fast_h2m 0.4.2

//! Tier-1 scanner state: escape context bitmask and the open-tag stack.

use crate::converter::tier1::tags::TagSpec;

/// Minimum output buffer capacity in bytes.
const OUTPUT_CAPACITY_MIN: usize = 1024;

/// Maximum output buffer capacity in bytes (256 KiB).
const OUTPUT_CAPACITY_MAX: usize = 256 * 1024;

/// Divisor applied to `input_len` to derive the initial output buffer capacity.
const OUTPUT_CAPACITY_DIVISOR: usize = 3;

/// Accumulated state for one `<table>` being assembled by the Tier-1 scanner.
///
/// When a `<table>` opens, a fresh `TableState` is pushed onto
/// `Tier1State::table_stack`.  Cells accumulate text into `current_cell`
/// instead of `Tier1State::output`.  On `</table>` the state is popped and
/// the completed GFM table is appended to the main output.
#[derive(Debug, Clone, Default)]
pub struct TableState {
    /// Completed rows; each row is a list of finished cell strings.
    pub rows: Vec<Vec<String>>,
    /// Row currently being assembled.
    pub current_row: Vec<String>,
    /// Cell text currently accumulating (active while inside a `<td>`/`<th>`).
    pub current_cell: String,
    /// True while the scanner is inside a `<thead>` section.
    pub in_thead: bool,
    /// True while the scanner is inside a `<td>` or `<th>`.
    pub in_cell: bool,
    /// True after the first `<tbody>` has closed — used to detect
    /// `<tbody>` → `<tfoot>` → `<tbody>` ordering violations.
    pub seen_tbody_close: bool,
    /// True after a `<tfoot>` open has been seen.
    pub seen_tfoot: bool,
    /// True if at least one `<th>` cell has been seen in this table.
    ///
    /// Tier-2 only uses the GFM table rendering path when `table_has_header`
    /// returns true (i.e. at least one `<th>` exists).  Without a `<th>`,
    /// Tier-2 may render the table as a layout/bulleted-list table depending
    /// on other conditions (link count, row count, etc.).
    pub has_th: bool,
    /// Number of `<a>` (link) elements seen inside the table so far.
    ///
    /// Used to detect the "link-heavy navigation table" pattern that Tier-2
    /// renders as a layout table: `row_count <= 2 && link_count >= 3`.
    pub link_count: usize,
    /// Column count of the first row (used to detect inconsistent column counts
    /// across rows, which triggers Tier-2's layout-table path).
    pub first_row_col_count: Option<usize>,
}

bitflags::bitflags! {
    /// Ambient escape contexts.  Set when we enter a tag that changes escape rules.
    #[derive(Debug, Default, Clone, Copy, PartialEq, Eq)]
    pub struct EscapeCtx: u8 {
        /// Inside a `<code>` span.
        const CODE       = 1 << 1;
        /// Inside a `<pre>` block.
        const PRE        = 1 << 2;
        /// Inside an `<a>` link.
        const LINK       = 1 << 3;
        /// Inside a `<blockquote>`.
        const BLOCKQUOTE = 1 << 4;
        /// Inside a heading element.
        const HEADING    = 1 << 5;
    }
}

/// One frame on the open-tag stack.
#[derive(Debug, Clone)]
pub struct OpenTag {
    /// Static tag specification for this element.
    pub spec: &'static TagSpec,
    /// Where this tag's content begins in the input buffer (byte index).
    pub content_start: usize,
    /// Snapshot of `escape_ctx` BEFORE this tag set its bits, so we can restore on close.
    pub prev_escape_ctx: EscapeCtx,
    /// For ordered list items: the current item counter (1-based).
    pub list_index: u16,
    /// For `<a>` tags: the href value (raw bytes from HTML, entity-decoded when emitted).
    pub link_href: Option<String>,
    /// For `<a>` tags: the title value (raw bytes from HTML, entity-decoded when emitted).
    pub link_title: Option<String>,
    /// For ordered lists: the start counter value.
    pub ol_start: u16,
    /// Byte range of the tag name in the original input (original case; callers
    /// must lowercase before comparing).
    pub name_range: std::ops::Range<usize>,
}

/// Mutable state threaded through the entire Tier-1 scan pass.
pub struct Tier1State {
    /// Open-tag stack; one frame per currently-open element.
    pub stack: Vec<OpenTag>,
    /// Current escape-context bitmask.
    pub escape_ctx: EscapeCtx,
    /// Accumulated Markdown output.
    pub output: String,
    /// Current list nesting depth (0 = top level).
    pub list_depth: u16,
    /// Tracks the output length before the most recent block-open separator was appended,
    /// so we can detect whether any content was actually emitted inside a block.
    pub last_block_sep_pos: usize,
    /// Stack of in-progress table states.  Pushed on `<table>` open, popped on
    /// `</table>` close.  Depth > 1 is a nested-table bail.
    pub table_stack: Vec<TableState>,
}

impl Tier1State {
    /// Create a new `Tier1State` pre-allocating output capacity based on `input_len`.
    pub fn new(input_len: usize) -> Self {
        Self {
            stack: Vec::with_capacity(16),
            escape_ctx: EscapeCtx::empty(),
            output: String::with_capacity(
                (input_len / OUTPUT_CAPACITY_DIVISOR)
                    .clamp(OUTPUT_CAPACITY_MIN, OUTPUT_CAPACITY_MAX),
            ),
            list_depth: 0,
            last_block_sep_pos: 0,
            table_stack: Vec::new(),
        }
    }

    /// Return a mutable reference to the current cell buffer when inside a
    /// table cell, or to `self.output` otherwise.
    ///
    /// This is the single dispatch point for "where does inline text land."
    pub fn cell_or_output_mut(&mut self) -> &mut String {
        if let Some(ts) = self.table_stack.last_mut()
            && ts.in_cell
        {
            return &mut ts.current_cell;
        }
        &mut self.output
    }

    /// True when the scanner is currently inside a table cell.
    pub fn in_table_cell(&self) -> bool {
        self.table_stack.last().is_some_and(|ts| ts.in_cell)
    }

    /// Ensure the output ends with exactly two newlines (blank-line separator).
    /// If the output is empty, do nothing.
    pub fn ensure_blank_line(&mut self) {
        let out = &mut self.output;
        if out.is_empty() {
            return;
        }
        if out.ends_with("\n\n") {
            return;
        }
        if out.ends_with('\n') {
            out.push('\n');
        } else {
            out.push_str("\n\n");
        }
    }

    /// Ensure the output ends with at least one newline.
    pub fn ensure_newline(&mut self) {
        if !self.output.is_empty() && !self.output.ends_with('\n') {
            self.output.push('\n');
        }
    }
}