pma 0.4.0

//! Parser and linter for the TODO.md format, v2.
//!
//! The format is specified in `docs/dev/design.md`. Parsing is line-based so
//! that later edits can rewrite single lines without re-rendering content the
//! parser does not own.

use std::collections::HashMap;
use std::fmt;

#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash, PartialOrd, Ord)]
pub enum Priority {
    Critical,
    High,
    Medium,
    Low,
}

impl Priority {
    pub const ALL: [Priority; 4] = [
        Priority::Critical,
        Priority::High,
        Priority::Medium,
        Priority::Low,
    ];

    pub fn name(self) -> &'static str {
        match self {
            Priority::Critical => "critical",
            Priority::High => "high",
            Priority::Medium => "medium",
            Priority::Low => "low",
        }
    }

    pub fn parse(s: &str) -> Option<Priority> {
        Self::ALL.into_iter().find(|p| p.name() == s)
    }
}

const SECTIONS: [(&str, Priority); 4] = [
    ("Critical", Priority::Critical),
    ("High", Priority::High),
    ("Medium", Priority::Medium),
    ("Low", Priority::Low),
];

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Item {
    /// 1-based line number of the item line.
    pub line: usize,
    pub priority: Priority,
    pub done: bool,
    pub text: String,
    pub tags: Vec<String>,
    /// `YYYY-MM-DD`, already validated.
    pub due: Option<String>,
    pub gh: Option<u64>,
    /// `id:xxxxx`, minted by `pma`; already validated.
    pub id: Option<String>,
    /// Text of the nearest `###` heading above the item in its section.
    pub group: Option<String>,
    /// Indented lines under the item, verbatim.
    pub description: Vec<String>,
}

impl Item {
    /// Identity across scans and edits: `id:`, else `gh:N`, else the text in
    /// comparable form. Text that reads as another kind of task's key, such
    /// as an item named `CI`, is prefixed with `item:`, so it cannot be taken
    /// for a signal, a campaign, a workflow unit or an id.
    pub fn key(&self) -> String {
        if let Some(id) = &self.id {
            return format!("id:{id}");
        }
        match self.gh {
            Some(n) => format!("gh:{n}"),
            None => self.text_key(),
        }
    }

    fn text_key(&self) -> String {
        let text = normal_text(&self.text);
        let reserved = matches!(text.as_str(), "ci" | "deps")
            || ["campaign:", "workflow:", "item:", "id:", "gh:"]
                .iter()
                .any(|p| text.starts_with(p));
        match reserved {
            true => format!("item:{text}"),
            false => text,
        }
    }

    /// Whether this is the task known by `key` or by `text`. Every name the
    /// item has answers: its id, its issue and its text, since a key recorded
    /// before an id or an issue was written into the line names it by one of
    /// the others.
    pub fn is_task(&self, key: &str, text: &str) -> bool {
        self.id.as_ref().is_some_and(|id| key == format!("id:{id}"))
            || self.gh.is_some_and(|n| key == format!("gh:{n}"))
            || self.text_key() == key
            || (!text.trim().is_empty() && normal_text(&self.text) == normal_text(text))
    }
}

/// Item text in comparable form: lowercase, single-spaced.
pub fn normal_text(text: &str) -> String {
    text.split_whitespace()
        .collect::<Vec<_>>()
        .join(" ")
        .to_lowercase()
}

#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
pub enum Severity {
    Warning,
    Error,
}

impl fmt::Display for Severity {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.write_str(match self {
            Severity::Warning => "warning",
            Severity::Error => "error",
        })
    }
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Diagnostic {
    pub line: usize,
    pub severity: Severity,
    pub message: String,
}

#[derive(Debug, Default)]
pub struct Parsed {
    pub items: Vec<Item>,
    pub diagnostics: Vec<Diagnostic>,
    /// Each `## Done` section, a v1 leftover.
    pub done_sections: Vec<DoneSection>,
}

#[derive(Debug, Clone, PartialEq, Eq)]
pub struct DoneSection {
    /// 1-based lines of the heading and of the section's last line.
    pub first: usize,
    pub last: usize,
    /// Line number and text of each `- [ ]` item, which v1 did not allow here.
    pub open: Vec<(usize, String)>,
}

impl Parsed {
    pub fn has_errors(&self) -> bool {
        self.diagnostics
            .iter()
            .any(|d| d.severity == Severity::Error)
    }

    fn report(&mut self, line: usize, severity: Severity, message: impl Into<String>) {
        self.diagnostics.push(Diagnostic {
            line,
            severity,
            message: message.into(),
        });
    }
}

/// Where the parser is: before any `##`, in a priority section, in v1's
/// `## Done`, or in another section.
#[derive(Clone, Copy)]
enum Place {
    Preamble,
    Known(Priority),
    Done,
    Other,
}

pub fn parse(text: &str) -> Parsed {
    let mut out = Parsed::default();
    let mut place = Place::Preamble;
    let mut seen_sections: HashMap<Priority, usize> = HashMap::new();
    let mut title_line: Option<usize> = None;
    let mut first_content = true;
    // The open fence: its character, its length and its line. It closes only on
    // a line of the same character at least as long, as CommonMark has it.
    let mut fence: Option<(u8, usize, usize)> = None;
    // Blank lines seen since the open item's last line. Kept so a description
    // that spans a blank line is carried verbatim.
    let mut blanks = 0;
    let mut open: Option<Item> = None;
    // Plain bullets outside the known sections, reported when nothing else is
    // an item: that file's tasks are invisible to pma.
    let mut ignored_bullets = 0;
    let mut group: Option<String> = None;

    for (index, raw) in text.lines().enumerate() {
        let n = index + 1;
        let line = raw.trim_end();

