.

.gitignore

@@ -1 +1,2 @@
 /target
+/test

src/cli.rs

@@ -1,5 +1,7 @@
 use std::path::PathBuf;
 
+use clap::CommandFactory;
+
 #[derive(Debug, clap::Parser)]
 #[command(author, version, about, long_about = None)]
 pub struct Args {
@@ -10,19 +12,60 @@ pub struct Args {
 #[derive(Debug, clap::Subcommand)]
 pub enum Command {
     Generate {
-        #[clap(short, long)]
         output: PathBuf,
-        #[clap(short, long, value_parser = clap::value_parser!(u32).range(1..))]
+        #[clap(short, long, default_value = "10", value_parser = clap::value_parser!(u32).range(1..))]
         lines: u32,
-        #[clap(long = "min-op", value_parser = clap::value_parser!(u32).range(1..))]
+        #[clap(long = "min-op", default_value = "2", value_parser = clap::value_parser!(u32).range(1..))]
         min_operands: u32,
-        #[clap(long = "max-op", value_parser = clap::value_parser!(u32).range(1..))]
+        #[clap(long = "max-op", default_value = "7", value_parser = clap::value_parser!(u32).range(1..))]
         max_operands: u32,
     },
     Translate {
-        #[clap(short, long)]
         input: PathBuf,
-        #[clap(short, long)]
         output: PathBuf,
     },
 }
+
+pub fn validate_args(args: Args) -> Args {
+    match _validate_args(args) {
+        Ok(args) => args,
+        Err(err) => {
+            let mut command = Args::command();
+            err.format(&mut command).exit();
+        }
+    }
+}
+
+fn _validate_args(args: Args) -> Result<Args, clap::Error> {
+    match &args.command {
+        Command::Generate {
+            min_operands,
+            max_operands,
+            ..
+        } => {
+            if min_operands > max_operands {
+                return Err(clap::Error::raw(
+                    clap::error::ErrorKind::ValueValidation,
+                    "min operands must not be greater than max operands",
+                ));
+            }
+        }
+        Command::Translate { input, output } => {
+            if !input.is_file() {
+                return Err(clap::Error::raw(
+                    clap::error::ErrorKind::ValueValidation,
+                    "input must be an existing file",
+                ));
+            }
+
+            if input == output {
+                return Err(clap::Error::raw(
+                    clap::error::ErrorKind::ValueValidation,
+                    "input and output must not be the same",
+                ));
+            }
+        }
+    }
+
+    Ok(args)
+}

src/generator.rs

@@ -0,0 +1,44 @@
+pub struct FileGenerator<'a, W: std::io::Write, R: rand::Rng> {
+    writer: &'a mut W,
+    rand: R,
+}
+
+impl<'a, W: std::io::Write, R: rand::Rng> FileGenerator<'a, W, R> {
+    const OPERANDS: &'static str = "+-*/";
+    const DIGITS: &'static str = "123456789";
+
+    pub fn new(writer: &'a mut W, rand: R) -> Self {
+        Self { writer, rand }
+    }
+
+    pub fn generate(
+        &mut self,
+        lines: u32,
+        min_operands: u32,
+        max_operands: u32,
+    ) -> anyhow::Result<()> {
+        for _ in 0..lines {
+            let operands = self.rand.gen_range(min_operands..max_operands + 1);
+            for _ in 0..operands {
+                let digit_idx = self.rand.gen_range(0..Self::DIGITS.len());
+                let operand_idx = self.rand.gen_range(0..Self::OPERANDS.len());
+
+                let digit = Self::DIGITS.get(digit_idx..digit_idx + 1).unwrap();
+                let operand = Self::OPERANDS.get(operand_idx..operand_idx + 1).unwrap();
+
+                self.writer.write_all(digit.as_bytes())?;
+                self.writer.write_all(b" ")?;
+                self.writer.write_all(operand.as_bytes())?;
+                self.writer.write_all(b" ")?;
+            }
+
+            let digit = self.rand.gen_range(0..Self::DIGITS.len());
+            let digit = Self::DIGITS.get(digit..digit + 1).unwrap();
+            self.writer.write_all(digit.as_bytes())?;
+
+            self.writer.write_all(b"\n")?;
+        }
+
+        Ok(())
+    }
+}

src/main.rs

@@ -1,54 +1,13 @@
-use std::{
-    collections::HashMap,
-    io::{Read, Write},
-    sync::OnceLock,
-};
+use std::{fs, io};
 
-use clap::{CommandFactory, Parser};
-use rand::Rng;
+use clap::Parser;
 
 mod cli;
+mod generator;
+mod translator;
 
