carta-readers 0.0.1

//! Dash-ruled tables: blocks whose columns are fixed by runs of `-` rather than the `|`/`+` borders
//! of a pipe or grid table. Three shapes share this module:
//!
//! * a single-line *headed* table — one header line above a dash ruling, then one row per line;
//! * a single-line *headerless* table — a dash ruling, then one row per line, closed by a second
//!   ruling; and
//! * a *multi-line* table — a dash ruling, an optional header closed by a second ruling, then rows
//!   separated by blank lines whose physical lines join into one cell each, closed by a final ruling.
//!
//! Every form slices each line into cells at the dash runs' start columns and reads per-column
//! alignment from a reference line (the header, or the first row when headerless). The single-line
//! forms leave their column widths unset; the multi-line form derives a fractional width for each
//! column from the ruling. Each cell's text is left raw for the inline phase.

use carta_ast::Alignment;
use carta_core::{Extension, Extensions};

/// A parsed dash-ruled table awaiting the inline phase: one [`Column`] per column, an optional
/// header row, the body rows, and any caption text (stripped of its marker, attached after the
/// block phase).
#[derive(Debug, Clone)]
pub(crate) struct TextTable {
    pub columns: Vec<Column>,
    /// Header cells, one per column; empty when the table has no header row.
    pub head: Vec<Cell>,
    /// Body rows, each a cell per column.
    pub body: Vec<Vec<Cell>>,
    pub caption: Option<String>,
    /// Attributes attached via the caption line when `table_attributes` is enabled.
    pub attr: carta_ast::Attr,
}

/// One column's alignment and width. `width` is `None` for an unsized column (the only kind a
/// single-line table produces).
#[derive(Debug, Clone)]
pub(crate) struct Column {
    pub align: Alignment,
    pub width: Option<f64>,
}

/// A cell's raw text: physical lines joined with `\n`, each break becoming a soft break when the
/// inline phase parses the text.
pub(crate) type Cell = String;

/// Whether `line` is a dash ruling: after trimming, a non-empty run of `-` and spaces with at least
/// one dash.
pub(crate) fn is_dash_line(line: &str) -> bool {
    let trimmed = line.trim();
    !trimmed.is_empty()
        && trimmed.bytes().all(|byte| matches!(byte, b'-' | b' '))
        && trimmed.contains('-')
}

/// Whether `line` opens a dash-led table: a dash ruling (only dashes and spaces) whose first run is
/// at least two dashes. Requiring a pure ruling keeps grid-table borders (`+---+`) and other
/// dash-bearing lines from opening one; a lone leading dash is a list marker, so it does not either.
pub(crate) fn opens_dash_table(line: &str) -> bool {
    is_dash_line(line) && dash_runs(line).first().is_some_and(|&(_, len)| len >= 2)
}

/// The maximal runs of `-` in `line`, each as `(start, length)` in character positions.
fn dash_runs(line: &str) -> Vec<(usize, usize)> {
    let mut runs = Vec::new();
    let mut run_start: Option<usize> = None;
    let mut count = 0;
    for (index, ch) in line.chars().enumerate() {
        count = index + 1;
        if ch == '-' {
            run_start.get_or_insert(index);
        } else if let Some(start) = run_start.take() {
            runs.push((start, index - start));
        }
    }
    if let Some(start) = run_start {
        runs.push((start, count - start));
    }
    runs
}

/// Parse the accumulated lines of a dash-table candidate, returning the table and how many of the
/// lines it consumed (any trailing lines belong to the next block). Returns `None` when the lines do
/// not form a complete, well-formed table, so the caller can fall back. A leading dash ruling first
/// tries the multi-line shape, then the single-line headerless shape; any other first line takes the
/// single-line headed shape, with the ruling on the second line.
pub(crate) fn parse(lines: &[&str], ext: Extensions) -> Option<(TextTable, usize)> {
    let first = *lines.first()?;
    if is_dash_line(first) {
        parse_multiline(lines, ext).or_else(|| parse_headerless(lines, ext))
    } else {
        parse_headed(lines, ext)
    }
}