        if line.is_empty() {
            blanks += 1;
            continue;
        }

        let indented = line.starts_with(' ') || line.starts_with('\t');
        if indented {
            match open.as_mut() {
                Some(item) => {
                    item.description
                        .extend(std::iter::repeat_n(String::new(), blanks));
                    item.description.push(raw.to_string());
                }
                None if matches!(place, Place::Known(_)) && fence.is_none() => {
                    out.report(n, Severity::Warning, "indented line is not under an item");
                }
                None => {}
            }
            blanks = 0;
            continue;
        }
        blanks = 0;
        finish(&mut open, &mut out);

        if first_content {
            first_content = false;
            if line != "# TODO" {
                out.report(n, Severity::Error, "the file must start with `# TODO`");
            }
        }

        match fence {
            Some((mark, len, _)) => {
                if fence_run(line, mark).is_some_and(|n| n >= len && n == line.len()) {
                    fence = None;
                }
                continue;
            }
            None => {
                if let Some((mark, len)) = b"`~"
                    .iter()
                    .copied()
                    .find_map(|m| fence_run(line, m).filter(|n| *n >= 3).map(|n| (m, n)))
                {
                    fence = Some((mark, len, n));
                    continue;
                }
            }
        }

        if line.starts_with("# ") {
            // A wrong first title is already reported above.
            match title_line {
                Some(first) => out.report(
                    n,
                    Severity::Error,
                    format!("a second `#` heading; the title is on line {first}"),
                ),
                None => title_line = Some(n),
            }
            continue;
        }

        // `##Critical` is not a Markdown heading, but its author meant one.
        let heading = match line.strip_prefix("## ") {
            Some(name) => Some((name, true)),
            None => line
                .strip_prefix("##")
                .filter(|rest| is_priority_name(rest.trim()))
                .map(|name| (name, false)),
        };
        if let Some((name, spaced)) = heading {
            if matches!(place, Place::Done)
                && let Some(section) = out.done_sections.last_mut()
            {
                section.last = n - 1;
            }
            place = section_heading(name.trim(), spaced, n, &mut seen_sections, &mut out);
            if matches!(place, Place::Done) {
                out.done_sections.push(DoneSection {
                    first: n,
                    last: text.lines().count(),
                    open: Vec::new(),
                });
            }
            group = None;
            continue;
        }
        // `###` alone clears the group; trimming removed any trailing space.
        if let Some(name) = line
            .strip_prefix("###")
            .filter(|rest| rest.is_empty() || rest.starts_with(' '))
        {
            group = Some(name.trim().to_string()).filter(|g| !g.is_empty());
            continue;
        }
        if line.starts_with('#') {
            // `####` and deeper change neither the section nor the group.
            continue;
        }

        match place {
            Place::Known(priority) => {
                if let Some(mut item) = item_line(line, n, priority, &mut out) {
                    item.group = group.clone();
                    open = Some(item);
                }
            }
            Place::Preamble | Place::Done | Place::Other => {
                if is_checkbox(line) {
                    let msg = match place {
                        Place::Preamble => "item outside a section is ignored",
                        Place::Done => "`## Done` is not part of format v2; `pma prune` removes it",
                        _ => "item in this section is ignored; use Critical, High, Medium or Low",
                    };
                    out.report(n, Severity::Warning, msg);
                    if let (Place::Done, Some(' '), Some(section)) =
                        (place, checkbox_mark(line), out.done_sections.last_mut())
                    {
                        section.open.push((n, line.to_string()));
                    }
                } else if is_bullet(line) {
                    ignored_bullets += 1;
                }
            }
        }
    }
    finish(&mut open, &mut out);

    if let Some((_, _, line)) = fence {
        out.report(
            line,
            Severity::Error,
            "this code fence is never closed, so no line after it is read",
        );
    }
    if first_content {
        out.report(1, Severity::Error, "the file must start with `# TODO`");
    }
    // A file with priority sections has adopted the format, so bullets outside
    // them are deliberate: notes, declined work, ideas.
    if out.items.is_empty() && ignored_bullets > 0 && seen_sections.is_empty() {
        out.report(
            1,
            Severity::Warning,
            format!(
                "no items; {ignored_bullets} list entries outside Critical, High, Medium and Low are ignored"
            ),
        );
    }
    check_duplicates(&mut out);
    out
}

/// How many of `mark` the line starts with, if any.
fn fence_run(line: &str, mark: u8) -> Option<usize> {
    let n = line.bytes().take_while(|&b| b == mark).count();
    (n > 0).then_some(n)
}

fn finish(open: &mut Option<Item>, out: &mut Parsed) {
    if let Some(item) = open.take() {
        out.items.push(item);
    }
}

fn is_priority_name(name: &str) -> bool {
    SECTIONS
        .iter()
        .any(|(known, _)| known.eq_ignore_ascii_case(name))
}

fn section_heading(
    name: &str,
    spaced: bool,
    n: usize,
    seen: &mut HashMap<Priority, usize>,
    out: &mut Parsed,
) -> Place {
    if name == "Done" {
        return Place::Done;
    }
    let Some((canonical, priority)) = SECTIONS
        .iter()
        .find(|(known, _)| known.eq_ignore_ascii_case(name))
    else {
        return Place::Other;
    };
    if !spaced || name != *canonical {
        out.report(
            n,
            Severity::Error,
            format!("write the heading as `## {canonical}`"),
        );
    }
    if let Some(first) = seen.insert(*priority, n) {
        out.report(
            n,
            Severity::Error,
            format!("`## {canonical}` appears again; the first is on line {first}"),
        );
    }
    Place::Known(*priority)
}

fn is_bullet(line: &str) -> bool {
    line.starts_with("- ") || line.starts_with("* ") || line.starts_with("+ ")
}

