/*
 * The first part of the Extract Method refactoring, Extract Block takes a piece of
 * code (given by its start and end statements) and turns it into a block.
 * 
 * We need to ensure that this is possible (see precondition checks), and possibly
 * move some declarations for variables that are used outside the selection out of
 * the generated block.
 */

aspect ExtractBlock {

	public Block Block.extractBlock(int begin, int end) {
		if(begin < 0 || end >= getNumStmt() || end < begin)
			throw new RefactoringException("indices out of range");
		lockAllNames();
		Block new_block = new Block(new List());
		insertStmt(end+1, new_block);
		
		// push statements into block
		while(end >= begin) {
			Stmt stmt = getStmt(end);
			if(stmt instanceof Case)
				throw new RefactoringException("cannot push case into block");
			if(stmt instanceof VariableDeclaration) {
				VariableDeclaration decl = (VariableDeclaration)stmt;
				if(usesAfter(decl, end+1)) {
					AssignSimpleExpr assgn = decl.split();
					removeStmt(end);
					if(assgn != null)
						++end;
					insertStmt(begin++, stmt);
				} else {
					removeStmt(end--);
					new_block.insertStmt(0, stmt);
				}
			} else {
				removeStmt(end--);
				new_block.insertStmt(0, stmt);
			}
		}
		
		return new_block;
	}
	
	public Block Block.doExtractBlock(int begin, int end) {
		Program root = programRoot();
		Block blk = extractBlock(begin, end);
		programRoot().eliminate(LOCKED_NAMES);
		return blk;
	}
	
	protected boolean Block.usesAfter(Variable v, int i) {
		for(int j=i+1;j<getNumStmt();++j)
			if(getStmt(j).mayRef(v))
				return true;
		return false;
	}
}