/**
 * A single deliverable part of a reminder. The bot's fire-reminder loop
 * walks these in order with ~1.5 s spacing between sends. The DB stores
 * one row per part in `reminder_messages` keyed by `position`.
 *
 *   { kind: "text",  textContent: "...", mediaId: null }    -> plain text
 *   { kind: "media", textContent: "...", mediaId: "uuid" } -> file w/ caption
 *   { kind: "media", textContent: null,  mediaId: "uuid" } -> file w/o caption
 *
 * `textContent` for a `media` part is the caption (sent by the bot via
 * the WhatsApp API's caption field, not as a separate text message).
 */
export interface MessagePart {
  kind: "text" | "media";
  textContent: string | null;
  mediaId: string | null;
}

export function isValidMessagePart(p: unknown): p is MessagePart {
  if (!p || typeof p !== "object") return false;
  const m = p as Partial<MessagePart>;
  if (m.kind !== "text" && m.kind !== "media") return false;
  if (m.textContent !== null && typeof m.textContent !== "string") return false;
  if (m.mediaId !== null && typeof m.mediaId !== "string") return false;
  if (m.kind === "text" && (!m.textContent || !m.textContent.trim())) return false;
  if (m.kind === "media" && !m.mediaId) return false;
  return true;
}

/**
 * Serialise a message stack into a single URL param. URI-encoded JSON
 * is shorter than base64-of-JSON for typical short-message stacks and
 * stays inside the ~2KB URL budget for 5–10 messages.
 */
export function encodeMessages(messages: MessagePart[]): string {
  return encodeURIComponent(JSON.stringify(messages));
}

export function decodeMessages(s: string | null | undefined): MessagePart[] | null {
  if (!s) return null;
  try {
    const parsed = JSON.parse(decodeURIComponent(s));
    if (!Array.isArray(parsed)) return null;
    const out = parsed.filter(isValidMessagePart);
    return out.length > 0 ? out : null;
  } catch {
    return null;
  }
}

/**
 * Backward-compat: if the wizard URL still carries the legacy single-
 * message fields (`text` / `mediaId` / `caption`) — bookmarked links,
 * old emails, etc. — synthesise a one-element MessagePart[] from them
 * so the new schema sees a uniform shape.
 */
export function legacyMessageToParts(
  text: string | null | undefined,
  mediaId: string | null | undefined,
  caption: string | null | undefined,
): MessagePart[] | null {
  if (mediaId) {
    return [
      {
        kind: "media",
        mediaId,
        textContent: caption?.trim() || text?.trim() || null,
      },
    ];
  }
  if (text && text.trim()) {
    return [{ kind: "text", textContent: text, mediaId: null }];
  }
  return null;
}