3 files changed, 1060 insertions, 0 deletions

diff --git a/src/downloader.rs b/src/downloader.rs
new file mode 100644
index 0000000..6d92166
--- /dev/null
+++ b/src/downloader.rs
@@ -0,0 +1,589 @@
+use std::collections::HashSet;
+use std::fs;
+use std::io::{Read, Write};
+use std::path::Path;
+
+use anyhow::{bail, Context, Result};
+use regex::Regex;
+use serde::Deserialize;
+
+// ---------------------------------------------------------------------------
+// Public event type for GUI progress reporting
+// ---------------------------------------------------------------------------
+
+#[cfg(feature = "gui")]
+use std::sync::mpsc;
+
+#[cfg(feature = "gui")]
+#[derive(Debug, Clone)]
+pub enum Event {
+    Log(String),
+    DownloadStart { name: String, total_bytes: u64 },
+    DownloadProgress { name: String, bytes: u64 },
+    DownloadComplete { name: String },
+    DownloadError { name: String, error: String },
+    Finished { success: bool, message: String },
+}
+
+// ---------------------------------------------------------------------------
+// API response types
+// ---------------------------------------------------------------------------
+
+#[derive(Deserialize)]
+pub struct ModInfo {
+    pub releases: Vec<Release>,
+}
+
+#[derive(Deserialize, Clone)]
+pub struct Release {
+    pub version: String,
+    pub info_json: Option<InfoJson>,
+}
+
+#[derive(Deserialize, Clone)]
+pub struct InfoJson {
+    #[serde(default)]
+    pub dependencies: Vec<String>,
+}
+
+// ---------------------------------------------------------------------------
+// Dependency model
+// ---------------------------------------------------------------------------
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum DepType {
+    Base,
+    Required,
+    Optional,
+    Incompatible,
+}
+
+#[derive(Debug, Clone)]
+pub struct Dependency {
+    pub dep_type: DepType,
+    pub name: String,
+}
+
+// ---------------------------------------------------------------------------
+// Constants
+// ---------------------------------------------------------------------------
+
+pub const MODINFO_API: &str = "https://re146.dev/factorio/mods/modinfo";
+pub const DOWNLOAD_BASE: &str = "https://mods-storage.re146.dev";
+
+fn dep_regex() -> &'static Regex {
+    static RE: std::sync::LazyLock<Regex> = std::sync::LazyLock::new(|| {
+        Regex::new(
+            r"(?i)^((?:)|(?:\?)|(?:\(\?\))|(?:!)|(?:~))(?:\s?)([%\w\s-]+)(?:\s{0,})(?:((?:=>)|(?:==)|(?:=)|(?:<=)|(?:>=)|(?:<)|(?:>)|(?:))(?:\s{0,})((\d+\.\d+\.\d+)|(\d+\.\d+)))?$",
+        )
+        .unwrap()
+    });
+    &RE
+}
+
+// ---------------------------------------------------------------------------
+// Mod name extraction
+// ---------------------------------------------------------------------------
+
+pub fn extract_mod_name(url_or_name: &str) -> Result<String> {
+    let re = Regex::new(r"(?i)^https?://mods\.factorio\.com/mod/([^\s/#?]{1,})").unwrap();
+    if let Some(caps) = re.captures(url_or_name) {
+        return Ok(caps[1].to_string());
+    }
+
+    let re2 =
+        Regex::new(r"(?i)^https?://mods\.factorio\.com/mods/([^\s/]{1,})/([^\s/#?]{1,})").unwrap();
+    if let Some(caps) = re2.captures(url_or_name) {
+        return Ok(caps[2].to_string());
+    }
+
+    if !url_or_name.contains('/') && !url_or_name.starts_with("http") {
+        return Ok(url_or_name.to_string());
+    }
+
+    bail!("Could not extract mod name from: {url_or_name}")
+}
+
+// ---------------------------------------------------------------------------
+// API helpers
+// ---------------------------------------------------------------------------
+
+pub fn fetch_modinfo(mod_name: &str) -> Result<ModInfo> {
+    let url = format!("{MODINFO_API}?id={mod_name}");
+    let resp = ureq::get(&url)
+        .header("Accept", "application/json")
+        .call()
+        .with_context(|| format!("Failed to fetch mod info for {mod_name}"))?;
+
+    if resp.status().as_u16() == 404 {
+        bail!("Mod '{mod_name}' not found on the portal");
+    }
+
+    let body_text = resp
+        .into_body()
+        .read_to_string()
+        .with_context(|| format!("Failed to read response body for {mod_name}"))?;
+
+    let modinfo: ModInfo = serde_json::from_str(&body_text)
+        .with_context(|| format!("Failed to parse mod info JSON for {mod_name}"))?;
+
+    if modinfo.releases.is_empty() {
+        bail!("No releases found for '{mod_name}'");
+    }
+
+    Ok(modinfo)
+}
+
+/// Fetch available versions for a mod. Returns (version, display_label) pairs.
