WIP add days transform impl

src/v/iceberg/BUILD

@@ -954,6 +954,7 @@ redpanda_cc_library(
     include_prefix = "iceberg",
     deps = [
         ":values",
+        "@seastar",
     ],
 )
 

src/v/iceberg/time_transform_visitor.cc

@@ -10,15 +10,26 @@
 
 #include "iceberg/values.h"
 
+#include <seastar/util/variant_utils.hh>
+
 namespace iceberg {
 
 namespace {
+
+static constexpr int64_t micros_per_s = 1'000'000;
+
 int32_t micros_to_hr(int64_t micros) {
     static constexpr int64_t s_per_hr = 3600;
-    static constexpr int64_t micros_per_s = 1000000;
     static constexpr int64_t micros_per_hr = micros_per_s * s_per_hr;
     return static_cast<int32_t>(micros / micros_per_hr);
 }
+
+int32_t micros_to_day(int64_t micros) {
+    static constexpr int64_t s_per_day = 86400;
+    static constexpr int64_t micros_per_day = micros_per_s * s_per_day;
+    return static_cast<int32_t>(micros / micros_per_day);
+}
+
 } // namespace
 
 int32_t hour_transform_visitor::operator()(const primitive_value& v) {
@@ -35,4 +46,15 @@ int32_t hour_transform_visitor::operator()(const primitive_value& v) {
       fmt::format("hourly_visitor not implemented for primitive value {}", v));
 }
 
+int32_t day_transform_visitor::operator()(const primitive_value& v) {
+    return ss::visit(
+      v,
+      [](const timestamp_value& v) { return micros_to_day(v.val); },
+      [](const timestamptz_value& v) { return micros_to_day(v.val); },
+      [](const auto& v) -> int32_t {
+          throw std::invalid_argument(fmt::format(
+            "day_transform_visitor not implemented for primitive value {}", v));
+      });
+}
+
 } // namespace iceberg

src/v/iceberg/time_transform_visitor.h

@@ -22,4 +22,14 @@ struct hour_transform_visitor {
     }
 };
 
+struct day_transform_visitor {
+    int32_t operator()(const primitive_value& v);
+
+    template<typename T>
+    int32_t operator()(const T& t) {
+        throw std::invalid_argument(
+          fmt::format("day_transform_visitor not implemented for value {}", t));
+    }
+};
+
 } // namespace iceberg

src/v/iceberg/transform_utils.cc

@@ -33,6 +33,11 @@ struct transform_applying_visitor {
         return v;
     }
 
+    value operator()(const day_transform&) {
+        int_value v{std::visit(day_transform_visitor{}, source_val_)};
+        return v;
+    }
+
     template<typename T>
     value operator()(const T&) {
         throw std::invalid_argument(