//! M3.6.4 — Reference Cycle Guard: Prevent R chunks from re-entering as evidence
//!
//! Extends M4.2's derived filter to detect when reference document text appears
//! in session transcripts and marks them as derived (not evidence).
//! Uses shingle matching at section granularity with configurable thresholds.


use std::collections::HashMap;

/// Artifact (skill or reference) in the manifest
#[derive(Debug, Clone)]
pub struct Artifact {
    pub kind: String,        // "skill" or "reference"
    pub name: String,
    pub sha256: String,
    pub shingles: Vec<String>,
    pub emitted_at: String,
}

/// Shingle match result
#[derive(Debug, Clone)]
pub struct ShingleMatch {
    pub artifact_sha: String,
    pub artifact_name: String,
    pub overlap_score: f32,  // 0.0-1.0
    pub matched_shingles_count: usize,
    pub total_shingles: usize,
}

/// Reference cycle guard configuration
#[derive(Debug, Clone)]
pub struct CycleGuardConfig {
    pub skill_threshold: f32,      // M4.2 default: 0.8 (high precision)
    pub reference_threshold: f32,  // M3.6.4 default: 0.5 (section-level match)
    pub min_shingle_overlap: usize, // Minimum shingles to consider a match
}

impl Default for CycleGuardConfig {
    fn default() -> Self {
        Self {
            skill_threshold: 0.80,
            reference_threshold: 0.50,
            min_shingle_overlap: 3,
        }
    }
}

/// Cycle guard orchestrator
pub struct ReferenceCycleGuard {
    config: CycleGuardConfig,
    artifact_manifest: HashMap<String, Artifact>,
}

impl ReferenceCycleGuard {
    pub fn new(config: CycleGuardConfig) -> Self {
        Self {
            config,
            artifact_manifest: HashMap::new(),
        }
    }

    /// Add an artifact to the manifest
    pub fn register_artifact(&mut self, artifact: Artifact) {
        self.artifact_manifest.insert(artifact.sha256.clone(), artifact);
    }

    /// Check if a chunk matches any reference in manifest
    pub fn detect_derived_reference(
        &self,
        _content: &str,
        content_shingles: &[String],
    ) -> Option<ShingleMatch> {
        // Compute shingle overlap with all reference artifacts
        for (_, artifact) in self.artifact_manifest.iter() {
            if artifact.kind != "reference" {
                continue;
            }

            let matches = self.shingle_overlap(content_shingles, &artifact.shingles);
            
            if matches.matched_count >= self.config.min_shingle_overlap {
                let overlap_score = matches.matched_count as f32 / artifact.shingles.len() as f32;
                
                if overlap_score >= self.config.reference_threshold {
                    return Some(ShingleMatch {
                        artifact_sha: artifact.sha256.clone(),
                        artifact_name: artifact.name.clone(),
                        overlap_score,
                        matched_shingles_count: matches.matched_count,
                        total_shingles: artifact.shingles.len(),
                    });
                }
            }
        }

        None
    }

    /// Compute shingle overlap between two sets
    fn shingle_overlap(
        &self,
        text_shingles: &[String],
        artifact_shingles: &[String],
    ) -> ShingleOverlapResult {
        let artifact_set: std::collections::HashSet<_> = artifact_shingles.iter().collect();
        let matched_count = text_shingles
            .iter()
            .filter(|s| artifact_set.contains(s))
            .count();

        ShingleOverlapResult { matched_count }
    }
}

struct ShingleOverlapResult {
    matched_count: usize,
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_cycle_guard_creation() {
        let guard = ReferenceCycleGuard::new(CycleGuardConfig::default());
        assert_eq!(guard.config.reference_threshold, 0.50);
        assert_eq!(guard.config.skill_threshold, 0.80);
    }

    #[test]
    fn test_register_reference_artifact() {
        let mut guard = ReferenceCycleGuard::new(CycleGuardConfig::default());
        
        let artifact = Artifact {
            kind: "reference".to_string(),
            name: "kubectl-debugging".to_string(),
            sha256: "abc123def456".to_string(),
            shingles: vec!["pod".to_string(), "logs".to_string()],
            emitted_at: "2026-08-21T10:00:00Z".to_string(),
        };

        guard.register_artifact(artifact);
        assert_eq!(guard.artifact_manifest.len(), 1);
    }

    #[test]
    fn test_detect_verbatim_reference() {
        let mut guard = ReferenceCycleGuard::new(CycleGuardConfig::default());
        
        let artifact = Artifact {
            kind: "reference".to_string(),
            name: "kubectl-guide".to_string(),
            sha256: "ref123".to_string(),
            shingles: vec![
                "kubectl logs".to_string(),
                "check pod".to_string(),
                "debug issue".to_string(),
            ],
            emitted_at: "2026-08-21T00:00:00Z".to_string(),
        };
        guard.register_artifact(artifact);

        // Verbatim match
        let content_shingles = vec![
            "kubectl logs".to_string(),
            "check pod".to_string(),
            "debug issue".to_string(),
        ];

        let result = guard.detect_derived_reference("test content", &content_shingles);
        
        assert!(result.is_some());
        let match_result = result.unwrap();
        assert_eq!(match_result.artifact_name, "kubectl-guide");
        assert!(match_result.overlap_score >= guard.config.reference_threshold);
    }

    #[test]
    fn test_ignore_low_overlap() {
        let mut guard = ReferenceCycleGuard::new(CycleGuardConfig::default());
        
        let artifact = Artifact {
            kind: "reference".to_string(),
            name: "guide".to_string(),
            sha256: "ref456".to_string(),
            shingles: vec!["a".to_string(), "b".to_string(), "c".to_string()],
            emitted_at: "2026-08-21T00:00:00Z".to_string(),
        };
        guard.register_artifact(artifact);

        // Only 1 shingle matches (below min_shingle_overlap=3)
        let content_shingles = vec!["a".to_string(), "x".to_string(), "y".to_string()];
        let result = guard.detect_derived_reference("content", &content_shingles);
        
        assert!(result.is_none());
    }

    #[test]
    fn test_skill_vs_reference_thresholds() {
        let config = CycleGuardConfig {
            skill_threshold: 0.80,
            reference_threshold: 0.50,
            min_shingle_overlap: 3,
        };

        assert!(config.skill_threshold > config.reference_threshold);
        println!("✓ Skill threshold {} > Reference threshold {}", 
            config.skill_threshold, config.reference_threshold);
    }

    #[test]
    fn test_derived_flag_in_log() {
        // Records marked as derived should have "derived": true in log
        let record_json = r#"
        {
            "kind": "transcript",
            "derived": true,
            "derived_from": "ref:abc123def456",
            "text": "kubectl logs showed the error"
        }
        "#;

        assert!(record_json.contains("\"derived\": true"));
        assert!(record_json.contains("derived_from"));
    }
}