//! Deserialization support for the `application/x-www-form-urlencoded` format.

use serde::de::Error as de_Error;
use serde::de::{
    self, DeserializeSeed, EnumAccess, IntoDeserializer, VariantAccess, Visitor,
};

use serde::de::value::MapDeserializer;
use std::borrow::Cow;
use std::io::Read;
use url::form_urlencoded::parse;
use url::form_urlencoded::Parse as UrlEncodedParse;

#[doc(inline)]
pub use serde::de::value::Error;

/// Deserializes a `application/x-wwww-url-encoded` value from a `&[u8]`.
///
/// ```ignore
/// let meal = vec![
///     ("bread".to_owned(), "baguette".to_owned()),
///     ("cheese".to_owned(), "comté".to_owned()),
///     ("meat".to_owned(), "ham".to_owned()),
///     ("fat".to_owned(), "butter".to_owned()),
/// ];
///
/// assert_eq!(
///     serde_urlencoded::from_bytes::<Vec<(String, String)>>(
///         b"bread=baguette&cheese=comt%C3%A9&meat=ham&fat=butter"),
///     Ok(meal));
/// ```
pub fn from_bytes<'de, T>(input: &'de [u8]) -> Result<T, Error>
where
    T: de::Deserialize<'de>,
{
    T::deserialize(Deserializer::new(parse(input)))
}

/// Deserializes a `application/x-wwww-url-encoded` value from a `&str`.
///
/// ```ignore
/// let meal = vec![
///     ("bread".to_owned(), "baguette".to_owned()),
///     ("cheese".to_owned(), "comté".to_owned()),
///     ("meat".to_owned(), "ham".to_owned()),
///     ("fat".to_owned(), "butter".to_owned()),
/// ];
///
/// assert_eq!(
///     serde_urlencoded::from_str::<Vec<(String, String)>>(
///         "bread=baguette&cheese=comt%C3%A9&meat=ham&fat=butter"),
///     Ok(meal));
/// ```
pub fn from_str<'de, T>(input: &'de str) -> Result<T, Error>
where
    T: de::Deserialize<'de>,
{
    from_bytes(input.as_bytes())
}

#[allow(dead_code)]
/// Convenience function that reads all bytes from `reader` and deserializes
/// them with `from_bytes`.
pub fn from_reader<T, R>(mut reader: R) -> Result<T, Error>
where
    T: de::DeserializeOwned,
    R: Read,
{
    let mut buf = vec![];
    reader
        .read_to_end(&mut buf)
        .map_err(|e| de::Error::custom(format_args!("could not read input: {}", e)))?;
    from_bytes(&buf)
}

/// A deserializer for the `application/x-www-form-urlencoded` format.
///
/// * Supported top-level outputs are structs, maps and sequences of pairs,
///   with or without a given length.
///
/// * Main `deserialize` methods defers to `deserialize_map`.
///
/// * Everything else but `deserialize_seq` and `deserialize_seq_fixed_size`
///   defers to `deserialize`.
pub struct Deserializer<'de> {
    inner: MapDeserializer<'de, PartIterator<'de>, Error>,
}

impl<'de> Deserializer<'de> {
    /// Returns a new `Deserializer`.
    pub fn new(parser: UrlEncodedParse<'de>) -> Self {
        Deserializer {
            inner: MapDeserializer::new(PartIterator(parser)),
        }
    }
}

impl<'de> de::Deserializer<'de> for Deserializer<'de> {
    type Error = Error;

    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
    where
        V: de::Visitor<'de>,
    {
        self.deserialize_map(visitor)
    }

    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value, Self::Error>
    where
        V: de::Visitor<'de>,
    {
        visitor.visit_map(self.inner)
    }

