Decode Chess Move

Question

As the title says, given a valid chess move in algebraic notation, produce the string describing the move.

Example:

fxg8=Q+  -> Pawn takes g8 promotes to Queen check
Bb7#     -> Bishop to b7 mate

Here is a list of all the keywords and their respective notation

R     -> Rook             x   -> takes
N     -> Knight           +   -> check
B     -> Bishop           #   -> mate
Q     -> Queen            =   -> promotes to
K     -> King             0-0 -> short castle
0-0-0 -> long castle

---

Note: Long and short castle can be represented with either number 0 or letter O uppercase. You can choose any you'd like.

From wiki: Both algebraic notation and descriptive notation indicate kingside castling as 0-0 and queenside castling as 0-0-0 (using the digit zero). Portable Game Notation and some publications use O-O for kingside castling and O-O-O for queenside castling (using the letter O) instead

---

Piece moves format follows {Piece name} to {square} Moves without a piece are consider pawn moves. Example:

g4  -> Pawn to g4
Nh7 -> Knight to h7

For ambiguous moves, input will specify both departure rank and file. Example:

Rh8b8 -> Rook h8 to b8
Qb3e6 -> Queen b3 to e6

---

Input

String with a valid chess move in algebraic notation

Output

String describing the move (Upper case or Lower case is ok)

---

Test Cases

fxg8=Q+  -> Pawn takes g8 promotes to Queen check
Bb7#     -> Bishop to b7 mate
0-0      -> short castle
0-0+     -> short castle check
0-0-0#   -> long castle mate
Rxg8     -> Rook takes g8
fxe6     -> Pawn takes e6
Ra8g8    -> Rook a8 to g8
Nb3#     -> Knight to b3 mate
a8=B     -> Pawn to a8 promotes to Bishop
Ra8xg8   -> Rook a8 takes g8

Answer 1

JavaScript (ES6), 206 bytes

Takes some inspiration from Neil's Retina answer. But in the end, this is quite different.

s=>[/O-O-/,/O-/,/.\d/g,/to (?=.*o)/,/x to/,..."=+#ORKBQN",/^.? /].map((r,j)=>s=s.replace(r,`long/short/ to $&// takes/ promotes to / check/ mate/ castle/Rook/King/Bishop/Queen/Knight/Pawn `.split`/`[j]))&&s

Try it online!

Decoding examples

e4
 to e4
Pawn to e4

fxg8=Q+
fx to g8=Q+
f takes g8=Q+
f takes g8 promotes to Q+
f takes g8 promotes to Q check
f takes g8 promotes to Queen check
Pawn takes g8 promotes to Queen check

Ra8g8
R to a8 to g8
R a8 to g8
Rook a8 to g8

---

Retina 0.8.2, 144 bytes

-4 bytes thanks to @Neil

The same logic back-ported to Retina.

O-O-
long
O-
short
.\d
 to $&
-2`to 

x to
 takes
=
 promotes to 
\+
 check
#
 mate
O
 castle
R
Rook
K
King
B
Bishop
Q
Queen
N
Knight
^.? 
Pawn 

Try it online!

Answer 2

Ruby -p, 249 bytes

-p flag loops over input, modifies it with these two fat regex functions, and spits it back out.

sub(/(^[a-g]?)?(.\d)?(x)?(?=.\d)|O(-O)+/){$4?%w(short long)[~/$//5]+' castle':"#{$1&&?P}#{' '+$2if$2} #{$3?:takes:'to'} "}
gsub(/[#+=B-R]/){|m|m[/\W/]?' '+%w(mate promotes\ to\  _ check)[m.ord%5]:%w(King Queen Rook Bishop Pawn).find{_1[m]}||:Knight}

Attempt This Online!

Partially ungolfed

sub(/(^[a-g]?)?(.\d)?(x)?(?=.\d)/) { # Replace the part that says which piece moves where
 "#{
    $1&&?P                           # 'P' (Pawn) if group 1 is present
                                     #  (matches if input starts with /[a-g]x/ or /.\d/)
   }#{
    ' '+$2if$2                       # Group 2 with leading space if present
                                     #  (for Qb3e6 -> Queen b3 to e6 etc.)
   } #{
    $3?:takes:'to'                   # 'takes' if group 3 (x) is present, else 'to'
                                     #  (uses label notation :takes to save bytes)
   } "
}
sub(/O(-O)+/) { # Replace castling notation (original program checks for group 4)
   %w(short long)                    # ['short', 'long']
                 [
                  ~/$/               # Index of end of input (3-4 if O-O, 5-6 if O-O-O)
                      /5]            # Divide by 5 to get correct index for short vs long
    + ' castle'                      # Add the ' castle' part
}
gsub(/[#+=B-R]/) {|m|                # Match checkmate, check, promotes, pieces
   m[/\W/]?                          # If non-letter (checkmate, check, promote)
    ' '+                             # Leading space
    ['mate','promotes to ', nil, 'check'][m.ord%5]
                                     # Match the corresponding phrase by using mod 5
                                     # '#' -> 0, '=' -> 1, '+' -> 3

