document.addEventListener('DOMContentLoaded', () => {
    // DOM Elements
    const dropZone = document.getElementById('drop-zone');
    const fileInput = document.getElementById('file-input');
    const filePreview = document.getElementById('file-preview');
    const fileName = document.getElementById('file-name');
    const fileSize = document.getElementById('file-size');
    const removeFileBtn = document.getElementById('remove-file-btn');
    const transcribeBtn = document.getElementById('transcribe-btn');
    
    const uploadSection = document.getElementById('upload-section');
    const processingSection = document.getElementById('processing-section');
    const resultSection = document.getElementById('result-section');
    
    const detectedLang = document.getElementById('detected-lang');
    const captionsList = document.getElementById('captions-list');
    const fullTextContent = document.getElementById('full-text-content');
    
    const copyTextBtn = document.getElementById('copy-text-btn');
    const downloadTxtBtn = document.getElementById('download-txt-btn');
    const downloadSrtBtn = document.getElementById('download-srt-btn');
    const newTranscriptionBtn = document.getElementById('new-transcription-btn');
    
    const tabBtns = document.querySelectorAll('.tab-btn');
    const tabContents = document.querySelectorAll('.tab-content');
    
    const toast = document.getElementById('toast');
    const toastMessage = document.getElementById('toast-message');

    // State
    let selectedFile = null;
    let transcriptionResult = null;

    // --- File Upload Logic ---
    
    // Click to upload
    dropZone.addEventListener('click', (e) => {
        if (e.target !== removeFileBtn && !removeFileBtn.contains(e.target)) {
            fileInput.click();
        }
    });

    fileInput.addEventListener('change', (e) => {
        if (e.target.files.length > 0) {
            handleFile(e.target.files[0]);
        }
    });

    // Drag and drop
    dropZone.addEventListener('dragover', (e) => {
        e.preventDefault();
        dropZone.classList.add('dragover');
    });

    dropZone.addEventListener('dragleave', () => {
        dropZone.classList.remove('dragover');
    });

    dropZone.addEventListener('drop', (e) => {
        e.preventDefault();
        dropZone.classList.remove('dragover');
        if (e.dataTransfer.files.length > 0) {
            handleFile(e.dataTransfer.files[0]);
        }
    });

    function handleFile(file) {
        // Validate file type
        const validTypes = ['video/mp4', 'video/quicktime', 'video/x-msvideo', 'video/webm', 'video/x-matroska'];
        if (!validTypes.includes(file.type) && !file.name.match(/\.(mp4|mov|avi|webm|mkv)$/i)) {
            showToast('Invalid file format. Please upload a video.', true);
            return;
        }

        // Validate file size (e.g., 50MB max to prevent huge uploads locally)
        const maxSize = 50 * 1024 * 1024;
        if (file.size > maxSize) {
            showToast('File is too large. Max size is 50MB.', true);
            return;
        }

        selectedFile = file;
        fileName.textContent = file.name;
        fileSize.textContent = formatBytes(file.size);
        
        dropZone.style.display = 'none';
        filePreview.classList.remove('hidden');
        transcribeBtn.classList.remove('hidden');
    }

    removeFileBtn.addEventListener('click', (e) => {
        e.stopPropagation();
        selectedFile = null;
        fileInput.value = '';
        dropZone.style.display = 'block';
        filePreview.classList.add('hidden');
        transcribeBtn.classList.add('hidden');
    });

    // --- API & Processing ---

    transcribeBtn.addEventListener('click', async () => {
        if (!selectedFile) return;

        // Show processing
        uploadSection.classList.add('hidden');
        processingSection.classList.remove('hidden');

        const formData = new FormData();
        formData.append('file', selectedFile);
        
        const apiKeyInput = document.getElementById('api-key-input');
        if (apiKeyInput && apiKeyInput.value.trim() !== '') {
            formData.append('api_key', apiKeyInput.value.trim());
        }

        let apiUrl = '/api/transcribe';
        // Fallback for local development if opened directly or via Live Server
        if (window.location.protocol === 'file:' || window.location.port === '5500' || window.location.hostname === '127.0.0.1' && window.location.port !== '8000') {
            apiUrl = 'http://127.0.0.1:8000/api/transcribe';
        }

        try {
            const response = await fetch(apiUrl, {
                method: 'POST',
                body: formData
            });

            if (!response.ok) {
                const errorData = await response.json().catch(() => ({}));
                throw new Error(errorData.detail || `Server error: ${response.status}`);
            }

            const data = await response.json();
            transcriptionResult = data;
            
            renderResults(data);
            
            processingSection.classList.add('hidden');
            resultSection.classList.remove('hidden');
            showToast('Transcription successful!');
            
