package util;

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

/**
 * [简要描述类的用途]
 *
 * <p>[更详细的说明，可以包括背景信息、用途等]</p>
 *
 * <p>注释中的段落使用 HTML 标签包裹，例如 `<p>` 或 `<ul>`。</p>
 *
 * @author cyq
 * @version V1.0
 * @since V1.0
 */
public class ObjectPathUtil {
    public record Rule(String targetPath, String mvelExpr) {}

    public sealed interface PathSeg permits KeySeg, IndexSeg {}

    public record KeySeg(String key) implements PathSeg {}
    public record IndexSeg(int index) implements PathSeg {}

    public static List<PathSeg> parsePath(String path) {
        List<PathSeg> result = new ArrayList<>();
        int i = 0;

        while (i < path.length()) {
            if (path.charAt(i) == '.') {
                i++;
                continue;
            }

            if (path.charAt(i) == '[') {
                int end = path.indexOf(']', i);
                int index = Integer.parseInt(path.substring(i + 1, end));
                result.add(new IndexSeg(index));
                i = end + 1;
            } else {
                int start = i;
                while (i < path.length()
                        && path.charAt(i) != '.'
                        && path.charAt(i) != '[') {
                    i++;
                }
                result.add(new KeySeg(path.substring(start, i)));
            }
        }
        return result;
    }

    public static Object putValue(Object root, List<PathSeg> path, Object value) {
        if (root == null) {
            root = (path.get(0) instanceof IndexSeg) ? new ArrayList<>() : new HashMap<>();
        }

        Object current = root;

        for (int i = 0; i < path.size(); i++) {
            PathSeg seg = path.get(i);
            boolean last = (i == path.size() - 1);

            if (seg instanceof KeySeg keySeg) {
                Map<String, Object> map = castMap(current);

                if (last) {
                    map.put(keySeg.key(), value);
                } else {
                    Object next = map.get(keySeg.key());
                    if (next == null) {
                        next = createNext(path.get(i + 1));
                        map.put(keySeg.key(), next);
                    }
                    current = next;
                }
            }

            if (seg instanceof IndexSeg indexSeg) {
                List<Object> list = castList(current);
                int idx = indexSeg.index();

                while (list.size() <= idx) {
                    list.add(null);
                }

                if (last) {
                    list.set(idx, value);
                } else {
                    Object next = list.get(idx);
                    if (next == null) {
                        next = createNext(path.get(i + 1));
                        list.set(idx, next);
                    }
                    current = next;
                }
            }
        }
        return root;
    }

    private static Map<String, Object> castMap(Object o) {
        if (o instanceof Map) return (Map<String, Object>) o;
        throw new IllegalStateException("Expected Map but got " + o);
    }

    private static List<Object> castList(Object o) {
        if (o instanceof List) return (List<Object>) o;
        throw new IllegalStateException("Expected List but got " + o);
    }

    private static Object createNext(PathSeg nextSeg) {
        return (nextSeg instanceof IndexSeg) ? new ArrayList<>() : new HashMap<>();
    }
}