From 2cb768bddc715c32e740a067652e7200c8d344f3 Mon Sep 17 00:00:00 2001
From: Eugeen Sablin <EugeenSablin@gmail.com>
Date: Sat, 10 Nov 2018 19:23:16 +0300
Subject: support reading enums from config

---
 src/de.rs | 146 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
 1 file changed, 142 insertions(+), 4 deletions(-)

(limited to 'src/de.rs')

diff --git a/src/de.rs b/src/de.rs
index 89d0c0c..e465d60 100644
--- a/src/de.rs
+++ b/src/de.rs
@@ -5,7 +5,7 @@ use std::borrow::Cow;
 use std::collections::hash_map::Drain;
 use std::collections::HashMap;
 use std::iter::Peekable;
-use value::{Value, ValueKind, ValueWithKey};
+use value::{Value, ValueKind, ValueWithKey, Table};
 
 // TODO: Use a macro or some other magic to reduce the code duplication here
 
@@ -113,9 +113,22 @@ impl<'de> de::Deserializer<'de> for ValueWithKey<'de> {
         }
     }
 
+    fn deserialize_enum<V>(
+        self,
+        name: &'static str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        // FIXME: find a way to extend_with_key
+        visitor.visit_enum(EnumAccess{ value: self.0, name: name, variants: variants })
+    }
+
     forward_to_deserialize_any! {
         char seq
-        bytes byte_buf map struct unit enum newtype_struct
+        bytes byte_buf map struct unit newtype_struct
         identifier ignored_any unit_struct tuple_struct tuple
     }
 }
@@ -231,9 +244,21 @@ impl<'de> de::Deserializer<'de> for Value {
         visitor.visit_newtype_struct(self)
     }
 
+    fn deserialize_enum<V>(
+        self,
+        name: &'static str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_enum(EnumAccess{ value: self, name: name, variants: variants })
+    }
+
     forward_to_deserialize_any! {
         char seq
-        bytes byte_buf map struct unit enum
+        bytes byte_buf map struct unit
         identifier ignored_any unit_struct tuple_struct tuple
     }
 }
@@ -334,6 +359,107 @@ impl<'de> de::MapAccess<'de> for MapAccess {
     }
 }
 
+struct EnumAccess {
+    value: Value,
+    name: &'static str,
+    variants: &'static [&'static str],
+}
+
+impl EnumAccess {
+    fn variant_deserializer(&self, name: &String) -> Result<StrDeserializer> {
+        self.variants
+            .iter()
+            .find(|&s| s.to_lowercase() == name.to_lowercase())
+            .map(|&s| StrDeserializer(s))
+            .ok_or(self.no_constructor_error(name))
+    }
+
+    fn table_deserializer(&self, table: &Table) -> Result<StrDeserializer> {
+        if table.len() == 1 {
+            self.variant_deserializer(table.iter().next().unwrap().0)
+        } else {
+            Err(self.structural_error())
+        }
+    }
+
+    fn no_constructor_error(&self, supposed_variant: &str) -> ConfigError {
+        ConfigError::Message(format!(
+            "enum {} does not have variant constructor {}",
+            self.name, supposed_variant
+        ))
+    }
+
+    fn structural_error(&self) -> ConfigError {
+        ConfigError::Message(format!(
+            "value of enum {} should be represented by either string or table with exactly one key",
+            self.name
+        ))
+    }
+}
+
+impl<'de> de::EnumAccess<'de> for EnumAccess {
+    type Error = ConfigError;
+    type Variant = Self;
+
+    fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant)>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        let value = {
+            let deserializer = match self.value.kind {
+                ValueKind::String(ref s) => self.variant_deserializer(s),
+                ValueKind::Table(ref t) => self.table_deserializer(&t),
+                _ => Err(self.structural_error()),
+            }?;
+            seed.deserialize(deserializer)?
+        };
+
+        Ok((value, self))
+    }
+}
+
+impl<'de> de::VariantAccess<'de> for EnumAccess {
+    type Error = ConfigError;
+
+    fn unit_variant(self) -> Result<()> {
+        Ok(())
+    }
+
+    fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        match self.value.kind {
+            ValueKind::Table(t) => seed.deserialize(t.into_iter().next().unwrap().1),
+            _ => unreachable!(),
+        }
+    }
+
+    fn tuple_variant<V>(self, _len: usize, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value.kind {
+            ValueKind::Table(t) => de::Deserializer::deserialize_seq(t.into_iter().next().unwrap().1, visitor),
+            _ => unreachable!(),
+        }
+    }
+
+    fn struct_variant<V>(
+        self,
+        _fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value.kind {
+            ValueKind::Table(t) => de::Deserializer::deserialize_map(t.into_iter().next().unwrap().1, visitor),
+            _ => unreachable!(),
+        }
+    }
+}
+
 impl<'de> de::Deserializer<'de> for Config {
     type Error = ConfigError;
 
@@ -438,9 +564,21 @@ impl<'de> de::Deserializer<'de> for Config {
         }
     }
 
+    fn deserialize_enum<V>(
+        self,
+        name: &'static str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_enum(EnumAccess{ value: self.cache, name: name, variants: variants })
+    }
+
     forward_to_deserialize_any! {
         char seq
-        bytes byte_buf map struct unit enum newtype_struct
+        bytes byte_buf map struct unit newtype_struct
         identifier ignored_any unit_struct tuple_struct tuple
     }
 }
-- 
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