Document Version History

Problem

Design DocumentVersionHistory to manage documents with fixed user access, immutable numbered versions, one selected version, and permanent deletion.

Requirements

Create a document. createDocument creates version 1 with the supplied content, selects it, makes the caller the owner, and assigns the supplied editor and viewer lists.
Preserve updates. An owner or editor can append the next numbered version with new full content. Earlier versions stay unchanged, and the new version becomes selected.
Select a version. An owner or editor can select any existing version without changing the stored history. A later update always uses the next number after the highest existing version.
Read the selection. An owner, editor, or viewer can read an object containing exactly the selected version and its content.
Delete a document. Only its owner can permanently delete a document and all its versions. Every later operation for that document fails with DocumentNotFoundError.
Enforce access. Users not listed on a document have no access, and viewers cannot update, select, or delete. A disallowed call raises AccessDeniedError and leaves all state unchanged.

API

Signature	Returns	Behavior
`DocumentVersionHistory()`	Not applicable	Creates an empty service.
`createDocument(actorId: string, documentId: string, content: string, editors: string[], viewers: string[])`	`integer`	Creates the document and returns `1`. Raises `DocumentExistsError` if the id is live. Raises `InvalidArgumentError` if an id or content is empty, the user lists overlap, or either list contains the actor. Failure changes no state.
`updateDocument(actorId: string, documentId: string, content: string)`	`integer`	Appends and selects a version, then returns its number. Raises `DocumentNotFoundError`, `AccessDeniedError`, or `InvalidArgumentError` for empty content. Failure changes no state.
`changeVersion(actorId: string, documentId: string, version: integer)`	`void`	Selects an existing version. Raises `DocumentNotFoundError`, `AccessDeniedError`, or `VersionNotFoundError`. Failure changes no state.
`getCurrentDocument(actorId: string, documentId: string)`	`object`	Returns `{"version": integer, "content": string}` for the selected version. Raises `DocumentNotFoundError` or `AccessDeniedError`.
`deleteDocument(actorId: string, documentId: string)`	`void`	Deletes the document and its history. Raises `DocumentNotFoundError` or `AccessDeniedError`. Failure changes no state.

Examples

Step	Operation	Result
1	`createDocument("alice", "spec", "draft", ["bob"], ["cara"])`	`1`
2	`updateDocument("bob", "spec", "reviewed")`	`2`
3	`changeVersion("alice", "spec", 1)`	`void`
4	`getCurrentDocument("cara", "spec")`	`{"version": 1, "content": "draft"}`
5	`updateDocument("cara", "spec", "blocked")`	`AccessDeniedError`; state unchanged
6	`deleteDocument("alice", "spec")`	`void`
7	`getCurrentDocument("alice", "spec")`	`DocumentNotFoundError`

Constraints

User ids and document ids contain from 1 through 100 Unicode scalar values.
Content contains from 1 through 10000 Unicode scalar values.
A document has at most 1000 users across all roles and 10000 versions.
At most 10000 documents and 100000 method calls occur per testcase.
Role assignments do not change after creation.

Notes

Calls are sequential and take effect in invocation order. Concurrent calls are outside scope. Access is supplied through editor and viewer id lists.