/**
 * Shared S3 upload utilities.
 *
 * Usage:
 *   const uploader = new S3Uploader({
 *     filenameEl:  document.getElementById('upload-filename'),
 *     percentEl:   document.getElementById('upload-percent'),
 *     progressBar: document.getElementById('progress-bar'),
 *   });
 *   uploader.upload(presignedUrl, file, s3Key, fallbackContentType)
 *     .then(s3Key => { ... })
 *     .catch(err => { ... });
 *   uploader.cancel();
 */

function S3Uploader(opts) {
    this.filenameEl  = opts.filenameEl;
    this.percentEl   = opts.percentEl;
    this.progressBar = opts.progressBar;
    this.speedEl     = opts.speedEl || null;
    this._xhr = null;
}

/** Start an upload. Returns a Promise resolving to the s3Key. */
S3Uploader.prototype.upload = function(url, file, s3Key, fallbackContentType, cacheControl) {
    var self = this;
    var startTime = Date.now();

    if (self.filenameEl)  self.filenameEl.textContent = file.name;
    if (self.percentEl)   self.percentEl.textContent = '0%';
    if (self.progressBar) self.progressBar.style.width = '0%';
    if (self.speedEl)     self.speedEl.textContent = '';

    return new Promise(function(resolve, reject) {
        var xhr = new XMLHttpRequest();
        self._xhr = xhr;

        xhr.upload.addEventListener('progress', function(e) {
            if (e.lengthComputable) {
                var percent = Math.round((e.loaded / e.total) * 100);
                if (self.percentEl)   self.percentEl.textContent = percent + '%';
                if (self.progressBar) self.progressBar.style.width = percent + '%';
                if (self.speedEl && e.loaded > 0) {
                    var elapsed = (Date.now() - startTime) / 1000;
                    if (elapsed > 0.5) {
                        var speed = e.loaded / elapsed;
                        var remaining = (e.total - e.loaded) / speed;
                        var speedStr = speed > 1024 * 1024
                            ? (speed / (1024 * 1024)).toFixed(1) + ' MB/s'
                            : (speed / 1024).toFixed(0) + ' KB/s';
                        var etaStr = remaining < 60
                            ? Math.ceil(remaining) + 's'
                            : Math.ceil(remaining / 60) + 'm ' + Math.ceil(remaining % 60) + 's';
                        self.speedEl.textContent = speedStr + ' \u2014 ' + etaStr + ' remaining';
                    }
                }
            }
        });

        xhr.addEventListener('load', function() {
            self._xhr = null;
            if (xhr.status >= 200 && xhr.status < 300) {
                resolve(s3Key);
            } else {
                reject(new Error('Upload failed: ' + xhr.status));
            }
        });

        xhr.addEventListener('error', function() {
            self._xhr = null;
            reject(new Error('Network error during upload'));
        });

        xhr.addEventListener('abort', function() {
            self._xhr = null;
            reject(new Error('Upload cancelled'));
        });

        xhr.open('PUT', url);
        xhr.setRequestHeader('Content-Type', file.type || fallbackContentType || 'application/octet-stream');
        if (cacheControl) xhr.setRequestHeader('Cache-Control', cacheControl);
        xhr.send(file);
    });
};

/** Abort any in-progress upload. */
S3Uploader.prototype.cancel = function() {
    if (this._xhr) {
        this._xhr.abort();
        this._xhr = null;
    }
};

/* Dropzone helpers — wire up drag/drop on an element */
function initDropzone(dropzoneEl, fileInputEl, onFile) {
    dropzoneEl.addEventListener('dragover', function(e) {
        e.preventDefault();
        dropzoneEl.classList.add('dragover');
    });
    dropzoneEl.addEventListener('dragleave', function() {
        dropzoneEl.classList.remove('dragover');
    });
    dropzoneEl.addEventListener('drop', function(e) {
        e.preventDefault();
        dropzoneEl.classList.remove('dragover');
        if (e.dataTransfer.files[0]) onFile(e.dataTransfer.files[0]);
    });
    dropzoneEl.addEventListener('click', function() {
        fileInputEl.click();
    });
    fileInputEl.addEventListener('change', function() {
        if (fileInputEl.files[0]) onFile(fileInputEl.files[0]);
    });
}