(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/gen-server/sqlUtils.ts

@@ -0,0 +1,90 @@
+import {DatabaseType} from 'typeorm';
+
+/**
+ *
+ * Generates an expression to simulate postgres's bit_or
+ * aggregate function in sqlite.  The expression is verbose,
+ * and has a term for each bit in the permission bitmap,
+ * but this seems ok since sqlite is only used in the dev
+ * environment.
+ * @param column: the sql column to aggregate
+ * @param bits: the maximum number of bits to consider
+ *
+ */
+export function sqliteBitOr(column: string, bits: number): string {
+  const parts: string[] = [];
+  let mask: number = 1;
+  for (let b = 0; b < bits; b++) {
+    parts.push(`((sum(${column}&${mask})>0)<<${b})`);
+    mask *= 2;
+  }
+  return `(${parts.join('+')})`;
+}
+
+/**
+ * Generates an expression to aggregate the named column
+ * by taking the bitwise-or of all the values it takes on.
+ * @param dbType: the type of database (sqlite and postgres are supported)
+ * @param column: the sql column to aggregate
+ * @param bits: the maximum number of bits to consider (used for sqlite variant)
+ */
+export function bitOr(dbType: DatabaseType, column: string, bits: number): string {
+  switch (dbType) {
+    case 'postgres':
+      return `bit_or(${column})`;
+    case 'sqlite':
+      return sqliteBitOr(column, bits);
+    default:
+      throw new Error(`bitOr not implemented for ${dbType}`);
+  }
+}
+
+/**
+ * Convert a json value returned by the database into a javascript
+ * object.  For postgres, the value is already unpacked, but for sqlite
+ * it is a string.
+ */
+export function readJson(dbType: DatabaseType, selection: any) {
+  switch (dbType) {
+    case 'postgres':
+      return selection;
+    case 'sqlite':
+      return JSON.parse(selection);
+    default:
+      throw new Error(`readJson not implemented for ${dbType}`);
+  }
+}
+
+export function now(dbType: DatabaseType) {
+  switch (dbType) {
+    case 'postgres':
+      return 'now()';
+    case 'sqlite':
+      return "datetime('now')";
+    default:
+      throw new Error(`now not implemented for ${dbType}`);
+  }
+}
+
+// Understands strings like: "-30 days" or "1 year"
+export function fromNow(dbType: DatabaseType, relative: string) {
+  switch (dbType) {
+    case 'postgres':
+      return `(now() + interval '${relative}')`;
+    case 'sqlite':
+      return `datetime('now','${relative}')`;
+    default:
+      throw new Error(`fromNow not implemented for ${dbType}`);
+  }
+}
+
+export function datetime(dbType: DatabaseType) {
+  switch (dbType) {
+    case 'postgres':
+      return 'timestamp with time zone';
+    case 'sqlite':
+      return "datetime";
+    default:
+      throw new Error(`now not implemented for ${dbType}`);
+  }
+}