//! A game session for GDScript, as host or as guest of a shared world.

use godot::prelude::*;
use grovewright_core::guest::Arrival;
use grovewright_core::host::Peer;
use grovewright_core::inventory::ItemId;
use grovewright_core::map::{Pos, Terrain};
use grovewright_core::mapgen::spawn_pos;
use grovewright_core::player::{PlayerId, PlayerKey};
use grovewright_core::protocol::{Action, Refusal};
use grovewright_core::world::World;

use crate::driver::{Driver, HOST_PEER};
use crate::events;

/// A session. The host runs the ticks and GDScript calls
/// [`GwSession::step`] once per tick; a guest runs the ticks its host sends,
/// one [`GwSession::step`] per tick that arrived. GDScript carries the
/// messages between the machines and reads the world back for display.
#[derive(GodotClass)]
#[class(base = RefCounted, init)]
pub struct GwSession {
    driver: Option<Driver>,
    last_error: GString,
}

#[godot_api]
impl GwSession {
    /// Simulation ticks per second.
    #[constant]
    const TICKS_PER_SECOND: i64 = grovewright_core::world::TICKS_PER_SECOND as i64;
    /// Ticks a player waits between two pickaxe hits.
    #[constant]
    const DIG_COOLDOWN_TICKS: i64 = grovewright_core::world::DIG_COOLDOWN_TICKS as i64;
    #[constant]
    const TERRAIN_GROUND: i64 = Terrain::Ground as i64;
    #[constant]
    const TERRAIN_SOFT_ROCK: i64 = Terrain::SoftRock as i64;
    #[constant]
    const TERRAIN_HARD_ROCK: i64 = Terrain::HardRock as i64;
    #[constant]
    const TERRAIN_BEDROCK: i64 = Terrain::Bedrock as i64;
    #[constant]
    const ITEM_STONE: i64 = grovewright_core::inventory::ITEM_STONE.0 as i64;
    /// Most players online at the same time.
    #[constant]
    const MAX_ONLINE_PLAYERS: i64 = grovewright_core::player::MAX_ONLINE_PLAYERS as i64;
    /// The connection number of the host, as a guest sees it.
    #[constant]
    const HOST_PEER: i64 = HOST_PEER as i64;
    /// Reasons a host turns a guest away, as in `refused` notices.
    #[constant]
    const REFUSED_OTHER_PROTOCOL: i64 = Refusal::OtherProtocol as i64;
    #[constant]
    const REFUSED_OTHER_RULES: i64 = Refusal::OtherRules as i64;
    #[constant]
    const REFUSED_WORLD_FULL: i64 = Refusal::WorldFull as i64;
    #[constant]
    const REFUSED_TOO_MANY_PLAYERS: i64 = Refusal::TooManyPlayers as i64;
    #[constant]
    const REFUSED_ALREADY_PLAYING: i64 = Refusal::AlreadyPlaying as i64;

    /// Hosts a fresh world from `seed`, replacing any running session.
    #[func]
    fn start_new(&mut self, seed: i64) {
        self.driver = Some(Driver::host(World::new(seed as u64)));
        self.last_error = GString::new();
    }

    /// Hosts a saved world. Returns false and keeps any running session if
    /// the save cannot be used; [`GwSession::last_error`] then says why.
    #[func]
    fn start_loaded(&mut self, save: PackedByteArray) -> bool {
        match World::load(save.as_slice()) {
            Ok(world) => {
                self.driver = Some(Driver::host(world));
                self.last_error = GString::new();
                true
            }
            Err(error) => {
                self.fail(&error.to_string());
                false
            }
        }
    }

    /// Becomes the guest of a host as the player `key` (16 bytes) named
    /// `name`, replacing any running session. The greeting waits in
    /// [`GwSession::take_messages`]; the world comes with the host's answer.
    #[func]
    fn start_guest(&mut self, key: PackedByteArray, name: GString) -> bool {
        let Some(key) = self.player_key(&key) else {
            return false;
        };
        self.driver = Some(Driver::guest(key, &name.to_string()));
        self.last_error = GString::new();
        true
    }

    /// Why the last call failed, or an empty text.
    #[func]
    fn last_error(&self) -> GString {
        self.last_error.clone()
    }

