lyra-engine/lyra-scripting/src/host.rs

use std::collections::HashMap;

use lyra_ecs::{ResourceObject, Entity, World};

use crate::ScriptWorldPtr;

#[derive(Debug, thiserror::Error)]
pub enum ScriptError {
    #[error("{0}")]
    #[cfg(feature = "lua")]
    MluaError(mlua::Error),

    #[error("{0}")]
    Other(anyhow::Error),
}

#[cfg(feature = "lua")]
impl From<mlua::Error> for ScriptError {
    fn from(value: mlua::Error) -> Self {
        ScriptError::MluaError(value)
    }
}

impl From<anyhow::Error> for ScriptError {
    fn from(value: anyhow::Error) -> Self {
        ScriptError::Other(value)
    }
}

#[derive(Clone, Hash, PartialEq, Eq)]
pub struct ScriptData {
    /// The script id
    pub script_id: u64,
    /// The name of the script
    pub name: String,
    /// The entity that this script exists on
    pub entity: Entity,
}

/// Provides an API to a scripting context.
pub trait ScriptApiProvider {
    /// The type used as the script's context.
    type ScriptContext;

    /// Prepare the ECS world for this api. Things like registering types with the type registry happen here.
    fn prepare_world(&mut self, world: &mut World) {}

    /// Exposes an API in the provided script context.
    fn expose_api(&mut self, ctx: &mut Self::ScriptContext) -> Result<(), ScriptError>;

    /// Setup a script right before its 'init' method is called.
    fn setup_script(&mut self, data: &ScriptData, ctx: &mut Self::ScriptContext) -> Result<(), ScriptError>;

    /// A function that is used to update a script's environment.
    /// 
    /// This is used to update stuff like the world pointer in the script context.
    fn update_script_environment(&mut self, world: ScriptWorldPtr, data: &ScriptData, ctx: &mut Self::ScriptContext) -> Result<(), ScriptError>;
}

/// A storage for a [`ScriptHost`]'s api providers
#[derive(Default)]
pub struct ScriptApiProviders<T: ScriptHost> {
    pub apis: Vec<Box<dyn ScriptApiProvider<ScriptContext = T::ScriptContext>>>,
}

impl<T: ScriptHost> ScriptApiProviders<T> {
    pub fn add_provider<P>(&mut self, provider: P)
    where
        P: ScriptApiProvider<ScriptContext = T::ScriptContext> + 'static
    {
        self.apis.push(Box::new(provider));
    }
}

pub trait ScriptHost: Default + ResourceObject {
    /// The type used as the script's context.
    type ScriptContext;

    /// Loads a script and creates a context for it.
    /// 
    /// Before the script is executed, the API providers are exposed to the script.
    fn load_script(&mut self, script: &[u8], script_data: &ScriptData,
        providers: &mut crate::ScriptApiProviders<Self>)
        -> Result<Self::ScriptContext, ScriptError>;

    /// Setup a script for execution.
    fn setup_script(&mut self, script_data: &ScriptData, ctx: &mut Self::ScriptContext,
        providers: &mut ScriptApiProviders<Self>) -> Result<(), ScriptError>;

    /// Executes the update step for the script.
    fn call_script(&mut self, world: ScriptWorldPtr, script_data: &crate::ScriptData,
        ctx: &mut Self::ScriptContext, providers: &mut crate::ScriptApiProviders<Self>,
        function_name: &str) -> Result<(), ScriptError>;
}

#[derive(Default)]
pub struct ScriptContexts<T> {
    contexts: HashMap<u64, T>,
}

impl<T> ScriptContexts<T> {
    pub fn new(contexts: HashMap<u64, T>) -> Self {
        Self {
            contexts,
        }
    }

    pub fn add_context(&mut self, script_id: u64, context: T) {
        self.contexts.insert(script_id, context);
    }

    pub fn get_context(&self, script_id: u64) -> Option<&T> {
        self.contexts.get(&script_id)
    }

    pub fn get_context_mut(&mut self, script_id: u64) -> Option<&mut T> {
        self.contexts.get_mut(&script_id)
    }

    pub fn has_context(&self, script_id: u64) -> bool {
        self.contexts.contains_key(&script_id)
    }
}