use std::collections::HashMap;
use std::rc::Rc;
use std::fmt;
use std::fmt::Write;

use crate::ast;
use crate::ast::{TypeBody, TypeSingletonName, Signature};
use crate::typechecking::TypeName;

//cf. p. 150 or so of Language Implementation Patterns
pub struct SymbolTable {
  pub values: HashMap<Rc<String>, Symbol> //TODO this will eventually have real type information
}

//TODO add various types of lookups here, maybe multiple hash tables internally? also make values
//non-public
impl SymbolTable {
  pub fn new() -> SymbolTable {
    SymbolTable { values: HashMap::new() }
  }

  pub fn lookup_by_name(&self, name: &Rc<String>) -> Option<&Symbol> {
    self.values.get(name)
  }
}

#[derive(Debug)]
pub struct Symbol {
  pub name: Rc<String>,
  pub spec: SymbolSpec,
}

impl fmt::Display for Symbol {
  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    write!(f, "<Name: {}, Spec: {}>", self.name, self.spec)
  }
}

#[derive(Debug)]
pub enum SymbolSpec {
  Func(Vec<TypeName>),
  DataConstructor {
    index: usize,
    type_name: Rc<String>,
    type_args: Vec<Rc<String>>,
  },
}

impl fmt::Display for SymbolSpec {
  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    use self::SymbolSpec::*;
    match self {
      Func(type_names) => write!(f, "Func({:?})", type_names),
      DataConstructor { index, type_name, type_args } => write!(f, "DataConstructor(idx: {})({:?} -> {})", index, type_args, type_name),
    }
  }
}

impl SymbolTable {
  /* note: this adds names for *forward reference* but doesn't actually create any types. solve that problem
   * later */
  pub fn add_top_level_symbols(&mut self, ast: &ast::AST) -> Result<(), String> {
    use self::ast::Statement;
    use self::ast::Declaration::*;
    for statement in ast.0.iter() {
      let statement = statement.node();
      if let Statement::Declaration(decl) = statement {
        match decl {
          FuncSig(signature) | FuncDecl(signature, _) => self.add_function_signature(signature)?,
          TypeDecl { name, body, mutable } => self.add_type_decl(name, body, mutable)?,
          _ => ()
        }
      }
    }
    Ok(())
  }
  pub fn debug_symbol_table(&self) -> String {
    let mut output = format!("Symbol table\n");
    for (name, sym) in &self.values {
      write!(output, "{} -> {}\n", name, sym).unwrap();
    }
    output
  }

  fn add_function_signature(&mut self, signature: &Signature) -> Result<(), String> {
    let mut local_type_context = LocalTypeContext::new();
    let types = signature.params.iter().map(|param| match param {
      (_, Some(type_identifier)) => Rc::new(format!("{:?}", type_identifier)),
      (_, None) => local_type_context.new_universal_type()
    }).collect();
    let spec = SymbolSpec::Func(types);
    self.values.insert(
      signature.name.clone(),
      Symbol { name: signature.name.clone(), spec }
    );
    Ok(())
  }

  fn add_type_decl(&mut self, type_name: &TypeSingletonName, body: &TypeBody, _mutable: &bool) -> Result<(), String> {
    use crate::ast::{TypeIdentifier, Variant};
    let TypeBody(variants) = body;
    let TypeSingletonName { name, .. } = type_name;
    //TODO figure out why _params isn't being used here
    for (index, var) in variants.iter().enumerate() {
      match var {
        Variant::UnitStruct(variant_name) => {
          let spec = SymbolSpec::DataConstructor {
            index,
            type_name: name.clone(),
            type_args: vec![],
          };
          self.values.insert(variant_name.clone(), Symbol { name: variant_name.clone(), spec });
        },
        Variant::TupleStruct(variant_name, tuple_members) => {
          let type_args = tuple_members.iter().map(|type_name| match type_name {
            TypeIdentifier::Singleton(TypeSingletonName { name, ..}) => name.clone(),
            TypeIdentifier::Tuple(_) => unimplemented!(),
          }).collect();
          let spec = SymbolSpec::DataConstructor {
            index,
            type_name: name.clone(),
            type_args
          };
          let symbol = Symbol { name: variant_name.clone(), spec };
          self.values.insert(variant_name.clone(), symbol);
        },
        Variant::Record { .. } => return Err(format!("Record types not supported yet")),
      }
    }
    Ok(())
  }
}

struct LocalTypeContext {
  state: u8
}
impl LocalTypeContext {
  fn new() -> LocalTypeContext {
    LocalTypeContext { state: 0 }
  }

  fn new_universal_type(&mut self) -> TypeName {
    let n = self.state;
    self.state += 1;
    Rc::new(format!("{}", (('a' as u8) + n) as char))
  }
}