/// Append-only event journal.
/// Every mutation to any dataset is recorded here as an immutable event.
/// Events are never modified or deleted — this IS the audit trail.
///
/// Storage: events buffer in memory, flush to Parquet periodically.
/// Query: load Parquet files, filter by entity/field/actor/time.

use arrow::array::{ArrayRef, RecordBatch, StringArray, UInt64Array};
use arrow::datatypes::{DataType, Field, Schema};
use chrono::{DateTime, Utc};
use object_store::ObjectStore;
use serde::{Deserialize, Serialize};
use std::sync::Arc;
use tokio::sync::RwLock;

use shared::arrow_helpers::record_batch_to_parquet;
use storaged::ops;

/// A single mutation event. Immutable once created.
#[derive(Debug, Clone, Serialize, Deserialize)]
pub struct Event {
    pub event_id: String,
    pub timestamp: DateTime<Utc>,
    pub entity_type: String,    // "candidate", "placement", "client", etc.
    pub entity_id: String,      // "CAND-00342"
    pub field: String,           // "phone", "*" for insert/delete
    pub action: String,          // "insert", "update", "delete"
    pub old_value: String,       // "" for inserts
    pub new_value: String,       // "" for deletes
    pub actor: String,           // "Sarah", "ingest_pipeline", "auto_matcher"
    pub source: String,          // "api", "ingest", "workspace", "agent"
    pub workspace_id: String,    // "" if not workspace-scoped
}

/// Arrow schema for journal Parquet files.
fn journal_schema() -> Arc<Schema> {
    Arc::new(Schema::new(vec![
        Field::new("event_id", DataType::Utf8, false),
        Field::new("timestamp", DataType::Utf8, false),
        Field::new("entity_type", DataType::Utf8, false),
        Field::new("entity_id", DataType::Utf8, false),
        Field::new("field", DataType::Utf8, false),
        Field::new("action", DataType::Utf8, false),
        Field::new("old_value", DataType::Utf8, true),
        Field::new("new_value", DataType::Utf8, true),
        Field::new("actor", DataType::Utf8, false),
        Field::new("source", DataType::Utf8, false),
        Field::new("workspace_id", DataType::Utf8, true),
    ]))
}

/// The event journal — buffers events in memory, flushes to Parquet.
#[derive(Clone)]
pub struct Journal {
    buffer: Arc<RwLock<Vec<Event>>>,
    store: Arc<dyn ObjectStore>,
    flush_threshold: usize,
    event_counter: Arc<std::sync::atomic::AtomicU64>,
}

impl Journal {
    pub fn new(store: Arc<dyn ObjectStore>, flush_threshold: usize) -> Self {
        Self {
            buffer: Arc::new(RwLock::new(Vec::new())),
            store,
            flush_threshold,
            event_counter: Arc::new(std::sync::atomic::AtomicU64::new(0)),
        }
    }

    /// Record a single event. Triggers flush if buffer exceeds threshold.
    pub async fn record(&self, mut event: Event) -> Result<(), String> {
        let seq = self.event_counter.fetch_add(1, std::sync::atomic::Ordering::Relaxed);
        event.event_id = format!("evt-{}-{seq}", event.timestamp.timestamp_millis());

        let should_flush = {
            let mut buf = self.buffer.write().await;
            buf.push(event);
            buf.len() >= self.flush_threshold
        };

        if should_flush {
            self.flush().await?;
        }

        Ok(())
    }

    /// Record a batch insert (multiple rows added to a dataset).
    pub async fn record_insert(
        &self,
        entity_type: &str,
        entity_id: &str,
        actor: &str,
        source: &str,
        workspace_id: &str,
    ) -> Result<(), String> {
        self.record(Event {
            event_id: String::new(),
            timestamp: Utc::now(),
            entity_type: entity_type.to_string(),
            entity_id: entity_id.to_string(),
            field: "*".to_string(),
            action: "insert".to_string(),
            old_value: String::new(),
            new_value: String::new(),
            actor: actor.to_string(),
            source: source.to_string(),
            workspace_id: workspace_id.to_string(),
        }).await
    }

