1 files changed, 127 insertions, 0 deletions
diff --git a/src/filter.c b/src/filter.c
new file mode 100644
index 00000000..581a7b72
--- /dev/null
+++ b/src/filter.c
@@ -0,0 +1,127 @@
+// Copyright 2019-2022 David Robillard <d@drobilla.net>
+// SPDX-License-Identifier: ISC
+
+#include "serd/filter.h"
+
+#include "serd/event.h"
+#include "serd/memory.h"
+#include "serd/statement.h"
+#include "serd/status.h"
+
+#include "memory.h"
+#include "sink.h"
+
+#include <assert.h>
+#include <stdbool.h>
+#include <stdlib.h>
+
+typedef struct {
+  const SerdSink* target;
+  SerdNode*       subject;
+  SerdNode*       predicate;
+  SerdNode*       object;
+  SerdNode*       graph;
+  bool            inclusive;
+} SerdFilterData;
+
+static void
+free_data(void* const handle)
+{
+  if (handle) {
+    SerdFilterData* const data      = (SerdFilterData*)handle;
+    SerdAllocator* const  allocator = data->target->allocator;
+
+    serd_node_free(allocator, data->subject);
+    serd_node_free(allocator, data->predicate);
+    serd_node_free(allocator, data->object);
+    serd_node_free(allocator, data->graph);
+    serd_afree(allocator, data);
+  }
+}
+
+static SerdStatus
+serd_filter_on_event(void* const handle, const SerdEvent* const event)
+{
+  const SerdFilterData* const data = (SerdFilterData*)handle;
+
+  if (event->type == SERD_STATEMENT) {
+    const bool matches = serd_statement_matches(event->statement.statement,
+                                                data->subject,
+                                                data->predicate,
+                                                data->object,
+                                                data->graph);
+
+    if (data->inclusive == matches) {
+      // Emit statement with reset flags to avoid confusing the writer
+      SerdEvent out_event       = *event;
+      out_event.statement.flags = 0U;
+      return serd_sink_write_event(data->target, &out_event);
+    }
+
+    return SERD_SUCCESS; // Skip statement
+  }
+
+  return event->type == SERD_END ? SERD_SUCCESS
+                                 : serd_sink_write_event(data->target, event);
+}
+
+SerdSink*
+serd_filter_new(const SerdWorld* const world,
+                const SerdSink* const  target,
+                const SerdNode* const  subject,
+                const SerdNode* const  predicate,
+                const SerdNode* const  object,
+                const SerdNode* const  graph,
+                const bool             inclusive)
+{
+  assert(world);
+  assert(target);
+
+  SerdAllocator* const  allocator = serd_world_allocator(world);
+  SerdFilterData* const data =
+    (SerdFilterData*)serd_wcalloc(world, 1, sizeof(SerdFilterData));
+
+  if (!data) {
+    return NULL;
+  }
+
+  data->target    = target;
+  data->inclusive = inclusive;
+
+  if (subject && serd_node_type(subject) != SERD_VARIABLE) {
+    if (!(data->subject = serd_node_copy(allocator, subject))) {
+      free_data(data);
+      return NULL;
+    }
+  }
+
+  if (predicate && serd_node_type(predicate) != SERD_VARIABLE) {
+    if (!(data->predicate = serd_node_copy(allocator, predicate))) {
+      free_data(data);
+      return NULL;
+    }
+  }
+
+  if (object && serd_node_type(object) != SERD_VARIABLE) {
+    if (!(data->object = serd_node_copy(allocator, object))) {
+      free_data(data);
+      return NULL;
+    }
+  }
+
+  if (graph && serd_node_type(graph) != SERD_VARIABLE) {
+    if (!(data->graph = serd_node_copy(allocator, graph))) {
+      free_data(data);
+      return NULL;
+    }
+  }
+
+  SerdSink* const sink =
+    serd_sink_new(allocator, data, serd_filter_on_event, free_data);
+
+  if (!sink) {
+    free_data(data);
+  }
+
+  return sink;
+}