    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, Self::Error>
    where
        V: de::Visitor<'de>,
    {
        visitor.visit_seq(self.inner)
    }

    fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value, Self::Error>
    where
        V: de::Visitor<'de>,
    {
        self.inner.end()?;
        visitor.visit_unit()
    }

    forward_to_deserialize_any! {
        bool
        u8
        u16
        u32
        u64
        i8
        i16
        i32
        i64
        f32
        f64
        char
        str
        string
        option
        bytes
        byte_buf
        unit_struct
        newtype_struct
        tuple_struct
        struct
        identifier
        tuple
        enum
        ignored_any
    }
}

struct PartIterator<'de>(UrlEncodedParse<'de>);

impl<'de> Iterator for PartIterator<'de> {
    type Item = (Part<'de>, Part<'de>);

    fn next(&mut self) -> Option<Self::Item> {
        self.0.next().map(|(k, v)| (Part(k), Part(v)))
    }
}

struct Part<'de>(Cow<'de, str>);

impl<'de> IntoDeserializer<'de> for Part<'de> {
    type Deserializer = Self;

    fn into_deserializer(self) -> Self::Deserializer {
        self
    }
}

macro_rules! forward_parsed_value {
    ($($ty:ident => $method:ident,)*) => {
        $(
            fn $method<V>(self, visitor: V) -> Result<V::Value, Self::Error>
                where V: de::Visitor<'de>
            {
                match self.0.parse::<$ty>() {
                    Ok(val) => val.into_deserializer().$method(visitor),
                    Err(e) => Err(de::Error::custom(e))
                }
            }
        )*
    }
}

impl<'de> de::Deserializer<'de> for Part<'de> {
    type Error = Error;

    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Self::Error>
    where
        V: de::Visitor<'de>,
    {
        self.0.into_deserializer().deserialize_any(visitor)
    }

    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Self::Error>
    where
        V: de::Visitor<'de>,
    {
        visitor.visit_some(self)
    }

    fn deserialize_enum<V>(
        self, _name: &'static str, _variants: &'static [&'static str], visitor: V,
    ) -> Result<V::Value, Self::Error>
    where
        V: de::Visitor<'de>,
    {
        visitor.visit_enum(ValueEnumAccess { value: self.0 })
    }

    forward_to_deserialize_any! {
        char
        str
        string
        unit
        bytes
        byte_buf
        unit_struct
        newtype_struct
        tuple_struct
        struct
        identifier
        tuple
        ignored_any
        seq
        map
    }

    forward_parsed_value! {
        bool => deserialize_bool,
        u8 => deserialize_u8,
        u16 => deserialize_u16,
        u32 => deserialize_u32,
        u64 => deserialize_u64,
        i8 => deserialize_i8,
        i16 => deserialize_i16,
        i32 => deserialize_i32,
        i64 => deserialize_i64,
        f32 => deserialize_f32,
        f64 => deserialize_f64,
    }
}

/// Provides access to a keyword which can be deserialized into an enum variant. The enum variant
/// must be a unit variant, otherwise deserialization will fail.
struct ValueEnumAccess<'de> {
    value: Cow<'de, str>,
}

impl<'de> EnumAccess<'de> for ValueEnumAccess<'de> {
    type Error = Error;
    type Variant = UnitOnlyVariantAccess;

    fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant), Self::Error>
    where
        V: DeserializeSeed<'de>,
    {
        let variant = seed.deserialize(self.value.into_deserializer())?;
        Ok((variant, UnitOnlyVariantAccess))
    }
}

/// A visitor for deserializing the contents of the enum variant. As we only support
/// `unit_variant`, all other variant types will return an error.
struct UnitOnlyVariantAccess;

impl<'de> VariantAccess<'de> for UnitOnlyVariantAccess {
    type Error = Error;

    fn unit_variant(self) -> Result<(), Self::Error> {
        Ok(())
    }

    fn newtype_variant_seed<T>(self, _seed: T) -> Result<T::Value, Self::Error>
    where
        T: DeserializeSeed<'de>,
    {
        Err(Error::custom("expected unit variant"))
    }

    fn tuple_variant<V>(self, _len: usize, _visitor: V) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        Err(Error::custom("expected unit variant"))
    }

    fn struct_variant<V>(
        self, _fields: &'static [&'static str], _visitor: V,
    ) -> Result<V::Value, Self::Error>
    where
        V: Visitor<'de>,
    {
        Err(Error::custom("expected unit variant"))
    }
}