/// Recognises any checkbox list entry, canonical or not.
fn is_checkbox(line: &str) -> bool {
    checkbox_mark(line).is_some_and(|mark| matches!(mark, ' ' | 'x' | 'X'))
}

fn checkbox_mark(line: &str) -> Option<char> {
    let rest = line
        .strip_prefix(['-', '*', '+'])
        .or_else(|| {
            let digits = line.trim_start_matches(|c: char| c.is_ascii_digit());
            (digits.len() < line.len())
                .then(|| digits.strip_prefix(['.', ')']))
                .flatten()
        })?
        .trim_start();
    let mark = rest.strip_prefix('[')?.chars().next()?;
    rest[1 + mark.len_utf8()..].starts_with(']').then_some(mark)
}

fn item_line(line: &str, n: usize, priority: Priority, out: &mut Parsed) -> Option<Item> {
    let canonical = match line.get(..5) {
        Some("- [ ]") => Some(false),
        Some("- [x]") => Some(true),
        _ => None,
    };
    let rest = &line[if canonical.is_some() { 5 } else { 0 }..];
    let Some(done) = canonical.filter(|_| rest.is_empty() || rest.starts_with(' ')) else {
        if is_checkbox(line) {
            out.report(
                n,
                Severity::Error,
                "write items as `- [ ] text` or `- [x] text`",
            );
        } else if is_bullet(line) {
            out.report(
                n,
                Severity::Error,
                "a list entry in this section must be a `- [ ]` item",
            );
        } else {
            out.report(n, Severity::Warning, "text in this section is not an item");
        }
        return None;
    };

    let words: Vec<&str> = rest.split_whitespace().collect();
    let mut split = words.len();
    while split > 0 && is_token(words[split - 1]) {
        split -= 1;
    }

    let mut item = Item {
        line: n,
        priority,
        done,
        text: words[..split].join(" "),
        tags: Vec::new(),
        due: None,
        gh: None,
        id: None,
        group: None,
        description: Vec::new(),
    };

    for word in &words[split..] {
        if let Some(date) = word.strip_prefix("due:") {
            if crate::dates::parse(date).is_none() {
                out.report(
                    n,
                    Severity::Error,
                    format!("`{word}` is not a date; write `due:YYYY-MM-DD`"),
                );
            } else if item.due.replace(date.to_string()).is_some() {
                out.report(n, Severity::Error, "more than one `due:`");
            }
        } else if let Some(number) = word.strip_prefix("gh:") {
            match number.parse::<u64>() {
                Ok(v) if v > 0 && !number.starts_with('0') => {
                    if item.gh.replace(v).is_some() {
                        out.report(n, Severity::Error, "more than one `gh:`");
                    }
                }
                _ => out.report(
                    n,
                    Severity::Error,
                    format!("`{word}` is not an issue number"),
                ),
            }
        } else if let Some(id) = caret_id(word) {
            if item.id.replace(id.to_string()).is_some() {
                out.report(n, Severity::Error, "more than one id");
            }
        } else if !item.tags.iter().any(|t| t == &word[1..]) {
            item.tags.push(word[1..].to_string());
        }
    }

    if let Some(last) = words[..split].last()
        && last.len() > 1
        && last.starts_with('#')
        && last[1..].bytes().all(|b| b.is_ascii_digit())
    {
        out.report(
            n,
            Severity::Warning,
            format!(
                "`{last}` is text; write `gh:{}` to link the issue",
                &last[1..]
            ),
        );
    }

    if item.text.is_empty() {
        out.report(n, Severity::Error, "the item has no text");
    }
    Some(item)
}

/// A trailing token: `#tag`, `due:...`, `gh:...` or an id, `^k3f9q`. A caret
/// word that is not an id, such as `^1.2`, is text. Malformed `due:` and `gh:`
/// values still count, so they are reported rather than read as text.
pub fn is_token(word: &str) -> bool {
    if word.starts_with("due:") || word.starts_with("gh:") || caret_id(word).is_some() {
        return true;
    }
    let Some(tag) = word.strip_prefix('#') else {
        return false;
    };
    tag.starts_with(|c: char| c.is_ascii_alphabetic())
        && tag
            .chars()
            .all(|c| c.is_ascii_alphanumeric() || c == '-' || c == '_')
}

/// Characters an id is written in: Crockford's base32, lowercase, without
/// `i`, `l`, `o` and `u`, so an id is not misread as a digit or a word.
const ID_ALPHABET: &[u8; 32] = b"0123456789abcdefghjkmnpqrstvwxyz";

/// Characters in an id. 32^5 values keep a clash between two branches that
/// each mint in one 200-item file near 1 in 1,600.
const ID_LEN: usize = 5;

fn is_id(s: &str) -> bool {
    s.len() == ID_LEN && s.bytes().all(|b| ID_ALPHABET.contains(&b))
}

/// The id in a word written `^k3f9q`, as Obsidian marks a block, if it is one.
fn caret_id(word: &str) -> Option<&str> {
    word.strip_prefix('^').filter(|id| is_id(id))
}

/// A fresh id no item in `text` holds. Random rather than sequential, so two
/// branches that each add an item do not mint the same one.
pub fn new_id(text: &str) -> String {
    use std::hash::{BuildHasher, Hasher};
    let taken: Vec<String> = parse(text).items.into_iter().filter_map(|i| i.id).collect();
    let state = std::collections::hash_map::RandomState::new();
    for n in 0u64.. {
        let mut h = state.build_hasher();
        h.write_u64(n);
        h.write_u128(
            std::time::SystemTime::now()
                .duration_since(std::time::UNIX_EPOCH)
                .map_or(0, |d| d.as_nanos()),
        );
        let mut bits = h.finish();
        let id: String = (0..ID_LEN)
            .map(|_| {
                let c = ID_ALPHABET[(bits & 31) as usize] as char;
                bits >>= 5;
                c
            })
            .collect();
        if !taken.contains(&id) {
            return id;
        }
    }
    unreachable!("an unused id exists")
}

