use std::sync::Mutex;

use elua::{AsLua, StdLibraries};

use crate::{ScriptHost, ScriptError, ScriptWorldPtr, ScriptEntity};

#[derive(Default)]
pub struct LuaHost;

fn try_call_lua_function(lua: &elua::State, fn_name: &str) -> Result<(), ScriptError> {
    let globals = lua.globals()?;

    if globals.has_key(fn_name)? {
        let lua_fn = globals.get::<_, elua::Function>(fn_name)?;
        lua_fn.exec(())
            .map_err(ScriptError::MluaError)?;
    }

    Ok(())
}

impl ScriptHost for LuaHost {
    type ScriptContext = Mutex<elua::State>;

    fn load_script(&mut self, script: &[u8], script_data: &crate::ScriptData, providers: &mut crate::ScriptApiProviders<Self>) -> Result<Self::ScriptContext, crate::ScriptError> {
        let mut ctx = Mutex::new({
            let s = elua::State::new();
            s.expose_libraries(StdLibraries::all());
            s
        });
        
        for provider in providers.apis.iter_mut() {
            provider.expose_api(script_data, &mut ctx)?;
        }

        let lua = ctx.lock().unwrap();
        lua.load(&script_data.name, script)?
            .execute(())
            .map_err(|e| ScriptError::MluaError(e))?;
        drop(lua);

        Ok(ctx)
    }

    fn setup_script(&mut self, script_data: &crate::ScriptData, ctx: &mut Self::ScriptContext, providers: &mut crate::ScriptApiProviders<Self>) -> Result<(), ScriptError> {
        for provider in providers.apis.iter_mut() {
            provider.setup_script(script_data, ctx)?;
        }

        Ok(())
    }

    /// Runs the update step of the lua script.
    /// 
    /// It looks for an `update` function with zero parameters in the [`ScriptContext`] and executes it.
    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> {
        for provider in providers.apis.iter_mut() {
            provider.update_script_environment(world.clone(), script_data, ctx)?;
        }

        let ctx = ctx.lock().expect("Failure to get Lua ScriptContext");
        
        let globals = ctx.globals()?;
        globals.set("world", world.as_lua(&ctx)?)?;
        globals.set("entity", ScriptEntity(script_data.entity).as_lua(&ctx)?)?;
        
        try_call_lua_function(&ctx, function_name)?;

        Ok(())
    }
}