/// Parse a headed table: a header line, a dash ruling, then one single-line row each until a closing
/// ruling (consumed) or the lines run out. Alignment comes from the header line; widths are unset.
fn parse_headed(lines: &[&str], ext: Extensions) -> Option<(TextTable, usize)> {
    if !ext.contains(Extension::SimpleTables) {
        return None;
    }
    let header = *lines.first()?;
    let ruling = *lines.get(1)?;
    if !is_dash_line(ruling) {
        return None;
    }
    let runs = dash_runs(ruling);
    if runs.is_empty() {
        return None;
    }
    let starts: Vec<usize> = runs.iter().map(|&(start, _)| start).collect();

    let mut body = Vec::new();
    let mut consumed = 2;
    for &line in lines.get(2..).unwrap_or(&[]) {
        consumed += 1;
        if is_dash_line(line) {
            break;
        }
        if line.trim().is_empty() {
            return None;
        }
        body.push(slice_row(line, &starts));
    }
    if body.is_empty() {
        return None;
    }

    let columns = column_specs(&runs, header);
    Some((
        TextTable {
            columns,
            head: slice_row(header, &starts),
            body,
            caption: None,
            attr: carta_ast::Attr::default(),
        },
        consumed,
    ))
}

/// Parse a headerless table: a dash ruling, then one single-line row each, closed by a second ruling
/// (required). Alignment comes from the first row; widths are unset.
fn parse_headerless(lines: &[&str], ext: Extensions) -> Option<(TextTable, usize)> {
    if !ext.contains(Extension::SimpleTables) {
        return None;
    }
    let top = *lines.first()?;
    if !is_dash_line(top) {
        return None;
    }
    let runs = dash_runs(top);
    if runs.is_empty() {
        return None;
    }
    let starts: Vec<usize> = runs.iter().map(|&(start, _)| start).collect();

    let mut body = Vec::new();
    let mut consumed = 1;
    let mut closed = false;
    for &line in lines.get(1..).unwrap_or(&[]) {
        consumed += 1;
        if is_dash_line(line) {
            closed = true;
            break;
        }
        if line.trim().is_empty() {
            return None;
        }
        body.push(slice_row(line, &starts));
    }
    if !closed || body.is_empty() {
        return None;
    }

    let reference = lines.get(1).copied().unwrap_or("");
    let columns = column_specs(&runs, reference);
    Some((
        TextTable {
            columns,
            head: Vec::new(),
            body,
            caption: None,
            attr: carta_ast::Attr::default(),
        },
        consumed,
    ))
}

/// Parse a multi-line table: a dash ruling, then an optional header — the lines up to a second
/// ruling that appears before any blank line — followed by rows separated by blank lines and closed
/// by a final ruling. Within a row the physical lines join into one cell each; alignment comes from
/// the header's first line, or the first row when there is no header; widths are fractions derived
/// from the ruling. Returns `None` when the body is empty, so a two-ruling block with single-line
/// rows falls back to the single-line headerless shape.
fn parse_multiline(lines: &[&str], ext: Extensions) -> Option<(TextTable, usize)> {
    if !ext.contains(Extension::MultilineTables) {
        return None;
    }
    let top = *lines.first()?;
    if !is_dash_line(top) {
        return None;
    }
    let runs = dash_runs(top);
    if runs.is_empty() {
        return None;
    }
    let starts: Vec<usize> = runs.iter().map(|&(start, _)| start).collect();