/// Writes a fresh `^id` at the end of the open item `is_task(key, task_text)`
/// names, and returns the new text and the id. `None` when no open item
/// matches, the item already has one, or the file has lint errors, where an
/// item cannot be told apart from its duplicate.
pub fn mint_id(text: &str, key: &str, task_text: &str) -> Option<(String, String)> {
    let parsed = parse(text);
    if parsed.has_errors() {
        return None;
    }
    let item = parsed
        .items
        .into_iter()
        .find(|i| !i.done && i.id.is_none() && i.is_task(key, task_text))?;
    let id = new_id(text);
    let edited = add_token(text, item.line, &format!("^{id}"))?;
    Some((edited, id))
}

/// Ticks the open item that `is_task(key, task_text)` finished, where it
/// stands. Other bytes are unchanged. `None` when no open item matches.
pub fn mark_done(text: &str, key: &str, task_text: &str) -> Option<String> {
    let item = parse(text)
        .items
        .into_iter()
        .find(|i| !i.done && i.is_task(key, task_text))?;
    let mut lines: Vec<&str> = text.split_inclusive('\n').collect();
    let target = format!("- [x]{}", &lines[item.line - 1][5..]);
    lines[item.line - 1] = &target;
    Some(lines.concat())
}

#[derive(Debug, PartialEq)]
pub struct Pruned {
    pub text: String,
    pub items: Vec<Item>,
    /// Each removed `## Done` section.
    pub done_sections: Vec<DoneSection>,
}

/// Removes finished items with their descriptions, and each `## Done`
/// section whole. Blank lines before a section that ends the file go too.
/// Other lines are unchanged.
pub fn prune(text: &str) -> Pruned {
    let parsed = parse(text);
    let lines: Vec<&str> = text.split_inclusive('\n').collect();
    let mut drop = vec![false; lines.len()];
    let items: Vec<Item> = parsed.items.into_iter().filter(|i| i.done).collect();
    for item in &items {
        drop[item.line - 1..item.line + item.description.len()].fill(true);
    }
    for &DoneSection { first, last, .. } in &parsed.done_sections {
        let mut start = first - 1;
        if last == lines.len() {
            while start > 0 && lines[start - 1].trim().is_empty() {
                start -= 1;
            }
        }
        drop[start..last].fill(true);
    }
    Pruned {
        text: lines
            .iter()
            .zip(&drop)
            .filter(|(_, d)| !**d)
            .map(|(l, _)| *l)
            .collect(),
        items,
        done_sections: parsed.done_sections,
    }
}

/// Removes the finished item that `is_task(key, task_text)` names, with its
/// description. `None` when no finished item matches.
pub fn remove_done(text: &str, key: &str, task_text: &str) -> Option<String> {
    let item = parse(text)
        .items
        .into_iter()
        .find(|i| i.done && i.is_task(key, task_text))?;
    let lines: Vec<&str> = text.split_inclusive('\n').collect();
    let span = item.line - 1..item.line + item.description.len();
    Some(
        lines
            .iter()
            .enumerate()
            .filter(|(i, _)| !span.contains(i))
            .map(|(_, l)| *l)
            .collect(),
    )
}

/// Inserts an item into its priority section, with its description indented
/// under it. `None` when the section heading is absent: `pma` adds items, not
/// headings, so a file that does not declare the section is left alone.
///
/// The item goes before the section's first `###` heading, or at the end of the
/// section when it has none. Appending at the end would put it under whatever
/// group heading happened to be last and mislabel it.
pub fn insert(
    text: &str,
    priority: Priority,
    item: &str,
    description: Option<&str>,
) -> Option<String> {
    let want = SECTIONS.iter().find(|(_, p)| *p == priority)?.0;
    let lines: Vec<&str> = text.split_inclusive('\n').collect();
    let heading = lines.iter().position(|l| {
        l.trim_end()
            .strip_prefix("## ")
            .is_some_and(|name| name.trim() == want)
    })?;
    let mut at = lines.len();
    for (i, line) in lines.iter().enumerate().skip(heading + 1) {
        let trimmed = line.trim_end();
        if trimmed.starts_with("## ") || trimmed.starts_with("### ") {
            at = i;
            break;
        }
    }
    // Back over the blank lines that separate one section from the next, so
    // the item lands with the section it belongs to.
    while at > heading + 1 && lines[at - 1].trim().is_empty() {
        at -= 1;
    }
    let mut written = String::from("- [ ] ");
    written.push_str(item.trim());
    written.push('\n');
    for line in description.unwrap_or_default().lines() {
        written.push_str("  ");
        written.push_str(line.trim_end());
        written.push('\n');
    }
    let mut out: String = lines[..at].concat();
    if !out.ends_with("\n\n") {
        out.push('\n');
    }
    out.push_str(&written);
    let rest: String = lines[at..].concat();
    if !rest.is_empty() {
        out.push('\n');
        out.push_str(&rest);
    }
    Some(out)
}

/// Appends ` token` to the item on 1-based `line`, keeping the line ending.
/// `None` when that line is not an item.
pub fn add_token(text: &str, line: usize, token: &str) -> Option<String> {
    if !parse(text).items.iter().any(|i| i.line == line) {
        return None;
    }
    let mut lines: Vec<String> = text.split_inclusive('\n').map(String::from).collect();
    let target = lines.get_mut(line - 1)?;
    let body = target.trim_end_matches(['\r', '\n']).trim_end().to_string();
    let ending = target[target.trim_end_matches(['\r', '\n']).len()..].to_string();
    *target = format!("{body} {token}{ending}");
    Some(lines.concat())
}

