use rlua::{Context, MetaMethod, RegistryKey, Table, UserData, UserDataMethods, Value};
use std::collections::HashMap;

use crate::types::Result;

/// Stores Lua modules indexed by module name, and provides an
/// `rlua::MetaMethod` to enable `require`ing the stored modules by name
/// in an `rlua::Context`.
struct Searcher {
    /// A `HashMap` of Lua modules in `String` representation, indexed
    /// by module name.
    modules: HashMap<String, String>,

    /// An `rlua::RegistryKey` whose value is the Lua environment within
    /// which the user made the request to instantiate a `Searcher` for
    /// `modules`.
    globals: RegistryKey,
}

impl Searcher {
    fn new(modules: HashMap<String, String>, globals: RegistryKey) -> Self {
        Self { modules, globals }
    }
}

impl UserData for Searcher {
    fn add_methods<'lua, M: UserDataMethods<'lua, Self>>(methods: &mut M) {
        methods.add_meta_method(MetaMethod::Call, |lua_ctx, this, name: String| {
            match this.modules.get(&name) {
                Some(content) => Ok(Value::Function(
                    lua_ctx
                        .load(content)
                        .set_name(&name)?
                        .set_environment(lua_ctx.registry_value::<Table>(&this.globals)?)?
                        .into_function()?,
                )),
                None => Ok(Value::Nil),
            }
        });
    }
}

/// Extend `rlua::Context` to support `require`ing Lua modules by name.
pub trait AddSearcher<'a> {
    /// Add a `HashMap` of Lua modules indexed by module name to Lua’s
    /// `package.searchers` table in an `rlua::Context`, with lookup
    /// functionality provided by the `rlua_searcher::Searcher` struct.
    fn add_searcher(&self, modules: HashMap<String, String>) -> Result<()>;
}

impl<'a> AddSearcher<'a> for Context<'a> {
    fn add_searcher(&self, modules: HashMap<String, String>) -> Result<()> {
        let globals = self.globals();
        let searchers: Table = globals.get::<_, Table>("package")?.get("searchers")?;
        let registry_key = self.create_registry_value(globals)?;
        let searcher = Searcher::new(modules, registry_key);
        searchers
            .set(searchers.len()? + 1, searcher)
            .map_err(|e| e.into())
    }
}