//! # Lexical Environment
//!
//! https://tc39.github.io/ecma262/#sec-lexical-environment-operations
//!
//! The following operations are used to operate upon lexical environments
//! This is the entrypoint to lexical environments.
//!

use crate::environment::declerative_environment_record::DeclerativeEnvironmentRecord;
use crate::environment::environment_record_trait::EnvironmentRecordTrait;
use crate::environment::function_environment_record::{BindingStatus, FunctionEnvironmentRecord};
use crate::environment::global_environment_record::GlobalEnvironmentRecord;
use crate::environment::object_environment_record::ObjectEnvironmentRecord;
use crate::js::value::{Value, ValueData};
use gc::{Gc, GcCell};
use std::collections::hash_map::HashMap;
use std::collections::{HashSet, VecDeque};
use std::debug_assert;
use std::error;
use std::fmt;

/// Environments are wrapped in a Box and then in a GC wrapper
pub type Environment = Gc<GcCell<Box<EnvironmentRecordTrait>>>;

/// Give each environment an easy way to declare its own type
/// This helps with comparisons
#[derive(Debug)]
pub enum EnvironmentType {
    Declerative,
    Function,
    Global,
    Object,
}

pub struct LexicalEnvironment {
    environment_stack: VecDeque<Environment>,
}

/// An error that occurred during lexing or compiling of the source input.
#[derive(Debug, Clone)]
pub struct EnvironmentError {
    details: String,
}

impl EnvironmentError {
    pub fn new(msg: &str) -> EnvironmentError {
        EnvironmentError {
            details: msg.to_string(),
        }
    }
}

impl fmt::Display for EnvironmentError {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        write!(f, "{}", self.details)
    }
}

impl error::Error for EnvironmentError {
    fn description(&self) -> &str {
        &self.details
    }

    fn cause(&self) -> Option<&error::Error> {
        // Generic error, underlying cause isn't tracked.
        None
    }
}

impl LexicalEnvironment {
    pub fn new(global: Value) -> LexicalEnvironment {
        let global_env = new_global_environment(global.clone(), global.clone());
        let mut lexical_env = LexicalEnvironment {
            environment_stack: VecDeque::new(),
        };

        // lexical_env.push(global_env);
        lexical_env.environment_stack.push_back(global_env);
        lexical_env
    }

    pub fn push(&mut self, env: Environment) {
        let current_env: Environment = self.get_current_environment().clone();
        env.borrow_mut().set_outer_environment(current_env);
        self.environment_stack.push_back(env);
    }

    pub fn pop(&mut self) {
        self.environment_stack.pop_back();
    }

    pub fn get_global_object(&self) -> Option<Value> {
        let global = &self.environment_stack[0];
        global.borrow().get_global_object()
    }

    pub fn create_mutable_binding(&mut self, name: String, deletion: bool) {
        self.get_current_environment()
            .borrow_mut()
            .create_mutable_binding(name, deletion)
    }

    pub fn create_immutable_binding(&mut self, name: String, deletion: bool) {
        self.get_current_environment()
            .borrow_mut()
            .create_immutable_binding(name, deletion)
    }

    pub fn set_mutable_binding(&mut self, name: String, value: Value, strict: bool) {
        let env = self.get_current_environment();
        env.borrow_mut().set_mutable_binding(name, value, strict);
    }

    pub fn initialize_binding(&mut self, name: String, value: Value) {
        let env = self.get_current_environment();
        env.borrow_mut().initialize_binding(name, value);
    }

    /// get_current_environment_ref is used when you only need to borrow the environment
    /// (you only need to add a new variable binding, or you want to fetch a value)
    pub fn get_current_environment_ref(&self) -> &Environment {
        &self
            .environment_stack
            .get(self.environment_stack.len() - 1)
            .unwrap()
    }

    /// When neededing to clone an environment (linking it with another environnment)
    /// cloning is more suited. The GC will remove the env once nothing is linking to it anymore
    pub fn get_current_environment(&mut self) -> &mut Environment {
        self.environment_stack.back_mut().unwrap()
    }

    pub fn get_binding_value(&mut self, name: String) -> Value {
        let env: Environment = self.get_current_environment().clone();
        let borrowed_env = env.borrow();
        let result = borrowed_env.has_binding(&name);
        if result {
            return borrowed_env.get_binding_value(name, false);
        }

        // Check outer scope
        if borrowed_env.get_outer_environment().is_some() {
            let mut outer: Option<Environment> = borrowed_env.get_outer_environment();
            while outer.is_some() {
                if outer.as_ref().unwrap().borrow().has_binding(&name) {
                    return outer.unwrap().borrow().get_binding_value(name, false);
                }
                outer = outer.unwrap().borrow().get_outer_environment();
            }
        }

        Gc::new(ValueData::Undefined)
    }
}

pub fn new_declerative_environment(env: Option<Environment>) -> Environment {
    let boxed_env = Box::new(DeclerativeEnvironmentRecord {
        env_rec: HashMap::new(),
        outer_env: env,
    });

    Gc::new(GcCell::new(boxed_env))
}

pub fn new_function_environment(
    f: Value,
    new_target: Value,
    outer: Option<Environment>,
) -> Environment {
    debug_assert!(f.is_function());
    debug_assert!(new_target.is_object() || new_target.is_undefined());
    Gc::new(GcCell::new(Box::new(FunctionEnvironmentRecord {
        env_rec: HashMap::new(),
        function_object: f.clone(),
        this_binding_status: BindingStatus::Uninitialized, // hardcoding to unitialized for now until short functions are properly supported
        home_object: Gc::new(ValueData::Undefined),
        new_target: new_target,
        outer_env: outer, // this will come from Environment set as a private property of F - https://tc39.github.io/ecma262/#sec-ecmascript-function-objects
        this_value: Gc::new(ValueData::Undefined), // TODO: this_value should start as an Option as its not always there to begin with
    })))
}

pub fn new_object_environment(object: Value, environment: Option<Environment>) -> Environment {
    Gc::new(GcCell::new(Box::new(ObjectEnvironmentRecord {
        bindings: object,
        outer_env: environment,
        /// Object Environment Records created for with statements (13.11)
        /// can provide their binding object as an implicit this value for use in function calls.
        /// The capability is controlled by a withEnvironment Boolean value that is associated
        /// with each object Environment Record. By default, the value of withEnvironment is false
        /// for any object Environment Record.
        with_environment: false,
    })))
}

pub fn new_global_environment(global: Value, this_value: Value) -> Environment {
    let obj_rec = Box::new(ObjectEnvironmentRecord {
        bindings: global,
        outer_env: None,
        /// Object Environment Records created for with statements (13.11)
        /// can provide their binding object as an implicit this value for use in function calls.
        /// The capability is controlled by a withEnvironment Boolean value that is associated
        /// with each object Environment Record. By default, the value of withEnvironment is false
        /// for any object Environment Record.
        with_environment: false,
    });

    let dcl_rec = Box::new(DeclerativeEnvironmentRecord {
        env_rec: HashMap::new(),
        outer_env: None,
    });

    Gc::new(GcCell::new(Box::new(GlobalEnvironmentRecord {
        object_record: obj_rec,
        global_this_binding: this_value,
        declerative_record: dcl_rec,
        var_names: HashSet::new(),
    })))
}