import {
  getDocumentIconType,
  getSourceType,
} from '../../AttachmentCard/utils/mimeType'

/**
 * Format a byte count as a short human-readable string (`'379.5 KB'`).
 * Mirrors the meta line shown next to file attachments in the mobile chat
 * design — `EXT · SIZE`, e.g. `PDF · 379.5 KB`.
 */
export function formatFileSize(bytes: number): string {
  if (!Number.isFinite(bytes) || bytes < 0) return ''
  if (bytes < 1024) return `${bytes} B`
  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`
  if (bytes < 1024 * 1024 * 1024)
    return `${(bytes / (1024 * 1024)).toFixed(2)} MB`
  return `${(bytes / (1024 * 1024 * 1024)).toFixed(2)} GB`
}

const EXTENSION_LABEL_BY_DOCUMENT_TYPE: Record<string, string> = {
  pdf: 'PDF',
  doc: 'DOC',
  xls: 'XLS',
  csv: 'CSV',
  ppt: 'PPT',
  zip: 'ZIP',
  text: 'TXT',
  markdown: 'MD',
}

/**
 * Returns the short uppercase extension label shown in the meta line of
 * compact document / file attachments. Prefers the filename extension
 * when present (matches the mobile design which trusts the filename),
 * and falls back to a label derived from the MIME type.
 */
export function getFileExtensionLabel(
  mimeType?: string,
  filename?: string
): string | undefined {
  if (filename) {
    const lastDot = filename.lastIndexOf('.')
    if (lastDot > 0 && lastDot < filename.length - 1) {
      const ext = filename.slice(lastDot + 1)
      if (ext && ext.length <= 5) return ext.toUpperCase()
    }
  }

  if (!mimeType) return undefined

  const sourceType = getSourceType(mimeType)
  if (sourceType === 'document') {
    const docType = getDocumentIconType(mimeType)
    const docLabel = EXTENSION_LABEL_BY_DOCUMENT_TYPE[docType]
    if (docLabel) return docLabel
    if (mimeType === 'application/octet-stream') return undefined
  }

  const subtype = mimeType.split('/')[1]
  if (!subtype || subtype === '*') return undefined
  return subtype.toUpperCase()
}

/**
 * Build the meta line shown under the title in compact document / file
 * attachments — `EXT · SIZE` (`PDF · 379.5 KB`). Either part is dropped
 * when not available so audio / generic files still get a useful label.
 */
export function buildCompactMetaLabel(
  mimeType?: string,
  filename?: string,
  fileSize?: number
): string | undefined {
  const ext = getFileExtensionLabel(mimeType, filename)
  const size =
    typeof fileSize === 'number' && fileSize > 0
      ? formatFileSize(fileSize)
      : undefined
  return [ext, size].filter(Boolean).join(' · ') || undefined
}

/**
 * Derive a sensible filename from a URL — used as the fallback save name
 * when the attachment has no `filename` set. Returns `'download'` for
 * URLs we can't parse.
 */
export function filenameFromUrl(url: string): string {
  try {
    const parsed = new URL(url)
    const last = parsed.pathname.split('/').pop()
    return last && last.length > 0 ? decodeURIComponent(last) : 'download'
  } catch {
    return 'download'
  }
}