use std::collections::HashMap;
use std::collections::hash_map::Entry;
use std::rc::Rc;
use std::fmt;
use std::fmt::Write;
use std::iter::IntoIterator;

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

type LineNumber = u32;
type SymbolTrackTable = HashMap<Rc<String>, LineNumber>;

#[derive(PartialEq, Eq, Hash, Debug)]
struct PathToSymbol(Vec<Rc<String>>);

#[derive(Debug)]
struct ScopeSegment {
  scope_name: Rc<String>,
  scope_type: ScopeType,
}

#[derive(Debug)]
enum ScopeType {
  Function,
  Type,
}

//cf. p. 150 or so of Language Implementation Patterns
pub struct SymbolTable {
  values: HashMap<PathToSymbol, Symbol>,
}

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

  fn add_new_symbol(&mut self, name: &Rc<String>, path: &Vec<Rc<String>>, symbol: Symbol) {
    let mut vec = path.clone();
    vec.push(name.clone());
    let symbol_path = PathToSymbol(vec);
    self.values.insert(symbol_path, symbol);
  }

  pub fn lookup_by_name(&self, name: &Rc<String>) -> Option<&Symbol> {
    self.lookup_by_path(name, &vec![])
  }

  pub fn lookup_by_path(&self, name: &Rc<String>, path: &Vec<Rc<String>>) -> Option<&Symbol> {
    let mut vec = path.clone();
    vec.push(name.clone());
    let symbol_path = PathToSymbol(vec);
    self.values.get(&symbol_path)
  }
}

#[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>>,
  },
  RecordConstructor {
    fields: HashMap<Rc<String>, Rc<String>>
  },
  Binding
}

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),
      RecordConstructor { fields: _fields } => write!(f, "RecordConstructor( <fields> )"),
      Binding => write!(f, "Binding"),
    }
  }
}

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> {
    let mut scope_name_stack = Vec::new();
    self.add_symbols_from_scope(&ast.0, &mut scope_name_stack)
  }

  fn add_symbols_from_scope<'a>(&'a mut self, statements: &Vec<Meta<Statement>>, scope_name_stack: &mut Vec<Rc<String>>) -> Result<(), String> {
    use self::ast::Declaration::*;

    fn insert_and_check_duplicate_symbol(table: &mut SymbolTrackTable, name: &Rc<String>) -> Result<(), String> {
      match table.entry(name.clone()) {
        Entry::Occupied(o) => {
          let line_number = o.get(); //TODO make this actually work
          Err(format!("Duplicate definition: {}. It's already defined at {}", name, line_number))
        },
        Entry::Vacant(v) => {
          let line_number = 0; //TODO should work
          v.insert(line_number);
          Ok(())
        }
      }
    }

    let mut seen_identifiers: SymbolTrackTable = HashMap::new();

    for meta in statements.iter() {
      let statement = meta.node();
      if let Statement::Declaration(decl) = statement {
        match decl {
          FuncSig(ref signature) => {
            insert_and_check_duplicate_symbol(&mut seen_identifiers, &signature.name)?;
            self.add_function_signature(signature, scope_name_stack)?
          }
          FuncDecl(ref signature, ref body) => {
            insert_and_check_duplicate_symbol(&mut seen_identifiers, &signature.name)?;
            self.add_function_signature(signature, scope_name_stack)?;
            scope_name_stack.push(signature.name.clone());
            let output = self.add_symbols_from_scope(body, scope_name_stack);
            let _ = scope_name_stack.pop();
            output?
          },
          TypeDecl { name, body, mutable } => {
            insert_and_check_duplicate_symbol(&mut seen_identifiers, &name.name)?;
            self.add_type_decl(name, body, mutable, scope_name_stack)?
          },
          Binding { name, .. } => {
            insert_and_check_duplicate_symbol(&mut seen_identifiers, name)?;
            let symbol = Symbol { name: name.clone(), spec: SymbolSpec::Binding };
            self.add_new_symbol(name, scope_name_stack, symbol);
          }
          _ => ()
        }
      }
    }
    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, scope_name_stack: &mut Vec<Rc<String>>) -> 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.add_new_symbol(
      &signature.name,
      scope_name_stack,
      Symbol { name: signature.name.clone(), spec }
    );
    Ok(())
  }

  fn add_type_decl(&mut self, type_name: &TypeSingletonName, body: &TypeBody, _mutable: &bool, scope_name_stack: &mut Vec<Rc<String>>) -> Result<(), String> {
    use crate::ast::{TypeIdentifier, Variant};
    let TypeBody(variants) = body;
    let TypeSingletonName { name, .. } = type_name;
    //scope_name_stack.push(name.clone()); //TODO adding this makes variants scoped under their
    //type name and breaks a lot of things - don't add it until importing names works
    //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.add_new_symbol(variant_name, scope_name_stack, 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.add_new_symbol(variant_name, scope_name_stack, symbol);
        },
        //TODO if there is only one variant, and it is a record, it doesn't need to have an
        //explicit name
        Variant::Record { name, members: _members } => {
          let fields = HashMap::new();
          let spec = SymbolSpec::RecordConstructor { fields };
          let symbol = Symbol { name: name.clone(), spec };
          self.add_new_symbol(name, scope_name_stack, symbol);
        },
      }
    }
    //scope_name_stack.pop();
    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))
  }
}


