bake-readme 0.1.3

// Released under the MIT License.
// Copyright, 2026, by Samuel Williams.

use socketry_markdown::{
    MarkdownOptions, ParseOptions,
    mdast::{Html, InlineCode, Link, List, ListItem, Node, Paragraph, Text},
    to_mdast,
};
use std::ops::Range;

const RELEASES_SECTION: &str =
    "## Releases\n\nSee [releases.md](releases.md) for the release history.";
const RELEASES_START: &str = "<!-- bake-readme:releases:start -->";
const RELEASES_END: &str = "<!-- bake-readme:releases:end -->";
const PACKAGE_MARKER: &str = "<!-- bake-readme:package -->";
const RECENT_RELEASE_COUNT: usize = 3;

struct Heading {
    title: String,
    level: u8,
    start: usize,
    body_start: usize,
}

/// Cargo package fields used to add a generated entry to the `readme.md` See Also section.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct PackageMetadata {
    /// Cargo package name.
    pub name: String,
    /// Optional Cargo package description.
    pub description: Option<String>,
    /// Optional Cargo repository URL.
    pub repository: Option<String>,
}

/// A release entry parsed from the project's `releases.md` file.
#[derive(Clone, Debug, PartialEq, Eq)]
pub struct Release {
    /// Release heading, usually a version such as `v1.2.3`.
    pub name: String,
    /// Markdown content beneath the release heading.
    pub notes: String,
}

fn parse_markdown(document: &str) -> Option<Node> {
    to_mdast(document, &ParseOptions::default()).ok()
}

fn heading_text(node: &Node) -> String {
    let text = node.text_content();
    text.strip_suffix("\r\n")
        .or_else(|| text.strip_suffix('\n'))
        .or_else(|| text.strip_suffix('\r'))
        .unwrap_or(text.as_str())
        .to_owned()
}

fn after_line_ending(document: &str, offset: usize) -> usize {
    let Some(rest) = document.get(offset..) else {
        return offset;
    };

    if rest.starts_with("\r\n") {
        offset + 2
    } else if rest.starts_with('\r') || rest.starts_with('\n') {
        offset + 1
    } else {
        offset
    }
}

fn headings(document: &str) -> Vec<Heading> {
    let Some(root) = parse_markdown(document) else {
        return Vec::new();
    };
    let Some(children) = root.children() else {
        return Vec::new();
    };
    let mut headings = Vec::new();

    for node in children {
        let Node::Heading(heading) = node else {
            continue;
        };
        let Some(position) = heading.position.as_ref() else {
            continue;
        };
        headings.push(Heading {
            title: heading_text(node),
            level: heading.depth,
            start: position.start.offset,
            body_start: after_line_ending(document, position.end.offset),
        });
    }

    headings
}

fn trailing_blank_lines_start(document: &str, position: usize) -> Range<usize> {
    let prefix = &document[..position];
    let mut start = position;
    for line in prefix.split_inclusive('\n').rev() {
        if line.trim().is_empty() {
            start -= line.len();
        } else {
            break;
        }
    }
    start..position
}

fn newline(document: &str) -> &'static str {
    if document.contains("\r\n") {
        "\r\n"
    } else {
        "\n"
    }
}

fn rendered_package_entry(package: &PackageMetadata) -> String {
    let name = package.name.trim();
    let name_node = match package
        .repository
        .as_deref()
        .filter(|value| !value.trim().is_empty())
    {
        Some(repository) => Node::Link(Link {
            children: vec![Node::Text(Text {
                value: name.to_owned(),
                position: None,
            })],
            position: None,
            url: repository.to_owned(),
            title: None,
        }),
        None => Node::InlineCode(InlineCode {
            value: name.to_owned(),
            position: None,
            lang: None,
        }),
    };
    let description = package
        .description
        .as_deref()
        .map(str::split_whitespace)
        .map(|words| words.collect::<Vec<_>>())
        .filter(|words| !words.is_empty())
        .map(|words| words.join(" "));

    let mut children = vec![name_node];
    if let Some(description) = description {
        children.push(Node::Text(Text {
            value: format!(" — {description}"),
            position: None,
        }));
    }
    children.push(Node::Html(Html {
        value: PACKAGE_MARKER.to_owned(),
        position: None,
    }));

    let options = MarkdownOptions {
        bullet: '-',
        ..MarkdownOptions::default()
    };

