?)
+}
+
+pub fn from_stream<'a>(reference_date: &DateTime<Local>, stream: impl Iterator<Item = &'a String>) -> Result<Vec<DateTime<Local>>> {
+    let mut durations: Vec<DateTime<Local>> = vec![];
+    for val in stream {
+        durations.push(parse_datetime(reference_date, val)?);
+    }
+    return Ok(durations);
+}
+
+pub fn show_time(hours: i64, minutes: i64) -> String {
+    let pluralized_hours = match hours {
+        1 => "1 hour".to_string(),
+        _ => format!("{hours} hours"),
+    };
+    let pluralized_minutes = match minutes {
+        1 => "1 minute".to_string(),
+        _ => format!("{minutes} minutes"),
+    };
+
+    if hours == 0 {
+        return pluralized_minutes.to_string();
+    }
+
+    if minutes == 0 {
+        return pluralized_hours.to_string();
+    }
+
+    return format!("{pluralized_hours} and {pluralized_minutes}");
+}
+
+pub fn to_hrs_minutes(total_minutes: i64) -> (i64, i64) {
+    let minutes = total_minutes % 60;
+    let hours = total_minutes / 60;
+    (hours, minutes)
+}
+
+pub fn get_charaterized_time_remaining(
+    total_minutes: i64,
+    target_minutes: i64,
+    ended_at: DateTime<Local>,
+) -> String {
+    if total_minutes == target_minutes {
+        return "Exactly done".to_string();
+    }
+
+    if total_minutes > target_minutes {
+        let diff = total_minutes - target_minutes;
+        let (hours, minutes) = to_hrs_minutes(diff);
+        return format!("You have overworked {}", show_time(hours, minutes))
+    } else {
+        let diff = target_minutes - total_minutes;
+        let (hours, minutes) = to_hrs_minutes(diff);
+        let now = Local::now();
+        return if ended_at > now {
+            let end_at = (ended_at + Duration::minutes(diff)).time();
+            let end_str = end_at.format("%-I:%M %p");
+            format!(
+                "You have {} remaining (end at {} starting from {})",
+                show_time(hours, minutes),
+                end_str,
+                ended_at.format("%-I:%M %p"),
+            )
+        } else {
+            let end_at = (now + Duration::minutes(diff)).time();
+            let end_str = end_at.format("%-I:%M %p");
+            format!("You have {} remaining (end at {} starting now)", show_time(hours, minutes), end_str)
+        }
+    }
+}