# Copyright, 2012, by Samuel G. D. Williams. <http://www.codeotaku.com>
# 
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
# 
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
# 
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.


require 'strscan'

module Trenni
	# This scanner processes general markup into a sequence of events which are passed to a delegate.
	class Scanner
		OPENED_TAG = :opened
		CLOSED_TAG = :closed
		
		class ScanError < StandardError
			def initialize(message, scanner)
				@message = message

				@pos = scanner.pos
				@offset = calculate_line_number(scanner)
			end

			attr :offset

			def to_s
				if @offset
					"Scan Error: #{@message} @ [#{@offset[0]}:#{@offset[2]}]: #{@offset[4]}"
				else
					"Scan Error [#{@pos}]: #{@message}"
				end
			end
			
			protected
			
			def calculate_line_number(scanner)
				at = scanner.pos
				
				line_no = 1
				line_offset = offset = 0
				
				scanner.string.lines.each do |line|
					line_offset = offset
					offset += line.size
					
					if offset >= at
						return [line_no, line_offset, at - line_offset, offset, line]
					end
					
					line_no += 1
				end
				
				return nil
			end
		end
		
		def initialize(delegate)
			@delegate = delegate
		end

		def parse(string)
			scanner = StringScanner.new(string)

			until scanner.eos?
				start_pos = scanner.pos

				scan_text(scanner)
				scan_tag(scanner)

				if start_pos == scanner.pos
					raise ScanError.new("Scanner didn't move", scanner)
				end
			end
		end

		protected

		def scan_text(scanner)
			# Match any character data except the open tag character.
			if scanner.scan(/[^<]+/m)
				@delegate.text(scanner.matched)
			end
		end
		
		def scan_tag(scanner)
			if scanner.scan(/</)
				if scanner.scan(/\//)
					scan_tag_normal(scanner, CLOSED_TAG)
				elsif scanner.scan(/!\[CDATA\[/)
					scan_tag_cdata(scanner)
				elsif scanner.scan(/!/)
					scan_tag_comment(scanner)
				elsif scanner.scan(/\?/)
					scan_tag_instruction(scanner)
				else
					scan_tag_normal(scanner)
				end
			end
		end

		def scan_attributes(scanner)
			# Parse an attribute in the form of key="value" or key.
			while scanner.scan(/\s*([^\s=\/>]+)/um)
				name = scanner[1]
				if scanner.scan(/=((['"])(.*?)\2)/um)
					@delegate.attribute(name, scanner[3])
				else
					@delegate.attribute(name, true)
				end
			end
		end
		
		def scan_tag_normal(scanner, begin_tag_type = OPENED_TAG)
			if scanner.scan(/[^\s\/>]+/)
				@delegate.begin_tag(scanner.matched, begin_tag_type)
				
				scanner.scan(/\s*/)
				self.scan_attributes(scanner)
				scanner.scan(/\s*/)
				
				if scanner.scan(/\/>/)
					if begin_tag_type == CLOSED_TAG
						raise ScanError.new("Tag cannot be closed at both ends!", scanner)
					else
						@delegate.finish_tag(begin_tag_type, CLOSED_TAG)
					end
				elsif scanner.scan(/>/)
					@delegate.finish_tag(begin_tag_type, OPENED_TAG)
				else
					raise ScanError.new("Invalid characters in tag!", scanner)
				end
			else
				raise ScanError.new("Invalid tag!", scanner)
			end
		end

		def scan_tag_cdata(scanner)
			if scanner.scan_until(/(.*?)\]\]>/m)
				@delegate.cdata(scanner[1])
			else
				raise ScanError.new("CDATA segment is not closed!", scanner)
			end
		end
		
		def scan_tag_comment(scanner)
			if scanner.scan(/--/)
				if scanner.scan_until(/(.*?)-->/m)
					@delegate.comment("--" + scanner[1] + "--")
				else
					raise ScanError.new("Comment is not closed!", scanner)
				end
			else
				if scanner.scan_until(/(.*?)>/)
					@delegate.comment(scanner[1])
				else
					raise ScanError.new("Comment is not closed!", scanner)
				end
			end
		end
		
		def scan_tag_instruction(scanner)
			if scanner.scan_until(/(.*)\?>/)
				@delegate.instruction(scanner[1])
			end
		end
	end
end