solidb 1.2.2

//! Conflict Resolution Strategies for Offline Sync
//!
//! When concurrent modifications occur (version vectors are concurrent),
//! a conflict resolution strategy determines how to merge or select the winner.

use crate::sync::version_vector::{ConflictInfo, VectorComparison, VersionVector};
use serde_json::Value;
use std::sync::Arc;

/// Trait for conflict resolution strategies
#[async_trait::async_trait]
pub trait ConflictResolver: Send + Sync {
    /// Resolve a conflict between two versions of a document
    ///
    /// Returns the winning document and optionally a merged version
    async fn resolve(&self, conflict: &ConflictInfo) -> ConflictResolution;

    /// Get the name of this resolver
    fn name(&self) -> &'static str;
}

/// Result of conflict resolution
#[derive(Debug, Clone)]
pub enum ConflictResolution {
    /// Use the local version
    LocalWins,
    /// Use the remote version
    RemoteWins,
    /// Use a custom merged version
    Merged(Value),
    /// Keep both as conflicting (requires manual resolution)
    KeepBoth { local: Value, remote: Value },
}

/// Predefined conflict resolution strategies
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum ConflictResolutionStrategy {
    /// Last-write-wins based on HLC timestamp (default)
    LastWriteWins,
    /// Use the version with the higher lexicographical node ID (deterministic)
    Deterministic,
    /// Automatic merge for CRDT-compatible types
    AutomaticMerge,
    /// Keep both versions and require manual resolution
    Manual,
    /// Custom Lua script resolver (not implemented; falls back to Manual)
    CustomScript,
}

impl ConflictResolutionStrategy {
    /// Create a resolver for this strategy
    pub fn create_resolver(&self) -> Arc<dyn ConflictResolver> {
        match self {
            ConflictResolutionStrategy::LastWriteWins => Arc::new(LastWriteWinsResolver),
            ConflictResolutionStrategy::Deterministic => Arc::new(DeterministicResolver),
            ConflictResolutionStrategy::AutomaticMerge => Arc::new(AutomaticMergeResolver),
            ConflictResolutionStrategy::Manual => Arc::new(ManualResolver),
            // Audit L6: the unsandboxed Lua resolver that used to back this
            // variant was never wired up and was removed; conflicts under this
            // strategy are kept for manual resolution.
            ConflictResolutionStrategy::CustomScript => Arc::new(ManualResolver),
        }
    }
}

/// Last-Write-Wins resolver using HLC timestamps
pub struct LastWriteWinsResolver;

#[async_trait::async_trait]
impl ConflictResolver for LastWriteWinsResolver {
    async fn resolve(&self, conflict: &ConflictInfo) -> ConflictResolution {
        let local_ts = conflict.local_vector.hlc_timestamp();
        let remote_ts = conflict.remote_vector.hlc_timestamp();

        if local_ts > remote_ts {
            ConflictResolution::LocalWins
        } else if remote_ts > local_ts {
            ConflictResolution::RemoteWins
        } else {
            // Timestamps equal - use counter as tiebreaker
            let local_cnt = conflict.local_vector.hlc_counter();
            let remote_cnt = conflict.remote_vector.hlc_counter();

            if local_cnt >= remote_cnt {
                ConflictResolution::LocalWins
            } else {
                ConflictResolution::RemoteWins
            }
        }
    }

    fn name(&self) -> &'static str {
        "last_write_wins"
    }
}

/// Deterministic resolver using node ID comparison
/// Always produces the same winner given the same conflict
pub struct DeterministicResolver;

#[async_trait::async_trait]
impl ConflictResolver for DeterministicResolver {
    async fn resolve(&self, conflict: &ConflictInfo) -> ConflictResolution {
        // Get the node that made the most recent change in each vector
        let local_node = conflict
            .local_vector
            .nodes()
            .max()
            .map(|s| s.as_str())
            .unwrap_or("");
        let remote_node = conflict
            .remote_vector
            .nodes()
            .max()
            .map(|s| s.as_str())
            .unwrap_or("");

        if local_node >= remote_node {
            ConflictResolution::LocalWins
        } else {
            ConflictResolution::RemoteWins
        }
    }

    fn name(&self) -> &'static str {
        "deterministic"
    }
}

/// Automatic merge resolver for CRDT-compatible documents
pub struct AutomaticMergeResolver;

#[async_trait::async_trait]
impl ConflictResolver for AutomaticMergeResolver {
    async fn resolve(&self, conflict: &ConflictInfo) -> ConflictResolution {
        // Try to merge CRDT fields automatically
        if let (Some(local), Some(remote)) = (&conflict.local_data, &conflict.remote_data) {
            if let Some(merged) = attempt_crdt_merge(local, remote) {
                return ConflictResolution::Merged(merged);
            }
        }

        // Fall back to last-write-wins if automatic merge not possible
        let resolver = LastWriteWinsResolver;
        resolver.resolve(conflict).await
    }

    fn name(&self) -> &'static str {
        "automatic_merge"
    }
}

/// Manual resolver that keeps both versions
pub struct ManualResolver;

