use reqwest::header::HeaderMap;

/// A single page of items along with parsed pagination headers. Forgejo
/// follows Gitea's convention: `Link` header in RFC 5988 style plus
/// `X-Total-Count`.
pub struct Page<T> {
    pub items: Vec<T>,
    #[allow(dead_code)]
    pub next: Option<String>,
    #[allow(dead_code)]
    pub prev: Option<String>,
    #[allow(dead_code)]
    pub last: Option<String>,
    #[allow(dead_code)]
    pub first: Option<String>,
    #[allow(dead_code)]
    pub total: Option<u64>,
}

impl<T> Page<T> {
    pub fn from_headers(items: Vec<T>, headers: &HeaderMap) -> Self {
        let mut next = None;
        let mut prev = None;
        let mut last = None;
        let mut first = None;
        if let Some(link) = headers.get(reqwest::header::LINK) {
            if let Ok(link_str) = link.to_str() {
                for (url, rel) in parse_link_header(link_str) {
                    match rel.as_str() {
                        "next" => next = Some(url),
                        "prev" => prev = Some(url),
                        "last" => last = Some(url),
                        "first" => first = Some(url),
                        _ => {}
                    }
                }
            }
        }
        let total = headers
            .get("x-total-count")
            .and_then(|v| v.to_str().ok())
            .and_then(|v| v.parse().ok());
        Self {
            items,
            next,
            prev,
            last,
            first,
            total,
        }
    }
}

fn parse_link_header(value: &str) -> Vec<(String, String)> {
    let mut out = Vec::new();
    for part in value.split(',') {
        let part = part.trim();
        // `<url>; rel="name"`
        let Some((url_part, params)) = part.split_once(';') else {
            continue;
        };
        let url = url_part.trim().trim_start_matches('<').trim_end_matches('>');
        let rel = params
            .split(';')
            .map(str::trim)
            .find_map(|p| {
                let (k, v) = p.split_once('=')?;
                if k.trim().eq_ignore_ascii_case("rel") {
                    Some(v.trim().trim_matches('"').to_string())
                } else {
                    None
                }
            });
        if let Some(rel) = rel {
            out.push((url.to_string(), rel));
        }
    }
    out
}