Postgres original todos example

# TODOs Example

## Setup

1. Declare the database URL

    ```
    export DATABASE_URL="postgres://postgres:password@localhost/todos"
    ```

2. Create the database.

    ```
    $ sqlx db create
    ```

3. Run sql migrations

    ```
    $ sqlx migrate run
    ```

## Usage

Add a todo 

```
cargo run -- add "todo description"
```

Complete a todo.

```
cargo run -- done <todo id>
```

List all todos

```
cargo run
```

[package]
name = "todos"
version = "0.1.0"
edition = "2018"

[dependencies]
anyhow = "1.0.58"
sqlx = { version = "0.8.6", features = ["postgres", "runtime-tokio", "tls-native-tls"] }
clap = { version = "4.4.7", features = ["derive"] }
tokio = { version = "1.25.0", features = ["rt", "macros"]}
dotenvy = "0.15.7"

use clap::{Parser, Subcommand};
use sqlx::postgres::PgPool;
use std::env;

#[derive(Parser)]
struct Args {
    #[command(subcommand)]
    cmd: Option<Command>,
}

#[derive(Subcommand)]
enum Command {
    Add { description: String },
    Done { id: i64 },
}

#[tokio::main(flavor = "current_thread")]
async fn main() -> anyhow::Result<()> {
    let args = Args::parse();
    let pool = PgPool::connect(&env::var("DATABASE_URL")?).await?;

    match args.cmd {
        Some(Command::Add { description }) => {
            println!("Adding new todo with description '{description}'");
            let todo_id = add_todo(&pool, description).await?;
            println!("Added new todo with id {todo_id}");
        }
        Some(Command::Done { id }) => {
            println!("Marking todo {id} as done");
            if complete_todo(&pool, id).await? {
                println!("Todo {id} is marked as done");
            } else {
                println!("Invalid id {id}");
            }
        }
        None => {
            println!("Printing list of all todos");
            list_todos(&pool).await?;
        }
    }

    Ok(())
}

async fn add_todo(pool: &PgPool, description: String) -> anyhow::Result<i64> {
    let rec = sqlx::query!(
        r#"
INSERT INTO todos ( description )
VALUES ( $1 )
RETURNING id
        "#,
        description
    )
    .fetch_one(pool)
    .await?;

    Ok(rec.id)
}

async fn complete_todo(pool: &PgPool, id: i64) -> anyhow::Result<bool> {
    let rows_affected = sqlx::query!(
        r#"
UPDATE todos
SET done = TRUE
WHERE id = $1
        "#,
        id
    )
    .execute(pool)
    .await?
    .rows_affected();

    Ok(rows_affected > 0)
}

async fn list_todos(pool: &PgPool) -> anyhow::Result<()> {
    let recs = sqlx::query!(
        r#"
SELECT id, description, done
FROM todos
ORDER BY id
        "#
    )
    .fetch_all(pool)
    .await?;

    for rec in recs {
        println!(
            "- [{}] {}: {}",
            if rec.done { "x" } else { " " },
            rec.id,
            &rec.description,
        );
    }

    Ok(())
}

CREATE TABLE IF NOT EXISTS todos
(
    id          BIGSERIAL PRIMARY KEY,
    description TEXT    NOT NULL,
    done        BOOLEAN NOT NULL DEFAULT FALSE
);