import { Box, Link, stringWidth, Text } from '@hermes/ink'
import { Fragment, memo, type ReactNode, useMemo } from 'react'

import { ensureEmojiPresentation } from '../lib/emoji.js'
import { normalizeExternalUrl, urlSlugTitleLabel, useLinkTitle } from '../lib/externalLink.js'
import { BOX_CLOSE, BOX_OPEN, texToUnicode } from '../lib/mathUnicode.js'
import { highlightLine, isHighlightable } from '../lib/syntax.js'
import type { Theme } from '../theme.js'

// `\boxed{X}` regions in `texToUnicode` output are marked with the
// non-printable U+0001 / U+0002 sentinels. Split on them and render the
// boxed segment with `inverse + bold` so it reads as a highlighter-pen
// emphasis on top of whatever color the parent `<Text>` is using (the
// theme accent for math). The leading / trailing space inside the
// highlight gives a one-cell visual margin so the highlight reads as a
// block, not a hug.
const renderMath = (text: string): ReactNode => {
  if (!text.includes(BOX_OPEN)) {
    return text
  }

  const out: ReactNode[] = []
  let i = 0
  let key = 0

  while (i < text.length) {
    const start = text.indexOf(BOX_OPEN, i)

    if (start < 0) {
      out.push(text.slice(i))

      break
    }

    if (start > i) {
      out.push(text.slice(i, start))
    }

    const end = text.indexOf(BOX_CLOSE, start + 1)

    if (end < 0) {
      out.push(text.slice(start))

      break
    }

    out.push(
      <Text bold inverse key={key++}>
        {' '}
        {text.slice(start + 1, end)}{' '}
      </Text>
    )

    i = end + 1
  }

  return out
}

const FENCE_RE = /^\s*(`{3,}|~{3,})(.*)$/
const FENCE_CLOSE_RE = /^\s*(`{3,}|~{3,})\s*$/
const HR_RE = /^ {0,3}([-*_])(?:\s*\1){2,}\s*$/
const HEADING_RE = /^\s{0,3}(#{1,6})\s+(.*?)(?:\s+#+\s*)?$/
const SETEXT_RE = /^\s{0,3}(=+|-+)\s*$/
const FOOTNOTE_RE = /^\[\^([^\]]+)\]:\s*(.*)$/
const DEF_RE = /^\s*:\s+(.+)$/
const BULLET_RE = /^(\s*)[-+*]\s+(.*)$/
const TASK_RE = /^\[( |x|X)\]\s+(.*)$/
const NUMBERED_RE = /^(\s*)(\d+)[.)]\s+(.*)$/
const QUOTE_RE = /^\s*(?:>\s*)+/
const TABLE_DIVIDER_CELL_RE = /^:?-{3,}:?$/
const MD_URL_RE = '((?:[^\\s()]|\\([^\\s()]*\\))+?)'
const MD_IDENTIFIER_RE = '[A-Za-z_][A-Za-z0-9_]*'
const MD_DUNDER_IDENTIFIER_RE = `(?:${MD_IDENTIFIER_RE}__(?!\\w))`
const MD_UNDERSCORE_BOLD_RE = `(?<!\\w)__(?!${MD_DUNDER_IDENTIFIER_RE})(.+?)__(?!\\w)`
const MD_UNDERSCORE_ITALIC_RE = `(?<![\\w_])_(?!_)(.+?)(?<!_)_(?![\\w_])`
const STRIP_UNDERSCORE_BOLD_RE = new RegExp(MD_UNDERSCORE_BOLD_RE, 'g')
const STRIP_UNDERSCORE_ITALIC_RE = new RegExp(MD_UNDERSCORE_ITALIC_RE, 'g')

// Display math openers: `$$ ... $$` (TeX) and `\[ ... \]` (LaTeX). The
// opener is matched only when `$$` / `\[` appears at the very start of the
// trimmed line — `startsWith('$$')` used to fire on prose like
// `$$x+y$$ followed by more`, opening a block that never closed because the
// trailing `$$` on the same line was invisible to the close-scan loop.
const MATH_BLOCK_OPEN_RE = /^\s*(\$\$|\\\[)(.*)$/
const MATH_BLOCK_CLOSE_DOLLAR_RE = /^(.*?)\$\$\s*$/
const MATH_BLOCK_CLOSE_BRACKET_RE = /^(.*?)\\\]\s*$/

export const MEDIA_LINE_RE = /^\s*[`"']?MEDIA:\s*(\S+?)[`"']?\s*$/
export const AUDIO_DIRECTIVE_RE = /^\s*\[\[audio_as_voice\]\]\s*$/

