//! envy is a library for deserializing env vars into typesafe structs
//!
//! # Examples
//!
//! A typical use case for envy is deserializing configuration stored into an env into a struct
//! whose fields map to the names of env vars.
//!
//! Serde makes it easy to provide a deserializable struct with the
//! [serde_derive](https://crates.io/crates/serde_derive) crate. Simply ask for an instance of that
//! struct from envy's `from_env` function.
//!
//! ```no_run,ignore
//! #[macro_use]
//! extern crate serde_derive;
//!
//! extern crate envy;
//!
//! #[derive(Deserialize, Debug)]
//! struct Config {
//!   foo: u16,
//!   bar: bool,
//!   baz: String,
//!   boom: Option<u64>
//! }
//!
//! fn main() {
//!    match envy::from_env::<Config>() {
//!       Ok(config) => println!("{:#?}", config)
//!       Err(error) => panic!("{:#?}", error)
//!    }
//! }
//! ```
//!
//! Special treatment is given to collections. For config fields that store a `Vec` of values,
//! use and env var that uses a comma separated value
//!
//! All serde modifier should work as is
//!
//! If you wish to use enum types use the following
//!
//! ```no_run,ignore
//! #[macro_use]
//! extern crate serde_derive;
//!
//! extern crate envy;
//!
//! #[derive(Deserialize, Debug, PartialEq)]
//! #[serde(untagged)]
//! #[serde(field_identifier, rename_all = "lowercase")]
//! pub enum Size {
//!    Small,
//!    Medium,
//!    Large
//! }
//!
//! #[derive(Deserialize, Debug)]
//! struct Config {
//!  size: Size,
//! }
//!
//! fn main() {
//!    // set env var for size as `SIZE=medium`
//!    match envy::from_env::<Config>() {
//!       Ok(config) => println!("{:#?}", config)
//!       Err(error) => panic!("{:#?}", error)
//!    }
//! }
//! ```
#[macro_use]
extern crate serde;

use serde::de::value::{SeqDeserializer, MapDeserializer};
use serde::de::{self, IntoDeserializer};
use std::env;

mod errors;
pub use errors::Error;

/// A type result type specific to `envy::Errors`
pub type Result<T> = std::result::Result<T, Error>;

struct Vars<Iter>(Iter) where Iter: Iterator<Item = (String, String)>;

struct Val(String);

impl<'de> IntoDeserializer<'de, Error> for Val {
    type Deserializer = Self;

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

impl<Iter: Iterator<Item = (String, String)>> Iterator for Vars<Iter> {
    type Item = (Val, Val);

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

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

impl<'de, 'a> de::Deserializer<'de> for Val {
    type Error = Error;
    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value>
        where V: de::Visitor<'de>
    {
        self.0.into_deserializer().deserialize_any(visitor)
    }

    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value>
        where V: de::Visitor<'de>
    {
        let values = self.0.split(",").map(|v| Val(v.to_owned()));
        SeqDeserializer::new(values).deserialize_seq(visitor)
    }

    forward_parsed_values! {
        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,
    }

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

/// A deserializer for env vars
struct Deserializer<'de, Iter: Iterator<Item = (String, String)>> {
    inner: MapDeserializer<'de, Vars<Iter>, Error>,
}

impl<'de, Iter: Iterator<Item = (String, String)>> Deserializer<'de, Iter> {
    fn new(vars: Iter) -> Self {
        Deserializer { inner: MapDeserializer::new(Vars(vars)) }
    }
}

impl<'de, Iter: Iterator<Item = (String, String)>> de::Deserializer<'de>
    for Deserializer<'de, Iter> {
    type Error = Error;
    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value>
        where V: de::Visitor<'de>
    {
        self.deserialize_map(visitor)
    }

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

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

/// Deserializes a type based on information based on env variables
pub fn from_env<T>() -> Result<T>
    where T: de::DeserializeOwned
{
    from_iter(env::vars())
}

/// Deserializes a type based on an iterable of `(String, String)`
/// representing keys and values
pub fn from_iter<Iter, T>(iter: Iter) -> Result<T>
    where T: de::DeserializeOwned,
          Iter: Iterator<Item = (String, String)>
{
    T::deserialize(Deserializer::new(iter.map(|(k, v)| (k.to_lowercase(), v))))
}