add Sql and subsys::Database

iface/CMakeLists.txt

@@ -17,6 +17,8 @@ target_sources(nf7_iface
     common/leak_detector.hh
     common/mutex.hh
     common/observer.hh
+    common/observer.hh
+    common/sql.hh
     common/task.hh
     common/task_context.hh
     common/value.hh
@@ -25,6 +27,7 @@ target_sources(nf7_iface
     data/interface.hh
     data/wrap.hh
     subsys/concurrency.hh
+    subsys/database.hh
     subsys/interface.hh
     subsys/logger.hh
     subsys/parallelism.hh

iface/common/sql.hh

@@ -0,0 +1,63 @@
+// No copyright
+#pragma once
+
+#include <cstdint>
+#include <functional>
+#include <string>
+#include <variant>
+#include <vector>
+
+#include "iface/common/future.hh"
+#include "iface/common/void.hh"
+
+
+namespace nf7 {
+
+class Sql {
+ public:
+  class Command;
+
+ public:
+  struct Null final { };
+  using Value = std::variant<Null, int64_t, double, std::string>;
+
+  enum Result {
+    kRow,
+    kDone,
+  };
+
+ public:
+  Sql() = default;
+  virtual ~Sql() = default;
+
+  Sql(const Sql&) = delete;
+  Sql(Sql&&) = delete;
+  Sql& operator=(const Sql&) = delete;
+  Sql& operator=(Sql&&) = delete;
+
+ public:
+  virtual void Bind(uint64_t idx, const Value&) = 0;
+  virtual Value Fetch(uint64_t idx) const = 0;
+
+  virtual void Reset() = 0;
+  virtual Result Exec() = 0;
+};
+
+class Sql::Command {
+ public:
+  using Handler = std::function<void(Sql&)>;
+
+ public:
+  Command() = default;
+  virtual ~Command() = default;
+
+  Command(const Command&) = delete;
+  Command(Command&&) = delete;
+  Command& operator=(const Command&) = delete;
+  Command& operator=(Command&&) = delete;
+
+ public:
+  virtual Future<Void> Run(Handler&&) noexcept = 0;
+};
+
+}  // namespace nf7

iface/subsys/database.hh

@@ -0,0 +1,44 @@
+// No copyright
+#pragma once
+
+#include <functional>
+#include <memory>
+#include <string_view>
+#include <utility>
+
+#include "iface/common/future.hh"
+#include "iface/common/observer.hh"
+#include "iface/common/sql.hh"
+#include "iface/common/void.hh"
+#include "iface/subsys/interface.hh"
+
+
+namespace nf7::subsys {
+
+class Database : public Interface, public Observer<Void>::Target {
+ public:
+  using ColumnHandler = std::function<bool(const Sql&)>;
+
+ public:
+  using Interface::Interface;
+
+ public:
+  virtual Future<std::shared_ptr<Sql::Command>> Compile(
+      std::string_view) noexcept = 0;
+
+  virtual Future<Void> Exec(
+      std::string_view cmd, ColumnHandler&& f = {}) noexcept {
+    return Compile(cmd)
+        .ThenAnd([f = std::move(f)](auto& x) mutable {
+          return !f?
+            Future<Void> {Void {}}:
+            x->Run([f = std::move(f)](auto& x) mutable {
+              while (Sql::kRow == x.Exec()) {
+                f(x);
+              }
+            });
+        });
+  }
+};
+
+}  // namespace nf7::subsys