Learn D3, Jquery and Rust

D3.js is a JavaScript library for manipulating documents based on data. D3 helps you bring data to life using HTML, SVG and CSS. D3’s emphasis on web standards gives you the full capabilities of modern browsers without tying yourself to a proprietary framework, combining powerful visualization components and a data-driven approach to DOM manipulation.

In this lesson, we'll clean up some of our placeholder elements. We'll then look at D3's ordinal scale to create a color scale that maps our regions to colors. We'll apply the colors based on region to our data points via the SVG `g`(group) element to apply the color to both our bars and their corresponding inline labels.

Create a Color Scale with D3's scaleOrdinal

Looking at our bars against each other with the x-axis as a guide gives us some relative information, but doesn't deliver the most precise values. In this lesson, we'll add additional labels to show the exact values of each data point in the context of the individual bars.

Clarify Data in D3 with Additional Labels and Rounded Domain Values

In this lesson, we'll see how we can add labels down the y-axis using our band scale. We'll see how to render the labels in React and how we can precisely position the labels based on values calculated by D3 and our scales.

Render a Y Axis for a Bar Chart with D3 and React

In this lesson, we'll take advantage of our `xScale` and the bottom margin to create an axis to start giving our data meaning. We'll access `ticks` from the scale and then use React to render and position the SVG `rect` and `text` elements to create the x-axis for our chart.

Render an X Axis for a Bar Chart with D3 and React

When applying scales to data elements in D3, it's common to combine the scale with an accessor function in order to apply the scale to the appropriate key on a data object. In this lesson, we'll create scaled accessors to refactor and tighten up some existing code.

Create Scaled Accessor Functions from D3 Scales

A band scale allows us to map a discrete set of values to a continuous range. In this lesson, we'll use a band scale in D3 to take the distinct "region" keys in our sample data and map those to evenly spaced and sized elements on our y-axis. We'll use this band scale to show a bar in the bar chart for each region, setting their size and position based on this scale.

Layout SVG Elements on a Y Axis with a D3 Band Scale in React

Drawing data accurately requires a consistent and precise mechanism for mapping data values to pixels on the screen. We can accomplish this mapping in D3 using scales. There are various scales available in D3, depending on your needs. In this lesson we'll using a linear scale to map a data domain of continuous values to continuous range of pixel values. We'll render a new SVG element, setting its width from our scale.

Set an SVG Element's Width Based on a D3 Linear Scale in React

When you want to add data visualizations to your web app, D3 is pretty much the accepted standard.

In this course, we'll start from scratch and build out a bar chart for some sample data using D3's utilities to wrangle the data and then we'll handle the rendering with React.

We'll start by laying out the SVG element that will hold everything, then we'll move on to creating scales that will give us the information we need to render our data as well as axes to give our data some meaning.

Along the way, we'll cover accessor functions, linear scales, band scales and finally, we'll use an ordinal scale to map data objects to colors.

This course certainly won't cover all of D3, but we'll cover enough of the fundamentals to give you a solid jumping off point for future D3 and React data visualization work.

Introduction to Create a Bar Chart with React and D3

In this course, Chris takes a README-driven approach to build out a Rust CLI that supports content authoring for a digital garden.

Specifically, you'll work through the first command for the CLI, writing files. You start by initializing a new Cargo binary crate through creating the `write` command that allows you to create files (and their contents) to the folder that you set. 

Step by step you'll learn about:
- Handling user input
- Error handling
- Rust Move semantics
- Rust Copy semantics
- Integration testing

...and more!

Rust is a systems programming language that runs blazingly fast, prevents segfaults, and guarantees thread safety.

rust

Creating a Digital Garden CLI with Rust

While we have `test_write_with_title`
which tests the garden CLI with a given
title flag, we can also set up additional
tests, such as for using a written title
in the document for the filename.

Copy/pasting the code from test one into
test two is a lot of duplication, and
setting up the fake editor isn't going
to change across tests, so let's abstract
the creation of the temporary directory,
the fake editor script path, and the
`Command` itself into a utility function.

The port is relatively straightforward,
with the only changes being that we cut
off the `cmd` modifications before the
`.arg` calls, and now have to return
the `cmd` and the `temp_dir` in a tuple.

