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| 1 | <?php |
| 2 | |
| 3 | namespace Wikimedia\LangConv\Construct; |
| 4 | |
| 5 | use Wikimedia\Assert\Assert; |
| 6 | |
| 7 | /** |
| 8 | * A mutable FST. |
| 9 | */ |
| 10 | class MutableFST { |
| 11 | /** Special alphabet symbol for `nothing` used in AT&T format FST files. */ |
| 12 | public const EPSILON = '@0@'; |
| 13 | /** Special alphabet symbol for upper-side `?` used in AT&T format FST files. */ |
| 14 | public const UNKNOWN = '@_UNKNOWN_SYMBOL_@'; |
| 15 | /** Special alphabet symbol for lower-side `?` used in AT&T format FST files. */ |
| 16 | public const IDENTITY = '@_IDENTITY_SYMBOL_@'; |
| 17 | |
| 18 | private $alphabet = []; |
| 19 | private $states = []; |
| 20 | |
| 21 | /** |
| 22 | * Create a new MutableFST with the given alphabet. |
| 23 | * @param string[] $alphabet |
| 24 | */ |
| 25 | public function __construct( array $alphabet ) { |
| 26 | // Create start state |
| 27 | $this->newState(); |
| 28 | // Set up alphabet |
| 29 | foreach ( $alphabet as $tok ) { |
| 30 | $this->alphabet[$tok] = true; |
| 31 | } |
| 32 | $this->alphabet[self::EPSILON] = true; |
| 33 | $this->alphabet[self::IDENTITY] = true; |
| 34 | $this->alphabet[self::UNKNOWN] = true; |
| 35 | } |
| 36 | |
| 37 | /** |
| 38 | * Add a new state to this FST. |
| 39 | * @return State the new state. |
| 40 | */ |
| 41 | public function newState(): State { |
| 42 | $id = count( $this->states ); |
| 43 | $s = $this->states[] = new State( $id ); |
| 44 | return $s; |
| 45 | } |
| 46 | |
| 47 | /** |
| 48 | * Return the start state of this FST. |
| 49 | * @return State the start state. |
| 50 | */ |
| 51 | public function getStartState(): State { |
| 52 | return $this->states[0]; |
| 53 | } |
| 54 | |
| 55 | /** |
| 56 | * Apply the given FST to the array of input tokens. Symbols in |
| 57 | * 'upper' are matched and symbols in 'lower' are emitted. |
| 58 | * @param string[] $input |
| 59 | * @return array<array<string>> |
| 60 | */ |
| 61 | public function applyDown( array $input ): array { |
| 62 | return $this->applyUpDown( $input, true ); |
| 63 | } |
| 64 | |
| 65 | /** |
| 66 | * Apply the given FST to the array of input tokens. Symbols in |
| 67 | * 'lower' are matched and symbols in 'upper' are emitted. |
| 68 | * @param string[] $input |
| 69 | * @return array<array<string>> |
| 70 | */ |
| 71 | public function applyUp( array $input ): array { |
| 72 | return $this->applyUpDown( $input, false ); |
| 73 | } |
| 74 | |
| 75 | /** |
| 76 | * Apply the given FST to the array of input tokens. |
| 77 | * @param string[] $input array of input tokens |
| 78 | * @param bool $isDown Whether to apply 'up' or 'down' |
| 79 | * @return array<array<string>> |
| 80 | */ |
| 81 | private function applyUpDown( array $input, bool $isDown ): array { |
| 82 | // This is an extremely simple implementation, made for validating |
| 83 | // the FST not efficient execution. |
| 84 | $results = []; |
| 85 | $stack = []; |
| 86 | $flagRE = '/^@([PNRDCU])[.]([^.@]+)(?:[.]([^@]+))?@$/D'; |
| 87 | $addTok = static function ( $toks, $t ) use ( $flagRE ) { |
| 88 | if ( $t === self::EPSILON || preg_match( $flagRE, $t ) ) { |
| 89 | // skip token |
