//! V4L2 backend for video streaming (placeholder for future implementation)

use super::{VideoBackendTrait, VideoStats, VideoFormat};
use crate::error::{Result, VideoError};
use std::sync::Arc;
use std::sync::Mutex;
use tracing::{debug, info, trace, warn};

/// V4L2 backend implementation (placeholder)
pub struct V4L2Backend {
    device_path: String,
    is_initialized: bool,
    stats: Arc<Mutex<VideoStats>>,
    config: V4L2Config,
}

/// V4L2 configuration
#[derive(Debug, Clone)]
pub struct V4L2Config {
    pub device_path: String,
    pub width: u32,
    pub height: u32,
    pub fps: u32,
    pub format: VideoFormat,
    pub buffer_size: usize,
}

impl Default for V4L2Config {
    fn default() -> Self {
        Self {
            device_path: "/dev/video10".to_string(),
            width: 640,
            height: 480,
            fps: 30,
            format: VideoFormat::MJPEG,
            buffer_size: 0x10000, // 64KB
        }
    }
}

impl V4L2Backend {
    /// Create a new V4L2 backend
    pub fn new() -> Result<Self> {
        let stats = VideoStats {
            backend_type: super::VideoBackendType::V4L2,
            ..Default::default()
        };
        
        Ok(Self {
            device_path: "/dev/video10".to_string(),
            is_initialized: false,
            stats: Arc::new(Mutex::new(stats)),
            config: V4L2Config::default(),
        })
    }

    /// Create a new V4L2 backend with custom configuration
    pub fn with_config(config: V4L2Config) -> Result<Self> {
        let stats = VideoStats {
            backend_type: super::VideoBackendType::V4L2,
            ..Default::default()
        };
        
        Ok(Self {
            device_path: config.device_path.clone(),
            is_initialized: false,
            stats: Arc::new(Mutex::new(stats)),
            config,
        })
    }

    /// Check if V4L2 device exists and is accessible
    fn check_device(&self) -> Result<()> {
        use std::path::Path;
        
        if !Path::new(&self.device_path).exists() {
            return Err(VideoError::V4L2(format!("Device not found: {}", self.device_path)).into());
        }

        // TODO: Check device permissions and capabilities
        debug!("V4L2 device found: {}", self.device_path);
        Ok(())
    }

    /// Update statistics
    fn update_stats(&self, frame_size: usize) {
        let mut stats = self.stats.lock().unwrap();
        stats.frames_pushed += 1;
        stats.total_bytes += frame_size as u64;
        stats.backend_type = super::VideoBackendType::V4L2;
        stats.is_ready = self.is_initialized;
        
        // Calculate FPS (simple rolling average)
        // TODO: Implement proper FPS calculation
        stats.fps = 30.0; // Placeholder
    }
}

impl VideoBackendTrait for V4L2Backend {
    fn initialize(&mut self) -> Result<()> {
        if self.is_initialized {
            warn!("V4L2 backend already initialized");
            return Ok(());
        }

        info!("Initializing V4L2 backend...");
        
        // Check if device exists and is accessible
        if let Err(e) = self.check_device() {
            warn!("V4L2 device check failed: {}", e);
            return Err(e);
        }

        // TODO: Implement actual V4L2 device initialization
        // For now, this is a placeholder that simulates success
        debug!("V4L2 initialization (placeholder) - would open device: {}", self.device_path);
        debug!("Format: {}x{} @ {}fps ({})", 
               self.config.width, 
               self.config.height, 
               self.config.fps, 
               self.config.format.as_str());

        self.is_initialized = true;
        info!("V4L2 backend initialized successfully (placeholder)");
        
        Ok(())
    }

    fn push_frame(&self, frame_data: &[u8]) -> Result<()> {
        if !self.is_initialized {
            return Err(VideoError::DeviceNotReady.into());
        }

        trace!("Pushing frame to V4L2 (placeholder): {} bytes", frame_data.len());

        // TODO: Implement actual frame pushing to V4L2
        // For now, this is a placeholder that simulates success
        debug!("Would push frame of {} bytes to V4L2 device: {}", frame_data.len(), self.device_path);

        // Update statistics
        self.update_stats(frame_data.len());

        trace!("Frame processed successfully (placeholder)");
        Ok(())
    }

    fn get_stats(&self) -> VideoStats {
        self.stats.lock().unwrap().clone()
    }

    fn is_ready(&self) -> bool {
        self.is_initialized
    }

    fn shutdown(&mut self) -> Result<()> {
        if !self.is_initialized {
            return Ok(());
        }

        info!("Shutting down V4L2 backend (placeholder)...");

