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LESS compiler in Java based on less.js
/**
* Copyright (c) 2014 SQUARESPACE, Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.squarespace.less.exec;
import static com.squarespace.less.model.NodeType.BLOCK_DIRECTIVE;
import static com.squarespace.less.model.NodeType.MEDIA;
import static com.squarespace.less.model.NodeType.RULESET;
import static com.squarespace.less.model.NodeType.STYLESHEET;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Deque;
import java.util.EnumSet;
import java.util.Iterator;
import java.util.LinkedHashSet;
import java.util.List;
import java.util.Set;
import com.squarespace.less.LessContext;
import com.squarespace.less.core.Buffer;
import com.squarespace.less.core.LessInternalException;
import com.squarespace.less.core.LessUtils;
import com.squarespace.less.model.BlockDirective;
import com.squarespace.less.model.NodeType;
import com.squarespace.less.model.Ruleset;
/**
* Extremely simplistic model for CSS structure. Allows the LESS renderer
* to defer final output in order to suppress empty blocks, and eliminate
* duplicate rules. It also ensures that each nested block is emitted
* in the output model at the correct scope.
*/
public class CssModel {
/**
* Set of node types that can be children of a {@link Stylesheet}.
*/
private static final EnumSet STYLESHEET_ACCEPT = EnumSet.of(
STYLESHEET, RULESET, MEDIA, BLOCK_DIRECTIVE
);
/**
* Set of node types that can be children of a {@link Media} node.
*/
private static final EnumSet MEDIA_ACCEPT = EnumSet.of(
BLOCK_DIRECTIVE, RULESET
);
/**
* Set of node types that can be children of a {@link BlockDirective} node.
*/
private static final EnumSet BLOCK_DIRECTIVE_ACCEPT = EnumSet.of(
BLOCK_DIRECTIVE, RULESET
);
/**
* Set of node types that can be children of a {@link Ruleset} node.
*/
private static final EnumSet RULESET_ACCEPT = EnumSet.noneOf(NodeType.class);
/**
* Stack of CSS blocks.
*/
private final Deque stack = new ArrayDeque<>();
/**
* Internal buffer for rendering the CSS output.
*/
private final Buffer buffer;
/**
* Current block being operated on.
*/
private CssBlock current;
/**
* Constructs a CSS model with the given context.
*/
public CssModel(LessContext ctx) {
buffer = ctx.newBuffer();
current = new CssBlock(STYLESHEET);
}
/**
* Renders the CSS model into text form.
*/
public String render() {
if (current.type() != STYLESHEET) {
throw new LessInternalException("Serious error: stack was not fully popped.");
}
buffer.reset();
current.render(buffer);
return buffer.toString();
}
/**
* Appends a value to the current block.
*/
public CssModel value(String value) {
current.add(new CssValue(value));
return this;
}
/**
* Appends a comment to the current block.
*/
public CssModel comment(String value) {
current.add(new CssComment(value));
return this;
}
/**
* Add raw strings to the header of the current block.
*/
public CssModel header(String ... strings) {
for (String raw : strings) {
current.add(raw);
}
return this;
}
/**
* Pushes an empty block onto the stack and associates it with the given node type.
*/
public CssModel push(NodeType type) {
stack.push(current);
CssBlock child = new CssBlock(type);
defer(child);
current = child;
return this;
}
/**
* Pops a block from the top of the stack, setting flags indicating whether
* anything was appended to the block. This is used to prune empty blocks.
*/
public CssModel pop() {
CssBlock parent = current.parent();
parent.populated |= current.populated;
current = stack.pop();
return this;
}
/**
* Push this block up the stack until it finds its proper parent.
*/
private void defer(CssBlock block) {
if (current.accept(block)) {
return;
}
Iterator iter = stack.iterator();
while (iter.hasNext()) {
CssBlock candidate = iter.next();
if (candidate.accept(block)) {
return;
}
}
throw new LessInternalException("Serious error: no block accepted " + block.type());
}
/**
* Represents a CSS block that can contain other nodes and blocks.
*/
static class CssBlock extends CssNode {
private final List headers = new ArrayList<>();
private final Set nodes = new LinkedHashSet<>();
private final NodeType type;
private final EnumSet acceptFilter;
private CssBlock parent;
private boolean populated = false;
CssBlock(NodeType type) {
this.type = type;
switch (type) {
case BLOCK_DIRECTIVE:
acceptFilter = BLOCK_DIRECTIVE_ACCEPT;
break;
case MEDIA:
acceptFilter = MEDIA_ACCEPT;
break;
case RULESET:
acceptFilter = RULESET_ACCEPT;
break;
case STYLESHEET:
acceptFilter = STYLESHEET_ACCEPT;
break;
default:
throw new LessInternalException("Serious error: css model block cannot be " + type);
}
}
/**
* Determines if this block can accept a block of the given type as a
* child.
*/
public boolean accept(CssBlock block) {
if (acceptFilter.contains(block.type())) {
add(block);
block.setParent(this);
return true;
}
return false;
}
public CssBlock parent() {
return parent;
}
public void setParent(CssBlock parent) {
this.parent = parent;
}
public NodeType type() {
return type;
}
public boolean populated() {
return populated;
}
public void add(String header) {
headers.add(header);
}
public void add(CssNode node) {
// Ensure that the last unique rule (key + value) wins.
if (nodes.contains(node)) {
nodes.remove(node);
}
nodes.add(node);
populated |= node.populated();
}
@Override
public boolean isValue() {
return false;
}
@Override
public void render(Buffer buf) {
if (!populated) {
return;
}
if (!headers.isEmpty()) {
int size = headers.size();
for (int i = 0; i < size; i++) {
if (i > 0) {
buf.selectorSep();
}
buf.indent();
buf.append(headers.get(i));
}
buf.blockOpen();
}
Iterator iter = nodes.iterator();
while (iter.hasNext()) {
CssNode node = iter.next();
node.render(buf);
// If we're adding a rule, and we're not compressed or this is not the last
// rule in the ruleset, append the semicolon.
if (node instanceof CssValue && (!buf.compress() || iter.hasNext())) {
buf.ruleEnd();
}
}
if (!headers.isEmpty()) {
buf.blockClose();
}
}
}
/**
* Represents a simple value in a CSS model.
*/
static class CssValue extends CssNode {
private final String value;
CssValue(String value) {
this.value = value;
}
@Override
public boolean equals(Object obj) {
return (obj instanceof CssValue) ? LessUtils.safeEquals(value, ((CssValue)obj).value) : false;
}
@Override
public int hashCode() {
return value.hashCode();
}
@Override
public void render(Buffer buf) {
buf.indent();
buf.append(value);
}
}
/**
* Represents a comment in a CSS model.
*/
static class CssComment extends CssNode {
private final String value;
CssComment(String value) {
this.value = value;
}
@Override
public boolean equals(Object obj) {
return (obj instanceof CssComment) ? LessUtils.safeEquals(value, ((CssComment)obj).value) : false;
}
@Override
public int hashCode() {
return value.hashCode();
}
@Override
public void render(Buffer buf) {
buf.indent().append(value);
}
}
/**
* Abstract node in a CSS model.
*/
static abstract class CssNode {
public boolean isValue() {
return true;
}
public boolean populated() {
return true;
}
public abstract void render(Buffer buf);
}
}
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