// rss - RSS 2.0 feed generator for Lux
//
// Generates valid RSS 2.0 XML feeds from structured data.

import xml

// An RSS feed item
type Item =
    | Item(String, String, String, String, String)
    // Item(title, link, description, pubDate, guid)

// An RSS channel/feed
type Feed =
    | Feed(String, String, String, String, List<Item>)
    // Feed(title, link, description, language, items)

// Create a feed item
pub fn item(title: String, link: String, description: String, pubDate: String): Item =
    Item(title, link, description, pubDate, link)

// Create a feed item with custom GUID
pub fn itemWithGuid(title: String, link: String, description: String, pubDate: String, guid: String): Item =
    Item(title, link, description, pubDate, guid)

// Create an RSS feed
pub fn feed(title: String, link: String, description: String, items: List<Item>): Feed =
    Feed(title, link, description, "en", items)

// Create an RSS feed with language
pub fn feedWithLang(title: String, link: String, description: String, language: String, items: List<Item>): Feed =
    Feed(title, link, description, language, items)

// Access item fields
pub fn itemTitle(i: Item): String = match i { Item(t, _, _, _, _) => t, }
pub fn itemLink(i: Item): String = match i { Item(_, l, _, _, _) => l, }
pub fn itemDescription(i: Item): String = match i { Item(_, _, d, _, _) => d, }
pub fn itemPubDate(i: Item): String = match i { Item(_, _, _, p, _) => p, }
pub fn itemGuid(i: Item): String = match i { Item(_, _, _, _, g) => g, }

// Convert ISO date (2025-01-29) to RFC 822 format (29 Jan 2025 00:00:00 GMT)
pub fn isoToRfc822(isoDate: String): String =
    if String.length(isoDate) < 10 then isoDate
    else {
        let year = String.substring(isoDate, 0, 4)
        let month = String.substring(isoDate, 5, 7)
        let day = String.substring(isoDate, 8, 10)
        let monthName = if month == "01" then "Jan"
            else if month == "02" then "Feb"
            else if month == "03" then "Mar"
            else if month == "04" then "Apr"
            else if month == "05" then "May"
            else if month == "06" then "Jun"
            else if month == "07" then "Jul"
            else if month == "08" then "Aug"
            else if month == "09" then "Sep"
            else if month == "10" then "Oct"
            else if month == "11" then "Nov"
            else "Dec"
        day + " " + monthName + " " + year + " 00:00:00 GMT"
    }

// Render a single item to XML string
fn renderItemXml(i: Item): String =
    match i {
    Item(title, link, desc, pubDate, guid) =>
        xml.render(xml.el("item", [
            xml.textEl("title", title),
            xml.textEl("link", link),
            xml.textEl("description", desc),
            xml.textEl("pubDate", isoToRfc822(pubDate)),
            xml.textElAttr("guid", [xml.attr("isPermaLink", "true")], guid)
        ])),
}

// Render items to concatenated XML string
fn renderItemsXml(items: List<Item>): String =
    match List.head(items) {
    None => "",
    Some(i) => renderItemXml(i) + match List.tail(items) {
        Some(rest) => renderItemsXml(rest),
        None => "",
    },
}

// Render an RSS feed to XML string
pub fn render(f: Feed): String =
    match f {
    Feed(title, link, desc, lang, items) => {
        let itemsXml = renderItemsXml(items)
        "<?xml version=\"1.0\" encoding=\"UTF-8\"?>\n" +
        "<rss version=\"2.0\" xmlns:atom=\"http://www.w3.org/2005/Atom\">" +
        "<channel>" +
        "<title>" + xml.escape(title) + "</title>" +
        "<link>" + xml.escape(link) + "</link>" +
        "<description>" + xml.escape(desc) + "</description>" +
        "<language>" + lang + "</language>" +
        "<generator>Lux RSS Package</generator>" +
        itemsXml +
        "</channel></rss>"
    },
}