#[async_trait::async_trait]
impl ConflictResolver for ManualResolver {
    async fn resolve(&self, conflict: &ConflictInfo) -> ConflictResolution {
        ConflictResolution::KeepBoth {
            local: conflict.local_data.clone().unwrap_or(Value::Null),
            remote: conflict.remote_data.clone().unwrap_or(Value::Null),
        }
    }

    fn name(&self) -> &'static str {
        "manual"
    }
}

/// Attempt to automatically merge two documents using CRDT rules
/// Returns None if automatic merge is not possible
fn attempt_crdt_merge(local: &Value, remote: &Value) -> Option<Value> {
    match (local, remote) {
        // Merge objects field by field
        (Value::Object(local_map), Value::Object(remote_map)) => {
            let mut merged = serde_json::Map::new();

            // Add all fields from local
            for (key, value) in local_map {
                merged.insert(key.clone(), value.clone());
            }

            // Merge or overwrite with remote fields
            for (key, remote_value) in remote_map {
                if let Some(local_value) = local_map.get(key) {
                    // Field exists in both - try to merge
                    if let Some(merged_value) = attempt_crdt_merge(local_value, remote_value) {
                        merged.insert(key.clone(), merged_value);
                    } else {
                        // Can't merge - use remote (LWW)
                        merged.insert(key.clone(), remote_value.clone());
                    }
                } else {
                    // Field only in remote - add it
                    merged.insert(key.clone(), remote_value.clone());
                }
            }

            Some(Value::Object(merged))
        }
        // For primitive types, use remote (LWW behavior for non-CRDT fields)
        _ => None,
    }
}

/// Detect conflicts between two version vectors
pub fn detect_conflict(
    local_vector: &VersionVector,
    remote_vector: &VersionVector,
) -> Option<VectorComparison> {
    let comparison = local_vector.compare(remote_vector);

    match comparison {
        VectorComparison::Concurrent => Some(comparison),
        _ => None,
    }
}

/// Convenience function to resolve a conflict using a strategy
pub async fn resolve_conflict(
    strategy: ConflictResolutionStrategy,
    conflict: &ConflictInfo,
) -> ConflictResolution {
    let resolver = strategy.create_resolver();
    resolver.resolve(conflict).await
}

/// Apply conflict resolution to get the final document value
pub fn apply_resolution(
    resolution: &ConflictResolution,
    local: Option<&Value>,
    remote: Option<&Value>,
) -> Option<Value> {
    match resolution {
        ConflictResolution::LocalWins => local.cloned(),
        ConflictResolution::RemoteWins => remote.cloned(),
        ConflictResolution::Merged(merged) => Some(merged.clone()),
        ConflictResolution::KeepBoth { local, remote } => {
            // Create a conflict marker document
            let mut conflict_doc = serde_json::Map::new();
            conflict_doc.insert("_conflict".to_string(), Value::Bool(true));
            conflict_doc.insert("_local".to_string(), local.clone());
            conflict_doc.insert("_remote".to_string(), remote.clone());
            Some(Value::Object(conflict_doc))
        }
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::sync::version_vector::VersionVector;
    use serde_json::json;

    fn create_conflict_info(local_ts: u64, remote_ts: u64) -> ConflictInfo {
        let mut local_vector = VersionVector::new();
        local_vector.set_hlc(local_ts, 0);
        local_vector.increment("node-1");

        let mut remote_vector = VersionVector::new();
        remote_vector.set_hlc(remote_ts, 0);
        remote_vector.increment("node-2");

        ConflictInfo {
            document_key: "test-1".to_string(),
            collection: "test".to_string(),
            local_vector,
            remote_vector,
            local_data: Some(json!({"field": "local"})),
            remote_data: Some(json!({"field": "remote"})),
            detected_at: 0,
        }
    }

    #[tokio::test]
    async fn test_last_write_wins_local() {
        let resolver = LastWriteWinsResolver;
        let conflict = create_conflict_info(100, 50); // Local is newer

        let result = resolver.resolve(&conflict).await;
        assert!(matches!(result, ConflictResolution::LocalWins));
    }

    #[tokio::test]
    async fn test_last_write_wins_remote() {
        let resolver = LastWriteWinsResolver;
        let conflict = create_conflict_info(50, 100); // Remote is newer

        let result = resolver.resolve(&conflict).await;
        assert!(matches!(result, ConflictResolution::RemoteWins));
    }

    #[tokio::test]
    async fn test_deterministic_resolution() {
        let resolver = DeterministicResolver;
        let conflict = create_conflict_info(50, 50); // Same timestamp

        let result = resolver.resolve(&conflict).await;
        // node-2 > node-1 (lexicographically '2' > '1'), so remote wins
        assert!(matches!(result, ConflictResolution::RemoteWins));
    }

    #[tokio::test]
    async fn test_manual_resolution() {
        let resolver = ManualResolver;
        let conflict = create_conflict_info(50, 50);

        let result = resolver.resolve(&conflict).await;
        assert!(matches!(result, ConflictResolution::KeepBoth { .. }));
    }

    #[test]
    fn test_crdt_merge_objects() {
        let local = json!({
            "name": "Alice",
            "age": 30,
            "crdt_counter": { "_type": "GCounter", "value": 5 }
        });
        let remote = json!({
            "name": "Alice",
            "age": 31,
            "email": "alice@example.com"
        });

        let merged = attempt_crdt_merge(&local, &remote);
        assert!(merged.is_some());

        let merged = merged.unwrap();
        assert_eq!(merged["name"], "Alice");
        assert_eq!(merged["age"], 31); // Remote wins for age
        assert_eq!(merged["email"], "alice@example.com");
    }
}