overleaf/services/track-changes/app/coffee/DiffGenerator.js

/*
 * decaffeinate suggestions:
 * DS101: Remove unnecessary use of Array.from
 * DS102: Remove unnecessary code created because of implicit returns
 * DS207: Consider shorter variations of null checks
 * Full docs: https://github.com/decaffeinate/decaffeinate/blob/master/docs/suggestions.md
 */
let DiffGenerator;
var ConsistencyError = function(message) {
	const error = new Error(message);
	error.name = "ConsistencyError";
	error.__proto__ = ConsistencyError.prototype;
	return error;
};
ConsistencyError.prototype.__proto__ = Error.prototype;

const logger = require("logger-sharelatex");

module.exports = (DiffGenerator = {
	ConsistencyError,

	rewindUpdate(content, update) {
		for (let j = update.op.length - 1, i = j; j >= 0; j--, i = j) {
			const op = update.op[i];
			if (op.broken !== true) {
				try {
					content = DiffGenerator.rewindOp(content, op);
				} catch (e) {
					if (e instanceof ConsistencyError && (i = update.op.length - 1)) {
						// catch known case where the last op in an array has been
						// merged into a later op
						logger.error({err: e, update, op: JSON.stringify(op)}, "marking op as broken");
						op.broken = true;
					} else {
						throw e; // rethrow the execption
					}
				}
			}
		}
		return content;
	},

	rewindOp(content, op) {
		let p;
		if (op.i != null) {
			// ShareJS will accept an op where p > content.length when applied,
			// and it applies as though p == content.length. However, the op is
			// passed to us with the original p > content.length. Detect if that
			// is the case with this op, and shift p back appropriately to match
			// ShareJS if so.
			({ p } = op);
			const max_p = content.length - op.i.length;
			if (p > max_p) {
				logger.warn({max_p, p}, "truncating position to content length");
				p = max_p;
			}

			const textToBeRemoved = content.slice(p, p + op.i.length);
			if (op.i !== textToBeRemoved) {
				throw new ConsistencyError(
					`Inserted content, '${op.i}', does not match text to be removed, '${textToBeRemoved}'`
				);
			}

			return content.slice(0, p) + content.slice(p + op.i.length);

		} else if (op.d != null) {
			return content.slice(0, op.p) + op.d + content.slice(op.p);
		
		} else {
			return content;
		}
	},

	rewindUpdates(content, updates) {
		for (let update of Array.from(updates.reverse())) {
			try {
				content = DiffGenerator.rewindUpdate(content, update);
			} catch (e) {
				e.attempted_update = update; // keep a record of the attempted update
				throw e; // rethrow the exception
			}
		}
		return content;
	},

	buildDiff(initialContent, updates) {
		let diff = [ {u: initialContent} ];
		for (let update of Array.from(updates)) {
			diff = DiffGenerator.applyUpdateToDiff(diff, update);
		}
		diff = DiffGenerator.compressDiff(diff);
		return diff;
	},

	compressDiff(diff) {
		const newDiff = [];
		for (let part of Array.from(diff)) {
			const lastPart = newDiff[newDiff.length - 1];
			if ((lastPart != null) && ((lastPart.meta != null ? lastPart.meta.user : undefined) != null) && ((part.meta != null ? part.meta.user : undefined) != null)) {
				if ((lastPart.i != null) && (part.i != null) && (lastPart.meta.user.id === part.meta.user.id)) {
					lastPart.i += part.i;
					lastPart.meta.start_ts = Math.min(lastPart.meta.start_ts, part.meta.start_ts);
					lastPart.meta.end_ts = Math.max(lastPart.meta.end_ts, part.meta.end_ts);
				} else if ((lastPart.d != null) && (part.d != null) && (lastPart.meta.user.id === part.meta.user.id)) {
					lastPart.d += part.d;
					lastPart.meta.start_ts = Math.min(lastPart.meta.start_ts, part.meta.start_ts);
					lastPart.meta.end_ts = Math.max(lastPart.meta.end_ts, part.meta.end_ts);
				} else {
					newDiff.push(part);
				}
			} else {
				newDiff.push(part);
			}
		}
		return newDiff;
	},

	applyOpToDiff(diff, op, meta) {
		let consumedDiff;
		const position = 0;

		let remainingDiff = diff.slice();
		({consumedDiff, remainingDiff} = DiffGenerator._consumeToOffset(remainingDiff, op.p));
		const newDiff = consumedDiff;

		if (op.i != null) {
			newDiff.push({
				i: op.i,
				meta
			});
		} else if (op.d != null) {
			({consumedDiff, remainingDiff} = DiffGenerator._consumeDiffAffectedByDeleteOp(remainingDiff, op, meta));
			newDiff.push(...Array.from(consumedDiff || []));
		}

		newDiff.push(...Array.from(remainingDiff || []));

		return newDiff;
	},

	applyUpdateToDiff(diff, update) {
		for (let op of Array.from(update.op)) {
			if (op.broken !== true) {
				diff = DiffGenerator.applyOpToDiff(diff, op, update.meta);
			}
		}
		return diff;
	},

