module.exports = grammar({
  name: 'scl',
  
  extras: $ => [
    /\s/,
    $.line_comment,
    $.block_comment,
    $.c_style_comment
  ],
  
    conflicts: $ => [
      [$.case_item],
      [$.region_statement],
      [$.region_name],
      [$.case_statement],
      [$.var_declaration, $.var_temp_declaration],
      [$.var_declaration, $.var_constant_declaration],
      [$.var_declaration, $.var_retain_declaration],
      [$.var_declaration, $.var_non_retain_declaration]
    ],
  
  rules: {
    
    source_file: $ => repeat(
      choice(
        $.organization_block,
        $.function_block,
        $.function,
        $.statement
      )
    ),
    
    organization_block: $ => seq(
      'ORGANIZATION_BLOCK',
      field('name', $.string),
      optional(seq('TITLE', '=', choice($.string, $.identifier))),
      optional($.attribute_list),
      optional(seq('VERSION', ':', $.number)),
      repeat($.var_declaration),
      'BEGIN',
      repeat($.statement),
      'END_ORGANIZATION_BLOCK'
    ),
    
    function_block: $ => seq(
      'FUNCTION_BLOCK',
      field('name', $.string),
      optional(seq('TITLE', '=', choice($.string, $.identifier))),
      optional($.attribute_list),
      optional(seq('VERSION', ':', $.number)),
      repeat($.var_declaration),
      'BEGIN',
      repeat($.statement),
      'END_FUNCTION_BLOCK'
    ),

    function: $ => seq(
      'FUNCTION',
      field('name', $.string),
      optional(seq(':', $.type)),
      optional(seq('TITLE', '=', choice($.string, $.identifier))),
      optional($.attribute_list),
      optional(seq('VERSION', ':', $.number)),
      repeat(choice(
        $.var_declaration,
        $.var_temp_declaration,
        $.var_constant_declaration,
        $.var_retain_declaration,
        $.var_non_retain_declaration,
        $.block_comment
      )),
      'BEGIN',
      repeat($.statement),
      'END_FUNCTION'
    ),
    
    attribute_list: $ => seq(
      '{',
      $.attribute,
      repeat(seq(choice(',', ';'), $.attribute)),
      optional(choice(',', ';')),
      '}'
    ),
    
    attribute: $ => seq(
      $.identifier,
      ':=',
      $.attribute_value
    ),
    
    attribute_value: $ => choice(
      $.string,
      'TRUE', 'FALSE',
      $.identifier
    ),
    
    var_declaration: $ => seq(
      choice(
        'VAR_INPUT',
        'VAR_OUTPUT',
        'VAR_IN_OUT',
        'VAR',
        'VAR_TEMP',
        seq('VAR', 'CONSTANT'),
        seq('VAR', 'RETAIN'),
        seq('VAR', 'NON_RETAIN'),
        'VAR_CONSTANT',
        'VAR_RETAIN',
        'VAR_NON_RETAIN'
      ),
      repeat(choice($.var_item, $.block_comment)),
      'END_VAR'
    ),

    var_temp_declaration: $ => seq(
      'VAR_TEMP',
      repeat(choice($.var_item, $.block_comment)),
      'END_VAR'
    ),

    var_constant_declaration: $ => seq(
      choice(
        seq('VAR', 'CONSTANT'),
        'VAR_CONSTANT'
      ),
      repeat(choice($.var_item, $.block_comment)),
      'END_VAR'
    ),

    var_retain_declaration: $ => seq(
      choice(
        seq('VAR', 'RETAIN'),
        'VAR_RETAIN'
      ),
      repeat(choice($.var_item, $.block_comment)),
      'END_VAR'
    ),

    var_non_retain_declaration: $ => seq(
      choice(
        seq('VAR', 'NON_RETAIN'),
        'VAR_NON_RETAIN'
      ),
      repeat(choice($.var_item, $.block_comment)),
      'END_VAR'
    ),
    
    var_item: $ => seq(
      field('name', $.identifier),
      optional($.attribute_list),
      ':',
      field('type', $.type),
      optional(seq(':=', $.expression)),
      ';'
    ),
    
    type: $ => choice(
      'BOOL', 'Bool',
      'INT', 'Int', 'int',
      'DINT', 'DInt', 'dint',
      'SINT', 'SInt', 'sint',
      'USINT', 'USInt', 'usint',
      'UINT', 'UInt', 'uint',
      'WORD', 'Word', 'word',
      'DWORD', 'DWord', 'dword',
      'BYTE', 'Byte', 'byte',
      'REAL', 'Real', 'real',
      'LREAL', 'LReal', 'lreal',
      'TIME', 'Time', 'time',
      'TOD', 'Tod', 'tod',
      'DT', 'Dt', 'dt',
      'String', 'STRING', 'string',
      seq(choice('String', 'STRING', 'string'), '[', $.number, ']'),
      'WString', 'WSTRING', 'wstring',
      seq(choice('WString', 'WSTRING', 'wstring'), '[', $.number, ']'),
      'Char', 'CHAR', 'char',
      'WChar', 'WCHAR', 'wchar',
      seq('ARRAY', '[', $.number, '..', $.number, ']', 'OF', $.type),
      $.identifier,
      $.string
    ),
    
