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

use crate::schala::SourceMapHandle;
use crate::source_map::{SourceMap, LineNumber};
use crate::ast;
use crate::ast::{ItemId, TypeBody, TypeSingletonName, Signature, Statement, StatementKind, ModuleSpecifier};
use crate::typechecking::TypeName;


#[allow(unused_macros)]
macro_rules! fqsn {
  ( $( $name:expr ; $kind:tt),* ) => {
    {
      let mut vec = vec![];
      $(
        vec.push(crate::symbol_table::ScopeSegment::new(std::rc::Rc::new($name.to_string())));
      )*
      FullyQualifiedSymbolName(vec)
    }
  };
}

mod symbol_trie;
use symbol_trie::SymbolTrie;
mod test;

/// Keeps track of what names were used in a given namespace. Call try_register to add a name to
/// the table, or report an error if a name already exists.
struct DuplicateNameTrackTable {
  table: HashMap<Rc<String>, LineNumber>,
}

impl DuplicateNameTrackTable {
  fn new() -> DuplicateNameTrackTable {
    DuplicateNameTrackTable { table: HashMap::new() }
  }

  fn try_register(&mut self, name: &Rc<String>, id: &ItemId, source_map: &SourceMap) -> Result<(), LineNumber> {
    match self.table.entry(name.clone()) {
      Entry::Occupied(o) => {
        let line_number = o.get();
        Err(*line_number)
      },
      Entry::Vacant(v) => {
        let line_number = if let Some(loc) = source_map.lookup(id) {
          loc.line_num
        } else {
          0
        };
        v.insert(line_number);
        Ok(())
      }
    }
  }
}

#[derive(PartialEq, Eq, Hash, Debug, Clone, PartialOrd, Ord)]
pub struct FullyQualifiedSymbolName(pub Vec<ScopeSegment>);

impl fmt::Display for FullyQualifiedSymbolName {
  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    let FullyQualifiedSymbolName(v) = self;
    for segment in v {
      write!(f, "::{}", segment)?;
    }
    Ok(())
  }
}

#[derive(Debug, Clone, Eq, PartialEq, Hash, PartialOrd, Ord)]
pub struct ScopeSegment {
  pub name: Rc<String>, //TODO maybe this could be a &str, for efficiency?
}

impl fmt::Display for ScopeSegment {
  fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
    let kind = ""; //TODO implement some kind of kind-tracking here
    write!(f, "{}{}", self.name, kind)
  }
}

impl ScopeSegment {
  pub fn new(name: Rc<String>) ->  ScopeSegment {
    ScopeSegment { name }
  }
}


//cf. p. 150 or so of Language Implementation Patterns
pub struct SymbolTable {
  source_map_handle: SourceMapHandle,
  symbol_path_to_symbol: HashMap<FullyQualifiedSymbolName, Symbol>,
  id_to_fqsn: HashMap<ItemId, FullyQualifiedSymbolName>,
  symbol_trie: SymbolTrie,
}

impl SymbolTable {
  pub fn new(source_map_handle: SourceMapHandle) -> SymbolTable {
    SymbolTable {
      source_map_handle,
      symbol_path_to_symbol: HashMap::new(),
      id_to_fqsn: HashMap::new(),
      symbol_trie: SymbolTrie::new()
    }
  }

  pub fn map_id_to_fqsn(&mut self, id: &ItemId, fqsn: FullyQualifiedSymbolName) {
    self.id_to_fqsn.insert(id.clone(), fqsn);
  }

  pub fn get_fqsn_from_id(&self, id: &ItemId) -> Option<FullyQualifiedSymbolName> {
    self.id_to_fqsn.get(&id).cloned()
  }

  fn add_new_symbol(&mut self, local_name: &Rc<String>, scope_path: &Vec<ScopeSegment>, spec: SymbolSpec) {
    let mut vec: Vec<ScopeSegment> = scope_path.clone();
    vec.push(ScopeSegment { name: local_name.clone() });
    let fully_qualified_name = FullyQualifiedSymbolName(vec);
    let symbol = Symbol { local_name: local_name.clone(), fully_qualified_name: fully_qualified_name.clone(), spec };
    self.symbol_trie.insert(&fully_qualified_name);
    self.symbol_path_to_symbol.insert(fully_qualified_name, symbol);
  }

  pub fn lookup_by_fqsn(&self, fully_qualified_path: &FullyQualifiedSymbolName) -> Option<&Symbol> {
    self.symbol_path_to_symbol.get(fully_qualified_path)
  }

  pub fn lookup_children_of_fqsn(&self, path: &FullyQualifiedSymbolName) -> Vec<FullyQualifiedSymbolName> {
    self.symbol_trie.get_children(path)
  }
}

#[derive(Debug)]
pub struct Symbol {
  pub local_name: Rc<String>, //TODO does this need to be pub?
  fully_qualified_name: FullyQualifiedSymbolName,
  pub spec: SymbolSpec,
}

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

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

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 { type_name, index, ..} => write!(f, "RecordConstructor(idx: {})(<members> -> {})", index, type_name),
      Binding => write!(f, "Binding"),
      Type { name } => write!(f, "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> {
    let mut scope_name_stack = Vec::new();
    self.add_symbols_from_scope(&ast.statements, &mut scope_name_stack)
  }

