feat(pipeline): add pipeline header

test/pipeline.cpp

@@ -0,0 +1,75 @@
+#include "mosh-me/pipeline.hpp"
+#include <catch2/catch_all.hpp>
+#include <spdlog/fmt/fmt.h>
+#include <spdlog/fmt/ranges.h>
+
+using namespace mosh_me;
+
+class CountProducer : public PipeOutput<int>,
+                      public AsPipeSource<CountProducer, int> {
+private:
+  int counter_ = 0;
+
+public:
+  std::optional<int> pull() noexcept override {
+    if (auto i = counter_++; i < 10) {
+      return i;
+    } else {
+      return std::nullopt;
+    }
+  }
+};
+
+class Doubler : public PipeWorker<int, int>,
+                public AsPipeLink<Doubler, int, int> {
+public:
+  std::optional<int> pull() noexcept override {
+    return fetchInput().and_then(
+        [](int x) { return std::make_optional(x * 2); });
+  }
+};
+
+class Multiplier : public PipeWorker<int, int>,
+                   public AsPipeLink<Multiplier, int, int> {
+  int f_;
+
+public:
+  Multiplier(int f) : f_(f) {}
+  std::optional<int> pull() noexcept override {
+    return fetchInput().and_then(
+        [this](int x) { return std::make_optional(f_ * x); });
+  }
+};
+
+class Sum2 : public PipeWorker<int, int>, public AsPipeLink<Sum2, int, int> {
+private:
+  std::optional<int> last_;
+
+public:
+  std::optional<int> pull() noexcept override {
+    if (auto x = fetchInput(); x) {
+      if (last_) {
+        auto sum = *last_ + *x;
+        last_ = std::nullopt;
+        return sum;
+      } else {
+        last_ = x;
+        return pull();
+      }
+    }
+    return std::nullopt;
+  }
+};
+
+TEST_CASE("Pipeline") {
+  auto pipe = Sum2::link() << Doubler::link() << Multiplier::link(10)
+                           << CountProducer::link();
+
+  auto count = 0;
+  while (auto s = pipe.pull()) {
+    REQUIRE(*s == ((count * 2) * 20) + ((count * 2 + 1) * 20));
+    count++;
+  }
+
+  REQUIRE(count == 5);
+}