    /// True once there is a world: at once for a host, for a guest after
    /// the host's world arrived.
    #[func]
    fn is_running(&self) -> bool {
        self.world().is_some()
    }

    #[func]
    fn is_host(&self) -> bool {
        self.driver.as_ref().is_some_and(Driver::is_host)
    }

    /// True after the core stopped with an internal error.
    #[func]
    fn is_broken(&self) -> bool {
        self.driver.as_ref().is_some_and(Driver::is_broken)
    }

    /// Queues the entry of the host's own player for the next tick. `key`
    /// identifies the player across sessions and must have 16 bytes. A
    /// guest enters with [`GwSession::start_guest`] instead.
    #[func]
    fn join(&mut self, key: PackedByteArray, name: GString) -> bool {
        let Some(key) = self.player_key(&key) else {
            return false;
        };
        let Some(driver) = self.driver.as_mut() else {
            return false;
        };
        driver.join_local(key, &name.to_string())
    }

    /// A pickaxe hit of this machine's player on tile (`x`, `y`): the host
    /// queues it for the next tick, a guest sends it to the host. Does
    /// nothing before the player is in the world.
    #[func]
    fn dig(&mut self, x: i64, y: i64) {
        let (Some(driver), Some(pos)) = (self.driver.as_mut(), to_pos(x, y)) else {
            return;
        };
        driver.act(Action::Dig { pos });
    }

    /// Runs one tick and returns what happened, as dictionaries with a
    /// `type` entry. A host runs its next tick; a guest runs the oldest tick
    /// that arrived, or nothing if none is waiting.
    #[func]
    fn step(&mut self) -> Array<VarDictionary> {
        let mut happened = Array::new();
        let Some(driver) = self.driver.as_mut() else {
            return happened;
        };
        if let Some(events) = driver.step() {
            for event in &events {
                happened.push(&events::to_dictionary(event));
            }
        }
        if driver.is_broken() {
            self.fail("the simulation stopped after an internal error");
        }
        happened
    }

    /// Ticks that arrived at a guest and have not run yet.
    #[func]
    fn pending_ticks(&self) -> i64 {
        self.driver
            .as_ref()
            .map_or(0, |driver| driver.pending_ticks() as i64)
    }

    /// Hands over a message that arrived from `peer`. A guest answers with
    /// notices: `world_received` (entry `resync`), `refused` (entry
    /// `reason`, a `REFUSED_*` constant) or `protocol_error`, after which
    /// [`GwSession::last_error`] says what went wrong.
    #[func]
    fn receive(&mut self, peer: i64, bytes: PackedByteArray) -> Array<VarDictionary> {
        let mut notices = Array::new();
        let (Some(driver), Some(peer)) = (self.driver.as_mut(), to_peer(peer)) else {
            return notices;
        };
        match driver.receive(peer, bytes.as_slice()) {
            Ok(Arrival::Nothing) => {}
            Ok(Arrival::World { replaced }) => notices.push(&vdict! {
                "type" => "world_received",
                "resync" => replaced,
            }),
            Ok(Arrival::Refused(refusal)) => notices.push(&vdict! {
                "type" => "refused",
                "reason" => i64::from(refusal.code()),
            }),
            Err(error) => {
                self.fail(&error.to_string());
                notices.push(&vdict! { "type" => "protocol_error" });
            }
        }
        if self.is_broken() {
            self.fail("the simulation stopped after an internal error");
        }
        notices
    }

    /// The host learned that a guest connected as `peer`.
    #[func]
    fn connect_peer(&mut self, peer: i64) {
        if let (Some(driver), Some(peer)) = (self.driver.as_mut(), to_peer(peer)) {
            driver.connect(peer);
        }
    }

    /// The host learned that the connection `peer` closed.
    #[func]
    fn disconnect_peer(&mut self, peer: i64) {
        if let (Some(driver), Some(peer)) = (self.driver.as_mut(), to_peer(peer)) {
            driver.disconnect(peer);
        }
    }