We return the actual `Command` and `TempDir`,
yielding ownership to the calling function
because we have no further use for them here,
but the calling function will need to mutate
the `Command` more, and use `TempDir` to test.

```rust
fn setup_command() -> (Command, assert_fs::TempDir) {
    let temp_dir = assert_fs::TempDir::new().unwrap();

    let mut cmd = Command::cargo_bin("garden").unwrap();
    let fake_editor_path = std::env::current_dir()
        .expect("expect to be in a dir")
        .join("tests")
        .join("fake-editor.sh");
    if !fake_editor_path.exists() {
        panic!(
            "fake editor shell script could not be found"
        )
    }

    cmd.env("EDITOR", fake_editor_path.into_os_string())
        .env("GARDEN_PATH", temp_dir.path());
    (cmd, temp_dir)
}
```

The new write tests are considerably shorter
now and focus mostly on which subcommand to
call, and what the user interaction with that
subcommand is.

```rust

fn test_write_with_title() {
    let (mut cmd, temp_dir) = setup_command();
    let assert = cmd
        .arg("write")
        .arg("-t")
        .arg("atitle")
        .write_stdin("N\n".as_bytes())
        .assert();

    assert.success();

    temp_dir
        .child("atitle.md")
        .assert(predicate::path::exists());
}

fn test_write_with_written_title() {
    let (mut cmd, temp_dir) = setup_command();
    let assert = cmd
        .arg("write")
        .write_stdin("N\n".as_bytes())
        .assert();

    assert.success();

    temp_dir
        .child("testing.md")
        .assert(predicate::path::exists());
}
```

Abstracting test utilities inside integration test files

We can print lines to the terminal and
ask the user for various input. So let's
make the interface a bit more usable by
using colored output.

We can do this by bringing an extension
trait for formatting into scope:
`OwoColorize`.

Extension traits are one-off traits that
are used to add functions to a type that
our crate doesn't own. A crate can create
the new trait, then implement the
functions defined by that trait on a type
the crate doesn't own and if we bring that
trait into scope, the type will get the
extra functions. In this case, `OwoColorize`
is used for adding color functions to
formatters like Display and Debug.

We'll start with `ask_for_filename`

```rust
use color_eyre::owo_colors::OwoColorize;

fn ask_for_filename() -> Result<String> {
    rprompt::prompt_reply_stderr(&format!(
        "{}",
        "\
Enter filename
> "
        .blue()
        .bold(),
    ))
    .wrap_err("Failed to get filename")
    .map(|title| slug::slugify(title))
}
```

In `confirm_filename` we can use multiple
formatters to get different colors:

```rust
let result = rprompt::prompt_reply_stderr(&format!(
    "\
{} {}
Do you want a different title? (y/N): ",
    "current title:".green().bold(),
    raw_title,
))
.wrap_err("Failed to get input for y/n question")?;
```

Using owo_colors Extension Traits to colorize terminal output

`PathBuf` lets us check to see if a file
exists before writing to it, so we can
take advantage of that to make sure that
we don't overwrite a file that already
exists, even if the user has indicated
a title that would overwrite another file.

```
let mut i: usize = 0;
loop {
    let dest_filename = format!(
        "{}{}",
        filename,
        if i == 0 {
            "".to_string()
        } else {
            i.to_string()
        }
    );
    let mut dest = garden_path.join(dest_filename);
    dest.set_extension("md");
    if dest.exists() {
        i = i + 1;
    } else {
        fs::rename(garden_tmpfile, &dest)?;
        break;
    }
}
```

Checking for file existence with PathBuf to ensure unique filenames

We have been ignoring implementing tests for the write subcommand. Now is the time that we'll test the command we have been building.

We'll build out a fake editor script that our test will use to check if the command is functioning properly. We will then use `arg` to build the command as we would normally use it ourselves.

After writing the test, we'll see how to clean up after ourselves so that we aren't leaving testing artifacts leftover just from running a test.

---

How to integration test a cargo binary that calls
out to `EDITOR` for modifications and asks the
user for input.

First we'll create a fake editor script to use
instead of vim, etc.

`tests/fake_editor.sh` is a one-liner.

```shell
echo "testing" >> $1;
```

Then we'll write our test using `assert_cmd` to
build up a `Command` that points to the `garden`
binary in out `Cargo.toml`.

We grab the fake editor path script using
`std::env::current_dir()`, make sure the file
exists (which means we've grabbed the right
path), and spawn a new `Command` with the
`EDITOR` variable set to the fake editor
script. The equivalent call to our bin is

```shell
EDITOR=path/to/fake-editor.sh garden write -t atitle
```

And the rust code to execute.

```rust
fn test_write_with_title() {
    let mut cmd = Command::cargo_bin("garden").unwrap();
    let fake_editor_path = std::env::current_dir()
        .expect("expect to be in a dir")
        .join("tests")
        .join("fake-editor.sh");
    if !fake_editor_path.exists() {
        panic!(
            "fake editor shell script could not be found"
        )
    }

    let assert = cmd
        .env("EDITOR", fake_editor_path.into_os_string())
        .arg("write")
        .arg("-t")
        .arg("atitle")
        .write_stdin("N\n".as_bytes())
        .assert();

    assert.success();
}
```

Note that we're asserting that the command
exited sucessfully, and that we're inputing
`N\n` to the bin's stdin, which responds to
a request for user input after the editor
closes.

