/**
 * Attachment grouping.
 *
 * All PO attachments are stored as `PODocument` rows. The lifecycle stage an
 * attachment belongs to is encoded in the leading segment of its `storageKey`
 * (see `buildStorageKey` in `lib/storage.ts`), e.g. `po-document/<poId>/...`
 * or `receipt/<poId>/...`. This module derives a user-facing grouping from
 * that prefix so the PO details screen can show every attachment grouped by
 * type (submission, payment, delivery).
 */

export type AttachmentGroupKey = "submission" | "payment" | "delivery" | "other";

export interface AttachmentGroupMeta {
  key: AttachmentGroupKey;
  label: string;
  description: string;
}

/** Display order for attachment groups (lifecycle order). */
export const ATTACHMENT_GROUP_ORDER: AttachmentGroupKey[] = [
  "submission",
  "payment",
  "delivery",
  "other",
];

export const ATTACHMENT_GROUP_META: Record<AttachmentGroupKey, AttachmentGroupMeta> = {
  submission: {
    key: "submission",
    label: "Submission documents",
    description: "Uploaded with the purchase order (e.g. invoice, quotation).",
  },
  payment: {
    key: "payment",
    label: "Payment documents",
    description: "Uploaded at payment (e.g. payment proof).",
  },
  delivery: {
    key: "delivery",
    label: "Delivery receipts",
    description: "Uploaded at delivery confirmation (e.g. delivery receipt).",
  },
  other: {
    key: "other",
    label: "Other attachments",
    description: "",
  },
};

/**
 * Derive the lifecycle group of an attachment from its storage key prefix.
 * Unknown prefixes fall back to "other" so nothing is ever hidden.
 */
export function categorizeAttachment(storageKey: string): AttachmentGroupKey {
  const prefix = storageKey.split("/")[0];
  switch (prefix) {
    case "po-document":
      return "submission";
    case "payment-document":
    case "payment":
      return "payment";
    case "receipt":
      return "delivery";
    default:
      return "other";
  }
}

export interface AttachmentGroup<T> {
  meta: AttachmentGroupMeta;
  items: T[];
}

/**
 * Group attachments by lifecycle stage, returning only non-empty groups in
 * canonical lifecycle order. Item order within each group is preserved.
 */
export function groupAttachments<T extends { storageKey: string }>(
  documents: T[]
): AttachmentGroup<T>[] {
  const buckets = new Map<AttachmentGroupKey, T[]>();
  for (const doc of documents) {
    const key = categorizeAttachment(doc.storageKey);
    const bucket = buckets.get(key);
    if (bucket) bucket.push(doc);
    else buckets.set(key, [doc]);
  }

  return ATTACHMENT_GROUP_ORDER.flatMap((key) => {
    const items = buckets.get(key);
    return items && items.length > 0
      ? [{ meta: ATTACHMENT_GROUP_META[key], items }]
      : [];
  });
}