    // A header is the run of lines after the top ruling up to a second ruling, but only when that
    // ruling arrives before any blank line; a blank first means the table has no header.
    let mut separator: Option<usize> = None;
    let mut scan = 1;
    while let Some(&line) = lines.get(scan) {
        if is_dash_line(line) {
            separator = Some(scan);
            break;
        }
        if line.trim().is_empty() {
            break;
        }
        scan += 1;
    }
    let (header_lines, body_start) = match separator {
        Some(sep) if sep > 1 => (lines.get(1..sep)?.to_vec(), sep + 1),
        _ => (Vec::new(), 1),
    };

    let mut body_rows: Vec<Vec<&str>> = Vec::new();
    let mut current: Vec<&str> = Vec::new();
    let mut closed = false;
    let mut consumed = body_start;
    for &line in lines.get(body_start..).unwrap_or(&[]) {
        consumed += 1;
        if is_dash_line(line) {
            closed = true;
            break;
        }
        if line.trim().is_empty() {
            if !current.is_empty() {
                body_rows.push(std::mem::take(&mut current));
            }
            continue;
        }
        current.push(line);
    }
    if !current.is_empty() {
        body_rows.push(current);
    }
    if !closed || body_rows.is_empty() {
        return None;
    }

    let reference = header_lines
        .first()
        .copied()
        .or_else(|| body_rows.first().and_then(|row| row.first().copied()))
        .unwrap_or("");
    let columns = column_specs_multiline(&runs, reference);
    let head = if header_lines.is_empty() {
        Vec::new()
    } else {
        slice_group(&header_lines, &starts)
    };
    let body = body_rows
        .iter()
        .map(|row| slice_group(row, &starts))
        .collect();
    Some((
        TextTable {
            columns,
            head,
            body,
            caption: None,
            attr: carta_ast::Attr::default(),
        },
        consumed,
    ))
}

/// Build the column specs from the dash runs and a reference line that fixes each column's
/// alignment. Single-line tables leave every width unset.
fn column_specs(runs: &[(usize, usize)], reference: &str) -> Vec<Column> {
    let chars: Vec<char> = reference.chars().collect();
    runs.iter()
        .enumerate()
        .map(|(index, &(start, len))| {
            let next = runs
                .get(index + 1)
                .map_or(usize::MAX, |&(next_start, _)| next_start);
            Column {
                align: column_alignment(&chars, start, len, next),
                width: None,
            }
        })
        .collect()
}

/// Build the column specs for a multi-line table: the same per-column alignment as a single-line
/// table, paired with a fractional width read from the dash runs.
fn column_specs_multiline(runs: &[(usize, usize)], reference: &str) -> Vec<Column> {
    let chars: Vec<char> = reference.chars().collect();
    let widths = multiline_widths(runs);
    runs.iter()
        .enumerate()
        .map(|(index, &(start, len))| {
            let next = runs
                .get(index + 1)
                .map_or(usize::MAX, |&(next_start, _)| next_start);
            Column {
                align: column_alignment(&chars, start, len, next),
                width: widths.get(index).copied(),
            }
        })
        .collect()
}

/// Fractional column widths for a multi-line table: each column's character span over a fixed total
/// of 72. A column reaches from its dash run's start to the next run's start; the final column takes
/// its own run plus one, widened to the preceding column's span when the two are within two
/// characters so a slightly shorter last run still lines up.
fn multiline_widths(runs: &[(usize, usize)]) -> Vec<f64> {
    const TOTAL: f64 = 72.0;
    let mut widths = Vec::with_capacity(runs.len());
    for (index, &(start, len)) in runs.iter().enumerate() {
        let numerator = if let Some(&(next_start, _)) = runs.get(index + 1) {
            // An interior column spans from its run's start to the next run's start.
            next_start.saturating_sub(start)
        } else if let Some(&(prev_start, _)) = index.checked_sub(1).and_then(|prev| runs.get(prev))
        {
            // The last column takes its run plus one, widened to the preceding column's span when
            // the two are within two characters.
            let natural = len + 1;
            let prev_span = start.saturating_sub(prev_start);
            if natural + 2 >= prev_span {
                natural.max(prev_span)
            } else {
                natural
            }
        } else {
            // A lone column is its run plus one.
            len + 1
        };
        #[allow(clippy::cast_precision_loss)]
        // column spans are small line offsets, far inside f64's range
        let width = numerator as f64 / TOTAL;
        widths.push(width);
    }
    widths
}

