rss-fetch 0.1.0

use std::collections::HashMap;
use std::sync::Arc;

use tokio::sync::Mutex;

/// Maximum feed response size (10 MB).
const MAX_FEED_SIZE: u64 = 10 * 1024 * 1024;

/// Maximum article response size (5 MB).
const MAX_ARTICLE_SIZE: u64 = 5 * 1024 * 1024;

/// Default maximum number of entries returned by "list" action.
pub const DEFAULT_LIST_LIMIT: usize = 20;

/// A single RSS/Atom feed entry with an assigned numeric ID.
#[derive(Debug, Clone)]
pub struct FeedEntry {
    pub id: u32,
    pub title: String,
    pub url: String,
    pub published: String,
    pub summary: String,
}

/// Shared store that maps numeric IDs to article URLs.
/// Persists for the lifetime of the MCP server process.
#[derive(Debug, Clone, Default)]
pub struct EntryStore {
    inner: Arc<Mutex<StoreInner>>,
}

#[derive(Debug, Default)]
struct StoreInner {
    next_id: u32,
    entries: HashMap<u32, StoredEntry>,
}

#[derive(Debug, Clone)]
struct StoredEntry {
    url: String,
    title: String,
}

impl EntryStore {
    pub fn new() -> Self {
        Self::default()
    }

    /// Clear previous entries and store new ones.
    /// Returns the list of entries with assigned IDs.
    pub async fn store_entries(&self, entries: Vec<ParsedEntry>) -> anyhow::Result<Vec<FeedEntry>> {
        let mut inner = self.inner.lock().await;
        inner.entries.clear();
        inner.next_id = 1;

        let mut result = Vec::with_capacity(entries.len());
        for e in entries {
            let id = inner.next_id;
            inner.next_id = inner
                .next_id
                .checked_add(1)
                .ok_or_else(|| anyhow::anyhow!("entry ID overflow"))?;
            inner.entries.insert(
                id,
                StoredEntry {
                    url: e.url.clone(),
                    title: e.title.clone(),
                },
            );
            result.push(FeedEntry {
                id,
                title: e.title,
                url: e.url,
                published: e.published,
                summary: e.summary,
            });
        }
        Ok(result)
    }

    /// Look up the URL for a given numeric ID.
    pub async fn get_url(&self, id: u32) -> Option<(String, String)> {
        let inner = self.inner.lock().await;
        inner
            .entries
            .get(&id)
            .map(|e| (e.url.clone(), e.title.clone()))
    }
}

/// Intermediate parsed entry before ID assignment.
#[derive(Debug)]
pub struct ParsedEntry {
    pub title: String,
    pub url: String,
    pub published: String,
    pub summary: String,
}

/// Build a shared HTTP client with reasonable defaults.
pub fn build_http_client() -> reqwest::Result<reqwest::Client> {
    reqwest::Client::builder()
        .timeout(std::time::Duration::from_secs(30))
        .build()
}

/// Validate that a URL uses http or https scheme.
fn validate_url(url: &str) -> anyhow::Result<reqwest::Url> {
    let parsed = reqwest::Url::parse(url).map_err(|e| anyhow::anyhow!("invalid URL: {e}"))?;
    match parsed.scheme() {
        "http" | "https" => Ok(parsed),
        scheme => anyhow::bail!("unsupported URL scheme: {scheme}"),
    }
}

/// Check response size against limit via Content-Length header.
fn check_content_length(resp: &reqwest::Response, limit: u64) -> anyhow::Result<()> {
    if let Some(len) = resp.content_length() {
        if len > limit {
            anyhow::bail!("response too large: {len} bytes (limit: {limit} bytes)");
        }
    }
    Ok(())
}