// Inline markdown tokens, in priority order. The outer regex picks the
// leftmost match at each position, preferring earlier alternatives on tie —
// so `**` must come before `*`, `__` before `_`, etc. Each pattern owns its
// own capture groups; MdInline dispatches on which group matched.
//
// Subscript (`~x~`) is restricted to short alphanumeric runs so prose like
// `thing ~! more ~?` from Kimi / Qwen / GLM (kaomoji-style decorators)
// doesn't pair up the first `~` with the next one on the line and swallow
// the text between them as a dim `_`-prefixed span.
//
// Inline math (`$x$` and `\(x\)`) takes precedence over emphasis at the
// same start position because regex alternation is leftmost-first; a
// dollar-delimited span at column N wins over a `*` at column N+1, so
// `$P=a*b*c$` renders as math instead of having `*b*` corrupted into
// italics. Single-character minimums and "no space adjacent to delimiter"
// rules keep currency prose like `$5 to $10` from being swallowed.
export const INLINE_RE = new RegExp(
  [
    `!\\[(.*?)\\]\\(${MD_URL_RE}\\)`, // 1,2  image
    `\\[(.+?)\\]\\(${MD_URL_RE}\\)`, // 3,4  link
    `<((?:https?:\\/\\/|mailto:)[^>\\s]+|[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\\.[A-Za-z]{2,})>`, // 5   autolink
    `~~(.+?)~~`, // 6    strike
    `\`([^\\\`]+)\``, // 7    code
    `\\*\\*(.+?)\\*\\*`, // 8    bold *
    MD_UNDERSCORE_BOLD_RE, // 9    bold _
    `\\*(.+?)\\*`, // 10   italic *
    MD_UNDERSCORE_ITALIC_RE, // 11   italic _
    `==(.+?)==`, // 12   highlight
    `\\[\\^([^\\]]+)\\]`, // 13   footnote ref
    `\\^([^^\\s][^^]*?)\\^`, // 14   superscript
    `~([A-Za-z0-9]{1,8})~`, // 15   subscript
    `(https?:\\/\\/[^\\s<]+)`, // 16   bare URL — wrapped so it owns its own
    //                                capture group; without this, the math
    //                                spans below would land in m[16] and the
    //                                MdInline dispatcher would treat them as
    //                                bare URLs and render them as autolinks.
    `(?<!\\$)\\$([^\\s$](?:[^$\\n]*?[^\\s$])?)\\$(?!\\$)`, // 17   inline math $...$
    `\\\\\\(([^\\n]+?)\\\\\\)` // 18   inline math \(...\)
  ].join('|'),
  'g'
)

const indentDepth = (s: string) => Math.floor(s.replace(/\t/g, '  ').length / 2)

const splitRow = (row: string) =>
  row
    .trim()
    .replace(/^\|/, '')
    .replace(/\|$/, '')
    .split('|')
    .map(c => c.trim())

const isTableDivider = (row: string) => {
  const cells = splitRow(row)

  return cells.length > 1 && cells.every(c => TABLE_DIVIDER_CELL_RE.test(c))
}

const autolinkUrl = (raw: string) =>
  raw.startsWith('mailto:') || raw.startsWith('http') || !raw.includes('@') ? raw : `mailto:${raw}`

const defaultLinkLabel = (url: string) =>
  url.startsWith('mailto:') ? url.replace(/^mailto:/, '') : /^https?:\/\//i.test(url) ? urlSlugTitleLabel(url) : url

const pickFallbackLabel = (label: string | undefined, target: string): string | undefined => {
  const trimmed = label?.trim()

  if (!trimmed) {
    return undefined
  }

  return normalizeExternalUrl(trimmed) === target ? undefined : trimmed
}

interface ResolvedLinkProps {
  fallbackLabel?: string
  t: Theme
  url: string
}

function ResolvedLink({ fallbackLabel, t, url }: ResolvedLinkProps) {
  const fetched = useLinkTitle(url)
  const display = fetched || fallbackLabel || defaultLinkLabel(url)

  return (
    <Link url={url}>
      <Text color={t.color.accent} underline>
        {display}
      </Text>
    </Link>
  )
}

const renderResolvedLink = (k: number, t: Theme, rawUrl: string, label?: string) => {
  const target = normalizeExternalUrl(rawUrl)

  return <ResolvedLink fallbackLabel={pickFallbackLabel(label, target)} key={k} t={t} url={target} />
}

export const stripInlineMarkup = (v: string) =>
  v
    .replace(/!\[(.*?)\]\(((?:[^\s()]|\([^\s()]*\))+?)\)/g, '[image: $1] $2')
    .replace(/\[(.+?)\]\(((?:[^\s()]|\([^\s()]*\))+?)\)/g, '$1')
    .replace(/<((?:https?:\/\/|mailto:)[^>\s]+|[A-Za-z0-9._%+-]+@[A-Za-z0-9.-]+\.[A-Za-z]{2,})>/g, '$1')
    .replace(/~~(.+?)~~/g, '$1')
    .replace(/`([^`]+)`/g, '$1')
    .replace(/\*\*(.+?)\*\*/g, '$1')
    .replace(STRIP_UNDERSCORE_BOLD_RE, '$1')
    .replace(/\*(.+?)\*/g, '$1')
    .replace(STRIP_UNDERSCORE_ITALIC_RE, '$1')
    .replace(/==(.+?)==/g, '$1')
    .replace(/\[\^([^\]]+)\]/g, '[$1]')
    .replace(/\^([^^\s][^^]*?)\^/g, '^$1')
    .replace(/~([A-Za-z0-9]{1,8})~/g, '_$1')
    .replace(/(?<!\$)\$([^\s$](?:[^$\n]*?[^\s$])?)\$(?!\$)/g, '$1')
    .replace(/\\\(([^\n]+?)\\\)/g, '$1')

