agent-file-tools 0.55.0

use std::fmt;
use std::ops::RangeInclusive;

use url::Url;

/// One of the two GitHub resource kinds supported by the read scheme.
#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
pub enum GithubResourceKind {
    Issue,
    PullRequest,
}

impl GithubResourceKind {
    pub const fn scheme(self) -> &'static str {
        match self {
            Self::Issue => "issue",
            Self::PullRequest => "pr",
        }
    }

    pub const fn command(self) -> &'static str {
        match self {
            Self::Issue => "issue",
            Self::PullRequest => "pr",
        }
    }

    pub const fn label(self) -> &'static str {
        match self {
            Self::Issue => "Issue",
            Self::PullRequest => "Pull request",
        }
    }
}

/// Ordinals selected by a `/comments/<sel>` discussion drill-down.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct GithubCommentSelector {
    ranges: Vec<RangeInclusive<usize>>,
}

impl GithubCommentSelector {
    pub fn contains(&self, ordinal: usize) -> bool {
        self.ranges.iter().any(|range| range.contains(&ordinal))
    }

    pub fn first_out_of_range(&self, valid_end: usize) -> Option<usize> {
        self.ranges
            .iter()
            .flat_map(|range| [*range.start(), *range.end()])
            .find(|ordinal| *ordinal > valid_end)
    }
}

/// A validated `issue://` or `pr://` resource.
///
/// Short resources deliberately retain no inferred repository. `gh` resolves
/// those resources from the request's working directory, while explicit
/// resources carry the exact `OWNER/REPO` argument to pass to `gh -R`.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct GithubResource {
    pub kind: GithubResourceKind,
    pub number: u64,
    pub repository: Option<String>,
    pub comment_selector: Option<GithubCommentSelector>,
}

impl GithubResource {
    pub fn is_explicit(&self) -> bool {
        self.repository.is_some()
    }

    pub fn base_spelling(&self) -> String {
        match &self.repository {
            Some(repository) => format!("{}://{repository}/{}", self.kind.scheme(), self.number),
            None => format!("{}://{}", self.kind.scheme(), self.number),
        }
    }

    pub fn without_comment_selector(&self) -> Self {
        let mut resource = self.clone();
        resource.comment_selector = None;
        resource
    }
}

/// A typed error produced before a GitHub resource can enter the fetch path.
#[derive(Clone, Debug, Eq, PartialEq)]
pub struct InvalidGithubResource {
    resource: String,
    reason: String,
}

impl InvalidGithubResource {
    fn new(resource: &str, reason: impl Into<String>) -> Self {
        Self {
            resource: resource.to_string(),
            reason: reason.into(),
        }
    }

    pub fn code(&self) -> &'static str {
        "invalid_resource"
    }
}

impl fmt::Display for InvalidGithubResource {
    fn fmt(&self, formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            formatter,
            "invalid GitHub resource '{}': {}. Use issue://NUMBER, pr://NUMBER, issue://OWNER/REPO/NUMBER, or pr://OWNER/REPO/NUMBER; append /comments/<sel> for discussion ordinals",
            self.resource, self.reason
        )
    }
}

impl std::error::Error for InvalidGithubResource {}

/// Parse only the GitHub resource forms that the read command exposes.
///
/// This rejects query strings, fragments, ports, credentials, empty path
/// components, and alternate URL shapes rather than silently treating them as
/// filesystem paths or a different remote resource.
pub fn parse_resource(resource: &str) -> Result<GithubResource, InvalidGithubResource> {
    let parsed = Url::parse(resource)
        .map_err(|_| InvalidGithubResource::new(resource, "the URL is malformed"))?;
    let kind = match parsed.scheme() {
        "issue" => GithubResourceKind::Issue,
        "pr" => GithubResourceKind::PullRequest,
        _ => return Err(InvalidGithubResource::new(resource, "unsupported scheme")),
    };

    if parsed.query().is_some()
        || parsed.fragment().is_some()
        || parsed.port().is_some()
        || !parsed.username().is_empty()
        || parsed.password().is_some()
    {
        return Err(InvalidGithubResource::new(
            resource,
            "unsupported URL authority or suffix",
        ));
    }

    let authority = parsed
        .host_str()
        .ok_or_else(|| InvalidGithubResource::new(resource, "missing authority"))?;
    let path_segments: Vec<_> = parsed
        .path_segments()
        .map(|segments| segments.collect())
        .unwrap_or_default();

    // `issue://373` uses the URL authority for the number. It has no path.
    if parsed.path().is_empty() {
        return Ok(GithubResource {
            kind,
            number: parse_number(resource, authority)?,
            repository: None,
            comment_selector: None,
        });
    }

    // A short resource keeps its number in the authority, so its only accepted
    // path is the discussion drill-down suffix.
    if authority.bytes().all(|byte| byte.is_ascii_digit()) {
        if path_segments.len() == 2 && path_segments[0] == "comments" {
            return Ok(GithubResource {
                kind,
                number: parse_number(resource, authority)?,
                repository: None,
                comment_selector: Some(parse_comment_selector(resource, path_segments[1])?),
            });
        }
        return Err(InvalidGithubResource::new(
            resource,
            "unsupported short-resource suffix",
        ));
    }

