# Copyright (c) 2012-2024, Chris Pressey, Cat's Eye Technologies.
# This file is distributed under a 2-clause BSD license.  See LICENSES/ dir.
# SPDX-License-Identifier: LicenseRef-BSD-2-Clause-X-Velo

require 'velo/debug'

debug "loading scanner"

class Scanner
  def initialize s
    @string = s
    @text = nil
    @type = nil
    debug "created scanner with string '#{@string}'"
    scan
  end

  def text
    @text
  end

  def type
    @type
  end

  def eof?
    @type == 'EOF'
  end

  def set_token(text, type)
    @text = text
    @type = type
    debug "set_token '#{@text}' (#{@type})"
    #debug "string now '#{@string}'"
  end

  def scan
    scan_impl
    if $debug_scan
      puts "scanned '#{@text}' (#{@type})"
    end
    return @text
  end

  def scan_impl
    m = /\A[ \t]+/.match @string
    if not m.nil?
      @string = m.post_match
      #debug "consumed whitespace, string now '#{@string}'"
    end

    if @string.empty?
      set_token('EOF', 'EOF')
      return
    end

    m = /\A[\r\n;]+/.match @string
    if not m.nil?
      while not m.nil?
        @string = m.post_match
        m = /\A[ \t]*[\r\n;]+/.match @string
      end
      set_token('EOL', 'EOL')
      return
    end

    # check for any single character tokens
    m = /\A([(),.;=])/.match @string
    if m
      @string = m.post_match
      set_token(m[1], 'seperator')
      return
    end

    # check for arguments
    m = /\A\#(\d+)/.match @string
    if m
      @string = m.post_match
      set_token(m[1], 'arg')
      return
    end

    # check for strings of "word" characters
    m = /\A(\w+)/.match @string
    if m
      @string = m.post_match
      set_token(m[1], 'ident')
      return
    end

    # literal strings
    if @string[0] == ?{
      #debug "scanning strlit '#{@string}'"
      index = 1
      level = 1
      while level > 0
        if @string[index] == ?{
          level += 1
        elsif @string[index] == ?}
          level -= 1
        end
        index += 1
        if index >= @string.length
          index = @string.length
          break
        end
      end
      token = @string[1..index-2]
      @string = @string[index..-1]
      set_token(token, 'strlit')
      return
    end

    debug "scanner couldn't scan '#{@string}'"

    set_token('UNKNOWN', 'UNKNOWN')
  end

  def consume s
    if @text == s
      scan
      true
    else
      false
    end
  end

  def consume_type t
    if @type == t
      scan
      true
    else
      false
    end
  end

  def expect s
    if @text == s
      scan
    else
      raise VeloSyntaxError, "expected '#{s}', found '#{@text}'"
    end
  end

  def expect_types set
    if set.include? @type
      scan
    else
      raise VeloSyntaxError, "expected '#{t}', found '#{@text}' (#{@type})"
    end
  end
end

if $0 == __FILE__
  $debug = true
  s = Scanner.new(ARGV[0])
  until s.eof?
    s.scan
  end
end