//! Cross references in Markdown (hub spec §8): `#12`, `owner/name#12`,
//! change hashes and `@user` become links before rendering. Text inside
//! code spans and fences is left alone.

/// Where a repository's numbers live: issues and proposals.
pub struct Numbers<'a> {
    pub repo_url: &'a str,
    pub issues: &'a [i64],
    pub proposals: &'a [i64],
}

impl Numbers<'_> {
    /// Where `#n` points, and what it is: issues and proposals share one
    /// number space, so the link says which.
    fn url_for(&self, n: i64) -> Option<(String, &'static str)> {
        if self.proposals.contains(&n) {
            Some((format!("{}/proposal/{n}", self.repo_url), "proposal"))
        } else if self.issues.contains(&n) {
            Some((format!("{}/issue/{n}", self.repo_url), "issue"))
        } else {
            None
        }
    }
}

/// Link references in `text`. Cross-repository references link to the
/// other repository's issue page, which resolves to a proposal itself.
pub fn link(text: &str, numbers: &Numbers<'_>) -> String {
    let mut out = String::with_capacity(text.len() + 64);
    let mut in_fence = false;
    for line in text.split_inclusive('\n') {
        if line.trim_start().starts_with("```") {
            in_fence = !in_fence;
            out.push_str(line);
            continue;
        }
        if in_fence {
            out.push_str(line);
            continue;
        }
        // Split on inline code spans; only even segments are prose.
        for (i, seg) in line.split('`').enumerate() {
            if i > 0 {
                out.push('`');
            }
            if i % 2 == 0 {
                out.push_str(&link_prose(seg, numbers));
            } else {
                out.push_str(seg);
            }
        }
    }
    out
}

fn link_prose(seg: &str, numbers: &Numbers<'_>) -> String {
    let re = regex::Regex::new(r"(?P<pre>^|[^\w/\[])(?:(?P<slug>[A-Za-z0-9][A-Za-z0-9._-]*/[A-Za-z0-9][A-Za-z0-9._-]*)#(?P<xn>\d+)|#(?P<n>\d+)|@(?P<user>[A-Za-z0-9][A-Za-z0-9._-]{0,63})|(?P<hash>\b[0-9a-f]{12,64}\b))").unwrap();
    re.replace_all(seg, |c: &regex::Captures| {
        let pre = &c["pre"];
        if let Some(slug) = c.name("slug") {
            let n = &c["xn"];
            return format!("{pre}[{}#{n}](/{}/issue/{n})", slug.as_str(), slug.as_str());
        }
        if let Some(n) = c.name("n") {
            let num: i64 = n.as_str().parse().unwrap_or(0);
            return match numbers.url_for(num) {
                Some((url, kind)) => format!("{pre}[{kind} #{num}]({url})"),
                None => c[0].to_string(),
            };
        }
        if let Some(u) = c.name("user") {
            let name = u.as_str().trim_end_matches('.');
            return format!("{pre}[@{name}](/{name})");
        }
        if let Some(h) = c.name("hash") {
            let hex = h.as_str();
            return format!("{pre}[{}]({}/change/{hex})", &hex[..12.min(hex.len())], numbers.repo_url);
        }
        c[0].to_string()
    })
    .into_owned()
}

/// Issue numbers a change message closes: `closes #12`, `fixes #3`,
/// `resolved #7`.
/// Every bare `#N` a change message names, except those it closes
/// (`closes #N` records its own event) and other repositories' `a/b#N`.
pub fn references(message: &str) -> Vec<i64> {
    let re = regex::Regex::new(r"(?:^|[^\w/\[&])#(\d+)\b").unwrap();
    let closing = closes(message);
    let mut out: Vec<i64> = re.captures_iter(message).filter_map(|c| c[1].parse().ok()).filter(|n| !closing.contains(n)).collect();
    out.sort();
    out.dedup();
    out
}

pub fn closes(message: &str) -> Vec<i64> {
    let re = regex::Regex::new(r"(?i)\b(?:close[sd]?|fix(?:e[sd])?|resolve[sd]?)\s+#(\d+)").unwrap();
    let mut out: Vec<i64> = re.captures_iter(message).filter_map(|c| c[1].parse().ok()).collect();
    out.sort();
    out.dedup();
    out
}

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

    #[test]
    fn finds_references_but_not_closings_or_other_repositories() {
        assert_eq!(references("Faster blame (refs #14, #3)\n\nSee #3 again; closes #9; other/repo#5; a#2"), vec![3, 14]);
        assert!(references("Nothing to see; colour &#35;").is_empty());
        assert_eq!(references("#7 at the start"), vec![7]);
    }

    #[test]
    fn links_references_outside_code() {
        let n = Numbers { repo_url: "/a/b", issues: &[3], proposals: &[7] };
        let out = link("see #3 and #7 and #9, `#3` too, by @andy; a/b#3 and other/repo#5; hash deadbeefcafe1234\n```\n#3 @x\n```\n", &n);
        assert!(out.contains("[issue #3](/a/b/issue/3)"), "{out}");
        assert!(out.contains("[proposal #7](/a/b/proposal/7)"), "{out}");
        assert!(out.contains(" #9,"), "unknown numbers stay: {out}");
        assert!(out.contains("`#3`"), "code spans untouched: {out}");
        assert!(out.contains("[@andy](/andy)"), "{out}");
        assert!(out.contains("[other/repo#5](/other/repo/issue/5)"), "{out}");
        assert!(out.contains("[deadbeefcafe](/a/b/change/deadbeefcafe1234)"), "{out}");
        assert!(out.contains("```\n#3 @x\n```"), "fences untouched: {out}");
    }

    #[test]
    fn closing_keywords() {
        assert_eq!(closes("Fixes #12 and closes #3, resolved #12"), vec![3, 12]);
        assert!(closes("mentions #4 only").is_empty());
    }
}