    // Explicit resources use the authority for OWNER and begin their path with
    // REPO/NUMBER, optionally followed by comments/SELECTOR.
    if !valid_repository_component(authority)
        || path_segments.len() < 2
        || !valid_repository_component(path_segments[0])
    {
        return Err(InvalidGithubResource::new(
            resource,
            "unsupported authority or malformed repository path",
        ));
    }
    let comment_selector = match path_segments.as_slice() {
        [_, _] => None,
        [_, _, "comments", selector] => Some(parse_comment_selector(resource, selector)?),
        _ => {
            return Err(InvalidGithubResource::new(
                resource,
                "unsupported authority or malformed repository path",
            ))
        }
    };

    Ok(GithubResource {
        kind,
        number: parse_number(resource, path_segments[1])?,
        repository: Some(format!("{authority}/{}", path_segments[0])),
        comment_selector,
    })
}

fn parse_number(resource: &str, value: &str) -> Result<u64, InvalidGithubResource> {
    if value.is_empty() || !value.bytes().all(|byte| byte.is_ascii_digit()) {
        return Err(InvalidGithubResource::new(
            resource,
            "resource number must be numeric",
        ));
    }
    let number = value
        .parse::<u64>()
        .map_err(|_| InvalidGithubResource::new(resource, "resource number is out of range"))?;
    if number == 0 {
        return Err(InvalidGithubResource::new(
            resource,
            "resource number must be greater than zero",
        ));
    }
    Ok(number)
}

fn parse_comment_selector(
    resource: &str,
    selector: &str,
) -> Result<GithubCommentSelector, InvalidGithubResource> {
    let mut ranges = Vec::new();
    for item in selector.split(',') {
        if item.is_empty() {
            return Err(InvalidGithubResource::new(
                resource,
                "comment selector contains an empty item",
            ));
        }
        let range = if let Some((start, end)) = item.split_once('-') {
            if end.contains('-') {
                return Err(InvalidGithubResource::new(
                    resource,
                    "comment selector ranges contain exactly one hyphen",
                ));
            }
            let start = parse_ordinal(resource, start)?;
            let end = parse_ordinal(resource, end)?;
            if start > end {
                return Err(InvalidGithubResource::new(
                    resource,
                    "comment selector range start exceeds its end",
                ));
            }
            start..=end
        } else {
            let ordinal = parse_ordinal(resource, item)?;
            ordinal..=ordinal
        };
        ranges.push(range);
    }
    if ranges.is_empty() {
        return Err(InvalidGithubResource::new(
            resource,
            "comment selector is empty",
        ));
    }
    Ok(GithubCommentSelector { ranges })
}

fn parse_ordinal(resource: &str, value: &str) -> Result<usize, InvalidGithubResource> {
    if value.is_empty() || !value.bytes().all(|byte| byte.is_ascii_digit()) {
        return Err(InvalidGithubResource::new(
            resource,
            "comment selector ordinals must be positive integers",
        ));
    }
    let ordinal = value.parse::<usize>().map_err(|_| {
        InvalidGithubResource::new(resource, "comment selector ordinal is out of range")
    })?;
    if ordinal == 0 {
        return Err(InvalidGithubResource::new(
            resource,
            "comment selector ordinals must be greater than zero",
        ));
    }
    Ok(ordinal)
}

fn valid_repository_component(value: &str) -> bool {
    !value.is_empty()
        && value.len() <= 100
        && value
            .bytes()
            .all(|byte| byte.is_ascii_alphanumeric() || matches!(byte, b'-' | b'_' | b'.'))
}

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

    #[test]
    fn accepts_only_the_four_resource_forms() {
        assert_eq!(
            parse_resource("issue://373").unwrap(),
            GithubResource {
                kind: GithubResourceKind::Issue,
                number: 373,
                repository: None,
                comment_selector: None,
            }
        );
        assert_eq!(
            parse_resource("pr://Owner/repo-name/45").unwrap(),
            GithubResource {
                kind: GithubResourceKind::PullRequest,
                number: 45,
                repository: Some("Owner/repo-name".to_string()),
                comment_selector: None,
            }
        );

        for value in [
            "issue:///373",
            "issue://373/",
            "issue://owner/repo/not-a-number",
            "issue://owner/repo/0",
            "issue://owner/repo/1/extra",
            "issue://owner/repo/1?view=full",
            "issue://owner:secret@repo/1",
            "issue://github.com/owner/repo/1",
            "https://github.com/owner/repo/issues/1",
        ] {
            assert!(parse_resource(value).is_err(), "{value}");
        }
    }

    #[test]
    fn parses_comment_ordinal_selectors_for_short_and_explicit_resources() {
        let short = parse_resource("issue://373/comments/3,7").unwrap();
        let short_selector = short.comment_selector.as_ref().unwrap();
        assert!(short_selector.contains(3));
        assert!(short_selector.contains(7));
        assert!(!short_selector.contains(4));
        assert_eq!(short.base_spelling(), "issue://373");

        let explicit = parse_resource("pr://Owner/repo-name/45/comments/3-5").unwrap();
        let explicit_selector = explicit.comment_selector.as_ref().unwrap();
        assert!((3..=5).all(|ordinal| explicit_selector.contains(ordinal)));
        assert_eq!(explicit.base_spelling(), "pr://Owner/repo-name/45");

        for value in [
            "pr://45/comments/0",
            "pr://45/comments/",
            "pr://45/comments/5-3",
            "pr://45/comments/3-5-7",
            "pr://45/comments/3,,7",
            "pr://owner/repo/45/comments/3/extra",
        ] {
            assert!(parse_resource(value).is_err(), "{value}");
        }
    }
}