Note that this doesn't actually test for
the resulting file existence, and also that
we're writing our files out directly into
our default digital garden! We can solve
this with `assert_fs` and `predicates`.

We'll bring in both preludes (a prelude is
a bunch of stuff the library author thinks
will be useful to have around all the time)
and create a new temporary directory.

We'll use the `GARDEN_PATH` environment
variable to pass the temporary directory in
to the `garden` bin and that's it, we've
added a temporary directory to our test.
No more polluting the default garden!

```rust
use assert_fs::prelude::*;
use predicates::prelude::*;

fn test_write_with_title() {
    let temp_dir = assert_fs::TempDir::new().unwrap();

    let mut cmd = Command::cargo_bin("garden").unwrap();
    let fake_editor_path = std::env::current_dir()
        .expect("expect to be in a dir")
        .join("tests")
        .join("fake-editor.sh");
    if !fake_editor_path.exists() {
        panic!(
            "fake editor shell script could not be found"
        )
    }

    let assert = cmd
        .env("EDITOR", fake_editor_path.into_os_string())
        .env("GARDEN_PATH", temp_dir.path())
        .arg("write")
        .arg("-t")
        .arg("atitle")
        .write_stdin("N\n".as_bytes())
        .assert();

    assert.success();

    temp_dir
        .child("atitle.md")
        .assert(predicate::path::exists());
}
```

Now that's enough, but we can also check
to make sure the file we expect to exist
actually exists. `temp_dir.child` gives
us the possible file, and we can assert
on that file with a test from `predicates`
that tests to make sure the file exists.

```rust
temp_dir
    .child("atitle.md")
    .assert(predicate::path::exists());
```

Using assert_fs and predicates to integration test with a real temporary file system

What user experience do we want for the
act of writing?

We have a few options, including letting
users write directly in the console or giving
them a prepared file that they can then open
and write in.

Writing directly in the console doesn't give
a user access to their text editor of choice.
Which means lacking autocomplete, syntax
highlighting, snippets, and other functionality.

Creating a file and handling the path back to
the user doesn't quite work for us either, as
that reduces the utility of the garden write
command to the equivalent of running `touch
filename.md`.

So for our use case, we'd ideally like to open
the user's preferred editing environment,
whatever that happens to be, then wait for them
to be done with the file before continuing.

Since we're working with a CLI tool, we
can safely assume that our users either
know how to, or are willingly to learn how
to, set environment variables. This means we
can use the `EDITOR` variable to select an
editor to use. This is the same way `git commit`
works.

---

In Rust, there is a crate that handles not only
`EDITOR`, but also various fallbacks per-platform.
We'll take advantage of [edit](https://crates.io/crates/edit)
to call out to the user's choice of editor.

The quick usage of edit allows us to call the
`edit::edit` function, and get the user's data.

```rust
pub fn write(garden_path: PathBuf, title: Option<String>) -> Result<()> {
    dbg!(garden_path, title);
    let template = "# ";
    let content_from_user = edit::edit(template).wrap_err("unable to read writing")?;
    dbg!(content_from_user);
    todo!()
}
```

This results in a filename that looks like:
`.tmpBy0Yun` "somewhere else" on the filesystem,
in a location the user would never reasonably
find it. Ideally, if anything went wrong, the
user would be able to take a look at the
in-progress tempfile they were just working on,
which should be in an easily discoverable place
like the garden path.

*We don't want to lose a user's work.*

Additionally, the tempfile doesn't have a file
extension, which means that the user's editor
will be less likely to recognize it as a
markdown file, so we want to add `.md` to the
filepath.

```rust
use color_eyre::{eyre::WrapErr, Result};
use edit::{edit_file, Builder};
use std::io::{Read, Write};
use std::path::PathBuf;

const TEMPLATE: &[u8; 2] = b"# ";

pub fn write(garden_path: PathBuf, title: Option<String>) -> Result<()> {
    let (mut file, filepath) = Builder::new()
        .suffix(".md")
        .rand_bytes(5)
        .tempfile_in(&garden_path)
        .wrap_err("Failed to create wip file")?
        .keep()
        .wrap_err("Failed to keep tempfile")?;
    file.write_all(TEMPLATE)?;
    // let the user write whatever they want in their favorite editor
    // before returning to the cli and finishing up
    edit_file(filepath)?;
    // Read the user's changes back from the file into a string
    let mut contents = String::new();
    file.read_to_string(&mut contents)?;

    dbg!(contents);
    todo!()
}
```

We will use the `edit::Builder` API to generate
a random tempfile to let the user write content
into. The suffix is going to be `.md` and the
filename will be 5 random bytes. We also put
the tempfile in the garden path, which ensures
a user will be able to find it if necessary.