const SAFETY_MARGIN = 4
const MIN_COL_WIDTH = 3
const COL_GAP = 2 // the '  ' between columns
const TABLE_PADDING_LEFT = 2 // paddingLeft={2} on the outer <Box>

const renderTable = (k: number, rows: string[][], t: Theme, cols?: number) => {
  // Guard: empty table
  if (rows.length === 0 || rows[0]!.length === 0) {
    return null
  }

  const cellDisplayWidth = (raw: string) => stringWidth(stripInlineMarkup(raw))

  // Minimum width: longest word in a cell (to avoid breaking words)
  const minCellWidth = (raw: string) => {
    const text = stripInlineMarkup(raw)
    const words = text.split(/\s+/).filter(w => w.length > 0)

    if (words.length === 0) {
      return MIN_COL_WIDTH
    }

    return Math.max(...words.map(w => stringWidth(w)), MIN_COL_WIDTH)
  }

  const numCols = rows[0]!.length

  // Normalize ragged rows: ensure every row has exactly numCols cells
  const normalizedRows = rows.map(row => {
    if (row.length >= numCols) {
      return row.slice(0, numCols)
    }

    return [...row, ...Array<string>(numCols - row.length).fill('')]
  })

  // Ideal widths: max cell content per column
  const idealWidths = normalizedRows[0]!.map((_, ci) =>
    Math.max(...normalizedRows.map(r => cellDisplayWidth(r[ci] ?? '')), MIN_COL_WIDTH)
  )

  // Min widths: longest word per column
  const minWidths = normalizedRows[0]!.map((_, ci) =>
    Math.max(...normalizedRows.map(r => minCellWidth(r[ci] ?? '')), MIN_COL_WIDTH)
  )

  // Available width: cols minus table padding minus column gaps minus safety.
  // transcriptBodyWidth (source of cols) subtracts message gutter + scrollbar,
  // but NOT this table's paddingLeft — we subtract it here.
  const gapOverhead = (numCols - 1) * COL_GAP

  const availableWidth = cols
    ? Math.max(cols - TABLE_PADDING_LEFT - gapOverhead - SAFETY_MARGIN, numCols * MIN_COL_WIDTH)
    : Infinity

  const totalIdeal = idealWidths.reduce((a, b) => a + b, 0)
  const totalMin = minWidths.reduce((a, b) => a + b, 0)

  let columnWidths: number[]
  let needsWrap = false

  if (totalIdeal <= availableWidth) {
    // Tier 1: everything fits at ideal widths
    columnWidths = idealWidths
  } else if (totalMin <= availableWidth) {
    // Tier 2: proportional shrink — distribute extra space beyond minimums
    needsWrap = true
    const extraSpace = availableWidth - totalMin
    const overflows = idealWidths.map((ideal, i) => ideal - minWidths[i]!)
    const totalOverflow = overflows.reduce((a, b) => a + b, 0)

    if (totalOverflow === 0) {
      columnWidths = [...minWidths]
    } else {
      const rawAlloc = minWidths.map((min, i) => min + (overflows[i]! / totalOverflow) * extraSpace)

      columnWidths = rawAlloc.map(v => Math.floor(v))
      // Distribute rounding remainders to columns with largest fractional part
      let remainder = availableWidth - columnWidths.reduce((a, b) => a + b, 0)

      const fracs = rawAlloc.map((v, i) => ({ i, frac: v - Math.floor(v) })).sort((a, b) => b.frac - a.frac)

      for (const { i } of fracs) {
        if (remainder <= 0) {
          break
        }

        columnWidths[i]!++
        remainder--
      }
    }
  } else {
    // Tier 3: even min-widths don't fit — scale proportionally, allow hard breaks.
    // NOTE: Math.max(..., MIN_COL_WIDTH) can push total above availableWidth when
    // many columns are scaled below 3. This is caught by safetyOverflow → vertical fallback.
    needsWrap = true
    const scaleFactor = availableWidth / totalMin
    const rawAlloc = minWidths.map(w => w * scaleFactor)
    columnWidths = rawAlloc.map(v => Math.max(Math.floor(v), MIN_COL_WIDTH))
    let remainder = availableWidth - columnWidths.reduce((a, b) => a + b, 0)

