import type { GiteaClient } from "./client.js";
import type { RepoContext } from "./context.js";
import { classifyHttpError } from "./errors.js";

/** The raw-diff truncation limit, distinct from the body/comment limits. */
export const DIFF_TRUNCATE_LIMIT = 4000;

/**
 * A rendered pull-request diff. `truncated`/`original_length` are present only
 * when the diff was cut short — signalled as separate fields rather than an
 * inline hint, so the diff text itself stays a verbatim (if partial) prefix.
 */
export interface DiffResult {
  diff: string;
  truncated?: true;
  original_length?: number;
}

/**
 * Fetch a pull request's raw unified diff from `GET /pulls/{index}.diff`. The
 * generated client defaults every response to JSON parsing (its baseApiParams
 * set `format: "json"`), which would discard a plain-text diff body — so `text`
 * is forced per call to read the response verbatim.
 */
export async function fetchPullDiff(
  api: GiteaClient,
  context: RepoContext,
  number: number,
): Promise<string> {
  try {
    const response = await api.repos.repoDownloadPullDiffOrPatch(
      context.owner,
      context.name,
      number,
      "diff",
      undefined,
      { format: "text" },
    );
    return response.data ?? "";
  } catch (error) {
    throw classifyHttpError(error);
  }
}

/**
 * Truncate a diff to {@link DIFF_TRUNCATE_LIMIT}, reporting the original length
 * so the caller can offer `--full`. `full` returns the raw diff untouched.
 */
export function truncateDiff(diff: string, full: boolean): DiffResult {
  if (full || diff.length <= DIFF_TRUNCATE_LIMIT) {
    return { diff };
  }
  return {
    diff: diff.slice(0, DIFF_TRUNCATE_LIMIT),
    truncated: true,
    original_length: diff.length,
  };
}