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package ftbsc.lll.utils;

import org.objectweb.asm.Opcodes;
import org.objectweb.asm.tree.*;

import java.util.Comparator;

/**
 * Various methods for manipulating the stack.
 * Includes anything from instantiation to variable manipulation - just about
 * anything that loads stuff on or from the stack.
 */
public class StackUtils implements Opcodes {
   /**
    * Creates a new instance of an object, given its internal name, constructor descriptor and instructions to load
    * the parameters.
    * The created object is loaded on the stack.
    * @param name the internal name of the object to initialize, where
    *             the internal name of a class is its fully qualified name, where '.' are replaced by '/'
    * @param desc the descriptor of the constructor to call
    * @param args nodes containing instructions to load the constructor arguments, in the right order
    * @return an instruction list containing the opcodes needed to create the new object and load it on the stack.
    */
   public static InsnList instantiate(String name, String desc, AbstractInsnNode... args) {
      InsnSequence is = new InsnSequence();
      is.add(args);
      return instantiate(name, desc, is);
   }

   /**
    * Creates a new instance of an object, given its internal name, constructor descriptor and instructions to load
    * the parameters.
    * The created object is loaded on the stack.
    * @param name the internal name of the object to initialize, where
    *             the internal name of a class is its fully qualified name, where '.' are replaced by '/'
    * @param desc the descriptor of the constructor to call
    * @param args a list of instructions loading the constructor arguments onto the stack in the correct order
    * @return an instruction list containing the opcodes needed to create the new object and load it on the stack.
    */
   public static InsnList instantiate(String name, String desc, InsnList args) {
      InsnSequence list = new InsnSequence();
      list.add(new TypeInsnNode(NEW, name), new InsnNode(DUP));
      if(args != null) list.add(args);
      list.add(new MethodInsnNode(INVOKESPECIAL, name, "<init>", desc, false));
      return list;
   }


   /**
    * Creates a new local variable, lasting in scope from the first to the last label of the given method.
    * @param method the method for which to declare the local variable
    * @param name the variable's name
    * @param desc the type descriptor for the new variable
    * @return the index value of the new local variable
    */
   public static int addLocalVariable(MethodNode method, String name, String desc) {
      return addLocalVariable(
         method, name, desc,
         (LabelNode) PatternMatcher.builder().label().build().find(method).getFirst(),
         (LabelNode) PatternMatcher.builder().label().reverse().build().find(method).getFirst()
      );
   }

   /**
    * Creates a new local variable, lasting in scope between two given {@link LabelNode}s.
    * @param method the method for which to declare the local variable
    * @param name the variable's name
    * @param desc the type descriptor for the new variable
    * @param start the label at which the variable should enter scope
    * @param end the label at which the variable should go out of scope
    * @return the index value of the new local variable
    */
   public static int addLocalVariable(MethodNode method, String name, String desc, LabelNode start, LabelNode end) {
      final int targetIndex = findFirstFreeIndex(method);
      LocalVariableNode variable = new LocalVariableNode(name, desc, null, start, end, targetIndex);
      method.localVariables.add(variable);
      return targetIndex;
   }

   /**
    * Finds the first free index in the given {@link MethodNode}.
    * Used to create variables.
    * @param method the method to look in
    * @return the found index
    */
   public static int findFirstFreeIndex(MethodNode method) {
      return method.localVariables
         .stream()
         .max(Comparator.comparingInt(v -> v.index))
         .map(var -> var.desc.equals("J") || var.desc.equals("D")
            ? var.index + 2 //skip two if long or double - major java moment
            : var.index + 1)
         .orElse(0);
   }
}