use crate::chunk::Chunk;
use crate::value::Value;
use crate::vm::{Creature, Panic};
use ran::ran_u8;
use std::cell::RefCell;
use std::collections::HashMap;
use std::mem::swap;
use std::rc::Rc;
use std::time::{Duration, Instant};

const ANIMALS: [&str; 24] = [
    "tortoise",
    "hare",
    "squirrel",
    "hawk",
    "woodpecker",
    "cardinal",
    "coyote",
    "raccoon",
    "rat",
    "axolotl",
    "cormorant",
    "duck",
    "orca",
    "humbpack",
    "tern",
    "quokka",
    "koala",
    "kangaroo",
    "zebra",
    "hyena",
    "giraffe",
    "leopard",
    "lion",
    "hippopotamus",
];

#[derive(Debug, Clone, PartialEq)]
enum Status {
    Empty,
    Borrowed,
    Nested(Creature),
}

impl std::fmt::Display for Status {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match self {
            Status::Empty => write!(f, "empty"),
            Status::Borrowed => write!(f, "borrowed"),
            Status::Nested(creature) => write!(f, "nested {creature}"),
        }
    }
}

impl Status {
    pub fn receive(&mut self, msg: Value) {
        match self {
            Status::Nested(creature) => creature.receive(msg),
            Status::Borrowed => println!("sending a message to a borrowed process"),
            Status::Empty => println!("sending a message to a dead process"),
        }
    }
}

#[derive(Debug, Clone, PartialEq)]
pub struct Zoo {
    procs: Vec<Status>,
    empty: Vec<usize>,
    ids: HashMap<&'static str, usize>,
    dead: Vec<&'static str>,
    kill_list: Vec<&'static str>,
    sleeping: HashMap<&'static str, (Instant, Duration)>,
    active_idx: usize,
    active_id: &'static str,
}

impl Zoo {
    pub fn new() -> Zoo {
        Zoo {
            procs: vec![],
            empty: vec![],
            ids: HashMap::new(),
            kill_list: vec![],
            dead: vec![],
            sleeping: HashMap::new(),
            active_idx: 0,
            active_id: "",
        }
    }

    fn random_id(&self) -> String {
        let rand = ran_u8() as usize % 24;
        let idx = self.procs.len();
        format!("{}_{idx}", ANIMALS[rand])
    }

    fn new_id(&self) -> &'static str {
        let mut new = self.random_id();
        while self.dead.iter().any(|old| *old == new) {
            new = self.random_id();
        }
        new.leak()
    }

    pub fn put(&mut self, mut proc: Creature) -> &'static str {
        if self.empty.is_empty() {
            let id = self.new_id();
            let idx = self.procs.len();
            proc.id = id;
            self.procs.push(Status::Nested(proc));
            self.ids.insert(id, idx);
            id
        } else {
            let idx = self.empty.pop().unwrap();
            let rand = ran_u8() as usize % 24;
            let id = format!("{}_{idx}", ANIMALS[rand]).leak();
            proc.id = id;
            self.ids.insert(id, idx);
            self.procs[idx] = Status::Nested(proc);
            id
        }
    }

    pub fn kill(&mut self, id: &'static str) {
        self.kill_list.push(id);
    }

    pub fn sleep(&mut self, id: &'static str, ms: usize) {
        self.sleeping
            .insert(id, (Instant::now(), Duration::from_millis(ms as u64)));
    }

    pub fn is_alive(&self, id: &'static str) -> bool {
        if self.kill_list.contains(&id) {
            return false;
        }
        let idx = self.ids.get(id);
        match idx {
            Some(idx) => match self.procs.get(*idx) {
                Some(proc) => match proc {
                    Status::Empty => false,
                    Status::Borrowed => true,
                    Status::Nested(_) => true,
                },
                None => false,
            },
            None => false,
        }
    }

