(core) move home server into core

Summary: This moves enough server material into core to run a home server.  The data engine is not yet incorporated (though in manual testing it works when ported).

Test Plan: existing tests pass

Reviewers: dsagal

Reviewed By: dsagal

Differential Revision: https://phab.getgrist.com/D2552

app/common/roles.ts

@@ -0,0 +1,85 @@
+export const OWNER  = 'owners';
+export const EDITOR = 'editors';
+export const VIEWER = 'viewers';
+export const GUEST  = 'guests';
+export const MEMBER = 'members';
+
+// Roles ordered from most to least permissive.
+const roleOrder: Array<Role|null> = [OWNER, EDITOR, VIEWER, MEMBER, GUEST, null];
+
+export type BasicRole = 'owners'|'editors'|'viewers';
+export type NonMemberRole = BasicRole|'guests';
+export type NonGuestRole = BasicRole|'members';
+export type Role = NonMemberRole|'members';
+
+// Returns the BasicRole (or null) with the same effective access as the given role.
+export function getEffectiveRole(role: Role|null): BasicRole|null {
+  if (role === GUEST || role === MEMBER) {
+    return VIEWER;
+  } else {
+    return role;
+  }
+}
+
+export function canEditAccess(role: string|null): boolean {
+  return role === OWNER;
+}
+
+// Note that while canEdit has the same return value as canDelete, the functions are
+// kept separate as they may diverge in the future.
+export function canEdit(role: string|null): boolean {
+  return role === OWNER || role === EDITOR;
+}
+
+export function canDelete(role: string|null): boolean {
+  return role === OWNER || role === EDITOR;
+}
+
+export function canView(role: string|null): boolean {
+  return role !== null;
+}
+
+// Returns true if the role string is a valid role or null.
+export function isValidRole(role: string|null): role is Role|null {
+  return (roleOrder as Array<string|null>).includes(role);
+}
+
+// Returns true if the role string is a valid non-Guest, non-Member, non-null role.
+export function isBasicRole(role: string|null): role is BasicRole {
+  return Boolean(role && role !== GUEST && role !== MEMBER && isValidRole(role));
+}
+
+// Returns true if the role string is a valid non-Guest, non-null role.
+export function isNonGuestRole(role: string|null): role is NonGuestRole {
+  return Boolean(role && role !== GUEST && isValidRole(role));
+}
+
+/**
+ * Returns out of any number of group role names the one that offers more permissions. The function
+ * is overloaded so that the output type matches the specificity of the input values.
+ */
+export function getStrongestRole<T extends Role|null>(...args: T[]): T {
+  return getFirstMatchingRole(roleOrder, args);
+}
+
+/**
+ * Returns out of any number of group role names the one that offers fewer permissions. The function
+ * is overloaded so that the output type matches the specificity of the input values.
+ */
+export function getWeakestRole<T extends Role|null>(...args: T[]): T {
+  return getFirstMatchingRole(roleOrder.slice().reverse(), args);
+}
+
+// Returns which of the `anyOf` args comes first in `array`. Helper for getStrongestRole
+// and getWeakestRole.
+function getFirstMatchingRole<T extends Role|null>(array: Array<Role|null>, anyOf: T[]): T {
+  if (anyOf.length === 0) {
+    throw new Error(`getFirstMatchingRole: No roles given`);
+  }
+  for (const role of anyOf) {
+    if (!isValidRole(role)) {
+      throw new Error(`getFirstMatchingRole: Invalid role ${role}`);
+    }
+  }
+  return array.find((item) => anyOf.includes(item as T)) as T;
+}