test: add tests

Cargo.lock

@@ -1746,6 +1746,7 @@ dependencies = [
  "rand",
  "regex",
  "serde",
+ "shlex",
  "teloxide",
  "tempfile",
  "thiserror 2.0.16",
@@ -1755,6 +1756,7 @@ dependencies = [
  "tracing-bunyan-formatter",
  "tracing-log 0.2.0",
  "tracing-subscriber",
+ "url",
 ]
 
 [[package]]

Cargo.toml

@@ -14,6 +14,7 @@ infer = "0.19"
 rand = "0.9"
 regex = "1.11"
 serde = { version = "1.0", features = ["derive"] }
+shlex = "1.3.0"
 teloxide = { version = "0.17", features = ["macros"] }
 tempfile = "3"
 thiserror = "2.0"
@@ -28,6 +29,7 @@ tracing-appender = "0.2"
 tracing-bunyan-formatter = { version = "0.3", default-features = false }
 tracing-log = "0.2.0"
 tracing-subscriber = { version = "0.3", features = ["registry", "env-filter"] }
+url = "2.5"
 
 [lints.clippy]
 pedantic = "warn"

src/comments.rs

@@ -1,11 +1,20 @@
 use crate::error::{Error, Result};
 use rand::{rng, seq::IndexedRandom};
 use std::{
+    fmt::Display,
     path::Path,
     sync::{Arc, OnceLock},
 };
 use tokio::fs::read_to_string;
-static DISCLAIMER: &str = "(Roleplay — fictional messages for entertainment.)";
+
+const DISCLAIMER: &str = "(Roleplay — fictional messages for entertainment.)";
+pub const TELEGRAM_CAPTION_LIMIT: usize = 4096;
+const FALLBACK_COMMENTS: &[&str] = &[
+    "Oh come on, that's brilliant — and slightly chaotic, like always.",
+    "That is a proper bit of craftsmanship — then someone presses the red button.",
+    "Nice shot — looks good on the trailer, not so good on the gearbox.",
+    "Here you go. Judge for yourself.",
+];
 
 #[derive(Debug)]
 pub struct Comments {
@@ -17,12 +26,10 @@ impl Comments {
     /// Create a small dummy/default Comments instance (useful for tests or fallback).
     #[must_use]
     pub fn dummy() -> Self {
-        let lines = vec![
-            "Oh come on, that's brilliant — and slightly chaotic, like always.".into(),
-            "That is a proper bit of craftsmanship — then someone presses the red button.".into(),
-            "Nice shot — looks good on the trailer, not so good on the gearbox.".into(),
-            "Here you go. Judge for yourself.".into(),
-        ];
+        let lines = FALLBACK_COMMENTS
+            .iter()
+            .map(ToString::to_string)
+            .collect::<Vec<_>>();
         Self {
             disclaimer: DISCLAIMER.into(),
             lines: lines.into(),
@@ -33,14 +40,12 @@ impl Comments {
     ///
     /// # Errors
     ///
-    /// - Returns `Error::Io` if reading the file fails (propagated from
-    ///   `tokio::fs::read_to_string`).
-    /// - Returns `Error::Other` if the file contains no usable lines after
-    ///   filtering (empty or all-comment file).
+    /// - Returns `Error::Io` if reading the file fails.
+    /// - Returns `Error::Other` if the file contains no usable lines.
     pub async fn load_from_file<P: AsRef<Path>>(path: P) -> Result<Self> {
-        let s = read_to_string(path).await?;
+        let content = read_to_string(path).await?;
 
-        let lines = s
+        let lines = content
             .lines()
             .map(str::trim)
             .filter(|l| !l.is_empty() && !l.starts_with('#'))
@@ -57,20 +62,35 @@ impl Comments {
         })
     }
 
-    /// Pick a random comment as &str (no allocation). Falls back to a small static
-    /// string if the list is unexpectedly empty.
+    /// Pick a random comment. Falls back to a default if the list is empty.
     #[must_use]
     pub fn pick(&self) -> &str {
         let mut rng = rng();
         self.lines
             .choose(&mut rng)
-            .map_or("Here you go.", String::as_str)
+            .map_or(FALLBACK_COMMENTS[0], AsRef::as_ref)
     }
 