    pub fn clean_up(&mut self) {
        while let Some(id) = self.kill_list.pop() {
            if let Some(idx) = self.ids.get(id) {
                println!("buried process {id}");
                self.procs[*idx] = Status::Empty;
                self.empty.push(*idx);
                self.ids.remove(id);
                self.dead.push(id);
            }
        }

        self.sleeping
            .retain(|_, (instant, duration)| instant.elapsed() < *duration);

        println!(
            "currently sleeping processes: {}",
            self.sleeping
                .keys()
                .map(|id| id.to_string())
                .collect::<Vec<_>>()
                .join(" | ")
        );
    }

    pub fn catch(&mut self, id: &'static str) -> Creature {
        if let Some(idx) = self.ids.get(id) {
            let mut proc = Status::Borrowed;
            swap(&mut proc, &mut self.procs[*idx]);
            let Status::Nested(proc) = proc else {
                unreachable!("tried to borrow an empty or already-borrowed process {id}");
            };
            proc
        } else {
            unreachable!("tried to borrow a non-existent process {id}");
        }
    }

    pub fn release(&mut self, proc: Creature) {
        let id = proc.id;
        if let Some(idx) = self.ids.get(id) {
            let mut proc = Status::Nested(proc);
            swap(&mut proc, &mut self.procs[*idx]);
        }
        // Removed because, well, we shouldn't have creatures we don't know about
        // And since zoo.next now cleans (and thus kills) before the world releases its active process
        // We'll die if we execute this check
        // else {
        //     unreachable!("tried to return a process the world doesn't know about");
        // }
    }

    pub fn is_available(&self) -> bool {
        match &self.procs[self.active_idx] {
            Status::Empty => false,
            Status::Borrowed => false,
            Status::Nested(proc) => !self.sleeping.contains_key(proc.id),
        }
    }

    pub fn next(&mut self) -> &'static str {
        self.active_idx = (self.active_idx + 1) % self.procs.len();
        while !self.is_available() {
            self.clean_up();
            self.active_idx = (self.active_idx + 1) % self.procs.len();
            println!(
                "testing process availability: {}",
                self.procs[self.active_idx]
            );
        }
        match &self.procs[self.active_idx] {
            Status::Empty | Status::Borrowed => unreachable!(),
            Status::Nested(proc) => proc.id,
        }
    }

    pub fn send_msg(&mut self, id: &'static str, msg: Value) {
        let Some(idx) = self.ids.get(id) else {
            return;
        };
        self.procs[*idx].receive(msg);
    }
}

#[derive(Debug, Clone, PartialEq)]
pub struct World {
    zoo: Rc<RefCell<Zoo>>,
    active: Option<Creature>,
    main: &'static str,
    pub result: Option<Result<Value, Panic>>,
}

impl World {
    pub fn new(chunk: Chunk, debug: bool) -> World {
        let zoo = Rc::new(RefCell::new(Zoo::new()));
        let main = Creature::new(chunk, zoo.clone(), debug);
        let id = zoo.as_ref().borrow_mut().put(main);

        World {
            zoo,
            active: None,
            main: id,
            result: None,
        }
    }

    // pub fn spawn(&mut self, proc: Creature) -> Value {
    //     let id = self.zoo.put(proc);
    //     Value::Keyword(id)
    // }

    // pub fn send_msg(&mut self, id: &'static str, msg: Value) {
    //     let mut proc = self.zoo.catch(id);
    //     proc.receive(msg);
    //     self.zoo.release(proc);
    // }
    //
    fn next(&mut self) {
        let mut active = None;
        swap(&mut active, &mut self.active);
        let mut zoo = self.zoo.as_ref().borrow_mut();
        zoo.release(active.unwrap());
        // at the moment, active is None, process is released.
        // zoo should NOT need an id--it has a representation of the current active process
        // world has an active process for memory reasons
        // not for state-keeping reasons
        let new_active_id = zoo.next();
        let mut new_active_proc = zoo.catch(new_active_id);
        new_active_proc.reset_reductions();
        let mut new_active_opt = Some(new_active_proc);
        swap(&mut new_active_opt, &mut self.active);
    }