+#[cfg(feature = "gui")]
+pub fn fetch_versions(mod_name: &str) -> Result<Vec<(String, String)>> {
+    let modinfo = fetch_modinfo(mod_name)?;
+    let total = modinfo.releases.len();
+
+    let mut versions: Vec<(String, String)> = modinfo
+        .releases
+        .iter()
+        .enumerate()
+        .filter_map(|(i, r)| {
+            let v = r.version.clone();
+            if v.is_empty() {
+                return None;
+            }
+            let is_latest = i == total - 1;
+            let factorio_ver = r
+                .info_json
+                .as_ref()
+                .and_then(|j| j.dependencies.first())
+                .and_then(|d| {
+                    parse_dependency_string(d).and_then(|dep| {
+                        if dep.dep_type == DepType::Base && !dep.name.is_empty() {
+                            Some(dep.name)
+                        } else {
+                            None
+                        }
+                    })
+                })
+                .unwrap_or_default();
+
+            let mut label = v.clone();
+            if is_latest {
+                label.push_str(" (latest)");
+            }
+            if !factorio_ver.is_empty() {
+                label.push_str(&format!(" for {}", factorio_ver));
+            }
+            Some((v, label))
+        })
+        .collect();
+
+    versions.reverse();
+    Ok(versions)
+}
+
+pub fn find_release<'a>(modinfo: &'a ModInfo, target_version: Option<&str>) -> Option<&'a Release> {
+    match target_version {
+        Some(v) => modinfo.releases.iter().find(|r| r.version == v),
+        None => modinfo.releases.last(),
+    }
+}
+
+// ---------------------------------------------------------------------------
+// Dependency parsing
+// ---------------------------------------------------------------------------
+
+pub fn parse_dependency_string(input: &str) -> Option<Dependency> {
+    let re = dep_regex();
+    let caps = re.captures(input)?;
+
+    let name = caps[2].trim().to_string();
+
+    if name.eq_ignore_ascii_case("base") {
+        return Some(Dependency {
+            dep_type: DepType::Base,
+            name: "base".into(),
+        });
+    }
+
+    let dep_type = match &caps[1] {
+        "?" | "(?)" => DepType::Optional,
+        "!" => DepType::Incompatible,
+        _ => DepType::Required,
+    };
+
+    Some(Dependency {
+        dep_type,
+        name: name.trim().to_string(),
+    })
+}
+
+pub fn parse_dependencies(deps: &[String]) -> (Vec<Dependency>, Vec<Dependency>, Vec<Dependency>) {
+    let mut required = Vec::new();
+    let mut optional = Vec::new();
+    let mut incompatible = Vec::new();
+
+    for dep_str in deps.iter().rev() {
+        if let Some(dep) = parse_dependency_string(dep_str) {
+            match dep.dep_type {
+                DepType::Base => {}
+                DepType::Required => required.push(dep),
+                DepType::Optional => optional.push(dep),
+                DepType::Incompatible => incompatible.push(dep),
+            }
+        }
+    }
+
+    (required, optional, incompatible)
+}
+
+// ---------------------------------------------------------------------------
+// GUI download (channel-based)
+// ---------------------------------------------------------------------------
+
+#[cfg(feature = "gui")]
+fn gui_download_file(
+    url: &str,
+    file_path: &Path,
+    display_name: &str,
+    tx: &mpsc::Sender<Event>,
+) -> Result<()> {
+    let resp = ureq::get(url)
+        .call()
+        .with_context(|| format!("Failed to download {display_name}"))?;
+
+    let status = resp.status().as_u16();
+    if status == 404 {
+        bail!("File not found on storage: {display_name}");
+    }
+    if !(200..300).contains(&status) {
+        bail!("HTTP {status} while downloading {display_name}");
+    }
+
+    let total_size: u64 = resp