+    /// Build a caption by picking a random comment and truncating if necessary.
     #[must_use]
-    #[inline]
     pub fn build_caption(&self) -> String {
-        self.pick().to_string()
+        let mut caption = self.pick().to_string();
+
+        // Trancate if too long for Telegram
+        if caption.chars().count() > TELEGRAM_CAPTION_LIMIT {
+            let truncated = caption
+                .chars()
+                .take(TELEGRAM_CAPTION_LIMIT.saturating_sub(3))
+                .collect::<String>();
+            caption = format!("{truncated}...");
+        }
+        caption
+    }
+
+    /// Get a reference to the underlying lines for debugging or testing.
+    #[cfg(test)]
+    pub fn lines(&self) -> &[String] {
+        &self.lines
     }
 }
 
@@ -80,8 +100,7 @@ static GLOBAL_COMMENTS: OnceLock<Comments> = OnceLock::new();
 ///
 /// # Errors
 ///
-/// - Returns `Error::Other` when the global is already initialized (the
-///   underlying `OnceLock::set` fails).
+/// - Returns `Error::Other` when the global is already initialized.
 pub fn init_global_comments(comments: Comments) -> Result<()> {
     GLOBAL_COMMENTS
         .set(comments)
@@ -89,6 +108,59 @@ pub fn init_global_comments(comments: Comments) -> Result<()> {
 }
 
 /// Get global comments (if initialized). Returns Option<&'static Comments>.
+#[inline]
+#[must_use]
 pub fn global_comments() -> Option<&'static Comments> {
     GLOBAL_COMMENTS.get()
 }
+
+impl Display for Comments {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.build_caption())
+    }
+}
+
+impl From<Comments> for String {
+    fn from(value: Comments) -> Self {
+        value.to_string()
+    }
+}
+
+impl From<&Comments> for String {
+    fn from(value: &Comments) -> Self {
+        value.to_string()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn dummy_comments() {
+        let comments = Comments::dummy();
+        assert_eq!(comments.lines.len(), FALLBACK_COMMENTS.len());
+        assert!(!comments.lines.is_empty());
+    }
+
+    #[test]
+    fn build_caption_truncation() {
+        let long_comment = "A".repeat(TELEGRAM_CAPTION_LIMIT + 10);
+        let comments = Comments {
+            disclaimer: DISCLAIMER.into(),
+            lines: Arc::new(vec![long_comment]),
+        };
+
+        let caption = comments.build_caption();
+        assert_eq!(caption.chars().count(), TELEGRAM_CAPTION_LIMIT);
+        assert!(caption.ends_with("..."))
+    }
+
+    #[test]
+    fn pick_fallbakc() {
+        let empty_comment = Comments {
+            disclaimer: DISCLAIMER.into(),
+            lines: Arc::new(Vec::new()),
+        };
+        assert_eq!(empty_comment.pick(), FALLBACK_COMMENTS[0]);
+    }
+}

src/download.rs

@@ -1,12 +1,25 @@
 use crate::{
     error::{Error, Result},
-    utils::{MediaKind, detect_media_kind_async, send_media_from_path},
+    utils::{
+        IMAGE_EXTSTENSIONS, MediaKind, VIDEO_EXTSTENSIONS, detect_media_kind_async,
+        send_media_from_path,
+    },
 };
 use futures::{StreamExt, stream};
-use std::{path::PathBuf, process::Stdio};
+use std::{
+    cmp::min,
+    env,
+    ffi::OsStr,
+    fs::{self, metadata},
+    path::{Path, PathBuf},
+    process::Stdio,
+};
 use teloxide::{Bot, types::ChatId};
 use tempfile::{TempDir, tempdir};
 use tokio::{fs::read_dir, process::Command};
+use tracing::{info, warn};
+
+const FORBIDDEN_EXTENSIONS: &[&str] = &["json", "txt", "log"];
 
 /// `TempDir` guard + downloaded files. Keep this value alive until you're
 /// done sending files so the temporary directory is not deleted.
@@ -19,6 +32,8 @@ pub struct DownloadResult {
 /// Run a command in a freshly created temporary directory and collect
 /// regular files produced there.
 ///
+/// # Arguments
+///
 /// `cmd` is the command name (e.g. "yt-dlp" or "instaloader").
 /// `args` are the command arguments (owned Strings so callers can build dynamic args).
 ///
@@ -29,7 +44,7 @@ pub struct DownloadResult {
 /// - `Error::NoMediaFound` if no files were produced.
 #[allow(clippy::similar_names)]
 async fn run_command_in_tempdir(cmd: &str, args: &[&str]) -> Result<DownloadResult> {
-    let tmp = tempdir().map_err(Error::from)?;
+    let tmp = tempdir()?;
     let cwd = tmp.path().to_path_buf();
 
