use std::sync::Mutex;

use serde::{Deserialize, Serialize};

use crate::progress::ReadingPosition;

/// Maximum number of events before oldest are dropped to prevent unbounded memory growth.
const MAX_BUFFER_SIZE: usize = 1000;

// Global event buffer, protected by a Mutex for thread safety.
static EVENT_BUFFER: Mutex<Vec<ReadingEvent>> = Mutex::new(Vec::new());

/// Push a reading event into the global buffer.
/// If the buffer exceeds MAX_BUFFER_SIZE, the oldest event is dropped.
#[deprecated(since = "0.2.0", note = "Use events_v2::push_heartbeat_v2 etc. instead")]
pub fn push_reading_event(event: ReadingEvent) {
    match EVENT_BUFFER.lock() {
        Ok(mut buf) => {
            if buf.len() >= MAX_BUFFER_SIZE {
                buf.remove(0);
            }
            buf.push(event);
        }
        Err(_) => { /* poison: silently drop event */ }
    }
}

#[deprecated(since = "0.2.0", note = "Use events_v2::push_position_changed_v2 instead")]
/// Record a position change as a PositionChanged event.
pub fn update_reading_position(material_id: &str, position: ReadingPosition) {
    let event = ReadingEvent::PositionChanged {
        material_id: material_id.to_string(),
        position,
        timestamp_ms: now_ms(),
    };
    push_reading_event(event);
}

/// Export all pending events without clearing.
#[deprecated(since = "0.2.0", note = "Use events_v2::export_pending_events_v2 instead")]
pub fn export_pending_events() -> Vec<ReadingEvent> {
    EVENT_BUFFER.lock().map(|buf| buf.clone()).unwrap_or_default()
}

/// Remove the first `count` events after successful upload.
pub fn clear_exported_events(count: usize) {
    if let Ok(mut buf) = EVENT_BUFFER.lock() {
        let n = count.min(buf.len());
        buf.drain(..n);
    }
}

fn now_ms() -> i64 {
    use std::time::SystemTime;
    SystemTime::now()
        .duration_since(SystemTime::UNIX_EPOCH)
        .map(|d| d.as_millis() as i64)
        .unwrap_or(0)
}

#[derive(Debug, Clone, PartialEq, Serialize, Deserialize, uniffi::Enum)]
#[serde(tag = "type")]
pub enum ReadingEvent {
    MaterialOpened {
        material_id: String,
        timestamp_ms: i64,
    },
    MaterialClosed {
        material_id: String,
        timestamp_ms: i64,
        active_seconds: u32,
    },
    PositionChanged {
        material_id: String,
        position: ReadingPosition,
        timestamp_ms: i64,
    },
    Heartbeat {
        material_id: String,
        active_seconds: u32,
        position: Option<ReadingPosition>,
        timestamp_ms: i64,
    },
    MarkedAsRead {
        material_id: String,
        timestamp_ms: i64,
    },
}

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

    // Serialize event buffer tests to prevent races on the global EVENT_BUFFER.
    static TEST_LOCK: Mutex<()> = Mutex::new(());

    fn setup() {
        clear_exported_events(usize::MAX);
    }

    #[test]
    fn test_material_opened_serde() {
        let e = ReadingEvent::MaterialOpened {
            material_id: "abc".into(),
            timestamp_ms: 1000,
        };
        let json = serde_json::to_string(&e).unwrap();
        assert!(json.contains("\"type\":\"MaterialOpened\""));
        let back: ReadingEvent = serde_json::from_str(&json).unwrap();
        assert_eq!(back, e);
    }

    #[test]
    fn test_material_closed_serde() {
        let e = ReadingEvent::MaterialClosed {
            material_id: "abc".into(),
            timestamp_ms: 2000,
            active_seconds: 120,
        };
        let json = serde_json::to_string(&e).unwrap();
        let back: ReadingEvent = serde_json::from_str(&json).unwrap();
        assert_eq!(back, e);
    }

    #[test]
    fn test_position_changed_serde() {
        let e = ReadingEvent::PositionChanged {
            material_id: "abc".into(),
            position: ReadingPosition::Markdown { block_id: "h1".into(), scroll_progress: 0.5 },
            timestamp_ms: 3000,
        };
        let json = serde_json::to_string(&e).unwrap();
        let back: ReadingEvent = serde_json::from_str(&json).unwrap();
        assert_eq!(back, e);
    }

    #[test]
    fn test_heartbeat_serde() {
        let e = ReadingEvent::Heartbeat {
            material_id: "abc".into(),
            active_seconds: 15,
            position: None,
            timestamp_ms: 4000,
        };
        let json = serde_json::to_string(&e).unwrap();
        let back: ReadingEvent = serde_json::from_str(&json).unwrap();
        assert_eq!(back, e);
    }

    #[test]
    fn test_heartbeat_with_position_serde() {
        let e = ReadingEvent::Heartbeat {
            material_id: "abc".into(),
            active_seconds: 15,
            position: Some(ReadingPosition::Pdf { page_number: 3, page_progress: 0.5, overall_progress: 0.1 }),
            timestamp_ms: 5000,
        };
        let json = serde_json::to_string(&e).unwrap();
        let back: ReadingEvent = serde_json::from_str(&json).unwrap();
        assert_eq!(back, e);
    }

    #[test]
    fn test_marked_as_read_serde() {
        let e = ReadingEvent::MarkedAsRead {
            material_id: "abc".into(),
            timestamp_ms: 6000,
        };
        let json = serde_json::to_string(&e).unwrap();
        let back: ReadingEvent = serde_json::from_str(&json).unwrap();
        assert_eq!(back, e);
    }

    #[test]
    fn test_push_and_export() {
        let _guard = TEST_LOCK.lock().unwrap();
        setup();
        push_reading_event(ReadingEvent::MaterialOpened {
            material_id: "m1".into(),
            timestamp_ms: 1000,
        });
        push_reading_event(ReadingEvent::MarkedAsRead {
            material_id: "m1".into(),
            timestamp_ms: 2000,
        });
        let events = export_pending_events();
        assert_eq!(events.len(), 2);
    }

    #[test]
    fn test_clear_exported() {
        let _guard = TEST_LOCK.lock().unwrap();
        setup();
        push_reading_event(ReadingEvent::MaterialOpened {
            material_id: "m1".into(),
            timestamp_ms: 1000,
        });
        push_reading_event(ReadingEvent::MaterialOpened {
            material_id: "m2".into(),
            timestamp_ms: 2000,
        });
        push_reading_event(ReadingEvent::MaterialOpened {
            material_id: "m3".into(),
            timestamp_ms: 3000,
        });
        clear_exported_events(2);
        let events = export_pending_events();
        assert_eq!(events.len(), 1);
    }

    #[test]
    fn test_update_reading_position() {
        let _guard = TEST_LOCK.lock().unwrap();
        setup();
        update_reading_position(
            "m1",
            ReadingPosition::Markdown { block_id: "h1".into(), scroll_progress: 0.5 },
        );
        let events = export_pending_events();
        assert_eq!(events.len(), 1);
        assert!(matches!(events[0], ReadingEvent::PositionChanged { .. }));
    }

    #[test]
    fn test_empty_export() {
        let _guard = TEST_LOCK.lock().unwrap();
        setup();
        let events = export_pending_events();
        assert!(events.is_empty());
    }
}