const PREC = {
  COMMA: -1,
  PRIORITY: 1,

  OR: 1,        //=> or
  AND: 2,       //=> and
  COMPARE: 3,   //=> < <= == ~= >= >
  BIT_OR: 4,    //=> |
  BIT_NOT: 5,   //=> ~
  BIT_AND: 6,   //=> &
  SHIFT: 7,     //=> << >>
  CONCAT: 8,    //=> ..
  PLUS: 9,      //=> + -
  MULTI: 10,    //=> * / // %
  UNARY: 11,    //=> not # - ~
  POWER: 12     //=> ^
}

module.exports = grammar({
  name: 'lua',

  extras: $ => [
    $.comment,
    /[\s\n]/
  ],

  inline: $ => [
    $._statement
  ],

  conflicts: $ => [
    [$._prefix],
    [$._expression, $._variable_declarator],
    [$._expression, $.function_call_statement],
    [$.function_name, $.function_name_field]
  ],

  externals: $ => [
    $.comment,
    $.string
  ],

  rules: {
    program: $ => seq(repeat($._statement), optional($.return_statement)),

    // Return statement
    return_statement: $ => seq(
      'return',
      optional(commaSeq($._expression)),
      optional($._empty_statement)
    ),

    // Statements
    _statement: $ => choice(
      alias($._expression, $.expression),

      $.variable_declaration,
      $.local_variable_declaration,

      $.do_statement,
      $.if_statement,
      $.while_statement,
      $.repeat_statement,
      $.for_statement,
      $.for_in_statement,

      $.goto_statement,
      $.break_statement,

      $.label_statement,
      $._empty_statement,

      alias($.function_statement, $.function),
      alias($.local_function_statement, $.local_function),
      alias($.function_call_statement, $.function_call)
    ),

    // Statements: Variable eclarations
    variable_declaration: $ => seq(
      commaSeq(alias($._variable_declarator, $.variable_declarator)),
      '=',
      commaSeq($._expression)
    ),

    local_variable_declaration: $ => seq(
      'local',
      alias($._local_variable_declarator, $.variable_declarator),
      optional(seq('=', commaSeq($._expression)))
    ),

    _variable_declarator: $ => choice(
      $.identifier,
      seq($._prefix, '[', $._expression, ']'),
      $.field_expression
    ),

    field_expression: $ => seq($._prefix, '.', alias($.identifier, $.property_identifier)),

    _local_variable_declarator: $ => commaSeq($.identifier),

    // Statements: Control statements
    do_statement: $ => seq(
      'do',
      repeat($._statement),
      optional($.return_statement),
      'end'
    ),

    if_statement: $ => seq(
      'if',
      alias($._expression, $.condition_expression),
      'then',
      repeat($._statement),
      optional($.return_statement),
      repeat($.elseif),
      optional($.else),
      'end'
    ),

    elseif: $ => seq(
      'elseif',
      alias($._expression, $.condition_expression),
      'then',
      repeat($._statement),
      optional($.return_statement)
    ),

    else: $ => seq(
      'else',
      repeat($._statement),
      optional($.return_statement)
    ),

    while_statement: $ => seq(
      'while',
      alias($._expression, $.condition_expression),
      'do',
      repeat($._statement),
      optional($.return_statement),
      'end'
    ),

    repeat_statement: $ => seq(
      'repeat',
      repeat($._statement),
      optional($.return_statement),
      'until',
      alias($._expression, $.condition_expression)
    ),

    // Statements: For statements
    for_statement: $ => seq(
      'for',
      alias($._loop_expression, $.loop_expression),
      'do',
      repeat($._statement),
      optional($.return_statement),
      'end'
    ),

    for_in_statement: $ => seq(
      'for',
      alias($._in_loop_expression, $.loop_expression),
      'do',
      repeat($._statement),
      optional($.return_statement),
      'end'
    ),

    _loop_expression: $ => seq(
      $.identifier,
      '=',
      $._expression,
      ',',
      $._expression,
      optional(seq(',', $._expression))
    ),

    _in_loop_expression: $ => seq(
      commaSeq($.identifier),
      'in',
      commaSeq($._expression),
    ),

    // Statements: Simple statements
    goto_statement: $ => seq(
      'goto',
      $.identifier
    ),

    break_statement: $ => 'break',

    // Statements: Void statements
    label_statement: $ => seq(
      '::',
      $.identifier,
      '::'
    ),

