From e4b13d4ccbc83c39dd901b3adf50c65f866bf6d4 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Mon, 14 Jun 2021 08:23:10 +0530
Subject: [PATCH] Start work on ICU tokenizer for FTS

---
 setup/extensions.json               |  5 ++
 src/calibre/constants.py            |  9 ++++
 src/calibre/db/sqlite_extension.cpp | 76 +++++++++++++++++++++++++++++
 src/calibre/db/tests/fts.py         | 17 +++++++
 4 files changed, 107 insertions(+)
 create mode 100644 src/calibre/db/sqlite_extension.cpp
 create mode 100644 src/calibre/db/tests/fts.py

diff --git a/setup/extensions.json b/setup/extensions.json
index d887aca3b3..c9e5305227 100644
--- a/setup/extensions.json
+++ b/setup/extensions.json
@@ -71,6 +71,11 @@
         "sources": "calibre/library/sqlite_custom.c",
         "inc_dirs": "!sqlite_inc_dirs"
     },
+    {
+        "name": "sqlite_extension",
+        "sources": "calibre/db/sqlite_extension.cpp",
+        "inc_dirs": "!sqlite_inc_dirs"
+    },
     {
         "name": "lzx",
         "sources": "calibre/utils/lzx/lzxmodule.c calibre/utils/lzx/compressor.c calibre/utils/lzx/lzxd.c calibre/utils/lzx/lzc.c calibre/utils/lzx/lzxc.c",
diff --git a/src/calibre/constants.py b/src/calibre/constants.py
index d945cac855..330ef1e0e1 100644
--- a/src/calibre/constants.py
+++ b/src/calibre/constants.py
@@ -320,6 +320,15 @@ class Plugins(collections.Mapping):
         except Exception as err:
             return None, str(err)
 
+    def load_apsw_extension(self, conn, name):
+        conn.enableloadextension(True)
+        try:
+            ext = 'pyd' if iswindows else 'so'
+            path = os.path.join(plugins_loc, f'{name}.{ext}')
+            conn.loadextension(path, f'calibre_{name}_init')
+        finally:
+            conn.enableloadextension(False)
+
 
 plugins = None
 if plugins is None:
diff --git a/src/calibre/db/sqlite_extension.cpp b/src/calibre/db/sqlite_extension.cpp
new file mode 100644
index 0000000000..f45749e8e0
--- /dev/null
+++ b/src/calibre/db/sqlite_extension.cpp
@@ -0,0 +1,76 @@
+/*
+ * sqlite_extension.cpp
+ * Copyright (C) 2021 Kovid Goyal <kovid at kovidgoyal.net>
+ *
+ * Distributed under terms of the GPL3 license.
+ */
+
+#define UNICODE
+#include <Python.h>
+
+
+#include <stdlib.h>
+
+#include <sqlite3ext.h>
+SQLITE_EXTENSION_INIT1
+
+static int
+fts5_api_from_db(sqlite3 *db, fts5_api **ppApi) {
+    sqlite3_stmt *pStmt = 0;
+    *ppApi = 0;
+    int rc = sqlite3_prepare(db, "SELECT fts5(?1)", -1, &pStmt, 0);
+    if (rc == SQLITE_OK) {
+        sqlite3_bind_pointer(pStmt, 1, reinterpret_cast<void *>(ppApi), "fts5_api_ptr", 0);
+        (void)sqlite3_step(pStmt);
+        rc = sqlite3_finalize(pStmt);
+    }
+    return rc;
+}
+
+
+extern "C" {
+#ifdef _MSC_VER
+#define MYEXPORT __declspec(dllexport)
+#else
+#define MYEXPORT __attribute__ ((visibility ("default")))
+#endif
+
+MYEXPORT int
+calibre_sqlite_extension_init(sqlite3 *db, char **pzErrMsg, const sqlite3_api_routines *pApi){
+    SQLITE_EXTENSION_INIT2(pApi);
+    fts5_api *fts5api = NULL;
+    int rc = fts5_api_from_db(db, &fts5api);
+    if (rc != SQLITE_OK) {
+        *pzErrMsg = (char*)"Failed to get FTS 5 API with error code";
+        return rc;
+    }
+    if (!fts5api || fts5api->iVersion < 2) {
+        *pzErrMsg = (char*)"FTS 5 iVersion too old or NULL pointer";
+        return SQLITE_ERROR;
+    }
+    return SQLITE_OK;
+}
+}
+
+
+static PyMethodDef methods[] = {
+    {NULL, NULL, 0, NULL}
+};
+
+static int
+exec_module(PyObject *mod) { return 0; }
+
+static PyModuleDef_Slot slots[] = { {Py_mod_exec, (void*)exec_module}, {0, NULL} };
+
+static struct PyModuleDef module_def = {
+    .m_base     = PyModuleDef_HEAD_INIT,
+    .m_name     = "sqlite_extension",
+    .m_doc      = "Implement ICU based tokenizer for FTS5",
+    .m_methods  = methods,
+    .m_slots    = slots,
+};
+
+
+extern "C" {
+CALIBRE_MODINIT_FUNC PyInit_sqlite_extension(void) { return PyModuleDef_Init(&module_def); }
+}
diff --git a/src/calibre/db/tests/fts.py b/src/calibre/db/tests/fts.py
new file mode 100644
index 0000000000..6ebb8d02e4
--- /dev/null
+++ b/src/calibre/db/tests/fts.py
@@ -0,0 +1,17 @@
+#!/usr/bin/env python
+# vim:fileencoding=UTF-8:ts=4:sw=4:sta:et:sts=4:ai
+# License: GPLv3 Copyright: 2021, Kovid Goyal <kovid at kovidgoyal.net>
+
+
+from calibre.db.tests.base import BaseTest
+
+
+class FTSTest(BaseTest):
+
+    def test_basic_fts(self):  # {{{
+        from apsw import Connection
+        from calibre.constants import plugins
+
+        conn = Connection(':memory:')
+        plugins.load_apsw_extension(conn, 'sqlite_extension')
+    # }}}