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//! Reference another [`State`] in the same [`Txn`] context.

use std::collections::HashSet;
use std::fmt;
use std::str::FromStr;

use async_trait::async_trait;
use destream::de;
use destream::en::{EncodeMap, Encoder, IntoStream, ToStream};
use log::debug;
use safecast::TryCastFrom;

use tc_error::*;
use tcgeneric::{Id, Instance};

use crate::route::Public;
use crate::scalar::{Scope, Value, SELF};
use crate::state::State;
use crate::txn::Txn;

use super::Refer;

const EMPTY_SLICE: &[usize] = &[];

/// A reference to the [`State`] at a given [`Id`] within the same transaction context.
#[derive(Clone, Eq, PartialEq, Hash, Ord, PartialOrd)]
pub struct IdRef {
    to: Id,
}

impl IdRef {
    pub fn into_id(self) -> Id {
        self.to
    }

    pub fn id(&'_ self) -> &'_ Id {
        &self.to
    }
}

#[async_trait]
impl Refer for IdRef {
    fn requires(&self, deps: &mut HashSet<Id>) {
        if self.to != SELF {
            deps.insert(self.to.clone());
        }
    }

    async fn resolve<'a, T: Instance + Public>(
        self,
        context: &'a Scope<'a, T>,
        _txn: &'a Txn,
    ) -> TCResult<State> {
        debug!("IdRef::resolve {}", self);
        context.resolve_id(self.id())
    }
}

impl PartialEq<Id> for IdRef {
    fn eq(&self, other: &Id) -> bool {
        self.id() == other
    }
}

impl From<Id> for IdRef {
    fn from(to: Id) -> IdRef {
        IdRef { to }
    }
}

impl FromStr for IdRef {
    type Err = TCError;

    #[inline]
    fn from_str(to: &str) -> TCResult<IdRef> {
        if !to.starts_with('$') || to.len() < 2 {
            Err(TCError::bad_request("Invalid Ref", to))
        } else {
            Ok(IdRef {
                to: to[1..].parse()?,
            })
        }
    }
}

impl TryCastFrom<Value> for IdRef {
    fn can_cast_from(value: &Value) -> bool {
        match value {
            Value::String(s) => Self::from_str(s).is_ok(),
            _ => false,
        }
    }

    fn opt_cast_from(value: Value) -> Option<Self> {
        match value {
            Value::String(s) => Self::from_str(&s).ok(),
            _ => None,
        }
    }
}

impl From<IdRef> for Id {
    fn from(r: IdRef) -> Id {
        r.to
    }
}

impl fmt::Display for IdRef {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "${}", self.to)
    }
}

#[async_trait]
impl de::FromStream for IdRef {
    type Context = ();

    async fn from_stream<D: de::Decoder>(context: (), d: &mut D) -> Result<Self, D::Error> {
        let id_ref = String::from_stream(context, d).await?;
        id_ref.parse().map_err(de::Error::custom)
    }
}

impl<'en> ToStream<'en> for IdRef {
    fn to_stream<E: Encoder<'en>>(&'en self, e: E) -> Result<E::Ok, E::Error> {
        let mut map = e.encode_map(Some(1))?;
        map.encode_entry(self.to_string(), EMPTY_SLICE)?;
        map.end()
    }
}

impl<'en> IntoStream<'en> for IdRef {
    fn into_stream<E: Encoder<'en>>(self, e: E) -> Result<E::Ok, E::Error> {
        let mut map = e.encode_map(Some(1))?;
        map.encode_entry(self.to_string(), EMPTY_SLICE)?;
        map.end()
    }
}