From 458654c9a3891e0f61258842a7b30b4d6cf246ed Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Thu, 29 Aug 2019 13:33:18 +1000
Subject: [PATCH] parse/enum: add lookup-by-function

---
 parse/enum.hpp      | 87 +++++++++++++++++++++++++++++++++++++++------
 test/parse/enum.cpp | 28 ++++++++++++---
 2 files changed, 101 insertions(+), 14 deletions(-)

diff --git a/parse/enum.hpp b/parse/enum.hpp
index 77d4e08a..bc969db1 100644
--- a/parse/enum.hpp
+++ b/parse/enum.hpp
@@ -60,6 +60,47 @@ namespace cruft::parse::enumeration {
         };
 
 
+        template <typename EnumT>
+        struct lookup_callback : public lookup_base {
+            using function_t =  std::function<EnumT(cruft::view<char const*>&)>;
+
+            lookup_callback (
+                 function_t &&_callback
+            ) : m_callback (std::move (_callback))
+            { ; }
+
+            i08 as_i08 (cruft::view<char const*> &str) const& override { return get<i08> (str); }
+            i16 as_i16 (cruft::view<char const*> &str) const& override { return get<i16> (str); }
+            i32 as_i32 (cruft::view<char const*> &str) const& override { return get<i32> (str); }
+            i64 as_i64 (cruft::view<char const*> &str) const& override { return get<i64> (str); }
+
+            u08 as_u08 (cruft::view<char const*> &str) const& override { return get<u08> (str); }
+            u16 as_u16 (cruft::view<char const*> &str) const& override { return get<u16> (str); }
+            u32 as_u32 (cruft::view<char const*> &str) const& override { return get<u32> (str); }
+            u64 as_u64 (cruft::view<char const*> &str) const& override { return get<u64> (str); }
+
+        private:
+            template <typename ValueT>
+            ValueT
+            get (cruft::view<char const*> &str) const&
+            {
+                if constexpr (std::is_same_v<ValueT, underlying_else_identity_t<EnumT>>) {
+                    // Double check the callee changes the remaining string size.
+                    auto const len = str.size ();
+                    auto const res = m_callback (str);
+                    if (len == str.size ())
+                        throw std::invalid_argument ("Unknown enum value");
+                    return static_cast<ValueT> (res);
+                } else {
+                    throw std::runtime_error ("Invalid underlying type");
+                }
+            }
+
+
+            function_t m_callback;
+        };
+
+
         /// A simple lookup from a supplied mapping of strings-to-underlying,
         /// specialised on the EnumT that the lookup is targetting.
         template <typename EnumT>
@@ -118,6 +159,25 @@ namespace cruft::parse::enumeration {
             std::unique_ptr<lookup_base>
         >&
         cache (void);
+
+
+        template <typename EnumT>
+        cookie
+        setup [[nodiscard]] (std::unique_ptr<lookup_base> &&lookup)
+        {
+            auto &cache = detail::cache ();
+            auto const index = cruft::typeidx<EnumT> ();
+
+            auto [pos, success] = cache.insert ({
+                index,
+                std::move (lookup)
+            });
+
+            if (!success)
+                LOG_WARN ("duplicate parse setup for %! was ignored", cruft::type_name<EnumT> ());
+
+            return cookie {};
+        }
     };
 
 
@@ -131,19 +191,26 @@ namespace cruft::parse::enumeration {
     cookie
     setup [[nodiscard]] (std::map<std::string_view, EnumT> mapping)
     {
-        auto &cache = detail::cache ();
-
-        auto const index = cruft::typeidx<EnumT> ();
-        auto lookup = std::make_unique<detail::lookup_concrete<EnumT>> (std::move (mapping));
-
-        auto [pos, success] = cache.insert ({ index, std::move (lookup) });
-        if (!success)
-            LOG_WARN ("duplicate parse setup for %! was ignored", cruft::type_name<EnumT> ());
-
-        return cookie {};
+        return detail::setup<EnumT> (
+            std::make_unique<
+                detail::lookup_concrete<EnumT>
+            > (std::move (mapping))
+        );
     };
 
 
+    template <typename EnumT>
+    cookie
+    setup [[nodiscard]] (std::function<EnumT(cruft::view<char const*>&)> &&func)
+    {
+        return detail::setup<EnumT> (
+            std::make_unique<
+                detail::lookup_callback<EnumT>
+            > (std::move (func))
+        );
+    }
+
+
     /// Lookup an enumeration value given a string representation.
     ///
     /// The string view is taken by reference and will be modified so that it
diff --git a/test/parse/enum.cpp b/test/parse/enum.cpp
index 4be58f44..b524d144 100644
--- a/test/parse/enum.cpp
+++ b/test/parse/enum.cpp
@@ -3,15 +3,13 @@
 #include "std.hpp"
 #include "tap.hpp"
 
-enum enumeration_t : u16 { FOO, BAR = 2, QUX = 257 };
-
-enum class enum_class { VALUE };
-
 int main ()
 {
     cruft::TAP::logger tap;
 
     {
+        enum enumeration_t : u16 { FOO, BAR = 2, QUX = 257 };
+
         auto const cookie = cruft::parse::enumeration::setup<enumeration_t> ({
             { "FOO", FOO },
             { "BAR", BAR },
@@ -34,6 +32,8 @@ int main ()
     }
 
     {
+        enum class enum_class { VALUE };
+
         auto const cookie = cruft::parse::enumeration::setup<enum_class> ({
             { "VALUE", enum_class::VALUE },
         });
@@ -45,5 +45,25 @@ int main ()
         );
     }
 
+    {
+        enum class func_enum { ASDF };
+
+        auto const cookie = cruft::parse::enumeration::setup<func_enum> ([] (auto &str) {
+            if (equal (str, "ASDF")) {
+                str = str.consume (4);
+                return func_enum::ASDF;
+            }
+            throw std::runtime_error ("Invalid enum value");
+        });
+
+        (void)cookie;
+
+        tap.expect_eq (
+            func_enum::ASDF,
+            cruft::parse::from_string<func_enum> ("ASDF"),
+            "function enum lookup"
+        );
+    }
+
     return tap.status ();
 }
\ No newline at end of file