gitmost/packages/git-sync/src/engine/cycle.ts

import { VaultGit } from "./git.js";
import { GitSyncClient } from "./client.types.js";
import { Settings } from "./settings.js";
import { readExisting, computePullActions, applyPullActions } from "./pull.js";
import { runPush } from "./push.js";

/**
 * Absolute-path filesystem primitives the cycle needs. Injected (not imported)
 * so the engine stays IO-free and unit-testable. `mkdir` is recursive; `rm` is
 * force (a missing file is a no-op).
 */
export interface CycleFs {
  readFile: (absPath: string) => Promise<string>;
  writeFile: (absPath: string, text: string) => Promise<void>;
  mkdir: (absDir: string) => Promise<void>;
  rm: (absPath: string) => Promise<void>;
}

export interface RunCycleDeps {
  spaceId: string;
  /** The Docmost seam (reads for pull, writes for push). */
  client: GitSyncClient;
  /** The per-space git vault (a real working repo). */
  vault: VaultGit;
  /** Engine settings; `vaultPath` roots the relPath -> absolute-path mapping. */
  settings: Settings;
  fs: CycleFs;
  log: (line: string) => void;
  /**
   * Delete-cap hook (the ONLY caller-specific policy). Called with the push
   * dry-run's planned delete count (`Number.POSITIVE_INFINITY` when the dry-run
   * itself failed, so the hook can fail safe) and the live client; returns the
   * client to use for the REAL apply. The default (omitted) applies every op
   * unmodified. gitmost uses it to neutralize deletes when over its cap.
   *
   * When omitted, NO dry-run is performed (one fewer push planning pass).
   */
  resolveApplyClient?: (
    plannedDeletes: number,
    client: GitSyncClient,
  ) => GitSyncClient;
}

export interface RunCycleResult {
  ran: boolean;
  /** Set when the cycle short-circuited without running pull/push. */
  skipped?: "merge-in-progress";
  pull?: { written: number; deleted: number; conflict: boolean };
  push?: { mode: string; failures: number };
}

/**
 * Run ONE full reconcile cycle for a space: PULL (Docmost -> vault) then PUSH
 * (vault -> Docmost), under the engine's required branch choreography. This is
 * the single entry point the app drives — it owns the staging order so it can
 * never drift from the engine it ships with.
 *
 * Staging (the ⭐ data-loss-critical order, SPEC §6/§9):
 *   1. assertGitAvailable + ensureRepo (the git state store must exist).
 *   2. refuse on an unresolved merge (a prior conflicting pull); next checkout
 *      would fail otherwise.
 *   3. ensureBranch('docmost','main') + checkout('docmost'). Pull writes MUST
 *      land on `docmost`, not `main`: applyPullActions commits on `docmost`,
 *      then checks out `main` and merges docmost -> main. Writing Docmost
 *      content straight onto `main` would clobber local file edits before push
 *      can diff them.
 *   4. PULL: readExisting -> listSpaceTree -> computePullActions -> apply.
 *   5. PUSH: optional dry-run to feed the delete-cap hook, then the real apply.
 *
 * Lock + cap POLICY live in the caller; this owns only the mechanics.
 */
export async function runCycle(deps: RunCycleDeps): Promise<RunCycleResult> {
  const { spaceId, client, vault, settings, fs, log, resolveApplyClient } =
    deps;
  const vaultRoot = settings.vaultPath;
  const abs = (relPath: string) => `${vaultRoot}/${relPath}`;

  // 1. The engine state store is git: make sure the repo + branches exist
  //    before any tracked-file listing or diff.
  await vault.assertGitAvailable();
  await vault.ensureRepo();

  // 2. Refuse to run on top of an unresolved merge (SPEC §9): a prior
  //    conflicting pull leaves the vault mid-merge; the next checkout would fail.
  if (await vault.isMergeInProgress()) {
    log(
      `vault has an unresolved merge — resolve it (or 'git merge --abort') ` +
        `and re-run (SPEC §9); skipping cycle.`,
    );
    return { ran: false, skipped: "merge-in-progress" };
  }

  // 3. Pull writes happen on `docmost`; be on it BEFORE applying (see docstring).
  await vault.ensureBranch("docmost", "main");
  await vault.checkout("docmost");

  // 4. PULL --------------------------------------------------------------------
  const existing = await readExisting({
    listTracked: () => vault.listTrackedFiles("*.md"),
    readFile: (relPath) => fs.readFile(abs(relPath)),
  });

  const tree = await client.listSpaceTree(spaceId);
  const pullActions = computePullActions({
    pages: tree.pages,
    treeComplete: tree.complete,
    existing,
  });

  const pullResult = await applyPullActions(
    {
      client,
      git: vault,
      writeFile: (absPath, text) => fs.writeFile(absPath, text),
      mkdir: (absDir) => fs.mkdir(absDir),
      rm: (absPath) => fs.rm(absPath),
      log,
    },
    pullActions,
    vaultRoot,
  );

  // 5. PUSH --------------------------------------------------------------------
  const pushDeps = {
    settings,
    git: vault,
    makeClient: () => client,
    readFile: (relPath: string) => fs.readFile(abs(relPath)),
    writeFile: (relPath: string, text: string) => fs.writeFile(abs(relPath), text),
    log,
  };

  let applyClient = client;
  if (resolveApplyClient) {
    // Plan the push as a DRY-RUN first to read the delete count, then let the
    // caller decide the apply client (e.g. neutralize deletes over a cap). A
    // failed dry-run yields Infinity so the hook can fail safe.
    let plannedDeletes: number;
    try {
      const dry = await runPush(pushDeps, { dryRun: true });
      plannedDeletes = dry.planned?.deletes ?? 0;
    } catch (err) {
      log(
        `push dry-run planning failed (${
          err instanceof Error ? err.message : String(err)
        }); deferring deletion policy to the cap hook (fail-safe).`,
      );
      plannedDeletes = Number.POSITIVE_INFINITY;
    }
    applyClient = resolveApplyClient(plannedDeletes, client);
  }

  const pushResult = await runPush(
    { ...pushDeps, makeClient: () => applyClient },
    { dryRun: false },
  );

  return {
    ran: true,
    pull: {
      written: pullResult.written,
      deleted: pullResult.deleted,
      conflict: pullResult.merge.conflict,
    },
    push: {
      mode: pushResult.mode,
      failures: pushResult.failures?.length ?? 0,
    },
  };
}