| 90 | } else { |
| 91 | $toks[] = $t; |
| 92 | } |
| 93 | return $toks; |
| 94 | }; |
| 95 | $stack[] = [ $this->getStartState(), 0, [], [] ]; |
| 96 | while ( count( $stack ) > 0 ) { |
| 97 | [ $state, $pos, $flags, $emitted ] = array_pop( $stack ); |
| 98 | $tok = $pos < count( $input ) ? $input[$pos] : null; |
| 99 | if ( $tok !== null && !isset( $this->alphabet[$tok] ) ) { |
| 100 | $tok = self::UNKNOWN; |
| 101 | } |
| 102 | foreach ( $state->edges as $e ) { |
| 103 | if ( $isDown ) { |
| 104 | $match = $e->upper; |
| 105 | $output = $e->lower; |
| 106 | } else { |
| 107 | $match = $e->lower; |
| 108 | $output = $e->upper; |
| 109 | } |
| 110 | // Treat IDENTITY and UNKNOWN as identical (applyDown/applyUp) |
| 111 | if ( $match === self::IDENTITY ) { |
| 112 | $match = self::UNKNOWN; |
| 113 | } |
| 114 | if ( $output === self::UNKNOWN ) { |
| 115 | $output = self::IDENTITY; |
| 116 | } |
| 117 | // Does this edge match? |
| 118 | if ( $output === self::IDENTITY && $tok !== null ) { |
| 119 | $output = $input[$pos]; |
| 120 | } |
| 121 | if ( $match === self::EPSILON ) { |
| 122 | $stack[] = [ $e->to, $pos, $flags, $addTok( $emitted, $output ) ]; |
| 123 | } elseif ( preg_match( $flagRE, $match, $flagInfo, PREG_UNMATCHED_AS_NULL ) === 1 ) { |
| 124 | $op = $flagInfo[1]; |
| 125 | $feature = $flagInfo[2]; |
| 126 | $value = $flagInfo[3] ?? null; |
| 127 | $f = $flags[$feature] ?? null; |
| 128 | if ( $op === 'P' ) { |
| 129 | Assert::invariant( $value !== null, "P not C!" ); |
| 130 | $flags[$feature] = $value; |
| 131 | } elseif ( $op === 'C' ) { |
| 132 | Assert::invariant( $value === null, "C not P!" ); |
| 133 | $flags[$feature] = null; |
| 134 | } elseif ( $op === 'N' ) { |
| 135 | // @phan-suppress-next-line PhanImpossibleCondition |
| 136 | Assert::invariant( false, 'N not supported' ); |
| 137 | } elseif ( $op === 'R' || $op === 'D' ) { |
| 138 | $m = ( $value === null ) ? ( $f !== null ) : ( $f === $value ); |
| 139 | if ( $op === 'R' ? ( !$m ) : $m ) { |
| 140 | continue; |
| 141 | } |
| 142 | } elseif ( $op === 'U' ) { |
| 143 | Assert::invariant( $value !== null, "Unify with what?" ); |
| 144 | if ( $f === null || $f === $value ) { |
| 145 | $flags[$feature] = $value; |
| 146 | } else { |
| 147 | continue; |
| 148 | } |
| 149 | } |
| 150 | $stack[] = [ $e->to, $pos, $flags, $addTok( $emitted, $output ) ]; |
| 151 | } elseif ( $match === $tok && $tok !== null ) { |
| 152 | $stack[] = [ $e->to, $pos + 1, $flags, $addTok( $emitted, $output ) ]; |
| 153 | } |
| 154 | } |
| 155 | if ( $tok === null && $state->isFinal ) { |
| 156 | $results[] = $emitted; |
| 157 | } |
| 158 | } |
| 159 | return $results; |
| 160 | } |
| 161 | |
| 162 | /** |
| 163 | * Perform simple optimization on the FST, trimming unreachable states |
| 164 | * and attempting to combine edges containing epsilons. |
| 165 | */ |
| 166 | public function optimize(): void { |
| 167 | $reachable = []; |
| 168 | $stateWorklist = []; |
| 169 | $stateWorklist[$this->getStartState()->id] = $this->getStartState(); |
| 170 | while ( count( $stateWorklist ) > 0 ) { |
| 171 | $state = array_pop( $stateWorklist ); |
| 172 | $reachable[$state->id] = true; |