+        .headers()
+        .get("content-length")
+        .and_then(|v| v.to_str().ok())
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(0);
+
+    let _ = tx.send(Event::DownloadStart {
+        name: display_name.to_string(),
+        total_bytes: total_size,
+    });
+
+    let mut reader = resp.into_body().into_reader();
+    let mut file = fs::File::create(file_path)
+        .with_context(|| format!("Failed to create file {}", file_path.display()))?;
+
+    let mut buf = [0u8; 256 * 1024];
+    let mut downloaded: u64 = 0;
+    loop {
+        let n = reader
+            .read(&mut buf)
+            .with_context(|| format!("Read error while downloading {display_name}"))?;
+        if n == 0 {
+            break;
+        }
+        file.write_all(&buf[..n])
+            .with_context(|| format!("Write error for {}", file_path.display()))?;
+        downloaded += n as u64;
+        let _ = tx.send(Event::DownloadProgress {
+            name: display_name.to_string(),
+            bytes: downloaded,
+        });
+    }
+
+    let _ = tx.send(Event::DownloadComplete {
+        name: display_name.to_string(),
+    });
+    Ok(())
+}
+
+#[cfg(feature = "gui")]
+fn gui_download_mod_with_deps(
+    mod_name: &str,
+    output: &Path,
+    target_version: Option<&str>,
+    include_optional: bool,
+    downloaded: &mut HashSet<String>,
+    analyzed: &mut HashSet<String>,
+    tx: &mpsc::Sender<Event>,
+) -> Result<()> {
+    if analyzed.contains(mod_name) {
+        return Ok(());
+    }
+
+    if mod_name == "space-age" {
+        let _ = tx.send(Event::Log(format!(
+            "Skipping reserved dependency '{mod_name}'"
+        )));
+        return Ok(());
+    }
+
+    let modinfo = fetch_modinfo(mod_name)?;
+
+    let release = find_release(&modinfo, target_version)
+        .with_context(|| format!("Version not found for '{mod_name}'"))?;
+
+    let version = &release.version;
+    let _ = tx.send(Event::Log(format!("Processing: {mod_name} v{version}")));
+    analyzed.insert(mod_name.to_string());
+
+    let file_name = format!("{mod_name}_{version}.zip");
+    let file_path = output.join(&file_name);
+
+    if !file_path.exists() {
+        fs::create_dir_all(output)?;
+        let download_url = format!("{DOWNLOAD_BASE}/{mod_name}/{version}.zip");
+
+        if let Err(e) = gui_download_file(&download_url, &file_path, &file_name, tx) {
+            let _ = tx.send(Event::DownloadError {
+                name: file_name.clone(),
+                error: e.to_string(),
+            });
+            return Err(e);
+        }
+        downloaded.insert(mod_name.to_string());
+    } else {
+        let _ = tx.send(Event::Log(format!("Already downloaded: {file_name}")));
+    }
+
+    if let Some(info_json) = &release.info_json {
+        let (required, optional, _incompatible) = parse_dependencies(&info_json.dependencies);
+
+        let mut deps = required;
+        if include_optional {
+            deps.extend(optional);
+        }
+
+        for dep in &deps {
+            if dep.name == "base" || downloaded.contains(&dep.name) || analyzed.contains(&dep.name)
+            {
+                continue;
+            }
+            let _ = tx.send(Event::Log(format!("-> Fetching dependency: {}", dep.name)));
+            if let Err(e) = gui_download_mod_with_deps(
+                &dep.name,
+                output,
+                None,
+                include_optional,
+                downloaded,
+                analyzed,
+                tx,
+            ) {
+                let _ = tx.send(Event::Log(format!(
+                    "Error processing dependency {}: {}",
+                    dep.name, e
+                )));
+            }
+        }
+    }
+
+    Ok(())
+}
+
+/// Entry point for GUI downloads. Runs the full pipeline and sends events via the channel.
