Basic support for import: place import declarations on top of input file

and print it as it is. #83 and #19

src/main/antlr3/com/github/sommeri/less4j/core/parser/Less.g

@@ -165,7 +165,6 @@ tokens {
 styleSheet
 @init {enterRule(retval, RULE_STYLESHEET);}
     : ( a+=charSet* //the original ? was replaced by *, because it is possible (even if it makes no sense) and less.js is able to handle such situation
-        a+=imports*
         a+=bodylist
         EOF ) -> ^(STYLE_SHEET ($a)*)
     ;
@@ -186,7 +185,7 @@ finally { leaveRule(); }
 //
 imports
 @init {enterRule(retval, RULE_IMPORTS);}
-    : IMPORT_SYM (STRING|URI) (mediaQuery (COMMA mediaQuery)*)? SEMI
+    : (IMPORT_SYM | IMPORT_ONCE_SYM | IMPORT_MULTIPLE_SYM)^ (term) (mediaQuery (COMMA mediaQuery)*)? SEMI!
     ;
 finally { leaveRule(); }
 
@@ -256,6 +255,7 @@ bodyset
     | keyframes
     | page
     | fontface
+    | imports
     ;
 
 variabledeclaration
@@ -377,6 +377,7 @@ general_body
                | (reusableStructure)=>a+=reusableStructure
                | a+=pageMarginBox 
                | a+=variabledeclaration
+               | a+=imports
              )*
              (  
                 ( (declaration)=>a+=declaration RBRACE)
@@ -1106,7 +1107,9 @@ IDENT : '-'? NMSTART NMCHAR* ;
 fragment HASH_FRAGMENT : '#' NAME ;
 HASH : HASH_FRAGMENT ;
 
-IMPORT_SYM : '@' I M P O R T ;
+IMPORT_SYM : '@' I M P O R T;
+IMPORT_ONCE_SYM : '@' I M P O R T MINUS O N C E;
+IMPORT_MULTIPLE_SYM : '@' I M P O R T  MINUS M U L T I P L E;
 PAGE_SYM : '@' P A G E ;
 MEDIA_SYM : '@' M E D I A ;
 FONT_FACE_SYM : '@' F O N T MINUS F A C E ;
@@ -1195,10 +1198,10 @@ NUMBER
 // url and uri.
 URI : (U R L
         '('
-            ((WS)=>WS)? (URL|STRING) WS?
+            ((WS)=>WS)? (URL) WS?
         ')') => (U R L
         '('
-            ((WS)=>WS)? (URL|STRING) WS?
+            ((WS)=>WS)? (URL) WS?
         ')')
         | U R L { $type=IDENT; }
     ;

src/main/java/com/github/sommeri/less4j/core/ast/ASTCssNodeType.java

@@ -1,5 +1,5 @@
 package com.github.sommeri.less4j.core.ast;
 
 public enum ASTCssNodeType {
-  UNKNOWN, CSS_CLASS, DECLARATION, STYLE_SHEET, RULE_SET, SELECTOR, SIMPLE_SELECTOR, PSEUDO_CLASS, PSEUDO_ELEMENT, SELECTOR_ATTRIBUTE, ID_SELECTOR, CHARSET_DECLARATION, FONT_FACE, IDENTIFIER_EXPRESSION, COMPOSED_EXPRESSION, STRING_EXPRESSION, NUMBER, COLOR_EXPRESSION, FUNCTION, MEDIA, COMMENT, DECLARATIONS_BODY, SELECTOR_OPERATOR, SELECTOR_COMBINATOR, EXPRESSION_OPERATOR, NTH, NAMED_EXPRESSION, MEDIA_QUERY, MEDIA_EXPRESSION, MEDIUM, MEDIUM_MODIFIER, MEDIUM_TYPE, MEDIUM_EX_FEATURE, VARIABLE_DECLARATION, VARIABLE, INDIRECT_VARIABLE, PARENTHESES_EXPRESSION, SIGNED_EXPRESSION, ARGUMENT_DECLARATION, MIXIN_REFERENCE, GUARD_CONDITION, COMPARISON_EXPRESSION, GUARD, NESTED_SELECTOR_APPENDER, REUSABLE_STRUCTURE, FAULTY_EXPRESSION, ESCAPED_SELECTOR, ESCAPED_VALUE, INTERPOLABLE_NAME, FIXED_NAME_PART, VARIABLE_NAME_PART, KEYFRAMES, KEYFRAMES_NAME, KEYFRAMES_BODY, REUSABLE_STRUCTURE_NAME, VIEWPORT, GENERAL_BODY, PAGE, NAME, PAGE_MA, PAGE_MARGIN_BOX
+  UNKNOWN, CSS_CLASS, DECLARATION, STYLE_SHEET, RULE_SET, SELECTOR, SIMPLE_SELECTOR, PSEUDO_CLASS, PSEUDO_ELEMENT, SELECTOR_ATTRIBUTE, ID_SELECTOR, CHARSET_DECLARATION, FONT_FACE, IDENTIFIER_EXPRESSION, COMPOSED_EXPRESSION, STRING_EXPRESSION, NUMBER, COLOR_EXPRESSION, FUNCTION, MEDIA, COMMENT, DECLARATIONS_BODY, SELECTOR_OPERATOR, SELECTOR_COMBINATOR, EXPRESSION_OPERATOR, NTH, NAMED_EXPRESSION, MEDIA_QUERY, MEDIA_EXPRESSION, MEDIUM, MEDIUM_MODIFIER, MEDIUM_TYPE, MEDIUM_EX_FEATURE, VARIABLE_DECLARATION, VARIABLE, INDIRECT_VARIABLE, PARENTHESES_EXPRESSION, SIGNED_EXPRESSION, ARGUMENT_DECLARATION, MIXIN_REFERENCE, GUARD_CONDITION, COMPARISON_EXPRESSION, GUARD, NESTED_SELECTOR_APPENDER, REUSABLE_STRUCTURE, FAULTY_EXPRESSION, ESCAPED_SELECTOR, ESCAPED_VALUE, INTERPOLABLE_NAME, FIXED_NAME_PART, VARIABLE_NAME_PART, KEYFRAMES, KEYFRAMES_NAME, KEYFRAMES_BODY, REUSABLE_STRUCTURE_NAME, VIEWPORT, GENERAL_BODY, PAGE, NAME, PAGE_MA, PAGE_MARGIN_BOX, IMPORT
 }

