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85 lines
2.2 KiB
85 lines
2.2 KiB
// Copyright (c) 2017 Couchbase, Inc.
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//
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package vellum
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// Automaton represents the general contract of a byte-based finite automaton
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type Automaton interface {
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// Start returns the start state
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Start() int
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// IsMatch returns true if and only if the state is a match
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IsMatch(int) bool
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// CanMatch returns true if and only if it is possible to reach a match
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// in zero or more steps
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CanMatch(int) bool
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// WillAlwaysMatch returns true if and only if the current state matches
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// and will always match no matter what steps are taken
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WillAlwaysMatch(int) bool
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// Accept returns the next state given the input to the specified state
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Accept(int, byte) int
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}
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// AutomatonContains implements an generic Contains() method which works
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// on any implementation of Automaton
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func AutomatonContains(a Automaton, k []byte) bool {
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i := 0
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curr := a.Start()
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for a.CanMatch(curr) && i < len(k) {
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curr = a.Accept(curr, k[i])
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if curr == noneAddr {
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break
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}
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i++
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}
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if i != len(k) {
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return false
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}
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return a.IsMatch(curr)
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}
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// AlwaysMatch is an Automaton implementation which always matches
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type AlwaysMatch struct{}
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// Start returns the AlwaysMatch start state
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func (m *AlwaysMatch) Start() int {
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return 0
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}
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// IsMatch always returns true
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func (m *AlwaysMatch) IsMatch(int) bool {
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return true
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}
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// CanMatch always returns true
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func (m *AlwaysMatch) CanMatch(int) bool {
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return true
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}
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// WillAlwaysMatch always returns true
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func (m *AlwaysMatch) WillAlwaysMatch(int) bool {
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return true
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}
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// Accept returns the next AlwaysMatch state
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func (m *AlwaysMatch) Accept(int, byte) int {
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return 0
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}
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// creating an alwaysMatchAutomaton to avoid unnecessary repeated allocations.
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var alwaysMatchAutomaton = &AlwaysMatch{}
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