use stopwatch::Stopwatch;

use std::time::Duration;
use std::cell::RefCell;
use std::rc::Rc;
use std::collections::HashSet;

use itertools::Itertools;
use schala_repl::{ProgrammingLanguageInterface,
ComputationRequest, ComputationResponse,
LangMetaRequest, LangMetaResponse, GlobalOutputStats,
DebugResponse, DebugAsk};
use crate::{ast, reduced_ast, tokenizing, parsing, eval, typechecking, symbol_table};

/// 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.
pub struct Schala {
  source_reference: SourceReference,
  state: eval::State<'static>,
  symbol_table: Rc<RefCell<symbol_table::SymbolTable>>,
  type_context: typechecking::TypeContext<'static>,
  active_parser: Option<parsing::Parser>,
}

impl Schala {
  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 {
      source_reference: SourceReference::new(),
      symbol_table: symbols.clone(),
      state: eval::State::new(symbols),
      type_context: typechecking::TypeContext::new(),
      active_parser: None,
    }
  }

  /// 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!("prelude.schala");
    let mut s = Schala::new_blank_env();

    let request = ComputationRequest { source: prelude, debug_requests: HashSet::default() };
    let response = s.run_computation(request);
    if let Err(msg) = response.main_output {
      panic!("Error in prelude, panicking: {}", msg);
    }
    s
  }

  fn handle_debug_immediate(&self, request: DebugAsk) -> DebugResponse {
    use DebugAsk::*;
    match request {
      Timing => DebugResponse { ask: Timing, value: format!("Invalid") },
      ByStage { stage_name, token } => match &stage_name[..] {
        "symbol-table" => {
          let value = self.symbol_table.borrow().debug_symbol_table();
          DebugResponse {
            ask: ByStage { stage_name: format!("symbol-table"), token },
            value
          }
        },
        s => {
          DebugResponse {
            ask: ByStage { stage_name: s.to_string(), token: None },
            value: format!("Not-implemented")
          }
        }
      }
    }
  }
}

fn tokenizing(input: &str, _handle: &mut Schala, comp: Option<&mut PassDebugArtifact>) -> Result<Vec<tokenizing::Token>, String> {
  let tokens = tokenizing::tokenize(input);
  comp.map(|comp| {
    let token_string = tokens.iter().map(|t| t.to_string_with_metadata()).join(", ");
    comp.add_artifact(token_string);
  });

  let errors: Vec<String> = tokens.iter().filter_map(|t| t.get_error()).collect();
  if errors.len() == 0 {
    Ok(tokens)
  } else {
    Err(format!("{:?}", errors))
  }
}

fn parsing(input: Vec<tokenizing::Token>, handle: &mut Schala, comp: Option<&mut PassDebugArtifact>) -> Result<ast::AST, String> {
  use crate::parsing::Parser;
  use ParsingDebugType::*;

  let mut parser = handle.active_parser.take().unwrap_or_else(|| Parser::new(input));
  let ast = parser.parse();

  comp.map(|comp| {
    let debug_format = comp.parsing.as_ref().unwrap_or(&CompactAST);
    let debug_info = match debug_format {
      CompactAST => match ast{
        Ok(ref ast) => ast.compact_debug(),
        Err(_) => "Error - see output".to_string(),
      },
      ExpandedAST => match ast{
        Ok(ref ast) => ast.expanded_debug(),
        Err(_) => "Error - see output".to_string(),
      },
      Trace => parser.format_parse_trace(),
    };
    comp.add_artifact(debug_info);
  });
  ast.map_err(|err| format_parse_error(err, handle))
}

fn format_parse_error(error: parsing::ParseError, handle: &mut Schala) -> String {
  let line_num = error.token.line_num;
  let ch = error.token.char_num;
  let line_from_program = handle.source_reference.get_line(line_num);
  let location_pointer = format!("{}^", " ".repeat(ch));

  let line_num_digits = format!("{}", line_num).chars().count();
  let space_padding = " ".repeat(line_num_digits);

  let production = match error.production_name {
    Some(n) => format!("\n(from production \"{}\")", n),
    None => "".to_string()
  };

  format!(r#"
{error_msg}{production}
{space_padding} |
{line_num} | {}
{space_padding} | {}
"#, line_from_program, location_pointer, error_msg=error.msg, space_padding=space_padding, line_num=line_num, production=production
)
}

fn symbol_table(input: ast::AST, handle: &mut Schala, comp: Option<&mut PassDebugArtifact>) -> Result<ast::AST, String> {
  let () = handle.symbol_table.borrow_mut().add_top_level_symbols(&input)?;
  comp.map(|comp| {
    let debug = handle.symbol_table.borrow().debug_symbol_table();
    comp.add_artifact(debug);
  });
  Ok(input)
}

fn scope_resolution(mut input: ast::AST, handle: &mut Schala, _com: Option<&mut PassDebugArtifact>) -> Result<ast::AST, String> {
  let mut symbol_table = handle.symbol_table.borrow_mut();
  let mut resolver = crate::scope_resolution::ScopeResolver::new(&mut symbol_table);
  let () = resolver.resolve(&mut input)?;
  Ok(input)
}

fn typechecking(input: ast::AST, handle: &mut Schala, comp: Option<&mut PassDebugArtifact>) -> Result<ast::AST, String> {
  let result = handle.type_context.typecheck(&input);

  comp.map(|comp| {
    comp.add_artifact(match result {
      Ok(ty) => ty.to_string(),
      Err(err) => format!("Type error: {}", err.msg)
    });
  });