    Node::List(List {
        children: vec![Node::ListItem(ListItem {
            children: vec![Node::Paragraph(Paragraph {
                children,
                position: None,
            })],
            position: None,
            spread: false,
            checked: None,
        })],
        position: None,
        ordered: false,
        start: None,
        spread: false,
    })
    .to_markdown_with_options(&options)
    .expect("generated package entries are valid Markdown")
    .trim_end()
    .to_owned()
}

fn section_end(document: &str, headings: &[Heading], index: usize) -> usize {
    let heading = &headings[index];
    headings
        .iter()
        .skip(index + 1)
        .find(|next| next.level <= heading.level)
        .map_or(document.len(), |next| next.start)
}

/// Parse the newest versioned release entries, excluding the Unreleased section.
pub fn recent_releases(document: &str) -> Vec<Release> {
    let headings = headings(document);
    let Some((releases_index, releases_heading)) = headings
        .iter()
        .enumerate()
        .find(|(_, heading)| heading.level == 1 && heading.title == "Releases")
    else {
        return Vec::new();
    };
    let releases_end = section_end(document, &headings, releases_index);

    headings
        .iter()
        .enumerate()
        .filter(|(_, heading)| {
            heading.level == 2
                && heading.start >= releases_heading.body_start
                && heading.start < releases_end
                && !heading.title.eq_ignore_ascii_case("Unreleased")
        })
        .take(RECENT_RELEASE_COUNT)
        .map(|(index, heading)| Release {
            name: heading.title.to_owned(),
            notes: document[heading.body_start..section_end(document, &headings, index)]
                .trim()
                .to_owned(),
        })
        .collect()
}

fn rendered_recent_releases(releases: &[Release], line_ending: &str) -> String {
    let mut content = String::from("See [releases.md](releases.md) for the full release history.");

    for release in releases {
        content.push_str(line_ending);
        content.push_str(line_ending);
        content.push_str("### ");
        content.push_str(&release.name);
        if !release.notes.is_empty() {
            content.push_str(line_ending);
            content.push_str(line_ending);
            content.push_str(
                &release
                    .notes
                    .replace("\r\n", "\n")
                    .replace('\n', line_ending),
            );
        }
    }

    content
}

fn marker_line(document: &str, range: Range<usize>, marker: &str) -> Option<(usize, usize)> {
    let root = parse_markdown(document)?;
    let mut found = None;
    root.walk(|node| {
        if found.is_some() {
            return;
        }
        let Node::Html(html) = node else {
            return;
        };
        if html.value.trim() != marker {
            return;
        }
        let Some(position) = node.position() else {
            return;
        };
        let offset = position.start.offset;
        if offset < range.start || offset >= range.end {
            return;
        }
        found = Some(source_line_range(document, offset));
    });
    found
}

fn source_line_range(document: &str, offset: usize) -> (usize, usize) {
    let start = document[..offset]
        .rfind('\n')
        .map_or(0, |newline| newline + 1);
    let end = document[offset..]
        .find('\n')
        .map_or(document.len(), |newline| offset + newline + 1);
    (start, end)
}

fn contains_link_to(document: &str, range: Range<usize>, destination: &str) -> bool {
    let Some(root) = parse_markdown(document) else {
        return false;
    };
    let mut definitions = Vec::new();
    root.walk(|node| {
        if let Node::Definition(definition) = node
            && definition.url == destination
        {
            definitions.push(definition.identifier.clone());
        }
    });
    let mut found = false;
    root.walk(|node| {
        if found {
            return;
        }
        let matches = match node {
            Node::Link(link) => link.url == destination,
            Node::LinkReference(reference) => definitions.contains(&reference.identifier),
            _ => false,
        };
        if matches
            && node
                .position()
                .is_some_and(|position| range.contains(&position.start.offset))
        {
            found = true;
        }
    });
    found
}

fn replace_generated_releases(
    document: &str,
    body: Range<usize>,
    releases: &[Release],
) -> Option<String> {
    let start = marker_line(document, body.clone(), RELEASES_START);
    let end = marker_line(document, body.clone(), RELEASES_END);
    let line_ending = newline(document);
    let content = rendered_recent_releases(releases, line_ending);

    if let (Some((_, start_end)), Some((end_start, _))) = (start, end) {
        if start_end <= end_start {
            let mut updated = String::with_capacity(document.len() + content.len());
            updated.push_str(&document[..start_end]);
            updated.push_str(&content);
            updated.push_str(line_ending);
            updated.push_str(&document[end_start..]);
            return Some(updated);
        }
        return None;
    }

