/**
 * context.ts — Extract parent conversation context for subagent inheritance.
 */

import type { ExtensionContext } from "@earendil-works/pi-coding-agent";

interface TextContentBlock {
  type: "text";
  text?: string;
}

function isTextContentBlock(value: unknown): value is TextContentBlock {
  return (
    typeof value === "object" &&
    value !== null &&
    "type" in value &&
    value.type === "text"
  );
}

/** Extract text from a message content block array. */
export function extractText(content: unknown[]): string {
  return content
    .filter(isTextContentBlock)
    .map((c) => c.text ?? "")
    .join("\n");
}

/**
 * Build a text representation of the parent conversation context.
 * Used when context is "fork" to give the subagent visibility
 * into what has been discussed/done so far.
 */
export function buildParentContext(ctx: ExtensionContext): string {
  const entries = ctx.sessionManager.getBranch();
  if (!entries || entries.length === 0) {
    return "";
  }

  const parts: string[] = [];

  for (const entry of entries) {
    if (entry.type === "message") {
      const msg = entry.message;
      if (msg.role === "user") {
        const text =
          typeof msg.content === "string"
            ? msg.content
            : extractText(msg.content);
        if (text.trim()) {
          parts.push(`[User]: ${text.trim()}`);
        }
      } else if (msg.role === "assistant") {
        const text = extractText(msg.content);
        if (text.trim()) {
          parts.push(`[Assistant]: ${text.trim()}`);
        }
      }
      // Skip toolResult messages — too verbose for context
    } else if (entry.type === "compaction" && entry.summary) {
      // Include compaction summaries — they're already condensed
      parts.push(`[Summary]: ${entry.summary}`);
    }
  }

  if (parts.length === 0) {
    return "";
  }

  return `# Parent Conversation Context
The following is the conversation history from the parent session that spawned you.
Use this context to understand what has been discussed and decided so far.

${parts.join("\n\n")}

---
# Your Task (below)
`;
}