module.exports = grammar({
  name: 'scl',
  
  extras: $ => [
    /\s/,
    $.line_comment,
    $.block_comment,
    $.c_style_comment
  ],
  
    conflicts: $ => [
      [$.case_item],
      [$.region_statement],
      [$.region_name],
      [$.case_statement],
      [$.fb_call, $.function_call],
      [$.fb_parameter, $.parameter],
      [$.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,
        $.type_definition,
        $.data_block,
        $.statement
      )
    ),
    
    type_definition: $ => seq(
      alias('TYPE', $.keyword),
      field('name', choice($.string, $.identifier)),
      optional(seq(alias('TITLE', $.keyword), '=', choice($.string, $.identifier))),
      optional($.attribute_list),
      optional(seq(alias('VERSION', $.keyword), ':', $.number)),
      alias('STRUCT', $.keyword),
      repeat(choice($.var_item, $.block_comment)),
      alias('END_STRUCT', $.keyword),
      alias('END_TYPE', $.keyword)
    ),
    
    data_block: $ => seq(
      alias('DATA_BLOCK', $.keyword),
      field('name', choice($.string, $.identifier)),
      optional(seq(alias('TITLE', $.keyword), '=', choice($.string, $.identifier))),
      optional($.attribute_list),
      optional(seq(alias('VERSION', $.keyword), ':', $.number)),
      optional(choice(
        alias('NON_RETAIN', $.keyword),
        alias('RETAIN', $.keyword)
      )),
      optional($.var_declaration),
      alias('BEGIN', $.keyword),
      repeat($.statement),
      alias('END_DATA_BLOCK', $.keyword)
    ),
    
    organization_block: $ => seq(
      alias('ORGANIZATION_BLOCK', $.keyword),
      field('name', $.string),
      optional(seq(alias('TITLE', $.keyword), '=', choice($.string, $.identifier))),
      optional($.attribute_list),
      optional(seq(alias('VERSION', $.keyword), ':', $.number)),
      repeat($.var_declaration),
      alias('BEGIN', $.keyword),
      repeat($.statement),
      alias('END_ORGANIZATION_BLOCK', $.keyword)
    ),
    
    function_block: $ => seq(
      alias('FUNCTION_BLOCK', $.keyword),
      field('name', $.string),
      optional(seq(alias('TITLE', $.keyword), '=', choice($.string, $.identifier))),
      optional($.attribute_list),
      optional(seq(alias('VERSION', $.keyword), ':', $.number)),
      repeat($.var_declaration),
      alias('BEGIN', $.keyword),
      repeat($.statement),
      alias('END_FUNCTION_BLOCK', $.keyword)
    ),

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

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

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

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

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

    fb_call: $ => seq(
      field('instance', choice($.prefixed_identifier, $.identifier)),
      '(',
      optional(seq(
        $.fb_parameter_list
      )),
      ')'
    ),

    fb_parameter_list: $ => seq(
      $.fb_parameter,
      repeat(seq(',', $.fb_parameter))
    ),

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

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

    repeat_statement: $ => seq(
      alias('REPEAT', $.keyword),
      repeat($.statement),
      alias('UNTIL', $.keyword),
      $.expression,
      alias('END_REPEAT', $.keyword)
    ),
    
    region_statement: $ => seq(
      alias('REGION', $.keyword),
      $.region_name,
      repeat($.statement),
      alias('END_REGION', $.keyword),
      optional($.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(alias('NOT', $.operator), $.expression),
      seq('+', $.expression),
      seq('-', $.expression)
    )),
    
    binary_expression: $ => choice(
      prec.left(2, seq($.expression, alias('OR', $.operator), $.expression)),
      prec.left(3, seq($.expression, alias('XOR', $.operator), $.expression)),
      prec.left(4, seq($.expression, alias('AND', $.operator), $.expression)),
      prec.left(5, seq($.expression, choice('=', '<>'), $.expression)),
      prec.left(6, seq($.expression, choice('<', '>', '<=', '>='), $.expression)),
      prec.left(7, seq($.expression, choice('+', '-'), $.expression)),
      prec.left(8, seq($.expression, choice('*', '/', alias('MOD', $.operator)), $.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]/, '""')), '"')
    ),

    string_type: $ => seq(
      choice(alias('STRING', $.type_builtin), alias('String', $.type_builtin), alias('string', $.type_builtin), alias('WSTRING', $.type_builtin), alias('WString', $.type_builtin), alias('wstring', $.type_builtin)),
      optional(seq('[', $.number, ']'))
    ),

    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: $ => alias('EXIT', $.keyword),

    continue_statement: $ => alias('CONTINUE', $.keyword)
    
  }
});