-- math-omit.lua
-- Replace any math with a placeholder and ensure a space before it when appropriate.
local PH = "[math omitted]"

function Math(el)
    -- Emit the placeholder as a Str; spacing is fixed in Para/Plain below.
    return pandoc.Str(PH)
end

local function ensure_space_before_ph(inlines)
    local out = {}
    for i = 1, #inlines do
        local cur = inlines[i]
        if cur.t == "Str" and cur.text == PH then
            local prev = out[#out]
            local need_space = true

            -- No space if it's the first token in the block
            if not prev then
                need_space = false
            elseif prev.t == "Space" then
                need_space = false
            elseif prev.t == "Str" then
                -- If previous char is an opening bracket/paren/slash/hyphen or whitespace, skip
                local last = prev.text:sub(-1)
                if last:match("[%(%[%{%/%-]") or last:match("%s") then
                    need_space = false
                end
            end

            if need_space then table.insert(out, pandoc.Space()) end
            table.insert(out, cur)
        else
            table.insert(out, cur)
        end
    end
    return out
end

function Para(el)
    el.content = ensure_space_before_ph(el.content)
    return el
end

function Plain(el)
    el.content = ensure_space_before_ph(el.content)
    return el
end