/** Serene --- Yet an other Lisp
*
* Copyright (c) 2020  Sameer Rahmani <lxsameer@gnu.org>
*
* This program is free software; you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 2 of the License.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */
use crate::builtins::{BuiltInFn, BUILTINS};
use crate::values;

use std::collections::HashMap;

/// This enum describes the type of the values in the scope.
/// Most values are LLVMValue's which are just some LLVM IR
/// representation.
/// But sometimes we're going to have lookups for build in symbols
/// like `def`, `if`, `fn` and so on.
pub enum ScopeElementType<'a> {
    Value(values::Value<'a>),
    BuiltinCall(BuiltInFn),
}

/// This struct describes the values in the scope.
struct ScopeElement<'a> {
    element_type: ScopeElementType<'a>,
    public: bool,
}

/// Lookup the given key `k` in the builtins and return a
/// ScopeElement from it
fn builtin_lookup<'a>(k: &'a str) -> Option<ScopeElement<'a>> {
    match BUILTINS.get(k) {
        Some(v) => Some(ScopeElement {
            element_type: ScopeElementType::BuiltinCall(v),
            public: true,
        }),
        None => None,
    }
}

/// Scopes in **Serene** are simply represented by hashmaps. Each
/// Scope optionally has a parent scope that lookups fallback to
/// if the lookup key is missing from the current scope.
pub struct Scope<'a> {
    parent: Option<Box<Scope<'a>>>,
    symbol_table: HashMap<String, ScopeElement<'a>>,
}

impl<'a> Scope<'a> {
    pub fn new(_parent: Option<Scope>) -> Scope {
        let p = match _parent {
            Some(x) => Some(Box::new(x)),
            None => None,
        };

        Scope {
            parent: p,
            symbol_table: HashMap::new(),
        }
    }

    /// Lookup the given `key` in the scope and if it is not in the current
    /// scope look it up in the `parent` scope.
    pub fn lookup(&self, key: &'a str) -> Option<ScopeElement<'a>> {
        let v = self.symbol_table.get(key);

        if let None = v {
            return match &self.parent {
                Some(x) => x.lookup(key),
                None => builtin_lookup(key),
            };
        }

        v.map(|x| *x)
    }

    pub fn insert(&mut self, key: &str, val: Value<'a>, public: bool) {
        let v = ScopeElement {
            public,
            element_type: ScopeElementType::Value(val),
        };
        self.symbol_table.insert(key.to_string(), v);
    }
}