liquid fixes to FHIRPath

org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/FHIRLexer.java

@@ -76,6 +76,7 @@ public class FHIRLexer {
   private SourceLocation currentStartLocation;
   private int id;
   private String name;
+  private boolean liquidMode; // in liquid mode, || terminates the expression and hands the parser back to the host
 
   public FHIRLexer(String source, String name) throws FHIRLexerException {
     this.source = source == null ? "" : source;
@@ -272,6 +273,12 @@ public class FHIRLexer {
           throw error("Unterminated string");
         cursor++;
         current = "`"+source.substring(currentStart+1, cursor-1)+"`";
+      } else if (ch == '|' && liquidMode) {
+        cursor++;
+        ch = source.charAt(cursor);
+        if (ch == '|')
+          cursor++;
+        current = source.substring(currentStart, cursor);
       } else if (ch == '@'){
         int start = cursor;
         cursor++;
@@ -520,5 +527,11 @@ public class FHIRLexer {
   public String getSource() {
     return source;
   }
+  public boolean isLiquidMode() {
+    return liquidMode;
+  }
+  public void setLiquidMode(boolean liquidMode) {
+    this.liquidMode = liquidMode;
+  }
 
 }

org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/FHIRPathEngine.java

@@ -262,6 +262,7 @@ public class FHIRPathEngine {
   private String location; // for error messages
   private boolean allowPolymorphicNames;
   private boolean doImplicitStringConversion;
+  private boolean liquidMode; // in liquid mode, || terminates the expression and hands the parser back to the host
 
   // if the fhir path expressions are allowed to use constants beyond those defined in the specification
   // the application can implement them by providing a constant resolver 
@@ -6034,5 +6035,13 @@ public class FHIRPathEngine {
     this.allowPolymorphicNames = allowPolymorphicNames;
   }
 
+  public boolean isLiquidMode() {
+    return liquidMode;
+  }
+
+  public void setLiquidMode(boolean liquidMode) {
+    this.liquidMode = liquidMode;
+  }
+
 
 }

org.hl7.fhir.r5/src/main/java/org/hl7/fhir/r5/utils/LiquidEngine.java

@@ -93,6 +93,7 @@ public class LiquidEngine implements IEvaluationContext {
     this.externalHostServices = hostServices;
     engine = new FHIRPathEngine(context);
     engine.setHostServices(this);
+    engine.setLiquidMode(true);
   }
 
   public ILiquidEngineIncludeResolver getIncludeResolver() {
@@ -152,22 +153,82 @@ public class LiquidEngine implements IEvaluationContext {
     }
 
   }
+  
+  private enum LiquidFilter {
+    PREPEND;
+    
+    public static LiquidFilter fromCode(String code) {
+      if ("prepend".equals(code)) {
+        return PREPEND;
+      }
+      return null;
+    }
+  }
 
+  private class LiquidExpressionNode {
+    private LiquidFilter filter; // null at root
+    private ExpressionNode expression; // null for some filters
+    public LiquidExpressionNode(LiquidFilter filter, ExpressionNode expression) {
+      super();
+      this.filter = filter;
+      this.expression = expression;
+    }
+    
+  }
+  
   private class LiquidStatement extends LiquidNode {
     private String statement;
-    private ExpressionNode compiled;
+    private List<LiquidExpressionNode> compiled = new ArrayList<>();
 
     @Override
     public void evaluate(StringBuilder b, Base resource, LiquidEngineContext ctxt) throws FHIRException {
-      if (compiled == null)
-        compiled = engine.parse(statement);
-      List<Base> items = engine.evaluate(ctxt, resource, resource, resource, compiled);
+      if (compiled.size() == 0) {
+        FHIRLexer lexer = new FHIRLexer(statement, "liquid statement");
+        lexer.setLiquidMode(true);
+        compiled.add(new LiquidExpressionNode(null, engine.parse(lexer)));
+        while (!lexer.done()) {
+          if (lexer.getCurrent().equals("||")) {
+            lexer.next();
+            String f = lexer.getCurrent();
+            LiquidFilter filter = LiquidFilter.fromCode(f);
+            if (filter == null) {
+              lexer.error("Unknown Liquid filter '"+f+"'");
+            }
+            lexer.next();
+            if (!lexer.done() && lexer.getCurrent().equals(":")) {
+              lexer.next();
+              compiled.add(new LiquidExpressionNode(filter, engine.parse(lexer)));
+            } else {
+              compiled.add(new LiquidExpressionNode(filter, null));
+            }
+          } else {
+            lexer.error("Unexpected syntax parsing liquid statement");
+          }
+        }
+      }
+      
+      String t = null;
+      for (LiquidExpressionNode i : compiled) {
+        if (i.filter == null) { // first
+          t = stmtToString(ctxt, engine.evaluate(ctxt, resource, resource, resource, i.expression));
+        } else switch (i.filter) {
+        case PREPEND:
+          t = stmtToString(ctxt, engine.evaluate(ctxt, resource, resource, resource, i.expression)) + t;
+          break;
+        }
+      }
+      b.append(t);
+    }
+
+    private String stmtToString(LiquidEngineContext ctxt, List<Base> items) {
+      StringBuilder b = new StringBuilder();
       boolean first = true;
       for (Base i : items) {
         if (first) first = false; else b.append(", ");
         String s = renderingSupport != null ? renderingSupport.renderForLiquid(ctxt.externalContext, i) : null;
         b.append(s != null ? s : engine.convertToString(i));
       }
+      return b.toString();
     }
   }