use stopwatch::Stopwatch;

use std::cell::RefCell;
use std::rc::Rc;

use schala_repl::{ProgrammingLanguageInterface,
ComputationRequest, ComputationResponse,
LangMetaRequest, LangMetaResponse, GlobalOutputStats};
use crate::{reduced_ast, tokenizing, parsing, eval, typechecking, symbol_table};
use crate::error::SchalaError;

pub type SymbolTableHandle = Rc<RefCell<symbol_table::SymbolTable>>;

/// All the state necessary to parse and execute a Schala program are stored in this struct.
/// `state` represents the execution state for the AST-walking interpreter, the other fields
/// should be self-explanatory.
#[allow(dead_code)]
pub struct Schala {
  source_reference: SourceReference,
  state: eval::State<'static>,
  symbol_table: SymbolTableHandle,
  resolver: crate::scope_resolution::ScopeResolver<'static>,
  type_context: typechecking::TypeContext<'static>,
  active_parser: parsing::Parser,
}

impl Schala {
  //TODO implement documentation for language items
  /*
  fn handle_docs(&self, source: String) -> LangMetaResponse {
    LangMetaResponse::Docs {
      doc_string: format!("Schala item `{}` : <<Schala-lang documentation not yet implemented>>", source)
    }
  }
  */
}

impl Schala {
  /// Creates a new Schala environment *without* any prelude.
  fn new_blank_env() -> Schala {
    let symbols = Rc::new(RefCell::new(symbol_table::SymbolTable::new()));
    Schala {
      //TODO maybe these can be the same structure
      source_reference: SourceReference::new(),
      symbol_table: symbols.clone(),
      resolver: crate::scope_resolution::ScopeResolver::new(symbols.clone()),
      state: eval::State::new(),
      type_context: typechecking::TypeContext::new(),
      active_parser: parsing::Parser::new()
    }
  }

  /// Creates a new Schala environment with the standard prelude, which is defined as ordinary
  /// Schala code in the file `prelude.schala`
  pub fn new() -> Schala {
    let prelude = include_str!("../source-files/prelude.schala");
    let mut env = Schala::new_blank_env();

    let response = env.run_pipeline(prelude);
    if let Err(err) = response {
      panic!("Error in prelude, panicking: {}", err.display());
    }
    env
  }

  /// This is where the actual action of interpreting/compilation happens.
  /// Note: this should eventually use a query-based system for parallelization, cf.
  /// https://rustc-dev-guide.rust-lang.org/overview.html
  fn run_pipeline(&mut self, source: &str) -> Result<String, SchalaError> {
    // 1st stage - tokenization
    // TODO tokenize should return its own error type
    let tokens = tokenizing::tokenize(source);
    if let Some(err) = SchalaError::from_tokens(&tokens) {
      return Err(err)
    }

    //2nd stage - parsing
    self.active_parser.add_new_tokens(tokens);
    let mut ast = self.active_parser.parse()
      .map_err(|err| SchalaError::from_parse_error(err, &self.source_reference))?;

    // Symbol table
    self.symbol_table.borrow_mut().add_top_level_symbols(&ast)
      .map_err(|err| SchalaError::from_string(err, Stage::Symbols))?;

    // Scope resolution - requires mutating AST
    self.resolver.resolve(&mut ast)
      .map_err(|err| SchalaError::from_string(err, Stage::ScopeResolution))?;

    // Typechecking
    // TODO typechecking not working
    let _overall_type = self.type_context.typecheck(&ast)
      .map_err(SchalaError::from_type_error);

    // Reduce AST - TODO this doesn't produce an error yet, but probably should
    let symbol_table = self.symbol_table.borrow();
    let reduced_ast = reduced_ast::reduce(&ast, &symbol_table);

    // Tree-walking evaluator. TODO fix this
    let evaluation_outputs = self.state.evaluate(reduced_ast, true);
    let text_output: Result<Vec<String>, String> = evaluation_outputs
      .into_iter()
      .collect();

    let text_output: Result<Vec<String>, SchalaError> = text_output
      .map_err(|err| SchalaError::from_string(err, Stage::Evaluation));

    let eval_output: String = text_output
      .map(|v| { Iterator::intersperse(v.into_iter(), "\n".to_owned()).collect() })?;

      Ok(eval_output)
  }
}


/// Represents lines of source code
pub(crate) struct SourceReference {
  lines: Option<Vec<String>>
}

impl SourceReference {
  fn new() -> SourceReference {
    SourceReference { lines: None }
  }

  fn load_new_source(&mut self, source: &str) {
    //TODO this is a lot of heap allocations - maybe there's a way to make it more efficient?
    self.lines = Some(source.lines().map(|s| s.to_string()).collect()); }

  pub fn get_line(&self, line: usize) -> String {
    self.lines.as_ref().and_then(|x| x.get(line).map(|s| s.to_string())).unwrap_or(format!("NO LINE FOUND"))
  }
}

#[allow(dead_code)]
#[derive(Clone, Copy, Debug)]
pub(crate) enum Stage {
  Tokenizing,
  Parsing,
  Symbols,
  ScopeResolution,
  Typechecking,
  AstReduction,
  Evaluation,
}

fn stage_names() -> Vec<&'static str> {
  vec![
    "tokenizing",
    "parsing",
    "symbol-table",
    "scope-resolution",
    "typechecking",
    "ast-reduction",
    "ast-walking-evaluation"
  ]
}


impl ProgrammingLanguageInterface for Schala {
  type Config = ();
  fn language_name() -> String {
    "Schala".to_owned()
  }

  fn source_file_suffix() -> String {
    "schala".to_owned()
  }

  fn run_computation(&mut self, request: ComputationRequest<Self::Config>) -> ComputationResponse {
    let ComputationRequest { source, debug_requests: _, config: _ } = request;
    self.source_reference.load_new_source(source);
    let sw = Stopwatch::start_new();

    let main_output = self.run_pipeline(source)
      .map_err(|schala_err| schala_err.display());

    let global_output_stats = GlobalOutputStats {
      total_duration: sw.elapsed(),
      stage_durations: vec![]
    };

    ComputationResponse {
      main_output,
      global_output_stats,
      debug_responses: vec![]
    }
  }

  fn request_meta(&mut self, request: LangMetaRequest) -> LangMetaResponse {
    match request {
      LangMetaRequest::StageNames => LangMetaResponse::StageNames(stage_names().iter().map(|s| s.to_string()).collect()),
      _ => LangMetaResponse::Custom { kind: format!("not-implemented"), value: format!("") }
    }
  }
}