`wrap_err` (which requires the `eyre::WrapErr`
trait in scope) wraps the potential error
resulting from these calls with additional context,
making the original error the source, and we can
keep chaining after that. We `keep` the tempfile,
which would otherwise be deleted when all handles
closed, because if anything goes wrong after the
user inputs data, we want to make sure we don't
lose that data.

After the file is created, we write our template
out to the file before passing control to the
user. This requires the `std::io::Write` trait
in scope. We use a const for the file template
because it won't change. To make the `TEMPLATE`
a const, we also need to give it a type, which
is a two element byte array. Change the string
to see how the byte array length is checked at
compile time.

Since we have access to the `file` already, we
can read the contents back into a string after
the user is done editing. This requires having
the `std::io::Read` trait in scope.

And now we've let the user write into a file
which will stick around as long as we need it
to, and importantly will stick around if any
errors happen in the execution of the program,
so we lose no user data and can remove the
temporary file at the end of the program
ourselves if all goes well.

Passing control to the user's favorite editor (such as VSCode) from the CLI

Given the potential `document_title` we now
want to ask the user if the title is still
what they want to use so that we can write
the file to disk. This will involve two
paths depending on if we have an existing
potential option or not.

We will need to use `ask_for_filename` in
`confirm_filename`, so we'll write that branch
first.

```rust
let filename = match document_title {
    Some(raw_title) => {
        // confirm_filename()?
        todo!()
    }
    None => ask_for_filename(),
};
```

`rprompt` allows us to ask for a small amount
of input from the user (compared to the  much
larger input possible by passing control to
the user's editor).

We'll use `rprompt::prompt_reply_stderr` to
get a response from the user, and `.wrap_err`
to add context to the error if anything goes
wrong.

```rust
fn ask_for_filename() -> Result<String> {
    rprompt::prompt_reply_stderr(
        "\
Enter filename
> ",
    )
    .wrap_err("Failed to get filename")
}
```

We'll use the same behavior for the first
part of `confirm_filename`. We'll also
need to use our first lifetime to account
for the shared reference argument.

`match` can match against multiple values
for the same branch, so we'll take advantage
of that to handle branches for Ns and Ys, as
well as the default case. If anything goes
wrong, such as someone inputting an "a",
we'll fall through using `loop` and ask again
until we get a usable answer

```rust
fn confirm_filename(raw_title: &str) -> Result<String> {
    loop {
        // prompt defaults to uppercase character in question
        // this is a convention, not a requirement enforced by
        // the code
        let result = rprompt::prompt_reply_stderr(&format!(
            "\
current title: `{}`
Do you want a different title? (y/N): ",
            raw_title,
        ))
        .wrap_err("Failed to get input for y/n question")?;

        match result.as_str() {
            "y" | "Y" => break ask_for_filename(),
            "n" | "N" | "" => {
                // the capital N in the prompt means "default",
                // so we handle "" as input here
                break Ok(slug::slugify(raw_title));
            }
            _ => {
                // ask again because something went wrong
            }
        };
    }
}
```

While filenames can technically have spaces
in them, we're going to slugify our filenames
like urls for a few reasons. One is that
when starting out, many programmers fail to
quote filename arguments in their bash scripts,
which results in filenames with spaces being
treated as separate arguments. Another is
that this is a digital garden CLI, and
digital gardens are often stored in git,
accessed from multiple file systems, as well
as from URLs. While strictly speaking we don't
need to slugify our filenames, we will here
so as to adhere to a safer set of characters.

```
cargo add slug
```

We'll map over the `Result` from `rprompt`
which allows us to operate on the internal
value if it's `Ok`.

```rust
fn ask_for_filename() -> Result<String> {
    rprompt::prompt_reply_stderr(
        "\
Enter filename
> ",
    )
    .wrap_err("Failed to get filename")
    .map(|title| slug::slugify(title))
}
```

We'll also use slugify in `confirm_filename`

```rust
match result.as_str() {
    "y" | "Y" => break ask_for_filename(),
    "n" | "N" | "" => {
        // the capital N in the prompt means "default",
        // so we handle "" as input here
        break Ok(slug::slugify(raw_title));
    }
    _ => {
        // ask again because something went wrong
    }
};
```

The fact that `confirm_filename` and
`ask_for_filename` have the same return type
is important because the branches of a `match`
need to return the same type.

Prompting the user for input with rprompt and loop

We want to build out functionality to let the user
write into a file in their garden. To do that, we
have to know the location of their garden.

We'll start by implementing a function to get the
default garden path.

```rust
fn get_default_garden_dir() -> Result<PathBuf> {
    let user_dirs = UserDirs::new().ok_or_else(|| eyre!("Could not find home directory"))?;
    Ok(user_dirs.home_dir().join(".garden"))
}
```

This uses the user's system directories via the
`directories` crate to find their home dir. We
then add `.garden` to the home dir for the default
garden.

Ideally, we would want the user to be able to
specify their garden path. Using structopt, we
can let them specify it as a short, long, or
env var.

