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

mod key;
mod part;
mod value;

use serde::ser;
use std::borrow::Cow;
use std::error;
use std::fmt;
use std::str;
use url::form_urlencoded::Serializer as UrlEncodedSerializer;
use url::form_urlencoded::Target as UrlEncodedTarget;

/// Serializes a value into a querystring.
///
/// ```
/// # #[macro_use]
/// # extern crate serde_derive;
/// # extern crate serde_qs;
/// #[derive(Deserialize, Serialize)]
/// struct Query {
///     name: String,
///     age: u8,
///     occupation: String,   
/// }
///
/// # fn main(){
/// let q =  Query {
///     name: "Alice".to_owned(),
///     age: 24,
///     occupation: "Student".to_owned(),   
/// };
///
///
/// assert_eq!(
///     serde_qs::to_string(&q),
///     Ok("name=Alice&age=24&occupation=Student".to_owned()));
/// # }
/// ```
pub fn to_string<T: ser::Serialize>(input: &T) -> Result<String, Error> {
    let mut urlencoder = UrlEncodedSerializer::new("".to_owned());
    input.serialize(Serializer::new(&mut urlencoder))?;
    Ok(urlencoder.finish())
}

/// A serializer for the querystring format.
///
/// * Supported top-level inputs are structs, maps and sequences of pairs,
///   with or without a given length.
///
/// * Supported keys and values are integers, bytes (if convertible to strings),
///   unit structs and unit variants.
///
/// * Newtype structs defer to their inner values.
pub struct Serializer<'output, Target: 'output + UrlEncodedTarget> {
    urlencoder: &'output mut UrlEncodedSerializer<Target>,
}

impl<'output, Target: 'output + UrlEncodedTarget> Serializer<'output, Target> {
    /// Returns a new `Serializer`.
    pub fn new(urlencoder: &'output mut UrlEncodedSerializer<Target>) -> Self {
        Serializer { urlencoder: urlencoder }
    }
}

/// Errors returned during serializing to querystring.
#[derive(Clone, Debug, PartialEq, Eq)]
pub enum Error {
    Custom(Cow<'static, str>),
    Utf8(str::Utf8Error),
}

impl fmt::Display for Error {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match *self {
            Error::Custom(ref msg) => msg.fmt(f),
            Error::Utf8(ref err) => write!(f, "invalid UTF-8: {}", err),
        }
    }
}

impl error::Error for Error {
    fn description(&self) -> &str {
        match *self {
            Error::Custom(ref msg) => msg,
            Error::Utf8(ref err) => error::Error::description(err),
        }
    }

    /// The lower-level cause of this error, in the case of a `Utf8` error.
    fn cause(&self) -> Option<&error::Error> {
        match *self {
            Error::Custom(_) => None,
            Error::Utf8(ref err) => Some(err),
        }
    }
}

impl ser::Error for Error {
    fn custom<T: fmt::Display>(msg: T) -> Self {
        Error::Custom(format!("{}", msg).into())
    }
}

/// Sequence serializer.
pub struct SeqSerializer<'output, T: 'output + UrlEncodedTarget> {
    inner: ser::Impossible<&'output mut UrlEncodedSerializer<T>, Error>,
}

/// Tuple serializer.
///
/// Never instantiated, tuples are not supported at top-level.
pub struct TupleSerializer<'output, T: 'output + UrlEncodedTarget> {
    inner: ser::Impossible<&'output mut UrlEncodedSerializer<T>, Error>,
}

/// Tuple struct serializer.
///
/// Never instantiated, tuple structs are not supported.
pub struct TupleStructSerializer<'output, T: 'output + UrlEncodedTarget> {
    inner: ser::Impossible<&'output mut UrlEncodedSerializer<T>, Error>,
}

/// Tuple variant serializer.
///
/// Never instantiated, tuple variants are not supported.
pub struct TupleVariantSerializer<'output, T: 'output + UrlEncodedTarget> {
    inner: ser::Impossible<&'output mut UrlEncodedSerializer<T>, Error>,
}

/// Map serializer.
pub struct MapSerializer<'output, Target: 'output + UrlEncodedTarget> {
    urlencoder: &'output mut UrlEncodedSerializer<Target>,
    key: Option<Cow<'static, str>>,
}

/// Struct serializer.
pub struct StructSerializer<'output, Target: 'output + UrlEncodedTarget> {
    urlencoder: &'output mut UrlEncodedSerializer<Target>,
}