    // Upgrade the simple link generated by earlier versions of this task.
    if document[body.clone()].trim() == "See [releases.md](releases.md) for the release history." {
        let replacement = format!(
            "{line_ending}{RELEASES_START}{line_ending}{content}{line_ending}{RELEASES_END}{line_ending}{line_ending}"
        );
        let mut updated = String::with_capacity(document.len() + replacement.len());
        updated.push_str(&document[..body.start]);
        updated.push_str(&replacement);
        updated.push_str(&document[body.end..]);
        return Some(updated);
    }

    None
}

/// Add or refresh a marked summary of the most recent releases.
///
/// Project-authored Releases sections remain untouched. Sections generated by
/// this task are marked so later updates can refresh their release entries.
pub fn update_releases_section(document: &str, releases: &[Release]) -> String {
    let document_headings = headings(document);
    if let Some((index, heading)) = document_headings
        .iter()
        .enumerate()
        .find(|(_, heading)| heading.title == "Releases")
    {
        let body = heading.body_start..section_end(document, &document_headings, index);
        return replace_generated_releases(document, body, releases)
            .unwrap_or_else(|| document.to_owned());
    }

    let document = ensure_releases_section(document);
    let generated_headings = headings(&document);
    let Some((index, heading)) = generated_headings
        .iter()
        .enumerate()
        .find(|(_, heading)| heading.title == "Releases")
    else {
        return document;
    };
    let body = heading.body_start..section_end(&document, &generated_headings, index);
    replace_generated_releases(&document, body, releases).unwrap_or(document)
}

fn update_see_also_section(document: &str, package: Option<&PackageMetadata>) -> String {
    let headings = headings(document);
    let Some(package) = package else {
        return document.to_owned();
    };
    let entry = rendered_package_entry(package);
    let newline = newline(document);

    if let Some((index, heading)) = headings
        .iter()
        .enumerate()
        .find(|(_, heading)| heading.title == "See Also")
    {
        let end = section_end(document, &headings, index);
        let body = &document[heading.body_start..end];
        let repository_is_linked_elsewhere = package
            .repository
            .as_deref()
            .filter(|repository| !repository.trim().is_empty())
            .is_some_and(|repository| {
                contains_link_to(document, 0..heading.start, repository)
                    || contains_link_to(document, end..document.len(), repository)
            });
        if let Some((line_start, line_end)) =
            marker_line(document, heading.body_start..end, PACKAGE_MARKER)
        {
            let line = &document[line_start..line_end];
            let line_ending = if line.ends_with("\r\n") {
                "\r\n"
            } else if line.ends_with('\n') {
                "\n"
            } else {
                ""
            };
            if repository_is_linked_elsewhere
                && package.repository.as_deref().is_some_and(|repository| {
                    contains_link_to(document, line_start..line_end, repository)
                })
            {
                let remaining_body = format!(
                    "{}{}",
                    &document[heading.body_start..line_start],
                    &document[line_end..end]
                );

                if remaining_body.trim().is_empty() {
                    let section_start = trailing_blank_lines_start(document, heading.start).start;
                    let mut updated = String::with_capacity(document.len());
                    updated.push_str(&document[..section_start]);
                    if !updated.is_empty() && !updated.ends_with("\n\n") {
                        if updated.ends_with('\n') {
                            updated.push_str(newline);
                        } else {
                            updated.push_str(newline);
                            updated.push_str(newline);
                        }
                    }
                    updated.push_str(&document[end..]);
                    return updated;
                }

                let mut updated = String::with_capacity(document.len());
                updated.push_str(&document[..line_start]);
                updated.push_str(&document[line_end..]);
                return updated;
            }

            let mut updated = String::with_capacity(document.len() + entry.len());
            updated.push_str(&document[..line_start]);
            updated.push_str(&entry);
            updated.push_str(line_ending);
            updated.push_str(&document[line_end..]);
            return updated;
        }

        if repository_is_linked_elsewhere
            || package.repository.as_deref().is_some_and(|repository| {
                contains_link_to(document, heading.body_start..end, repository)
            })
        {
            return document.to_owned();
        }

        let mut insertion = heading.body_start;
        while insertion < end {
            let remaining = &document[insertion..end];
            let Some(line_end) = remaining.find('\n').map(|index| insertion + index + 1) else {
                break;
            };
            if document[insertion..line_end].trim().is_empty() {
                insertion = line_end;
            } else {
                break;
            }
        }
        let prefix = &document[..insertion];
        let leading = if insertion == heading.body_start
            && (!prefix.ends_with('\n') || !body.starts_with('\n'))
        {
            newline
        } else {
            ""
        };
        let mut updated = String::with_capacity(document.len() + entry.len() + 4);
        updated.push_str(prefix);
        updated.push_str(leading);
        updated.push_str(&entry);
        updated.push_str(newline);
        updated.push_str(newline);
        updated.push_str(&document[insertion..]);
        return updated;
    }

