-- Copyright 2006-2020 Mitchell. See LICENSE.
-- AWK LPeg lexer.
-- Modified by Wolfgang Seeberg 2012, 2013.

local lexer = require('lexer')
local token, word_match = lexer.token, lexer.word_match
local P, S = lpeg.P, lpeg.S

local lex = lexer.new('awk')

local LEFTBRACKET = '['
local RIGHTBRACKET = ']'
local SLASH = '/'
local BACKSLASH = '\\'
local CARET = '^'
local CR = '\r'
local LF = '\n'
local CRLF = CR .. LF
local DQUOTE = '"'
local DELIMITER_MATCHES = {['('] = ')', ['['] = ']'}
local COMPANION = {['('] = '[', ['['] = '('}
local CC = {
  alnum = 1, alpha = 1, blank = 1, cntrl = 1, digit = 1, graph = 1, lower = 1,
  print = 1, punct = 1, space = 1, upper = 1, xdigit = 1
}
local LastRegexEnd = 0
local BackslashAtCommentEnd = 0
local KW_BEFORE_RX = {
  case = 1, ['do'] = 1, ['else'] = 1, exit = 1, print = 1, printf = 1,
  ['return'] = 1
}

local function findKeyword(input, e)
  local i = e
  while i > 0 and input:find("^[%l]", i) do i = i - 1 end
  local w = input:sub(i + 1, e)
  if i == 0 then
    return KW_BEFORE_RX[w] == 1
  elseif input:find("^[%u%d_]", i) then
    return false
  else
    return KW_BEFORE_RX[w] == 1
  end
end

local function isRegex(input, i)
  while i >= 1 and input:find('^[ \t]', i) do i = i - 1 end
  if i < 1 then return true end
  if input:find("^[-!%%&(*+,:;<=>?[^{|}~\f]", i) or findKeyword(input, i) then
    return true
  elseif input:sub(i, i) == SLASH then
    return i ~= LastRegexEnd -- deals with /xx/ / /yy/.
  elseif input:find('^[]%w)."]', i) then
    return false
  elseif input:sub(i, i) == LF then
    if i == 1 then return true end
    i = i - 1
    if input:sub(i, i) == CR then
      if i == 1 then return true end
      i = i - 1
    end
  elseif input:sub(i, i) == CR then
    if i == 1 then return true end
    i = i - 1
  else
    return false
  end
  if input:sub(i, i) == BACKSLASH and i ~= BackslashAtCommentEnd then
    return isRegex(input, i - 1)
  else
    return true
  end
end

local function eatCharacterClass(input, s, e)
  local i = s
  while i <= e do
    if input:find('^[\r\n]', i) then
      return false
    elseif input:sub(i, i + 1) == ':]' then
      local str = input:sub(s, i - 1)
      return CC[str] == 1 and i + 1
    end
    i = i + 1
  end
  return false
end

local function eatBrackets(input, i, e)
  if input:sub(i, i) == CARET then i = i + 1 end
  if input:sub(i, i) == RIGHTBRACKET then i = i + 1 end
  while i <= e do
    if input:find('^[\r\n]', i) then
      return false
    elseif input:sub(i, i) == RIGHTBRACKET then
      return i
    elseif input:sub(i, i + 1) == '[:' then
      i = eatCharacterClass(input, i + 2, e)
      if not i then return false end
    elseif input:sub(i, i) == BACKSLASH then
      i = i + 1
      if input:sub(i, i + 1) == CRLF then i = i + 1 end
    end
    i = i + 1
  end
  return false
end

local function eatRegex(input, i)
  local e = #input
  while i <= e do
    if input:find('^[\r\n]', i) then
      return false
    elseif input:sub(i, i) == SLASH then
      LastRegexEnd = i
      return i
    elseif input:sub(i, i) == LEFTBRACKET then
      i = eatBrackets(input, i + 1, e)
      if not i then return false end
    elseif input:sub(i, i) == BACKSLASH then
      i = i + 1
      if input:sub(i, i + 1) == CRLF then i = i + 1 end
    end
    i = i + 1
  end
  return false
end

local ScanRegexResult
local function scanGawkRegex(input, index)
  if isRegex(input, index - 2) then
    local i = eatRegex(input, index)
    if not i then
      ScanRegexResult = false
      return false
    end
    local rx = input:sub(index - 1, i)
    for bs in rx:gmatch("[^\\](\\+)[BSsWwy<>`']") do
      -- /\S/ is special, but /\\S/ is not.
      if #bs % 2 == 1 then return i + 1 end
    end
    ScanRegexResult = i + 1
  else
    ScanRegexResult = false
  end
  return false
end
-- Is only called immediately after scanGawkRegex().
local function scanRegex()
  return ScanRegexResult
end

local function scanString(input, index)
  local i = index
  local e = #input
  while i <= e do
    if input:find('^[\r\n]', i) then
      return false
    elseif input:sub(i, i) == DQUOTE then
      return i + 1
    elseif input:sub(i, i) == BACKSLASH then
      i = i + 1
      -- lexer.range() doesn't handle CRLF.
      if input:sub(i, i + 1) == CRLF then i = i + 1 end
    end
    i = i + 1
  end
  return false
end