src/main/java/com/github/sommeri/less4j/core/ast/Import.java

@@ -0,0 +1,76 @@
+package com.github.sommeri.less4j.core.ast;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import com.github.sommeri.less4j.core.parser.HiddenTokenAwareTree;
+import com.github.sommeri.less4j.utils.ArraysUtils;
+
+public class Import extends ASTCssNode {
+
+  private ImportKind kind = ImportKind.IMPORT;
+  private Expression urlExpression;
+  private List<MediaQuery> mediums = new ArrayList<MediaQuery>();
+
+  public Import(HiddenTokenAwareTree underlyingStructure) {
+    super(underlyingStructure);
+  }
+
+  public ImportKind getKind() {
+    return kind;
+  }
+
+  public void setKind(ImportKind kind) {
+    this.kind = kind;
+  }
+
+  public Expression getUrlExpression() {
+    return urlExpression;
+  }
+
+  public void setUrlExpression(Expression urlExpression) {
+    this.urlExpression = urlExpression;
+  }
+
+  public List<MediaQuery> getMediums() {
+    return mediums;
+  }
+
+  public void setMediums(List<MediaQuery> mediums) {
+    this.mediums = mediums;
+  }
+
+  public void add(MediaQuery medium) {
+    mediums.add(medium);
+  }
+
+  @Override
+  public List<? extends ASTCssNode> getChilds() {
+    List<ASTCssNode> result = ArraysUtils.asNonNullList((ASTCssNode)urlExpression);
+    result.addAll(mediums);
+    return result;
+  }
+
+  @Override
+  public Import clone() {
+    Import result = (Import) super.clone();
+    result.urlExpression = urlExpression==null? null : urlExpression.clone();
+    result.mediums = ArraysUtils.deeplyClonedList(mediums);
+    result.configureParentToAllChilds();
+    return result;
+  }
+
+//@Override
+//public String toString() {
+//}
+
+  @Override
+  public ASTCssNodeType getType() {
+    return ASTCssNodeType.IMPORT;
+  }
+
+  public enum ImportKind {
+    IMPORT, IMPORT_ONCE, IMPORT_MULTIPLE
+  }
+
+}

src/main/java/com/github/sommeri/less4j/core/compiler/LessToCssCompiler.java

@@ -1,9 +1,12 @@
 package com.github.sommeri.less4j.core.compiler;
 
 import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Comparator;
 import java.util.List;
 
 import com.github.sommeri.less4j.core.ast.ASTCssNode;
+import com.github.sommeri.less4j.core.ast.ASTCssNodeType;
 import com.github.sommeri.less4j.core.ast.Body;
 import com.github.sommeri.less4j.core.ast.Declaration;
 import com.github.sommeri.less4j.core.ast.Expression;
@@ -34,20 +37,40 @@ public LessToCssCompiler(ProblemsHandler problemsHandler) {
   public ASTCssNode compileToCss(StyleSheet less) {
     ScopeExtractor scopeBuilder = new ScopeExtractor();
     Scope scope = scopeBuilder.extractScope(less);
-    
+
     ReferencesSolver referencesSolver = new ReferencesSolver(problemsHandler);
     referencesSolver.solveReferences(less, scope);
-    
+
     //just a safety measure
     evaluateExpressions(less);
     freeNestedRuleSets(less);
+    sortTopLevelElements(less);
 
     return less;
   }
 
+  private void sortTopLevelElements(StyleSheet less) {
+    Collections.sort(less.getChilds(), new Comparator<ASTCssNode>() {
+
+      @Override
+      public int compare(ASTCssNode first, ASTCssNode second) {
+        return code(first) - code(second);
+      }
+
+      private int code(ASTCssNode node) {
+        if (node.getType() == ASTCssNodeType.CHARSET_DECLARATION)
+          return 0;
+        if (node.getType() == ASTCssNodeType.IMPORT)
+          return 1;
+
+        return 2;
+      }
+    });
+  }
+
   private void freeNestedRuleSets(Body<ASTCssNode> body) {
     NestedRulesCollector nestedRulesCollector = new NestedRulesCollector();
-    
+
     List<? extends ASTCssNode> childs = new ArrayList<ASTCssNode>(body.getChilds());
     for (ASTCssNode kid : childs) {
       switch (kid.getType()) {