//! Drift detection for local Episteme operations.
//!
//! Tracks changes between current code claims and prior observations.

use stemedb_core::types::Assertion;
use tracing::{debug, info, instrument};

use crate::types::{predicates, DriftResult, Observation, Verdict};
use crate::AphoriaError;

use super::helpers::assertion_to_prior_observation;
use super::local::LocalEpisteme;

impl LocalEpisteme {
    /// Check for drift between current claims and prior observations.
    ///
    /// A drift is detected when a claim's value differs from a previously
    /// recorded observation for the same concept path. Only claims that
    /// have no authority conflict should be passed here.
    ///
    /// Returns a list of drift results for claims whose values changed.
    #[instrument(skip(self, claims), fields(claim_count = claims.len()))]
    pub async fn check_drift(
        &self,
        claims: &[Observation],
    ) -> Result<Vec<DriftResult>, AphoriaError> {
        let mut drifts = Vec::new();

        for claim in claims {
            // Look up prior observations for this concept
            let observations = self.fetch_observations_for_concept(&claim.concept_path).await?;

            // If there's a prior observation, check if the value changed
            if let Some(prior_assertion) = observations.first() {
                // Value differs - this is drift
                if prior_assertion.object != claim.value {
                    let prior = assertion_to_prior_observation(prior_assertion);

                    drifts.push(DriftResult {
                        claim: claim.clone(),
                        prior,
                        verdict: Verdict::Drift,
                    });

                    debug!(
                        concept_path = %claim.concept_path,
                        prior_value = ?prior_assertion.object,
                        current_value = ?claim.value,
                        "Drift detected"
                    );
                }
            }
        }

        info!(drifts = drifts.len(), "Drift check complete");
        Ok(drifts)
    }

    /// Fetch prior observations for a specific concept path.
    ///
    /// Returns observations sorted by timestamp descending (most recent first).
    #[instrument(skip(self), fields(concept_path = %concept_path))]
    pub async fn fetch_observations_for_concept(
        &self,
        concept_path: &str,
    ) -> Result<Vec<Assertion>, AphoriaError> {
        use stemedb_storage::PredicateIndexStore;

        // Get all observation hashes from the predicate index
        let hashes =
            self.predicate_index_store.get_by_predicate(predicates::OBSERVATION).await.map_err(
                |e| {
                    AphoriaError::Storage(format!(
                        "Failed to get observation hashes for predicate index: {e}"
                    ))
                },
            )?;

        let mut observations = Vec::new();

        for hash in hashes {
            if let Some(assertion) = self.load_assertion_by_hash(&hash).await {
                // Check if this observation is for the same concept (subject match)
                // The observation's subject should match the concept_path
                if assertion.subject == concept_path {
                    observations.push(assertion);
                }
            }
        }

        // Sort by timestamp descending (most recent first)
        observations.sort_by(|a, b| b.timestamp.cmp(&a.timestamp));

        debug!(concept_path, count = observations.len(), "Fetched observations for concept");
        Ok(observations)
    }
}