    /// Messages to send, oldest first, as dictionaries with the entries
    /// `peer` and `bytes`. They must arrive reliably and in this order.
    #[func]
    fn take_messages(&mut self) -> Array<VarDictionary> {
        let mut messages = Array::new();
        if let Some(driver) = self.driver.as_mut() {
            for (peer, bytes) in driver.take_messages() {
                messages.push(&vdict! {
                    "peer" => i64::from(peer),
                    "bytes" => &PackedByteArray::from(bytes.as_slice()),
                });
            }
        }
        messages
    }

    /// Connections the host has given up. Close them after sending the
    /// messages that are waiting for them.
    #[func]
    fn take_closing(&mut self) -> PackedInt64Array {
        let peers: Vec<i64> = self
            .driver
            .as_mut()
            .map(|driver| driver.take_closing().into_iter().map(i64::from).collect())
            .unwrap_or_default();
        PackedInt64Array::from(peers.as_slice())
    }

    /// Divergences the host's guests reported, as dictionaries with the
    /// entries `peer`, `tick` and `hash` (16 hexadecimal digits).
    #[func]
    fn take_divergences(&mut self) -> Array<VarDictionary> {
        let mut reports = Array::new();
        if let Some(driver) = self.driver.as_mut() {
            for divergence in driver.take_divergences() {
                reports.push(&vdict! {
                    "peer" => i64::from(divergence.peer),
                    "tick" => divergence.tick as i64,
                    "hash" => format!("{:016x}", divergence.hash),
                });
            }
        }
        reports
    }

    /// The recording of a guest's world that diverged from the host's, or
    /// empty. Taking it empties it.
    #[func]
    fn take_diverged_recording(&mut self) -> PackedByteArray {
        self.driver
            .as_mut()
            .and_then(Driver::take_diverged_recording)
            .map_or_else(PackedByteArray::new, |bytes| {
                PackedByteArray::from(bytes.as_slice())
            })
    }

    /// Number of the host's guests.
    #[func]
    fn guest_count(&self) -> i64 {
        self.driver
            .as_ref()
            .map_or(0, |driver| driver.guest_count() as i64)
    }

    /// The player of the host's guest at `peer`, or -1.
    #[func]
    fn player_of_peer(&self, peer: i64) -> i64 {
        let (Some(driver), Some(peer)) = (self.driver.as_ref(), to_peer(peer)) else {
            return -1;
        };
        driver
            .player_of(peer)
            .map_or(-1, |player| i64::from(player.0))
    }

    /// Number of ticks the world has run.
    #[func]
    fn tick(&self) -> i64 {
        self.world().map_or(0, |world| world.tick() as i64)
    }

    #[func]
    fn map_width(&self) -> i64 {
        self.world()
            .map_or(0, |world| i64::from(world.map().width()))
    }

    #[func]
    fn map_height(&self) -> i64 {
        self.world()
            .map_or(0, |world| i64::from(world.map().height()))
    }

    /// The terrain of every tile, row by row (`TERRAIN_*` constants).
    #[func]
    fn terrain_codes(&self) -> PackedByteArray {
        self.tile_bytes(|terrain, _| terrain as u8)
    }

    /// The hits every tile has taken, row by row.
    #[func]
    fn damage_codes(&self) -> PackedByteArray {
        self.tile_bytes(|_, damage| damage)
    }

    /// The terrain of tile (`x`, `y`), or -1 outside the map.
    #[func]
    fn terrain_at(&self, x: i64, y: i64) -> i64 {
        self.tile(x, y).map_or(-1, |(terrain, _)| terrain as i64)
    }

    /// Whether a figure can stand on tile (`x`, `y`).
    #[func]
    fn is_walkable(&self, x: i64, y: i64) -> bool {
        self.tile(x, y)
            .is_some_and(|(terrain, _)| terrain.is_walkable())
    }

    /// The tile where figures appear.
    #[func]
    fn spawn_point(&self) -> Vector2i {
        self.world().map_or(Vector2i::ZERO, |world| {
            let spawn = spawn_pos(world.map());
            Vector2i::new(spawn.x, spawn.y)
        })
    }

    /// Index of this machine's player in the world, or -1 before it is in.
    #[func]
    fn local_player(&self) -> i64 {
        self.driver
            .as_ref()
            .and_then(Driver::local_player)
            .map_or(-1, |id| i64::from(id.0))
    }