    const fracs = rawAlloc.map((v, i) => ({ i, frac: v - Math.floor(v) })).sort((a, b) => b.frac - a.frac)

    for (const { i } of fracs) {
      if (remainder <= 0) {
        break
      }

      columnWidths[i]!++
      remainder--
    }
  }

  // Grapheme-safe hard-break: prefer Intl.Segmenter, fall back to code-point split
  const segmenter =
    typeof Intl !== 'undefined' && 'Segmenter' in Intl
      ? new (Intl as any).Segmenter(undefined, { granularity: 'grapheme' })
      : null

  const graphemes = (s: string): string[] =>
    segmenter ? [...segmenter.segment(s)].map((seg: { segment: string }) => seg.segment) : [...s]

  // Word-wrap plain text to fit within `width` display columns.
  // Operates on stripped text for correct width measurement.
  const wrapCell = (raw: string, width: number, hard: boolean): string[] => {
    const text = stripInlineMarkup(raw)

    if (width <= 0) {
      return [text]
    }

    if (stringWidth(text) <= width) {
      return [text]
    }

    const words = text.split(/\s+/).filter(w => w.length > 0)
    const lines: string[] = []
    let current = ''
    let currentWidth = 0

    for (const word of words) {
      const w = stringWidth(word)

      if (currentWidth === 0) {
        if (hard && w > width) {
          for (const ch of graphemes(word)) {
            const cw = stringWidth(ch)

            if (currentWidth + cw > width && current) {
              lines.push(current)
              current = ''
              currentWidth = 0
            }

            current += ch
            currentWidth += cw
          }
        } else {
          current = word
          currentWidth = w
        }
      } else if (currentWidth + 1 + w <= width) {
        current += ' ' + word
        currentWidth += 1 + w
      } else {
        lines.push(current)
        current = word
        currentWidth = w
      }
    }

    if (current) {
      lines.push(current)
    }

    return lines.length > 0 ? lines : ['']
  }

  const isHard = totalMin > availableWidth // tier 3 needs hard word breaks
  const sep = columnWidths.map(w => '─'.repeat(Math.max(1, w))).join('  ')

  // When wrapping isn't needed, build single-line strings per row.
  // All cells render as plain text via stripInlineMarkup.
  // TODO: follow-up — format to ANSI then wrap with wrapAnsi for inline markdown preservation.
  // See free-code/src/components/MarkdownTable.tsx L44-L62 for approach.
  if (!needsWrap) {
    const buildRowString = (row: string[]): string =>
      row
        .map((cell, ci) => {
          const text = stripInlineMarkup(cell)
          const pad = ' '.repeat(Math.max(0, columnWidths[ci]! - stringWidth(text)))
          const gap = ci < numCols - 1 ? '  ' : ''

          return text + pad + gap
        })
        .join('')

    return (
      <Box flexDirection="column" key={k} paddingLeft={TABLE_PADDING_LEFT}>
        {normalizedRows.map((row, ri) => (
          <Fragment key={ri}>
            <Text bold={ri === 0} color={ri === 0 ? t.color.accent : undefined} wrap="truncate-end">
              {buildRowString(row)}
            </Text>
            {ri === 0 && normalizedRows.length > 1 ? (
              <Text color={t.color.muted} dimColor wrap="truncate-end">
                {sep}
              </Text>
            ) : null}
          </Fragment>
        ))}
      </Box>
    )
  }

  // Wrapping path: build multi-line rows as complete strings.
  type LineEntry = { text: string; kind: 'header' | 'separator' | 'body' }

  const buildRowLines = (row: string[]): string[] => {
    const cellLines = row.map((cell, ci) => wrapCell(cell, columnWidths[ci]!, isHard))

    const maxLines = Math.max(...cellLines.map(l => l.length), 1)

    const result: string[] = []

    for (let li = 0; li < maxLines; li++) {
      let line = ''

      for (let ci = 0; ci < numCols; ci++) {
        const cl = cellLines[ci] ?? ['']
        const cellText = li < cl.length ? cl[li]! : ''
        const pad = ' '.repeat(Math.max(0, columnWidths[ci]! - stringWidth(cellText)))
        line += cellText + pad

        if (ci < numCols - 1) {
          line += '  '
        }
      }

      result.push(line)
    }

    return result
  }

  // Build all lines with metadata for styling, tracking tallest body row
  const allEntries: LineEntry[] = []
  let tallestBodyRow = 0
  normalizedRows.forEach((row, ri) => {
    const kind = ri === 0 ? ('header' as const) : ('body' as const)
    const rowLines = buildRowLines(row)
    rowLines.forEach(text => allEntries.push({ text, kind }))

    if (ri > 0) {
      tallestBodyRow = Math.max(tallestBodyRow, rowLines.length)
    }

    if (ri === 0 && normalizedRows.length > 1) {
      allEntries.push({ text: sep, kind: 'separator' })
    }
  })

