// Copyright 2021 Google LLC
// 
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
// 
// https://www.apache.org/licenses/LICENSE-2.0
// 
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

identifier_part = @{ (ASCII_ALPHANUMERIC | "_" | "@" | "/")+ }
identifier = @{
  identifier_part ~ ("." | "-" | "+" ) ~ identifier
  | identifier_part
}
symbol = {
  identifier
  | literal_string
}
literal_string = { "\"" ~ (!"\"" ~ ANY)* ~ "\"" }
whitespace = _{ " " }

parents_op = { "-" }
children_op = { "+" }

dag_range_op = { ":" }
range_op = { ".." }
range_ops = _{ dag_range_op | range_op }

union_op = { "|" }
intersection_op = { "&" }
difference_op = { "~" }
infix_op = _{ union_op | intersection_op | difference_op }

function_name = @{ (ASCII_ALPHANUMERIC | "_")+ }
function_arguments = {
  (whitespace* ~ expression ~ whitespace* ~ ",")* ~ whitespace* ~ expression ~ whitespace*
  | whitespace*
}

primary = {
  function_name ~ "(" ~ function_arguments ~ ")"
  | "(" ~ expression ~ ")"
  | symbol
}

neighbors_expression = { primary ~ (parents_op | children_op)* }

range_expression = {
  neighbors_expression ~ range_ops ~ neighbors_expression
  | neighbors_expression ~ range_ops
  | range_ops ~ neighbors_expression
  | neighbors_expression
}

infix_expression = {
  whitespace* ~ range_expression ~ whitespace* ~ (infix_op ~ whitespace* ~ range_expression ~ whitespace*)*
}

expression = {
  whitespace* ~ infix_expression ~ whitespace*
}

program = _{ SOI ~ expression ~ EOI }