/// Replaces a TODO.md with `text` atomically: a temporary file in the same
/// directory is written, flushed to disk and renamed over it, so a crash leaves
/// the old file or the new one, never a truncated one. A symlink is followed,
/// and the file keeps its permissions.
pub fn save(path: &std::path::Path, text: &str) -> std::io::Result<()> {
    use std::io::Write;
    let target = std::fs::canonicalize(path).unwrap_or_else(|_| path.to_path_buf());
    let name = target
        .file_name()
        .map(|n| n.to_string_lossy().into_owned())
        .unwrap_or_else(|| "TODO.md".into());
    let tmp = target.with_file_name(format!(".{name}.pma-tmp"));
    let written = (|| {
        let mut file = std::fs::File::create(&tmp)?;
        file.write_all(text.as_bytes())?;
        file.sync_all()?;
        if let Ok(meta) = std::fs::metadata(&target) {
            std::fs::set_permissions(&tmp, meta.permissions())?;
        }
        std::fs::rename(&tmp, &target)
    })();
    if written.is_err() {
        let _ = std::fs::remove_file(&tmp);
    }
    written
}

/// Unsynced items are identified by their normalised text, and synced ones by
/// `gh:N`, so either repeating breaks identity.
fn check_duplicates(out: &mut Parsed) {
    let mut texts: HashMap<String, usize> = HashMap::new();
    let mut issues: HashMap<u64, usize> = HashMap::new();
    let mut ids: HashMap<&str, usize> = HashMap::new();
    let mut found = Vec::new();

    for item in &out.items {
        if !item.done
            && !item.text.is_empty()
            && let Some(first) = texts.insert(item.text.to_lowercase(), item.line)
        {
            found.push((
                item.line,
                format!("same text as the open item on line {first}"),
            ));
        }
        if let Some(gh) = item.gh
            && let Some(first) = issues.insert(gh, item.line)
        {
            found.push((item.line, format!("`gh:{gh}` is also on line {first}")));
        }
        if let Some(id) = item.id.as_deref()
            && let Some(first) = ids.insert(id, item.line)
        {
            found.push((item.line, format!("id `^{id}` is also on line {first}")));
        }
    }
    for (line, message) in found {
        out.report(line, Severity::Error, message);
    }
}

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

    fn messages(text: &str) -> Vec<(usize, Severity, String)> {
        parse(text)
            .diagnostics
            .into_iter()
            .map(|d| (d.line, d.severity, d.message))
            .collect()
    }

    fn assert_clean(text: &str) -> Parsed {
        let parsed = parse(text);
        assert!(
            parsed.diagnostics.is_empty(),
            "unexpected diagnostics: {:?}",
            parsed.diagnostics
        );
        parsed
    }

    fn assert_reports(text: &str, line: usize, severity: Severity, fragment: &str) {
        let found = messages(text);
        assert!(
            found
                .iter()
                .any(|(l, s, m)| *l == line && *s == severity && m.contains(fragment)),
            "no {severity} containing {fragment:?} on line {line}; got {found:?}"
        );
    }

    const SPEC_EXAMPLE: &str = "# TODO

## Critical

- [ ] segfault on empty input #bug gh:42

## High

- [ ] support ggml 0.9 due:2026-10-01

## Medium

- [ ] flaky test on linux #urgent

## Low

- [x] drop python 3.9
";

    #[test]
    fn spec_example_parses_clean() {
        let parsed = assert_clean(SPEC_EXAMPLE);
        let summary: Vec<_> = parsed
            .items
            .iter()
            .map(|i| (i.line, i.priority, i.done, i.text.as_str()))
            .collect();
        assert_eq!(
            summary,
            vec![
                (5, Priority::Critical, false, "segfault on empty input"),
                (9, Priority::High, false, "support ggml 0.9"),
                (13, Priority::Medium, false, "flaky test on linux"),
                (17, Priority::Low, true, "drop python 3.9"),
            ]
        );
        assert_eq!(parsed.items[0].tags, ["bug"]);
        assert_eq!(parsed.items[0].gh, Some(42));
        assert_eq!(parsed.items[1].due.as_deref(), Some("2026-10-01"));
        assert_eq!(parsed.items[2].tags, ["urgent"]);
    }

    #[test]
    fn only_trailing_words_are_tokens() {
        let parsed = assert_clean(
            "# TODO\n\n## High\n\n- [ ] port C# #bindings to due:parser module #api\n",
        );
        let item = &parsed.items[0];
        assert_eq!(item.text, "port C# #bindings to due:parser module");
        assert_eq!(item.tags, ["api"]);
        assert_eq!(item.due, None);
    }

    #[test]
    fn description_is_carried_verbatim_across_blank_lines() {
        let parsed =
            assert_clean("# TODO\n\n## Low\n\n- [ ] item\n  first\n\n    second\n\n- [ ] next\n");
        assert_eq!(parsed.items[0].description, ["  first", "", "    second"]);
        assert!(parsed.items[1].description.is_empty());
    }

    #[test]
    fn crlf_line_endings_are_accepted() {
        let parsed = assert_clean("# TODO\r\n\r\n## High\r\n\r\n- [ ] item #tag\r\n");
        assert_eq!(parsed.items[0].tags, ["tag"]);
    }

    #[test]
    fn other_sections_and_deeper_headings() {
        let text =
            "# TODO\n\n## Notes\n\nprose\n- [ ] ignored\n\n## High\n\n### parser\n\n- [ ] kept\n";
        let parsed = parse(text);
        assert_eq!(parsed.items.len(), 1);
        assert_eq!(parsed.items[0].priority, Priority::High);
        assert_reports(text, 6, Severity::Warning, "ignored");
        assert_eq!(parsed.diagnostics.len(), 1);
    }

