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-- center-v.lua
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-- Pandoc Lua filter for converting ~V~ section break symbols
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-- into properly centered paragraphs in EPUB/DOCX/HTML output.
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--
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-- Handles multiple input patterns that Obsidian might produce:
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--   1. <center>\n~V~\n</center>  (HTML blocks wrapping subscript)
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--   2. Raw ~V~ as a paragraph
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--   3. The tilde-based subscript interpretation (~V~ → subscript V)
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local function make_centered()
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  if FORMAT == "epub" or FORMAT == "epub3" or FORMAT == "html" or FORMAT == "html5" then
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    return pandoc.RawBlock("html", '<p style="text-align: center;">~V~</p>')
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  elseif FORMAT == "docx" or FORMAT == "openxml" then
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    return pandoc.RawBlock("openxml", [[
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<w:p>
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  <w:pPr><w:jc w:val="center"/></w:pPr>
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  <w:r><w:t xml:space="preserve">~V~</w:t></w:r>
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</w:p>
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]])
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  else
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    return pandoc.Para({pandoc.Str("~V~")})
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  end
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end
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function Pandoc(doc)
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  local newblocks = {}
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  local i = 1
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  while i <= #doc.blocks do
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    local b1 = doc.blocks[i]
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    local b2 = doc.blocks[i+1]
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    local b3 = doc.blocks[i+2]
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    -- Pattern 1: <center> block + subscript V + </center> block
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    if b1 and b2 and b3
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       and b1.t == "RawBlock" and b1.format == "html" and b1.text:match("^<center>%s*$")
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       and b2.t == "Plain"
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       and #b2.content == 1
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       and b2.content[1].t == "Subscript"
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       and #b2.content[1].content == 1
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       and b2.content[1].content[1].t == "Str"
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       and b2.content[1].content[1].text == "V"
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       and b3.t == "RawBlock" and b3.format == "html" and b3.text:match("^</center>%s*$")
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    then
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      table.insert(newblocks, make_centered())
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      i = i + 3
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    -- Pattern 2: Single paragraph containing just "~V~"
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    elseif b1 and b1.t == "Para"
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       and #b1.content == 1
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       and b1.content[1].t == "Str"
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       and b1.content[1].text == "~V~"
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    then
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      table.insert(newblocks, make_centered())
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      i = i + 1
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    -- Pattern 3: Plain block with subscript V (standalone, no center tags)
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    elseif b1 and b1.t == "Plain"
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       and #b1.content == 1
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       and b1.content[1].t == "Subscript"
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       and #b1.content[1].content == 1
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       and b1.content[1].content[1].t == "Str"
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       and b1.content[1].content[1].text == "V"
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    then
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      table.insert(newblocks, make_centered())
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      i = i + 1
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    -- Pattern 4: Para with Str "~" + Subscript "V" + Str "~" (tilde interpreted separately)
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    elseif b1 and b1.t == "Para"
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       and #b1.content == 3
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       and b1.content[1].t == "Str" and b1.content[1].text == "~"
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       and b1.content[2].t == "Subscript"
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       and #b1.content[2].content == 1
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       and b1.content[2].content[1].t == "Str"
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       and b1.content[2].content[1].text == "V"
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       and b1.content[3].t == "Str" and b1.content[3].text == "~"
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    then
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      table.insert(newblocks, make_centered())
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      i = i + 1
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    else
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      table.insert(newblocks, b1)
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      i = i + 1
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    end
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  end
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  doc.blocks = newblocks
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  return doc
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end