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import { basename, dirname, splitExtension } from './path.js';
import { sortEntries } from './vfs-file.js';
import type { ConflictReason, Hash, VFSEntry } from './types.js';
export type Side = 'a' | 'b';
/** Immediate classification of a conflict, as reported back from `sync()`. */
export type ConflictKind = 'content' | 'location' | 'delete-edit' | 'kind';
export interface ConflictReport {
uuid: string;
kind: ConflictKind;
/** Where the winning version ended up. */
path: string;
winner: Side;
a?: VFSEntry;
b?: VFSEntry;
/** The losing version, parked as a copy. Absent when nothing was at risk. */
copy?: VFSEntry;
/** Ancestor hash, when the chain turned one up. Feeds the three-way view. */
base?: Hash;
/**
* Both sides are text and small enough that a three-way merge is worth
* trying. `sync()` is what actually tries it — the merge itself stays pure.
*/
text?: boolean;
}
/**
* `'edits'` (default) keeps a copy only when both sides had real content — the
* case where a silent overwrite would destroy data. `'always'` also keeps the
* content when a delete wins. `false` never keeps copies.
*/
export type ConflictCopyPolicy = 'always' | 'edits' | false;
export interface ConflictNameInfo {
path: string;
peerId: string;
hash: string;
entry: VFSEntry;
}
export interface MergeSide {
peerId: string;
entries: VFSEntry[];
/**
* Has *this* peer ever heard of this uuid — by entry, by log, or by snapshot?
*
* Deliberately one-sided. The shared {@link MergeOptions.history} is the union
* of both peers' knowledge and would answer "yes" to everything, which is
* exactly wrong for the path fallback: the question there is whether the
* *other* side has never seen this identity.
*/
knows?: (uuid: string) => boolean;
}
export interface MergeOptions {
/**
* Ancestry, gathered from whatever the caller was willing to read. An empty
* history is legal and merely pessimistic: every divergence then reads as a
* real conflict, which costs copies and never costs correctness.
*/
history?: History;
conflictCopies?: ConflictCopyPolicy;
conflictName?: (info: ConflictNameInfo) => string;
/** True for paths that get a three-way text merge. Drives {@link ConflictReport.text}. */
text?: (path: string) => boolean;
/** Size from which a conflict copy stays on the peer that made it (§4). */
heldAt?: number;
}
export interface MergeResult {
entries: VFSEntry[];
conflicts: ConflictReport[];
}
/** Above this, a conflict copy does not travel — the entry does, the bytes do not. */
export const HELD_AT = 64 * 1024 * 1024;
/** `notes.md` -> `notes (conflict device-b 1f4a9c2e).md` */
export function defaultConflictName(info: ConflictNameInfo): string {
const dir = dirname(info.path);
const [stem, ext] = splitExtension(basename(info.path));
const name = `${stem} (conflict ${info.peerId} ${info.hash.slice(0, 8)})${ext}`;
return dir ? `${dir}/${name}` : name;
}
export interface MergeItem {
uuid: string;
a?: VFSEntry;
b?: VFSEntry;
}
/**
* Lines up the same file across two peers.
*
* By `uuid` first. Uuids only disagree when two peers discovered the same file
* independently, so what is left unmatched falls back to matching by `path` —
* but only between live entries of the same kind whose uuid the other side has
* never heard of, by entry *or* by log. That guard is what the base tree used
* to provide in v1: without it a delete-and-recreate at the same path merges
* into the entry it replaced.
*/
export function pairEntries(a: MergeSide, b: MergeSide): MergeItem[] {
const items = new Map<string, MergeItem>();
const item = (uuid: string): MergeItem => {
let found = items.get(uuid);
if (!found) items.set(uuid, (found = { uuid }));
return found;
};
for (const entry of a.entries) item(entry.uuid).a = entry;
for (const entry of b.entries) item(entry.uuid).b = entry;
const knownToA = new Set(a.entries.map((entry) => entry.uuid));
const knownToB = new Set(b.entries.map((entry) => entry.uuid));
const strangerToA = (uuid: string) => !knownToA.has(uuid) && !a.knows?.(uuid);
const strangerToB = (uuid: string) => !knownToB.has(uuid) && !b.knows?.(uuid);
const loose = new Map<string, MergeItem>();
for (const candidate of items.values()) {
const entry = candidate.b;
if (!entry || candidate.a || entry.deleted || !strangerToA(entry.uuid)) continue;
loose.set(`${entry.kind}:${entry.path}`, candidate);
}
for (const candidate of [...items.values()]) {
const entry = candidate.a;
if (!entry || candidate.b || entry.deleted || !strangerToB(entry.uuid)) continue;
const key = `${entry.kind}:${entry.path}`;
const other = loose.get(key);
if (!other) continue;
loose.delete(key);
const uuid = candidate.uuid < other.uuid ? candidate.uuid : other.uuid;
items.delete(candidate.uuid);
items.delete(other.uuid);
items.set(uuid, { uuid, a: candidate.a, b: other.b });
}
return [...items.values()];
}
/**
* Merges two peers' entry lists into the one both will adopt.
