# -*- coding: utf-8 -*-

# Scanner for the Lua[http://lua.org] programming lanuage.
#
# The language’s complete syntax is defined in
# {the Lua manual}[http://www.lua.org/manual/5.2/manual.html],
# which is what this scanner tries to conform to.
class CodeRay::Scanners::Lua < CodeRay::Scanners::Scanner

  register_for :lua
  file_extension "lua"
  title "Lua"

  # Keywords used in Lua.
  KEYWORDS = %w[and break do else elseif end
  for function goto if in
  local not or repeat return
  then until while
  ]

  # Constants set by the Lua core.
  PREDEFINED_CONSTANTS = %w[false true nil]

  # The expressions contained in this array are parts of Lua’s `basic'
  # library. Although it’s not entirely necessary to load that library,
  # it is highly recommended and one would have to provide own implementations
  # of some of these expressions if one does not do so. They however aren’t
  # keywords, neither are they constants, but nearly predefined, so they
  # get tagged as `predefined' rather than anything else.
  #
  # This list excludes values of form `_UPPERCASE' because the Lua manual
  # requires such identifiers to be reserved by Lua anyway and they are
  # highlighted directly accordingly, without the need for specific
  # identifiers to be listed here.
  PREDEFINED_EXPRESSIONS = %w[
  assert collectgarbage dofile error getmetatable
  ipairs load loadfile next pairs pcall print
  rawequal rawget rawlen rawset select setmetatable
  tonumber tostring type xpcall
  ]

  # Automatic token kind selection for normal words.
  IDENT_KIND = CodeRay::WordList.new(:ident)
    .add(KEYWORDS, :keyword)
    .add(PREDEFINED_CONSTANTS, :predefined_constant)
    .add(PREDEFINED_EXPRESSIONS, :predefined)

  protected

  # Scanner initialization.
  def setup
    @state       = :initial
    @brace_depth = 0
  end

  # CodeRay entry hook. Starts parsing.
  def scan_tokens(encoder, options)
    @encoder = encoder
    @options = options

    send(:"handle_state_#@state") until eos?

    @encoder
  end

  def handle_state_initial
    if match = scan(/\-\-\[\=*\[/)   #--[[ long (possibly multiline) comment ]]
      @num_equals = match.count("=") # Number must match for comment end
      @encoder.begin_group(:comment)
      @encoder.text_token(match, :delimiter)
      @state = :long_comment

    elsif match = scan(/--.*?$/) # --Lua comment
      @encoder.text_token(match, :comment)

    elsif match = scan(/\[=*\[/)     # [[ long (possibly multiline) string ]]
      @num_equals = match.count("=") # Number must match for comment end
      @encoder.begin_group(:string)
      @encoder.text_token(match, :delimiter)
      @state = :long_string

    elsif match = scan(/::\s*[a-zA-Z_][a-zA-Z0-9_]+\s*::/) # ::goto_label::
      @encoder.text_token(match, :label)

    elsif match = scan(/_[A-Z]+/) # _UPPERCASE are names reserved for Lua
      @encoder.text_token(match, :predefined)

    elsif match = scan(/[a-zA-Z_][a-zA-Z0-9_]*/) # Normal letters (or letters followed by digits)
      kind = IDENT_KIND[match]

      # Extra highlighting for entities following certain keywords
      if kind == :keyword and match == "function"
        @state = :function_expected
      elsif kind == :keyword and match == "goto"
        @state = :goto_label_expected
      elsif kind == :keyword and match == "local"
        @state = :local_var_expected
      end

      @encoder.text_token(match, kind)

    elsif match = scan(/{/) # Opening table brace {
      @encoder.begin_group(:table)
      @encoder.text_token(match, @brace_depth >= 1 ? :inline_delimiter : :delimiter)
      @brace_depth += 1
      @state        = :table

    elsif match = scan(/}/) # Closing table brace }
      if @brace_depth == 1
        @brace_depth = 0
        @encoder.text_token(match, :delimiter)
      elsif @brace_depth == 0 # Mismatched brace
        @encoder.text_token(match, :error)
      else
        @brace_depth -= 1
        @encoder.text_token(match, :inline_delimiter)
        @state = :table
      end
      @encoder.end_group(:table)

    elsif match = scan(/["']/) # String delimiters " and '
      @encoder.begin_group(:string)
      @encoder.text_token(match, :delimiter)
      @start_delim = match
      @state       = :string

                      # ↓Prefix                hex number ←|→ decimal number
    elsif match = scan(/-? (?:0x\h* \. \h+ (?:p[+\-]?\d+)? | \d*\.\d+ (?:e[+\-]?\d+)?)/ix) # hexadecimal constants have no E power, decimal ones no P power
      @encoder.text_token(match, :float)

                      # ↓Prefix         hex number ←|→ decimal number
    elsif match = scan(/-? (?:0x\h+ (?:p[+\-]?\d+)? | \d+ (?:e[+\-]?\d+)?)/ix) # hexadecimal constants have no E power, decimal ones no P power
      @encoder.text_token(match, :integer)

    elsif match = scan(/[\+\-\*\/%^\#=~<>\(\)\[\]:;,] | \.(?!\d)/x) # Operators
      @encoder.text_token(match, :operator)

    elsif match = scan(/\s+/) # Space
      @encoder.text_token(match, :space)

    else # Invalid stuff. Note that Lua doesn’t accept multibyte chars outside of strings, hence these are also errors.
      @encoder.text_token(getch, :error)
    end

