// Grammar for the FilterBar query language.
//
// Supports:
//   - regex("...")                      raw-text regex search over log lines
//   - metric_name[param] <op> value     metric comparisons
//   - json[field] <op> value            JSON field comparisons (line parsed as JSON)
//   - sequence <op> value               reserved metric name (no [param])
//   - timestamp <op> value              reserved metric name (no [param])
//   - `and` / `or` boolean combinators, with `and` binding tighter than `or`
//   - parenthesized sub-expressions

WHITESPACE = _{ " " | "\t" | "\n" | "\r" }

file = { SOI ~ or_expr ~ EOI }

or_expr = { and_expr ~ (or_kw ~ and_expr)* }
and_expr = { term ~ (and_kw ~ term)* }

term = _{ regex_expr | comparison | "(" ~ or_expr ~ ")" }

// These must be atomic (`@`): a non-atomic rule would let pest's implicit
// whitespace insertion slip in between the keyword and its own boundary
// check below, which breaks the lookahead (it would see the first
// non-whitespace character *after* skipping the separating space, instead
// of the character immediately following the keyword).
and_kw = @{ "and" ~ !(ASCII_ALPHANUMERIC | "_") }
or_kw = @{ "or" ~ !(ASCII_ALPHANUMERIC | "_") }

regex_expr = { "regex" ~ "(" ~ string_literal ~ ")" }

string_literal = ${ "\"" ~ inner_str ~ "\"" }
inner_str = @{ (escaped_char | !("\"" | "\\") ~ ANY)* }
escaped_char = @{ "\\" ~ ANY }

comparison = _{ json_comparison | metric_comparison }

// `json[field] <op> value` must be tried before `metric_comparison` since "json" is
// otherwise a syntactically valid (if never declared) metric name.
json_comparison = { "json" ~ "[" ~ param ~ "]" ~ op ~ value }
metric_comparison = { metric ~ ("[" ~ param ~ "]")? ~ op ~ value }

metric = @{ ident }
param = @{ ident }
ident = @{ (ASCII_ALPHANUMERIC | "_")+ }

op = { "<=" | ">=" | "==" | "!=" | "<" | ">" }

value = @{ (!(WHITESPACE | ")") ~ ANY)+ }