working minimal cli

.gitignore

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+# Generated by Cargo
+# will have compiled files and executables
+debug/
+target/
+
+# Remove Cargo.lock from gitignore if creating an executable, leave it for libraries
+# More information here https://doc.rust-lang.org/cargo/guide/cargo-toml-vs-cargo-lock.html
+Cargo.lock
+
+# These are backup files generated by rustfmt
+**/*.rs.bk
+
+# MSVC Windows builds of rustc generate these, which store debugging information
+*.pdb

Cargo.toml

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+[package]
+name = "rusty-journal"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+anyhow = "1.0"
+home = "0.5"
+serde_json = "1.0"
+structopt = "0.3"
+
+[dependencies.chrono]
+features = ["serde"]  # We're also going to need the serde feature for the chrono crate, so we can serialize the DateTime field.
+version = "0.4"
+
+[dependencies.serde]  # Add serde in its own section.
+features = ["derive"] # We'll need the derive feature.
+version = "1.0"

README.md

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+# Rusty Journal
+The application is a command line task tracker. It records our tasks in a text file, displays them as a list in the terminal, and lets us mark them as done.
+
+This programme follows the Microsoft Learning Path for [Rust](https://learn.microsoft.com/de-de/training/modules/rust-create-command-line-program/)
+
+1. install rust toolchain with [rustup](https://rustup.rs)
+2. `cargo run` to start the app
+
+Try it out:
+```sh
+cargo run -- -j test-journal.json add "buy milk"
+cargo run -- -j test-journal.json add "take the dog for a walk"
+cargo run -- -j test-journal.json add "water the plants"
+cargo run -- -j test-journal.json list
+cargo run -- -j test-journal.json done 2
+cargo run -- -j test-journal.json list
+```
+
+To compile the programme, switch to the terminal and execute the command `cargo run --release`.
+
+The compiled binary (the executable) is located in the `target/release/` directory and is named after the project name. If you are using macOS or Linux, it will be called `rusty-journal`. If you use Windows, it is called `rusty-journal.exe`.

src/cli.rs

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+use std::path::PathBuf;
+use structopt::StructOpt;
+
+#[derive(Debug, StructOpt)]
+pub enum Action {
+    /// Write tasks to the journal file.
+    Add {
+        /// The task description text.
+        #[structopt()]
+        text: String,
+    },
+    /// Remove an entry from the journal file by position.
+    Done {
+        #[structopt()]
+        position: usize,
+    },
+    /// List all tasks in the journal file.
+    List,
+}
+
+#[derive(Debug, StructOpt)]
+#[structopt(
+    name = "Rusty Journal",
+    about = "A command line to-do app written in Rust"
+)]
+pub struct CommandLineArgs {
+    #[structopt(subcommand)]
+    pub action: Action,
+
+    /// Use a different journal file.
+    #[structopt(parse(from_os_str), short, long)]
+    pub journal_file: Option<PathBuf>,
+}

src/main.rs

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+use anyhow::anyhow;
+use std::path::PathBuf;
+use structopt::StructOpt;
+mod cli;
+mod tasks;
+
+use cli::{Action::*, CommandLineArgs};
+use tasks::Task;
+
+fn find_default_journal_file() -> Option<PathBuf> {
+    home::home_dir().map(|mut path| {
+        path.push(".rust-journal.json");
+        path
+    })
+}
+
+fn main() -> anyhow::Result<()> {
+    let CommandLineArgs {
+        action,
+        journal_file,
+    } = CommandLineArgs::from_args();
+
+    let journal_file = journal_file
+        .or_else(find_default_journal_file)
+        .ok_or(anyhow!("Failed to find journal file."))?;
+
+    match action {
+        Add { text } => tasks::add_task(journal_file, Task::new(text)),
+        List => tasks::list_tasks(journal_file),
+        Done { position } => tasks::complete_task(journal_file, position),
+    }?;
+    Ok(())
+}

src/tasks.rs

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+use chrono::{serde::ts_seconds, DateTime, Local, Utc};
+use serde::Deserialize;
+use serde::Serialize;
+use std::fmt;
+use std::fs::{File, OpenOptions};
+use std::io::{Error, ErrorKind, Result, Seek, SeekFrom};
+use std::path::PathBuf;
+
+#[derive(Debug, Deserialize, Serialize)]
+pub struct Task {
+    pub text: String,
+
+    #[serde(with = "ts_seconds")]
+    pub created_at: DateTime<Utc>,
+}
+
+impl Task {
+    pub fn new(text: String) -> Task {
+        let created_at: DateTime<Utc> = Utc::now();
+        Task { text, created_at }
+    }
+}
+
+fn collect_tasks(mut file: &File) -> Result<Vec<Task>> {
+    file.seek(SeekFrom::Start(0))?; // Rewind the file before.
+    let tasks = match serde_json::from_reader(file) {
+        Ok(tasks) => tasks,
+        Err(e) if e.is_eof() => Vec::new(),
+        Err(e) => Err(e)?,
+    };
+    file.seek(SeekFrom::Start(0))?; // Rewind the file after.
+    Ok(tasks)
+}
+
+pub fn add_task(journal_path: PathBuf, task: Task) -> Result<()> {
+    let file = OpenOptions::new()
+        .read(true)
+        .write(true)
+        .create(true)
+        .open(journal_path)?;
+    let mut tasks = collect_tasks(&file)?;
+    tasks.push(task);
+    serde_json::to_writer(file, &tasks)?;
+    Ok(())
+}
+
+pub fn complete_task(journal_path: PathBuf, task_position: usize) -> Result<()> {
+    // Open the file.
+    let file = OpenOptions::new()
+        .read(true)
+        .write(true)
+        .open(journal_path)?;
+
+    // Consume file's contents as a vector of tasks.
+    let mut tasks = collect_tasks(&file)?;
+
+    // Try to remove the task.
+    if task_position == 0 || task_position > tasks.len() {
+        return Err(Error::new(ErrorKind::InvalidInput, "Invalid Task ID"));
+    }
+    tasks.remove(task_position - 1);
+
+    // Write the modified task list back into the file.
+    file.set_len(0)?;
+    serde_json::to_writer(file, &tasks)?;
+    Ok(())
+}
+
+pub fn list_tasks(journal_path: PathBuf) -> Result<()> {
+    // Open the file.
+    let file = OpenOptions::new().read(true).open(journal_path)?;
+    // Parse the file and collect the tasks.
+    let tasks = collect_tasks(&file)?;
+
+    // Enumerate and display tasks, if any.
+    if tasks.is_empty() {
+        println!("Task list is empty!");
+    } else {
+        let mut order: u32 = 1;
+        for task in tasks {
+            println!("{}: {}", order, task);
+            order += 1;
+        }
+    }
+
+    Ok(())
+}
+
+impl fmt::Display for Task {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        let created_at = self.created_at.with_timezone(&Local).format("%F %H:%M");
+        write!(f, "{:<50} [{}]", self.text, created_at)
+    }
+}