-- Copyright 2017 Michael Forney. See LICENSE.
-- Copyright 2017 David B. Lamkins. See LICENSE.
-- xs LPeg lexer.

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

local M = {_NAME = 'xs'}

-- Whitespace.
local ws = token(l.WHITESPACE, l.space^1)

-- Comments.
local comment = token(l.COMMENT, '#' * l.nonnewline^0)

-- Strings.
local str = l.delimited_range("'", false, true)
local herestr = '<<<' * str
local heredoc = '<<' * P(function(input, index)
  local s, e, _, delimiter =
    input:find('[ \t]*(["\']?)([%w!"%%+,-./:?@_~]+)%1', index)
  if s == index and delimiter then
    delimiter = delimiter:gsub('[%%+-.?]', '%%%1')
    local _, e = input:find('[\n\r]'..delimiter..'[\n\r]', e)
    return e and e + 1 or #input + 1
  end
end)
local string = token(l.STRING, str + herestr + heredoc)

-- Numbers.
local number = token(l.NUMBER, l.integer + l.float)

-- Keywords.
local keyword = token(l.KEYWORD, word_match({
  'access', 'alias', 'catch', 'cd', 'dirs', 'echo', 'else', 'escape', 'eval',
  'exec', 'exit', 'false', 'fn-', 'fn', 'for', 'forever', 'fork', 'history',
  'if', 'jobs', 'let', 'limit', 'local', 'map', 'omap', 'popd', 'printf',
  'pushd', 'read', 'result', 'set-', 'switch', 'throw', 'time', 'true',
  'umask', 'until', 'unwind-protect', 'var', 'vars', 'wait', 'whats', 'while',
  ':lt', ':le', ':gt', ':ge', ':eq', ':ne', '~', '~~', '...', '.',
}, '!"%*+,-./:?@[]~'))

-- Constants.
local constant = token(l.CONSTANT, '$&' * l.word)

-- Identifiers.
local identifier = token(l.IDENTIFIER, l.word)

-- Variables.
local variable = token(l.VARIABLE,
                       '$' * S('"#')^-1 * ('*' + l.digit^1 + l.word))

-- Operators.
local operator = token(l.OPERATOR, S('@`=!<>*&^|;?()[]{}') + '\\\n')

M._rules = {
  {'whitespace', ws},
  {'keyword', keyword},
  {'constant', constant},
  {'identifier', identifier},
  {'string', string},
  {'comment', comment},
  {'number', number},
  {'variable', variable},
  {'operator', operator},
}

M._foldsymbols = {
  _patterns = {'[{}]', '#'},
  [l.OPERATOR] = {['{'] = 1, ['}'] = -1},
  [l.COMMENT] = {['#'] = l.fold_line_comments('#')}
}

return M