+#[cfg(feature = "gui")]
+pub fn run_gui_download(
+    mod_url: &str,
+    output: &Path,
+    target_version: Option<String>,
+    include_optional: bool,
+    tx: mpsc::Sender<Event>,
+) {
+    let result = (|| -> Result<()> {
+        let mod_name = extract_mod_name(mod_url)?;
+        let _ = tx.send(Event::Log(format!("Starting download: {mod_name}")));
+
+        let mut downloaded = HashSet::new();
+        let mut analyzed = HashSet::new();
+
+        gui_download_mod_with_deps(
+            &mod_name,
+            output,
+            target_version.as_deref(),
+            include_optional,
+            &mut downloaded,
+            &mut analyzed,
+            &tx,
+        )?;
+
+        Ok(())
+    })();
+
+    match result {
+        Ok(()) => {
+            let _ = tx.send(Event::Finished {
+                success: true,
+                message: "All mods downloaded successfully.".into(),
+            });
+        }
+        Err(e) => {
+            let _ = tx.send(Event::Finished {
+                success: false,
+                message: format!("Download failed: {e}"),
+            });
+        }
+    }
+}
+
+// ---------------------------------------------------------------------------
+// CLI download (prints progress to stdout)
+// ---------------------------------------------------------------------------
+
+#[cfg(not(feature = "gui"))]
+fn cli_download_file(url: &str, file_path: &Path, display_name: &str) -> Result<()> {
+    let resp = ureq::get(url)
+        .call()
+        .with_context(|| format!("Failed to download {display_name}"))?;
+
+    let status = resp.status().as_u16();
+    if status == 404 {
+        bail!("File not found on storage: {display_name}");
+    }
+    if !(200..300).contains(&status) {
+        bail!("HTTP {status} while downloading {display_name}");
+    }
+
+    let total_size: u64 = resp
+        .headers()
+        .get("content-length")
+        .and_then(|v| v.to_str().ok())
+        .and_then(|v| v.parse().ok())
+        .unwrap_or(0);
+
+    println!(
+        "  Downloading: {display_name} ({:.1} MB)",
+        total_size as f64 / 1_048_576.0
+    );
+
+    let mut reader = resp.into_body().into_reader();
+    let mut file = fs::File::create(file_path)
+        .with_context(|| format!("Failed to create file {}", file_path.display()))?;
+
+    let mut buf = [0u8; 256 * 1024];
+    let mut downloaded: u64 = 0;
+    let mut last_pct: u32 = 0;
+    loop {
+        let n = reader
+            .read(&mut buf)
+            .with_context(|| format!("Read error while downloading {display_name}"))?;
+        if n == 0 {
+            break;
+        }
+        file.write_all(&buf[..n])
+            .with_context(|| format!("Write error for {}", file_path.display()))?;
+        downloaded += n as u64;
+
+        if total_size > 0 {
+            let pct = (downloaded * 100 / total_size) as u32;
+            if pct / 10 != last_pct / 10 {
+                last_pct = pct;
+                print!("\r  {} {}%", display_name, pct);
+                let _ = std::io::Write::flush(&mut std::io::stdout());
+            }
+        }
+    }
+    println!("\r  {} Done.", display_name);
+    Ok(())
+}
+
+#[cfg(not(feature = "gui"))]
+fn cli_download_mod_with_deps(
+    mod_name: &str,
+    output: &Path,
+    target_version: Option<&str>,
+    include_optional: bool,
+    downloaded: &mut HashSet<String>,
+    analyzed: &mut HashSet<String>,
+) -> Result<()> {
+    if analyzed.contains(mod_name) {
+        return Ok(());
+    }
+
+    if mod_name == "space-age" {
+        println!("Skipping reserved dependency '{mod_name}'");
+        return Ok(());
+    }
+
+    let modinfo = fetch_modinfo(mod_name)?;
+
+    let release = find_release(&modinfo, target_version)
+        .with_context(|| format!("Version not found for '{mod_name}'"))?;
+
+    let version = &release.version;
+    println!("Processing: {mod_name} v{version}");
+    analyzed.insert(mod_name.to_string());
+