/// Slice a group of physical lines (a header or a multi-line row) into per-column cells, joining each
/// column's non-blank pieces across the lines with `\n` so the inline phase reads them as soft
/// breaks.
fn slice_group(lines: &[&str], starts: &[usize]) -> Vec<Cell> {
    let sliced: Vec<Vec<Cell>> = lines.iter().map(|line| slice_row(line, starts)).collect();
    (0..starts.len())
        .map(|col| {
            sliced
                .iter()
                .filter_map(|row| row.get(col))
                .filter(|piece| !piece.is_empty())
                .cloned()
                .collect::<Vec<_>>()
                .join("\n")
        })
        .collect()
}

/// A column's alignment, read by comparing where the reference text sits to where the dashes are.
/// The column spans `[start, next)` and the dashes run `[start, start + len)`. Within the column,
/// the reference text's first and last non-blank columns fix its extent. Text indented from the
/// dashes' left edge frees the left side; text ending before the dashes' right edge frees the right.
/// Both free is centered, only the left free is right-aligned, only the right free is left-aligned,
/// neither is the default. A column whose reference text is blank keeps the default.
fn column_alignment(reference: &[char], start: usize, len: usize, next: usize) -> Alignment {
    let dash_end = start + len;
    let lo = start.min(reference.len());
    let hi = next.min(reference.len());
    let slice = reference.get(lo..hi).unwrap_or(&[]);
    let Some(first) = slice.iter().position(|ch| *ch != ' ') else {
        return Alignment::AlignDefault;
    };
    let last = slice.iter().rposition(|ch| *ch != ' ').unwrap_or(first);
    let text_start = lo + first;
    let text_end = lo + last + 1;
    let left_free = text_start > start;
    let right_free = text_end < dash_end;
    match (left_free, right_free) {
        (true, true) => Alignment::AlignCenter,
        (true, false) => Alignment::AlignRight,
        (false, true) => Alignment::AlignLeft,
        (false, false) => Alignment::AlignDefault,
    }
}

/// Slice one physical line into per-column text. Column `i` spans from run `i`'s start column to run
/// `i + 1`'s start column, with the last column running to the line's end; each piece is trimmed.
fn slice_row(line: &str, starts: &[usize]) -> Vec<Cell> {
    let chars: Vec<char> = line.chars().collect();
    starts
        .iter()
        .enumerate()
        .map(|(index, &start)| {
            let end = starts.get(index + 1).copied().unwrap_or(chars.len());
            let lo = start.min(chars.len());
            let hi = end.min(chars.len()).max(lo);
            chars
                .get(lo..hi)
                .map(|piece| piece.iter().collect::<String>())
                .unwrap_or_default()
                .trim()
                .to_owned()
        })
        .collect()
}

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

    const SIMPLE: Extensions = Extensions::from_list(&[Extension::SimpleTables]);
    const MULTILINE: Extensions = Extensions::from_list(&[Extension::MultilineTables]);
    const BOTH: Extensions =
        Extensions::from_list(&[Extension::SimpleTables, Extension::MultilineTables]);

    fn width(table: &TextTable, col: usize) -> Option<f64> {
        table.columns.get(col).and_then(|column| column.width)
    }

    fn cell(table: &TextTable, row: usize, col: usize) -> &str {
        table
            .body
            .get(row)
            .and_then(|cells| cells.get(col))
            .map(String::as_str)
            .expect("cell present")
    }

    fn head_cell(table: &TextTable, col: usize) -> &str {
        table
            .head
            .get(col)
            .map(String::as_str)
            .expect("header cell present")
    }

    fn align(table: &TextTable, col: usize) -> &Alignment {
        table
            .columns
            .get(col)
            .map(|column| &column.align)
            .expect("column present")
    }

    #[test]
    fn dash_line_accepts_only_dashes_and_spaces() {
        assert!(is_dash_line("-----"));
        assert!(is_dash_line("--- ---"));
        assert!(is_dash_line("  -- -- "));
        assert!(!is_dash_line(""));
        assert!(!is_dash_line("   "));
        assert!(!is_dash_line("--=--"));
        assert!(!is_dash_line("- x"));
    }