    /// Record a field update.
    pub async fn record_update(
        &self,
        entity_type: &str,
        entity_id: &str,
        field: &str,
        old_value: &str,
        new_value: &str,
        actor: &str,
        source: &str,
        workspace_id: &str,
    ) -> Result<(), String> {
        self.record(Event {
            event_id: String::new(),
            timestamp: Utc::now(),
            entity_type: entity_type.to_string(),
            entity_id: entity_id.to_string(),
            field: field.to_string(),
            action: "update".to_string(),
            old_value: old_value.to_string(),
            new_value: new_value.to_string(),
            actor: actor.to_string(),
            source: source.to_string(),
            workspace_id: workspace_id.to_string(),
        }).await
    }

    /// Record a batch of events from a dataset ingest.
    pub async fn record_ingest(
        &self,
        entity_type: &str,
        count: usize,
        actor: &str,
        source_file: &str,
    ) -> Result<(), String> {
        self.record(Event {
            event_id: String::new(),
            timestamp: Utc::now(),
            entity_type: entity_type.to_string(),
            entity_id: format!("batch:{count}"),
            field: "*".to_string(),
            action: "ingest".to_string(),
            old_value: String::new(),
            new_value: format!("{count} rows from {source_file}"),
            actor: actor.to_string(),
            source: "ingest".to_string(),
            workspace_id: String::new(),
        }).await
    }

    /// Flush buffer to Parquet. Called automatically at threshold or manually.
    pub async fn flush(&self) -> Result<usize, String> {
        let events = {
            let mut buf = self.buffer.write().await;
            if buf.is_empty() { return Ok(0); }
            std::mem::take(&mut *buf)
        };

        let n = events.len();
        let batch = events_to_batch(&events)?;
        let parquet = record_batch_to_parquet(&batch)?;

        let ts = Utc::now().format("%Y%m%d_%H%M%S_%3f");
        let key = format!("journal/{ts}.parquet");
        ops::put(&self.store, &key, parquet).await?;

        tracing::info!("journal: flushed {n} events to {key}");
        Ok(n)
    }

    /// Query journal: get all events for a specific entity.
    pub async fn get_entity_history(&self, entity_id: &str) -> Result<Vec<Event>, String> {
        let mut all_events = Vec::new();

        // Check in-memory buffer first
        {
            let buf = self.buffer.read().await;
            for e in buf.iter() {
                if e.entity_id == entity_id {
                    all_events.push(e.clone());
                }
            }
        }

        // Load from persisted journal files
        let keys = ops::list(&self.store, Some("journal/")).await?;
        for key in &keys {
            if !key.ends_with(".parquet") { continue; }
            let data = ops::get(&self.store, key).await?;
            let (_, batches) = shared::arrow_helpers::parquet_to_record_batches(&data)?;
            for batch in &batches {
                let events = batch_to_events(batch)?;
                for e in events {
                    if e.entity_id == entity_id {
                        all_events.push(e);
                    }
                }
            }
        }

        all_events.sort_by_key(|e| e.timestamp);
        Ok(all_events)
    }

    /// Query journal: get recent events (last N).
    pub async fn get_recent(&self, limit: usize) -> Result<Vec<Event>, String> {
        let mut all_events = Vec::new();

        // Buffer
        {
            let buf = self.buffer.read().await;
            all_events.extend(buf.iter().cloned());
        }

        // Persisted (load most recent files first)
        let mut keys = ops::list(&self.store, Some("journal/")).await?;
        keys.sort();
        keys.reverse();

        for key in &keys {
            if !key.ends_with(".parquet") { continue; }
            if all_events.len() >= limit { break; }
            let data = ops::get(&self.store, key).await?;
            let (_, batches) = shared::arrow_helpers::parquet_to_record_batches(&data)?;
            for batch in &batches {
                all_events.extend(batch_to_events(batch)?);
            }
        }

        all_events.sort_by_key(|e| e.timestamp);
        all_events.reverse();
        all_events.truncate(limit);
        Ok(all_events)
    }

