import java.util.List;

public class ProgressMonitor implements Runnable {

    private final String fileName;
    private final int totalSizeMB;
    private final List<ChunkStatus> chunks;
    private final long monitorDelayMs;
    private double previousTotalDownloadedMB;
    private long previousTimeMs;


    public ProgressMonitor(DownloadConfig config, List<ChunkStatus> chunks) {
        this.fileName = config.getFileName();
        this.totalSizeMB = config.getTotalSizeMB();
        this.chunks = chunks;
        this.monitorDelayMs = 500;
        this.previousTotalDownloadedMB = 0.0;
        this.previousTimeMs = System.currentTimeMillis();
    }

    @Override
    public void run() {
        // Repeatedly check chunk progress until all chunks are completed.
        // In each loop:
        // 1. Read the downloaded size from every chunk
        // 2. Add all downloaded amounts to totalDownloadedMB
        // 3. Count completed chunks
        // 4. Print a progress message
        // 5. If completedChunks == chunks.size(), print a final monitor message and stop
        // 6. Otherwise, sleep for monitorDelayMs and continue
        while (true) {
            double totalDownloadedMB = 0.0;
            int completedChunks = 0;

            for (ChunkStatus chunk : chunks) {
                totalDownloadedMB += chunk.getDownloadedMB();

                if (chunk.isCompleted()) {
                    completedChunks++;
                }
            }

            double percent = 0.0;
            if (totalSizeMB > 0) {
                percent = (totalDownloadedMB * 100.0) / totalSizeMB;
            }

            long currentTimeMs = System.currentTimeMillis();
            long timeDiffMs = currentTimeMs - previousTimeMs;
            double downloadedDiff = totalDownloadedMB - previousTotalDownloadedMB;

            double speedMBps = 0.0;
            if (timeDiffMs > 0){
                speedMBps = (downloadedDiff * 1000.0) / timeDiffMs;
            }

            double etaSeconds = 0.0;
            if (speedMBps > 0 && totalDownloadedMB < totalSizeMB){
                double remainingMB =totalSizeMB - totalDownloadedMB;
                etaSeconds = remainingMB / speedMBps;
            }

            previousTotalDownloadedMB = totalDownloadedMB;
            previousTimeMs = currentTimeMs;


            int barWidth = 50;
            int filledWidth = (int)(barWidth * percent / 100.0);

            System.out.print("[");
            for (int i = 0; i < barWidth; i++) {
                if (i < filledWidth){
                    System.out.print("=");
                }else if (i == filledWidth && percent< 100){
                    System.out.print(">");
                }else {
                    System.out.print(" ");
                }
            }
            System.out.print("]");

            System.out.printf(
                    "Progress for %s: %.1f/%.1f MB (%.2f%%), completed chunks: %d/%d%n , ETA: %s",
                    fileName,
                    totalDownloadedMB,
                    (double) totalSizeMB,
                    percent,
                    completedChunks,
                    chunks.size(),
                    speedMBps,
                    formatETA(etaSeconds)
            );

            if (completedChunks == chunks.size()){
                System.out.println("All chunks have been downloaded successfully!");
                break;
            }

            try {
                Thread.sleep(monitorDelayMs);
            } catch (InterruptedException e) {
                System.out.println("Progress monitor interrupted.");
                return;
            }
        }
    }
    private String formatETA(double etaSeconds){
        if (etaSeconds <= 0){
            return "Calculating ...";
        }
        int hours = (int)(etaSeconds/3600);
        int minutes = (int)((etaSeconds%3600)/60);
        int secondes = (int)(etaSeconds %60);

        if (hours > 0){
            return String.format("%dh %dm %ds" , hours, minutes, secondes);
        }else if(minutes > 0){
            return String.format("%dm %ds" , minutes, secondes);
        }else{
            return String.format("%ds", secondes);
        }
    }
}