In our README, we'll specify how this should work.

````

```shell
GARDEN_PATH=~/github/my-digital-garden garden write
garden -p ~/github/my-digital-garden write
garden --garden_path ~/github/my-digital-garden write
```
````

And in our `Opt` struct, we can tell structopt how to
handle it. Putting this in our `Opt` struct instead of
our `Command` enum make it a global flag that can be
specified for all subcommands.

```rust
struct Opt {
    #[structopt(parse(from_os_str), short = "p", long, env)]
    garden_path: Option<PathBuf>,

    #[structopt(subcommand)]
    cmd: Command,
}
```

structopt is only handling the user input, so in
`main()` we still need to fall back to the
default if the `garden_path` is not specified.

```rust
let garden_path = match opt.garden_path {
    Some(pathbuf) => Ok(pathbuf),
    None => get_default_garden_dir().wrap_err("`garden_path` was not supplied"),
}?;
```

if we force an `Err` in `get_default_garden_dir`
We can see how the wrapped errors end up stacking.

```
Error:
   0: `garden_path` was not supplied
   1: Could not find home directory
```

We'll also change the signature of `write` to
accept the pathbuf.

```
Command::Write { title } => write(garden_path, title),
```

Note that we need to import `PathBuf`. We can also
`dbg!` the garden path and title to see their
values.

```rust
use std::path::PathBuf;

pub fn write(garden_path: PathBuf, title: Option<String>) -> Result<()> {
    dbg!(garden_path, title);
    todo!()
}
```

Adding support for global flags that apply for all subcommands with structopt

In our subcommand match we'll add a new function called
`write` to handle our `Write` subcommand. We'll pass it
the argument title and we'll "import" it from a library
called `digital_garden`. 

```rust
use digital_garden::write;

fn main() -> Result<()> {
    color_eyre::install()?;

    let opt = Opt::from_args();
    dbg!(&opt);
    match opt.cmd {
        Command::Write { title } => write(title),
    }
}
```

To create this library, add a new section in `Cargo.toml`.
We can give our library a name and set which file to treat
as the entrypoint. `src/lib.rs` is the default file for
a library crate, but we can also be explicit about what we
want to happen.

```toml
[lib]
name = "digital_garden"
path = "src/lib.rs"
```

This leaves us with two crates, a binary crate, of which we
can have any amount, and a library crate, of which we can
only have 0 or 1.

We'll create the `src/lib.rs` file with the following
contents.

```rust
mod write;

pub use write::write;
```

Rust's module system is explicit, so when we write
`mod write`, we are saying that the library `digital_garden`
has a module `write`, such that the path to the module is
`digital_garden::write`.

In our case `digital_garden::write` corresponds to a file
at `src/write.rs`.

Secondly, the `pub use write::write` says that we have a
function called `write` in the module called `write` and
that the function will be exposed from lib publicly, so
people who have the `digital_garden` library installed
will be able to use the write function as
`digital_garden::write`.

In JavaScript the closest analogue is exporting a function
from another file that exports it.

```js
export { write } from './write.js';
```

By using use, we're shortening the public path to the write
function. A private module "write" with a function "write"
also exists at `digital_garden::write::write`. If you try
to use this path, Rust will tell you there is a private
module there.

Finally, in `src/write.rs`, we can write a public function
that matches the return type of our main function, since
we're using it as the return value from our match function.

We'll accept an `Option<String>` as an argument as well,
since that's what we expect from the cli arguments.

```rust
use color_eyre::Result;

pub fn write(_title: Option<String>) -> Result<()> {
    todo!()
}
```

The purpose of creating this module path is because we
know that we're going to set up more modules for each
subcommand in the future, and we can control both the
placement of our code on disk, as well as the path users
will interact with to use our module.

Creating a library crate to support a Rust binary crate in the same package

After getting the user's input, we need to
figure out a filename to write the file out
as. We can either use the title the user
passed in, or we can try to use heuristics
to find a title from the markdown content.

We can combine the user's title from the cli
arguments (an `Option`) with the logic we
use as a heuristic for the markdown (also
an `Option`).

```rust
// use `title` if the user passed it in,
// otherwise try to find a heading in the markdown
let document_title = title.or_else(|| {
    contents
        .lines()
        .find(|v| v.starts_with("# "))
        // markdown headings are required to have `# ` with
        // at least one space
        .map(|maybe_line| maybe_line.trim_start_matches("# ").to_string())
});
```

`option.or_else()` returns the original
option if it is a `Some` value, or executes
the function to return a different `Option`
if not. So `document_title` is an
`Option<String>` either way and we've
covered all of the possible scenarios:

1. the user has passed in a title
2. the user has written content with a heading
3. the user has done neither of these

Which leaves us to our markdown heuristic.

