package org.checkerframework.javacutil.trees;

import java.util.StringTokenizer;

import javax.annotation.processing.ProcessingEnvironment;

import com.sun.source.tree.ExpressionTree;
import com.sun.tools.javac.processing.JavacProcessingEnvironment;
import com.sun.tools.javac.tree.JCTree.JCExpression;
import com.sun.tools.javac.tree.TreeMaker;
import com.sun.tools.javac.util.Context;
import com.sun.tools.javac.util.List;
import com.sun.tools.javac.util.ListBuffer;
import com.sun.tools.javac.util.Names;

/**
 * A Utility class for parsing Java expression snippets, and converting them
 * to proper Javac AST nodes.
 *
 * This is useful for parsing {@code EnsuresNonNull*},
 * and {@code KeyFor} values.
 *
 * Currently, it handles four tree types only:
 * <ul>
 *  <li>Identifier tree (e.g. {@code id})</li>
 *  <li>Literal tree (e.g. 2, 3)</li>
 *  <li>Method invocation tree (e.g. {@code method(2, 3)})</li>
 *  <li>Member select tree (e.g. {@code Class.field}, {@code instance.method()})
 *  <li>Array access tree (e.g. {@code array[id]})</li>
 * </ul>
 *
 * Notable limitation: Doesn't handle spaces, or non-method-argument
 * parenthesis.
 *
 * It's implemented via a Recursive-Descend parser.
 */
public class TreeParser {
    private static final String DELIMS = ".[](),";
    private static final String SENTINAL = "";

    private final TreeMaker maker;
    private final Names names;

    public TreeParser(ProcessingEnvironment env) {
        Context context = ((JavacProcessingEnvironment)env).getContext();
        maker = TreeMaker.instance(context);
        names = Names.instance(context);
    }

    /**
     * Parses the snippet in the string as an internal Javac AST expression
     * node
     *
     * @param s the java snippet
     * @return  the AST corresponding to the snippet
     */
    public ExpressionTree parseTree(String s) {
        tokenizer = new StringTokenizer(s, DELIMS, true);
        token = tokenizer.nextToken();

        try {
            return parseExpression();
        } catch (Exception e) {
            throw new ParseError(e);
        } finally {
            tokenizer = null;
            token = null;
        }
    }

    StringTokenizer tokenizer = null;
    String token = null;

    private String nextToken() {
        token = tokenizer.hasMoreTokens() ? tokenizer.nextToken() : SENTINAL;
        return token;
    }

    JCExpression fromToken(String token) {
        // Optimization
        if ("true".equals(token)) {
            return maker.Literal(true);
        } else if ("false".equals(token)) {
            return maker.Literal(false);
        }

        if (Character.isLetter(token.charAt(0)))
            return maker.Ident(names.fromString(token));

        Object value = null;
        try {
            value = Integer.valueOf(token);
        } catch (Exception e2) { try {
            value = Double.valueOf(token);
        } catch (Exception ef) {}}
        assert value != null;
        return maker.Literal(value);
    }

    JCExpression parseExpression() {
        JCExpression tree = fromToken(token);

        while (tokenizer.hasMoreTokens()) {
            String delim = nextToken();
            if (".".equals(delim)) {
                nextToken();
                tree = maker.Select(tree,
                        names.fromString(token));
            } else if ("(".equals(delim)) {
                nextToken();
                ListBuffer<JCExpression> args = new ListBuffer<>();
                while (!")".equals(token)) {
                    JCExpression arg = parseExpression();
                    args.append(arg);
                    if (",".equals(token))
                        nextToken();
                }
                // For now, handle empty args only
                assert ")".equals(token);
                tree = maker.Apply(List.<JCExpression>nil(),
                        tree, args.toList());
            } else if ("[".equals(token)) {
                nextToken();
                JCExpression index = parseExpression();
                assert "]".equals(token);
                tree = maker.Indexed(tree, index);
            } else {
                return tree;
            }
        }

        return tree;
    }

    class ParseError extends RuntimeException {
        private static final long serialVersionUID = 1887754619522101929L;

        ParseError(Throwable cause) {
            super(cause);
        }
    }
}