export interface DirtyState {
  currentMainRevision: number;
  committedMainRevision: number;
  dirty: boolean;
}

export type DirtyStateResult =
  | { ok: true; state: DirtyState }
  | { ok: false; state: DirtyState; errorCode: "DIRTY_REVISION_INVALID" | "DIRTY_REVISION_STALE" | "DIRTY_SAVE_REVISION_MISMATCH" };

function validRevision(revision: number): boolean {
  return Number.isSafeInteger(revision) && revision >= 0;
}

export function createDirtyState(revision = 0): DirtyState {
  if (!validRevision(revision)) throw new Error("DIRTY_REVISION_INVALID");
  return { currentMainRevision: revision, committedMainRevision: revision, dirty: false };
}

export function recoverDirtyState(currentMainRevision: number, committedMainRevision: number): DirtyState {
  if (!validRevision(currentMainRevision) || !validRevision(committedMainRevision) || currentMainRevision < committedMainRevision) {
    throw new Error("DIRTY_REVISION_INVALID");
  }
  return { currentMainRevision, committedMainRevision, dirty: currentMainRevision !== committedMainRevision };
}

export function acceptMainTransaction(state: DirtyState, revision: number): DirtyStateResult {
  if (!validRevision(revision)) return { ok: false, state, errorCode: "DIRTY_REVISION_INVALID" };
  if (revision <= state.currentMainRevision) return { ok: false, state, errorCode: "DIRTY_REVISION_STALE" };
  return {
    ok: true,
    state: { ...state, currentMainRevision: revision, dirty: revision !== state.committedMainRevision },
  };
}

export function acceptMainSave(state: DirtyState, revision: number): DirtyStateResult {
  if (!validRevision(revision)) return { ok: false, state, errorCode: "DIRTY_REVISION_INVALID" };
  if (revision !== state.currentMainRevision) return { ok: false, state, errorCode: "DIRTY_SAVE_REVISION_MISMATCH" };
  return { ok: true, state: { currentMainRevision: revision, committedMainRevision: revision, dirty: false } };
}

export function acceptHistoryTransaction(state: DirtyState, revision: number, matchesCommittedContent: boolean): DirtyStateResult {
  if (!validRevision(revision)) return { ok: false, state, errorCode: "DIRTY_REVISION_INVALID" };
  if (revision <= state.currentMainRevision) return { ok: false, state, errorCode: "DIRTY_REVISION_STALE" };
  return {
    ok: true,
    state: {
      currentMainRevision: revision,
      committedMainRevision: matchesCommittedContent ? revision : state.committedMainRevision,
      dirty: !matchesCommittedContent,
    },
  };
}