    #[test]
    fn items_take_the_nearest_level_three_heading_in_their_section() {
        let text = "# TODO\n\n## High\n\n- [ ] ungrouped\n\n### Security Hardening \n\n- [ ] a\n\n#### detail\n\n- [ ] b\n\n### \n\n- [ ] c\n\n## Low\n\n- [ ] d\n\n### Later\n\n- [ ] e\n";
        let groups: Vec<_> = parse(text)
            .items
            .into_iter()
            .map(|i| (i.text, i.group))
            .collect();
        let g = |s: &str| Some(s.to_string());
        assert_eq!(
            groups,
            [
                ("ungrouped".into(), None),
                ("a".into(), g("Security Hardening")),
                ("b".into(), g("Security Hardening")),
                ("c".into(), None),
                ("d".into(), None),
                ("e".into(), g("Later")),
            ]
        );
    }

    #[test]
    fn a_file_whose_tasks_are_all_plain_bullets_is_flagged() {
        let text = "# TODO\n\n## Ideas\n\n- one\n- two\n\n```\n- fenced\n```\n";
        assert_reports(text, 1, Severity::Warning, "no items; 2 list entries");
        assert_clean("# TODO\n\n## Ideas\n\n- one\n\n## Low\n\n- [ ] real\n");
        assert_clean("# TODO\n\n## High\n");
        assert_clean("# TODO\n\n## Low\n\n## Declined\n\n- not doing this\n");
    }

    #[test]
    fn fenced_code_is_not_structure() {
        let parsed = assert_clean(
            "# TODO\n\n## High\n\n```\n## Done\n- [ ] not an item\n```\n\n- [ ] real\n",
        );
        assert_eq!(parsed.items.len(), 1);
        assert_eq!(parsed.items[0].priority, Priority::High);
    }

    #[test]
    fn a_fence_closes_only_on_its_own_kind_and_length() {
        let item = |text: &str| parse(text).items.len();
        // Three backticks do not close four, and backticks do not close tildes.
        let four = "# TODO\n\n## High\n\n````\n```\n- [ ] hidden\n````\n\n- [ ] real\n";
        assert_eq!(item(four), 1);
        assert_clean(four);
        let tilde = "# TODO\n\n## High\n\n~~~\n```\n- [ ] hidden\n~~~\n\n- [ ] real\n";
        assert_eq!(item(tilde), 1);
        assert_clean(tilde);
        // A longer closing run closes; one followed by text does not.
        let longer = "# TODO\n\n## High\n\n```\n- [ ] hidden\n```` x\n`````\n- [ ] real\n";
        assert_eq!(item(longer), 1);
        assert_clean(longer);
    }

    #[test]
    fn an_unclosed_fence_is_an_error_at_its_opening_line() {
        let text = "# TODO\n\n## High\n\n- [ ] seen\n\n```rust\n- [ ] hidden\n";
        assert_reports(text, 7, Severity::Error, "never closed");
        assert_eq!(parse(text).items.len(), 1);
        let mismatched = "# TODO\n\n## High\n\n````\n```\n";
        assert_reports(mismatched, 5, Severity::Error, "never closed");
    }

    #[test]
    fn title_is_required() {
        assert_reports("## High\n", 1, Severity::Error, "must start with `# TODO`");
        assert_reports(
            "\n\nintro\n# TODO\n",
            3,
            Severity::Error,
            "must start with `# TODO`",
        );
        assert_reports("", 1, Severity::Error, "must start with `# TODO`");
        assert_reports(
            "# TODO\n\n# Other\n",
            3,
            Severity::Error,
            "second `#` heading",
        );
        assert_reports(
            "```\n# TODO\n```\n",
            1,
            Severity::Error,
            "must start with `# TODO`",
        );
        assert_eq!(
            messages("# Tasks\n").len(),
            1,
            "a wrong title is reported once"
        );
    }

    #[test]
    fn section_names_are_exact() {
        assert_reports(
            "# TODO\n\n## critical\n",
            3,
            Severity::Error,
            "`## Critical`",
        );
        for bad in ["##Critical", "##critical", "##High "] {
            let text = format!("# TODO\n\n{bad}\n\n- [ ] item\n");
            assert_eq!(messages(&text).len(), 1, "{bad} is reported once");
            assert_reports(&text, 3, Severity::Error, "write the heading as `## ");
            assert_eq!(parse(&text).items.len(), 1, "{bad} opens its section");
        }
        assert_clean("# TODO\n\n##Notes\n\n## Low\n");
        assert_reports(
            "# TODO\n\n## High\n\n## High\n",
            5,
            Severity::Error,
            "first is on line 3",
        );
    }

    #[test]
    fn noncanonical_items_are_errors() {
        for bad in [
            "* [ ] x", "- [X] x", "-[ ] x", "1. [ ] x", "+ [x] x", "- [ ]x",
        ] {
            let text = format!("# TODO\n\n## High\n\n{bad}\n");
            assert_reports(&text, 5, Severity::Error, "write items as");
            assert!(parse(&text).items.is_empty(), "{bad} was read as an item");
        }
        assert_reports(
            "# TODO\n\n## High\n\n- plain bullet\n",
            5,
            Severity::Error,
            "must be a `- [ ]` item",
        );
        assert_reports(
            "# TODO\n\n## High\n\nsome prose\n",
            5,
            Severity::Warning,
            "not an item",
        );
        assert_reports(
            "# TODO\n\n## High\n\n**bold** prose\n",
            5,
            Severity::Warning,
            "not an item",
        );
        assert_reports(
            "# TODO\n\n## High\n\n  stray\n",
            5,
            Severity::Warning,
            "not under an item",
        );
    }

