use std::cell::{Ref, RefCell};
use std::rc::Rc;

use serde::Serialize;
use serde::de::DeserializeOwned;
use serde_json::{Map, Value};
use uuid::Uuid;

use crate::error::AppError;

const SESSION_USER_KEY: &str = "session:user_uid";

#[derive(Clone)]
pub struct Session(Rc<RefCell<SessionInner>>);

#[derive(Debug, Clone, Default, PartialEq, Eq)]
pub enum SessionStatus {
    Changed,
    Purged,
    Renewed,
    #[default]
    Unchanged,
}

#[derive(Default)]
struct SessionInner {
    state: Map<String, Value>,
    status: SessionStatus,
}

impl Session {
    pub fn new() -> Self {
        Self::default()
    }

    pub fn from_state(state: Map<String, Value>) -> Self {
        Self(Rc::new(RefCell::new(SessionInner {
            state,
            status: SessionStatus::Unchanged,
        })))
    }

    pub fn get<T: DeserializeOwned>(&self, key: &str) -> Result<Option<T>, AppError> {
        if let Some(value) = self.0.borrow().state.get(key) {
            Ok(Some(serde_json::from_value(value.clone())?))
        } else {
            Ok(None)
        }
    }

    pub fn contains_key(&self, key: &str) -> bool {
        self.0.borrow().state.contains_key(key)
    }

    pub fn entries(&self) -> Ref<'_, Map<String, Value>> {
        Ref::map(self.0.borrow(), |inner| &inner.state)
    }

    pub fn status(&self) -> SessionStatus {
        Ref::map(self.0.borrow(), |inner| &inner.status).clone()
    }

    pub fn insert<T: Serialize>(&self, key: impl Into<String>, value: T) -> Result<(), AppError> {
        let mut inner = self.0.borrow_mut();

        if inner.status != SessionStatus::Purged {
            if inner.status != SessionStatus::Renewed {
                inner.status = SessionStatus::Changed;
            }
            let val = serde_json::to_value(&value)?;
            inner.state.insert(key.into(), val);
        }

        Ok(())
    }

    pub fn update<T: Serialize + DeserializeOwned, F>(
        &self,
        key: impl Into<String>,
        updater: F,
    ) -> Result<(), AppError>
    where
        F: FnOnce(T) -> T,
    {
        let mut inner = self.0.borrow_mut();
        let key_str = key.into();

        if let Some(val) = inner.state.get(&key_str) {
            if inner.status == SessionStatus::Purged {
                return Ok(());
            }

            let value: T = serde_json::from_value(val.clone())?;
            let updated = serde_json::to_value(updater(value))?;

            if inner.status != SessionStatus::Renewed {
                inner.status = SessionStatus::Changed;
            }
            inner.state.insert(key_str, updated);
        }

        Ok(())
    }

    pub fn update_or<T: Serialize + DeserializeOwned, F>(
        &self,
        key: &str,
        default: T,
        updater: F,
    ) -> Result<(), AppError>
    where
        F: FnOnce(T) -> T,
    {
        if self.contains_key(key) {
            self.update(key, updater)
        } else {
            self.insert(key, default)
        }
    }

    pub fn remove(&self, key: &str) -> Option<Value> {
        let mut inner = self.0.borrow_mut();

        if inner.status != SessionStatus::Purged {
            if inner.status != SessionStatus::Renewed {
                inner.status = SessionStatus::Changed;
            }
            return inner.state.remove(key);
        }

        None
    }

    pub fn remove_as<T: DeserializeOwned>(&self, key: &str) -> Option<Result<T, AppError>> {
        self.remove(key)
            .map(|value| serde_json::from_value(value).map_err(AppError::Json))
    }

    pub fn clear(&self) {
        let mut inner = self.0.borrow_mut();

        if inner.status != SessionStatus::Purged {
            if inner.status != SessionStatus::Renewed {
                inner.status = SessionStatus::Changed;
            }
            inner.state.clear();
        }
    }

    pub fn purge(&self) {
        let mut inner = self.0.borrow_mut();
        inner.status = SessionStatus::Purged;
        inner.state.clear();
    }

    pub fn renew(&self) {
        let mut inner = self.0.borrow_mut();

        if inner.status != SessionStatus::Purged {
            inner.status = SessionStatus::Renewed;
        }
    }

    pub fn user(&self) -> Option<Uuid> {
        self.get::<Uuid>(SESSION_USER_KEY).ok().flatten()
    }

    pub fn set_user(&self, uid: Uuid) {
        let _ = self.insert(SESSION_USER_KEY, uid);
    }

    pub fn clear_user(&self) {
        let _ = self.remove(SESSION_USER_KEY);
    }

    pub fn take_state(&self) -> SessionState {
        let mut inner = self.0.borrow_mut();
        std::mem::take(&mut inner.state)
    }

    pub fn mark_unchanged(&self) {
        self.0.borrow_mut().status = SessionStatus::Unchanged;
    }
}

impl Default for Session {
    fn default() -> Self {
        Self(Rc::new(RefCell::new(SessionInner::default())))
    }
}

pub type SessionState = Map<String, Value>;

#[derive(Debug, Clone, Copy)]
pub struct SessionUser(pub Uuid);