use std::ops::Add;

use hashbrown::HashMap;

use crate::ast::{Clause, Expr};
use crate::foreign::{Atom, Atomic, ExternFn};
use crate::interner::Tok;
use crate::representations::location::Location;
use crate::representations::project::{ProjectExt, ProjectModule, ProjectTree};
use crate::representations::tree::{ModEntry, ModMember, Module};
use crate::representations::{Primitive, VName};
use crate::utils::{pushed, Substack};

/// A lightweight module tree that can be built declaratively by hand to
/// describe libraries of external functions in Rust. It implements [Add] for
/// added convenience
#[derive(Clone, Debug)]
pub enum ConstTree {
  /// A function or constant
  Const(Expr<VName>),
  /// A submodule
  Tree(HashMap<Tok<String>, ConstTree>),
}
impl ConstTree {
  /// Describe a [Primitive]
  pub fn primitive(primitive: Primitive) -> Self {
    Self::Const(Expr {
      location: Location::Unknown,
      value: Clause::P(primitive),
    })
  }
  /// Describe an [ExternFn]
  pub fn xfn(xfn: impl ExternFn + 'static) -> Self {
    Self::primitive(Primitive::ExternFn(Box::new(xfn)))
  }
  /// Describe an [Atomic]
  pub fn atom(atom: impl Atomic + 'static) -> Self {
    Self::primitive(Primitive::Atom(Atom(Box::new(atom))))
  }
  /// Describe a module
  pub fn tree(arr: impl IntoIterator<Item = (Tok<String>, Self)>) -> Self {
    Self::Tree(arr.into_iter().collect())
  }
  /// Namespace the tree with the list of names
  pub fn namespace(
    pref: impl IntoIterator<Item = Tok<String>>,
    data: Self,
  ) -> Self {
    let mut iter = pref.into_iter();
    if let Some(ns) = iter.next() {
      Self::tree([(ns, Self::namespace(iter, data))])
    } else {
      data
    }
  }
  /// Unwrap the table of subtrees from a tree
  ///
  /// # Panics
  ///
  /// If this is a leaf node aka. constant and not a namespace
  pub fn unwrap_tree(self) -> HashMap<Tok<String>, Self> {
    match self {
      Self::Tree(map) => map,
      _ => panic!("Attempted to unwrap leaf as tree"),
    }
  }
}
impl Add for ConstTree {
  type Output = ConstTree;

  fn add(self, rhs: ConstTree) -> Self::Output {
    if let (Self::Tree(t1), Self::Tree(mut t2)) = (self, rhs) {
      let mut product = HashMap::new();
      for (key, i1) in t1 {
        if let Some(i2) = t2.remove(&key) {
          product.insert(key, i1 + i2);
        } else {
          product.insert(key, i1);
        }
      }
      product.extend(t2.into_iter());
      Self::Tree(product)
    } else {
      panic!("cannot combine tree and value fields")
    }
  }
}

fn from_const_tree_rec(
  path: Substack<Tok<String>>,
  consts: HashMap<Tok<String>, ConstTree>,
  file: &[Tok<String>],
) -> ProjectModule<VName> {
  let mut items = HashMap::new();
  let path_v = path.iter().rev_vec_clone();
  for (name, item) in consts {
    items.insert(name.clone(), ModEntry {
      exported: true,
      member: match item {
        ConstTree::Const(c) => ModMember::Item(c),
        ConstTree::Tree(t) =>
          ModMember::Sub(from_const_tree_rec(path.push(name), t, file)),
      },
    });
  }
  let exports = (items.keys())
    .map(|name| (name.clone(), pushed(&path_v, name.clone())))
    .collect();
  Module {
    items,
    imports: vec![],
    extra: ProjectExt {
      exports,
      file: Some(file.to_vec()),
      ..Default::default()
    },
  }
}

/// Convert a map of [ConstTree] into a [ProjectTree] that can be used with the
/// layered parsing system
pub fn from_const_tree(
  consts: HashMap<Tok<String>, ConstTree>,
  file: &[Tok<String>],
) -> ProjectTree<VName> {
  let module = from_const_tree_rec(Substack::Bottom, consts, file);
  ProjectTree(module)
}