     let output = Command::new(cmd)
@@ -39,27 +54,50 @@ async fn run_command_in_tempdir(cmd: &str, args: &[&str]) -> Result<DownloadResu
         .stdout(Stdio::null())
         .stderr(Stdio::piped())
         .output()
-        .await
-        .map_err(Error::from)?;
+        .await?;
 
     if !output.status.success() {
         let stderr = String::from_utf8_lossy(&output.stderr).trim().to_string();
+
+        if stderr.is_empty() {
             return Err(Error::Other(format!("{cmd} failed: {stderr}")));
         }
 
-    // collect files produced in tempdir (async)
+        let err = match cmd {
+            "instaloader" => Error::instaloader_failed(stderr),
+            "yt-dlp" => Error::ytdlp_failed(stderr),
+            _ => Error::Other(format!("{cmd} failed: {stderr}")),
+        };
+        return Err(err);
+    }
+
+    // Collect files produced in tempdir (async)
     let mut rd = read_dir(&cwd).await?;
     let mut files = Vec::new();
     while let Some(entry) = rd.next_entry().await? {
-        if entry.file_type().await?.is_file() {
-            files.push(entry.path());
+        let path = entry.path();
+        // Filter out non-media files (logs, metadata, etc.)
+        if is_potential_media_file(&path) {
+            files.push(path);
         }
     }
 
+    info!(files = files.len(), "Collected files from tempdir");
+
     if files.is_empty() {
+        let dir_contents = fs::read_dir(&cwd)
+            .map(|rd| {
+                rd.filter_map(std::result::Result::ok)
+                    .map(|e| e.path())
+                    .collect::<Vec<_>>()
+            })
+            .unwrap_or_default();
+        warn!(dir_contents = ?dir_contents, "No media files found in tempdir");
         return Err(Error::NoMediaFound);
     }
 
+    files.sort();
+
     Ok(DownloadResult {
         tempdir: tmp,
         files,
@@ -90,23 +128,32 @@ pub async fn download_instaloader(shortcode: &str) -> Result<DownloadResult> {
 ///
 /// - Propagates `run_command_in_tempdir` errors.
 pub async fn download_ytdlp(url: &str, cookies: Option<&str>) -> Result<DownloadResult> {
+    let default_format = "bestvideo[ext=mp4][vcodec^=avc1]+bestaudio/best";
+    let format_selector = env::var("YTDLP_FORMAT").unwrap_or_else(|_| default_format.into());
+
     let mut args = vec![
         "--no-playlist",
         "--merge-output-format",
         "mp4",
         "-f",
-        "bestvideo[ext=mp4][vcodec^=avc1]+bestaudio/best",
+        &format_selector,
         "--restrict-filenames",
         "-o",
         "%(id)s.%(ext)s",
+        "--no-warnings",
+        "--quiet",
     ];
 
-    if let Some(c) = cookies {
-        args.push("--cookies");
-        args.push(c);
+    if let Some(cookie_path) = cookies {
+        if Path::new(cookie_path).exists() {
+            args.extend(["--cookies", cookie_path]);
+        } else {
+            warn!("Cookies file not found: {cookie_path}");
+        }
     }
 
-    args.push(url);
+    let quoted_url = shlex::try_quote(url)?;
+    args.push(&quoted_url);
 
     run_command_in_tempdir("yt-dlp", &args).await
 }
@@ -119,10 +166,20 @@ pub async fn download_ytdlp(url: &str, cookies: Option<&str>) -> Result<Download
 /// # Errors
 ///
 /// - Propagates `send_media_from_path` errors or returns NoMediaFound/UnknownMediaKind.
-pub async fn process_download_result(bot: &Bot, chat_id: ChatId, dr: DownloadResult) -> Result<()> {
-    // detect kinds in parallel
-    let concurrency = 8;
-    let results = stream::iter(dr.files.into_iter().map(|path| async move {
+pub async fn process_download_result(
+    bot: &Bot,
+    chat_id: ChatId,
+    mut dr: DownloadResult,
+) -> Result<()> {
+    info!(files = dr.files.len(), "Processing download result");
+
+    if dr.files.is_empty() {
+        return Err(Error::NoMediaFound);
+    }
+
+    // Detect kinds in parallel with limiter concurrency
+    let concurrency = min(8, dr.files.len());
+    let results = stream::iter(dr.files.drain(..).map(|path| async move {
         let kind = detect_media_kind_async(&path).await;
         match kind {
             MediaKind::Unknown => None,
@@ -133,26 +190,76 @@ pub async fn process_download_result(bot: &Bot, chat_id: ChatId, dr: DownloadRes
     .collect::<Vec<Option<(PathBuf, MediaKind)>>>()
     .await;
 