-static OPERANDS: &str = "+-*/";
-static DIGITS: &str = "123456789";
-
-static TRANSLATION_TABLE: OnceLock<HashMap<&'static str, &'static str>> = OnceLock::new();
-
-fn valudate_args(args: cli::Args) -> Result<cli::Args, clap::Error> {
-    match &args.command {
-        cli::Command::Generate {
-            min_operands,
-            max_operands,
-            ..
-        } => {
-            if min_operands > max_operands {
-                return Err(clap::Error::raw(
-                    clap::error::ErrorKind::ValueValidation,
-                    "min operands must not be greater than max operands",
-                ));
-            }
-        }
-        cli::Command::Translate { input, output } => {
-            if input == output {
-                return Err(clap::Error::raw(
-                    clap::error::ErrorKind::ValueValidation,
-                    "input and output must not be the same",
-                ));
-            }
-        }
-    }
-
-    Ok(args)
-}
-
-fn main() {
-    let args = match valudate_args(cli::Args::parse()) {
-        Ok(args) => args,
-        Err(err) => {
-            let mut command = cli::Args::command();
-            err.format(&mut command).exit();
-        }
-    };
+fn main() -> anyhow::Result<()> {
+    let args = cli::validate_args(cli::Args::parse());
 
     match args.command {
         cli::Command::Generate {
@@ -57,68 +16,24 @@ fn main() {
             min_operands,
             max_operands,
         } => {
-            let mut rand = rand::thread_rng();
-            let mut output = std::fs::File::create(output).unwrap();
-            for _ in 0..lines {
-                let operands = rand.gen_range(min_operands..max_operands + 1);
-                for _ in 0..operands {
-                    let digit = rand.gen_range(0..DIGITS.len());
-                    let operand = rand.gen_range(0..OPERANDS.len());
-
-                    let digit = DIGITS.get(digit..digit + 1).unwrap();
-                    let operand = OPERANDS.get(operand..operand + 1).unwrap();
-
-                    output.write(digit.as_bytes()).unwrap();
-                    output.write(b" ").unwrap();
-                    output.write(operand.as_bytes()).unwrap();
-                    output.write(b" ").unwrap();
-                }
-
-                let digit = rand.gen_range(0..DIGITS.len());
-                let digit = DIGITS.get(digit..digit + 1).unwrap();
-                output.write(digit.as_bytes()).unwrap();
-
-                output.write(b"\n").unwrap();
+            if !fs::exists(output.parent().unwrap())? {
+                fs::create_dir_all(output.parent().unwrap())?;
             }
+            let mut output = io::BufWriter::new(fs::File::create(output)?);
+
+            let rand = rand::thread_rng();
+
+            let mut generator = generator::FileGenerator::new(&mut output, rand);
+            generator.generate(lines, min_operands, max_operands)?;
         }
         cli::Command::Translate { input, output } => {
-            let table = TRANSLATION_TABLE.get_or_init(|| {
-                HashMap::from([
-                    ("+", "add"),
-                    ("-", "subtract"),
-                    ("*", "multiply by"),
-                    ("/", "divide by"),
-                    ("0", "zero"),
-                    ("1", "one"),
-                    ("2", "two"),
-                    ("3", "three"),
-                    ("4", "four"),
-                    ("5", "five"),
-                    ("6", "six"),
-                    ("7", "seven"),
-                    ("8", "eight"),
-                    ("9", "nine"),
-                ])
-            });
+            let mut input = io::BufReader::new(fs::File::open(input)?);
+            let mut output = io::BufWriter::new(fs::File::create(output)?);
 
-            let mut input = std::fs::File::open(input).unwrap();
-            let mut output = std::fs::File::create(output).unwrap();
-
-            let mut buf = [0u8; 1];
-
-            loop {
-                match input.read(&mut buf) {
-                    Ok(0) => break,
-                    Ok(_) => {
-                        let digit = std::str::from_utf8(&buf).unwrap();
-                        match table.get(digit) {
-                            Some(translation) => output.write(translation.as_bytes()).unwrap(),
-                            None => output.write(digit.as_bytes()).unwrap(),
-                        };
-                    }
-                    Err(err) => panic!("{}", err),
-                }
-            }
+            let mut translator = translator::FileTranslator::new(&mut input, &mut output);
+            translator.translate()?;
         }
     }
+
+    Ok(())
 }

src/translator.rs

@@ -0,0 +1,50 @@
+use std::{collections::HashMap, sync::LazyLock};
+
+pub struct FileTranslator<'a, R: std::io::Read, W: std::io::Write> {
+    reader: &'a mut R,
+    writer: &'a mut W,
+}
+
+static TRANSLATION_TABLE: LazyLock<HashMap<&'static str, &'static str>> = LazyLock::new(|| {
+    HashMap::from([
+        ("+", "add"),
+        ("-", "subtract"),
+        ("*", "multiply by"),
+        ("/", "divide by"),
+        ("0", "zero"),
+        ("1", "one"),
+        ("2", "two"),
+        ("3", "three"),
+        ("4", "four"),
+        ("5", "five"),
+        ("6", "six"),
+        ("7", "seven"),
+        ("8", "eight"),
+        ("9", "nine"),
+    ])
+});
+
+impl<'a, R: std::io::Read, W: std::io::Write> FileTranslator<'a, R, W> {
+    pub fn new(reader: &'a mut R, writer: &'a mut W) -> Self {
+        Self { reader, writer }
+    }
+
+    pub fn translate(&mut self) -> anyhow::Result<()> {
+        let mut buf = [0u8; 1];
+
+        loop {
+            match self.reader.read(&mut buf)? {
+                0 => break,
+                _ => {
+                    let digit = std::str::from_utf8(&buf)?;
+                    match TRANSLATION_TABLE.get(digit) {
+                        Some(translation) => self.writer.write_all(translation.as_bytes())?,
+                        None => self.writer.write_all(digit.as_bytes())?,
+                    };
+                }
+            }
+        }
+
+        Ok(())
+    }
+}