-- purpose: prevent isRegex() from entering a comment line that ends with a
-- backslash.
local function scanComment(input, index)
  local _, i = input:find('[^\r\n]*', index)
  if input:sub(i, i) == BACKSLASH then BackslashAtCommentEnd = i end
  return i + 1
end

local function scanFieldDelimiters(input, index)
  local i = index
  local e = #input
  local left = input:sub(i - 1, i - 1)
  local count = 1
  local right = DELIMITER_MATCHES[left]
  local left2 = COMPANION[left]
  local count2 = 0
  local right2 = DELIMITER_MATCHES[left2]
  while i <= e do
    if input:find('^[#\r\n]', i) then
      return false
    elseif input:sub(i, i) == right then
      count = count - 1
      if count == 0 then return count2 == 0 and i + 1 end
    elseif input:sub(i, i) == left then
      count = count + 1
    elseif input:sub(i, i) == right2 then
      count2 = count2 - 1
      if count2 < 0 then return false end
    elseif input:sub(i, i) == left2 then
      count2 = count2 + 1
    elseif input:sub(i, i) == DQUOTE then
      i = scanString(input, i + 1)
      if not i then return false end
      i = i - 1
    elseif input:sub(i, i) == SLASH then
      if isRegex(input, i - 1) then
        i = eatRegex(input, i + 1)
        if not i then return false end
      end
    elseif input:sub(i, i) == BACKSLASH then
      if input:sub(i + 1, i + 2) == CRLF then
        i = i + 2
      elseif input:find('^[\r\n]', i + 1) then
        i = i + 1
      end
    end
    i = i + 1
  end
  return false
end

-- Whitespace.
lex:add_rule('whitespace', token(lexer.WHITESPACE, lexer.space^1))

-- Comments.
lex:add_rule('comment', token(lexer.COMMENT, '#' * P(scanComment)))

-- Strings.
lex:add_rule('string', token(lexer.STRING, DQUOTE * P(scanString)))

-- No leading sign because it might be binary.
local float =
  ((lexer.digit^1 * ('.' * lexer.digit^0)^-1) + ('.' * lexer.digit^1)) *
  (S('eE') * S('+-')^-1 * lexer.digit^1)^-1

-- Fields. E.g. $1, $a, $(x), $a(x), $a[x], $"1", $$a, etc.
lex:add_rule('field', token('field', P('$') * S('$+-')^0 * (
  float +
  lexer.word^0 * '(' * P(scanFieldDelimiters) +
  lexer.word^1 * ('[' * P(scanFieldDelimiters))^-1 +
  '"' * P(scanString) +
  '/' * P(eatRegex) * '/')))
lex:add_style('field', lexer.styles.label)

-- Regular expressions.
-- Slash delimited regular expressions are preceded by most operators or
-- the keywords 'print' and 'case', possibly on a preceding line. They
-- can contain unescaped slashes and brackets in brackets. Some escape
-- sequences like '\S', '\s' have special meanings with Gawk. Tokens that
-- contain them are displayed differently.
lex:add_rule('gawkRegex', token('gawkRegex', SLASH * P(scanGawkRegex)))
lex:add_style('gawkRegex', lexer.styles.preprocessor .. {underlined = true})
lex:add_rule('regex', token(lexer.REGEX, SLASH * P(scanRegex)))

-- Operators.
lex:add_rule('gawkOperator', token('gawkOperator', P("|&") + "@" + "**=" +
  "**"))
lex:add_style('gawkOperator', lexer.styles.operator .. {underlined = true})
lex:add_rule('operator', token(lexer.OPERATOR, S('!%&()*+,-/:;<=>?[\\]^{|}~')))

-- Numbers.
lex:add_rule('gawkNumber', token('gawkNumber', lexer.hex_num + lexer.oct_num))
lex:add_style('gawkNumber', lexer.styles.number .. {underlined = true})
lex:add_rule('number', token(lexer.NUMBER, float))

-- Keywords.
lex:add_rule('keyword', token(lexer.KEYWORD, word_match[[
  BEGIN END atan2 break close continue cos delete do else exit exp fflush for
  function getline gsub if in index int length log match next nextfile print
  printf rand return sin split sprintf sqrt srand sub substr system tolower
  toupper while
]]))

lex:add_rule('builtInVariable', token('builtInVariable', word_match[[
  ARGC ARGV CONVFMT ENVIRON FILENAME FNR FS NF NR OFMT OFS ORS RLENGTH RS RSTART
  SUBSEP
]]))
lex:add_style('builtInVariable', lexer.styles.constant)

lex:add_rule('gawkBuiltInVariable', token('gawkBuiltInVariable', word_match[[
  ARGIND BINMODE ERRNO FIELDWIDTHS FPAT FUNCTAB IGNORECASE LINT PREC PROCINFO
  ROUNDMODE RT SYMTAB TEXTDOMAIN
]]))
lex:add_style(
  'gawkBuiltInVariable', lexer.styles.constant .. {underlined = true})

-- Functions.
lex:add_rule('function', token(lexer.FUNCTION, lexer.word * #P('(')))

-- Identifiers.
lex:add_rule('identifier', token(lexer.IDENTIFIER, lexer.word))

-- Fold points.
lex:add_fold_point(lexer.OPERATOR, '{', '}')
lex:add_fold_point(lexer.COMMENT, lexer.fold_consecutive_lines('#'))

return lex
