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import type {IClock, IClockVector, ITimestampStruct, ITimespanStruct} from './types';
export class Timestamp implements ITimestampStruct {
constructor(
public readonly sid: number,
public time: number,
) {}
}
export class Timespan implements ITimespanStruct {
constructor(
public readonly sid: number,
public time: number,
public span: number,
) {}
}
/**
* A factory function for creating a new timestamp.
*
* @param sid Session ID.
* @param time Logical clock sequence number.
* @returns A new timestamp.
*/
export const ts = (sid: number, time: number): ITimestampStruct => new Timestamp(sid, time);
/**
* A factory function for creating a new timespan.
*
* @param sid Session ID.
* @param time Logical clock sequence number.
* @param span Length of the timespan.
* @returns A new timespan.
*/
export const tss = (sid: number, time: number, span: number): ITimespanStruct => new Timespan(sid, time, span);
/**
* Advance a timestamp by a number of cycles.
*
* @param stamp A reference timestamp.
* @param cycles Number of cycles to advance.
* @returns A new timestamp.
*/
export const tick = (stamp: ITimestampStruct, cycles: number): ITimestampStruct => ts(stamp.sid, stamp.time + cycles);
/**
* Compares for equality two timestamps, time first.
*
* @returns True if timestamps are equal.
*/
export const equal = (ts1: ITimestampStruct, ts2: ITimestampStruct): boolean =>
ts1.time === ts2.time && ts1.sid === ts2.sid;
/**
* Compares two timestamps, time first.
*
* @returns 1 if current timestamp is larger, -1 if smaller, and 0 otherwise.
*/
export const compare = (ts1: ITimestampStruct, ts2: ITimestampStruct): -1 | 0 | 1 => {
const t1 = ts1.time;
const t2 = ts2.time;
if (t1 > t2) return 1;
if (t1 < t2) return -1;
const s1 = ts1.sid;
const s2 = ts2.sid;
if (s1 > s2) return 1;
if (s1 < s2) return -1;
return 0;
};
/**
* Checks if the first timespan contains the second timespan.
*
* @param ts1 Start of container timespan.
* @param span1 Length of container timespan.
* @param ts2 Start of contained timespan.
* @param span2 Length of contained timespan.
* @returns Returns true if the first timespan contains the second timespan.
*/
export const contains = (ts1: ITimestampStruct, span1: number, ts2: ITimestampStruct, span2: number): boolean => {
Iif (ts1.sid !== ts2.sid) return false;
const t1 = ts1.time;
const t2 = ts2.time;
Iif (t1 > t2) return false;
Iif (t1 + span1 < t2 + span2) return false;
return true;
};
/**
* Checks if a timespan contains the `ts2` point.
*
* @param ts1 Start of container timespan.
* @param span1 Length of container timespan.
* @param ts2 A point in time.
* @returns Returns true if the first timespan contains the `ts2` point.
*/
export const containsId = (ts1: ITimestampStruct, span1: number, ts2: ITimestampStruct): boolean => {
if (ts1.sid !== ts2.sid) return false;
const t1 = ts1.time;
const t2 = ts2.time;
if (t1 > t2) return false;
if (t1 + span1 < t2 + 1) return false;
return true;
};
/**
* Returns a human-readable string representation of the timestamp.
*
* @param id A timestamp.
* @returns Human-readable string representation of the timestamp.
*/
export const printTs = (id: ITimestampStruct): string => {
if (id.sid === SESSION.SERVER) return '.' + id.time;
let session = '' + id.sid;
if (session.length > 4) session = '..' + session.slice(session.length - 4);
return session + '.' + id.time;
};
/**
* Advances a given timestamp by a number of cycles and then returns a timespan
* starting from that position.
*
* @param ts A start timestamp.
* @param tick Number of cycles to advance the starting timestamp.
* @param span Length of the timespan.
* @returns A new timespan.
