use std::sync::atomic::{AtomicBool, AtomicU64, AtomicUsize, Ordering};
use std::sync::{Arc, Mutex};
use std::time::Instant;

use rayon::prelude::*;

use crate::encoder::OutputEncoder;
use crate::error::{PixstripError, Result};
use crate::loader::ImageLoader;
use crate::operations::resize::resize_image;
use crate::operations::watermark::apply_watermark;
use crate::operations::{Flip, Rotation};
use crate::pipeline::ProcessingJob;
use crate::types::ImageFormat;

#[derive(Debug, Clone)]
pub struct ProgressUpdate {
    pub current: usize,
    pub total: usize,
    pub current_file: String,
    pub succeeded_so_far: usize,
    pub failed_so_far: usize,
}

#[derive(Debug, Clone)]
pub struct BatchResult {
    pub total: usize,
    pub succeeded: usize,
    pub failed: usize,
    pub cancelled: bool,
    pub total_input_bytes: u64,
    pub total_output_bytes: u64,
    pub errors: Vec<(String, String)>,
    pub elapsed_ms: u64,
}

pub struct PipelineExecutor {
    cancel_flag: Arc<AtomicBool>,
    pause_flag: Arc<AtomicBool>,
    thread_count: usize,
    pause_on_error: bool,
}

impl PipelineExecutor {
    pub fn new() -> Self {
        Self {
            cancel_flag: Arc::new(AtomicBool::new(false)),
            pause_flag: Arc::new(AtomicBool::new(false)),
            thread_count: num_cpus(),
            pause_on_error: false,
        }
    }

    pub fn with_cancel(cancel_flag: Arc<AtomicBool>) -> Self {
        Self {
            cancel_flag,
            pause_flag: Arc::new(AtomicBool::new(false)),
            thread_count: num_cpus(),
            pause_on_error: false,
        }
    }

    pub fn with_cancel_and_pause(
        cancel_flag: Arc<AtomicBool>,
        pause_flag: Arc<AtomicBool>,
    ) -> Self {
        Self {
            cancel_flag,
            pause_flag,
            thread_count: num_cpus(),
            pause_on_error: false,
        }
    }

    pub fn set_thread_count(&mut self, count: usize) {
        self.thread_count = if count == 0 { num_cpus() } else { count };
    }

    pub fn set_pause_on_error(&mut self, pause: bool) {
        self.pause_on_error = pause;
    }

    pub fn execute<F>(&self, job: &ProcessingJob, mut on_progress: F) -> Result<BatchResult>
    where
        F: FnMut(ProgressUpdate) + Send,
    {
        let start = Instant::now();
        let total = job.sources.len();

        if total == 0 {
            return Ok(BatchResult {
                total: 0,
                succeeded: 0,
                failed: 0,
                cancelled: false,
                total_input_bytes: 0,
                total_output_bytes: 0,
                errors: Vec::new(),
                elapsed_ms: 0,
            });
        }

        // Use single-threaded path when thread_count is 1
        if self.thread_count <= 1 {
            return self.execute_sequential(job, on_progress);
        }

        // Build a scoped rayon thread pool with the configured count
        let pool = rayon::ThreadPoolBuilder::new()
            .num_threads(self.thread_count)
            .build()
            .map_err(|e| PixstripError::Processing {
                operation: "thread_pool".into(),
                reason: e.to_string(),
            })?;

        let completed = AtomicUsize::new(0);
        let succeeded_count = AtomicUsize::new(0);
        let failed_count = AtomicUsize::new(0);
        let input_bytes = AtomicU64::new(0);
        let output_bytes = AtomicU64::new(0);
        let cancelled = AtomicBool::new(false);
        let errors: Mutex<Vec<(String, String)>> = Mutex::new(Vec::new());

        // Channel for progress updates from worker threads to the callback
        let (tx, rx) = std::sync::mpsc::channel::<ProgressUpdate>();

        let cancel_flag = &self.cancel_flag;
        let pause_flag = &self.pause_flag;
        let pause_on_error = self.pause_on_error;

        // Run the parallel work in a scoped thread so we can drain progress concurrently
        std::thread::scope(|scope| {
            // Spawn the rayon pool work
            let tx_clone = tx.clone();
            let completed_ref = &completed;
            let succeeded_ref = &succeeded_count;
            let failed_ref = &failed_count;
            let input_bytes_ref = &input_bytes;
            let output_bytes_ref = &output_bytes;
            let cancelled_ref = &cancelled;
            let errors_ref = &errors;

            let worker = scope.spawn(move || {
                pool.install(|| {
                    job.sources.par_iter().enumerate().for_each(|(idx, source)| {
                        // Check cancel
                        if cancel_flag.load(Ordering::Relaxed) {
                            cancelled_ref.store(true, Ordering::Relaxed);
                            return;
                        }

