eranos/src/lib/profileTabsEvent.ts

/**
 * Kind 16769 — Profile Tabs
 *
 * Replaceable event. One per user.
 *
 * Each tab is a `tab` tag whose third element is a JSON-encoded NIP-01 filter:
 *   ["tab", "<label>", "<filterJSON>"]
 *
 * Variables (`$name`) may appear in filter string values. They are defined by
 * `var` tags that extract values from referenced Nostr events:
 *   ["var", "$name", "<tag-to-extract>", "<event-pointer>"]
 *
 * The only runtime variable is `$me` — the profile owner's pubkey.
 */
import { z } from 'zod';
import type { NostrEvent, NostrFilter } from '@nostrify/nostrify';

export const PROFILE_TABS_KIND = 16769;

// ─── Types ───────────────────────────────────────────────────────────────────

/** A variable definition parsed from a `var` tag. */
export interface TabVarDef {
  /** Variable name including the `$` prefix, e.g. `"$follows"`. */
  name: string;
  /** Tag name to extract from the referenced event, e.g. `"p"`. */
  tagName: string;
  /** Event pointer: `e:<id>` or `a:<kind>:<pubkey>:<d-tag>`. May contain variables. */
  pointer: string;
}

/**
 * A tab filter is a standard NIP-01 filter object that may contain
 * variable placeholders (`$name`) in string positions.
 * After variable resolution, it becomes a plain `NostrFilter`.
 */
export type TabFilter = Record<string, unknown>;

/** A single profile tab. */
export interface ProfileTab {
  label: string;
  filter: TabFilter;
}

/** The full parsed result of a kind 16769 event. */
export interface ProfileTabsData {
  tabs: ProfileTab[];
  vars: TabVarDef[];
}

// ─── Zod schemas for strict validation ───────────────────────────────────────

/** Schema for a NIP-01 filter object (lenient — allows variable strings). */
const TabFilterSchema = z.record(z.string(), z.unknown());

// ─── Parsing ─────────────────────────────────────────────────────────────────

/** Parse a kind 16769 event into ProfileTabsData. Discards malformed entries. */
export function parseProfileTabs(event: NostrEvent): ProfileTabsData {
  if (event.kind !== PROFILE_TABS_KIND) return { tabs: [], vars: [] };

  const tabs: ProfileTab[] = [];
  const vars: TabVarDef[] = [];

  for (const tag of event.tags) {
    if (tag[0] === 'tab' && tag.length >= 3) {
      const label = tag[1];
      if (!label) continue;
      try {
        const raw = JSON.parse(tag[2]);
        const parsed = TabFilterSchema.safeParse(raw);
        if (!parsed.success) continue;
        tabs.push({ label, filter: parsed.data });
      } catch {
        // skip malformed filter JSON
      }
    } else if (tag[0] === 'var' && tag.length >= 4) {
      const name = tag[1];
      const tagName = tag[2];
      const pointer = tag[3];
      if (!name?.startsWith('$') || !tagName || !pointer) continue;
      vars.push({ name, tagName, pointer });
    }
  }

  return { tabs, vars };
}

// ─── Building ────────────────────────────────────────────────────────────────

/** Build event tags for a kind 16769 event from ProfileTabsData. */
export function buildProfileTabsTags(data: ProfileTabsData): string[][] {
  const tags: string[][] = [
    ['alt', 'Custom profile tabs'],
  ];

  for (const v of data.vars) {
    tags.push(['var', v.name, v.tagName, v.pointer]);
  }

  for (const tab of data.tabs) {
    tags.push(['tab', tab.label, JSON.stringify(tab.filter)]);
  }

  return tags;
}

// ─── Variable Resolution ─────────────────────────────────────────────────────

/**
 * Resolve a single event pointer string, substituting runtime variables.
 * Returns `{ type: 'e', id }` or `{ type: 'a', kind, pubkey, dTag }`.
 */
export function resolvePointer(
  pointer: string,
  runtimeVars: Record<string, string>,
): { type: 'e'; id: string } | { type: 'a'; kind: number; pubkey: string; dTag: string } | null {
  // Substitute runtime vars in the pointer string
  let resolved = pointer;
  for (const [name, value] of Object.entries(runtimeVars)) {
    resolved = resolved.replaceAll(name, value);
  }

  if (resolved.startsWith('e:')) {
    return { type: 'e', id: resolved.slice(2) };
  }

  if (resolved.startsWith('a:')) {
    const parts = resolved.slice(2).split(':');
    if (parts.length < 3) return null;
    const kind = parseInt(parts[0], 10);
    if (isNaN(kind)) return null;
    return { type: 'a', kind, pubkey: parts[1], dTag: parts[2] };
  }

  return null;
}

/**
 * Resolve all variables in a filter, producing a standard NostrFilter.
 *
 * @param filter - The tab filter with variable placeholders.
 * @param resolvedVars - Map from variable name (e.g. `"$follows"`) to resolved values.
 * @param runtimeVars - Map of runtime variables (e.g. `{ "$me": "pubkey" }`).
 */
export function resolveFilter(
  filter: TabFilter,
  resolvedVars: Record<string, string[]>,
  runtimeVars: Record<string, string>,
): NostrFilter {
  const allVars: Record<string, string[]> = { ...resolvedVars };
  // Runtime scalar vars are treated as single-element arrays for expansion
  for (const [name, value] of Object.entries(runtimeVars)) {
    if (!(name in allVars)) {
      allVars[name] = [value];
    }
  }

  const result: Record<string, unknown> = {};

  for (const [key, value] of Object.entries(filter)) {
    if (Array.isArray(value)) {
      // Expand variables in arrays (splice in-place)
      const expanded: unknown[] = [];
      for (const item of value) {
        if (typeof item === 'string' && item.startsWith('$') && item in allVars) {
          expanded.push(...allVars[item]);
        } else {
          expanded.push(item);
        }
      }
      result[key] = expanded;
    } else if (typeof value === 'string' && value.startsWith('$') && value in allVars) {
      // Scalar string variable — expand to array if multiple values, otherwise keep as string
      const vals = allVars[value];
      result[key] = vals.length === 1 ? vals[0] : vals;
    } else {
      result[key] = value;
    }
  }

  return result as NostrFilter;
}