//! Reading the state of a project's outline.
//!
//! The snowflake template's outline files are scaffolds made entirely of HTML
//! comments, one per story beat:
//!
//! ```text
//! ## Act I – Setup (≈ 25 % of the story)
//!
//! <!-- Opening Image / Hook: A vivid snapshot of the ordinary world. -->
//!
//! <!-- Inciting Incident: An event that disrupts the status-quo. -->
//! ```
//!
//! The app strips comments everywhere else, which means these files render and
//! export as blank — there is nothing to see and no way to tell how much of the
//! outline is actually written. This module reads the scaffold back: the beats
//! it names, and which of them have prose under them yet.

/// One beat of an outline, and whether it has been written.
#[derive(Debug, Clone, PartialEq, Eq)]
pub struct Beat {
    /// The heading this beat sits under, e.g. `Act I – Setup`.
    pub section: String,
    /// The beat's name, taken from the start of its prompt comment.
    pub name: String,
    /// Whether any prose has been written for it.
    pub filled: bool,
}

/// Read an outline file's beats and their state.
///
/// A beat is "filled" when there is ordinary text between its prompt comment
/// and the next prompt or heading — which is exactly where you would type it.
pub fn beats(markdown: &str) -> Vec<Beat> {
    let mut out: Vec<Beat> = Vec::new();
    let mut section = String::new();
    let mut rest = markdown;

    // Text seen since the last prompt, which decides whether it is filled.
    let mut pending_prose = String::new();

    while let Some(start) = rest.find("<!--") {
        let before = &rest[..start];
        // Anything before this comment belongs to the previous beat.
        pending_prose.push_str(before);
        if let Some(heading) = last_heading(before) {
            // A heading closes the previous beat and opens a new section.
            settle(&mut out, &mut pending_prose);
            section = heading;
        }
        settle(&mut out, &mut pending_prose);

        let Some(end) = rest[start + 4..].find("-->") else {
            break;
        };
        let body = &rest[start + 4..start + 4 + end];
        if let Some(name) = prompt_name(body) {
            out.push(Beat {
                section: section.clone(),
                name,
                filled: false,
            });
        }
        rest = &rest[start + 4 + end + 3..];
    }
    pending_prose.push_str(rest);
    if let Some(heading) = last_heading(rest) {
        settle(&mut out, &mut pending_prose);
        let _ = heading; // a trailing heading opens nothing
    }
    settle(&mut out, &mut pending_prose);
    out
}

/// Credit whatever prose has accumulated to the most recent beat, then clear it.
fn settle(beats: &mut [Beat], pending: &mut String) {
    if has_prose(pending) {
        if let Some(last) = beats.last_mut() {
            last.filled = true;
        }
    }
    pending.clear();
}

/// Whether a run of text contains anything a writer would call content —
/// headings and blank lines do not count.
fn has_prose(text: &str) -> bool {
    text.lines()
        .map(str::trim)
        .any(|line| !line.is_empty() && !line.starts_with('#'))
}

/// The last markdown heading in a run of text, if any.
fn last_heading(text: &str) -> Option<String> {
    text.lines().rev().find_map(|line| {
        let trimmed = line.trim();
        let hashes = trimmed.len() - trimmed.trim_start_matches('#').len();
        if hashes == 0 {
            return None;
        }
        let name = trimmed[hashes..].trim();
        (!name.is_empty()).then(|| name.to_string())
    })
}

/// The beat name at the start of a prompt comment: everything before its first
/// colon, which is how the template writes them (`Midpoint: A major turning…`).
fn prompt_name(body: &str) -> Option<String> {
    let text = body.trim();
    if text.is_empty() {
        return None;
    }
    let name = match text.split_once(':') {
        Some((name, _)) => name.trim(),
        // A comment with no colon is a note, not a beat prompt.
        None => return None,
    };
    // Prompt names are labels; a long one is a sentence that happened to have
    // a colon in it.
    if name.is_empty() || name.split_whitespace().count() > 8 {
        return None;
    }
    Some(name.to_string())
}

/// How many of `beats` are written, and how many there are.
pub fn progress(beats: &[Beat]) -> (usize, usize) {
    (beats.iter().filter(|b| b.filled).count(), beats.len())
}

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

    const SCAFFOLD: &str = "\
## Act I – Setup (≈ 25 % of the story)

<!-- Opening Image / Hook: A vivid snapshot of the ordinary world. -->

<!-- Inciting Incident: An event that disrupts the status-quo. -->

## Act II – Confrontation

<!-- Midpoint: A major turning point. -->
";

    #[test]
    fn an_untouched_scaffold_has_no_beats_written() {
        let beats = beats(SCAFFOLD);
        assert_eq!(beats.len(), 3);
        assert!(beats.iter().all(|b| !b.filled));
        assert_eq!(progress(&beats), (0, 3));
    }

    #[test]
    fn beat_names_and_their_sections_are_read() {
        let beats = beats(SCAFFOLD);
        assert_eq!(beats[0].name, "Opening Image / Hook");
        assert_eq!(beats[0].section, "Act I – Setup (≈ 25 % of the story)");
        assert_eq!(beats[1].name, "Inciting Incident");
        assert_eq!(beats[2].name, "Midpoint");
        assert_eq!(beats[2].section, "Act II – Confrontation");
    }

    #[test]
    fn prose_after_a_prompt_marks_it_written() {
        let written = "\
## Act I

<!-- Opening Image: the prompt. -->

Ada stands on the ice, counting bolts.

<!-- Inciting Incident: the prompt. -->
";
        let beats = beats(written);
        assert_eq!(progress(&beats), (1, 2));
        assert!(beats[0].filled, "the beat with prose under it");
        assert!(!beats[1].filled, "the one still empty");
    }

    #[test]
    fn a_heading_does_not_count_as_prose() {
        let text = "<!-- A: prompt -->\n\n## Act II\n\n<!-- B: prompt -->\n";
        let beats = beats(text);
        assert_eq!(progress(&beats), (0, 2));
    }

    #[test]
    fn prose_after_the_last_prompt_still_counts() {
        let text = "<!-- Climax: prompt -->\n\nShe opens the gate.\n";
        let beats = beats(text);
        assert_eq!(progress(&beats), (1, 1));
    }

    #[test]
    fn a_comment_without_a_colon_is_a_note_not_a_beat() {
        let text = "<!-- just a note to self -->\n\n<!-- Climax: prompt -->\n";
        let beats = beats(text);
        assert_eq!(beats.len(), 1);
        assert_eq!(beats[0].name, "Climax");
    }

    #[test]
    fn an_unterminated_comment_does_not_hang_or_panic() {
        let beats = beats("<!-- Climax: prompt -->\n\n<!-- broken");
        assert_eq!(beats.len(), 1);
    }

    #[test]
    fn a_file_with_no_comments_yields_nothing() {
        assert!(beats("# Just prose\n\nWords.\n").is_empty());
        assert!(beats("").is_empty());
    }

    /// Prose written *before* the first prompt belongs to no beat and must not
    /// be credited to one that comes later.
    #[test]
    fn prose_before_the_first_prompt_credits_nothing() {
        let text = "Some preamble.\n\n<!-- Climax: prompt -->\n";
        assert_eq!(progress(&beats(text)), (0, 1));
    }
}