/// Struct variant serializer.
///
/// Never instantiated, struct variants are not supported.
pub struct StructVariantSerializer<'output, T: 'output + UrlEncodedTarget> {
    inner: ser::Impossible<&'output mut UrlEncodedSerializer<T>, Error>,
}

impl<'output, Target> ser::Serializer for Serializer<'output, Target>
    where Target: 'output + UrlEncodedTarget,
{
    type Ok = &'output mut UrlEncodedSerializer<Target>;
    type Error = Error;
    type SerializeSeq = SeqSerializer<'output, Target>;
    type SerializeTuple = TupleSerializer<'output, Target>;
    type SerializeTupleStruct = TupleStructSerializer<'output, Target>;
    type SerializeTupleVariant = TupleVariantSerializer<'output, Target>;
    type SerializeMap = MapSerializer<'output, Target>;
    type SerializeStruct = StructSerializer<'output, Target>;
    type SerializeStructVariant = StructVariantSerializer<'output, Target>;

    /// Returns an error.
    fn serialize_bool(self, _v: bool) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_i8(self, _v: i8) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_i16(self, _v: i16) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_i32(self, _v: i32) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_i64(self, _v: i64) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_u8(self, _v: u8) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_u16(self, _v: u16) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_u32(self, _v: u32) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_u64(self, _v: u64) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_f32(self, _v: f32) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_f64(self, _v: f64) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_char(self, _v: char) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_str(self, _value: &str) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_bytes(self, _value: &[u8]) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_unit(self) -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_unit_struct(self,
                             _name: &'static str)
                             -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_unit_variant(self,
                              _name: &'static str,
                              _variant_index: usize,
                              _variant: &'static str)
                              -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Serializes the inner value, ignoring the newtype name.
    fn serialize_newtype_struct<T: ?Sized + ser::Serialize>
        (self,
         _name: &'static str,
         value: &T)
         -> Result<Self::Ok, Error> {
        value.serialize(self)
    }

    /// Returns an error.
    fn serialize_newtype_variant<T: ?Sized + ser::Serialize>
        (self,
         _name: &'static str,
         _variant_index: usize,
         _variant: &'static str,
         _value: &T)
         -> Result<Self::Ok, Error> {
        Err(Error::top_level())
    }

    /// Returns `Ok`.
    fn serialize_none(self) -> Result<Self::Ok, Error> {
        Ok(self.urlencoder)
    }

    /// Serializes the given value.
    fn serialize_some<T: ?Sized + ser::Serialize>
        (self,
         value: &T)
         -> Result<Self::Ok, Error> {
        value.serialize(self)
    }

    /// Serialize a sequence, given length (if any) is ignored.
    fn serialize_seq(self,
                     _len: Option<usize>)
                     -> Result<Self::SerializeSeq, Error> {
        Err(Error::top_level())
    }

    /// Serializes a sequence, given length is ignored.
    fn serialize_seq_fixed_size(self,
                                _len: usize)
                                -> Result<Self::SerializeSeq, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_tuple(self,
                       _len: usize)
                       -> Result<Self::SerializeTuple, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_tuple_struct(self,
                              _name: &'static str,
                              _len: usize)
                              -> Result<Self::SerializeTupleStruct, Error> {
        Err(Error::top_level())
    }

    /// Returns an error.
    fn serialize_tuple_variant
        (self,
         _name: &'static str,
         _variant_index: usize,
         _variant: &'static str,
         _len: usize)
         -> Result<Self::SerializeTupleVariant, Error> {
        Err(Error::top_level())
    }

    /// Serializes a map, given length is ignored.
    fn serialize_map(self,
                     _len: Option<usize>)
                     -> Result<Self::SerializeMap, Error> {
        Ok(MapSerializer {
            urlencoder: self.urlencoder,
            key: None,
        })
    }

    /// Serializes a struct, given length is ignored.
    fn serialize_struct(self,
                        _name: &'static str,
                        _len: usize)
                        -> Result<Self::SerializeStruct, Error> {
        Ok(StructSerializer { urlencoder: self.urlencoder })
    }

    /// Returns an error.
    fn serialize_struct_variant
        (self,
         _name: &'static str,
         _variant_index: usize,
         _variant: &'static str,
         _len: usize)
         -> Result<Self::SerializeStructVariant, Error> {
        Err(Error::top_level())
    }
}

impl<'output, Target> ser::SerializeSeq for SeqSerializer<'output, Target>
    where Target: 'output + UrlEncodedTarget,
{
    type Ok = &'output mut UrlEncodedSerializer<Target>;
    type Error = Error;

    fn serialize_element<T: ?Sized + ser::Serialize>(&mut self,
                                                     value: &T)
                                                     -> Result<(), Error> {
        self.inner.serialize_element(value)
    }