                        // Wait while paused
                        while pause_flag.load(Ordering::Relaxed) {
                            std::thread::sleep(std::time::Duration::from_millis(100));
                            if cancel_flag.load(Ordering::Relaxed) {
                                cancelled_ref.store(true, Ordering::Relaxed);
                                return;
                            }
                        }

                        if cancelled_ref.load(Ordering::Relaxed) {
                            return;
                        }

                        let file_name = source
                            .path
                            .file_name()
                            .and_then(|n| n.to_str())
                            .unwrap_or("unknown")
                            .to_string();

                        let current = completed_ref.fetch_add(1, Ordering::Relaxed) + 1;

                        let _ = tx_clone.send(ProgressUpdate {
                            current,
                            total,
                            current_file: file_name.clone(),
                            succeeded_so_far: succeeded_ref.load(Ordering::Relaxed),
                            failed_so_far: failed_ref.load(Ordering::Relaxed),
                        });

                        let loader = ImageLoader::new();
                        let encoder = OutputEncoder::new();

                        match Self::process_single_static(job, source, &loader, &encoder, idx) {
                            Ok((in_size, out_size)) => {
                                succeeded_ref.fetch_add(1, Ordering::Relaxed);
                                input_bytes_ref.fetch_add(in_size, Ordering::Relaxed);
                                output_bytes_ref.fetch_add(out_size, Ordering::Relaxed);
                            }
                            Err(e) => {
                                failed_ref.fetch_add(1, Ordering::Relaxed);
                                if let Ok(mut errs) = errors_ref.lock() {
                                    errs.push((file_name, e.to_string()));
                                }
                                if pause_on_error {
                                    pause_flag.store(true, Ordering::Relaxed);
                                }
                            }
                        }
                    });
                });
                // Drop sender so the receiver loop ends
                drop(tx_clone);
            });

            // Drop the original sender so only the worker's clone keeps the channel open
            drop(tx);

            // Drain progress updates on this thread (the calling thread)
            for update in rx {
                on_progress(update);
            }

            // Wait for worker to finish (it already has by the time rx is drained)
            let _ = worker.join();
        });

        Ok(BatchResult {
            total,
            succeeded: succeeded_count.load(Ordering::Relaxed),
            failed: failed_count.load(Ordering::Relaxed),
            cancelled: cancelled.load(Ordering::Relaxed),
            total_input_bytes: input_bytes.load(Ordering::Relaxed),
            total_output_bytes: output_bytes.load(Ordering::Relaxed),
            errors: errors.into_inner().unwrap_or_default(),
            elapsed_ms: start.elapsed().as_millis() as u64,
        })
    }

    fn execute_sequential<F>(&self, job: &ProcessingJob, mut on_progress: F) -> Result<BatchResult>
    where
        F: FnMut(ProgressUpdate) + Send,
    {
        let start = Instant::now();
        let total = job.sources.len();
        let loader = ImageLoader::new();
        let encoder = OutputEncoder::new();

        let mut result = BatchResult {
            total,
            succeeded: 0,
            failed: 0,
            cancelled: false,
            total_input_bytes: 0,
            total_output_bytes: 0,
            errors: Vec::new(),
            elapsed_ms: 0,
        };

        for (i, source) in job.sources.iter().enumerate() {
            if self.cancel_flag.load(Ordering::Relaxed) {
                result.cancelled = true;
                break;
            }

            while self.pause_flag.load(Ordering::Relaxed) {
                std::thread::sleep(std::time::Duration::from_millis(100));
                if self.cancel_flag.load(Ordering::Relaxed) {
                    result.cancelled = true;
                    break;
                }
            }
            if result.cancelled {
                break;
            }

            let file_name = source
                .path
                .file_name()
                .and_then(|n| n.to_str())
                .unwrap_or("unknown")
                .to_string();

            on_progress(ProgressUpdate {
                current: i + 1,
                total,
                current_file: file_name.clone(),
                succeeded_so_far: result.succeeded,
                failed_so_far: result.failed,
            });

            match Self::process_single_static(job, source, &loader, &encoder, i) {
                Ok((input_size, output_size)) => {
                    result.succeeded += 1;
                    result.total_input_bytes += input_size;
                    result.total_output_bytes += output_size;
                }
                Err(e) => {
                    result.failed += 1;
                    result.errors.push((file_name, e.to_string()));
                    if self.pause_on_error {
                        self.pause_flag.store(true, Ordering::Relaxed);
                    }
                }
            }
        }

        result.elapsed_ms = start.elapsed().as_millis() as u64;
        Ok(result)
    }

    fn process_single_static(
        job: &ProcessingJob,
        source: &crate::types::ImageSource,
        loader: &ImageLoader,
        encoder: &OutputEncoder,
        index: usize,
    ) -> std::result::Result<(u64, u64), PixstripError> {
        let input_size = std::fs::metadata(&source.path)
            .map(|m| m.len())
            .unwrap_or(0);