    # It may be that we’re scanning a full-blown subexpression of a table
    # (tables can contain full expressions in parts).
    # If this is the case, return to :table scanning state.
    @state = :table if @state == :initial && @brace_depth >= 1
  end

  def handle_state_function_expected
    if match = scan(/\(.*?\)/m) # x = function() # "Anonymous" function without explicit name
      @encoder.text_token(match, :operator)
      @state = :initial
    elsif match = scan(/[a-zA-Z_] (?:[a-zA-Z0-9_\.] (?!\.\d))* [\.\:]/x) # function tbl.subtbl.foo() | function tbl:foo() # Colon only allowed as last separator
      @encoder.text_token(match, :ident)
    elsif match = scan(/[a-zA-Z_][a-zA-Z0-9_]*/) # function foo()
      @encoder.text_token(match, :function)
      @state = :initial
    elsif match = scan(/\s+/) # Between the `function' keyword and the ident may be any amount of whitespace
      @encoder.text_token(match, :space)
    else
      @encoder.text_token(getch, :error)
      @state = :initial
    end
  end

  def handle_state_goto_label_expected
    if match = scan(/[a-zA-Z_][a-zA-Z0-9_]*/)
      @encoder.text_token(match, :label)
      @state = :initial
    elsif match = scan(/\s+/) # Between the `goto' keyword and the label may be any amount of whitespace
      @encoder.text_token(match, :space)
    else
      @encoder.text_token(getch, :error)
    end
  end

  def handle_state_local_var_expected
    if match = scan(/function/) # local function ...
      @encoder.text_token(match, :keyword)
      @state = :function_expected
    elsif match = scan(/[a-zA-Z_][a-zA-Z0-9_]*/)
      @encoder.text_token(match, :local_variable)
    elsif match = scan(/,/)
      @encoder.text_token(match, :operator)
    elsif match = scan(/=/)
      @encoder.text_token(match, :operator)
      # After encountering the equal sign, arbitrary expressions are
      # allowed again, so just return to the main state for further
      # parsing.
      @state = :initial
    elsif match = scan(/\n/)
      @encoder.text_token(match, :space)
      @state = :initial
    elsif match = scan(/\s+/)
      @encoder.text_token(match, :space)
    else
      @encoder.text_token(getch, :error)
    end
  end

  def handle_state_long_comment
    if match = scan(/.*?(?=\]={#@num_equals}\])/m)
      @encoder.text_token(match, :content)

      delim = scan(/\]={#@num_equals}\]/)
      @encoder.text_token(delim, :delimiter)
    else # No terminator found till EOF
      @encoder.text_token(rest, :error)
      terminate
    end
    @encoder.end_group(:comment)
    @state = :initial
  end

  def handle_state_long_string
    if match = scan(/.*?(?=\]={#@num_equals}\])/m) # Long strings do not interpret any escape sequences
      @encoder.text_token(match, :content)

      delim = scan(/\]={#@num_equals}\]/)
      @encoder.text_token(delim, :delimiter)
    else # No terminator found till EOF
      @encoder.text_token(rest, :error)
      terminate
    end
    @encoder.end_group(:string)
    @state = :initial
  end

  def handle_state_string
    if match = scan(/[^\\#@start_delim\n]+/) # Everything except \ and the start delimiter character is string content (newlines are only allowed if preceeded by \ or \z)
      @encoder.text_token(match, :content)
    elsif match = scan(/\\(?:['"abfnrtv\\]|z\s*|x\h\h|\d{1,3}|\n)/m)
      @encoder.text_token(match, :char)
    elsif match = scan(Regexp.compile(@start_delim))
      @encoder.text_token(match, :delimiter)
      @encoder.end_group(:string)
      @state = :initial
    elsif match = scan(/\n/) # Lua forbids unescaped newlines in normal non-long strings
      @encoder.text_token("\\n\n", :error) # Visually appealing error indicator--otherwise users may wonder whether the highlighter cannot highlight multine strings
      @encoder.end_group(:string)
      @state = :initial
    else
      @encoder.text_token(getch, :error)
    end
  end

  def handle_state_table
    if match = scan(/[,;]/)
      @encoder.text_token(match, :operator)
    elsif match = scan(/[a-zA-Z_][a-zA-Z0-9_]* (?=\s*=)/x)
      @encoder.text_token(match, :key)
      @encoder.text_token(scan(/\s+/), :space) if check(/\s+/)
      @encoder.text_token(scan(/=/), :operator)
      @state = :initial
    elsif match = scan(/\s+/m)
      @encoder.text_token(match, :space)
    else
      # Note this clause doesn’t advance the scan pointer, it’s a kind of
      # "retry with other options" (the :initial state then of course
      # advances the pointer).
      @state = :initial
    end
  end

end