// 蒸馏质量回溯 — LLM 反向验证 L0 → L1 蒸馏质量
// 深度整合步骤 4：采样 20 条 → L1→L0' 重建 → cosine 比较

use reqwest::blocking::Client;
use serde::{Deserialize, Serialize};
use std::time::Duration;

/// 质量回溯样本
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct QualitySample {
    pub memory_id: String,
    pub distilled_content: String,    // L1 蒸馏后内容
    pub original_episode: String,     // L0 原始对话
    pub category: String,
    pub tier: String,                 // fresh / core / useful / not-useful
}

/// 回溯结果
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct QualityBacktraceResult {
    pub score: f64,                     // 整体 cos(L0, L0') 平均
    pub low_info_loss: usize,           // score < 0.7 的条目数
    pub hallucinations: usize,          // 疑似幻觉数
    pub total: usize,
    pub details: Vec<SampleBacktrace>,
}

#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct SampleBacktrace {
    pub memory_id: String,
    pub cosine: f64,
    pub verdict: String,    // pass / retry / hallucination
    pub re_distilled: String,
}

/// 质量回溯器
pub struct QualityBacktracer {
    pub llm_endpoint: String,    // LLM API 端点 (new-api / molfang)
    pub llm_model: String,
    pub client: Client,
    pub score_threshold: f64,   // 信息损失阈值 (默认 0.7)
}

impl QualityBacktracer {
    pub fn new(llm_endpoint: &str, llm_model: &str) -> Self {
        Self {
            llm_endpoint: llm_endpoint.to_string(),
            llm_model: llm_model.to_string(),
            client: Client::builder()
                .timeout(Duration::from_secs(30))
                .build()
                .unwrap_or_default(),
            score_threshold: 0.7,
        }
    }

    /// 执行质量回溯
    pub fn backtrace(
        &self,
        samples: &[QualitySample],
        embed_fn: &dyn Fn(&str) -> Result<Vec<f32>, Box<dyn std::error::Error>>,
    ) -> Result<QualityBacktraceResult, Box<dyn std::error::Error>> {
        let mut details = Vec::new();
        let mut low_info_count = 0usize;
        let mut hallucination_count = 0usize;
        let mut total_cosine = 0.0f64;

        for sample in samples {
            // Step 1: LLM 反向重建 L0' from L1
            let re_distilled = match self.reverse_distill(&sample.distilled_content) {
                Ok(r) => r,
                Err(e) => {
                    eprintln!("[quality] 反向蒸馏失败 for {}: {}", sample.memory_id, e);
                    continue;
                }
            };

            // Step 2: 计算 cos(L0, L0')
            let l0_vec = embed_fn(&sample.original_episode)?;
            let l0_prime_vec = embed_fn(&re_distilled)?;
            let cosine = cosine_similarity(&l0_vec, &l0_prime_vec);

            // Step 3: 判定
            let verdict = if cosine < 0.5 {
                hallucination_count += 1;
                "hallucination"
            } else if cosine < self.score_threshold {
                low_info_count += 1;
                "retry"
            } else {
                "pass"
            };

            total_cosine += cosine;

            details.push(SampleBacktrace {
                memory_id: sample.memory_id.clone(),
                cosine,
                verdict: verdict.to_string(),
                re_distilled,
            });
        }

        let total = details.len();
        let score = if total > 0 { total_cosine / total as f64 } else { 0.0 };

        let result = QualityBacktraceResult {
            score,
            low_info_loss: low_info_count,
            hallucinations: hallucination_count,
            total,
            details,
        };

        eprintln!(
            "[quality] backtrace {} samples: score={:.3}, low_info={}, hallucinations={}",
            total, score, low_info_count, hallucination_count,
        );

        Ok(result)
    }

    /// LLM 反向蒸馏 — L1 → L0' 重建
    fn reverse_distill(&self, distilled: &str) -> Result<String, Box<dyn std::error::Error>> {
        let prompt = format!(
            "你看到了一条蒸馏后的记忆事实：\n\n{}\n\n请还原这段事实可能来自怎样的原始对话。只输出还原后的对话文本，不要解释。",
            distilled
        );

        let body = serde_json::json!({
            "model": self.llm_model,
            "messages": [
                {"role": "user", "content": prompt}
            ],
            "temperature": 0.3,
            "max_tokens": 200
        });

        let resp = self.client
            .post(&self.llm_endpoint)
            .header("Content-Type", "application/json")
            .body(serde_json::to_string(&body)?)
            .send()?
            .text()?;

        let parsed: serde_json::Value = serde_json::from_str(&resp)?;
        let content = parsed["choices"][0]["message"]["content"]
            .as_str()
            .unwrap_or("")
            .to_string();

        Ok(content)
    }
}

/// 分层抽样策略：从不同 tier 抽取样本
pub fn stratified_sample(
    samples: &[QualitySample],
    fresh: usize,
    core: usize,
    useful: usize,
    not_useful: usize,
) -> Vec<QualitySample> {
    let mut selected = Vec::new();

    let mut by_tier: std::collections::HashMap<&str, Vec<&QualitySample>> =
        std::collections::HashMap::new();

    for s in samples {
        by_tier.entry(&s.tier).or_insert_with(Vec::new).push(s);
    }

    let tiers = [
        ("fresh", fresh),
        ("core", core),
        ("useful", useful),
        ("not_useful", not_useful),
    ];

    for (tier, count) in &tiers {
        if let Some(list) = by_tier.get(tier) {
            let take = (*count).min(list.len());
            for s in list.iter().take(take) {
                selected.push((*s).clone());
            }
        }
    }

    eprintln!(
        "[quality] stratified sample: {} total (fresh={}, core={}, useful={}, not_useful={})",
        selected.len(), fresh, core, useful, not_useful
    );

    selected
}

fn cosine_similarity(a: &[f32], b: &[f32]) -> f64 {
    let n = a.len().min(b.len());
    if n == 0 {
        return 0.0;
    }
    let (mut dot, mut na, mut nb) = (0.0f64, 0.0f64, 0.0f64);
    for i in 0..n {
        let ai = a[i] as f64;
        let bi = b[i] as f64;
        dot += ai * bi;
        na += ai * ai;
        nb += bi * bi;
    }
    let denom = na.sqrt() * nb.sqrt();
    if denom > 1e-10 {
        (dot / denom).max(0.0)
    } else {
        0.0
    }
}