rho-coding-agent 1.19.1

use super::*;

#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub(in crate::tui) struct MarkdownStreamPrefix {
    pub(in crate::tui) byte_index: usize,
    pub(in crate::tui) ends_with_wrap: bool,
}

/// Drainable and previewable ends of a pending markdown buffer.
///
/// `drain` is safe to commit permanently. `preview_end` may extend through the
/// stable open-line prefix so already-drawn prose stays visible while a later
/// inline marker is still incomplete. Preview never commits; only drain does.
#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
pub(in crate::tui) struct MarkdownStreamBounds {
    pub(in crate::tui) drain: MarkdownStreamPrefix,
    pub(in crate::tui) preview_end: Option<usize>,
}

pub(in crate::tui) fn markdown_stream_bounds(
    text: &str,
    width: usize,
    in_code_block: bool,
) -> MarkdownStreamBounds {
    let current_line_start = text.rfind('\n').map_or(0, |index| index + '\n'.len_utf8());
    let current_line_in_code_block =
        line_starts_in_code_block(text, current_line_start, in_code_block);
    let current_line = &text[current_line_start..];
    let mut drain = MarkdownStreamPrefix {
        byte_index: current_line_start,
        ends_with_wrap: false,
    };

    if current_line.is_empty() || starts_with_code_fence_fragment(current_line) {
        return MarkdownStreamBounds {
            drain,
            preview_end: None,
        };
    }

    if current_line_in_code_block {
        let complete =
            complete_hard_wrap_prefix(current_line, code_block_stream_content_width(width));
        if complete.byte_index > 0 {
            drain.byte_index = current_line_start + complete.byte_index;
            drain.ends_with_wrap = complete.ends_with_wrap;
        }
        return MarkdownStreamBounds {
            drain,
            preview_end: previewable_prefix_end(current_line_start, current_line, true),
        };
    }

    // Only wrap/preview inside the stable prefix. Open markers stay pending so
    // already-drawn prose is not pulled back when the span finally closes shorter.
    let stable_line_len = inline_markdown_stable_prefix_len(current_line);
    let stable_line = &current_line[..stable_line_len];
    let preview_end = previewable_prefix_end(current_line_start, stable_line, false);

    if !matches!(
        heading_stream_state(current_line),
        HeadingStreamState::NotHeading
    ) {
        // Headings drain only once the line completes.
        return MarkdownStreamBounds { drain, preview_end };
    }

    if stable_line_len == 0 {
        return MarkdownStreamBounds {
            drain,
            preview_end: None,
        };
    }

    let rendered_line = markdown_inline_text(stable_line);
    let complete = complete_word_wrap_prefix(&rendered_line, width);
    if complete.byte_index == 0 {
        return MarkdownStreamBounds { drain, preview_end };
    }

    if let Some(wrapped) =
        stable_wrap_drain_prefix(stable_line, &rendered_line[..complete.byte_index], complete)
    {
        drain.byte_index = current_line_start + wrapped.byte_index;
        drain.ends_with_wrap = wrapped.ends_with_wrap;
    }

    MarkdownStreamBounds { drain, preview_end }
}

/// Map a rendered soft-wrap cut back onto the stable source prefix.
fn stable_wrap_drain_prefix(
    stable_line: &str,
    rendered_prefix: &str,
    complete: CompleteStreamPrefix,
) -> Option<CompleteStreamPrefix> {
    let mut matched = None;
    for candidate in stable_line
        .char_indices()
        .map(|(index, _)| index)
        .chain(std::iter::once(stable_line.len()))
        .skip(1)
    {
        // Candidates already sit inside the stable prefix. The only remaining
        // local hazard is a short prefix that looks like an open fence marker.
        if starts_with_code_fence_fragment(&stable_line[..candidate]) {
            continue;
        }
        let candidate_source = &stable_line[..candidate];
        let candidate_rendered = markdown_inline_text(candidate_source);
        if candidate_rendered == rendered_prefix {
            matched = Some(CompleteStreamPrefix {
                byte_index: candidate,
                ends_with_wrap: complete.ends_with_wrap,
            });
        } else if candidate_source.len() != candidate_rendered.len()
            && !candidate_source
                .chars()
                .last()
                .is_some_and(char::is_whitespace)
            && candidate_rendered.starts_with(rendered_prefix)
        {
            matched = Some(CompleteStreamPrefix {
                byte_index: candidate,
                ends_with_wrap: false,
            });
        }
    }
    matched
}

/// Byte end of the live preview when the stable open-line prefix renders non-empty.
///
/// Uses a local width check on the current line only. Prior complete lines are
/// already covered by the drain bound; re-running `markdown_lines` over the full
/// prefix is unnecessary for a non-zero visibility test.
fn previewable_prefix_end(
    current_line_start: usize,
    stable_line: &str,
    line_in_code_block: bool,
) -> Option<usize> {
    if stable_line.is_empty() {
        return None;
    }
    let rendered_width = if line_in_code_block {
        display_width(stable_line)
    } else {
        display_width(&markdown_inline_text(stable_line))
    };
    (rendered_width > 0).then_some(current_line_start + stable_line.len())
}

#[derive(Clone, Copy, Debug, Default, PartialEq, Eq)]
struct CompleteStreamPrefix {
    byte_index: usize,
    ends_with_wrap: bool,
}

fn complete_word_wrap_prefix(text: &str, width: usize) -> CompleteStreamPrefix {
    wrap_markdown_line_ranges(text, width)
        .into_iter()
        .rfind(|range| {
            range.end < text.len() || display_width(&text[range.clone()]) >= width.max(1)
        })
        .map(|range| CompleteStreamPrefix {
            byte_index: range.end,
            ends_with_wrap: true,
        })
        .unwrap_or_default()
}

fn complete_hard_wrap_prefix(text: &str, width: usize) -> CompleteStreamPrefix {
    let width = width.max(1);
    let mut line_width = 0;
    let mut last_complete = 0;
    for (index, ch) in text.char_indices() {
        let ch_width = char_display_width(ch);
        if line_width > 0 && line_width + ch_width > width {
            last_complete = index;
            line_width = 0;
        }
        line_width += ch_width;
        let next = index + ch.len_utf8();
        if line_width >= width {
            last_complete = next;
            line_width = 0;
        }
    }

    if last_complete == 0 {
        CompleteStreamPrefix::default()
    } else {
        CompleteStreamPrefix {
            byte_index: last_complete,
            ends_with_wrap: true,
        }
    }
}

fn line_starts_in_code_block(text: &str, line_start: usize, in_code_block: bool) -> bool {
    let mut active_fence = in_code_block.then_some(CodeFence {
        marker: '`',
        length: 3,
    });
    for complete_line in text[..line_start].split_inclusive('\n') {
        let line = complete_line.trim_end_matches('\n');
        if active_fence.is_some_and(|fence| is_closing_fence(line, fence)) {
            active_fence = None;
        } else if active_fence.is_none() {
            active_fence = parse_opening_fence(line);
        }
    }
    active_fence.is_some()
}

fn code_block_stream_content_width(width: usize) -> usize {
    let width = width.max(1);
    match width {
        1 => 1,
        2 | 3 => width - 1,
        width => width - 4,
    }
}

fn starts_with_code_fence_fragment(line: &str) -> bool {
    let trimmed = line.trim_start();
    !trimmed.is_empty()
        && (trimmed.starts_with("```") || (trimmed.len() < 3 && "```".starts_with(trimmed)))
}