  Ok(input)
}

fn ast_reducing(input: ast::AST, handle: &mut Schala, comp: Option<&mut PassDebugArtifact>) -> Result<reduced_ast::ReducedAST, String> {
  let ref symbol_table = handle.symbol_table.borrow();
  let output = reduced_ast::reduce(&input, symbol_table);
  comp.map(|comp| comp.add_artifact(format!("{:?}", output)));
  Ok(output)
}

fn eval(input: reduced_ast::ReducedAST, handle: &mut Schala, comp: Option<&mut PassDebugArtifact>) -> Result<String, String> {
  comp.map(|comp| comp.add_artifact(handle.state.debug_print()));
  let evaluation_outputs = handle.state.evaluate(input, true);
  let text_output: Result<Vec<String>, String> = evaluation_outputs
    .into_iter()
    .collect();

  let eval_output: Result<String, String> = text_output
    .map(|v| { v.into_iter().intersperse(format!("\n")).collect() });
  eval_output
}

/// Represents lines of source code
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()); }

  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"))
  }
}

enum ParsingDebugType {
  CompactAST,
  ExpandedAST,
  Trace
}

#[derive(Default)]
struct PassDebugArtifact {
  parsing: Option<ParsingDebugType>,
  artifacts: Vec<String>

}
impl PassDebugArtifact {
  fn add_artifact(&mut self, artifact: String) {
    self.artifacts.push(artifact)
  }
}

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


impl ProgrammingLanguageInterface for Schala {
  fn get_language_name(&self) -> String { format!("Schala") }
  fn get_source_file_suffix(&self) -> String { format!("schala") }

  fn run_computation(&mut self, request: ComputationRequest) -> ComputationResponse {
    struct PassToken<'a> {
      schala: &'a mut Schala,
      stage_durations: &'a mut Vec<(String, Duration)>,
      sw: &'a Stopwatch,
      debug_requests: &'a HashSet<DebugAsk>,
      debug_responses: &'a mut Vec<DebugResponse>,
    }

    fn output_wrapper<Input, Output, F>(n: usize, func: F, input: Input, token: &mut PassToken) -> Result<Output, String>
      where F: Fn(Input, &mut Schala, Option<&mut PassDebugArtifact>) -> Result<Output, String>
    {
      let stage_names = stage_names();
      let cur_stage_name = stage_names[n];
      let ask = token.debug_requests.iter().find(|ask| ask.is_for_stage(cur_stage_name));

      let parsing = match ask {
        Some(DebugAsk::ByStage { token, .. }) if cur_stage_name == "parsing" => Some(
          token.as_ref().map(|token| match &token[..] {
            "compact" => ParsingDebugType::CompactAST,
            "expanded" => ParsingDebugType::ExpandedAST,
            "trace" => ParsingDebugType::Trace,
            _ => ParsingDebugType::CompactAST,
          }).unwrap_or(ParsingDebugType::CompactAST)
        ),
        _ => None,
      };

      let mut debug_artifact = ask.map(|_| PassDebugArtifact {
        parsing, ..Default::default()
      });

      let output = func(input, token.schala, debug_artifact.as_mut());

      //TODO I think this is not counting the time since the *previous* stage
      token.stage_durations.push((cur_stage_name.to_string(), token.sw.elapsed()));
      if let Some(artifact) = debug_artifact {
        for value in artifact.artifacts.into_iter() {
          let resp = DebugResponse { ask: ask.unwrap().clone(), value };
          token.debug_responses.push(resp);
        }
      }
      output
    }

    let ComputationRequest { source, debug_requests } = request;
    self.source_reference.load_new_source(source);
    let sw = Stopwatch::start_new();
    let mut stage_durations = Vec::new();
    let mut debug_responses = Vec::new();
    let mut tok = PassToken { schala: self, stage_durations: &mut stage_durations, sw: &sw, debug_requests: &debug_requests, debug_responses: &mut debug_responses };

    let main_output: Result<String, String> = Ok(source)
      .and_then(|source| output_wrapper(0, tokenizing, source, &mut tok))
      .and_then(|tokens| output_wrapper(1, parsing, tokens, &mut tok))
      .and_then(|ast| output_wrapper(2, symbol_table, ast, &mut tok))
      .and_then(|ast| output_wrapper(3, scope_resolution, ast, &mut tok))
      .and_then(|ast| output_wrapper(4, typechecking, ast, &mut tok))
      .and_then(|ast| output_wrapper(5, ast_reducing, ast, &mut tok))
      .and_then(|reduced_ast| output_wrapper(6, eval, reduced_ast, &mut tok));

    let total_duration = sw.elapsed();
    let global_output_stats = GlobalOutputStats {
      total_duration, stage_durations
    };

    ComputationResponse {
      main_output,
      global_output_stats,
      debug_responses,
    }
  }

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