    let target = headings
        .iter()
        .find(|heading| heading.title == "Contributing");
    if package
        .repository
        .as_deref()
        .is_some_and(|repository| contains_link_to(document, 0..document.len(), repository))
    {
        return document.to_owned();
    }
    let section = format!("## See Also{newline}{newline}{entry}");

    if let Some(target) = target {
        let insertion = trailing_blank_lines_start(document, target.start).start;
        let prefix = &document[..insertion];
        let preceding_newlines = prefix
            .chars()
            .rev()
            .take_while(|character| *character == '\n')
            .count();
        let leading = if insertion == 0 || preceding_newlines >= 2 {
            ""
        } else if preceding_newlines == 1 {
            newline
        } else if newline == "\r\n" {
            "\r\n\r\n"
        } else {
            "\n\n"
        };
        let mut updated = String::with_capacity(document.len() + section.len() + 8);
        updated.push_str(prefix);
        updated.push_str(leading);
        updated.push_str(&section);
        updated.push_str(newline);
        updated.push_str(newline);
        updated.push_str(&document[target.start..]);
        updated
    } else {
        let separator = if document.is_empty() || document.ends_with("\n\n") {
            ""
        } else if document.ends_with('\n') {
            newline
        } else if newline == "\r\n" {
            "\r\n\r\n"
        } else {
            "\n\n"
        };
        let mut updated = String::with_capacity(document.len() + section.len() + 4);
        updated.push_str(document);
        updated.push_str(separator);
        updated.push_str(&section);
        updated.push_str(newline);
        updated
    }
}

/// Add the default Releases section if the document has no real Releases heading.
///
/// The section is inserted before a `See Also` or `Contributing` heading when
/// present; otherwise it is appended. Headings inside fenced code blocks and
/// block quotes are ignored. If a Releases section already exists, the original
/// document is returned byte for byte.
pub fn ensure_releases_section(document: &str) -> String {
    let headings = headings(document);
    if headings.iter().any(|heading| heading.title == "Releases") {
        return document.to_owned();
    }

    let target = headings
        .iter()
        .find(|heading| matches!(heading.title.as_str(), "See Also" | "Contributing"));

    let newline = newline(document);
    let section = RELEASES_SECTION.replace('\n', newline);

    if let Some(target) = target {
        let insertion = trailing_blank_lines_start(document, target.start).start;
        let prefix = &document[..insertion];
        let preceding_newlines = prefix
            .chars()
            .rev()
            .take_while(|character| *character == '\n')
            .count();
        let leading = if insertion == 0 || preceding_newlines >= 2 {
            ""
        } else if preceding_newlines == 1 {
            newline
        } else {
            if newline == "\r\n" {
                "\r\n\r\n"
            } else {
                "\n\n"
            }
        };
        let mut updated = String::with_capacity(document.len() + section.len() + 8);
        updated.push_str(prefix);
        updated.push_str(leading);
        updated.push_str(&section);
        updated.push_str(newline);
        updated.push_str(newline);
        updated.push_str(&document[target.start..]);
        updated
    } else {
        let separator = if document.is_empty() || document.ends_with("\n\n") {
            ""
        } else if document.ends_with('\n') {
            newline
        } else if newline == "\r\n" {
            "\r\n\r\n"
        } else {
            "\n\n"
        };
        let mut updated =
            String::with_capacity(document.len() + section.len() + separator.len() + 1);
        updated.push_str(document);
        updated.push_str(separator);
        updated.push_str(&section);
        updated.push_str(newline);
        updated
    }
}

/// Add or refresh metadata-derived See Also content and the standard Releases section.
///
/// The generated package entry is marked with an HTML comment so subsequent
/// updates can refresh it while preserving the rest of a project-owned section.
pub fn update_document(document: &str, package: Option<&PackageMetadata>) -> String {
    let updated = update_see_also_section(document, package);
    ensure_releases_section(&updated)
}

/// Add or refresh metadata-derived See Also content and recent release entries.
pub fn update_document_with_releases(
    document: &str,
    package: Option<&PackageMetadata>,
    releases: &[Release],
) -> String {
    let updated = update_see_also_section(document, package);
    update_releases_section(&updated, releases)
}