  // Post-render safety condition: compute max line width.
  const maxLineWidth = Math.max(...allEntries.map(e => stringWidth(e.text)))
  const safetyOverflow = cols != null && maxLineWidth > cols - TABLE_PADDING_LEFT - SAFETY_MARGIN

  // Scaled vertical threshold — 2-3 col tables stay tabular even with tall cells
  const maxRowLinesThreshold = numCols <= 3 ? 8 : numCols <= 6 ? 5 : 4

  const useVertical = tallestBodyRow > maxRowLinesThreshold || safetyOverflow

  if (useVertical) {
    // Edge case: header-only table
    if (normalizedRows.length <= 1) {
      return (
        <Box flexDirection="column" key={k} paddingLeft={TABLE_PADDING_LEFT}>
          <Text bold color={t.color.accent} wrap="wrap-trim">
            {normalizedRows[0]!.map(h => stripInlineMarkup(h)).join(' · ')}
          </Text>
        </Box>
      )
    }

    const headers = normalizedRows[0]!
    const dataRows = normalizedRows.slice(1)
    const sepWidth = Math.max(1, cols ? Math.min(cols - TABLE_PADDING_LEFT - 1, 40) : 40)

    return (
      <Box flexDirection="column" key={k} paddingLeft={TABLE_PADDING_LEFT}>
        {dataRows.map((row, ri) => (
          <Fragment key={ri}>
            {ri > 0 ? (
              <Text color={t.color.muted} dimColor>
                {'─'.repeat(sepWidth)}
              </Text>
            ) : null}
            {headers.map((header, ci) => {
              const cell = row[ci] ?? ''
              const label = stripInlineMarkup(header) || `Col ${ci + 1}`

              return (
                <Text key={ci} wrap="wrap-trim">
                  <Text bold color={t.color.accent}>
                    {label}:
                  </Text>{' '}
                  {stripInlineMarkup(cell)}
                </Text>
              )
            })}
          </Fragment>
        ))}
      </Box>
    )
  }

  // Render wrapped horizontal rows — one <Text> per visual line.
  return (
    <Box flexDirection="column" key={k} paddingLeft={TABLE_PADDING_LEFT}>
      {allEntries.map((entry, i) => (
        <Text
          bold={entry.kind === 'header'}
          color={entry.kind === 'header' ? t.color.accent : entry.kind === 'separator' ? t.color.muted : undefined}
          dimColor={entry.kind === 'separator'}
          key={i}
          wrap="truncate-end"
        >
          {entry.text}
        </Text>
      ))}
    </Box>
  )
}

function MdInline({ t, text }: { t: Theme; text: string }) {
  const parts: ReactNode[] = []

  let last = 0

  for (const m of text.matchAll(INLINE_RE)) {
    const i = m.index ?? 0
    const k = parts.length

    if (i > last) {
      parts.push(<Text key={k}>{text.slice(last, i)}</Text>)
    }

    if (m[1] && m[2]) {
      parts.push(
        <Text color={t.color.muted} key={parts.length}>
          [image: {m[1]}] {m[2]}
        </Text>
      )
    } else if (m[3] && m[4]) {
      parts.push(renderResolvedLink(parts.length, t, m[4], m[3]))
    } else if (m[5]) {
      parts.push(renderResolvedLink(parts.length, t, autolinkUrl(m[5]), m[5].replace(/^mailto:/, '')))
    } else if (m[6]) {
      parts.push(
        <Text key={parts.length} strikethrough>
          <MdInline t={t} text={m[6]} />
        </Text>
      )
    } else if (m[7]) {
      // Code is the one wrap that does NOT recurse — inline `code` spans
      // are verbatim by definition. Letting MdInline reprocess them
      // would corrupt regex examples and shell snippets.
      parts.push(
        <Text color={t.color.accent} dimColor key={parts.length}>
          {m[7]}
        </Text>
      )
    } else if (m[8] ?? m[9]) {
      // Recurse into bold / italic / strike / highlight so nested
      // `$...$` math (and other inline tokens) inside a `**bolded
      // statement with $\mathbb{Z}$ math**` actually render. Without
      // this the inner content is dropped into a single `<Text bold>`
      // verbatim and the math renderer never sees it.
      parts.push(
        <Text bold key={parts.length}>
          <MdInline t={t} text={m[8] ?? m[9]!} />
        </Text>
      )
    } else if (m[10] ?? m[11]) {
      parts.push(
        <Text italic key={parts.length}>
          <MdInline t={t} text={m[10] ?? m[11]!} />
        </Text>
      )
    } else if (m[12]) {
      parts.push(
        <Text backgroundColor={t.color.diffAdded} color={t.color.diffAddedWord} key={parts.length}>
          <MdInline t={t} text={m[12]} />
        </Text>
      )
    } else if (m[13]) {
      parts.push(
        <Text color={t.color.muted} key={parts.length}>
          [{m[13]}]
        </Text>
      )
    } else if (m[14]) {
      parts.push(
        <Text color={t.color.muted} key={parts.length}>
          ^{m[14]}
        </Text>
      )
    } else if (m[15]) {
      parts.push(
        <Text color={t.color.muted} key={parts.length}>
          _{m[15]}
        </Text>
      )
    } else if (m[16]) {
      // Bare URL — trim trailing prose punctuation into a sibling text node
      // so `see https://x.com/, which…` keeps the comma outside the link.
      const url = m[16].replace(/[),.;:!?]+$/g, '')

