ceremonyclient/pebble/internal/dsl/predicates.go
Cassandra Heart 2e2a1e4789
v1.2.0 (#31)
2024-01-03 01:31:42 -06:00

137 lines
3.3 KiB
Go

// Copyright 2023 The LevelDB-Go and Pebble Authors. All rights reserved. Use
// of this source code is governed by a BSD-style license that can be found in
// the LICENSE file.
package dsl
import (
"fmt"
"go/token"
"strconv"
"strings"
"sync/atomic"
"github.com/cockroachdb/errors"
)
// Predicate encodes conditional logic that yields a boolean.
type Predicate[E any] interface {
Evaluate(E) bool
String() string
}
// Not returns a Predicate that negates the provided predicate.
func Not[E any](p Predicate[E]) Predicate[E] { return not[E]{Predicate: p} }
// And returns a Predicate that evaluates to true if all its operands evaluate
// to true.
func And[E any](preds ...Predicate[E]) Predicate[E] { return and[E](preds) }
// Or returns a Predicate that evaluates to true if any of its operands evaluate
// true.
func Or[E any](preds ...Predicate[E]) Predicate[E] { return or[E](preds) }
// OnIndex returns a Predicate that evaluates to true on its N-th call.
func OnIndex[E any](n int32) *Index[E] {
p := new(Index[E])
p.Int32.Store(n)
return p
}
// Index is a Predicate that evaluates to true only on its N-th invocation.
type Index[E any] struct {
atomic.Int32
}
// String implements fmt.Stringer.
func (p *Index[E]) String() string {
return fmt.Sprintf("(OnIndex %d)", p.Int32.Load())
}
// Evaluate implements Predicate.
func (p *Index[E]) Evaluate(E) bool { return p.Int32.Add(-1) == -1 }
type not[E any] struct {
Predicate[E]
}
func (p not[E]) String() string { return fmt.Sprintf("(Not %s)", p.Predicate.String()) }
func (p not[E]) Evaluate(e E) bool { return !p.Predicate.Evaluate(e) }
type and[E any] []Predicate[E]
func (p and[E]) String() string {
var sb strings.Builder
sb.WriteString("(And")
for i := 0; i < len(p); i++ {
sb.WriteRune(' ')
sb.WriteString(p[i].String())
}
sb.WriteRune(')')
return sb.String()
}
func (p and[E]) Evaluate(e E) bool {
ok := true
for i := range p {
ok = ok && p[i].Evaluate(e)
}
return ok
}
type or[E any] []Predicate[E]
func (p or[E]) String() string {
var sb strings.Builder
sb.WriteString("(Or")
for i := 0; i < len(p); i++ {
sb.WriteRune(' ')
sb.WriteString(p[i].String())
}
sb.WriteRune(')')
return sb.String()
}
func (p or[E]) Evaluate(e E) bool {
ok := false
for i := range p {
ok = ok || p[i].Evaluate(e)
}
return ok
}
func parseNot[E any](p *Parser[Predicate[E]], s *Scanner) Predicate[E] {
preds := parseVariadicPredicate(p, s)
if len(preds) != 1 {
panic(errors.Newf("dsl: not accepts exactly 1 argument, given %d", len(preds)))
}
return not[E]{Predicate: preds[0]}
}
func parseAnd[E any](p *Parser[Predicate[E]], s *Scanner) Predicate[E] {
return And[E](parseVariadicPredicate[E](p, s)...)
}
func parseOr[E any](p *Parser[Predicate[E]], s *Scanner) Predicate[E] {
return Or[E](parseVariadicPredicate[E](p, s)...)
}
func parseOnIndex[E any](p *Parser[Predicate[E]], s *Scanner) Predicate[E] {
i, err := strconv.ParseInt(s.Consume(token.INT).Lit, 10, 32)
if err != nil {
panic(err)
}
s.Consume(token.RPAREN)
return OnIndex[E](int32(i))
}
func parseVariadicPredicate[E any](p *Parser[Predicate[E]], s *Scanner) (ret []Predicate[E]) {
tok := s.Scan()
for tok.Kind == token.LPAREN || tok.Kind == token.IDENT {
ret = append(ret, p.ParseFromPos(s, tok))
tok = s.Scan()
}
assertTok(tok, token.RPAREN)
return ret
}