    #[test]
    fn tokens_are_validated() {
        let item = |s: &str| format!("# TODO\n\n## High\n\n- [ ] thing {s}\n");
        assert_reports(&item("due:2026-02-30"), 5, Severity::Error, "not a date");
        assert_reports(&item("due:tomorrow"), 5, Severity::Error, "not a date");
        assert_reports(
            &item("due:2026-01-01 due:2026-01-02"),
            5,
            Severity::Error,
            "more than one `due:`",
        );
        assert_reports(&item("gh:0"), 5, Severity::Error, "not an issue number");
        assert_reports(&item("gh:x1"), 5, Severity::Error, "not an issue number");
        assert_reports(
            &item("gh:1 gh:2"),
            5,
            Severity::Error,
            "more than one `gh:`",
        );
        assert_reports(&item("#42"), 5, Severity::Warning, "write `gh:42`");
        assert_clean(&item("due:2028-02-29"));
    }

    #[test]
    fn items_need_text_and_may_be_finished_in_place() {
        assert_clean("# TODO\n\n## Low\n\n- [x] closed\n");
        assert_reports(
            "# TODO\n\n## Low\n\n- [ ] #only-tags\n",
            5,
            Severity::Error,
            "no text",
        );
        assert_reports("# TODO\n\n## Low\n\n- [ ]\n", 5, Severity::Error, "no text");
    }

    #[test]
    fn mark_done_ticks_the_item_in_place() {
        let text = "# TODO\n\n## High\n\n- [ ] first #bug\n  why\n- [ ] Second  gh:4\n- [x] old\n";
        let out = mark_done(text, "first", "").unwrap();
        assert_eq!(
            out,
            "# TODO\n\n## High\n\n- [x] first #bug\n  why\n- [ ] Second  gh:4\n- [x] old\n"
        );
        assert_clean(&out);
        assert_eq!(
            mark_done(text, "old", "old"),
            None,
            "finished items are not open"
        );
        assert_eq!(mark_done(text, "missing", ""), None);
        assert!(
            mark_done(text, "second", "SECOND").is_some(),
            "a key that gained gh:N still matches by text"
        );
        assert_eq!(
            mark_done("# TODO\r\n\r\n## Low\r\n- [ ] a gh:2", "gh:2", "").unwrap(),
            "# TODO\r\n\r\n## Low\r\n- [x] a gh:2"
        );
        let fenced = "# TODO\n\n## Low\n\n```\n- [ ] a\n```\n- [ ] a\n";
        assert!(
            mark_done(fenced, "a", "")
                .unwrap()
                .ends_with("```\n- [ ] a\n```\n- [x] a\n")
        );
    }

    #[test]
    fn prune_removes_finished_items_with_their_descriptions() {
        let text = "# TODO\r\n\r\n## High\r\n\r\n- [x] done #bug\r\n  why\r\n\r\n  more\r\n- [ ] open\r\n  kept\r\n\r\n## Low\r\n\r\n```\r\n- [x] fenced\r\n```\r\n- [x] last";
        let pruned = prune(text);
        assert_eq!(
            pruned.text,
            "# TODO\r\n\r\n## High\r\n\r\n- [ ] open\r\n  kept\r\n\r\n## Low\r\n\r\n```\r\n- [x] fenced\r\n```\r\n"
        );
        let removed: Vec<_> = pruned
            .items
            .iter()
            .map(|i| (i.line, i.text.as_str()))
            .collect();
        assert_eq!(removed, [(5, "done"), (17, "last")]);
        assert!(pruned.done_sections.is_empty());
        assert_clean(&pruned.text);
        assert_eq!(prune(&pruned.text).text, pruned.text);
    }

    #[test]
    fn prune_removes_done_sections_whole() {
        let text = "# TODO\n\n## Low\n\n- [ ] a\n\n## Done\n\n### old\n\n- [x] b\n  why\nprose\n- [ ] open\n```\n## Notes\n```\n\n## Notes\n\nkept\n\n## Done\n\n- [x] c\n\n";
        assert_reports(text, 11, Severity::Warning, "`pma prune` removes it");
        let pruned = prune(text);
        let spans: Vec<_> = pruned
            .done_sections
            .iter()
            .map(|d| (d.first, d.last, d.open.clone()))
            .collect();
        assert_eq!(
            spans,
            [
                (7, 18, vec![(14, "- [ ] open".to_string())]),
                (23, 26, vec![])
            ]
        );
        assert!(pruned.items.is_empty());
        assert_eq!(
            pruned.text,
            "# TODO\n\n## Low\n\n- [ ] a\n\n## Notes\n\nkept\n"
        );
        assert_clean(&pruned.text);
    }

    #[test]
    fn remove_done_takes_one_finished_item_and_its_description() {
        let text = "# TODO\n\n## High\n\n- [x] done\n  why\n- [x] other\n- [ ] open\n";
        assert_eq!(
            remove_done(text, "done", "done").unwrap(),
            "# TODO\n\n## High\n\n- [x] other\n- [ ] open\n"
        );
        assert_eq!(
            remove_done(text, "open", "open"),
            None,
            "an open item stays"
        );
        assert_eq!(remove_done(text, "missing", "missing"), None);
    }

    #[test]
    fn add_token_appends_to_item_lines_only() {
        let text = "# TODO\r\n\r\n## Critical\r\n\r\n- [ ] crash #bug  \r\n- [ ] last";
        let out = add_token(text, 5, "gh:12").unwrap();
        assert_eq!(
            out,
            "# TODO\r\n\r\n## Critical\r\n\r\n- [ ] crash #bug gh:12\r\n- [ ] last"
        );
        assert_eq!(parse(&out).items[0].gh, Some(12));
        assert!(
            add_token(text, 6, "gh:3")
                .unwrap()
                .ends_with("- [ ] last gh:3")
        );
        assert_eq!(add_token(text, 3, "gh:1"), None, "a heading is not an item");
        assert_eq!(add_token(text, 99, "gh:1"), None);
    }