      parts.push(renderResolvedLink(parts.length, t, url))

      if (url.length < m[16].length) {
        parts.push(<Text key={parts.length}>{m[16].slice(url.length)}</Text>)
      }
    } else if (m[17] ?? m[18]) {
      // Inline math is run through `texToUnicode` (Greek letters, ℕℤℚℝ,
      // operators, sub/superscripts, fractions) and rendered in italic
      // accent. Italic is the disambiguator — links use accent+underline,
      // so without italic readers can't tell `\mathbb{R}` (math) from a
      // hyperlinked word. Anything `texToUnicode` doesn't recognise is
      // preserved verbatim, so unfamiliar commands just look like their
      // raw LaTeX rather than vanishing.
      parts.push(
        <Text color={t.color.accent} italic key={parts.length}>
          {renderMath(texToUnicode(m[17] ?? m[18]!))}
        </Text>
      )
    }

    last = i + m[0].length
  }

  if (last < text.length) {
    parts.push(<Text key={parts.length}>{text.slice(last)}</Text>)
  }

  return <Text wrap="wrap-trim">{parts.length ? parts : text}</Text>
}

// Cross-instance parsed-children cache: useMemo's per-instance cache dies
// on remount, so virtualization re-parses every row that scrolls back into
// view. Theme-keyed WeakMap drops stale palettes; inner Map is LRU-bounded.
const MD_CACHE_LIMIT = 512
const mdCache = new WeakMap<Theme, Map<string, ReactNode[]>>()

const cacheBucket = (t: Theme) => {
  const b = mdCache.get(t)

  if (b) {
    return b
  }

  const fresh = new Map<string, ReactNode[]>()
  mdCache.set(t, fresh)

  return fresh
}

const cacheGet = (b: Map<string, ReactNode[]>, key: string) => {
  const v = b.get(key)

  if (v) {
    b.delete(key)
    b.set(key, v)
  }

  return v
}

const cacheSet = (b: Map<string, ReactNode[]>, key: string, v: ReactNode[]) => {
  b.set(key, v)

  if (b.size > MD_CACHE_LIMIT) {
    b.delete(b.keys().next().value!)
  }
}

function MdImpl({ cols, compact, t, text }: MdProps) {
  const nodes = useMemo(() => {
    const bucket = cacheBucket(t)
    const cacheKey = `${compact ? '1' : '0'}|${cols ?? ''}|${text}`
    const cached = cacheGet(bucket, cacheKey)

    if (cached) {
      return cached
    }

    const lines = ensureEmojiPresentation(text).split('\n')
    const nodes: ReactNode[] = []

    let prevKind: Kind = null
    let i = 0

    const gap = () => {
      if (nodes.length && prevKind !== 'blank') {
        nodes.push(<Text key={`gap-${nodes.length}`}> </Text>)
        prevKind = 'blank'
      }
    }

    const start = (kind: Exclude<Kind, null | 'blank'>) => {
      if (prevKind && prevKind !== 'blank' && prevKind !== kind) {
        gap()
      }

      prevKind = kind
    }

    while (i < lines.length) {
      const line = lines[i]!
      const key = nodes.length

      if (!line.trim()) {
        if (!compact) {
          gap()
        }

        i++

        continue
      }

      if (AUDIO_DIRECTIVE_RE.test(line)) {
        i++

        continue
      }

      const media = line.match(MEDIA_LINE_RE)?.[1]

      if (media) {
        start('paragraph')
        nodes.push(
          <Text color={t.color.muted} key={key} wrap="wrap-trim">
            {'▸ '}

            <Link url={/^(?:\/|[a-z]:[\\/])/i.test(media) ? `file://${media}` : media}>
              <Text color={t.color.accent} underline>
                {media}
              </Text>
            </Link>
          </Text>
        )
        i++

        continue
      }

      const fence = line.match(FENCE_RE)

      if (fence) {
        const char = fence[1]![0] as '`' | '~'
        const len = fence[1]!.length
        const lang = fence[2]!.trim().toLowerCase()
        const block: string[] = []

        for (i++; i < lines.length; i++) {
          const close = lines[i]!.match(FENCE_CLOSE_RE)?.[1]

          if (close && close[0] === char && close.length >= len) {
            break
          }

          block.push(lines[i]!)
        }

        if (i < lines.length) {
          i++
        }

        if (['md', 'markdown'].includes(lang)) {
          start('paragraph')
          nodes.push(<Md cols={cols} compact={compact} key={key} t={t} text={block.join('\n')} />)

          continue
        }

        start('code')

        const isDiff = lang === 'diff'
        const highlighted = !isDiff && isHighlightable(lang)

        nodes.push(
          <Box flexDirection="column" key={key} paddingLeft={2}>
            {lang && !isDiff && <Text color={t.color.muted}>{'─ ' + lang}</Text>}