    #[test]
    fn opener_skips_list_markers_and_short_runs() {
        // A first run of two or more dashes opens a table candidate.
        assert!(opens_dash_table("--"));
        assert!(opens_dash_table("---- ----"));
        assert!(opens_dash_table("-- --"));
        // A single leading dash is a list marker, not a border.
        assert!(!opens_dash_table("-"));
        assert!(!opens_dash_table("- -"));
        assert!(!opens_dash_table("- - -"));
    }

    #[test]
    fn dash_runs_finds_positions_and_lengths() {
        assert_eq!(dash_runs("---- ---"), vec![(0, 4), (5, 3)]);
        assert_eq!(dash_runs("  -- --"), vec![(2, 2), (5, 2)]);
        assert_eq!(dash_runs(""), Vec::new());
    }

    #[test]
    fn headed_table_reads_header_and_rows() {
        let lines = ["Right Left Center", "----- ---- ------", "12    12   12"];
        let (table, consumed) = parse(&lines, SIMPLE).expect("table");
        assert_eq!(consumed, 3);
        assert_eq!(table.columns.len(), 3);
        assert_eq!(head_cell(&table, 0), "Right");
        assert_eq!(head_cell(&table, 2), "Center");
        assert_eq!(cell(&table, 0, 1), "12");
        // Header text flush within each run leaves the default alignment.
        assert!(matches!(align(&table, 0), Alignment::AlignDefault));
        assert!(table.head.iter().all(|_| true) && table.columns.iter().all(|c| c.width.is_none()));
    }

    #[test]
    fn headed_table_alignment_from_spacing() {
        // Run columns four wide: flush-left, centered, padded-right, and exactly filled.
        let lines = [
            "ab    cd  ef ghij",
            "---- ---- ---- ----",
            "X    Y    Z    W",
        ];
        let (table, _) = parse(&lines, SIMPLE).expect("table");
        assert!(matches!(align(&table, 0), Alignment::AlignLeft));
        assert!(matches!(align(&table, 1), Alignment::AlignCenter));
        assert!(matches!(align(&table, 2), Alignment::AlignDefault));
        assert!(matches!(align(&table, 3), Alignment::AlignLeft));
    }

    #[test]
    fn headed_table_closes_at_trailing_ruling() {
        let lines = ["H1 H2", "-- --", "a  b", "-- --", "c  d"];
        let (table, consumed) = parse(&lines, SIMPLE).expect("table");
        // The second ruling closes the table; the row after it is left for the next block.
        assert_eq!(consumed, 4);
        assert_eq!(table.body.len(), 1);
        assert_eq!(cell(&table, 0, 0), "a");
    }

    #[test]
    fn headerless_table_needs_a_closing_ruling() {
        let closed = ["--- ---", "1 2", "---"];
        let (table, consumed) = parse(&closed, SIMPLE).expect("table");
        assert_eq!(consumed, 3);
        assert!(table.head.is_empty());
        assert_eq!(cell(&table, 0, 0), "1 2");
        assert_eq!(cell(&table, 0, 1), "");
        // Without the closing ruling there is no table.
        let open = ["--- ---", "1 2"];
        assert!(parse(&open, SIMPLE).is_none());
    }

    #[test]
    fn headerless_alignment_from_first_row() {
        let lines = [
            "-------- --------",
            "  r         l1",
            "x         y",
            "--------- -------",
        ];
        let (table, _) = parse(&lines, SIMPLE).expect("table");
        // Column zero's first-row text is padded on both sides; column one's reaches the right edge.
        assert!(matches!(align(&table, 0), Alignment::AlignCenter));
    }

    #[test]
    fn gap_whitespace_joins_the_left_cell() {
        let lines = ["----- -----", "a         b", "-----------"];
        let (table, _) = parse(&lines, SIMPLE).expect("table");
        assert_eq!(cell(&table, 0, 0), "a");
        assert_eq!(cell(&table, 0, 1), "b");
    }

    #[test]
    fn disabled_extensions_parse_nothing() {
        let lines = ["--- ---", "1 2", "---"];
        assert!(parse(&lines, Extensions::empty()).is_none());
    }