    #[test]
    fn save_replaces_the_file_and_keeps_its_mode_and_link() {
        use std::os::unix::fs::PermissionsExt;
        let dir = std::env::temp_dir().join(format!("pma-todo-save-{}", std::process::id()));
        let _ = std::fs::remove_dir_all(&dir);
        std::fs::create_dir_all(&dir).unwrap();
        let real = dir.join("real.md");
        std::fs::write(&real, "# TODO\n\nold, and longer than the new text\n").unwrap();
        std::fs::set_permissions(&real, std::fs::Permissions::from_mode(0o640)).unwrap();
        let link = dir.join("TODO.md");
        std::os::unix::fs::symlink(&real, &link).unwrap();

        save(&link, "# TODO\n").unwrap();
        assert_eq!(std::fs::read_to_string(&real).unwrap(), "# TODO\n");
        assert!(
            std::fs::symlink_metadata(&link).unwrap().is_symlink(),
            "the link is written through, not replaced"
        );
        let mode = std::fs::metadata(&real).unwrap().permissions().mode() & 0o777;
        assert_eq!(mode, 0o640);
        let left: Vec<_> = std::fs::read_dir(&dir)
            .unwrap()
            .map(|e| e.unwrap().file_name())
            .collect();
        assert_eq!(left.len(), 2, "no temporary file is left: {left:?}");
        let _ = std::fs::remove_dir_all(dir);
    }

    /// An id, a trailing `^k3f9q`, names the item whatever its text or its
    /// issue, and every name the item has still answers.
    #[test]
    fn an_id_is_the_items_identity() {
        let parsed = assert_clean(
            "# TODO\n\n## High\n\n- [ ] fix the lexer #bug ^7hq2m gh:4\n- [ ] other\n",
        );
        let item = &parsed.items[0];
        assert_eq!(
            (item.text.as_str(), item.id.as_deref(), item.gh),
            ("fix the lexer", Some("7hq2m"), Some(4))
        );
        assert_eq!(item.key(), "id:7hq2m");
        for (key, text) in [
            ("id:7hq2m", ""),
            ("gh:4", ""),
            ("fix the lexer", ""),
            ("x", "Fix The Lexer"),
        ] {
            assert!(item.is_task(key, text), "{key} {text}");
        }
        assert!(!item.is_task("id:7hq2n", ""));
        assert_eq!(parsed.items[1].key(), "other");
    }

    /// Only a trailing caret word of five id characters is an id. Any other
    /// caret word, such as a version constraint, is text.
    #[test]
    fn a_caret_word_is_text_unless_it_is_an_id() {
        for (line, id, text) in [
            ("- [ ] bump serde to ^1.2", None, "bump serde to ^1.2"),
            ("- [ ] shout ^HELLO", None, "shout ^HELLO"),
            ("- [ ] short ^7hq2", None, "short ^7hq2"),
            ("- [ ] has an l ^7hqlm", None, "has an l ^7hqlm"),
            (
                "- [ ] ^7hq2m earlier is text",
                None,
                "^7hq2m earlier is text",
            ),
            ("- [ ] maybe ^maybe", Some("maybe"), "maybe"),
            ("- [ ] real #bug ^7hq2m", Some("7hq2m"), "real"),
        ] {
            let parsed = assert_clean(&format!("# TODO\n\n## High\n\n{line}\n"));
            let item = &parsed.items[0];
            assert_eq!(
                (item.id.as_deref(), item.text.as_str()),
                (id, text),
                "{line}"
            );
        }
        assert_reports(
            "# TODO\n\n## High\n\n- [ ] ^7hq2m\n",
            5,
            Severity::Error,
            "no text",
        );
        assert_reports(
            "# TODO\n\n## High\n\n- [ ] two ^7hq2m ^7hq2n\n",
            5,
            Severity::Error,
            "more than one id",
        );
    }

    #[test]
    fn an_id_is_unique_in_its_file() {
        assert_reports(
            "# TODO\n\n## High\n\n- [ ] a ^7hq2m\n- [x] b ^7hq2m\n",
            6,
            Severity::Error,
            "id `^7hq2m` is also on line 5",
        );
    }

    /// `pma` writes an id at the end of the item a task names, once, and never
    /// into a file whose items cannot be told apart.
    #[test]
    fn mint_id_writes_a_fresh_id_once() {
        let text = "# TODO\n\n## High\n\n- [ ] first ^00000\n- [ ] second #bug\n  why\n";
        let (edited, id) = mint_id(text, "second", "").unwrap();
        assert!(is_id(&id) && id != "00000", "{id}");
        assert_eq!(
            edited,
            format!("# TODO\n\n## High\n\n- [ ] first ^00000\n- [ ] second #bug ^{id}\n  why\n")
        );
        assert_eq!(parse(&edited).items[1].key(), format!("id:{id}"));
        assert_eq!(mint_id(&edited, "second", ""), None, "it has one");
        assert_eq!(mint_id(text, "first", ""), None, "it had one");
        assert_eq!(mint_id(text, "missing", ""), None);
        assert_eq!(
            mint_id("# TODO\n\n## High\n\n- [ ] a\n- [ ] a\n", "a", ""),
            None
        );
        let ids: std::collections::BTreeSet<String> = (0..200).map(|_| new_id(text)).collect();
        assert!(ids.len() > 190, "ids are drawn at random: {}", ids.len());
        assert!(ids.iter().all(|id| is_id(id)), "{ids:?}");
    }

    #[test]
    fn duplicates_break_identity() {
        let text = "# TODO\n\n## High\n\n- [ ] Fix  it gh:3\n\n## Low\n\n- [ ] fix it\n- [ ] other gh:3\n- [x] fix it\n";
        assert_reports(text, 9, Severity::Error, "open item on line 5");
        assert_reports(text, 10, Severity::Error, "also on line 5");
        assert_eq!(
            parse(text).diagnostics.len(),
            2,
            "a finished repeat is not a duplicate"
        );
    }
}