// Eryn Wells <eryn@erynwells.me>

use chessfriend_board::{fen::FromFenStr, Board};
use chessfriend_core::{Color, Piece, Shape, Square};
use chessfriend_moves::Builder as MoveBuilder;
use chessfriend_position::{fen::ToFenStr, PlacePieceStrategy, Position, ValidateMove};
use clap::{Arg, Command};
use rustyline::error::ReadlineError;
use rustyline::DefaultEditor;

struct CommandResult {
    should_continue: bool,
    should_print_position: bool,
}

impl Default for CommandResult {
    fn default() -> Self {
        CommandResult {
            should_continue: true,
            should_print_position: true,
        }
    }
}

struct State {
    position: Position,
}

fn command_line() -> Command {
    // strip out usage
    const PARSER_TEMPLATE: &str = "\
        {all-args}
    ";

    Command::new("explorer")
        .multicall(true)
        .arg_required_else_help(true)
        .subcommand_required(true)
        .subcommand_value_name("CMD")
        .subcommand_help_heading("COMMANDS")
        .help_template(PARSER_TEMPLATE)
        .subcommand(Command::new("fen").about("Print the current position as a FEN string"))
        .subcommand(
            Command::new("make")
                .arg(Arg::new("from").required(true))
                .arg(Arg::new("to").required(true))
                .about("Make a move"),
        )
        .subcommand(
            Command::new("place")
                .arg(Arg::new("color").required(true))
                .arg(Arg::new("piece").required(true))
                .arg(Arg::new("square").required(true))
                .about("Place a piece on the board"),
        )
        .subcommand(
            Command::new("sight")
                .arg(Arg::new("square").required(true))
                .about("Show sight of a piece on a square"),
        )
        .subcommand(
            Command::new("moves")
                .arg(Arg::new("square").required(true))
                .about("Show moves of a piece on a square"),
        )
        .subcommand(Command::new("print").about("Print the board"))
        .subcommand(Command::new("quit").alias("exit").about("Quit the program"))
        .subcommand(Command::new("starting").about("Reset the board to the starting position"))
}

fn respond(line: &str, state: &mut State) -> Result<CommandResult, String> {
    let args = shlex::split(line).ok_or("error: Invalid quoting")?;
    let matches = command_line()
        .try_get_matches_from(args)
        .map_err(|e| e.to_string())?;

    let mut result = CommandResult::default();

    match matches.subcommand() {
        Some(("print", _matches)) => {}
        Some(("quit", _matches)) => {
            result.should_continue = false;
            result.should_print_position = false;
        }
        Some(("fen", _matches)) => {
            println!(
                "{}",
                state
                    .position
                    .to_fen_str()
                    .map_err(|_| "error: Unable to generate FEN for current position")?
            );

            result.should_print_position = false;
        }
        Some(("make", matches)) => {
            let from_square = Square::from_algebraic_str(
                matches.get_one::<String>("from").ok_or("Missing square")?,
            )
            .map_err(|_| "Error: invalid square specifier")?;

            let to_square = Square::from_algebraic_str(
                matches.get_one::<String>("to").ok_or("Missing square")?,
            )
            .map_err(|_| "Error: invalid square specifier")?;

            let ply = MoveBuilder::new()
                .from(from_square)
                .to(to_square)
                .build()
                .map_err(|err| format!("Error: {err:?}"))?;

            state
                .position
                .make_move(ply, ValidateMove::Yes)
                .map_err(|err| format!("Error: {err}"))?;
        }
        Some(("place", matches)) => {
            let color = matches
                .get_one::<String>("color")
                .ok_or("Missing color descriptor")?;
            let color = Color::try_from(color).map_err(|_| "Invalid color descriptor")?;

            let shape = matches
                .get_one::<String>("piece")
                .ok_or("Missing piece descriptor")?;
            let shape = Shape::try_from(shape).map_err(|_| "Invalid piece descriptor")?;

            let square = matches
                .get_one::<String>("square")
                .ok_or("Missing square")?;
            let square = Square::from_algebraic_str(square)
                .map_err(|_| "Error: invalid square specifier")?;

            let piece = Piece::new(color, shape);

            state
                .position
                .place_piece(piece, square, PlacePieceStrategy::default())
                .map_err(|err| format!("Error: could not place piece: {err:?}"))?;
        }
        Some(("sight", matches)) => {
            let square = matches
                .get_one::<String>("square")
                .ok_or("Missing square")?;
            let square = Square::from_algebraic_str(square)
                .map_err(|_| "Error: invalid square specifier")?;

            let sight = state.position.sight(square);

            let display = state.position.display().highlight(sight);
            println!("\n{display}");

            result.should_print_position = false;
        }
        Some(("moves", matches)) => {
            let square = matches
                .get_one::<String>("square")
                .ok_or("Missing square")?;
            let square = Square::from_algebraic_str(square)
                .map_err(|_| "Error: invalid square specifier")?;

            let movement = state.position.movement(square);

            let display = state.position.display().highlight(movement);
            println!("\n{display}");

            result.should_print_position = false;
        }
        Some(("starting", _matches)) => {
            let starting_position = Position::starting();
            state.position = starting_position;
        }
        Some((name, _matches)) => unimplemented!("{name}"),
        None => unreachable!("Subcommand required"),
    }

    Ok(result)
}

fn main() -> Result<(), String> {
    let mut editor = DefaultEditor::new().map_err(|err| format!("Error: {err}"))?;

    let starting_position = Position::starting();
    let mut state = State {
        position: starting_position,
    };

    let mut should_print_position = true;

    loop {
        if should_print_position {
            println!("{}", &state.position);
            println!("{} to move.", state.position.board.active_color);
        }

        let readline = editor.readline("\n? ");
        match readline {
            Ok(line) => {
                let line = line.trim();
                if line.is_empty() {
                    continue;
                }

                match respond(line, &mut state) {
                    Ok(result) => {
                        should_print_position = result.should_print_position;
                        if !result.should_continue {
                            break;
                        }
                    }
                    Err(message) => println!("{message}"),
                }
            }
            Err(ReadlineError::Interrupted) => {
                println!("CTRL-C");
                break;
            }
            Err(ReadlineError::Eof) => {
                println!("CTRL-D");
                break;
            }
            Err(err) => {
                println!("Error: {err}");
                break;
            }
        }
    }

    Ok(())
}