// Server-side GitHub backup for resumes.
//
// Commits the full resume set to a private GitHub repo via the Contents API so
// resumes survive a browser-cache wipe. Configured entirely through env vars so
// no secrets live in the repo:
//
//   GITHUB_BACKUP_TOKEN   fine-grained PAT with Contents:read/write on the backup repo
//   GITHUB_BACKUP_REPO    "owner/repo" (e.g. JsonLord/magic-resume-backup)
//   GITHUB_BACKUP_BRANCH  branch to commit to (default: main)
//   GITHUB_BACKUP_PATH    file path in the repo (default: data/resumes.json)
//
// When the token/repo are absent the API route reports "not configured" instead
// of erroring, so the app runs fine without backup enabled.

export type BackupConfig = {
  token: string;
  repo: string;
  branch: string;
  path: string;
};

export const getBackupConfig = (): BackupConfig | null => {
  const token = process.env.GITHUB_BACKUP_TOKEN;
  const repo = process.env.GITHUB_BACKUP_REPO;
  if (!token || !repo) return null;
  return {
    token,
    repo,
    branch: process.env.GITHUB_BACKUP_BRANCH || "main",
    path: process.env.GITHUB_BACKUP_PATH || "data/resumes.json",
  };
};

const gh = (cfg: BackupConfig, path: string, init: RequestInit = {}) =>
  fetch(`https://api.github.com${path}`, {
    ...init,
    headers: {
      Authorization: `Bearer ${cfg.token}`,
      Accept: "application/vnd.github+json",
      "X-GitHub-Api-Version": "2022-11-28",
      "User-Agent": "magic-resume-backup",
      ...(init.headers || {}),
    },
  });

// contents API wants a raw "/" in the path, not %2F
const contentsUrl = (cfg: BackupConfig) =>
  `/repos/${cfg.repo}/contents/${cfg.path
    .split("/")
    .map(encodeURIComponent)
    .join("/")}`;

const toBase64 = (text: string) => Buffer.from(text, "utf8").toString("base64");
const fromBase64 = (b64: string) =>
  Buffer.from(b64, "base64").toString("utf8");

type CurrentFile = { sha: string; content: string } | { sha: null; content: null };

const getCurrentFile = async (cfg: BackupConfig): Promise<CurrentFile> => {
  const res = await gh(cfg, `${contentsUrl(cfg)}?ref=${encodeURIComponent(cfg.branch)}`);
  if (res.status === 404) return { sha: null, content: null };
  if (!res.ok) {
    throw new Error(`GitHub GET ${res.status}: ${(await res.text()).slice(0, 300)}`);
  }
  const json = (await res.json()) as { sha: string; content: string };
  return { sha: json.sha, content: fromBase64(json.content.replace(/\n/g, "")) };
};

export type BackupPayload = {
  version: number;
  updatedAt: string;
  count: number;
  resumes: Record<string, unknown>;
};

// Commit the given resumes. Skips the commit when content is byte-identical to
// what's already stored (avoids a stream of no-op commits on every keystroke).
export const backupResumes = async (
  cfg: BackupConfig,
  resumes: Record<string, unknown>
): Promise<{ committed: boolean; commit?: string }> => {
  const payload: BackupPayload = {
    version: 1,
    updatedAt: new Date().toISOString(),
    count: Object.keys(resumes).length,
    resumes,
  };
  // Stable serialization: drop the volatile updatedAt when comparing so an
  // unchanged resume set doesn't produce a new commit just because time passed.
  const comparable = (text: string) =>
    text.replace(/"updatedAt":\s*"[^"]*",?\s*/, "");
  const text = JSON.stringify(payload, null, 2);

  const current = await getCurrentFile(cfg);
  if (current.content !== null && comparable(current.content) === comparable(text)) {
    return { committed: false };
  }

  const res = await gh(cfg, contentsUrl(cfg), {
    method: "PUT",
    body: JSON.stringify({
      message: `backup: ${payload.count} resume(s) @ ${payload.updatedAt}`,
      content: toBase64(text),
      branch: cfg.branch,
      ...(current.sha ? { sha: current.sha } : {}),
    }),
  });
  if (!res.ok) {
    throw new Error(`GitHub PUT ${res.status}: ${(await res.text()).slice(0, 300)}`);
  }
  const json = (await res.json()) as { commit?: { sha?: string } };
  return { committed: true, commit: json.commit?.sha };
};

// Read the latest backup for restore. Returns null when nothing is backed up yet.
export const readBackup = async (
  cfg: BackupConfig
): Promise<BackupPayload | null> => {
  const current = await getCurrentFile(cfg);
  if (current.content === null) return null;
  try {
    return JSON.parse(current.content) as BackupPayload;
  } catch {
    return null;
  }
};