-    let mut media = results
+    let mut media_items = results
         .into_iter()
         .flatten()
-        .collect::<Vec<(PathBuf, MediaKind)>>();
+        .filter(|(path, _)| {
+            metadata(path)
+                .map(|m| m.is_file() && m.len() > 0)
+                .unwrap_or(false)
+        })
+        .collect::<Vec<_>>();
 
-    if media.is_empty() {
+    if media_items.is_empty() {
         return Err(Error::NoMediaFound);
     }
 
     // deterministic ordering
-    media.sort_by_key(|(p, _)| p.clone());
+    media_items.sort_by(|(p1, _), (p2, _)| p1.cmp(p2));
+
+    info!(media_items = media_items.len(), "Sending media to chat");
 
     // prefer video over image
-    if let Some((path, MediaKind::Video)) = media.iter().find(|(_, k)| *k == MediaKind::Video) {
-        return send_media_from_path(bot, chat_id, path.clone(), Some(MediaKind::Video)).await;
+    if let Some((path, MediaKind::Video)) = media_items.iter().find(|(_, k)| *k == MediaKind::Video)
+    {
+        return send_media_from_path(bot, chat_id, path.clone(), MediaKind::Video).await;
     }
 
-    if let Some((path, MediaKind::Image)) = media.iter().find(|(_, k)| *k == MediaKind::Image) {
-        return send_media_from_path(bot, chat_id, path.clone(), Some(MediaKind::Image)).await;
+    if let Some((path, MediaKind::Image)) = media_items.iter().find(|(_, k)| *k == MediaKind::Image)
+    {
+        return send_media_from_path(bot, chat_id, path.clone(), MediaKind::Image).await;
     }
 
     Err(Error::NoMediaFound)
 }
+
+/// Filter function to determine if a file is potentially media based on name/extension.
+fn is_potential_media_file(path: &Path) -> bool {
+    if let Some(filename) = path.file_name().and_then(OsStr::to_str) {
+        // Skip common non-media files
+        if filename.starts_with('.') || filename.to_lowercase().contains("metadata") {
+            return false;
+        }
+    }
+
+    let ext = match path.extension().and_then(OsStr::to_str) {
+        Some(e) => e.to_lowercase(),
+        None => return false,
+    };
+
+    if FORBIDDEN_EXTENSIONS
+        .iter()
+        .any(|forbidden| forbidden.eq_ignore_ascii_case(&ext))
+    {
+        return false;
+    }
+
+    VIDEO_EXTSTENSIONS
+        .iter()
+        .chain(IMAGE_EXTSTENSIONS.iter())
+        .any(|allowed| allowed.eq_ignore_ascii_case(&ext))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn is_potential_media_file_() {
+        assert!(is_potential_media_file(Path::new("video.mp4")));
+        assert!(is_potential_media_file(Path::new("image.jpg")));
+        assert!(!is_potential_media_file(Path::new(".DS_Store")));
+        assert!(!is_potential_media_file(Path::new("metadata.json")));
+        assert!(!is_potential_media_file(Path::new("download.log")));
+    }
+}

src/error.rs

@@ -17,12 +17,21 @@ pub enum Error {
     #[error("unknown media kind")]
     UnknownMediaKind,
 
+    #[error("validation failed: {0}")]
+    ValidationFailed(String),
+
     #[error("teloxide error: {0}")]
     Teloxide(#[from] teloxide::RequestError),
 
