use super::deserializer::Deserializer;
use super::read::Fused;
use super::read::Read;
use crate::error::{Error, ErrorCode, Result};
use core::iter::FusedIterator;
use core::marker::PhantomData;
use serde::de;

/// Iterator that deserializes a stream into multiple EnCom values.
///
/// A stream deserializer can be created from any EnCom deserializer using the
/// `Deserializer::into_iter` method.
///
/// The data can consist of any EnCom value. Values need to be a self-delineating value e.g.
/// arrays, objects, or strings, or be followed by whitespace or a self-delineating value.
///
/// ```
/// use serde_encom::{Deserializer, Value};
///
/// fn main() {
///     let data = "{\"k\": 3}1\"cool\"\"stuff\" 3{}  [0, 1, 2]";
///
///     let stream = Deserializer::from_str(data).into_iter::<Value>();
///
///     for value in stream {
///         println!("{}", value.unwrap());
///     }
/// }
/// ```
pub struct StreamDeserializer<'de, R, T> {
    pub(crate) de: Deserializer<R>,
    pub(crate) offset: usize,
    pub(crate) failed: bool,
    pub(crate) output: PhantomData<T>,
    pub(crate) lifetime: PhantomData<&'de ()>,
}

impl<'de, R, T> StreamDeserializer<'de, R, T>
where
    R: Read<'de>,
    T: de::Deserialize<'de>,
{
    /// Create an EnCom stream deserializer from one of the possible serde_encom
    /// input sources.
    ///
    /// Typically it is more convenient to use one of these methods instead:
    ///
    ///   - Deserializer::from_str(...).into_iter()
    ///   - Deserializer::from_slice(...).into_iter()
    ///   - Deserializer::from_reader(...).into_iter()
    pub fn new(read: R) -> Self {
        let offset = read.byte_offset();
        StreamDeserializer {
            de: Deserializer::new(read),
            offset,
            failed: false,
            output: PhantomData,
            lifetime: PhantomData,
        }
    }

    /// Returns the number of bytes so far deserialized into a successful `T`.
    ///
    /// If a stream deserializer returns an EOF error, new data can be joined to
    /// `old_data[stream.byte_offset()..]` to try again.
    ///
    /// ```
    /// let data = b"0 1 ";
    ///
    /// let de = serde_encom::Deserializer::from_slice(data);
    /// let mut stream = de.into_iter::<Vec<i32>>();
    /// assert_eq!(0, stream.byte_offset());
    ///
    /// println!("{:?}", stream.next()); // [0]
    /// assert_eq!(3, stream.byte_offset());
    ///
    /// println!("{:?}", stream.next()); // [1]
    /// assert_eq!(7, stream.byte_offset());
    ///
    /// println!("{:?}", stream.next()); // error
    /// assert_eq!(8, stream.byte_offset());
    ///
    /// // If err.is_eof(), can join the remaining data to new data and continue.
    /// let remaining = &data[stream.byte_offset()..];
    /// ```
    ///
    /// *Note:* In the future this method may be changed to return the number of
    /// bytes so far deserialized into a successful T *or* syntactically valid
    /// EnCom skipped over due to a type error. See [serde-rs/json#70] for an
    /// example illustrating this.
    ///
    /// [serde-rs/json#70]: https://github.com/serde-rs/json/issues/70
    pub fn byte_offset(&self) -> usize {
        self.offset
    }

    fn peek_end_of_value(&mut self) -> Result<()> {
        match self.de.peek()? {
            Some(b' ' | b'\n' | b'\t' | b'\r' | b'{' | b'}' | b':') | None => Ok(()),
            Some(_) => {
                let position = self.de.read.peek_position();
                Err(Error::syntax(
                    ErrorCode::TrailingCharacters,
                    position.line,
                    position.column,
                ))
            }
        }
    }
}

impl<'de, R, T> Iterator for StreamDeserializer<'de, R, T>
where
    R: Read<'de>,
    T: de::Deserialize<'de>,
{
    type Item = Result<T>;

    fn next(&mut self) -> Option<Result<T>> {
        if R::SHOULD_EARLY_RETURN_IF_FAILED && self.failed {
            return None;
        }

        // skip whitespaces, if any
        // this helps with trailing whitespaces, since whitespaces between
        // values are handled for us.
        match self.de.parse_whitespace() {
            Ok(None) => {
                self.offset = self.de.read.byte_offset();
                None
            }
            Ok(Some(b)) => {
                // If the value does not have a clear way to show the end of the value
                // (like numbers, null, true etc.) we have to look for whitespace or
                // the beginning of a self-delineated value.
                let self_delineated_value = match b {
                    b'{' => true,
                    _ => false,
                };
                self.offset = self.de.read.byte_offset();
                let result = de::Deserialize::deserialize(&mut self.de);

                Some(match result {
                    Ok(value) => {
                        self.offset = self.de.read.byte_offset();
                        if self_delineated_value {
                            Ok(value)
                        } else {
                            self.peek_end_of_value().map(|()| value)
                        }
                    }
                    Err(e) => {
                        self.de.read.set_failed(&mut self.failed);
                        Err(e)
                    }
                })
            }
            Err(e) => {
                self.de.read.set_failed(&mut self.failed);
                Some(Err(e))
            }
        }
    }
}

impl<'de, R, T> FusedIterator for StreamDeserializer<'de, R, T>
where
    R: Read<'de> + Fused,
    T: de::Deserialize<'de>,
{
}