# A markdown line.
class MDLine

	# Location of `self` in the original input.
	var location: MDLocation

	# Text contained in this line.
	var value: String is writable

	# Is this line empty?
	# Lines containing only spaces are considered empty.
	var is_empty: Bool = true is writable

	# Previous line in `MDBlock` or null if first line.
	var prev: nullable MDLine = null is writable

	# Next line in `MDBlock` or null if last line.
	var next: nullable MDLine = null is writable

	# Is the previous line empty?
	var prev_empty: Bool = false is writable

	# Is the next line empty?
	var next_empty: Bool = false is writable

	# Initialize a new MDLine from its string value
	init do
		self.leading = process_leading
		if leading != value.length then
			self.is_empty = false
			self.trailing = process_trailing
		end
	end

	# Set `value` as an empty String and update `leading`, `trailing` and is_`empty`.
	fun clear do
		value = ""
		leading = 0
		trailing = 0
		is_empty = true
		if prev != null then prev.as(not null).next_empty = true
		if next != null then next.as(not null).prev_empty = true
	end

	# Number or leading spaces on this line.
	var leading: Int = 0 is writable

	# Compute `leading` depending on `value`.
	fun process_leading: Int do
		var count = 0
		var value = self.value
		while count < value.length and value[count] == ' ' do count += 1
		if leading == value.length then clear
		return count
	end

	# Number of trailing spaces on this line.
	var trailing: Int = 0 is writable

	# Compute `trailing` depending on `value`.
	fun process_trailing: Int do
		var count = 0
		var value = self.value
		while value[value.length - count - 1] == ' ' do
			count += 1
		end
		return count
	end

	# Count the amount of `ch` in this line.
	# Return A value > 0 if this line only consists of `ch` end spaces.
	fun count_chars(ch: Char): Int do
		var count = 0
		for c in value do
			if c == ' ' then
				continue
			end
			if c == ch then
				count += 1
				continue
			end
			count = 0
			break
		end
		return count
	end

	# Count the amount of `ch` at the start of this line ignoring spaces.
	fun count_chars_start(ch: Char): Int do
		var count = 0
		for c in value do
			if c == ' ' then
				continue
			end
			if c == ch then
				count += 1
			else
				break
			end
		end
		return count
	end

	# Last XML line if any.
	private var xml_end_line: nullable MDLine = null

	# Does `value` contains valid XML markup?
	private fun check_html: Bool do
		var tags = new Array[String]
		var tmp = new FlatBuffer
		var pos = leading
		if pos + 1 < value.length and value[pos + 1] == '!' then
			if read_xml_comment(self, pos) > 0 then return true
		end
		pos = value.read_xml(tmp, pos, false)
		var tag: String
		if pos > -1 then
			tag = tmp.xml_tag
			if not tag.is_html_block then
				return false
			end
			if tag == "hr" then
				xml_end_line = self
				return true
			end
			tags.add tag
			var line: nullable MDLine = self
			while line != null do
				while pos < line.value.length and line.value[pos] != '<' do
					pos += 1
				end
				if pos >= line.value.length then
					if pos - 2 >= 0 and line.value[pos - 2] == '/' then
						tags.pop
						if tags.is_empty then
							xml_end_line = line
							break
						end
					end
					line = line.next
					pos = 0
				else
					tmp = new FlatBuffer
					var new_pos = line.value.read_xml(tmp, pos, false)
					if new_pos > 0 then
						tag = tmp.xml_tag
						if tag.is_html_block and not tag == "hr" then
							if tmp[1] == '/' then
								if tags.last != tag then
									return false
								end
								tags.pop
							else
								tags.add tag
							end
						end
						if tags.is_empty then
							xml_end_line = line
							break
						end
						pos = new_pos
					else
						pos += 1
					end
				end
			end
			return tags.is_empty
		end
		return false
	end

	# Read a XML comment.
	# Used by `check_html`.
	private fun read_xml_comment(first_line: MDLine, start: Int): Int do
		var line: nullable MDLine = first_line
		if start + 3 < line.as(not null).value.length then
			if line.as(not null).value[2] == '-' and line.as(not null).value[3] == '-' then
				var pos = start + 4
				while line != null do
					while pos < line.value.length and line.value[pos] != '-' do
						pos += 1
					end
					if pos == line.value.length then
						line = line.next
						pos = 0
					else
						if pos + 2 < line.value.length then
							if line.value[pos + 1] == '-' and line.value[pos + 2] == '>' then
								first_line.xml_end_line = line
								return pos + 3
							end
						end
						pos += 1
					end
				end
			end
		end
		return -1
	end

	# Extract the text of `self` without leading and trailing.
	fun text: String do return value.substring(leading, value.length - trailing)
end