| 173 | $edgeWorklist = $state->edges; // worklist |
| 174 | while ( count( $edgeWorklist ) > 0 ) { |
| 175 | $edge = array_pop( $edgeWorklist ); |
| 176 | if ( $edge === null ) { |
| 177 | continue; /* removed edge */ |
| 178 | } |
| 179 | |
| 180 | if ( $edge->to->isFinal ) { |
| 181 | if ( !isset( $reachable[$edge->to->id] ) ) { |
| 182 | $stateWorklist[$edge->to->id] = $edge->to; |
| 183 | } |
| 184 | continue; |
| 185 | } |
| 186 | $nEdge = count( $edge->to->edges ); |
| 187 | if ( $nEdge === 0 ) { |
| 188 | $state->edges[$edge->id] = null; // remove |
| 189 | // XXX requeue all states which point to this |
| 190 | continue; |
| 191 | } elseif ( $nEdge === 1 ) { |
| 192 | $nextEdge = $edge->to->edges[0]; |
| 193 | if ( $nextEdge === null ) { |
| 194 | /* deleted. Fall through. */ |
| 195 | } elseif ( |
| 196 | $edge->lower === self::EPSILON && |
| 197 | $nextEdge->upper === self::EPSILON |
| 198 | ) { |
| 199 | $edge->lower = $nextEdge->lower; |
| 200 | $edge->to = $nextEdge->to; |
| 201 | $edgeWorklist[] = $edge; |
| 202 | continue; |
| 203 | } elseif ( |
| 204 | $edge->upper === self::EPSILON && |
| 205 | $nextEdge->lower == self::EPSILON |
| 206 | ) { |
| 207 | $edge->upper = $nextEdge->upper; |
| 208 | $edge->to = $nextEdge->to; |
| 209 | $edgeWorklist[] = $edge; |
| 210 | continue; |
| 211 | } elseif ( |
| 212 | $edge->upper === self::EPSILON && |
| 213 | $edge->lower === self::EPSILON |
| 214 | ) { |
| 215 | $edge->upper = $nextEdge->upper; |
| 216 | $edge->lower = $nextEdge->lower; |
| 217 | $edge->to = $nextEdge->to; |
| 218 | $edgeWorklist[] = $edge; |
| 219 | continue; |
| 220 | } elseif ( |
| 221 | $nextEdge->upper === self::EPSILON && |
| 222 | $nextEdge->lower === self::EPSILON |
| 223 | ) { |
| 224 | $edge->to = $nextEdge->to; |
| 225 | $edgeWorklist[] = $edge; |
| 226 | continue; |
| 227 | } |
| 228 | } |
| 229 | // fall through |
| 230 | if ( !isset( $reachable[$edge->to->id] ) ) { |
| 231 | $stateWorklist[$edge->to->id] = $edge->to; |
| 232 | } |
| 233 | } |
| 234 | } |
| 235 | // Renumber states and edges |
| 236 | $j = 0; |
| 237 | for ( $i = 0; $i < count( $this->states ); $i++ ) { |
| 238 | $s = $this->states[$i]; |
| 239 | if ( isset( $reachable[$s->id] ) ) { |
| 240 | $s->id = $j++; |
| 241 | $this->states[$s->id] = $s; |
| 242 | // renumber edges |
| 243 | $k = 0; |
| 244 | for ( $l = 0; $l < count( $s->edges ); $l++ ) { |
| 245 | $e = $s->edges[$l]; |
| 246 | if ( $e !== null ) { |
| 247 | $e->id = $k++; |
| 248 | $s->edges[$e->id] = $e; |
| 249 | } |
| 250 | } |
| 251 | array_splice( $s->edges, $k ); |
| 252 | } |
| 253 | } |
| 254 | array_splice( $this->states, $j ); |
| 255 | } |
| 256 | |
| 257 | /** |
| 258 | * Write an AT&T format description of this FST to the given filehandle. |
| 259 | * @param resource $handle |
| 260 | */ |
| 261 | public function writeATT( $handle ): void { |
| 262 | // Write an AT&T format FST file |
| 263 | foreach ( $this->states as $state ) { |
| 264 | $state->writeATT( $handle ); |
| 265 | } |
| 266 | // Now write the final states |
| 267 | foreach ( $this->states as $state ) { |
| 268 | if ( $state->isFinal ) { |
| 269 | fwrite( $handle, strval( $state->id ) . "\n" ); |
| 270 | } |
| 271 | } |
| 272 | } |
| 273 | } |