Markdown headings are required to have `# `
with at least one space, so we can turn
`contents` into an iterator and `find` the
first line that starts with `# `.

If we find one, we want to trim `# ` off of
the heading to get just the heading content,
so we can use `map` to operate on the value
inside of the `Option` returned by `find` if
it exists.

```rust
contents
    .lines()
    .find(|v| v.starts_with("# "))
    .map(|maybe_line| maybe_line.trim_start_matches("# ").to_string())
```

Now this code works fine, but it exposes a bug
in our file handling.

If we `write_all` to the `file`, that moves the
internal cursor to the end of that content. So
when we run our code now, `contents` is
skipping the first `# ` bytes, which means our
heuristic will only find the second heading in
the file.

To fix this, we can bring in the `std::io::Seek`
trait, and seek to the beginning of the file.

```rust
let mut contents = String::new();
file.seek(SeekFrom::Start(0))?;
file.read_to_string(&mut contents)?;
```

Using the Option type in Rust to pick from multiple values that might not exist

We can match on `opt.cmd` to determine which `Command`
variants was called. This lets us specify the variants
as match criteria and also destructure the values out
to use them.

```rust
    let opt = Opt::from_args();
    dbg!(&opt);
    match opt.cmd {
        Command::Write { title } => todo!(),
    }
```

As written, we run into two issues with this code.
One is that we aren't using `title` yet. In
destructuring, we can use the placeholder (`_`) in our
[pattern](https://doc.rust-lang.org/reference/patterns.html).

```
warning: unused variable: `title`
  --> src/main.rs:32:26
   |
32 |         Command::Write { title } => todo!(),
   |                          ^^^^^ help: try ignoring the field: `title: _`
   |
   = note: `#[warn(unused_variables)]` on by default
```

```rust
fn main() -> Result<()> {
    color_eyre::install()?;

    let opt = Opt::from_args();
    dbg!(opt);
    match opt.cmd {
        Command::Write { title: _ } => todo!(),
    }
}
```

The second issue is that the `opt` variable is moved
before we try to destructure it. If we look at the
compiler output before we fixed the `title` issue we
see the value use after move pointing at `title`
specifically.

```
error[E0382]: use of moved value
m  --> src/main.rs:32:26
   |
29 |     let opt = Opt::from_args();
   |         --- move occurs because `opt` has type `Opt`, which does not implement the `Copy` trait
30 |     dbg!(opt);
   |     ---------- value moved here
31 |     match opt.cmd {
32 |         Command::Write { title } => todo!(),
   |                          ^^^^^ value used here after move
```

If we look at it after fixing the unused `title`,
we see the compiler point at `opt.cmd`.

```
error[E0382]: use of moved value: `opt.cmd`
  --> src/main.rs:31:11
   |
29 |     let opt = Opt::from_args();
   |         --- move occurs because `opt` has type `Opt`, which does not implement the `Copy` trait
30 |     dbg!(opt);
   |     ---------- value moved here
31 |     match opt.cmd {
   |           ^^^^^^^ value used here after move
```

This is because opt is moved into the `dbg` call because
it doesn't implement the `Copy` trait. Now, we could
implement or derive `Copy` for `Opt` if `Command` can
implement `Copy`, but we can not implement `Copy` for
`Command`. This is because `String` does not, and can not,
implement `Copy`, and we have a `String` in our `title`.

Without diving into the depths of `Copy`, [`Clone`](https://doc.rust-lang.org/std/clone/trait.Clone.html),
and allocation, there is something we have that already
implements `Copy`, so we don't need to.

Shared references implement `Copy`.

So instead of passing `opt` into `dbg!`, and thus using
move semantics (which are the default in Rust), we can
pass a shared reference in: `dgb!(&opt)` which lets us
use copy semantics.

The difference between move semantics and copy semantics
in this case is that we can access `opt` after passing it
to `dbg!`.

Under the hood, both a copy and a move can result in bits
being copied in memory, although this is sometimes
optimized away. -- [Copy](https://doc.rust-lang.org/std/marker/trait.Copy.html)

```rust
fn main() -> Result<()> {
    let opt = Opt::from_args();
    dbg!(&opt);
    match opt.cmd {
        Command::Write { title: _ } => todo!(),
    }
}
```

Matching structopt commands and using Rust values after move

Cargo allows us to execute a few different kinds of tests,
including integration and unit. For now we'll talk about
integration tests for our CLI. Integration tests
live in `/tests` and only have access to the public
interface of a crate.

In this case, we'll run the `garden` binary using
`assert_cmd` and assert various things about the
execution and output. For example, that the binary
exits successfully and that stderr has no output.

`cargo test` allows us to run all tests.

To restrict the number of tests that run to only the two
that work, we can use `cargo test help` to restrict
cargo to only running tests that match the keyword "help",
or use `#[ignore]` on a test we want to ignore.