*/
export const interval = (ts: ITimestampStruct, tick: number, span: number): ITimespanStruct =>
new Timespan(ts.sid, ts.time + tick, span);
/**
* Represents a *Logical Clock*, which can be advanced by a number of cycles.
*/
export class LogicalClock extends Timestamp implements IClock {
/**
* Returns a new timestamp, which is the current clock value, and advances the
* clock by a number of cycles.
*
* @param cycles Number of cycles to advance the clock.
* @returns A new timestamp, which is the current clock value.
*/
public tick(cycles: number): ITimestampStruct {
const timestamp = new Timestamp(this.sid, this.time);
this.time += cycles;
return timestamp;
}
}
/**
* Represents a clock vector, which is a local logical clock together with a set
* of logical clocks of other peers.
*/
export class ClockVector extends LogicalClock implements IClockVector {
/**
* A set of logical clocks of other peers.
*/
public readonly peers = new Map<number, ITimestampStruct>();
/**
* Advances local time every time we see any timestamp with higher time value.
* This is an idempotent method which can be called every time a new timestamp
* is observed, it advances the local time only if the observed timestamp is
* greater than the current local time.
*
* @param id The time stamp we observed.
* @param span Length of the time span.
*/
public observe(id: ITimestampStruct, span: number) {
// if (this.time < ts.time) throw new Error('TIME_TRAVEL');
const edge = id.time + span - 1;
const sid = id.sid;
if (sid !== this.sid) {
const clock = this.peers.get(id.sid);
if (!clock) this.peers.set(id.sid, ts(sid, edge));
else if (edge > clock.time) clock.time = edge;
}
if (edge >= this.time) this.time = edge + 1;
}
/**
* Returns a deep copy of the current vector clock with the same session ID.
*
* @returns A new vector clock, which is a clone of the current vector clock.
*/
public clone(): ClockVector {
return this.fork(this.sid);
}
/**
* Returns a deep copy of the current vector clock with a different session ID.
*
* @param sessionId The session ID of the new vector clock.
* @returns A new vector clock, which is a fork of the current vector clock.
*/
public fork(sessionId: number): ClockVector {
const clock = new ClockVector(sessionId, this.time);
if (sessionId !== this.sid) clock.observe(tick(this, -1), 1);
// biome-ignore lint: using .forEach() on Map is the fastest way to iterate
this.peers.forEach((peer) => {
clock.observe(peer, 1);
});
return clock;
}
/**
* Returns a human-readable string representation of the clock vector.
*
* @param tab String to use for indentation.
* @returns Human-readable string representation of the clock vector.
*/
public toString(tab: string = ''): string {
const last = this.peers.size;
let i = 1;
let lines = '';
// biome-ignore lint: using .forEach() on Map is the fastest way to iterate
this.peers.forEach((clock) => {
const isLast = i === last;
lines += `\n${tab}${isLast ? '└─' : '├─'} ${clock.sid}.${clock.time}`;
i++;
});
return `clock ${this.sid}.${this.time}${lines}`;
}
}
/**
* Implements a clock vector with a fixed session ID. The *server clock*
* is used when the CRDT is powered by a central server.
*/
export class ServerClockVector extends LogicalClock implements IClockVector {
/** A stub for other peers. Not used in the server clock. */
public readonly peers = new Map<number, ITimespanStruct>();
public observe(ts: ITimespanStruct, span: number) {
Iif (ts.sid > 8) throw new Error('INVALID_SERVER_SESSION');
if (this.time < ts.time) throw new Error('TIME_TRAVEL');
const time = ts.time + span;
if (time > this.time) this.time = time;
}
public clone(): ServerClockVector {
return this.fork();
}
public fork(): ServerClockVector {
return new ServerClockVector(SESSION.SERVER, this.time);
}
/**
* Returns a human-readable string representation of the clock vector.
*
* @returns Human-readable string representation of the clock vector.
*/
public toString(): string {
return `clock ${this.sid}.${this.time}`;
}
}
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