--- Tic-tac-toe is a paper-and-pencil game for two players who take turns marking the spaces
--- in a three-by-three grid with X or O.
---
--- The player who succeeds in placing three of their marks in a horizontal, vertical, or
--- diagonal row is the winner. It is a solved game, with a forced draw assuming best play from both players.
---
--- The module Logic.Game contains the game logic.
module Web.TicTacToe;

open import Stdlib.Data.Nat.Ord;
open import Stdlib.Prelude;
open import Logic.Game;

-- Functions provided by the host

axiom hostLog : String → IO;

-- XCoord → YCoord → Width → Height → Color → IO
axiom hostFillRect : ℕ → ℕ → ℕ → ℕ → String → IO;

-- XCoord → YCoord → Text → Size → Color → Align → IO
axiom hostFillText : ℕ → ℕ → String → ℕ → String → ℕ → IO;

-- Nat extension

foreign c {
  int div(n, d) {
    return n/d;
  \}
};

infixl 7 div;
axiom div : ℕ → ℕ → ℕ;

compile div {
  c ↦ "div";
};

-- IO extensions

axiom IOUnit : IO;
compile IOUnit {
  c ↦ "0";
};

sequenceIO : List IO → IO;
sequenceIO ≔ foldr (>>) IOUnit;

mapIO : {A : Type} → (A → IO) → List A → IO;
mapIO f xs ≔ sequenceIO (map f xs);

-- List extensions

zip : {A : Type} → {B : Type} → List A → List B → List (A × B);
zip (a ∷ as) (b ∷ bs) ≔ (a , b) ∷ zip as bs;
zip _ _ ≔ nil;

rangeAux : ℕ → ℕ → List ℕ;
rangeAux _ zero ≔ nil;
rangeAux m (suc n) ≔ m ∷ rangeAux (suc m) n;

range : ℕ → List ℕ;
range n ≔ rangeAux zero n;

enumerate : {A : Type} → List A → List (ℕ × A);
enumerate l ≔ zip (range (length l)) l;

-- Formatting constants

squareWidth : ℕ;
squareWidth ≔ 100;

textSize : ℕ;
textSize ≔ 30;

xTextOffset : ℕ;
xTextOffset ≔ 50;

yTextOffset : ℕ;
yTextOffset ≔ 60;

canvasPadding : ℕ;
canvasPadding ≔ 8;

textColor : String;
textColor ≔ "#000000";

backgroundColor : String;
backgroundColor ≔ "#c4434e";

lightBackgroundColor : String;
lightBackgroundColor ≔ "#c7737a";

-- Rendering

inductive Align {
  left : Align;
  right : Align;
  center : Align;
};

alignNum : Align → ℕ;
alignNum left ≔ zero;
alignNum right ≔ one;
alignNum center ≔ two;

renderText : String → ℕ → ℕ → Align → IO;
renderText t row col a ≔ hostFillText ((squareWidth * row) + xTextOffset) ((squareWidth * col) + yTextOffset) t textSize textColor (alignNum a);

renderSymbol : Symbol → ℕ → ℕ → IO;
renderSymbol s row col ≔ renderText (showSymbol s) row col center;

renderNumber : ℕ → ℕ → ℕ → IO;
renderNumber n row col ≔ renderText (natToStr n) row col center;

renderSquare : ℕ → ℕ → Square → IO;
renderSquare row col (occupied s) ≔
    hostFillRect (squareWidth * row) (squareWidth * col) squareWidth squareWidth backgroundColor
    >> renderSymbol s row col;
renderSquare row col (empty n) ≔
    hostFillRect (squareWidth * row) (squareWidth * col) squareWidth squareWidth lightBackgroundColor
    >> renderNumber n row col;

renderRowAux : ℕ → (ℕ × Square) → IO;
renderRowAux col (row , s) ≔ renderSquare row col s;

renderRow : ℕ × (List Square) → IO;
renderRow (n , xs) ≔ mapIO (renderRowAux n) (enumerate xs);

renderBoard : Board → IO;
renderBoard (board squares) ≔ mapIO renderRow (enumerate squares);

renderFooterText : String → IO;
renderFooterText msg ≔ renderText msg 0 3 left;

nextPlayerText : Symbol → String;
nextPlayerText s ≔ "Next player: " ++str (showSymbol s);

renderError : Error → IO;
renderError noError ≔ IOUnit;
renderError (continue msg) ≔ renderText msg 0 3 left;
renderError (terminate msg) ≔ renderText msg 0 3 left;

renderGameState : GameState → IO;
renderGameState (state b _ (terminate msg)) ≔ renderBoard b >> renderFooterText msg;
renderGameState (state b p (continue msg)) ≔ renderBoard b >> renderFooterText (nextPlayerText p) >> renderText (msg) 0 4 left;
renderGameState (state b p _) ≔ renderBoard b >> renderFooterText (nextPlayerText p);

renderAndReturn : GameState → GameState;
renderAndReturn s ≔ const s (renderGameState s);

selectedSquare : ℕ → ℕ → ℕ;
selectedSquare row col ≔ 3 * (col div squareWidth) + (row div squareWidth) + 1;

-- API

initGame : GameState;
initGame ≔ const beginState (renderGameState beginState >> renderText "Click on a square to make a move" 0 4 left);

move : GameState → ℕ → ℕ → GameState;
move (state b p (terminate e)) x y ≔ renderAndReturn (state b p (terminate e));
move s x y ≔ renderAndReturn (playMove (validMove (selectedSquare x y)) s);

end;