+    let file_name = format!("{mod_name}_{version}.zip");
+    let file_path = output.join(&file_name);
+
+    if !file_path.exists() {
+        fs::create_dir_all(output)?;
+        let download_url = format!("{DOWNLOAD_BASE}/{mod_name}/{version}.zip");
+
+        if let Err(e) = cli_download_file(&download_url, &file_path, &file_name) {
+            eprintln!("Error downloading {file_name}: {e}");
+            return Err(e);
+        }
+        downloaded.insert(mod_name.to_string());
+    } else {
+        println!("Already downloaded: {file_name}");
+    }
+
+    if let Some(info_json) = &release.info_json {
+        let (required, optional, _incompatible) = parse_dependencies(&info_json.dependencies);
+
+        let mut deps = required;
+        if include_optional {
+            deps.extend(optional);
+        }
+
+        for dep in &deps {
+            if dep.name == "base" || downloaded.contains(&dep.name) || analyzed.contains(&dep.name)
+            {
+                continue;
+            }
+            println!("-> Fetching dependency: {}", dep.name);
+            if let Err(e) = cli_download_mod_with_deps(
+                &dep.name,
+                output,
+                None,
+                include_optional,
+                downloaded,
+                analyzed,
+            ) {
+                eprintln!("Error processing dependency {}: {}", dep.name, e);
+            }
+        }
+    }
+
+    Ok(())
+}
+
+/// Entry point for CLI downloads. Prints progress to stdout.
+#[cfg(not(feature = "gui"))]
+pub fn run_cli_download(
+    mod_url: &str,
+    output: &Path,
+    target_version: Option<&str>,
+    include_optional: bool,
+) -> Result<()> {
+    let mod_name = extract_mod_name(mod_url)?;
+    println!("Starting download: {mod_name}");
+    println!("Output directory: {}", output.display());
+
+    let mut downloaded = HashSet::new();
+    let mut analyzed = HashSet::new();
+
+    cli_download_mod_with_deps(
+        &mod_name,
+        output,
+        target_version,
+        include_optional,
+        &mut downloaded,
+        &mut analyzed,
+    )?;
+
+    println!("\nAll mods downloaded successfully.");
+    Ok(())
+}
diff --git a/src/gui.rs b/src/gui.rs
new file mode 100644
index 0000000..5fe1092
--- /dev/null
+++ b/src/gui.rs
@@ -0,0 +1,369 @@
+use std::path::PathBuf;
+use std::sync::mpsc;
+use std::sync::mpsc::TryRecvError;
+use std::sync::{Arc, Mutex};
+use std::thread;
+
+use egui::{Color32, ProgressBar, ScrollArea, TextEdit};
+use rfd::FileDialog;
+
+use crate::downloader::{self, Event};
+
+pub struct App {
+    mod_url: String,
+    output_path: String,
+    target_version: String,
+    include_optional: bool,
+
+    versions: Vec<(String, String)>,
+    loading_versions: bool,
+    version_handle: Option<Arc<Mutex<Option<Vec<(String, String)>>>>>,
+
+    downloading: bool,
+    finished: bool,
+
+    downloads: Vec<DownloadState>,
+    log_entries: Vec<LogEntry>,
+
+    receiver: Option<mpsc::Receiver<Event>>,
+}
+
+struct DownloadState {
+    name: String,
+    total_bytes: u64,
+    downloaded_bytes: u64,
+    complete: bool,
+    error: Option<String>,
+}
+
+struct LogEntry {
+    text: String,
+    is_error: bool,
+}
+
+impl App {
+    pub fn new() -> Self {
+        Self {
+            mod_url: String::new(),
+            output_path: std::env::current_dir()
+                .map(|p| p.display().to_string())
+                .unwrap_or_default(),
+            target_version: String::new(),
+            include_optional: false,
+            versions: Vec::new(),
+            loading_versions: false,
+            version_handle: None,
+            downloading: false,
+            finished: false,
+            downloads: Vec::new(),
+            log_entries: Vec::new(),
+            receiver: None,
+        }
+    }
+
+    fn log(&mut self, text: String, is_error: bool) {
+        self.log_entries.push(LogEntry { text, is_error });
+        if self.log_entries.len() > 500 {
