import { mkdir, readFile, writeFile } from "node:fs/promises";
import { dirname, join } from "node:path";

/**
 * The PR-level summary snapshot is a markdown file the agent edits in place
 * during a Review / IncrementalReview run. The server seeds the file with
 * either the previous run's snapshot (incremental) or a stub scaffold (first
 * run), lets the agent edit it with its native file-editing tools, then
 * reads it back at end-of-run and persists it to `WorkflowRun.summarySnapshot`.
 *
 * The snapshot is an internal artifact — it is consumed by future agent runs
 * as durable cross-run context, not surfaced to humans. User-visible summary
 * content lives in the Review / IncrementalReview review bodies, governed by
 * `action/modes.ts`.
 *
 * Edit-in-place avoids the output-token tax of a tool call that regurgitates
 * the full snapshot, and gives incremental runs a clean surface that
 * range-diffs cleanly across runs because the section headings are stable.
 */

export const SUMMARY_FILE_NAME = "pullfrog-summary.md";

/**
 * minimal seed for first-run PRs. just a header + a one-line note about
 * what this file is for. structure is intentionally NOT prescribed —
 * different PRs warrant different organization, and the agent should pick
 * a shape that fits this PR. the agent's prompt (see selectMode.ts
 * `buildSummaryAddendum`) carries the actual instructions for what to
 * capture and how.
 *
 * keeping the seed short also makes the unchanged-from-seed gate more
 * sensitive — any meaningful edit moves the file off the seed, so
 * `persistSummary` can reliably skip the DB write when the agent didn't
 * touch the file.
 */
export const SUMMARY_SCAFFOLD = `# PR summary

<!-- durable cross-run context. edit in place; the next agent run reads this
     before reviewing new commits. structure however serves the PR best. -->
`;

const MIN_SNAPSHOT_LENGTH = 60;
/** PG TEXT can hold ~1GB but a sane cap protects the DB / API payloads. */
const MAX_SNAPSHOT_LENGTH = 32_768;

export function summaryFilePath(tmpdir: string): string {
  return join(tmpdir, SUMMARY_FILE_NAME);
}

/** seed the summary file with previous snapshot (incremental) or scaffold (first run). */
export async function seedSummaryFile(params: {
  tmpdir: string;
  previousSnapshot: string | null;
}): Promise<string> {
  const path = summaryFilePath(params.tmpdir);
  await mkdir(dirname(path), { recursive: true });
  const seed =
    params.previousSnapshot && params.previousSnapshot.trim().length >= MIN_SNAPSHOT_LENGTH
      ? params.previousSnapshot
      : SUMMARY_SCAFFOLD;
  await writeFile(path, seed, "utf8");
  return path;
}

/** read + validate the summary file written by the agent.
 * returns null when the file is missing or fails sanity checks. */
export async function readSummaryFile(path: string): Promise<string | null> {
  let raw: string;
  try {
    raw = await readFile(path, "utf8");
  } catch {
    return null;
  }
  const trimmed = raw.trim();
  if (trimmed.length < MIN_SNAPSHOT_LENGTH) return null;
  if (trimmed.length > MAX_SNAPSHOT_LENGTH) return trimmed.slice(0, MAX_SNAPSHOT_LENGTH);
  return trimmed;
}