The third test will be ignored because we have yet to
build out our functionality.

Integration testing Cargo binaries with assert_cmd

The StructOpt crate allows us to derive our human person functionality from our Struct definitions. 

We will create a `structop` for our `write` subcommand that will take a short and long flag for our `title` argument

---

```
cargo add structopt
```

structopt allows us to derive argument parsing functionality from our
structs. The name is a play on `struct Opt {}`. To do this we need to
`derive(StructOpt)` on our struct. In this case we have a subcommand,
so we'll set up one of the fields on the `Opt` struct to be a
`structopt(subcommand)`. This subcommand value will be an enum,
indicating that only one subcommand can be used at a time.

structopt also gives us tools to specify one of three argument types:

* positional
* short
* long

By default every argument is a positional argument, which means that in
this case if we left it as-is, the CLI would function as

```
garden write my-title
```

We want to use a flag, so we'll use structopt to generate short and long
flags for the title argument with `structopt(short, long)`. That gives
the use the option of `-t` and `--title` to specify a title.

structopt also contains some type processing, so all we need to do is
specify that title is an optional string and the flags will become
optional. That is: a user can specify or not specify a title.

```rust
struct Opt {
    #[structopt(subcommand)]
    cmd: Command,
}
enum Command {
    Write {
        #[structopt(short, long)]
        title: Option<String>,
    },
}
```

After setting up `struct Opt`, we can parse the args and use
the dbg!() macro to print them to the console so we can see
what they look like.

```rust
let opt = Opt::from_args();
dbg!(opt);
```

To do that we also need to `derive(Debug)` in addition to
structopt on both the enum and the struct.

Given input like

```
garden write
```

We will see the following output.

```rust
[src/main.rs:21] opt = Opt {
    cmd: Write {
        title: None,
    },
}
```

We can choose to `cargo build` and then `./target/debug/garden write`
or we can use `cargo run -- write`. The `--` ensures that our arguments
get passed to the CLI we're building and not `cargo run`. This is
especially relevant when passing something like `--help`.

Setting up git-like subcommands using structopt

Creating powerful and context-aware tools for Cursor IDE becomes straightforward when leveraging information directly from your current project. In this lesson, you'll learn how to build a custom MCP (model context protocol) tool that intelligently requests essential details—such as the current project path and conversation summaries—from your Cursor project.

Workflow demonstrated in this lesson:

- Define MCP tool parameters to request specific project details.
- Pass project path and conversation summaries into your MCP tool.
- Automatically write or update files within your current project using these parameters.

Key benefits:

- Automate tasks with precision based on your active project's context.
- Simplify interactions by creating AI-driven CLI commands tailored to your needs.
- Open endless possibilities for integrating external APIs and advanced automation.

Through this practical demonstration, you'll gain a versatile technique for enhancing your development workflow in Cursor IDE.

[https://github.com/johnlindquist/mcp-cursor-tool-starter](https://github.com/johnlindquist/mcp-cursor-tool-starter)

John Lindquist

Build MCP Tools Using Project Context for Custom Cursor IDE Automation

Setting up custom MCP (Machine Command Protocol) servers in Cursor can involve tedious steps, such as configuring node paths or referencing additional commands. This lesson shows how to streamline this process by bundling your MCP server directly into a standalone executable.

Workflow demonstrated in this lesson:

- Use a simple MCP server project starter.
- Run a single bundling command to create an executable.
- Right-click the generated executable, copy its full path, and add that directly to your Cursor settings.

Key benefits:

- Eliminates the need for complex node path configurations.
- Simplifies the setup and integration of custom MCP servers into Cursor.
- Makes the server executable instantly accessible within your Cursor environment.

By following this streamlined approach, you can quickly and easily integrate custom MCP servers into Cursor, making your development workflow cleaner and more efficient.

[https://github.com/johnlindquist/mcp-cursor-tool-starter]()

Easy MCP Server Setup in Cursor IDE with Bundled Executables

TanStack Router is the foundation for TanStack Start, which is gaining significant attention due to its innovative approach to application development.

This course focuses on getting effective TanStack Router, a modern and scalable routing solution for React applications. You will learn how to:
- set up and scaffold new applications,
- use file-based routing
- create nested routes
- manage dynamic route parameters and more.

The course covers advanced features like route loaders, caching strategies, and lifecycle hooks, which are crucial for enhancing application performance and user experience.

By understanding TanStack Router, you can build more efficient, type-safe, and maintainable applications, leveraging its integration with data fetching libraries like TanStack Query.

This knowledge is essential for developers looking to improve their routing skills and stay ahead in the field.

Tomasz Ducin

Up and Running with Tanstack Router and React

Learn TanStack Router for React: set up apps, use file-based routing, manage routes, and boost app performance.


In this lesson, we explore how TanStack Router integrates with the [native browser history API](https://developer.mozilla.org/en-US/docs/Web/API/History) to manage navigation.