    /// Get buffer stats.
    pub async fn stats(&self) -> JournalStats {
        let buf = self.buffer.read().await;
        let keys = ops::list(&self.store, Some("journal/")).await.unwrap_or_default();
        JournalStats {
            buffer_events: buf.len(),
            flush_threshold: self.flush_threshold,
            persisted_files: keys.len(),
            total_events_created: self.event_counter.load(std::sync::atomic::Ordering::Relaxed),
        }
    }
}

#[derive(Debug, Clone, Serialize)]
pub struct JournalStats {
    pub buffer_events: usize,
    pub flush_threshold: usize,
    pub persisted_files: usize,
    pub total_events_created: u64,
}

fn events_to_batch(events: &[Event]) -> Result<RecordBatch, String> {
    let schema = journal_schema();
    let arrays: Vec<ArrayRef> = vec![
        Arc::new(StringArray::from(events.iter().map(|e| e.event_id.as_str()).collect::<Vec<_>>())),
        Arc::new(StringArray::from(events.iter().map(|e| e.timestamp.to_rfc3339()).collect::<Vec<_>>())),
        Arc::new(StringArray::from(events.iter().map(|e| e.entity_type.as_str()).collect::<Vec<_>>())),
        Arc::new(StringArray::from(events.iter().map(|e| e.entity_id.as_str()).collect::<Vec<_>>())),
        Arc::new(StringArray::from(events.iter().map(|e| e.field.as_str()).collect::<Vec<_>>())),
        Arc::new(StringArray::from(events.iter().map(|e| e.action.as_str()).collect::<Vec<_>>())),
        Arc::new(StringArray::from(events.iter().map(|e| e.old_value.as_str()).collect::<Vec<_>>())),
        Arc::new(StringArray::from(events.iter().map(|e| e.new_value.as_str()).collect::<Vec<_>>())),
        Arc::new(StringArray::from(events.iter().map(|e| e.actor.as_str()).collect::<Vec<_>>())),
        Arc::new(StringArray::from(events.iter().map(|e| e.source.as_str()).collect::<Vec<_>>())),
        Arc::new(StringArray::from(events.iter().map(|e| e.workspace_id.as_str()).collect::<Vec<_>>())),
    ];
    RecordBatch::try_new(schema, arrays).map_err(|e| format!("batch error: {e}"))
}

fn batch_to_events(batch: &RecordBatch) -> Result<Vec<Event>, String> {
    let get_col = |i: usize| -> Result<&StringArray, String> {
        batch.column(i).as_any().downcast_ref::<StringArray>()
            .ok_or_else(|| format!("column {i} not string"))
    };

    let event_ids = get_col(0)?;
    let timestamps = get_col(1)?;
    let entity_types = get_col(2)?;
    let entity_ids = get_col(3)?;
    let fields = get_col(4)?;
    let actions = get_col(5)?;
    let old_values = get_col(6)?;
    let new_values = get_col(7)?;
    let actors = get_col(8)?;
    let sources = get_col(9)?;
    let workspace_ids = get_col(10)?;

    let mut events = Vec::with_capacity(batch.num_rows());
    for i in 0..batch.num_rows() {
        events.push(Event {
            event_id: event_ids.value(i).to_string(),
            timestamp: timestamps.value(i).parse().unwrap_or_else(|_| Utc::now()),
            entity_type: entity_types.value(i).to_string(),
            entity_id: entity_ids.value(i).to_string(),
            field: fields.value(i).to_string(),
            action: actions.value(i).to_string(),
            old_value: old_values.value(i).to_string(),
            new_value: new_values.value(i).to_string(),
            actor: actors.value(i).to_string(),
            source: sources.value(i).to_string(),
            workspace_id: workspace_ids.value(i).to_string(),
        });
    }
    Ok(events)
}