    #[test]
    fn multiline_headed_reads_header_rows_and_widths() {
        let lines = [
            "--------   --------   --------",
            "Left         Center      Right",
            "--------   --------   --------",
            "a            b            c",
            "",
            "spread       over         two",
            "             lines",
            "--------   --------   --------",
        ];
        let (table, consumed) = parse(&lines, MULTILINE).expect("table");
        assert_eq!(consumed, lines.len());
        // The header line between the two rulings forms the header row.
        assert_eq!(head_cell(&table, 0), "Left");
        assert_eq!(head_cell(&table, 2), "Right");
        // Alignment is read from the header line.
        assert!(matches!(align(&table, 0), Alignment::AlignLeft));
        assert!(matches!(align(&table, 1), Alignment::AlignRight));
        assert!(matches!(align(&table, 2), Alignment::AlignRight));
        // Two rows: one single-line, one whose middle column folds two physical lines.
        assert_eq!(table.body.len(), 2);
        assert_eq!(cell(&table, 0, 1), "b");
        assert_eq!(cell(&table, 1, 1), "over\nlines");
        assert_eq!(cell(&table, 1, 2), "two");
        // The short last run widens to its predecessor's span, so every column shares one width.
        assert_eq!(width(&table, 0), Some(11.0 / 72.0));
        assert_eq!(width(&table, 2), Some(11.0 / 72.0));
    }

    #[test]
    fn multiline_headerless_reads_first_row_and_widths() {
        let lines = [
            "----- -----",
            "  a       b",
            "  cont",
            "",
            "x         y",
            "----- -----",
        ];
        let (table, consumed) = parse(&lines, MULTILINE).expect("table");
        assert_eq!(consumed, lines.len());
        assert!(table.head.is_empty());
        // With no header, the first row fixes alignment; column zero is indented and short.
        assert!(matches!(align(&table, 0), Alignment::AlignCenter));
        assert_eq!(table.body.len(), 2);
        assert_eq!(cell(&table, 0, 0), "a\ncont");
        assert_eq!(cell(&table, 0, 1), "b");
        assert_eq!(cell(&table, 1, 0), "x");
        assert_eq!(width(&table, 0), Some(6.0 / 72.0));
    }

    #[test]
    fn multiline_single_column_width_is_run_plus_one() {
        let lines = ["------", "alpha", "", "beta", "------"];
        let (table, consumed) = parse(&lines, MULTILINE).expect("table");
        assert_eq!(consumed, lines.len());
        assert_eq!(table.columns.len(), 1);
        assert_eq!(table.body.len(), 2);
        assert_eq!(width(&table, 0), Some(7.0 / 72.0));
    }

    #[test]
    fn multiline_last_column_widens_to_its_predecessor() {
        // The last run (five dashes, a natural width of six) is within two of the first column's
        // span of seven, so it widens to match: both columns share a width of seven seventy-seconds.
        let lines = ["------ -----", "x      y", "", "p      q", "------ -----"];
        let (table, _) = parse(&lines, MULTILINE).expect("table");
        assert_eq!(width(&table, 0), Some(7.0 / 72.0));
        assert_eq!(width(&table, 1), Some(7.0 / 72.0));
    }

    #[test]
    fn multiline_requires_its_extension() {
        let lines = ["------", "alpha", "", "beta", "------"];
        // With only simple tables enabled, the blank-separated body is not a table.
        assert!(parse(&lines, SIMPLE).is_none());
        assert!(parse(&lines, MULTILINE).is_some());
    }

    #[test]
    fn two_rulings_single_line_rows_stay_simple() {
        // A dash-led block with single-line rows and no blank is a single-line headerless table:
        // multi-line parsing finds no body and the simple headerless shape claims it, widths unset.
        let lines = ["----- -----", "a     b", "c     d", "-----------"];
        let (table, _) = parse(&lines, BOTH).expect("table");
        assert_eq!(table.body.len(), 2);
        assert!(table.head.is_empty());
        assert!(table.columns.iter().all(|column| column.width.is_none()));
    }
}