import java.util.Stack;
import java.util.HashMap;
import java.util.ArrayList;

/**
 * Class that defines the memory space for the SILLY interpreter.
 *   @author Dave Reed
 *   @version 1/20/25
 */
public class MemorySpace {
    private Stack<ScopeRec> runtimeStack;

    /**
     * Constructs a memory space with a single (global) scope record.
     */
    public MemorySpace() {
        this.runtimeStack = new Stack<ScopeRec>();
        this.runtimeStack.push(new ScopeRec(null));
    }
    
    /**
     * Adds a new scope to the top of the runtime stack (linked to previous top).
     */
    public void beginNestedScope() {
    	this.runtimeStack.push(new ScopeRec(this.runtimeStack.peek()));
    }
    
    /**
     * Removes the current scope from the top of the runtime stack.
     */
    public void endCurrentScope() {
    	this.runtimeStack.pop();
    }   	

    /**
     * Declares a variable (without storing an actual value).
     *   @param variable the variable to be declared
     */
    public void declareVariable(Token variable) {
        this.runtimeStack.peek().storeInScope(variable, null);
    }
    
    /** 
     * Determines if a variable is already declared.
     * @param variable the variable to be found
     * @return true if it is declared and/or assigned; else, false
     */
    public boolean isDeclared(Token variable) {
    	return (this.findScopeinStack(variable) != null);
    }
    
    /**
     * Stores a variable/value in the runtime stack.
     *   @param variable the variable name
     *   @param val the value to be stored under that name
     */
    public void storeValue(Token variable, DataValue val)  {
    	this.findScopeinStack(variable).storeInScope(variable, val);
    }

    /**
     * Determines the value associated with a variable in memory.
     *   @param variable the variable to look up
     *   @return the value associated with that variable
     */      
    public DataValue lookupValue(Token variable) {
    	return this.findScopeinStack(variable).lookupInScope(variable);
    }

    /////////////////////////////////////////////////////////////////////////////
    
    /**
     * Locates the Scope in the stackSegment that contains the specified variable.
     * @param variable the variable being searched for
     * @return the Scope containing that variable
     */
    private ScopeRec findScopeinStack(Token variable) {
    	ScopeRec stepper = this.runtimeStack.peek();
    	while (stepper != null && !stepper.declaredInScope(variable)) {
    		stepper = stepper.getParentScope();
    	}
    	return stepper;
    }
}