Move the source files into a new default directory.

src/main/java/org/nwapw/abacus/lexing/Lexer.java

@@ -0,0 +1,144 @@
+package org.nwapw.abacus.lexing;
+
+import org.nwapw.abacus.lexing.pattern.EndNode;
+import org.nwapw.abacus.lexing.pattern.Match;
+import org.nwapw.abacus.lexing.pattern.Pattern;
+import org.nwapw.abacus.lexing.pattern.PatternNode;
+
+import java.util.*;
+
+/**
+ * A lexer that can generate tokens of a given type given a list of regular expressions
+ * to operate on.
+ * @param <T> the type used to identify which match belongs to which pattern.
+ */
+public class Lexer<T> {
+
+    /**
+     * An entry that represents a pattern that has been registered with the lexer.
+     * @param <T> the type used to identify the pattern.
+     */
+    private static class PatternEntry<T>{
+        /**
+         * The name of the entry.
+         */
+        public String name;
+        /**
+         * The id of the entry.
+         */
+        public T id;
+
+        /**
+         * Creates a new pattern entry with the given name and id.
+         * @param name the name of the pattern entry.
+         * @param id the id of the pattern entry.
+         */
+        public PatternEntry(String name, T id){
+            this.name = name;
+            this.id = id;
+        }
+
+        @Override
+        public int hashCode() {
+            return Objects.hash(name, id);
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            return obj instanceof PatternEntry &&
+                    ((PatternEntry) obj).name.equals(name) &&
+                    ((PatternEntry) obj).id.equals(id);
+        }
+    }
+
+    /**
+     * The registered patterns.
+     */
+    private Map<PatternEntry<T>, Pattern<T>> patterns;
+
+    /**
+     * Creates a new lexer with no registered patterns.
+     */
+    public Lexer(){
+        patterns = new HashMap<>();
+    }
+
+    /**
+     * Registers a single pattern.
+     * @param pattern the pattern regex
+     * @param id the ID by which to identify the pattern.
+     */
+    public void register(String pattern, T id){
+        Pattern<T> compiledPattern = new Pattern<>(pattern, id);
+        if(compiledPattern.getHead() != null) patterns.put(new PatternEntry<>(pattern, id), compiledPattern);
+    }
+
+    /**
+     * Unregisters a pattern.
+     * @param pattern the pattern to unregister
+     * @param id the ID by which to identify the pattern.
+     */
+    public void unregister(String pattern, T id){
+        patterns.remove(new PatternEntry<>(pattern, id));
+    }
+
+    /**
+     * Reads one token from the given string.
+     * @param from the string to read from
+     * @param startAt the index to start at
+     * @param compare the comparator used to sort tokens by their ID.
+     * @return the best match.
+     */
+    public Match<T> lexOne(String from, int startAt, Comparator<T> compare){
+        ArrayList<Match<T>> matches = new ArrayList<>();
+        HashSet<PatternNode<T>> currentSet = new HashSet<>();
+        HashSet<PatternNode<T>> futureSet = new HashSet<>();
+        int index = startAt;
+        for(Pattern<T> pattern : patterns.values()){
+            pattern.getHead().addInto(currentSet);
+        }
+        while(!currentSet.isEmpty()){
+            for(PatternNode<T> node : currentSet){
+                if(index < from.length() && node.matches(from.charAt(index))) {
+                    node.addOutputsInto(futureSet);
+                } else if(node instanceof EndNode){
+                    matches.add(new Match<>(from.substring(startAt, index), ((EndNode<T>) node).getPatternId()));
+                }
+            }
+
+            HashSet<PatternNode<T>> tmp = currentSet;
+            currentSet = futureSet;
+            futureSet = tmp;
+            futureSet.clear();
+
+            index++;
+        }
+        matches.sort((a, b) -> compare.compare(a.getType(), b.getType()));
+        if(compare != null) {
+            matches.sort(Comparator.comparingInt(a -> a.getContent().length()));
+        }
+        return matches.isEmpty() ? null : matches.get(matches.size() - 1);
+    }
+
+    /**
+     * Reads all tokens from a string.
+     * @param from the string to start from.
+     * @param startAt the index to start at.
+     * @param compare the comparator used to sort matches by their IDs.
+     * @return the resulting list of matches, in order, or null on error.
+     */
+    public List<Match<T>> lexAll(String from, int startAt, Comparator<T> compare){
+        int index = startAt;
+        ArrayList<Match<T>> matches = new ArrayList<>();
+        Match<T> lastMatch = null;
+        while(index < from.length() && (lastMatch = lexOne(from, index, compare)) != null){
+            int length = lastMatch.getContent().length();
+            if(length == 0) return null;
+            matches.add(lastMatch);
+            index += length;
+        }
+        if(lastMatch == null) return null;
+        return matches;
+    }
+
+}