/// Fetch and parse an RSS/Atom feed from a URL.
/// Returns a list of parsed entries (no IDs yet).
pub async fn fetch_and_parse_feed(
    client: &reqwest::Client,
    url: &str,
) -> anyhow::Result<(String, Vec<ParsedEntry>)> {
    let validated = validate_url(url)?;

    let resp = client.get(validated).send().await?;
    check_content_length(&resp, MAX_FEED_SIZE)?;
    let bytes = resp.bytes().await?;
    let feed = feed_rs::parser::parse(&bytes[..])?;

    let feed_title = feed
        .title
        .map(|t| t.content)
        .unwrap_or_else(|| "(untitled feed)".to_string());

    let entries = feed
        .entries
        .into_iter()
        .map(|entry| {
            let title = entry
                .title
                .map(|t| t.content)
                .unwrap_or_else(|| "(no title)".to_string());

            let url = entry
                .links
                .first()
                .map(|l| l.href.clone())
                .unwrap_or_default();

            let published = entry
                .published
                .or(entry.updated)
                .map(|d| d.format("%Y-%m-%d").to_string())
                .unwrap_or_else(|| "-".to_string());

            let summary = entry
                .summary
                .map(|s| truncate_text(&strip_html_simple(&s.content), 80))
                .unwrap_or_default();

            ParsedEntry {
                title,
                url,
                published,
                summary,
            }
        })
        .collect();

    Ok((feed_title, entries))
}

/// Format a list of feed entries as a Markdown table.
///
/// `total` is the total number of entries in the feed (before truncation).
/// When `total > entries.len()`, a note about truncation is appended.
pub fn format_entries_as_markdown(feed_title: &str, entries: &[FeedEntry], total: usize) -> String {
    let mut out = String::with_capacity(entries.len() * 100);
    out.push_str(&format!("## {feed_title}\n\n"));
    out.push_str("| # | Title | Date |\n");
    out.push_str("|---|-------|------|\n");

    for e in entries {
        let title_display = truncate_text(&e.title, 60);
        out.push_str(&format!(
            "| {} | [{}]({}) | {} |\n",
            e.id, title_display, e.url, e.published
        ));
    }

    if total > entries.len() {
        out.push_str(&format!(
            "\n*Showing {} of {} articles. Use `limit` to see more. Use `get` with # to read.*",
            entries.len(),
            total
        ));
    } else {
        out.push_str(&format!(
            "\n*{} articles. Use `get` with # to read.*",
            entries.len()
        ));
    }
    out
}

/// Fetch an article page and extract its text content.
pub async fn fetch_article_text(client: &reqwest::Client, url: &str) -> anyhow::Result<String> {
    let validated = validate_url(url)?;

    let resp = client
        .get(validated)
        .header("User-Agent", "rss-fetch-mcp/0.1")
        .send()
        .await?;
    check_content_length(&resp, MAX_ARTICLE_SIZE)?;

    let html = resp.text().await?;
    let text = html2text::from_read(html.as_bytes(), 80)?;

    Ok(text)
}

/// Strip HTML tags, skipping content inside `<script>` and `<style>` elements.
fn strip_html_simple(html: &str) -> String {
    let mut result = String::with_capacity(html.len());
    let mut in_tag = false;
    let mut in_skip = false;
    let mut tag_buf = String::new();

    for ch in html.chars() {
        if ch == '<' {
            in_tag = true;
            tag_buf.clear();
            continue;
        }
        if ch == '>' {
            in_tag = false;
            let tag_name = tag_buf
                .split_whitespace()
                .next()
                .unwrap_or("")
                .to_lowercase();
            if tag_name == "script" || tag_name == "style" {
                in_skip = true;
            } else if tag_name == "/script" || tag_name == "/style" {
                in_skip = false;
            }
            continue;
        }
        if in_tag {
            tag_buf.push(ch);
            continue;
        }
        if !in_skip {
            result.push(ch);
        }
    }
    result
}

/// Truncate text to a max character count, appending "..." if needed.
fn truncate_text(s: &str, max: usize) -> String {
    let char_count = s.chars().count();
    if char_count <= max {
        s.to_string()
    } else {
        let truncated: String = s.chars().take(max.saturating_sub(3)).collect();
        format!("{truncated}...")
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn strip_html_basic() {
        assert_eq!(
            strip_html_simple("<p>Hello <b>world</b></p>"),
            "Hello world"
        );
    }

    #[test]
    fn strip_html_empty() {
        assert_eq!(strip_html_simple(""), "");
    }

    #[test]
    fn strip_html_skips_script() {
        let html = "<p>before</p><script>alert('xss')</script><p>after</p>";
        assert_eq!(strip_html_simple(html), "beforeafter");
    }