*
* Content and location stay separate dimensions — "renamed on one side, edited
* on the other" is not a conflict — and the rule inside each is the same as v1:
* the more recent `updated` wins, with the hash as tiebreak so both peers reach
* the same answer without another round trip.
*
* What replaces the common ancestor is {@link History}: instead of asking "did
* this side change since the base?", the merge asks "is the loser's version an
* ancestor of the winner's?" and follows the `prev` chain to find out.
*/
export function mergeEntries(a: MergeSide, b: MergeSide, options: MergeOptions = {}): MergeResult {
const history = options.history ?? new History();
const policy = options.conflictCopies ?? 'edits';
const nameConflict = options.conflictName ?? defaultConflictName;
const heldAt = options.heldAt ?? HELD_AT;
const conflicts: ConflictReport[] = [];
const entries: VFSEntry[] = [];
const copies: VFSEntry[] = [];
for (const item of pairEntries(a, b)) {
const left = item.a;
const right = item.b;
// ---- one side only: new file, or a delete whose tombstone was pruned
if (left && !right) {
entries.push(solo(item.uuid, left, history));
continue;
}
if (right && !left) {
entries.push(solo(item.uuid, right, history));
continue;
}
if (!left || !right) continue;
// ---- content dimension
const winner = pickNewer(left, right);
const loser = winner === left ? right : left;
const sameContent = left.hash === right.hash && !!left.deleted === !!right.deleted;
let kind: ConflictKind | null = null;
let content = winner;
let ancestor: Hash | undefined;
if (sameContent) {
content = winner;
} else if (descends(history, item.uuid, winner, loser)) {
// The loser is behind: propagation, not a conflict.
content = winner;
ancestor = loser.hash ?? undefined;
} else if (descends(history, item.uuid, loser, winner)) {
// The *newer* one is the ancestor — a clock ran backwards, or a peer
// relayed an old version with a fresh timestamp. Ancestry beats the clock.
content = loser;
ancestor = winner.hash ?? undefined;
} else {
content = winner;
kind = left.deleted || right.deleted ? 'delete-edit' : 'content';
}
// ---- location dimension, resolved independently of the content
let path: string;
let prevPath: string | undefined;
if (left.path === right.path) {
path = left.path;
prevPath = content.prevPath;
} else {
const leftMoved = history.movedFrom(item.uuid, left.path, right.path, left.prevPath);
const rightMoved = history.movedFrom(item.uuid, right.path, left.path, right.prevPath);
const mover = leftMoved === rightMoved ? pickNewer(left, right) : leftMoved ? left : right;
path = mover.path;
prevPath = mover.prevPath ?? (mover === left ? right.path : left.path);
if (leftMoved === rightMoved && !kind) kind = 'location';
}
const merged: VFSEntry = {
uuid: item.uuid,
kind: content.kind,
path,
hash: content.hash,
size: content.size,
created: Math.min(left.created, right.created),
updated: content.updated,
peerId: content.peerId,
};
if (content.deleted) merged.deleted = true;
if (content.prev !== undefined) merged.prev = content.prev;
if (content.prev2) merged.prev2 = content.prev2;
if (prevPath && prevPath !== path && !merged.deleted) merged.prevPath = prevPath;
if (content.conflictOf) {
merged.conflictOf = content.conflictOf;
if (content.reason) merged.reason = content.reason;
if (content.base) merged.base = content.base;
if (content.held) merged.held = content.held;
}
entries.push(merged);
if (!kind) continue;
const side: Side = content === left ? 'a' : 'b';
const beaten = side === 'a' ? right : left;
const report: ConflictReport = {
uuid: item.uuid,
kind,
path,
winner: side,
a: left,
b: right,
...(ancestor ? { base: ancestor } : {}),
};
// A location conflict puts no content at risk — the file lands on one of
// the two paths and that is that — so a copy would only duplicate it.
const atRisk = kind !== 'location' && !!beaten.hash;
const keep = policy === 'always' ? atRisk : policy === 'edits' ? atRisk && !!content.hash : false;
if (kind === 'content' && options.text?.(path) && left.hash && right.hash) report.text = true;
if (keep) {
const copy = conflictCopy(item.uuid, beaten, path, kind, nameConflict, heldAt);
copies.push(copy);
report.copy = copy;
}
conflicts.push(report);
}
for (const copy of copies) if (!entries.some((entry) => entry.uuid === copy.uuid)) entries.push(copy);
return {
entries: sortEntries(resolvePathCollisions(entries, conflicts, nameConflict)),
conflicts,
};
}
/**
* The version one side has and the other does not.
*
* The interesting case is the third one: absent on the far side, and no
* tombstone either. That is exactly what a pruned tombstone looks like, so the
* log and its cumulative snapshot get asked before the entry is taken as new —
* without that question a delete comes back to life every time it meets a peer
* that never heard about it.
