package bjc.dicelang.v1.ast;

import bjc.dicelang.v1.ast.nodes.IDiceASTNode;
import bjc.dicelang.v1.ast.nodes.OperatorDiceNode;
import bjc.dicelang.v1.ast.nodes.VariableDiceNode;
import bjc.utils.data.IHolder;
import bjc.utils.data.ITree;
import bjc.utils.data.Identity;
import bjc.utils.data.TopDownTransformResult;
import bjc.utils.data.Tree;
import bjc.utils.funcdata.IMap;

/**
 * Sanitize the references in an AST so that a variable that refers to itself in
 * its definition has the occurance of it replaced with its previous definition
 *
 * @author ben
 *
 */
public class DiceASTReferenceSanitizer {
	private static ITree<IDiceASTNode> doSanitize(ITree<IDiceASTNode> ast,
			IMap<String, ITree<IDiceASTNode>> enviroment) {
		if(ast.getChildrenCount() != 2)
			throw new UnsupportedOperationException("Assignment must have two arguments.");

		ITree<IDiceASTNode> nameTree = ast.getChild(0);
		ITree<IDiceASTNode> valueTree = ast.getChild(1);

		if(!DiceASTUtils.containsSimpleVariable(nameTree)) {
			if(nameTree.getHead() == OperatorDiceNode.ARRAY) {
				IHolder<Boolean> allSimpleVariables = new Identity<>(true);

				nameTree.doForChildren((child) -> {
					if(allSimpleVariables.getValue()) {
						boolean isSimple = DiceASTUtils.containsSimpleVariable(child);

						allSimpleVariables.replace(isSimple);
					}
				});

				if(!allSimpleVariables.getValue()) throw new UnsupportedOperationException(
						"Array assignment must be between variables and"
								+ " a expression/array of expressions");

				if(valueTree.getHead() == OperatorDiceNode.ARRAY) {
					if(nameTree.getChildrenCount() != valueTree.getChildrenCount())
						throw new UnsupportedOperationException(
								"Array assignment between arrays must be"
										+ " between two arrays of equal length");
				}
			} else
				throw new UnsupportedOperationException(
						"Assignment must be between a variable and a expression");
		}

		if(nameTree.getHead() == OperatorDiceNode.ARRAY) {
			if(valueTree.getHead() == OperatorDiceNode.ARRAY) {
				IHolder<Integer> childCounter = new Identity<>(0);

				ITree<IDiceASTNode> returnTree = new Tree<>(OperatorDiceNode.ARRAY);

				nameTree.doForChildren((child) -> {
					String variableName = child.transformHead((node) -> {
						return ((VariableDiceNode) node).getVariable();
					});

					ITree<IDiceASTNode> currentValue = valueTree.getChild(childCounter.getValue());

					ITree<IDiceASTNode> sanitizedSubtree = doSingleSanitize(ast, enviroment, child,
							currentValue, variableName);

					if(sanitizedSubtree == null) {
						ITree<IDiceASTNode> oldTree = new Tree<>(ast.getHead(), child,
								currentValue);

						returnTree.addChild(oldTree);
					} else {
						returnTree.addChild(sanitizedSubtree);
					}

					childCounter.transform((count) -> count + 1);
				});

				return returnTree;
			}

			ITree<IDiceASTNode> returnTree = new Tree<>(OperatorDiceNode.ARRAY);

			nameTree.doForChildren((child) -> {
				String variableName = child
						.transformHead((node) -> ((VariableDiceNode) node).getVariable());

				ITree<IDiceASTNode> sanitizedChild = doSingleSanitize(ast, enviroment, child, valueTree,
						variableName);
				if(sanitizedChild == null) {
					ITree<IDiceASTNode> oldTree = new Tree<>(ast.getHead(), child, valueTree);

					returnTree.addChild(oldTree);
				} else {
					returnTree.addChild(sanitizedChild);
				}
			});

			return returnTree;
		}

		String variableName = nameTree.transformHead((node) -> ((VariableDiceNode) node).getVariable());

		ITree<IDiceASTNode> sanitizedTree = doSingleSanitize(ast, enviroment, nameTree, valueTree,
				variableName);

		if(sanitizedTree == null) return ast;

		return sanitizedTree;
	}

	private static ITree<IDiceASTNode> doSingleSanitize(ITree<IDiceASTNode> ast,
			IMap<String, ITree<IDiceASTNode>> enviroment, ITree<IDiceASTNode> nameTree,
			ITree<IDiceASTNode> valueTree, String variableName) {
		if(enviroment.containsKey(variableName)) {
			// @ is a meta-variable standing for the left side of an
			// assignment
			ITree<IDiceASTNode> oldVal = enviroment.put("@", enviroment.get(variableName));

			// We should always inline out references to last,
			// because it
			// will always change
			ITree<IDiceASTNode> inlinedValue = DiceASTInliner.selectiveInline(valueTree, enviroment,
					variableName, "last", "@");

			if(oldVal != null) {
				enviroment.put("@", oldVal);
			} else {
				enviroment.remove("@");
			}

			return new Tree<>(ast.getHead(), nameTree, inlinedValue);
		}

		return null;
	}

	/**
	 * Sanitize the references in an AST
	 *
	 * @param ast
	 * @param enviroment
	 * @return The sanitized AST
	 */
	public static ITree<IDiceASTNode> sanitize(ITree<IDiceASTNode> ast,
			IMap<String, ITree<IDiceASTNode>> enviroment) {
		return ast.topDownTransform(DiceASTReferenceSanitizer::shouldSanitize, (subTree) -> {
			return doSanitize(subTree, enviroment);
		});
	}

	private static TopDownTransformResult shouldSanitize(IDiceASTNode node) {
		if(!node.isOperator()) return TopDownTransformResult.SKIP;

		switch((OperatorDiceNode) node) {
		case ASSIGN:
			return TopDownTransformResult.TRANSFORM;
		case ARRAY:
		case LET:
			return TopDownTransformResult.PASSTHROUGH;
		case ADD:
		case COMPOUND:
		case DIVIDE:
		case GROUP:
		case MULTIPLY:
		case SUBTRACT:
		default:
			return TopDownTransformResult.SKIP;
		}
	}
}