gc-alexandria/src/lib/utils/mime.ts

/**
 * Determine the type of Nostr event based on its kind number
 * Following NIP specification for kind ranges:
 * - Replaceable: 0, 3, 10000-19999 (only latest stored)
 * - Ephemeral: 20000-29999 (not stored)
 * - Addressable: 30000-39999 (latest per d-tag stored)
 * - Regular: all other kinds (stored by relays)
 */
function getEventType(kind: number): 'regular' | 'replaceable' | 'ephemeral' | 'addressable' {
  // Check special ranges first
  if (kind >= 30000 && kind < 40000) {
    return 'addressable';
  }
  
  if (kind >= 20000 && kind < 30000) {
    return 'ephemeral';
  }
  
  if ((kind >= 10000 && kind < 20000) || kind === 0 || kind === 3) {
    return 'replaceable';
  }
  
  // Everything else is regular
  return 'regular';
}

/**
 * Get MIME tags for a Nostr event based on its kind number
 * Returns an array of tags: [["m", mime-type], ["M", nostr-mime-type]]
 * Following NKBIP-06 and NIP-94 specifications
 */
export function getMimeTags(kind: number): [string, string][] {
  // Default tags for unknown kinds
  let mTag: [string, string] = ["m", "text/plain"];
  let MTag: [string, string] = ["M", "note/generic/nonreplaceable"];

  // Determine replaceability based on event type
  const eventType = getEventType(kind);
  const replaceability = (eventType === 'replaceable' || eventType === 'addressable') 
    ? "replaceable" 
    : "nonreplaceable";

  switch (kind) {
    // Short text note
    case 1:
      mTag = ["m", "text/plain"];
      MTag = ["M", `note/microblog/${replaceability}`];
      break;

    // Generic reply
    case 1111:
      mTag = ["m", "text/plain"];
      MTag = ["M", `note/comment/${replaceability}`];
      break;

    // Issue
    case 1621:
      mTag = ["m", "text/markdown"];
      MTag = ["M", `git/issue/${replaceability}`];
      break;

    // Issue comment
    case 1622:
      mTag = ["m", "text/markdown"];
      MTag = ["M", `git/comment/${replaceability}`];
      break;

    // Book metadata
    case 30040:
      mTag = ["m", "application/json"];
      MTag = ["M", `meta-data/index/${replaceability}`];
      break;

    // Book content
    case 30041:
      mTag = ["m", "text/asciidoc"];
      MTag = ["M", `article/publication-content/${replaceability}`];
      break;

    // Wiki page
    case 30818:
      mTag = ["m", "text/asciidoc"];
      MTag = ["M", `article/wiki/${replaceability}`];
      break;

    // Long-form note
    case 30023:
      mTag = ["m", "text/markdown"];
      MTag = ["M", `article/long-form/${replaceability}`];
      break;

    // Add more cases as needed...
  }

  return [mTag, MTag];
}