     #[error("join error: {0}")]
     Join(#[from] tokio::task::JoinError),
 
+    #[error("rate limit exceeded")]
+    RateLimit,
+
+    #[error("")]
+    QuoteError(#[from] shlex::QuoteError),
+
     #[error("other: {0}")]
     Other(String),
 }
@@ -42,6 +51,11 @@ impl Error {
     pub fn ytdlp_failed(text: impl Into<String>) -> Self {
         Self::YTDLPFailed(text.into())
     }
+
+    #[inline]
+    pub fn validation_falied(text: impl Into<String>) -> Self {
+        Self::ValidationFailed(text.into())
+    }
 }
 
 pub type Result<T> = std::result::Result<T, Error>;

src/lib.rs

@@ -4,3 +4,4 @@ pub mod error;
 pub mod handlers;
 pub mod telemetry;
 pub mod utils;
+pub mod validate;

src/utils.rs

@@ -1,5 +1,5 @@
 use crate::{
-    comments::global_comments,
+    comments::{Comments, global_comments},
     error::{Error, Result},
 };
 use std::{
@@ -13,10 +13,10 @@ use teloxide::{
     types::{ChatId, InputFile},
 };
 use tokio::{fs::File, io::AsyncReadExt};
+use tracing::warn;
 
-const TELEGRAM_CAPTION_LIMIT: usize = 1024;
-static VIDEO_EXTS: &[&str] = &["mp4", "webm", "mov", "mkv", "avi"];
-static IMAGE_EXTS: &[&str] = &["jpg", "jpeg", "png", "webp"];
+pub const VIDEO_EXTSTENSIONS: &[&str] = &["mp4", "webm", "mov", "mkv", "avi", "m4v", "3gp"];
+pub const IMAGE_EXTSTENSIONS: &[&str] = &["jpg", "jpeg", "png", "webp", "gif", "bmp"];
 
 /// Simple media kind enum shared by handlers.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
@@ -27,26 +27,25 @@ pub enum MediaKind {
 }
 
 /// Detect media kind first by extension, then by content/magic (sync).
-/// NOTE: `infer::get_from_path` is blocking — use `detect_media_kind_async` in
-/// async contexts to avoid blocking the Tokio runtime.
 pub fn detect_media_kind(path: &Path) -> MediaKind {
     if let Some(ext) = path.extension().and_then(OsStr::to_str) {
-        if VIDEO_EXTS.iter().any(|e| e.eq_ignore_ascii_case(ext)) {
+        let compare = |e: &&str| e.eq_ignore_ascii_case(ext);
+        if VIDEO_EXTSTENSIONS.iter().any(compare) {
             return MediaKind::Video;
         }
-        if IMAGE_EXTS.iter().any(|e| e.eq_ignore_ascii_case(ext)) {
+        if IMAGE_EXTSTENSIONS.iter().any(compare) {
             return MediaKind::Image;
         }
     }
 
+    // Fallback to MIME type detection
     if let Ok(Some(kind)) = infer::get_from_path(path) {
-        let mt = kind.mime_type();
-        if mt.starts_with("video/") {
-            return MediaKind::Video;
-        }
-        if mt.starts_with("image/") {
-            return MediaKind::Image;
-        }
+        let mime_type = kind.mime_type();
+        return match mime_type.split('/').next() {
+            Some("video") => MediaKind::Video,
+            Some("image") => MediaKind::Image,
+            _ => MediaKind::Unknown,
+        };
     }
 
     MediaKind::Unknown
@@ -56,21 +55,24 @@ pub fn detect_media_kind(path: &Path) -> MediaKind {
 /// sample asynchronously and run `infer::get` on the buffer.
 pub async fn detect_media_kind_async(path: &Path) -> MediaKind {
     if let Some(ext) = path.extension().and_then(OsStr::to_str) {
-        if VIDEO_EXTS.iter().any(|e| e.eq_ignore_ascii_case(ext)) {
+        let compare = |e: &&str| e.eq_ignore_ascii_case(ext);
+        if VIDEO_EXTSTENSIONS.iter().any(compare) {
             return MediaKind::Video;
         }
-        if IMAGE_EXTS.iter().any(|e| e.eq_ignore_ascii_case(ext)) {
+        if IMAGE_EXTSTENSIONS.iter().any(compare) {
             return MediaKind::Image;
         }
     }
 