        // TODO: Implement actual V4L2 device cleanup
        // For now, this is a placeholder that simulates success

        self.is_initialized = false;
        info!("V4L2 backend shut down successfully (placeholder)");

        Ok(())
    }
}

impl Drop for V4L2Backend {
    fn drop(&mut self) {
        if self.is_initialized {
            // Try to shutdown gracefully (synchronous)
            let _ = self.shutdown();
        }
    }
}

/// V4L2 device information (placeholder)
#[derive(Debug, Clone)]
pub struct V4L2DeviceInfo {
    pub device_path: String,
    pub driver_name: String,
    pub card_name: String,
    pub bus_info: String,
    pub capabilities: u32,
}

impl V4L2DeviceInfo {
    /// Create new device info
    pub fn new(device_path: String) -> Self {
        Self {
            device_path,
            driver_name: "Unknown".to_string(),
            card_name: "Unknown".to_string(),
            bus_info: "Unknown".to_string(),
            capabilities: 0,
        }
    }

    /// Check if device supports video output
    pub fn supports_video_output(&self) -> bool {
        // TODO: Implement capability checking
        true
    }

    /// Check if device supports MJPEG format
    pub fn supports_mjpeg(&self) -> bool {
        // TODO: Implement format checking
        true
    }
}

/// V4L2 format information (placeholder)
#[derive(Debug, Clone)]
pub struct V4L2Format {
    pub width: u32,
    pub height: u32,
    pub pixel_format: u32,
    pub field: u32,
    pub bytes_per_line: u32,
    pub size_image: u32,
    pub colorspace: u32,
}

impl V4L2Format {
    /// Create new format
    pub fn new(width: u32, height: u32, pixel_format: u32) -> Self {
        Self {
            width,
            height,
            pixel_format,
            field: 1, // V4L2_FIELD_NONE
            bytes_per_line: 0,
            size_image: width * height * 2, // Estimate for MJPEG
            colorspace: 1, // V4L2_COLORSPACE_SMPTE170M
        }
    }

    /// Get format description
    pub fn description(&self) -> String {
        format!("{}x{} @ {} bytes", self.width, self.height, self.size_image)
    }
}

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

    #[test]
    fn test_v4l2_config_default() {
        let config = V4L2Config::default();
        assert_eq!(config.device_path, "/dev/video10");
        assert_eq!(config.width, 640);
        assert_eq!(config.height, 480);
        assert_eq!(config.fps, 30);
        assert!(matches!(config.format, VideoFormat::MJPEG));
        assert_eq!(config.buffer_size, 0x10000);
    }

    #[test]
    fn test_v4l2_backend_creation() {
        let backend = V4L2Backend::new();
        assert!(backend.is_ok());
        
        let backend = backend.unwrap();
        assert!(!backend.is_initialized);
        assert_eq!(backend.device_path, "/dev/video10");
    }

    #[test]
    fn test_v4l2_backend_with_config() {
        let config = V4L2Config {
            device_path: "/dev/video20".to_string(),
            width: 1280,
            height: 720,
            fps: 60,
            ..Default::default()
        };
        
        let backend = V4L2Backend::with_config(config);
        assert!(backend.is_ok());
    }

    #[test]
    fn test_v4l2_device_info() {
        let device_info = V4L2DeviceInfo::new("/dev/video10".to_string());
        assert_eq!(device_info.device_path, "/dev/video10");
        assert_eq!(device_info.driver_name, "Unknown");
        assert!(device_info.supports_video_output());
        assert!(device_info.supports_mjpeg());
    }

    #[test]
    fn test_v4l2_format() {
        let format = V4L2Format::new(640, 480, 0x47504A4D); // MJPEG
        assert_eq!(format.width, 640);
        assert_eq!(format.height, 480);
        assert_eq!(format.pixel_format, 0x47504A4D);
        assert_eq!(format.description(), "640x480 @ 614400 bytes");
    }

    #[test]
    fn test_v4l2_backend_stats() {
        let backend = V4L2Backend::new().unwrap();
        let stats = backend.get_stats();
        
        assert_eq!(stats.frames_pushed, 0);
        assert_eq!(stats.total_bytes, 0);
        assert!(!stats.is_ready);
        assert!(matches!(stats.backend_type, super::super::VideoBackendType::V4L2));
    }

    #[test]
    fn test_v4l2_backend_ready_state() {
        let backend = V4L2Backend::new().unwrap();
        assert!(!backend.is_ready());
    }
}