*/
function solo(uuid: string, entry: VFSEntry, history: History): VFSEntry {
const last = history.last(uuid);
if (last?.deleted && last.at > entry.updated && !entry.deleted) {
return {
...entry,
hash: null,
size: 0,
updated: last.at,
deleted: true,
prev: entry.hash,
};
}
return { ...entry, uuid };
}
function descends(history: History, uuid: string, of: VFSEntry, ancestor: VFSEntry): boolean {
if (!ancestor.hash) return false;
return history.descends(uuid, of.hash, ancestor.hash, [of.prev, of.prev2]);
}
function conflictCopy(
uuid: string,
loser: VFSEntry,
path: string,
kind: ConflictKind,
nameConflict: (info: ConflictNameInfo) => string,
heldAt: number,
): VFSEntry {
const reason: ConflictReason = kind === 'delete-edit' ? 'delete-edit' : kind === 'kind' ? 'kind' : 'binary';
const copy: VFSEntry = {
// Deterministic: re-merging the same pair yields the same copy rather than
// piling up near-duplicates on every pass.
uuid: `conflict:${uuid}:${loser.hash}`,
kind: loser.kind,
path: nameConflict({ path, peerId: loser.peerId, hash: loser.hash as string, entry: loser }),
hash: loser.hash,
size: loser.size,
created: loser.updated,
updated: loser.updated,
peerId: loser.peerId,
conflictOf: uuid,
reason,
};
if (loser.prev) copy.base = loser.prev;
// A 700 MB re-dump would otherwise be 700 MB on every peer until someone
// resolved it. The entry travels; the bytes stay put until asked for.
if (loser.size >= heldAt) copy.held = loser.peerId;
return copy;
}
/**
* Two entries on one path.
*
* v2 records directories, so a file and a folder can now claim the same name —
* and unlike a content conflict, parking the loser is not a local edit: a
* directory moves with everything under it. The winner is picked by the same
* deterministic rule as everywhere else, and the loser (with its subtree) is
* renamed aside in one go, so the tree is never inconsistent halfway through.
*
* Moving a loser aside can collide in turn, and not rarely: a conflict copy
* derives its name from the same path, peer and hash, so a version parked here
* and the copy made of that same version land on the identical name. Grouping
* once would leave two live entries on one path — the one thing the tree may
* not contain, because the second one to be written wins on disk and the other
* is silently gone. So this runs to a fixed point, and it terminates because
* every aside name is strictly longer than the name it was derived from.
*/
function resolvePathCollisions(
entries: VFSEntry[],
conflicts: ConflictReport[],
nameConflict: (info: ConflictNameInfo) => string,
): VFSEntry[] {
for (let round = 0; round <= entries.length; round++) {
const byPath = new Map<string, VFSEntry[]>();
for (const entry of entries) {
if (entry.deleted) continue;
const bucket = byPath.get(entry.path);
if (bucket) bucket.push(entry);
else byPath.set(entry.path, [entry]);
}
// By path, so that both peers work through a round in the same order —
// insertion order would follow how the merge happened to build the array.
const collided = [...byPath]
.filter(([, bucket]) => bucket.length > 1)
.sort(([left], [right]) => (left < right ? -1 : 1));
if (collided.length === 0) break;
const moves: Array<{ from: string; to: string }> = [];
for (const [path, bucket] of collided) {
const ranked = [...bucket].sort((x, y) => (pickNewer(x, y) === x ? -1 : 1));
const keeper = ranked[0] as VFSEntry;
for (const loser of ranked.slice(1)) {
const aside = nameConflict({
path,
peerId: loser.peerId,
hash: loser.hash ?? loser.uuid,
entry: loser,
});
moves.push({ from: loser.path, to: aside });
loser.prevPath = loser.path;
loser.path = aside;
loser.conflictOf ??= keeper.uuid;
loser.reason ??= keeper.kind === loser.kind ? 'binary' : 'kind';
// `winner` here is an index into this report's own `a`/`b`, not into the
// arguments of `sync(a, b)`: a path collision is between two entries, and
// which peer contributed each is not the question being answered.
conflicts.push({
uuid: loser.uuid,
kind: keeper.kind === loser.kind ? 'content' : 'kind',
path,
winner: 'a',
a: keeper,
b: loser,
copy: loser,
});
}
}
// A directory that lost its path takes its whole subtree along.
for (const move of moves) {
for (const entry of entries) {
if (!entry.path.startsWith(`${move.from}/`)) continue;
entry.prevPath = entry.path;
entry.path = `${move.to}${entry.path.slice(move.from.length)}`;
}
}
}
return entries;
}
/**
* Newest `updated` wins; ties break on hash, then on peer, so both sides pick
* the same one from the same two entries without talking.
*/
export function pickNewer(left: VFSEntry, right: VFSEntry): VFSEntry {
if (left.updated !== right.updated) return left.updated > right.updated ? left : right;
const leftKey = `${left.hash ?? ''}|${left.peerId}|${left.uuid}`;
const rightKey = `${right.hash ?? ''}|${right.peerId}|${right.uuid}`;
return leftKey >= rightKey ? left : right;
}
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