import { showLoader, hideLoader, showAlert } from '../ui.js';
import { downloadFile, readFileAsArrayBuffer } from '../utils/helpers.js';
import { state } from '../state.js';
import { PDFDocument } from 'pdf-lib';
import Sortable from 'sortablejs';

const alternateMergeState = {
    pdfDocs: {},
};

export async function setupAlternateMergeTool() {
    const optionsDiv = document.getElementById('alternate-merge-options');
    const processBtn = document.getElementById('process-btn') as HTMLButtonElement;
    const fileList = document.getElementById('alternate-file-list');

    if (!optionsDiv || !processBtn || !fileList) return;

    optionsDiv.classList.remove('hidden');
    processBtn.disabled = false;
    processBtn.onclick = alternateMerge;
    
    fileList.innerHTML = ''; 
    alternateMergeState.pdfDocs = {}; 

    showLoader('Loading PDF documents...');
    try {
        for (const file of state.files) {
            const pdfBytes = await readFileAsArrayBuffer(file);
            alternateMergeState.pdfDocs[file.name] = await PDFDocument.load(pdfBytes as ArrayBuffer, {
                ignoreEncryption: true
            });
            const pageCount = alternateMergeState.pdfDocs[file.name].getPageCount();

            const li = document.createElement('li');
            li.className = 'bg-gray-700 p-3 rounded-lg border border-gray-600 flex items-center justify-between';
            li.dataset.fileName = file.name;

            const infoDiv = document.createElement('div');
            infoDiv.className = 'flex items-center gap-2 truncate'; 

            const nameSpan = document.createElement('span');
            nameSpan.className = 'truncate font-medium text-white';
            nameSpan.textContent = file.name;

            const pagesSpan = document.createElement('span');
            pagesSpan.className = 'text-sm text-gray-400 flex-shrink-0';   
            pagesSpan.textContent = `(${pageCount} pages)`;
            
            infoDiv.append(nameSpan, pagesSpan);

            const dragHandle = document.createElement('div');
            dragHandle.className = 'drag-handle cursor-move text-gray-400 hover:text-white p-1 rounded';
            dragHandle.innerHTML = `<svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2"><circle cx="9" cy="5" r="1"/><circle cx="15" cy="5" r="1"/><circle cx="9" cy="12" r="1"/><circle cx="15" cy="12" r="1"/><circle cx="9" cy="19" r="1"/><circle cx="15" cy="19" r="1"/></svg>`;

            li.append(infoDiv, dragHandle); 
            fileList.appendChild(li);
        }

        Sortable.create(fileList, {
            handle: '.drag-handle',
            animation: 150,
        });

    } catch (error) {
        showAlert('Error', 'Failed to load one or more PDF files. They may be corrupted or password-protected.');
        console.error(error);
    } finally {
        hideLoader();
    }
}

export async function alternateMerge() {
    if (Object.keys(alternateMergeState.pdfDocs).length < 2) {
        showAlert('Not Enough Files', 'Please upload at least two PDF files to alternate and mix.');
        return;
    }

    showLoader('Alternating and mixing pages...');
    try {
        const newPdfDoc = await PDFDocument.create();
        const fileList = document.getElementById('alternate-file-list');
        const sortedFileNames = Array.from(fileList.children).map(li => (li as HTMLElement).dataset.fileName);

        const loadedDocs = sortedFileNames.map(name => alternateMergeState.pdfDocs[name]);
        const pageCounts = loadedDocs.map(doc => doc.getPageCount());
        const maxPages = Math.max(...pageCounts);

        for (let i = 0; i < maxPages; i++) {
            for (const doc of loadedDocs) {
                if (i < doc.getPageCount()) {
                    const [copiedPage] = await newPdfDoc.copyPages(doc, [i]);
                    newPdfDoc.addPage(copiedPage);
                }
            }
        }
        
        const mergedPdfBytes = await newPdfDoc.save();
        downloadFile(new Blob([new Uint8Array(mergedPdfBytes)], { type: 'application/pdf' }), 'alternated-mixed.pdf');
        showAlert('Success', 'PDFs have been mixed successfully!');

    } catch (e) {
        console.error('Alternate Merge error:', e);
        showAlert('Error', 'An error occurred while mixing the PDFs.');
    } finally {
        hideLoader();
    }
}