+            self.log_entries.remove(0);
+        }
+    }
+
+    fn find_or_create_download(&mut self, name: &str) -> &mut DownloadState {
+        if let Some(pos) = self.downloads.iter().position(|d| d.name == name) {
+            &mut self.downloads[pos]
+        } else {
+            self.downloads.push(DownloadState {
+                name: name.to_string(),
+                total_bytes: 0,
+                downloaded_bytes: 0,
+                complete: false,
+                error: None,
+            });
+            self.downloads.last_mut().unwrap()
+        }
+    }
+
+    fn poll_events(&mut self) {
+        let mut events = Vec::new();
+        if let Some(ref rx) = self.receiver {
+            loop {
+                match rx.try_recv() {
+                    Ok(event) => events.push(event),
+                    Err(TryRecvError::Empty) => break,
+                    Err(TryRecvError::Disconnected) => {
+                        self.downloading = false;
+                        self.receiver = None;
+                        break;
+                    }
+                }
+            }
+        }
+        for event in events {
+            self.handle_event(event);
+        }
+    }
+
+    fn handle_event(&mut self, event: Event) {
+        match event {
+            Event::Log(text) => self.log(text, false),
+            Event::DownloadStart { name, total_bytes } => {
+                self.log(format!("Downloading: {name}"), false);
+                let dl = self.find_or_create_download(&name);
+                dl.total_bytes = total_bytes;
+                dl.downloaded_bytes = 0;
+                dl.complete = false;
+                dl.error = None;
+            }
+            Event::DownloadProgress { name, bytes } => {
+                let dl = self.find_or_create_download(&name);
+                dl.downloaded_bytes = bytes;
+            }
+            Event::DownloadComplete { name } => {
+                let dl = self.find_or_create_download(&name);
+                dl.complete = true;
+                dl.downloaded_bytes = dl.total_bytes;
+                self.log(format!("Downloaded: {name}"), false);
+            }
+            Event::DownloadError { name, error } => {
+                let dl = self.find_or_create_download(&name);
+                dl.error = Some(error.clone());
+                self.log(format!("Error: {name} - {error}"), true);
+            }
+            Event::Finished { success, message } => {
+                self.log(message.clone(), !success);
+                self.downloading = false;
+                self.finished = true;
+                self.receiver = None;
+            }
+        }
+    }
+
+    fn start_download(&mut self) {
+        let mod_url = self.mod_url.trim().to_string();
+        if mod_url.is_empty() {
+            return;
+        }
+
+        let output = PathBuf::from(&self.output_path);
+        let target_version = if self.target_version.trim().is_empty() {
+            None
+        } else {
+            Some(self.target_version.trim().to_string())
+        };
+        let include_optional = self.include_optional;
+
+        let (tx, rx) = mpsc::channel();
+        self.receiver = Some(rx);
+        self.downloading = true;
+        self.finished = false;
+        self.downloads.clear();
+        self.log_entries.clear();
+
+        self.log("Starting download...".into(), false);
+
+        thread::spawn(move || {
+            downloader::run_gui_download(&mod_url, &output, target_version, include_optional, tx);
+        });
+    }
+
+    fn load_versions(&mut self) {
+        let mod_url = self.mod_url.trim().to_string();
+        if mod_url.is_empty() {
+            return;
+        }
+
+        self.loading_versions = true;
+        let result: Arc<Mutex<Option<Vec<(String, String)>>>> = Arc::new(Mutex::new(None));
+        self.version_handle = Some(result.clone());
+
+        thread::spawn(move || {
+            let name = downloader::extract_mod_name(&mod_url);
