using BuildFlow.Infrastructure.AI;
using FluentAssertions;
using Xunit;

namespace BuildFlow.Rag.Tests;

/// <summary>
/// [R5] 关键词提取器单元测试：Ngram 滑窗（确定性兜底）与 jieba 分词（生产默认）。
/// 纯本地计算，不依赖 PG/Redis 等基础设施。
/// </summary>
public class KeywordExtractorTests
{
    [Fact]
    public void Ngram_ChineseShortSegment_KeptWhole()
    {
        var result = new NgramKeywordExtractor().Extract("知识库是什么");
        // 连续中文段 "知识库是什么"（6 字 > 4）应产生 2-4 字滑窗子串
        result.Should().Contain("知识库");
        result.Should().Contain("是什么");
        result.Should().NotContain("知"); // 单字 n-gram 不产生
    }

    [Fact]
    public void Ngram_EnglishWords_LowercasedAndFiltered()
    {
        var result = new NgramKeywordExtractor().Extract("What is the Vector Database");
        result.Should().Contain("vector").And.Contain("database");
        result.Should().NotContain("what").And.NotContain("is").And.NotContain("the"); // 停用词
    }

    [Fact]
    public void Ngram_Deduplicates()
    {
        var result = new NgramKeywordExtractor().Extract("检索 检索");
        result.Count.Should().Be(result.Distinct().Count());
    }

    [Fact]
    public void Jieba_RealWords_NoNoiseSubstrings()
    {
        var result = new JiebaKeywordExtractor().Extract("如何搭建企业知识库检索系统");
        // 分词应产出真实词汇，而非全量 n-gram 子串
        result.Should().Contain("知识库");
        result.Should().Contain("检索");
        // 全量 2-4 字滑窗会产生 "何搭" 之类噪声子串，jieba 不应出现
        result.Should().NotContain("何搭");
        // 停用词 "如何" 应被过滤
        result.Should().NotContain("如何");
    }

    [Fact]
    public void Jieba_EnglishLowercased()
    {
        var result = new JiebaKeywordExtractor().Extract("pgvector Hybrid Search");
        result.Should().Contain("pgvector").And.Contain("hybrid").And.Contain("search");
    }

    [Fact]
    public void Jieba_EmptyInput_ReturnsEmpty()
    {
        new JiebaKeywordExtractor().Extract("").Should().BeEmpty();
        new NgramKeywordExtractor().Extract("").Should().BeEmpty();
    }

    [Fact]
    public void Jieba_ComparedToNgram_FewerKeywords()
    {
        const string question = "如何搭建企业知识库检索系统";
        var jiebaCount = new JiebaKeywordExtractor().Extract(question).Count;
        var ngramCount = new NgramKeywordExtractor().Extract(question).Count;
        // R5 的核心收益：真词数量显著少于 n-gram 子串数量（召回 SQL 参数收敛）
        jiebaCount.Should().BeLessThan(ngramCount);
    }
}