        // Load image
        let mut img = loader.load_pixels(&source.path)?;

        // Rotation
        if let Some(ref rotation) = job.rotation {
            img = match rotation {
                Rotation::None => img,
                Rotation::Cw90 => img.rotate90(),
                Rotation::Cw180 => img.rotate180(),
                Rotation::Cw270 => img.rotate270(),
                Rotation::AutoOrient => img,
            };
        }

        // Flip
        if let Some(ref flip) = job.flip {
            img = match flip {
                Flip::None => img,
                Flip::Horizontal => img.fliph(),
                Flip::Vertical => img.flipv(),
            };
        }

        // Resize
        if let Some(ref config) = job.resize {
            img = resize_image(&img, config)?;
        }

        // Watermark (after resize so watermark is at correct scale)
        if let Some(ref config) = job.watermark {
            img = apply_watermark(img, config)?;
        }

        // Determine output format
        let output_format = if let Some(ref convert) = job.convert {
            let input_fmt = source.original_format.unwrap_or(ImageFormat::Jpeg);
            convert.output_format(input_fmt)
        } else {
            source.original_format.unwrap_or(ImageFormat::Jpeg)
        };

        // Determine quality
        let quality = job.compress.as_ref().map(|c| match c {
            crate::operations::CompressConfig::Preset(preset) => {
                encoder.quality_for_format(output_format, preset)
            }
            crate::operations::CompressConfig::Custom {
                jpeg_quality,
                png_level: _,
                webp_quality,
                avif_quality: _,
            } => match output_format {
                ImageFormat::Jpeg => jpeg_quality.unwrap_or(85),
                ImageFormat::WebP => webp_quality.map(|q| q as u8).unwrap_or(80),
                _ => 85,
            },
        });

        // Determine output path (with rename if configured)
        let output_path = if let Some(ref rename) = job.rename {
            let stem = source
                .path
                .file_stem()
                .and_then(|s| s.to_str())
                .unwrap_or("output");
            let ext = output_format.extension();

            if let Some(ref template) = rename.template {
                let dims = Some((img.width(), img.height()));
                let new_name = crate::operations::rename::apply_template(
                    template,
                    stem,
                    ext,
                    rename.counter_start + index as u32,
                    dims,
                );
                job.output_dir.join(new_name)
            } else {
                let new_name = rename.apply_simple(stem, ext, index as u32 + 1);
                job.output_dir.join(new_name)
            }
        } else {
            job.output_path_for(source, Some(output_format))
        };

        // Ensure output directory exists
        if let Some(parent) = output_path.parent() {
            std::fs::create_dir_all(parent).map_err(PixstripError::Io)?;
        }

        // Encode and save
        encoder.encode_to_file(&img, &output_path, output_format, quality)?;

        // Metadata stripping: re-encoding through the image crate naturally
        // strips all EXIF/metadata. No additional action is needed for
        // StripAll, Privacy, or Custom modes. KeepAll mode would require
        // copying EXIF tags back from the source file using little_exif.
        if let Some(ref meta_config) = job.metadata {
            if matches!(meta_config, crate::operations::MetadataConfig::KeepAll) {
                copy_metadata_from_source(&source.path, &output_path);
            }
        }

        let output_size = std::fs::metadata(&output_path)
            .map(|m| m.len())
            .unwrap_or(0);

        Ok((input_size, output_size))
    }
}

impl Default for PipelineExecutor {
    fn default() -> Self {
        Self::new()
    }
}

fn num_cpus() -> usize {
    std::thread::available_parallelism()
        .map(|n| n.get())
        .unwrap_or(1)
}

fn copy_metadata_from_source(source: &std::path::Path, output: &std::path::Path) {
    // Best-effort: try to copy EXIF from source to output using little_exif.
    // If it fails (e.g. non-JPEG, no EXIF), silently continue.
    let Ok(metadata) = little_exif::metadata::Metadata::new_from_path(source) else {
        return;
    };
    let _: std::result::Result<(), std::io::Error> = metadata.write_to_file(output);
}