+            let versions = match name {
+                Ok(name) => downloader::fetch_versions(&name).ok().unwrap_or_default(),
+                Err(_) => Vec::new(),
+            };
+            *result.lock().unwrap() = Some(versions);
+        });
+    }
+
+    fn browse_output(&mut self) {
+        if let Some(path) = FileDialog::new().pick_folder() {
+            self.output_path = path.display().to_string();
+        }
+    }
+}
+
+impl eframe::App for App {
+    fn logic(&mut self, ctx: &egui::Context, _frame: &mut eframe::Frame) {
+        self.poll_events();
+
+        // Check version loading result
+        if self.loading_versions {
+            let result = if let Some(ref handle) = self.version_handle {
+                handle.lock().ok().and_then(|mut g| g.take())
+            } else {
+                None
+            };
+            if let Some(versions) = result {
+                self.versions = versions;
+                self.loading_versions = false;
+                self.version_handle = None;
+            }
+        }
+
+        if self.downloading {
+            ctx.request_repaint();
+        }
+    }
+
+    fn ui(&mut self, ui: &mut egui::Ui, _frame: &mut eframe::Frame) {
+        ui.heading("Factorio Mod Downloader");
+        ui.separator();
+
+        // ── Input section ──
+        ui.horizontal(|ui| {
+            ui.label("Mod URL:");
+            ui.add_sized(
+                [ui.available_width() - 10.0, 20.0],
+                TextEdit::singleline(&mut self.mod_url)
+                    .hint_text("https://mods.factorio.com/mod/... or mod name"),
+            );
+        });
+
+        ui.horizontal(|ui| {
+            ui.label("Output:");
+            ui.add_sized(
+                [ui.available_width() - 80.0, 20.0],
+                TextEdit::singleline(&mut self.output_path).hint_text("Download directory"),
+            );
+            if ui.button("Browse").clicked() {
+                self.browse_output();
+            }
+        });
+
+        ui.horizontal(|ui| {
+            ui.label("Version:");
+            let version_enabled = !self.downloading && !self.versions.is_empty();
+            ui.add_enabled_ui(version_enabled, |ui| {
+                egui::ComboBox::from_id_salt("version_combo")
+                    .width(200.0)
+                    .selected_text(if self.target_version.is_empty() {
+                        "Latest"
+                    } else {
+                        &self.target_version
+                    })
+                    .show_ui(ui, |ui| {
+                        if ui.selectable_label(false, "Latest").clicked() {
+                            self.target_version.clear();
+                        }
+                        for (ver, label) in &self.versions {
+                            if ui.selectable_label(self.target_version == *ver, label).clicked() {
+                                self.target_version = ver.clone();
+                            }
+                        }
+                    });
+            });
+
+            if ui
+                .add_enabled(
+                    !self.downloading && !self.loading_versions,
+                    egui::Button::new(if self.loading_versions {
+                        "Loading..."
+                    } else {
+                        "Load Versions"
+                    }),
+                )
+                .clicked()
+            {
+                self.load_versions();
+            }
+
+            ui.checkbox(&mut self.include_optional, "Include optional deps");
+        });
+
+        ui.add_space(8.0);
+
+        // ── Download button ──
+        let can_download = !self.downloading
+            && !self.mod_url.trim().is_empty()
+            && !self.output_path.is_empty();
+
+        if ui
+            .add_enabled(
+                can_download,
+                egui::Button::new(if self.downloading {
+                    "Downloading..."