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

    let mut seen_identifiers = DuplicateNameTrackTable::new();
    let mut seen_modules = DuplicateNameTrackTable::new();

    for statement in statements.iter() {
      match statement {
        Statement { kind: StatementKind::Declaration(decl), id } => {
          match decl {
            FuncSig(ref signature) => {
              seen_identifiers.try_register(&signature.name, &id, &self.source_map_handle.borrow())
                .map_err(|line| format!("Duplicate function definition: {}. It's already defined at {}", signature.name, line))?;
              self.add_function_signature(signature, scope_name_stack)?
            }
            FuncDecl(ref signature, ref body) => {
              seen_identifiers.try_register(&signature.name, &id, &self.source_map_handle.borrow())
                .map_err(|line| format!("Duplicate function definition: {}. It's already defined at {}", signature.name, line))?;
              self.add_function_signature(signature, scope_name_stack)?;
              scope_name_stack.push(ScopeSegment{
                name: signature.name.clone(),
              });
              let output = self.add_symbols_from_scope(body, scope_name_stack);
              scope_name_stack.pop();
              output?
            },
            TypeDecl { name, body, mutable } => {
              seen_identifiers.try_register(&name.name, &id, &self.source_map_handle.borrow())
                .map_err(|line| format!("Duplicate type definition: {}. It's already defined at {}", name.name, line))?;
              self.add_type_decl(name, body, mutable, scope_name_stack)?
            },
            Binding { name, .. } => {
              seen_identifiers.try_register(&name, &id, &self.source_map_handle.borrow())
                .map_err(|line| format!("Duplicate variable definition: {}. It's already defined at {}", name, line))?;
              self.add_new_symbol(name, scope_name_stack, SymbolSpec::Binding);
            }
            _ => ()
          }
        },
        Statement { kind: StatementKind::Module(ModuleSpecifier { name, contents}), id } => {
          seen_modules.try_register(&name, &id, &self.source_map_handle.borrow())
            .map_err(|line| format!("Duplicate module definition: {}. It's already defined at {}", name, line))?;
          scope_name_stack.push(ScopeSegment { name: name.clone() });
          let output = self.add_symbols_from_scope(contents, scope_name_stack);
          scope_name_stack.pop();
          output?
        },
        _ => ()
      }
    }
    Ok(())
  }
  pub fn debug_symbol_table(&self) -> String {
    let mut output = format!("Symbol table\n");
    let mut sorted_symbols: Vec<(&FullyQualifiedSymbolName, &Symbol)> = self.symbol_path_to_symbol.iter().collect();
    sorted_symbols.sort_by(|(fqsn, _), (other_fqsn, _)| fqsn.cmp(other_fqsn));
    for (name, sym) in sorted_symbols.iter() {
      write!(output, "{} -> {}\n", name, sym).unwrap();
    }
    output
  }

  fn add_function_signature(&mut self, signature: &Signature, scope_name_stack: &mut Vec<ScopeSegment>) -> Result<(), String> {
    let mut local_type_context = LocalTypeContext::new();
    let types = signature.params.iter().map(|param| match param.anno {
      Some(ref type_identifier) => Rc::new(format!("{:?}", type_identifier)),
      None => local_type_context.new_universal_type()
    }).collect();
    self.add_new_symbol(&signature.name, scope_name_stack, SymbolSpec::Func(types));
    Ok(())
  }

  //TODO handle type mutability
  fn add_type_decl(&mut self, type_name: &TypeSingletonName, body: &TypeBody, _mutable: &bool, scope_name_stack: &mut Vec<ScopeSegment>) -> Result<(), String> {
    use crate::ast::{TypeIdentifier, Variant};
    let TypeBody(variants) = body;
    let ref type_name = type_name.name;


    let type_spec = SymbolSpec::Type {
      name: type_name.clone(),
    };
    self.add_new_symbol(type_name, &scope_name_stack, type_spec);

    scope_name_stack.push(ScopeSegment{
      name: type_name.clone(),
    });
    //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: type_name.clone(),
            type_args: vec![],
          };
          self.add_new_symbol(variant_name, scope_name_stack, spec);
        },
        Variant::TupleStruct(variant_name, tuple_members) => {
          //TODO fix the notion of a tuple type
          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: type_name.clone(),
            type_args
          };
          self.add_new_symbol(variant_name, scope_name_stack, spec);
        },
        Variant::Record { name, members: defined_members } => {
          let mut members = HashMap::new();
          let mut duplicate_member_definitions = Vec::new();
          for (member_name, member_type) in defined_members {
            match members.entry(member_name.clone()) {
              Entry::Occupied(_) => duplicate_member_definitions.push(member_name.clone()),
              Entry::Vacant(v) => {
                v.insert(match member_type {
                  TypeIdentifier::Singleton(TypeSingletonName { name, ..}) => name.clone(),
                  TypeIdentifier::Tuple(_) => unimplemented!(),
                });
              }
            }
          }
          if duplicate_member_definitions.len() != 0 {
            return Err(format!("Duplicate member(s) in definition of type {}: {:?}", type_name, duplicate_member_definitions));
          }
          let spec = SymbolSpec::RecordConstructor { index, type_name: type_name.clone(), members };
          self.add_new_symbol(name, scope_name_stack, spec);
        },
      }
    }
    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))
  }
}