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// Copyright (c) 2017 Couchbase, Inc.
//
// 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
//
// http://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.
package vellum
// Automaton represents the general contract of a byte-based finite automaton
type Automaton interface {
// Start returns the start state
Start() int
// IsMatch returns true if and only if the state is a match
IsMatch(int) bool
// CanMatch returns true if and only if it is possible to reach a match
// in zero or more steps
CanMatch(int) bool
// WillAlwaysMatch returns true if and only if the current state matches
// and will always match no matter what steps are taken
WillAlwaysMatch(int) bool
// Accept returns the next state given the input to the specified state
Accept(int, byte) int
}
// AutomatonContains implements an generic Contains() method which works
// on any implementation of Automaton
func AutomatonContains(a Automaton, k []byte) bool {
i := 0
curr := a.Start()
for a.CanMatch(curr) && i < len(k) {
curr = a.Accept(curr, k[i])
if curr == noneAddr {
break
}
i++
}
if i != len(k) {
return false
}
return a.IsMatch(curr)
}
// AlwaysMatch is an Automaton implementation which always matches
type AlwaysMatch struct{}
// Start returns the AlwaysMatch start state
func (m *AlwaysMatch) Start() int {
return 0
}
// IsMatch always returns true
func (m *AlwaysMatch) IsMatch(int) bool {
return true
}
// CanMatch always returns true
func (m *AlwaysMatch) CanMatch(int) bool {
return true
}
// WillAlwaysMatch always returns true
func (m *AlwaysMatch) WillAlwaysMatch(int) bool {
return true
}
// Accept returns the next AlwaysMatch state
func (m *AlwaysMatch) Accept(int, byte) int {
return 0
}
// creating an alwaysMatchAutomaton to avoid unnecessary repeated allocations.
var alwaysMatchAutomaton = &AlwaysMatch{}
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