#!/usr/bin/env BQN
# The game is controlled with the vim movement keys:
# h: left, j: down, k: up, l: right
# it needs a VT-100 compatible terminal

Merge←{ # Merges a row of tiles to the right
  moved←4⊸↑⌾⌽ 0⊸≠⊸/𝕩 # remove empty tiles to move the tiles as far as possible
  m←⌽0∾˜(¬⊸∧`=˝˘)⌾⌽2↕moved # which tiles to merge
  r←(⟨∞⟩){t←⊑m ⋄ m↩1↓m ⋄ t◶⟨𝕨∾𝕩,(¯1↓𝕨)∾𝕩+¯1⊑𝕨⟩@}˜´moved # Merge tiles
  4⊸↑⌾⌽⌽∞⊸≠⊸/r # Resize the result
}
Step←>·Merge¨<˘   # Merges each row of the board
Up←Step⌾(⌽⍉∘⌽)    # Each direction merges the board
Down←Step⌾⍉       # by rotating it to the correct orientation, merging the rows and reversing the rotation
Right←Step
Left←Step⌾(⌽˘)    
Spawn←{i←(•rand.Range∘≠⊑⊢)(0⊸= /○⥊ ↕∘≢)𝕩 ⋄ 2˙⌾(i⊸⊑) 𝕩} # Spawns a 2 at a random empty position
Lose←Left∘Right∘Down∘Up⊸≡ # Losing condition, no moves change the board
Win←∨´·∨˝2048⊸= #  Winning condition, 2048!

board←Spawn 4‿4⥊0
e←@+27
•term.RawMode 1 # 
•Out e∾"[?25l"∾e∾"[2J"∾e∾"[H" # Cursor to origin, hide it and clear screen
{𝕤⋄
    •Out e∾"[H" # Cursor to origin
    •Out "Controls: h: left, j: down, k: up, l: right, q: quit"
    •Show board 
    key←•term.CharB @ # Read key
    {𝕤⋄•Out e∾"[?12l"∾e∾"[?25h"⋄•Exit 0}⍟(key='q')@ # Quit key?
    move←⊑(key="hjkl")/Left‿Down‿Up‿Right # Get movement function from the key
    {𝕤⋄board↩Spawn∘Move 𝕩}⍟(Move⊸≢) board # Generate the next board if the move is valid
    {𝕤⋄•Out "You win!" ⋄ •Exit 0}⍟Win board
    {𝕤⋄•Out "You lose!" ⋄ •Exit 1}⍟Lose board
}•_While_{𝕤⋄¬Lose board}@
•Out e∾"[?12l"∾e∾"[?25h" # Restore the cursor