From 6cb013214e9f393bd6d2c5fa3b50de567e9efac1 Mon Sep 17 00:00:00 2001
From: Kamila Szewczyk <kspalaiologos@gmail.com>
Date: Thu, 13 Apr 2023 10:23:00 +0200
Subject: [PATCH] chinese postman algorithm

---
 .../runtime/graph/ChinesePostman.java         | 25 +++++++++
 .../kamilalisp/runtime/graph/GraphPath.java   | 52 +++++++++++++++++++
 .../kamilalisp/runtime/lib/AlgorithmLib.java  |  1 +
 3 files changed, 78 insertions(+)
 create mode 100644 src/main/java/palaiologos/kamilalisp/runtime/graph/ChinesePostman.java
 create mode 100644 src/main/java/palaiologos/kamilalisp/runtime/graph/GraphPath.java

diff --git a/src/main/java/palaiologos/kamilalisp/runtime/graph/ChinesePostman.java b/src/main/java/palaiologos/kamilalisp/runtime/graph/ChinesePostman.java
new file mode 100644
index 00000000..2d27792d
--- /dev/null
+++ b/src/main/java/palaiologos/kamilalisp/runtime/graph/ChinesePostman.java
@@ -0,0 +1,25 @@
+package palaiologos.kamilalisp.runtime.graph;
+
+import org.jgrapht.alg.cycle.BergeGraphInspector;
+import org.jgrapht.graph.DefaultEdge;
+import palaiologos.kamilalisp.atom.Atom;
+import palaiologos.kamilalisp.atom.Environment;
+import palaiologos.kamilalisp.atom.Lambda;
+import palaiologos.kamilalisp.atom.PrimitiveFunction;
+
+import java.util.List;
+
+public class ChinesePostman extends PrimitiveFunction implements Lambda {
+    @Override
+    public Atom apply(Environment env, List<Atom> args) {
+        assertArity(args, 1);
+        GraphWrapper wp = args.get(0).getUserdata(GraphWrapper.class);
+        var inspector = new org.jgrapht.alg.cycle.ChinesePostman<Atom, DefaultEdge>();
+        return new Atom(new GraphPath(inspector.getCPPSolution(wp.getGraph())));
+    }
+
+    @Override
+    protected String name() {
+        return "graph:chinese-postman";
+    }
+}
diff --git a/src/main/java/palaiologos/kamilalisp/runtime/graph/GraphPath.java b/src/main/java/palaiologos/kamilalisp/runtime/graph/GraphPath.java
new file mode 100644
index 00000000..8faec7cc
--- /dev/null
+++ b/src/main/java/palaiologos/kamilalisp/runtime/graph/GraphPath.java
@@ -0,0 +1,52 @@
+package palaiologos.kamilalisp.runtime.graph;
+
+import org.jgrapht.graph.DefaultEdge;
+import palaiologos.kamilalisp.atom.Atom;
+import palaiologos.kamilalisp.atom.Userdata;
+
+import java.math.BigDecimal;
+import java.math.BigInteger;
+
+public class GraphPath implements Userdata {
+    private final org.jgrapht.GraphPath<Atom, DefaultEdge> path;
+
+    public GraphPath(org.jgrapht.GraphPath<Atom, DefaultEdge> path) {
+        this.path = path;
+    }
+
+    @Override
+    public Atom field(Object key) {
+        if(!(key instanceof String s))
+            throw new IllegalArgumentException("key must be a string");
+        switch (s) {
+            case "length" -> {
+                return new Atom(BigInteger.valueOf(path.getLength()));
+            }
+            case "weight" -> {
+                return new Atom(BigDecimal.valueOf(path.getWeight()));
+            }
+            case "start" -> {
+                return path.getStartVertex();
+            }
+            case "end" -> {
+                return path.getEndVertex();
+            }
+            case "vertices" -> {
+                return new Atom(path.getVertexList());
+            }
+            default -> {
+                throw new IllegalArgumentException("unknown key: " + key);
+            }
+        }
+    }
+
+    @Override
+    public String toDisplayString() {
+        return "graph:path of length " + path.getLength();
+    }
+
+    @Override
+    public String typeName() {
+        return "graph:path";
+    }
+}
diff --git a/src/main/java/palaiologos/kamilalisp/runtime/lib/AlgorithmLib.java b/src/main/java/palaiologos/kamilalisp/runtime/lib/AlgorithmLib.java
index 5e486ea8..971822f5 100644
--- a/src/main/java/palaiologos/kamilalisp/runtime/lib/AlgorithmLib.java
+++ b/src/main/java/palaiologos/kamilalisp/runtime/lib/AlgorithmLib.java
@@ -138,6 +138,7 @@ public static void register(Environment env) {
         env.setPrimitive("graph:is-berge-graph", new Atom(new BergeGraphTest()));
         env.setPrimitive("graph:bron-kerbosch-clique-finder", new Atom(new BronKerboschCliqueFinder()));
         env.setPrimitive("graph:chordal-graph-maximum-clique-finder", new Atom(new ChordalGraphMaximumCliqueFinder()));
+        env.setPrimitive("graph:chinese-postman", new Atom(new ChinesePostman()));
 
         env.setPrimitive("regex:matches?", "⍫⊖∊?", new Atom(new RegexMatches()));
         env.setPrimitive("regex:replace", "⍫⊖⍆", new Atom(new RegexReplace()));