write.lua

local function set_item_first(ast)
	for i, v in ipairs(ast) do
		local t = v.type
		if t == "enum" or t == "item" then
			-- check if it is the first item/enum of that level
			if i == 1 then
				v.first = true
			else
				for j = i - 1, 1, -1 do
					if ast[j].type ~= "item" and ast[j].type ~= "enum" then
						v.first = true
						break
					elseif ast[j].type == t and ast[j].level == v.level then
						v.first = false
						break
					elseif ast[j].level < v.level then
						v.first = true
						break
					end
				end
			end
		end
	end
end

local function set_item_last(ast)
	local len = #ast
	for i, v in ipairs(ast) do
		local t = v.type
		if t == "enum" or t == "item" then
			-- check if it is the last item/enum of that level
			if i == len then
				v.last = true
			else
				for j = i + 1, len do
					if ast[j].type ~= "item" and ast[j].type ~= "enum" then
						v.last = true
						break
					elseif ast[j].type == t and ast[j].level == v.level then
						v.last = false
						break
					elseif ast[j].level < v.level then
						v.last = true
						break
					end
				end
			end
		end
	end
end

--[[
elements:
- header
- latex environment
- item
- enum
- code
- other
- citation
- verbatim
- math
- latex_cmd
- italic
- bold
- text
--]]

local function walk(ast, out, config)
	if ast.type == nil then
		for _, v in ipairs(ast) do
			walk(v, out, config)
		end
	else
		if ast.type == "header" then
			out[1] = out[1] .. "\n\\"
			if ast.level > #config.header then
				ast.level = #config.header -- max level
			end
			out[1] = out[1] .. config.header[ast.level]

			out[1] = out[1] .. "{"
			walk(ast.content, out, config)
			out[1] = out[1] .. "}"
		elseif ast.type == "latex" then
			out[1] = out[1] .. "\n" .. ast.content
		elseif ast.type == "item" then
			if ast.first then
				out[1] = out[1] .. "\n\\begin{itemize}"
			end
			out[1] = out[1] .. "\n\\item "
			walk(ast.content, out, config)
			if ast.last then
				out[1] = out[1] .. "\n\\end{itemize}"
			end
		elseif ast.type == "enum" then -- TODO: add
			if ast.first then
				out[1] = out[1] .. "\n\\begin{enumerate}"
			end
			out[1] = out[1] .. "\n\\item" -- TODO: the space after \item is not always needed
			walk(ast.content, out, config)
			if ast.last then
				out[1] = out[1] .. "\n\\end{enumerate}"
			end
		elseif ast.type == "code" then
			-- TODO: add code type
			out[1] = out[1] .. "\n\\begin{verbatim}\n" .. ast.content .. "\\end{verbatim}"
		elseif ast.type == "other" then
			walk(ast.content, out, config)
		elseif ast.type == "paren_citation" then
			out[1] = out[1] .. "\\" .. config.paren_citation .. "{" .. table.concat(ast.content, ", ") .. "}"
		elseif ast.type == "citation" then
			out[1] = out[1] .. "\\" .. config.citation .. "{" .. ast.content .. "}"
		elseif ast.type == "verbatim" then
			out[1] = out[1] .. "\\texttt{" .. ast.content .. "}"
		elseif ast.type == "math" or ast.type == "latex_cmd" then
			out[1] = out[1] .. ast.content
		elseif ast.type == "italic" then
			out[1] = out[1] .. "\\emph{"
			walk(ast.content, out, config)
			out[1] = out[1] .. "}"
		elseif ast.type == "bold" then
			out[1] = out[1] .. "\\textbf{"
			walk(ast.content, out, config)
			out[1] = out[1] .. "}"
		elseif ast.type == "strikethrough" then
			out[1] = out[1] .. "\\sout{"
			walk(ast.content, out, config)
			out[1] = out[1] .. "}"
		elseif ast.type == "text" then
			out[1] = out[1] .. ast.content
		else
			error("Unknown type: " .. ast.type)
		end
	end
end

local function write(ast, config)
	set_item_first(ast)
	set_item_last(ast)

	local output = { "" }
	walk(ast, output, config)
	return output[1]:sub(2) -- remove first newline that was added
end

return write