# frozen_string_literal: true

require 'dev/ui'
require 'strscan'

module Dev
  module UI
    class Formatter
      SGR_MAP = {
        # presentational
        'red'       => '31',
        'green'     => '32',
        'yellow'    => '33',
        'blue'      => '34',
        'magenta'   => '35',
        'cyan'      => '36',
        'bold'      => '1',
        'italic'    => '3',
        'underline' => '4',
        'reset'     => '0',

        # semantic
        'error'   => '31', # red
        'success' => '32', # success
        'warning' => '33', # yellow
        'info'    => '34', # blue
        'command' => '36', # cyan
      }.freeze

      BEGIN_EXPR = '{{'
      END_EXPR   = '}}'

      SCAN_FUNCNAME = /\w+:/
      SCAN_GLYPH    = /.}}/
      SCAN_BODY     = /
        .*?
        (
          #{BEGIN_EXPR} |
          #{END_EXPR}   |
          \z
        )
      /mx

      DISCARD_BRACES = 0..-3

      LITERAL_BRACES = :__literal_braces__

      class FormatError < StandardError
        attr_accessor :input, :index

        def initialize(message = nil, input = nil, index = nil)
          super(message)
          @input = input
          @index = index
        end
      end

      def initialize(text)
        @text = text
      end

      def format(sgr_map = SGR_MAP, enable_color: true)
        @nodes = []
        stack = parse_body(StringScanner.new(@text))
        prev_fmt = nil
        content = @nodes.each_with_object(String.new) do |(text, fmt), str|
          if prev_fmt != fmt && enable_color
            text = apply_format(text, fmt, sgr_map)
          end
          str << text
          prev_fmt = fmt
        end

        stack.reject! { |e| e == LITERAL_BRACES }

        return content unless enable_color
        return content if stack == prev_fmt

        unless stack.empty? && (@nodes.size.zero? || @nodes.last[1].empty?)
          content << apply_format('', stack, sgr_map)
        end
        content
      end

      private

      def apply_format(text, fmt, sgr_map)
        sgr = fmt.each_with_object(String.new('0')) do |name, str|
          next if name == LITERAL_BRACES
          begin
            str << ';' << sgr_map.fetch(name)
          rescue KeyError
            raise FormatError.new(
              "invalid format specifier: #{name}",
              @text,
              -1
            )
          end
        end
        Dev::UI::ANSI.sgr(sgr) + text
      end

      def parse_expr(sc, stack)
        if match = sc.scan(SCAN_GLYPH)
          glyph_handle = match[0]
          begin
            glyph = Glyph.lookup(glyph_handle)
            emit(glyph.char, [glyph.color.name.to_s])
          rescue Glyph::InvalidGlyphHandle
            index = sc.pos - 2 # rewind past '}}'
            raise FormatError.new(
              "invalid glyph handle at index #{index}: '#{glyph_handle}'",
              @text,
              index
            )
          end
        elsif match = sc.scan(SCAN_FUNCNAME)
          funcname = match.chop
          stack.push(funcname)
        else
          # We read a {{ but it's not apparently Formatter syntax.
          # We could error, but it's nicer to just pass through as text.
          # We do kind of assume that the text will probably have balanced
          # pairs of {{ }} at least.
          emit('{{', stack)
          stack.push(LITERAL_BRACES)
        end
        parse_body(sc, stack)
        stack
      end

      def parse_body(sc, stack = [])
        match = sc.scan(SCAN_BODY)
        if match && match.end_with?(BEGIN_EXPR)
          emit(match[DISCARD_BRACES], stack)
          parse_expr(sc, stack)
        elsif match && match.end_with?(END_EXPR)
          emit(match[DISCARD_BRACES], stack)
          if stack.pop == LITERAL_BRACES
            emit('}}', stack)
          end
          parse_body(sc, stack)
        elsif match
          emit(match, stack)
        else
          emit(sc.rest, stack)
        end
        stack
      end

      def emit(text, stack)
        return if text.nil? || text.empty?
        @nodes << [text, stack.reject { |n| n == LITERAL_BRACES }]
      end
    end
  end
end