module.exports = grammar({
  name: "restedlang",

  rules: {
    source_file: ($) => repeat($.item),
    item: ($) => choice($._declaration, $._expression, $.attribute, $.request),

    request: ($) =>
      prec.right(seq($.request_method, $.endpoint, optional($.block))),
    request_method: (_$) => choice("get", "post", "put", "patch", "delete"),
    endpoint: ($) => choice($._expression, $.url_literal, $.pathname_literal),
    url_literal: (_$) => /https?:[^{]*/,
    pathname_literal: (_$) => /\/[^{]*/,

    _declaration: ($) => choice($.constant_declaration, $.variable_declaration),
    constant_declaration: ($) =>
      seq("set", $.constant_identifier, $._expression),
    variable_declaration: ($) => seq("let", $.identifier, "=", $._expression),

    attribute: ($) => seq("@", $.identifier, optional($.parameter_list)),

    _expression: ($) =>
      choice(
        $.call,
        $.identifier,
        $.number,
        $.string,
        $.template_string,
        $.boolean,
        $.array,
        $.object,
        "null"
      ),
    identifier: (_$) => /[a-z_][_\w]*/,
    constant_identifier: (_$) => /[A-Z_][A-Z_\d]*/,
    number: (_$) => /\d+(\.\d*)?/,
    boolean: (_$) => choice("true", "false"),
    string: (_$) => seq('"', /[^"]*/, '"'),
    template_string: ($) =>
      seq("`", repeat(choice($.template_chars, $.template_substitution)), "`"),
    template_chars: (_$) => choice(/[^`${]+/, /\$/),
    template_substitution: ($) => seq("${", $._expression, "}"),
    call: ($) => prec(1, seq($._expression, $.parameter_list)),
    array: ($) => seq("[", commaSep($._expression), "]"),
    object: ($) => seq("{", commaSep($.pair), "}"),
    pair: ($) =>
      seq(
        field("key", choice($.identifier, $.string)),
        ":",
        field("value", $._expression)
      ),

    parameter_list: ($) => seq("(", optional($._expression), ")"),

    block: ($) => seq("{", repeat($._statement), "}"),

    _statement: ($) => choice($.header_statement, $.body_statement),
    header_statement: ($) => seq("header", $.string, $._expression),
    body_statement: ($) => seq("body", $._expression),

    line_comment: (_$) => token(seq("//", /[^\r\n]*/)),
  },

  extras: ($) => [$.line_comment, /\s/],
});

/**
 * Taken from: https://github.com/tree-sitter/tree-sitter-javascript/blob/master/grammar.js#L1269
 * Creates a rule to match one or more of the rules separated by a comma
 *
 * @param {Rule} rule
 *
 * @return {SeqRule}
 *
 */
function commaSep1(rule) {
  return seq(rule, repeat(seq(",", rule)));
}

/**
 * Taken from: https://github.com/tree-sitter/tree-sitter-javascript/blob/master/grammar.js#L1269
 * Creates a rule to optionally match one or more of the rules separated by a comma
 *
 * @param {Rule} rule
 *
 * @return {ChoiceRule}
 *
 */
function commaSep(rule) {
  return optional(commaSep1(rule));
}