package org.jsoup.safety;

import org.jsoup.helper.Validate;
import org.jsoup.nodes.*;
import org.jsoup.parser.Tag;
import org.jsoup.select.NodeTraversor;
import org.jsoup.select.NodeVisitor;

import java.util.List;

/**
 The whitelist based HTML cleaner. Use to ensure that end-user provided HTML contains only the elements and attributes
 that you are expecting; no junk, and no cross-site scripting attacks!
 <p/>
 The HTML cleaner parses the input as HTML and then runs it through a white-list, so the output HTML can only contain
 HTML that is allowed by the whitelist.
 <p/>
 It is assumed that the input HTML is a body fragment; the clean methods only pull from the source's body, and the
 canned white-lists only allow body contained tags.
 <p/>
 Rather than interacting directly with a Cleaner object, generally see the {@code clean} methods in {@link org.jsoup.Jsoup}.
 */
public class Cleaner {
    private Whitelist whitelist;

    /**
     Create a new cleaner, that sanitizes documents using the supplied whitelist.
     @param whitelist white-list to clean with
     */
    public Cleaner(Whitelist whitelist) {
        Validate.notNull(whitelist);
        this.whitelist = whitelist;
    }

    /**
     Creates a new, clean document, from the original dirty document, containing only elements allowed by the whitelist.
     The original document is not modified. Only elements from the dirt document's <code>body</code> are used.
     @param dirtyDocument Untrusted base document to clean.
     @return cleaned document.
     */
    public Document clean(Document dirtyDocument) {
        Validate.notNull(dirtyDocument);

        Document clean = Document.createShell(dirtyDocument.baseUri());
        if (dirtyDocument.body() != null) // frameset documents won't have a body. the clean doc will have empty body.
            copySafeNodes(dirtyDocument.body(), clean.body());

        return clean;
    }

    /**
     Determines if the input document is valid, against the whitelist. It is considered valid if all the tags and attributes
     in the input HTML are allowed by the whitelist.
     <p/>
     This method can be used as a validator for user input forms. An invalid document will still be cleaned successfully
     using the {@link #clean(Document)} document. If using as a validator, it is recommended to still clean the document
     to ensure enforced attributes are set correctly, and that the output is tidied.
     @param dirtyDocument document to test
     @return true if no tags or attributes need to be removed; false if they do
     */
    public boolean isValid(Document dirtyDocument) {
        Validate.notNull(dirtyDocument);

        Document clean = Document.createShell(dirtyDocument.baseUri());
        int numDiscarded = copySafeNodes(dirtyDocument.body(), clean.body());
        return numDiscarded == 0;
    }

    /**
     Iterates the input and copies trusted nodes (tags, attributes, text) into the destination.
     */
    private final class CleaningVisitor implements NodeVisitor {
        private int numDiscarded = 0;
        private final Element root;
        private Element destination; // current element to append nodes to

        private CleaningVisitor(Element root, Element destination) {
            this.root = root;
            this.destination = destination;
        }

        public void head(Node source, int depth) {
            if (source instanceof Element) {
                Element sourceEl = (Element) source;

                if (whitelist.isSafeTag(sourceEl.tagName())) { // safe, clone and copy safe attrs
                    ElementMeta meta = createSafeElement(sourceEl);
                    Element destChild = meta.el;
                    destination.appendChild(destChild);

                    numDiscarded += meta.numAttribsDiscarded;
                    destination = destChild;
                } else if (source != root) { // not a safe tag, so don't add. don't count root against discarded.
                    numDiscarded++;
                }
            } else if (source instanceof TextNode) {
                TextNode sourceText = (TextNode) source;
                TextNode destText = new TextNode(sourceText.getWholeText(), source.baseUri());
                destination.appendChild(destText);
            } else { // else, we don't care about comments, xml proc instructions, etc
                numDiscarded++;
            }
        }

        public void tail(Node source, int depth) {
            if (source instanceof Element && whitelist.isSafeTag(source.nodeName())) {
                destination = destination.parent(); // would have descended, so pop destination stack
            }
        }
    }

    private int copySafeNodes(Element source, Element dest) {
        CleaningVisitor cleaningVisitor = new CleaningVisitor(source, dest);
        NodeTraversor traversor = new NodeTraversor(cleaningVisitor);
        traversor.traverse(source);
        return cleaningVisitor.numDiscarded;
    }

    private ElementMeta createSafeElement(Element sourceEl) {
        String sourceTag = sourceEl.tagName();
        Attributes destAttrs = new Attributes();
        Element dest = new Element(Tag.valueOf(sourceTag), sourceEl.baseUri(), destAttrs);
        int numDiscarded = 0;

        Attributes sourceAttrs = sourceEl.attributes();
        for (Attribute sourceAttr : sourceAttrs) {
            if (whitelist.isSafeAttribute(sourceTag, sourceEl, sourceAttr))
                destAttrs.put(sourceAttr);
            else
                numDiscarded++;
        }
        Attributes enforcedAttrs = whitelist.getEnforcedAttributes(sourceTag);
        destAttrs.addAll(enforcedAttrs);

        return new ElementMeta(dest, numDiscarded);
    }

    private static class ElementMeta {
        Element el;
        int numAttribsDiscarded;

        ElementMeta(Element el, int numAttribsDiscarded) {
            this.el = el;
            this.numAttribsDiscarded = numAttribsDiscarded;
        }
    }

}