        } catch (error) {
            console.error('Transcription error:', error);
            showToast(error.message || 'Transcription failed', true);
            
            // Revert UI
            processingSection.classList.add('hidden');
            uploadSection.classList.remove('hidden');
        }
    });

    // --- Result Rendering ---

    function renderResults(data) {
        // Language detection
        let langName = 'Mixed / Unknown';
        if (data.segments && data.segments.length > 0) {
            const lang = data.segments[0].lang || 'hi-en';
            if (lang === 'en') langName = 'English';
            else if (lang === 'hi') langName = 'Hindi';
            else if (lang.includes('hi') && lang.includes('en')) langName = 'Hinglish';
            else langName = lang.toUpperCase();
        }
        detectedLang.textContent = `Detected: ${langName}`;

        // Render full text
        fullTextContent.textContent = data.text;

        // Render captions
        captionsList.innerHTML = '';
        if (data.segments && data.segments.length > 0) {
            data.segments.forEach(seg => {
                const item = document.createElement('div');
                item.className = 'caption-item';
                item.innerHTML = `
                    <div class="caption-ts">${seg.ts}</div>
                    <div class="caption-text">${seg.text}</div>
                `;
                captionsList.appendChild(item);
            });
        } else {
            captionsList.innerHTML = '<div style="padding:1rem;text-align:center;color:var(--text-muted)">No timeline data available.</div>';
        }
    }

    // --- Tabs Logic ---
    
    tabBtns.forEach(btn => {
        btn.addEventListener('click', () => {
            // Remove active classes
            tabBtns.forEach(b => b.classList.remove('active'));
            tabContents.forEach(c => c.classList.remove('active'));
            
            // Add active to clicked
            btn.classList.add('active');
            document.getElementById(btn.dataset.target).classList.add('active');
        });
    });

    // --- Actions ---

    copyTextBtn.addEventListener('click', () => {
        if (!transcriptionResult || !transcriptionResult.text) return;
        
        navigator.clipboard.writeText(transcriptionResult.text).then(() => {
            showToast('Text copied to clipboard');
        }).catch(err => {
            console.error('Copy failed', err);
            showToast('Failed to copy text', true);
        });
    });

    downloadTxtBtn.addEventListener('click', () => {
        if (!transcriptionResult || !transcriptionResult.text) return;
        downloadFile(transcriptionResult.text, 'transcript.txt', 'text/plain');
    });

    downloadSrtBtn.addEventListener('click', () => {
        if (!transcriptionResult || !transcriptionResult.srt) {
            showToast('SRT data not available', true);
            return;
        }
        downloadFile(transcriptionResult.srt, 'subtitles.srt', 'text/plain');
    });

    newTranscriptionBtn.addEventListener('click', () => {
        resultSection.classList.add('hidden');
        uploadSection.classList.remove('hidden');
        
        // Reset state
        removeFileBtn.click();
        transcriptionResult = null;
        
        // Reset tabs
        tabBtns[0].click();
    });

    function downloadFile(content, fileName, mimeType) {
        const blob = new Blob([content], { type: mimeType });
        const url = URL.createObjectURL(blob);
        const a = document.createElement('a');
        a.href = url;
        a.download = fileName;
        document.body.appendChild(a);
        a.click();
        document.body.removeChild(a);
        URL.revokeObjectURL(url);
    }

    // --- Utility ---

    function formatBytes(bytes, decimals = 2) {
        if (!+bytes) return '0 Bytes';
        const k = 1024;
        const dm = decimals < 0 ? 0 : decimals;
        const sizes = ['Bytes', 'KB', 'MB', 'GB'];
        const i = Math.floor(Math.log(bytes) / Math.log(k));
        return `${parseFloat((bytes / Math.pow(k, i)).toFixed(dm))} ${sizes[i]}`;
    }

    let toastTimeout;
    function showToast(message, isError = false) {
        toastMessage.textContent = message;
        
        if (isError) {
            toast.classList.add('error');
            toast.querySelector('i').className = 'fa-solid fa-circle-exclamation';
        } else {
            toast.classList.remove('error');
            toast.querySelector('i').className = 'fa-solid fa-circle-check';
        }
        
        toast.classList.add('show');
        
        clearTimeout(toastTimeout);
        toastTimeout = setTimeout(() => {
            toast.classList.remove('show');
        }, 3000);
    }
});