package com.diagnose.util;

import java.util.*;

public class StringMatcher {

    private final int GRAM_SIZE = 1;

    private Map<String, Set<Integer>> indexMap = new HashMap<>();
    private List<String> dataList;
    
    public StringMatcher(List<String> dataList) {
        this.dataList = dataList;
        buildIndex();
    }
    
    private void buildIndex() {
        // 为了平衡性能和内存，可以考虑只索引n-gram
        for (int i = 0; i < dataList.size(); i++) {
            String s = dataList.get(i);
            // 生成所有可能的子串或n-gram
            for (int j = 0; j < s.length() - GRAM_SIZE + 1; j++) {
                String gram = s.substring(j, j + GRAM_SIZE); // n-gram
                indexMap.computeIfAbsent(gram, k -> new HashSet<>()).add(i);
            }
        }
    }
    
    public List<String> search(String query, int limit) {
        // 如果查询字符串长度小于GRAM_SIZE，使用简单遍历
        if (query.length() < GRAM_SIZE) {
            return simpleSearch(query, limit);
        }
        
        Set<Integer> candidates = null;
        
        // 使用查询的n-gram找候选集
        for (int i = 0; i <= query.length() - GRAM_SIZE; i++) {
            String gram = query.substring(i, i + GRAM_SIZE);
            Set<Integer> indices = indexMap.getOrDefault(gram, Collections.emptySet());
            
            if (candidates == null) {
                candidates = new HashSet<>(indices);
            } else {
                candidates.retainAll(indices);
            }
            
            if (candidates.isEmpty()) {
                return Collections.emptyList();
            }
        }
        
        // 验证候选集
        List<String> result = new ArrayList<>();
        for (Integer idx : candidates) {
            if (dataList.get(idx).contains(query)) {
                result.add(dataList.get(idx));
                if (result.size() >= limit) {
                    break;
                }
            }
        }
        
        return result;
    }
    
    private List<String> simpleSearch(String query, int limit) {
        // 简单遍历法
        List<String> result = new ArrayList<>();
        for (String s : dataList) {
            if (s.contains(query)) {
                result.add(s);
                if (result.size() >= limit) {
                    break;
                }
            }
        }
        return result;
    }
}