            {block.map((l, j) => {
              if (highlighted) {
                return (
                  <Text key={j}>
                    {highlightLine(l, lang, t).map(([color, text], kk) =>
                      color ? (
                        <Text color={color} key={kk}>
                          {text}
                        </Text>
                      ) : (
                        <Text key={kk}>{text}</Text>
                      )
                    )}
                  </Text>
                )
              }

              const add = isDiff && l.startsWith('+')
              const del = isDiff && l.startsWith('-')
              const hunk = isDiff && l.startsWith('@@')

              return (
                <Text
                  backgroundColor={add ? t.color.diffAdded : del ? t.color.diffRemoved : undefined}
                  color={add ? t.color.diffAddedWord : del ? t.color.diffRemovedWord : hunk ? t.color.muted : undefined}
                  dimColor={isDiff && !add && !del && !hunk && l.startsWith(' ')}
                  key={j}
                >
                  {l}
                </Text>
              )
            })}
          </Box>
        )

        continue
      }

      const mathOpen = line.match(MATH_BLOCK_OPEN_RE)

      if (mathOpen) {
        const opener = mathOpen[1]!
        const closeRe = opener === '$$' ? MATH_BLOCK_CLOSE_DOLLAR_RE : MATH_BLOCK_CLOSE_BRACKET_RE
        const headRest = mathOpen[2] ?? ''
        const block: string[] = []

        // Single-line block: `$$x + y = z$$` or `\[x\]`. Capture inner content
        // and emit the block immediately. Without this, the close-scan loop
        // skips line `i` and treats the next opener as our closer, swallowing
        // every paragraph in between.
        const sameLineClose = headRest.match(closeRe)

        if (sameLineClose) {
          const inner = sameLineClose[1]!.trim()

          start('code')
          nodes.push(
            <Box flexDirection="column" key={key} paddingLeft={2}>
              {inner ? <Text color={t.color.accent}>{renderMath(texToUnicode(inner))}</Text> : null}
            </Box>
          )
          i++

          continue
        }

        // Multi-line block: scan ahead for a real closer before committing.
        // If none exists in the rest of the document, render this line as a
        // paragraph instead of consuming everything that follows.
        let closeIdx = -1

        for (let j = i + 1; j < lines.length; j++) {
          if (closeRe.test(lines[j]!)) {
            closeIdx = j

            break
          }
        }

        if (closeIdx < 0) {
          start('paragraph')
          nodes.push(<MdInline key={key} t={t} text={line} />)
          i++

          continue
        }

        if (headRest.trim()) {
          block.push(headRest)
        }

        for (let j = i + 1; j < closeIdx; j++) {
          block.push(lines[j]!)
        }

        const tail = lines[closeIdx]!.match(closeRe)![1]!.trimEnd()

        if (tail.trim()) {
          block.push(tail)
        }

        start('code')
        nodes.push(
          <Box flexDirection="column" key={key} paddingLeft={2}>
            {block.map((l, j) => (
              <Text color={t.color.accent} key={j}>
                {renderMath(texToUnicode(l))}
              </Text>
            ))}
          </Box>
        )
        i = closeIdx + 1

        continue
      }

      const heading = line.match(HEADING_RE)?.[2]

      if (heading) {
        start('heading')
        nodes.push(
          <Text bold color={t.color.accent} key={key} wrap="wrap-trim">
            <MdInline t={t} text={heading} />
          </Text>
        )
        i++

        continue
      }

      if (i + 1 < lines.length && SETEXT_RE.test(lines[i + 1]!)) {
        start('heading')
        nodes.push(
          <Text bold color={t.color.accent} key={key} wrap="wrap-trim">
            <MdInline t={t} text={line.trim()} />
          </Text>
        )
        i += 2

        continue
      }

      if (HR_RE.test(line)) {
        start('rule')
        nodes.push(
          <Text color={t.color.muted} key={key}>
            {'─'.repeat(36)}
          </Text>
        )
        i++

        continue
      }

      const footnote = line.match(FOOTNOTE_RE)

      if (footnote) {
        start('list')
        nodes.push(
          <Text color={t.color.muted} key={key} wrap="wrap-trim">
            [{footnote[1]}] <MdInline t={t} text={footnote[2] ?? ''} />
          </Text>
        )
        i++

