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use std::time::SystemTime;

use futures::sync::mpsc;
use futures::{Future, Sink};

use crate::Tag;

#[derive(Debug)]
pub enum SpanReference<S> {
    ChildOf(S),
    FollowsFrom(S),
}

#[derive(Debug)]
pub struct Span<S>
where
    S: 'static + Sync + Send,
{
    inner: Option<Inner<S>>,
}

impl<S> Span<S>
where
    S: 'static + Send + Sync,
{
    pub fn new<O>(
        sender: mpsc::UnboundedSender<Span<S>>,
        operation_name: O,
        start_time: SystemTime,
        tags: Vec<Tag>,
        references: Vec<SpanReference<S>>,
        state: S,
        baggage_items: Vec<BaggageItem>,
    ) -> Self
    where
        O: Into<String>,
    {
        let context = SpanContext::new(state, baggage_items);
        let operation_name = operation_name.into();
        let finish_time = None;
        let inner = Some(Inner {
            sender,
            operation_name,
            start_time,
            finish_time,
            tags,
            references,
            context,
        });

        Self { inner }
    }

    pub fn context(&self) -> &SpanContext<S> {
        &self.inner.as_ref().unwrap().context
    }

    pub fn set_operation_name<O>(&mut self, op_name: O)
    where
        O: Into<String>,
    {
        if let Some(inner) = self.inner.as_mut() {
            inner.operation_name = op_name.into();
        }
    }

    pub fn operation_name(&self) -> &str {
        self.inner.as_ref().unwrap().operation_name.as_ref()
    }

    pub fn set_tag(&mut self, tag: Tag) {
        if let Some(inner) = self.inner.as_mut() {
            inner.tags.push(tag);
        }
    }

    pub fn is_finished(&self) -> bool {
        self.inner.as_ref().unwrap().finish_time.is_some()
    }

    pub fn finish(&mut self) {
        if self.inner.is_none() || self.is_finished() {
            return;
        }
        let inner = self.inner.as_mut().unwrap();
        inner.finish_time = Some(SystemTime::now());
        let sender = inner.sender.clone();
        tokio::spawn(
            sender
                .send(Span {
                    inner: self.inner.take(),
                })
                .map(|_| ())
                .map_err(|_| ()),
        );
    }
}

impl<S> Drop for Span<S>
where
    S: 'static + Send + Sync,
{
    fn drop(&mut self) {
        self.finish()
    }
}

#[derive(Debug)]
struct Inner<S>
where
    S: 'static + Send + Sync,
{
    sender: mpsc::UnboundedSender<Span<S>>,
    operation_name: String,
    start_time: SystemTime,
    finish_time: Option<SystemTime>,
    tags: Vec<Tag>,
    references: Vec<SpanReference<S>>,
    context: SpanContext<S>,
}

#[derive(Debug)]
pub struct SpanContext<S> {
    state: S,
    baggage_items: Vec<BaggageItem>,
}

impl<S> SpanContext<S> {
    pub fn new(state: S, baggage_items: Vec<BaggageItem>) -> Self {
        Self {
            state,
            baggage_items,
        }
    }

    pub fn state(&self) -> &S {
        &self.state
    }

    pub fn baggage_items(&self) -> &Vec<BaggageItem> {
        &self.baggage_items
    }
}

#[derive(Clone, Debug)]
pub struct BaggageItem {
    key: String,
    value: String,
}

impl BaggageItem {
    pub fn new(key: &str, value: &str) -> Self {
        Self {
            key: key.to_owned(),
            value: value.to_owned(),
        }
    }
}

pub trait SpanBuilder<S>
where
    S: Send + Sync,
{
    fn start(self) -> Span<S>;
    fn child_of(self, parent: &Span<S>) -> Self;
    fn start_time(self, time: SystemTime) -> Self;
    fn tag(self, tag: Tag) -> Self;
}