    statement: $ => choice(
      $.assignment,
      $.if_statement,
      $.case_statement,
      $.for_statement,
      $.while_statement,
      $.repeat_statement,
      $.region_statement,
      $.function_call,
      $.exit_statement,
      $.continue_statement,
      $.empty_statement,
      $.var_declaration,
      $.var_temp_declaration,
      $.var_constant_declaration,
      $.var_retain_declaration,
      $.var_non_retain_declaration
    ),

    empty_statement: $ => ';',
    
    assignment: $ => seq(
      field('target', $.lvalue),
      ':=',
      field('value', $.expression),
      ';'
    ),
    
    lvalue: $ => choice(
      $.identifier,
      $.prefixed_identifier,
      $.field_access,
      $.array_access,
      $.function_name
    ),

    function_name: $ => $.string,
    
    prefixed_identifier: $ => seq('#', $.identifier),
    
    field_access: $ => seq($.lvalue, '.', choice($.identifier, $.prefixed_identifier)),
    
    array_access: $ => seq($.lvalue, '[', $.expression, ']'),
    
    if_statement: $ => seq(
      'IF', $.expression, 'THEN',
      repeat($.statement),
      repeat($.elsif_clause),
      optional($.else_clause),
      'END_IF'
    ),
    
    elsif_clause: $ => seq(
      'ELSIF', $.expression, 'THEN', repeat($.statement)
    ),
    
    else_clause: $ => seq('ELSE', repeat($.statement)),
    
    case_statement: $ => seq(
      'CASE', $.expression, 'OF',
      repeat($.case_item),
      optional($.else_clause),
      'END_CASE',
      optional(';')
    ),
    
    case_item: $ => seq(
      choice($.number, $.identifier, $.prefixed_identifier, $.range),
      ':', repeat($.statement)
    ),
    
    range: $ => seq($.number, '..', $.number),
    
    for_statement: $ => seq(
      'FOR', $.identifier, ':=', $.expression, 'TO', $.expression, optional(seq('BY', $.expression)), 'DO',
      repeat($.statement),
      'END_FOR'
    ),

    while_statement: $ => seq(
      'WHILE', $.expression, 'DO',
      repeat($.statement),
      'END_WHILE'
    ),

    repeat_statement: $ => seq(
      'REPEAT',
      repeat($.statement),
      'UNTIL', $.expression, 'END_REPEAT'
    ),
    
    region_statement: $ => seq(
      'REGION', $.region_name,
      repeat($.statement),
      'END_REGION',
      optional($.region_name)
    ),

    region_name: $ => repeat1(
      choice(
        $.identifier,
        $.string,
        '/',
        '-'
      )
    ),
    
    function_call: $ => seq(
      choice($.identifier, $.string),
      '(',
      optional(seq(
        $.parameter_list,
        optional(seq('=>', $.identifier))
      )),
      ')'
    ),
    
    parameter_list: $ => seq(
      $.parameter,
      repeat(seq(',', $.parameter))
    ),
    
    parameter: $ => seq($.identifier, ':=', $.expression),
    
    expression: $ => choice(
      $.number,
      $.hex_number,
      $.time_value,
      $.identifier,
      $.prefixed_identifier,
      $.field_access,
      $.array_access,
      $.string,
      $.function_call,
      $.unary_expression,
      $.binary_expression,
      seq('(', $.expression, ')')
    ),
    
    unary_expression: $ => prec.right(10, choice(
      seq('NOT', $.expression),
      seq('+', $.expression),
      seq('-', $.expression)
    )),
    
    binary_expression: $ => choice(
      prec.left(2, seq($.expression, 'OR', $.expression)),
      prec.left(3, seq($.expression, 'XOR', $.expression)),
      prec.left(4, seq($.expression, 'AND', $.expression)),
      prec.left(5, seq($.expression, choice('=', '<>'), $.expression)),
      prec.left(6, seq($.expression, choice('<', '>', '<=', '>='), $.expression)),
      prec.left(7, seq($.expression, choice('+', '-'), $.expression)),
      prec.left(8, seq($.expression, choice('*', '/', 'MOD'), $.expression))
    ),
    
    number: $ => token(/\d+(\.\d+)?/),
    
    hex_number: $ => token(seq('16#', /[0-9A-Fa-f_]+/)),
    
    time_value: $ => token(seq('T#', /\d+(_?\d)*(ms|s|min|h)/)),
    
    string: $ => choice(
      seq("'", repeat(choice(/[^'\n]/, "''")), "'"),
      seq('"', repeat(choice(/[^"\n]/, '""')), '"')
    ),

    // Support for STRING type with length: STRING[80]
    string_type: $ => seq(
      choice('STRING', 'String', 'string', 'WSTRING', 'WString', 'wstring'),
      optional(seq('[', $.number, ']'))
    ),

    // Support for SCL character literals: 'A', WCHAR#'B'
    char_literal: $ => choice(
      seq("'", /[^']/, "'"),
      seq('WCHAR#', "'", /[^']/, "'")
    ),
    
    identifier: $ => /[a-zA-Z_][a-zA-Z0-9_]*/,
    
    line_comment: $ => token(seq('//', /.*/)),
    
    block_comment: $ => token(seq(
      '(*',
      repeat(choice(/[^*]/, seq('*', /[^)]/))),
      '*)'
    )),

    c_style_comment: $ => token(seq(
      '(/*',
      repeat(choice(/[^*]/, seq('*', /[^)]/))),
      '*/)'
    )),

    exit_statement: $ => 'EXIT',

    continue_statement: $ => 'CONTINUE'
    
  }
});