        while (i < lines.length && /^\s{2,}\S/.test(lines[i]!)) {
          nodes.push(
            <Box key={`${key}-cont-${i}`} paddingLeft={2}>
              <Text color={t.color.muted} wrap="wrap-trim">
                <MdInline t={t} text={lines[i]!.trim()} />
              </Text>
            </Box>
          )
          i++
        }

        continue
      }

      if (i + 1 < lines.length && DEF_RE.test(lines[i + 1]!)) {
        start('list')
        nodes.push(
          <Text bold key={key} wrap="wrap-trim">
            {line.trim()}
          </Text>
        )
        i++

        while (i < lines.length) {
          const def = lines[i]!.match(DEF_RE)?.[1]

          if (!def) {
            break
          }

          nodes.push(
            <Text key={`${key}-def-${i}`} wrap="wrap-trim">
              <Text color={t.color.muted}> · </Text>
              <MdInline t={t} text={def} />
            </Text>
          )
          i++
        }

        continue
      }

      const bullet = line.match(BULLET_RE)

      if (bullet) {
        start('list')

        const task = bullet[2]!.match(TASK_RE)
        const marker = task ? (task[1]!.toLowerCase() === 'x' ? '☑' : '☐') : '•'

        nodes.push(
          <Box key={key} paddingLeft={indentDepth(bullet[1]!) * 2}>
            <Text wrap="wrap-trim">
              <Text color={t.color.muted}>{marker} </Text>
              <MdInline t={t} text={task ? task[2]! : bullet[2]!} />
            </Text>
          </Box>
        )
        i++

        continue
      }

      const numbered = line.match(NUMBERED_RE)

      if (numbered) {
        start('list')
        nodes.push(
          <Box key={key} paddingLeft={indentDepth(numbered[1]!) * 2}>
            <Text wrap="wrap-trim">
              <Text color={t.color.muted}>{numbered[2]}. </Text>
              <MdInline t={t} text={numbered[3]!} />
            </Text>
          </Box>
        )
        i++

        continue
      }

      if (QUOTE_RE.test(line)) {
        start('quote')

        const quoteLines: Array<{ depth: number; text: string }> = []

        while (i < lines.length && QUOTE_RE.test(lines[i]!)) {
          const prefix = lines[i]!.match(QUOTE_RE)?.[0] ?? ''

          quoteLines.push({ depth: (prefix.match(/>/g) ?? []).length, text: lines[i]!.slice(prefix.length) })
          i++
        }

        nodes.push(
          <Box flexDirection="column" key={key}>
            {quoteLines.map((ql, qi) => (
              <Box key={qi} paddingLeft={Math.max(0, ql.depth - 1) * 2}>
                <Text color={t.color.muted} wrap="wrap-trim">
                  │ <MdInline t={t} text={ql.text} />
                </Text>
              </Box>
            ))}
          </Box>
        )

        continue
      }

      if (line.includes('|') && i + 1 < lines.length && isTableDivider(lines[i + 1]!)) {
        start('table')

        const rows: string[][] = [splitRow(line)]

        for (i += 2; i < lines.length && lines[i]!.includes('|') && lines[i]!.trim(); i++) {
          rows.push(splitRow(lines[i]!))
        }

        nodes.push(renderTable(key, rows, t, cols))

        continue
      }

      if (/^<\/?details\b/i.test(line)) {
        i++

        continue
      }

      const summary = line.match(/^<summary>(.*?)<\/summary>$/i)?.[1]

      if (summary) {
        start('paragraph')
        nodes.push(
          <Text color={t.color.muted} key={key} wrap="wrap-trim">
            ▶ {summary}
          </Text>
        )
        i++

        continue
      }

      if (/^<\/?[^>]+>$/.test(line.trim())) {
        start('paragraph')
        nodes.push(
          <Text color={t.color.muted} key={key} wrap="wrap-trim">
            {line.trim()}
          </Text>
        )
        i++

        continue
      }

      if (line.includes('|') && line.trim().startsWith('|')) {
        start('table')

        const rows: string[][] = []

        while (i < lines.length && lines[i]!.trim().startsWith('|')) {
          const row = lines[i]!.trim()

          if (!/^[|\s:-]+$/.test(row)) {
            rows.push(splitRow(row))
          }

          i++
        }

        if (rows.length) {
          nodes.push(renderTable(key, rows, t, cols))
        }

        continue
      }

      start('paragraph')
      nodes.push(<MdInline key={key} t={t} text={line} />)
      i++
    }

    cacheSet(bucket, cacheKey, nodes)

    return nodes
  }, [cols, compact, t, text])

  return <Box flexDirection="column">{nodes}</Box>
}

export const Md = memo(MdImpl)

type Kind = 'blank' | 'code' | 'heading' | 'list' | 'paragraph' | 'quote' | 'rule' | 'table' | null

interface MdProps {
  cols?: number
  compact?: boolean
  t: Theme
  text: string
}
