/*
 * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
 * or more contributor license agreements. Licensed under the Elastic License
 * 2.0 and the Server Side Public License, v 1; you may not use this file except
 * in compliance with, at your election, the Elastic License 2.0 or the Server
 * Side Public License, v 1.
 */

package org.elasticsearch.painless;

import org.elasticsearch.script.ScriptException;

import java.util.ArrayList;
import java.util.BitSet;
import java.util.List;
import java.util.Map;

/**
 * Abstract superclass on top of which all Painless scripts are built.
 */
public interface PainlessScript {

    /**
     * @return The name of the script retrieved from a static variable generated
     * during compilation of a Painless script.
     */
    String getName();

    /**
     * @return The source for a script retrieved from a static variable generated
     * during compilation of a Painless script.
     */
    String getSource();

    /**
     * @return The {@link BitSet} tracking the boundaries for statements necessary
     * for good exception messages.
     */
    BitSet getStatements();

    /**
     * Adds stack trace and other useful information to exceptions thrown
     * from a Painless script.
     * @param t The throwable to build an exception around.
     * @return The generated ScriptException.
     */
    default ScriptException convertToScriptException(Throwable t, Map<String, List<String>> extraMetadata) {
        // create a script stack: this is just the script portion
        List<String> scriptStack = new ArrayList<>();
        ScriptException.Position pos = null;
        for (StackTraceElement element : t.getStackTrace()) {
            if (WriterConstants.CLASS_NAME.equals(element.getClassName())) {
                // found the script portion
                int originalOffset = element.getLineNumber();
                if (originalOffset == -1) {
                    scriptStack.add("<<< unknown portion of script >>>");
                } else {
                    int offset = --originalOffset; // offset is 1 based, line numbers must be!
                    int startOffset = getPreviousStatement(offset);
                    if (startOffset == -1) {
                        assert false; // should never happen unless we hit exc in ctor prologue...
                        startOffset = 0;
                    }
                    int endOffset = getNextStatement(startOffset);
                    if (endOffset == -1) {
                        endOffset = getSource().length();
                    }
                    // TODO: if this is still too long, truncate and use ellipses
                    String snippet = getSource().substring(startOffset, endOffset);
                    scriptStack.add(snippet);
                    StringBuilder pointer = new StringBuilder();
                    for (int i = startOffset; i < offset; i++) {
                        pointer.append(' ');
                    }
                    pointer.append("^---- HERE");
                    scriptStack.add(pointer.toString());
                    pos = new ScriptException.Position(originalOffset, startOffset, endOffset);
                }
                break;
            // but filter our own internal stacks (e.g. indy bootstrap)
            } else if (shouldFilter(element) == false) {
                scriptStack.add(element.toString());
            }
        }
        ScriptException scriptException = new ScriptException("runtime error", t, scriptStack, getName(), PainlessScriptEngine.NAME, pos);
        for (Map.Entry<String, List<String>> entry : extraMetadata.entrySet()) {
            scriptException.addMetadata(entry.getKey(), entry.getValue());
        }
        return scriptException;
    }

    /** returns true for methods that are part of the runtime */
    default boolean shouldFilter(StackTraceElement element) {
        return element.getClassName().startsWith("org.elasticsearch.painless.") ||
               element.getClassName().startsWith("java.lang.invoke.") ||
               element.getClassName().startsWith("sun.invoke.");
    }

    /**
     * Finds the start of the first statement boundary that is on or before {@code offset}. If one is not found, {@code -1} is returned.
     */
    default int getPreviousStatement(int offset) {
        return getStatements().previousSetBit(offset);
    }

    /**
     * Finds the start of the first statement boundary that is after {@code offset}. If one is not found, {@code -1} is returned.
     */
    default int getNextStatement(int offset) {
        return getStatements().nextSetBit(offset + 1);
    }
}
