/**
 * Extract a text handoff of the parent session branch for planner context.
 * Mirrors pi-subagents buildParentContext shape so hosts that ignore
 * inheritContext still get conversation history in the planner prompt.
 */

export type BranchEntry = {
  type?: string;
  message?: {
    role?: string;
    content?: unknown;
  };
  summary?: string;
};

export type SessionBranchSource = {
  sessionManager?: {
    /** Real Pi returns session entries; typed loosely for ExtensionContext compatibility. */
    getBranch?: () => unknown;
  };
};

function extractText(content: unknown): string {
  if (typeof content === "string") return content;
  if (!Array.isArray(content)) return "";
  return content
    .filter((c: { type?: string }) => c?.type === "text")
    .map((c: { text?: string }) => c.text ?? "")
    .join("\n");
}

/**
 * Build a compact parent-conversation handoff from ExtensionContext-like objects.
 * Returns undefined when no usable history is present.
 */
export function extractParentContextText(
  ctx: SessionBranchSource | null | undefined,
  opts?: { maxChars?: number },
): string | undefined {
  try {
    const raw = ctx?.sessionManager?.getBranch?.();
    if (!Array.isArray(raw) || raw.length === 0) return undefined;
    const entries = raw as BranchEntry[];

    const parts: string[] = [];
    for (const entry of entries) {
      if (entry.type === "message" && entry.message) {
        const msg = entry.message;
        if (msg.role === "user") {
          const text = extractText(msg.content).trim();
          if (text) parts.push(`[User]: ${text}`);
        } else if (msg.role === "assistant") {
          const text = extractText(msg.content).trim();
          if (text) parts.push(`[Assistant]: ${text}`);
        }
        // Skip toolResult — too verbose for planner handoff
      } else if (entry.type === "compaction" && entry.summary?.trim()) {
        parts.push(`[Summary]: ${entry.summary.trim()}`);
      }
    }

    if (parts.length === 0) return undefined;

    let text = parts.join("\n\n");
    const max = opts?.maxChars ?? 80_000;
    if (text.length > max) {
      text = `…[truncated]\n\n${text.slice(text.length - max)}`;
    }
    return text;
  } catch {
    // Best-effort handoff — never fail goal start over transcript extract.
    return undefined;
  }
}