    #[test]
    fn strip_html_skips_style() {
        let html = "<p>text</p><style>body{color:red}</style><p>more</p>";
        assert_eq!(strip_html_simple(html), "textmore");
    }

    #[test]
    fn truncate_short_text() {
        assert_eq!(truncate_text("hello", 10), "hello");
    }

    #[test]
    fn truncate_long_text() {
        let result = truncate_text("this is a long sentence", 10);
        assert!(result.ends_with("..."));
        assert!(result.chars().count() <= 10);
    }

    #[test]
    fn truncate_multibyte() {
        let result = truncate_text("あいうえおかきくけこ", 5);
        assert!(result.ends_with("..."));
        assert!(result.chars().count() <= 5);
    }

    #[test]
    fn validate_url_accepts_https() {
        assert!(validate_url("https://example.com/feed.xml").is_ok());
    }

    #[test]
    fn validate_url_accepts_http() {
        assert!(validate_url("http://example.com/feed.xml").is_ok());
    }

    #[test]
    fn validate_url_rejects_file() {
        let err = validate_url("file:///etc/passwd").unwrap_err();
        assert!(err.to_string().contains("unsupported URL scheme"));
    }

    #[test]
    fn validate_url_rejects_ftp() {
        let err = validate_url("ftp://example.com/data").unwrap_err();
        assert!(err.to_string().contains("unsupported URL scheme"));
    }

    #[test]
    fn validate_url_rejects_invalid() {
        assert!(validate_url("not a url").is_err());
    }

    #[test]
    fn format_markdown_table() {
        let entries = vec![FeedEntry {
            id: 1,
            title: "Test Article".to_string(),
            url: "https://example.com/1".to_string(),
            published: "2026-02-14".to_string(),
            summary: "A test".to_string(),
        }];
        let md = format_entries_as_markdown("Test Feed", &entries, 1);
        assert!(md.contains("| 1 |"));
        assert!(md.contains("Test Article"));
        assert!(md.contains("## Test Feed"));
        assert!(md.contains("1 articles."));
    }

    #[test]
    fn format_markdown_table_truncated() {
        let entries = vec![FeedEntry {
            id: 1,
            title: "Article".to_string(),
            url: "https://example.com/1".to_string(),
            published: "2026-02-14".to_string(),
            summary: String::new(),
        }];
        let md = format_entries_as_markdown("Feed", &entries, 50);
        assert!(md.contains("Showing 1 of 50 articles"));
        assert!(md.contains("Use `limit` to see more"));
    }

    #[tokio::test]
    async fn entry_store_roundtrip() {
        let store = EntryStore::new();
        let parsed = vec![
            ParsedEntry {
                title: "Article A".to_string(),
                url: "https://a.com".to_string(),
                published: "2026-01-01".to_string(),
                summary: "sumA".to_string(),
            },
            ParsedEntry {
                title: "Article B".to_string(),
                url: "https://b.com".to_string(),
                published: "2026-01-02".to_string(),
                summary: "sumB".to_string(),
            },
        ];

        let entries = store.store_entries(parsed).await.unwrap();
        assert_eq!(entries.len(), 2);
        assert_eq!(entries[0].id, 1);
        assert_eq!(entries[1].id, 2);

        let (url, title) = store.get_url(1).await.unwrap();
        assert_eq!(url, "https://a.com");
        assert_eq!(title, "Article A");

        assert!(store.get_url(99).await.is_none());
    }

    #[tokio::test]
    async fn store_clears_on_new_list() {
        let store = EntryStore::new();
        let first = vec![ParsedEntry {
            title: "Old".to_string(),
            url: "https://old.com".to_string(),
            published: "-".to_string(),
            summary: String::new(),
        }];
        store.store_entries(first).await.unwrap();

        let second = vec![ParsedEntry {
            title: "New".to_string(),
            url: "https://new.com".to_string(),
            published: "-".to_string(),
            summary: String::new(),
        }];
        store.store_entries(second).await.unwrap();

        let (url, _) = store.get_url(1).await.unwrap();
        assert_eq!(url, "https://new.com");
    }
}