    /// The players who are online, by index.
    #[func]
    fn online_players(&self) -> PackedInt64Array {
        let online: Vec<i64> = self.world().map_or_else(Vec::new, |world| {
            world
                .players()
                .iter()
                .enumerate()
                .filter(|(_, player)| player.online)
                .map(|(index, _)| index as i64)
                .collect()
        });
        PackedInt64Array::from(online.as_slice())
    }

    /// The name of player `player`, or an empty text.
    #[func]
    fn player_name(&self, player: i64) -> GString {
        let name = u8::try_from(player)
            .ok()
            .and_then(|index| self.world()?.player(PlayerId(index)))
            .map_or("", |player| player.name.as_str());
        GString::from(name)
    }

    /// How many of `item` the local player carries.
    #[func]
    fn item_count(&self, item: i64) -> i64 {
        let (Some(world), Some(player), Ok(item)) = (
            self.world(),
            self.driver.as_ref().and_then(Driver::local_player),
            u16::try_from(item),
        ) else {
            return 0;
        };
        world
            .player(player)
            .map_or(0, |player| i64::from(player.inventory.count(ItemId(item))))
    }

    /// The world as a save, or empty. Only a healthy host saves.
    #[func]
    fn save(&self) -> PackedByteArray {
        self.driver
            .as_ref()
            .and_then(Driver::save)
            .map_or_else(PackedByteArray::new, |bytes| {
                PackedByteArray::from(bytes.as_slice())
            })
    }

    /// The recording of this machine's session, or empty if there is no
    /// healthy session with a world.
    #[func]
    fn recording_bytes(&self) -> PackedByteArray {
        self.driver
            .as_ref()
            .and_then(Driver::recording_bytes)
            .map_or_else(PackedByteArray::new, |bytes| {
                PackedByteArray::from(bytes.as_slice())
            })
    }

    /// The checksum of the world state, as 16 hexadecimal digits.
    #[func]
    fn state_hash_hex(&self) -> GString {
        self.world().map_or_else(GString::new, |world| {
            GString::from(format!("{:016x}", world.state_hash()).as_str())
        })
    }
}

impl GwSession {
    fn world(&self) -> Option<&World> {
        self.driver.as_ref()?.world()
    }

    fn fail(&mut self, reason: &str) {
        self.last_error = GString::from(reason);
    }

    /// A player key from GDScript bytes, or `None` with a reason.
    fn player_key(&mut self, bytes: &PackedByteArray) -> Option<PlayerKey> {
        match PlayerKey::try_from(bytes.as_slice()) {
            Ok(key) => Some(key),
            Err(_) => {
                self.fail("a player key has 16 bytes");
                None
            }
        }
    }

    fn tile(&self, x: i64, y: i64) -> Option<(Terrain, u8)> {
        let tile = self.world()?.map().get(to_pos(x, y)?)?;
        Some((tile.terrain, tile.damage))
    }

    fn tile_bytes(&self, byte: impl Fn(Terrain, u8) -> u8) -> PackedByteArray {
        let Some(world) = self.world() else {
            return PackedByteArray::new();
        };
        let bytes: Vec<u8> = world
            .map()
            .tiles()
            .iter()
            .map(|tile| byte(tile.terrain, tile.damage))
            .collect();
        PackedByteArray::from(bytes.as_slice())
    }
}

/// A tile position from GDScript integers, or `None` if it cannot exist.
fn to_pos(x: i64, y: i64) -> Option<Pos> {
    Some(Pos::new(i32::try_from(x).ok()?, i32::try_from(y).ok()?))
}

/// A connection number from GDScript, or `None` if it cannot exist.
fn to_peer(peer: i64) -> Option<Peer> {
    Peer::try_from(peer).ok()
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn positions_outside_the_i32_range_are_refused() {
        assert_eq!(to_pos(3, -4), Some(Pos::new(3, -4)));
        assert_eq!(to_pos(i64::from(i32::MAX) + 1, 0), None);
        assert_eq!(to_pos(0, i64::from(i32::MIN) - 1), None);
    }

    #[test]
    fn connection_numbers_outside_the_u32_range_are_refused() {
        assert_eq!(to_peer(1), Some(1));
        assert_eq!(to_peer(-1), None);
        assert_eq!(to_peer(i64::from(u32::MAX) + 1), None);
    }
}