sqlite: add transactions support

Fixes: #511

docs/types/sqlite.d.ts

@@ -49,6 +49,12 @@ declare module 'tjs:sqlite'{
         readOnly: boolean;
     }
 
+    export interface ITransaction extends Function {
+        deferred: Function;
+        immediate: Function;
+        exclusive: Function;
+    }
+
     export class Database {
         /**
          * Opens a SQLite database.
@@ -73,6 +79,45 @@ declare module 'tjs:sqlite'{
          */
         prepare(sql: string): IStatement;
 
+        /**
+         * Wrap the given function so it runs in a [transaction](https://sqlite.org/lang_transaction.html).
+         * When the (returned) function is invoked, it will start a new transaction. When the function returns,
+         * the transaction will be committed. If an exception is thrown, the transaction will be rolled back.
+         *
+         * ```js
+         * const ins = db.prepare('INSERT INTO test (txt, int) VALUES(?, ?)');
+         * const insMany = db.transaction(datas => {
+         *     for (const data of datas) {
+         *         ins.run(data);
+         *     }
+         * });
+         *
+         * insMany([
+         *     [ '1234', 1234 ],
+         *     [ '4321', 4321 ],
+         * ]);
+         * ```
+         * Transaction functions can be called from inside other transaction functions. When doing so,
+         * the inner transaction becomes a [savepoint](https://www.sqlite.org/lang_savepoint.html). If an error
+         * is thrown inside of a nested transaction function, the nested transaction function will roll back
+         * to the state just before the savepoint. If the error is not caught in the outer transaction function,
+         * this will cause the outer transaction function to roll back as well.
+         *
+         * Transactions also come with deferred, immediate, and exclusive versions:
+         *
+         * ```js
+         * insertMany(datas); // uses "BEGIN"
+         * insertMany.deferred(datas); // uses "BEGIN DEFERRED"
+         * insertMany.immediate(datas); // uses "BEGIN IMMEDIATE"
+         * insertMany.exclusive(datas); // uses "BEGIN EXCLUSIVE"
+         * ```
+         *
+         * NOTE: This implementation was mostly taken from [better-sqlite3](https://github.com/WiseLibs/better-sqlite3/blob/6acc3fcebe469969aa29319714b187a53ada0934/docs/api.md#transactionfunction---function).
+         *
+         * @param fn - The function to be wrapped in a transaction.
+         */
+        transaction(fn: Function): ITransaction;
+
         /**
          * Closes the database. No further operations can be performed afterwards.
          */

src/_sqlite3.c

@@ -229,6 +229,15 @@ static JSValue tjs_sqlite3_prepare(JSContext *ctx, JSValue this_val, int argc, J
     return obj;
 }
 
+static JSValue tjs_sqlite3_in_transaction(JSContext *ctx, JSValue this_val, int argc, JSValue *argv) {
+    TJSSqlite3Handle *h = tjs_sqlite3_get(ctx, argv[0]);
+
+    if (!h)
+        return JS_EXCEPTION;
+
+    return JS_NewBool(ctx, !sqlite3_get_autocommit(h->handle));
+}
+
 static JSValue tjs_sqlite3_stmt_finalize(JSContext *ctx, JSValue this_val, int argc, JSValue *argv) {
     TJSSqlite3Stmt *h = tjs_sqlite3_stmt_get(ctx, argv[0]);
 
@@ -512,6 +521,7 @@ static const JSCFunctionListEntry tjs_sqlite3_funcs[] = {
     TJS_CFUNC_DEF("close", 1, tjs_sqlite3_close),
     TJS_CFUNC_DEF("exec", 2, tjs_sqlite3_exec),
     TJS_CFUNC_DEF("prepare", 2, tjs_sqlite3_prepare),
+    TJS_CFUNC_DEF("in_transaction", 1, tjs_sqlite3_in_transaction),
     TJS_CFUNC_DEF("stmt_finalize", 1, tjs_sqlite3_stmt_finalize),
     TJS_CFUNC_DEF("stmt_expand", 1, tjs_sqlite3_stmt_expand),
     TJS_CFUNC_DEF("stmt_all", 2, tjs_sqlite3_stmt_all),