	_consumeToOffset(remainingDiff, totalOffset) {
		let part;
		const consumedDiff = [];
		let position = 0;
		while ((part = remainingDiff.shift())) {
			const length = DiffGenerator._getLengthOfDiffPart(part);
			if (part.d != null) {
				consumedDiff.push(part);
			} else if ((position + length) >= totalOffset) {
				const partOffset = totalOffset - position;
				if (partOffset > 0) {
					consumedDiff.push(DiffGenerator._slicePart(part, 0, partOffset));
				}
				if (partOffset < length) {
					remainingDiff.unshift(DiffGenerator._slicePart(part, partOffset));
				}
				break;
			} else {
				position += length;
				consumedDiff.push(part);
			}
		}

		return {
			consumedDiff,
			remainingDiff
		};
	},

	_consumeDiffAffectedByDeleteOp(remainingDiff, deleteOp, meta) {
		const consumedDiff = [];
		let remainingOp = deleteOp;
		while (remainingOp && (remainingDiff.length > 0)) {
			let newPart;
			({newPart, remainingDiff, remainingOp} = DiffGenerator._consumeDeletedPart(remainingDiff, remainingOp, meta));
			if (newPart != null) { consumedDiff.push(newPart); }
		}
		return {
			consumedDiff,
			remainingDiff
		};
	},

	_consumeDeletedPart(remainingDiff, op, meta) {
		let deletedContent, newPart, remainingOp;
		const part = remainingDiff.shift();
		const partLength = DiffGenerator._getLengthOfDiffPart(part);

		if (part.d != null) {
			// Skip existing deletes
			remainingOp = op;
			newPart = part;

		} else if (partLength > op.d.length) {
			// Only the first bit of the part has been deleted
			const remainingPart = DiffGenerator._slicePart(part, op.d.length);
			remainingDiff.unshift(remainingPart);

			deletedContent = DiffGenerator._getContentOfPart(part).slice(0, op.d.length);
			if (deletedContent !== op.d) {
				throw new ConsistencyError(`deleted content, '${deletedContent}', does not match delete op, '${op.d}'`);
			}

			if (part.u != null) {
				newPart = {
					d: op.d,
					meta
				};
			} else if (part.i != null) {
				newPart = null;
			}

			remainingOp = null;

		} else if (partLength === op.d.length) {
			// The entire part has been deleted, but it is the last part

			deletedContent = DiffGenerator._getContentOfPart(part);
			if (deletedContent !== op.d) {
				throw new ConsistencyError(`deleted content, '${deletedContent}', does not match delete op, '${op.d}'`);
			}

			if (part.u != null) {
				newPart = {
					d: op.d,
					meta
				};
			} else if (part.i != null) {
				newPart = null;
			}

			remainingOp = null;

		} else if (partLength < op.d.length) {
			// The entire part has been deleted and there is more

			deletedContent = DiffGenerator._getContentOfPart(part);
			const opContent = op.d.slice(0, deletedContent.length);
			if (deletedContent !== opContent) {
				throw new ConsistencyError(`deleted content, '${deletedContent}', does not match delete op, '${opContent}'`);
			}

			if (part.u) {
				newPart = {
					d: part.u,
					meta
				};
			} else if (part.i != null) {
				newPart = null;
			}

			remainingOp =
				{p: op.p, d: op.d.slice(DiffGenerator._getLengthOfDiffPart(part))};
		}

		return {
			newPart,
			remainingDiff,
			remainingOp
		};
	},

	_slicePart(basePart, from, to) {
		let part;
		if (basePart.u != null) {
			part = { u: basePart.u.slice(from, to) };
		} else if (basePart.i != null) {
			part = { i: basePart.i.slice(from, to) };
		}
		if (basePart.meta != null) {
			part.meta = basePart.meta;
		}
		return part;
	},

	_getLengthOfDiffPart(part) {
		return (part.u || part.d || part.i || '').length;
	},

	_getContentOfPart(part) {
		return part.u || part.d || part.i || '';
	}
});