//! 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> {

    // A keyword, then a list of numbers (#226): "Closes #1, #2 and #3",

    // "Fixes: #4 #5", "resolves #6 & #7". Another repository's a/b#N in

    // the list is not this repository's to close.

    let re = regex::Regex::new(

        r"(?i)\b(?:close[sd]?|fix(?:e[sd])?|resolve[sd]?):?\s+((?:[A-Za-z0-9._-]+/[A-Za-z0-9._-]+)?#\d+(?:(?:\s*,\s*(?:and\s+)?|\s+and\s+|\s*&\s*|\s+)(?:[A-Za-z0-9._-]+/[A-Za-z0-9._-]+)?#\d+)*)",

    )

    .unwrap();

    let item = regex::Regex::new(r"(?:^|[^\w/])#(\d+)").unwrap();

    let mut out: Vec<i64> =

        re.captures_iter(message).flat_map(|c| item.captures_iter(&c[1]).filter_map(|i| i[1].parse().ok()).collect::<Vec<i64>>()).collect();

    out.sort();

    out.dedup();

    out

}

#[cfg(test)]

mod tests {

    use super::*;

    #[test]

    fn a_closing_keyword_closes_every_number_it_lists() {

        // #226: commit 7a31f384's message closed only its first issue.

        assert_eq!(closes("Polish\n\nCloses #187, #188, #189, #190, #191, #192, #193, #194, #195, #196"), (187..=196).collect::<Vec<_>>());

        assert_eq!(closes("Closes #1, #2 and #3"), vec![1, 2, 3]);

        assert_eq!(closes("Closes #1, and #2"), vec![1, 2]);

        assert_eq!(closes("Fixes: #4 #5"), vec![4, 5]);

        assert_eq!(closes("resolves #6 & #7"), vec![6, 7]);

        assert_eq!(closes("Closes #1, closes #2\nFixed #8."), vec![1, 2, 8]);

        assert_eq!(closes("Closes #9, other/repo#10, #11"), vec![9, 11], "another repository's number is not ours");

        assert_eq!(closes("Refs #12, closes #13. See #14."), vec![13], "a list ends where the prose starts");

        assert!(closes("closest #1; disclosed #2").is_empty());

        assert_eq!(references("Closes #1, #2 and #3; refs #4"), vec![4], "listed closings are not plain references");

    }

    #[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 #").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());

    }

}