     // Read a small prefix (8 KiB) asynchronously and probe
-    if let Ok(mut f) = File::open(path).await {
-        let mut buf = vec![0u8; 8192];
-        match f.read(&mut buf).await {
-            Ok(n) if n > 0 => {
-                buf.truncate(n);
-                if let Some(k) = infer::get(&buf) {
+    match File::open(path).await {
+        Ok(mut file) => {
+            let mut buffer = vec![0u8; 8192];
+            if let Ok(n) = file.read(&mut buffer).await
+                && n > 0
+            {
+                buffer.truncate(n);
+                if let Some(k) = infer::get(&buffer) {
                     let mt = k.mime_type();
                     if mt.starts_with("video/") {
                         return MediaKind::Video;
@@ -80,8 +82,8 @@ pub async fn detect_media_kind_async(path: &Path) -> MediaKind {
                     }
                 }
             }
-            _ => {}
         }
+        Err(e) => warn!(path = ?path.display(), "Failed to read file for media detection: {e}"),
     }
 
     MediaKind::Unknown
@@ -96,18 +98,11 @@ pub async fn send_media_from_path(
     bot: &Bot,
     chat_id: ChatId,
     path: PathBuf,
-    kind: Option<MediaKind>,
+    kind: MediaKind,
 ) -> Result<()> {
-    let kind = kind.unwrap_or_else(|| detect_media_kind(&path));
-
-    let caption_opt = global_comments().map(|c| {
-        let mut caption = c.build_caption();
-        if caption.chars().count() > TELEGRAM_CAPTION_LIMIT {
-            caption = caption.chars().take(TELEGRAM_CAPTION_LIMIT - 1).collect();
-            caption.push_str("...");
-        }
-        caption
-    });
+    let caption_opt = global_comments()
+        .map(Comments::build_caption)
+        .filter(|caption| !caption.is_empty());
 
     match kind {
         MediaKind::Video => {
@@ -116,7 +111,7 @@ pub async fn send_media_from_path(
             if let Some(c) = caption_opt {
                 req = req.caption(c);
             }
-            req.await.map_err(Error::from)?;
+            req.await?;
         }
         MediaKind::Image => {
             let photo = InputFile::file(path);
@@ -124,14 +119,34 @@ pub async fn send_media_from_path(
             if let Some(c) = caption_opt {
                 req = req.caption(c);
             }
-            req.await.map_err(Error::from)?;
+            req.await?;
         }
         MediaKind::Unknown => {
             bot.send_message(chat_id, "No supported media found")
-                .await
-                .map_err(Error::from)?;
+                .await?;
             return Err(Error::UnknownMediaKind);
         }
     }
     Ok(())
 }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn detect_media_kind_by_extension() {
+        assert_eq!(detect_media_kind(Path::new("video.mp4")), MediaKind::Video);
+        assert_eq!(detect_media_kind(Path::new("image.jpg")), MediaKind::Image);
+        assert_eq!(
+            detect_media_kind(Path::new("unknown.txt")),
+            MediaKind::Unknown
+        );
+    }
+
+    #[test]
+    fn media_kind_case_insensitive() {
+        assert_eq!(detect_media_kind(Path::new("VIDEO.MP4")), MediaKind::Video);
+        assert_eq!(detect_media_kind(Path::new("IMAGE.JPG")), MediaKind::Image);
+    }
+}

src/validate/mod.rs

@@ -0,0 +1,23 @@
+pub mod utils;
+
+use crate::error::Result;
+use regex::Regex;
+use std::sync::OnceLock;
+
+/// Trait for validating platform-specific identifiers (e.g., shortcodes, URLs)
+/// extracted from user input.
+///
+/// Implementors should:
+/// - Check format (e.g., length, characters).
+/// - Canonicalize if needed (e.g., trim query params from a URL).
+/// - Return `Ok(canonical_id)` on success or `Err(Error::Other(...))` on failure.
+pub trait Validate {
+    /// Validate the input and return a canonicalized String (e.g., cleaned shortcode or URL).
+    fn validate(&self, input: &str) -> Result<String>;
+}
+
+/// Helper function to create a lazy static Regex (reused across impls).
+pub fn lazy_regex(pattern: &str) -> &'static Regex {
+    static RE: OnceLock<Regex> = OnceLock::new();
+    RE.get_or_init(|| Regex::new(pattern).expect("failed to compile validation regex"))
+}

src/validate/utils.rs

@@ -0,0 +1,10 @@
+use crate::error::{Error, Result};
+
+/// Trims whitespace and rejects empty strings.
+pub fn validate_non_empty(input: &str) -> Result<&str> {
+    let trimmed = input.trim();
+    if trimmed.is_empty() {
+        return Err(Error::validation_falied("input cannot be empty"));
+    }
+    Ok(trimmed)
+}