    _empty_statement: $ => ';',

    // Statements: Function statements
    function_statement: $ => seq(
      'function',
      $.function_name,
      $._function_body
    ),

    local_function_statement: $ => seq(
      'local',
      'function',
      $.identifier,
      $._function_body
    ),

    function_call_statement: $ => prec.dynamic(PREC.PRIORITY, choice(
      seq($._prefix, $.arguments),
      seq($._prefix, ':', alias($.identifier, $.method), $.arguments)
    )),

    arguments: $ => choice(
      seq('(', optional(commaSeq($._expression)), ')'),
      $.table,
      $.string
    ),

    function_name: $ => seq(
      choice($.identifier,
        $.function_name_field
      ),
      optional(seq(':', alias($.identifier, $.method)))
    ),

    function_name_field: $ => seq(
      field("object", $.identifier),
      repeat(seq('.', alias($.identifier, $.property_identifier))),
    ),

    parameters: $ => seq(
      '(',
      optional(seq(
        choice($.self, $.spread, $.identifier),
        repeat(seq(',', $.identifier)),
        optional(seq(',', $.spread))
      )),
      ')'
    ),

    _function_body: $ => seq(
      $.parameters,
      repeat($._statement),
      optional($.return_statement),
      'end'
    ),

    // Expressions
    _expression: $ => choice(
      $.spread,
      $._prefix,

      $.next,

      $.function_definition,

      $.table,

      $.binary_operation,
      $.unary_operation,

      $.string,
      $.number,
      $.nil,
      $.true,
      $.false,
      $.identifier
    ),

    // Expressions: Common
    spread: $ => '...',

    self: $ => 'self',

    next: $ => 'next',

    global_variable: $ => choice('_G', '_VERSION'),

    _prefix: $ => choice(
      $.self,
      $.global_variable,
      $._variable_declarator,
      prec(-1, alias($.function_call_statement, $.function_call)),
      seq('(', $._expression, ')')
    ),

    // Expressions: Function definition
    function_definition: $ => seq(
      'function',
      $._function_body
    ),

    // Expressions: Table expressions
    table: $ => seq(
      '{',
      optional($._field_sequence),
      '}'
    ),

    field: $ => choice(
      seq('[', $._expression, ']', '=', $._expression),
      seq($.identifier, '=', $._expression),
      $._expression
    ),

    _field_sequence: $ => prec(PREC.COMMA, seq(
      $.field,
      repeat(seq($._field_sep, $.field)),
      optional($._field_sep)
    )),

    _field_sep: $ => choice(',', ';'),

    // Expressions: Operation expressions
    binary_operation: $ => choice(
      ...[
        ['or', PREC.OR],
        ['and', PREC.AND],
        ['<', PREC.COMPARE],
        ['<=', PREC.COMPARE],
        ['==', PREC.COMPARE],
        ['~=', PREC.COMPARE],
        ['>=', PREC.COMPARE],
        ['>', PREC.COMPARE],
        ['|', PREC.BIT_OR],
        ['~', PREC.BIT_NOT],
        ['&', PREC.BIT_AND],
        ['<<', PREC.SHIFT],
        ['>>', PREC.SHIFT],
        ['+', PREC.PLUS],
        ['-', PREC.PLUS],
        ['*', PREC.MULTI],
        ['/', PREC.MULTI],
        ['//', PREC.MULTI],
        ['%', PREC.MULTI],
      ].map(([operator, precedence]) => prec.left(precedence, seq(
        $._expression,
        operator,
        $._expression
      ))),
      ...[
        ['..', PREC.CONCAT],
        ['^', PREC.POWER],
      ].map(([operator, precedence]) => prec.right(precedence, seq(
        $._expression,
        operator,
        $._expression
      )))
    ),

    unary_operation: $ => prec.left(PREC.UNARY, seq(
      choice('not', '#', '-', '~'),
      $._expression
    )),

    // Expressions: Primitives
    number: $ => {
      const decimal_digits = /[0-9]+/
      const signed_integer = seq(optional(choice('-', '+')), decimal_digits)
      const decimal_exponent_part = seq(choice('e', 'E'), signed_integer)

      const decimal_integer_literal = choice(
        '0',
        seq(optional('0'), /[1-9]/, optional(decimal_digits))
      )

      const hex_digits = /[a-fA-F0-9]+/
      const hex_exponent_part = seq(choice('p', 'P'), signed_integer)

      const decimal_literal = choice(
        seq(decimal_integer_literal, '.', optional(decimal_digits), optional(decimal_exponent_part)),
        seq('.', decimal_digits, optional(decimal_exponent_part)),
        seq(decimal_integer_literal, optional(decimal_exponent_part))
      )

      const hex_literal = seq(
        choice('0x', '0X'),
        hex_digits,
        optional(seq('.', hex_digits)),
        optional(hex_exponent_part)
      )

      return token(choice(
        decimal_literal,
        hex_literal
      ))
    },

    nil: $ => 'nil',
    true: $ => 'true',
    false: $ => 'false',

    // Identifier
    identifier: $ => /[a-zA-Z_][a-zA-Z0-9_]*/
  }
})

function commaSeq(rule) {
  return seq(rule, repeat(seq(',', rule)))
}