    fn end(self) -> Result<Self::Ok, Error> {
        self.inner.end()
    }
}


impl<'output, Target> ser::SerializeTuple for TupleSerializer<'output, Target>
    where Target: 'output + UrlEncodedTarget,
{
    type Ok = &'output mut UrlEncodedSerializer<Target>;
    type Error = Error;

    fn serialize_element<T: ?Sized + ser::Serialize>(&mut self,
                                                     value: &T)
                                                     -> Result<(), Error> {
        self.inner.serialize_element(value)
    }

    fn end(self) -> Result<Self::Ok, Error> {
        self.inner.end()
    }
}

impl<'output, Target> ser::SerializeTupleStruct
    for TupleStructSerializer<'output, Target>
    where Target: 'output + UrlEncodedTarget,
{
    type Ok = &'output mut UrlEncodedSerializer<Target>;
    type Error = Error;

    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
                                                   value: &T)
                                                   -> Result<(), Error> {
        self.inner.serialize_field(value)
    }

    fn end(self) -> Result<Self::Ok, Error> {
        self.inner.end()
    }
}

impl<'output, Target> ser::SerializeTupleVariant
    for TupleVariantSerializer<'output, Target>
    where Target: 'output + UrlEncodedTarget,
{
    type Ok = &'output mut UrlEncodedSerializer<Target>;
    type Error = Error;

    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
                                                   value: &T)
                                                   -> Result<(), Error> {
        self.inner.serialize_field(value)
    }

    fn end(self) -> Result<Self::Ok, Error> {
        self.inner.end()
    }
}

impl<'output, Target> ser::SerializeMap for MapSerializer<'output, Target>
    where Target: 'output + UrlEncodedTarget,
{
    type Ok = &'output mut UrlEncodedSerializer<Target>;
    type Error = Error;

    fn serialize_entry<K: ?Sized + ser::Serialize, V: ?Sized + ser::Serialize>
        (&mut self,
         key: &K,
         value: &V)
         -> Result<(), Error> {
        let key_sink = key::KeySink::new(|key| {
            let value_sink = value::ValueSink::new(self.urlencoder, &key);
            value.serialize(part::PartSerializer::new(value_sink))?;
            self.key = None;
            Ok(())
        });
        let entry_serializer = part::PartSerializer::new(key_sink);
        key.serialize(entry_serializer)
    }

    fn serialize_key<T: ?Sized + ser::Serialize>(&mut self,
                                                 key: &T)
                                                 -> Result<(), Error> {
        let key_sink = key::KeySink::new(|key| Ok(key.into()));
        let key_serializer = part::PartSerializer::new(key_sink);
        self.key = Some(key.serialize(key_serializer)?);
        Ok(())
    }

    fn serialize_value<T: ?Sized + ser::Serialize>(&mut self,
                                                   value: &T)
                                                   -> Result<(), Error> {
        {
            let key = self.key.as_ref().ok_or_else(|| Error::no_key())?;
            let value_sink = value::ValueSink::new(self.urlencoder, &key);
            value.serialize(part::PartSerializer::new(value_sink))?;
        }
        self.key = None;
        Ok(())
    }

    fn end(self) -> Result<Self::Ok, Error> {
        Ok(self.urlencoder)
    }
}

impl<'output, Target> ser::SerializeStruct for StructSerializer<'output, Target>
    where Target: 'output + UrlEncodedTarget,
{
    type Ok = &'output mut UrlEncodedSerializer<Target>;
    type Error = Error;

    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
                                                   key: &'static str,
                                                   value: &T)
                                                   -> Result<(), Error> {
        let value_sink = value::ValueSink::new(self.urlencoder, key);
        value.serialize(part::PartSerializer::new(value_sink))
    }

    fn end(self) -> Result<Self::Ok, Error> {
        Ok(self.urlencoder)
    }
}

impl<'output, Target> ser::SerializeStructVariant
    for StructVariantSerializer<'output, Target>
    where Target: 'output + UrlEncodedTarget,
{
    type Ok = &'output mut UrlEncodedSerializer<Target>;
    type Error = Error;

    fn serialize_field<T: ?Sized + ser::Serialize>(&mut self,
                                                   key: &'static str,
                                                   value: &T)
                                                   -> Result<(), Error> {
        self.inner.serialize_field(key, value)
    }

    fn end(self) -> Result<Self::Ok, Error> {
        self.inner.end()
    }
}

impl Error {
    fn top_level() -> Self {
        let msg = "top-level serializer supports only maps and structs";
        Error::Custom(msg.into())
    }

    fn no_key() -> Self {
        let msg = "tried to serialize a value before serializing key";
        Error::Custom(msg.into())
    }
}