1 files changed, 87 insertions, 0 deletions
diff --git a/graph/src/main/java/com/seaofnodes/graph/GraphJson.java b/graph/src/main/java/com/seaofnodes/graph/GraphJson.java
new file mode 100644
index 00000000..a63a0143
--- /dev/null
+++ b/graph/src/main/java/com/seaofnodes/graph/GraphJson.java
@@ -0,0 +1,87 @@
+package com.seaofnodes.graph;
+
+/** JSON for the shared graph model; no chapter or layout dependencies. */
+public class GraphJson {
+    public static String write(GraphSnapshot snap) {
+        var sb = new StringBuilder();
+        snap(sb, snap);
+        return sb.toString();
+    }
+
+    // Temporary envelope while the browser still renders DOT. The snapshot is
+    // complete on its own; step 2 can remove dot without changing its schema.
+    public static String frame(GraphSnapshot snap, int pos, String dot) {
+        var sb = new StringBuilder("{\"snap\":");
+        snap(sb, snap);
+        sb.append(",\"pos\":").append(pos).append(",\"dot\":");
+        str(sb, dot);
+        return sb.append('}').toString();
+    }
+
+    private static void snap(StringBuilder sb, GraphSnapshot snap) {
+        sb.append("{\"ver\":").append(snap.ver()).append(",\"comp\":");
+        str(sb, snap.comp());
+        sb.append(",\"step\":").append(snap.step()).append(",\"roots\":[");
+        int[] roots = snap.roots();
+        for( int i = 0; i < roots.length; i++ ) {
+            if( i > 0 ) sb.append(',');
+            sb.append(roots[i]);
+        }
+        sb.append("],\"nodes\":[");
+        var nodes = snap.nodes();
+        for( int i = 0; i < nodes.size(); i++ ) {
+            if( i > 0 ) sb.append(',');
+            var node = nodes.get(i);
+            sb.append("{\"id\":").append(node.id()).append(",\"label\":");
+            str(sb, node.label());
+            sb.append(",\"type\":");
+            str(sb, node.type());
+            sb.append(",\"kind\":");
+            str(sb, node.kind().name());
+            sb.append(",\"edges\":[");
+            var edges = node.edges();
+            for( int j = 0; j < edges.size(); j++ ) {
+                if( j > 0 ) sb.append(',');
+                var edge = edges.get(j);
+                sb.append("{\"idx\":").append(edge.idx())
+                  .append(",\"def\":").append(edge.def()).append(",\"role\":");
+                str(sb, edge.role().name());
+                sb.append(",\"label\":");
+                str(sb, edge.label());
+                sb.append('}');
+            }
+            sb.append("],\"proj\":");
+            var proj = node.proj();
+            if( proj == null ) sb.append("null");
+            else sb.append("{\"par\":").append(proj.par())
+                   .append(",\"idx\":").append(proj.idx()).append('}');
+            sb.append('}');
+        }
+        sb.append("]}");
+    }
+
+    private static void str(StringBuilder sb, String s) {
+        if( s == null ) { sb.append("null"); return; }
+        sb.append('"');
+        for( int i = 0; i < s.length(); i++ ) {
+            char c = s.charAt(i);
+            switch( c ) {
+            case '"' -> sb.append("\\\"");
+            case '\\' -> sb.append("\\\\");
+            case '\n' -> sb.append("\\n");
+            case '\r' -> sb.append("\\r");
+            case '\t' -> sb.append("\\t");
+            default -> {
+                // Escape controls and UTF-16 code units that cannot travel alone
+                // in UTF-8. Surrogate pairs round-trip through JSON as well.
+                if( c < 32 || Character.isSurrogate(c) ) {
+                    sb.append("\\u");
+                    for( int shift = 12; shift >= 0; shift -= 4 )
+                        sb.append("0123456789abcdef".charAt((c >> shift) & 15));
+                } else sb.append(c);
+            }
+            }
+        }
+        sb.append('"');
+    }
+}