As we navigate through different routes, the URL changes are stored in the browser's history, allowing users to use the forward and backward buttons to traverse their navigation history.

This functionality also **enables permalinks**, meaning users can copy and paste URLs to access specific routes directly.

Additionally, we learn how to programmatically interact with the history object to move forward or backward through the navigation stack, enhancing the user experience by providing full control over navigation actions.

This compatibility with the native history API ensures that TanStack Router applications behave similarly to traditional websites, offering a seamless and intuitive user experience.

Browse History in Tanstack Router

Browse history in TanStack React Router using the native history API for seamless navigation

In this lesson, we explore how to hook into TanStack Router's lifecycle hooks to execute custom logic during route changes.

The hooks we'll look into are: `onEnter`, `onStay`, and `onLeave`, which are triggered when entering, staying within, or leaving a route, respectively.

All hooks receive a detailed match parameter, providing information about the route's path, ID, and tons of other details.

This allows for the implementation of features like animations or logging when navigating between routes.

We also learn how to use these hooks to track and manage state changes as users interact with the application, making it easier to implement complex behaviors based on route transitions.

Hook into Route Lifecycle Hooks in Tanstack Router

Hook into TanStack React Router's lifecycle hooks for custom route logic and animations.

In this lesson, we learn how to handle not found errors in TanStack Router by using the `notFoundComponent` at both nested and global levels.

To trigger the display of a `notFoundComponent`, we must throw a specific error using the `notFound` function within a loader or other lifecycle method of a route. This approach allows us to provide custom error messages for specific routes or globally across the application.

We explore how to define a notFoundComponent within a specific route's configuration and how to set a `defaultNotFoundComponent` at the router global level, which applies to all routes unless overridden locally. This flexibility ensures that users receive meaningful feedback when encountering non-existent routes.

Provide NotFoundComponent at Nested Route or Global Level in Tanstack Router

Handle notFound errors in TanStack Router with notFoundComponent at nested or global levels.



In this lesson, we learn how to access dynamic route parameters using the `useParams` hook in TanStack Router.

When used with a specific `Route` object, `useParams` provides type-safe access to route parameters, ensuring that TypeScript knows the exact types of these parameters.

This approach eliminates the possibility of undefined/optional values, making it safer for accessing parameters like `employeeId`.

However, when using `useParams` globally without specifying a route, it requires an options object with `{ strict: false }`, which reduces type safety.

In this case, the hook can access parameters from any route in the application, but it does not guarantee their existence or type. This flexibility allows components to be reused across different routes, but it requires careful handling of potential errors.



Access Dynamic Route Parameters with useParams in Tanstack Router

Access dynamic route parameters with useParams in TanStack React Router for type-safe routing.

In this lesson, we learn how to reorganize file-based routes in TanStack Router to accommodate nested routing structures.

We explore how to create additional nested routes by converting files into directories, allowing for further nesting.

For example, to create a nested route like `/employees/$employeeId/edit`, we can create a **directory** (!) named `$employeeId` and place an `index.tsx` file inside it to define the route component for this nested route.

This approach provides flexibility in organizing files while maintaining the convention that file names and locations align with route paths. We also see how to adapt existing components and loaders to work with these reorganized routes, enabling features like edit forms or delete actions (or whatever) within nested routes.


Reorganize File-Based Routes in Tanstack Router

Reorganize file-based routes in TanStack Router for flexible nested routing.



In this lesson, we learn how to parametrize the loader for a nested route in TanStack Router.

We focus on a nested route like `/employees/$employeeId`, where the `$employeeId` is a **dynamic parameter**.

To fetch data for this route, we use a `loader` function that accesses the `$employeeId` parameter. This is achieved by using the params object available in the `loader` function, which contains the dynamic segments of the URL. We then use this parameter to call a function like `getEmployeeById`, which fetches specific employee details from an API.

We highlights that TanStack Router **automatically infers types** for these parameters, ensuring type safety for nested routes.

Parametrize Route Loader for Nested Route in Tanstack Router

Parametrize nested route loaders in TanStack Router using path parameters

In this lesson, we learn how to create nested routes and outlets in TanStack Router using file-based routing.

We start by creating a new `employees` directory and files to represent nested routes, such as `/employees/$employeeId`. The `$` symbol is used to denote dynamic parameters.

We then use the `<Link>` component from TanStack Router to create links to these nested routes, passing necessary parameters.

To render the nested content, we use the `<Outlet>` component (nested), which automatically renders child routes. This approach allows us to dynamically display stuff under a nested route.

All the time, the TanStack Router generator automatically updates the route tree based on file changes - our routing configuration remains consistent 🔥



Create Nested Route and Nested Outlets in Tanstack Router

Create nested routes and outlets in TanStack Router using file-based routing

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