#[cfg(test)]
mod symbol_table_tests {
  use super::*;
  use crate::util::quick_ast;

  macro_rules! values_in_table {
    //TODO multiple values
    ($source:expr, $single_value:expr) => {
      {
      let mut symbol_table = SymbolTable::new();
      let ast = quick_ast($source);
      symbol_table.add_top_level_symbols(&ast).unwrap();
      match symbol_table.lookup_by_name($single_value) {
        Some(_spec) => (),
        None => panic!(),
      };
      }
    }
  }

  #[test]
  fn basic_symbol_table() {
    values_in_table! { "let a = 10; fn b() { 20 }", &rc!(b) };
  }

  #[test]
  fn no_duplicates() {
    let source = r#"
    fn a() { 1 }
    fn b() { 2 }
    fn a() { 3 }
    "#;
    let mut symbol_table = SymbolTable::new();
    let ast = quick_ast(source);
    let output = symbol_table.add_top_level_symbols(&ast).unwrap_err();
    assert!(output.contains("Duplicate"))
  }

  #[test]
  fn no_duplicates_2() {
    let source = r#"
    let a = 20;
    let q = 39;
    let a = 30;
    "#;
    let mut symbol_table = SymbolTable::new();
    let ast = quick_ast(source);
    let output = symbol_table.add_top_level_symbols(&ast).unwrap_err();
    assert!(output.contains("Duplicate"))
  }

  #[test]
  fn no_duplicates_3() {
    let source = r#"
    fn a() {
      let a = 20
      let b = 40
      a + b
    }

    fn q() {
      let x = 30
      let x = 33
    }
    "#;
    let mut symbol_table = SymbolTable::new();
    let ast = quick_ast(source);
    let output = symbol_table.add_top_level_symbols(&ast).unwrap_err();
    assert!(output.contains("Duplicate"))
  }

  fn dont_falsely_detect_duplicates() {
    let source = r#"
    let a = 20;
    fn some_func() {
      let a = 40;
      77
    }
    let q = 39;
    "#;
    let mut symbol_table = SymbolTable::new();
    let ast = quick_ast(source);
    symbol_table.add_top_level_symbols(&ast).unwrap();
    assert!(symbol_table.lookup_by_path(&rc!(a), &vec![]).is_some());
    assert!(symbol_table.lookup_by_path(&rc!(a), &vec![rc!(some_func)]).is_some());
  }

  #[test]
  fn enclosing_scopes() {
    let source = r#"
fn outer_func(x) {
  fn inner_func(arg) {
    arg
  }
  x + inner_func(x)
}"#;
    let mut symbol_table = SymbolTable::new();
    let ast = quick_ast(source);
    symbol_table.add_top_level_symbols(&ast).unwrap();
    assert!(symbol_table.lookup_by_path(&rc!(outer_func), &vec![]).is_some());
    assert!(symbol_table.lookup_by_path(&rc!(inner_func), &vec![rc!(outer_func)]).is_some());
  }

  #[test]
  fn enclosing_scopes_2() {
    let source = r#"
fn outer_func(x) {
  fn inner_func(arg) {
    arg
  }

  fn second_inner_func() {
    fn another_inner_func() {
    }
  }

  inner_func(x)
}"#;
    let mut symbol_table = SymbolTable::new();
    let ast = quick_ast(source);
    symbol_table.add_top_level_symbols(&ast).unwrap();
    println!("{}", symbol_table.debug_symbol_table());
    assert!(symbol_table.lookup_by_path(&rc!(outer_func), &vec![]).is_some());
    assert!(symbol_table.lookup_by_path(&rc!(inner_func), &vec![rc!(outer_func)]).is_some());
    assert!(symbol_table.lookup_by_path(&rc!(second_inner_func), &vec![rc!(outer_func)]).is_some());
    assert!(symbol_table.lookup_by_path(&rc!(another_inner_func), &vec![rc!(outer_func), rc!(second_inner_func)]).is_some());
  }

  #[test]
  fn enclosing_scopes_3() {
    let source = r#"
fn outer_func(x) {
  fn inner_func(arg) {
    arg
  }

  fn second_inner_func() {
    fn another_inner_func() {
    }
    fn another_inner_func() {
    }
  }

  inner_func(x)
}"#;
    let mut symbol_table = SymbolTable::new();
    let ast = quick_ast(source);
    let output = symbol_table.add_top_level_symbols(&ast).unwrap_err();
    assert!(output.contains("Duplicate"))
  }
}