    // fn old_next(&mut self) {
    //     let id = self
    //         .zoo
    //         .as_ref()
    //         .borrow_mut()
    //         .next(self.active.as_ref().unwrap().id);
    //     println!("next id is {id}");
    //     let mut active = None;
    //     std::mem::swap(&mut active, &mut self.active);
    //     let mut holding_pen = self.zoo.as_ref().borrow_mut().catch(id);
    //     let mut active = active.unwrap();
    //     std::mem::swap(&mut active, &mut holding_pen);
    //     println!("now in the holding pen: {}", holding_pen.id);
    //     holding_pen.reset_reductions();
    //     self.zoo.as_ref().borrow_mut().release(holding_pen);
    //     let mut active = Some(active);
    //     std::mem::swap(&mut active, &mut self.active);
    // }

    // pub fn sleep(&mut self, id: &'static str) {
    //     // check if the id is the actually active process
    //     if self.active.id != id {
    //         panic!("attempted to sleep a process from outside that process: active = {}; to sleep: = {id}", self.active.id);
    //     }
    //     self.next(id);
    // }

    // pub fn panic(&mut self, id: &'static str, panic: Panic) {
    //     // TODO: devise some way of linking processes (study the BEAM on this)
    //     // check if the id is active
    //     if self.active.id != id {
    //         panic!("attempted to panic from a process from outside that process: active = {}; panicking = {id}; panic = {panic}", self.active.id);
    //     }
    //     // check if the process is `main`, and crash the program if it is
    //     if self.main == id {
    //         self.result = self.active.result.clone();
    //     }
    //     // kill the process
    //     self.zoo.kill(id);
    //     self.next(id);
    // }

    // pub fn complete(&mut self) {
    //     if self.main == self.active.id {
    //         self.result = self.active.result.clone();
    //     }
    //     self.next(id);
    // }

    pub fn activate_main(&mut self) {
        let main = self.zoo.as_ref().borrow_mut().catch(self.main);
        self.active = Some(main);
    }

    pub fn active_id(&mut self) -> &'static str {
        self.active.as_ref().unwrap().id
    }

    pub fn kill_active(&mut self) {
        let id = self.active_id();
        self.zoo.as_ref().borrow_mut().kill(id);
    }

    pub fn active_result(&mut self) -> &Option<Result<Value, Panic>> {
        &self.active.as_ref().unwrap().result
    }

    pub fn run(&mut self) {
        self.activate_main();
        loop {
            println!(
                "entering world loop; active process is {}",
                self.active_id()
            );
            self.active.as_mut().unwrap().interpret();
            println!("yielded from {}", self.active_id());
            match self.active_result() {
                None => (),
                Some(_) => {
                    if self.active_id() == self.main {
                        self.result = self.active_result().clone();
                        return;
                    }
                    println!("process died: {}", self.active_id());
                    self.kill_active();
                }
            }
            println!("getting next process");
            self.next();
            // self.clean_up();
        }
    }

    // TODO:
    // * [ ] Maybe I need to write this from the bottom up?
    //   What do processes need to do?
    //   - [ ] send a message to another process
    //   - [ ] tell the world to spawn a new process, get the pid back
    //   - [ ] receive its messages (always until something matches, or sleep if nothing matches)
    //   - [ ] delete a message from the mbx if it's a match (by idx)
    //   - [ ] yield
    //   - [ ] panic
    //   - [ ] complete
    //  Thus the other side of this looks like:
    //  * [x] Spawn a process
    //  * [x]
}

// Okay, some more thinking
// The world and process can't have mutable references to one another
// They will each need an Rc<RefCell<PostOffice>>
// All the message passing and world/proc communication will happen through there
// And ownership goes World -> Process A -> World -> Process B

// Both the world and a process will have an endless `loop`.
// But I already have three terms: Zoo, Creature, and World
// That should be enough indirection?
// To solve tomorrow.