+                } else if self.finished {
+                    "Download Again"
+                } else {
+                    "Start Download"
+                }),
+            )
+            .clicked()
+        {
+            self.start_download();
+        }
+
+        ui.add_space(8.0);
+
+        // ── Progress section ──
+        if !self.downloads.is_empty() {
+            egui::CollapsingHeader::new("Downloads")
+                .default_open(true)
+                .show(ui, |ui| {
+                    for dl in &self.downloads {
+                        let percentage = if dl.total_bytes > 0 {
+                            dl.downloaded_bytes as f32 / dl.total_bytes as f32
+                        } else {
+                            0.0
+                        };
+
+                        ui.horizontal(|ui| {
+                            let status = if dl.complete {
+                                "[OK]"
+                            } else if dl.error.is_some() {
+                                "[ERR]"
+                            } else {
+                                "[>>]"
+                            };
+                            ui.label(format!("{status} {}", dl.name));
+
+                            if let Some(ref err) = dl.error {
+                                ui.colored_label(Color32::RED, format!("Error: {err}"));
+                            } else if dl.total_bytes > 0 {
+                                ui.label(format!(
+                                    "{:.1} / {:.1} MB",
+                                    dl.downloaded_bytes as f64 / 1_048_576.0,
+                                    dl.total_bytes as f64 / 1_048_576.0
+                                ));
+                            }
+                        });
+
+                        let bar =
+                            ProgressBar::new(percentage).desired_width(ui.available_width());
+                        ui.add(bar);
+                    }
+                });
+        }
+
+        ui.add_space(8.0);
+
+        // ── Log section ──
+        egui::CollapsingHeader::new("Log")
+            .default_open(true)
+            .show(ui, |ui| {
+                ScrollArea::vertical()
+                    .max_height(300.0)
+                    .stick_to_bottom(true)
+                    .show(ui, |ui| {
+                        for entry in &self.log_entries {
+                            if entry.is_error {
+                                ui.colored_label(Color32::RED, &entry.text);
+                            } else {
+                                ui.label(&entry.text);
+                            }
+                        }
+                    });
+            });
+    }
+}
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..78f17f8
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,102 @@
+mod downloader;
+
+#[cfg(feature = "gui")]
+mod gui;
+
+// ---------------------------------------------------------------------------
+// GUI entry point (when the "gui" feature is enabled)
+// ---------------------------------------------------------------------------
+#[cfg(feature = "gui")]
+fn main() -> eframe::Result<()> {
+    let options = eframe::NativeOptions {
+        viewport: egui::ViewportBuilder::default()
+            .with_inner_size([800.0, 650.0])
+            .with_min_inner_size([600.0, 400.0]),
+        ..Default::default()
+    };
+
+    eframe::run_native(
+        "Factorio Mod Downloader",
+        options,
+        Box::new(|_cc| Ok(Box::new(gui::App::new()))),
+    )
+}
+
+// ---------------------------------------------------------------------------
+// CLI entry point (when the "gui" feature is disabled)
+// ---------------------------------------------------------------------------
+#[cfg(not(feature = "gui"))]
+fn main() {
+    let args: Vec<String> = std::env::args().collect();
+
+    if args.len() < 2 {
+        eprintln!("Factorio Mod Downloader (CLI)");
+        eprintln!();
+        eprintln!(
+            "Usage: {} <mod_url_or_name> [output_directory] [options]",
+            args[0]
+        );
+        eprintln!();
+        eprintln!("Options:");
+        eprintln!("  --version <VER>       Download a specific version instead of latest");
+        eprintln!("  --include-optional    Also download optional dependencies");
+        eprintln!();
+        eprintln!("Examples:");
+        eprintln!("  {} my-cool-mod", args[0]);
+        eprintln!(
+            "  {} https://mods.factorio.com/mod/my-cool-mod ./mods",
+            args[0]
+        );
+        eprintln!(
+            "  {} my-cool-mod ./mods --version 2.1.0 --include-optional",
+            args[0]
+        );
+        std::process::exit(1);
+    }
+
+    let mod_url = &args[1];
+
+    let output = if args.len() >= 3 && !args[2].starts_with("--") {
+        std::path::PathBuf::from(&args[2])
+    } else {
+        std::env::current_dir().unwrap_or_else(|_| std::path::PathBuf::from("."))
+    };
+
+    let mut target_version: Option<&str> = None;
+    let mut include_optional = false;
+
+    let mut i = if args.len() >= 3 && !args[2].starts_with("--") {
+        3
+    } else {
+        2
+    };
+    while i < args.len() {
+        match args[i].as_str() {
+            "--version" => {
+                if i + 1 < args.len() {
+                    target_version = Some(&args[i + 1]);
+                    i += 1;
+                } else {
+                    eprintln!("Error: --version requires a value");
+                    std::process::exit(1);
+                }
+            }
+            "--include-optional" => {
+                include_optional = true;
+            }
+            other => {
+                eprintln!("Unknown option: {other}");
+                std::process::exit(1);
+            }
+        }
+        i += 1;
+    }
+
+    match downloader::run_cli_download(mod_url, &output, target_version, include_optional) {
+        Ok(()) => {}
+        Err(e) => {
+            eprintln!("Error: {:#}", e);
+            std::process::exit(1);
+        }
+    }
+}