  :                                  # Otherwise (if letter)
    %w(King Queen Rook Bishop Pawn).find{_1[m]}
                                     # Find the piece that has that letter
    ||:Knight                        # If none found, it's a Knight (N can't match)
}
```

Answer 3

Charcoal, 165 146 bytes

ＦＳ≡ιx≔⊞ＯΦυ⊖Ｌκtakesυ-≔⟦⎇⊖Ｌυlong¦short⟧υ¿№βι≔⊞Ｏ⁺∨⁻υ⟦to⟧⟦Pawn⟧…⟦to⟧¬№υtakesιυ¿Σι⊞υ⁺⊟υι⊞υ§⪪”↶.⭆～»¤πη‽q∕¶lj,⊙↥⟲Qmº5σ¡²JＮ¤εlθw(LθΦG▶⁵@W｜]”¶⌕KQRBNO+#ι⪫υ 

Try it online! Link is to verbose version of code. Explanation:

ＦＳ≡ι

Loop over the characters of the input string.

x≔⊞ＯΦυ⊖Ｌκtakesυ

For x, push takes to the result, but remove any bare letters (which will be the source file of a pawn capture).

-≔⟦⎇⊖Ｌυlong¦short⟧υ

For -, change castle to short but short castle to long. (The castle comes from the O below.)

¿№βι≔⊞Ｏ⁺∨⁻υ⟦to⟧⟦Pawn⟧…⟦to⟧¬№υtakesιυ

For other lower case letters, this might be the source or the destination file. Remove any existing to and add a new to, unless there is a takes in the string. Then push the file to the result.

¿Σι⊞υ⁺⊟υι

For digits, append the rank to the file.

⊞υ§⪪”↶.⭆～»¤πη‽q∕¶lj,⊙↥⟲Qmº5σ¡²JＮ¤εlθw(LθΦG▶⁵@W｜]”¶⌕KQRBNO+#ι

For other characters, push the piece name or notation to the result.

⪫υ 

Join the collected words on spaces.

Answer 4

Retina 0.8.2, 176 172 171 bytes

(([A-Z])(..)?|(.?))(x)?(.\d)
$2$#4$*P $3$#3$* to$5 $6
ox
akes
O-O-
long
O-
short
O
 castle
#
 mate
\+
 check
=
 promotes to 
K
King
Q
Queen
R
Rook
B
Bishop
N
Knight
P
Pawn

Try it online! Link includes test cases. Explanation:

(([A-Z])(..)?|(.?))(x)?(.\d)
$2$#4$*P $3$#3$* to$5 $6

Identify the piece or pawn being moved, whether there is a disambiguation square for the piece, and its destination.

ox
akes

Fix up the case of a capture.

O-O-
long
O-
short
O
 castle

Process castling.

#
 mate
\+
 check
=
 promotes to 

Process other symbols.

K
King
Q
Queen
R
Rook
B
Bishop
N
Knight
P
Pawn

Expand the piece names.

Edit: Saved 4 bytes thanks to @Arnauld. Saved 1 byte thanks to @ValueInk.

Answer 5

C# .NET console app, 333 bytes

Assumes using System; using System.Text.RegularExpressions;

string m=Regex.Replace(args[0],"(?<!x)[a-h](?!.*[x|a-h])","t${0}"),r=m[0]>96?"Pawn ":m[0]<49?(m.Length>4?"long":"short")+" castle ":"";foreach(var c in m){int i="-0RNBQKx+#=t".IndexOf(c);r+=",,,Rook ,Knight ,Bishop ,Queen ,King ,takes ,check,mate,promotes to ,to ".Split(',')[i+1];if(c!=m[0]&i<0)r+=c+(c<57?" ":"");}Console.Write(r);

Commented

// add a 't' to the move string wherever "to" is needed
string m = Regex.Replace(args[0], "(?<!x)[a-h](?!.*[x|a-h])", "t${0}"), 

// start with 'Pawn' if the first character is a file, to or takes
    r = m[0] > 96 ? "Pawn " 

// decode castles now so we can ignore -,0 later
    : m[0]<49 ? (m.Length>4 ? "long" : "short") + " castle " : "";
    
// iterate through the move string 
foreach (var c in m) 
{
    // map each code to a word, with space where needed
    // 0,- map to empty string
    int i = "-0RNBQKx+#=t".IndexOf(c);
    r += ",,,Rook ,Knight ,Bishop ,Queen ,King ,takes ,check,mate,promotes to ,to ".Split(',')[i + 1];

    // anything that doesn't map is assumed to be a square reference and added to the result
    // except if it's the first character because if it's not x or t then it must be a file with no rank.
    // also add a space if it's a digit
    if (c != m[0] & i < 0)
        r += c + (c < 57 ? " " : "");
}

Console.Write(r);