<?php
#declare(strict_types = 1);
# PHP Notice:  Trying to access array offset on value of type bool in /var/www/html/dev.biotorrents.de/classes/seqhash.class.php on line 233

/**
 * Seqhash
 *
 * Implements Keoni's Seqhash algorithm for DNA/RNA/protein sequences,
 * e.g., v1_DCD_4b0616d1b3fc632e42d78521deb38b44fba95cca9fde159e01cd567fa996ceb9
 *
 * > The first element is the version tag (v1 for version 1).
 * > If there is ever a Seqhash version 2, this tag will differentiate seqhashes.
 *
 * > The second element is the metadata tag, which has 3 letters.
 * > The first letter codes for the sequenceType (D for DNA, R for RNA, and P for Protein).
 * > The second letter codes for whether or not the sequence is circular (C for Circular, L for Linear).
 * > The final letter codes for whether or not the sequence is double stranded (D for Double stranded, S for Single stranded).
 *
 * > The final element is the blake3 hash of the sequence (once rotated and complemented).
 *
 * Requires the php-blake3 extension from:
 * https://github.com/cypherbits/php-blake3
 *
 * @see https://blog.libredna.org/post/seqhash/
 * @see https://github.com/TimothyStiles/poly/blob/prime/hash.go
 * @see https://github.com/TimothyStiles/poly/blob/prime/hash_test.go
 */

class Seqhash
{
    /**
     * boothLeastRotation
     *
     * Gets the least rotation of a circular string.
     * @see https://en.wikipedia.org/wiki/Lexicographically_minimal_string_rotation
     */
    public function boothLeastRotation(string $Sequence)
    {
        # First concatenate the sequence to itself to avoid modular arithmatic
        # todo: Use buffers just for speed? May get annoying with larger sequences
        $Sequence = $Sequence . $Sequence;
        $LeastRotationIndex = 0;

        # Initializing failure slice
        $FailureSlice = array_fill(0, strlen($Sequence), -1);

        /*
        for ($i = 0; $i <= strlen($Sequence); $i++) {
            $FailureSlice[$i] = -1;
        }
        */

        # Iterate through each character in the doubled-over sequence
        for ($CharacterIndex = 1; $CharacterIndex < strlen($Sequence); $CharacterIndex++) {

            # Get character
            $Character = $Sequence[$CharacterIndex];

            # Get failure
            $Failure = $FailureSlice[$CharacterIndex - $LeastRotationIndex - 1];

            # While failure !== -1 and character !== the character found at the least rotation + failure + 1
            while ($Failure !== -1 && $Character !== $Sequence[$LeastRotationIndex + $Failure + 1]) {

                # If character is lexically less than whatever is at $LeastRotationIndex, update $LeastRotationIndex
                if ($Character < $Sequence[$LeastRotationIndex + $Failure + 1]) {
                    $LeastRotationIndex = $CharacterIndex - $Failure - 1;
                }

                # Update failure using previous failure as index?
                $Failure = $FailureSlice[$Failure];
            } # while

            # If character does not equal whatever character is at leastRotationIndex plus failure
            if ($Character !== $Sequence[$LeastRotationIndex + $Failure + 1]) {

                # If character is lexically less then what is rotated, $LeastRotatationIndex gets value of $CharacterIndex
                if ($Character < $Sequence[$LeastRotationIndex]) {
                    $LeastRotationIndex = $CharacterIndex;
                }

                # Assign -1 to whatever is at the index of difference between character and rotation indices
                $FailureSlice[$CharacterIndex - $LeastRotationIndex] = -1;
    
            # If character does equal whatever character is at $LeastRotationIndex + $Failure
            } else {
                # Assign $Failure + 1 at the index of difference between character and rotation indices
                $FailureSlice[$CharacterIndex - $LeastRotationIndex] = $Failure + 1;
            }
        } # for

        return $LeastRotationIndex;
    }


    /**
     * rotateSequence
     *
     * Rotates circular sequences to a deterministic point.
     */
    public function rotateSequence(string $Sequence)
    {
        $RotationIndex = $this->boothLeastRotation($Sequence);

        # Writing the same sequence twice
        # PHP has no strings.Builder.WriteString
        $ConcatenatedSequence = $Sequence . $Sequence;

        # https://stackoverflow.com/a/2423867
        $Length = $RotationIndex % strlen($Sequence);
        return substr($Sequence, $Length) . substr($Sequence, 0, $Length);
    }


    /**
     * reverseComplement
     *
     * Takes the reverse complement of a sequence.
     * Doesn't validate the sequence alphabet first.
     */
    public function reverseComplement(string $Sequence)
    {
        # Normalize the sequence
        $Sequence = strtoupper($Sequence);

        /**
         * Provides 1:1 mapping between bases and their complements.
         * Kind of ghetto, but lowercase replaces help stop extra flips.
         * @see https://github.com/TimothyStiles/poly/blob/prime/sequence.go
         */
        $RuneMap = [
            'A' => 't',
            'B' => 'v',
            'C' => 'g',
            'D' => 'h',
            'G' => 'c',
            'H' => 'd',
            'K' => 'm',
            'M' => 'k',
            'N' => 'n',
            'R' => 'y',
            'S' => 's',
            'T' => 'a',
            'U' => 'a',
            'V' => 'b',
            'W' => 'w',
            'Y' => 'r',
        ];

        return $ComplementString = strtoupper(
            str_replace(
                array_keys($RuneMap),
                array_values($RuneMap),
                $Sequence
            )
        );
    }


    /**
     * hash
     *
     * Create a Seqhash from a string.
     */
    public function hash(
        string $Sequence,
        string $SequenceType,
        bool   $Circular = false,
        bool   $DoubleStranded = true
    ) {
        # Check for Blake3 support
        if (!extension_loaded('blake3')) {
            throw new Exception('Please install and enable the php-blake3 extension.');
        }

        # By definition, Seqhashes are of uppercase sequences
        $Sequence = strtoupper($Sequence);

        # If RNA, convert to a DNA sequence
        # The hash itself between a DNA and RNA sequence will not be different,
        # but their Seqhash will have a different metadata string (R vs. D)
        if ($SequenceType === 'RNA') {
            $Sequence = str_replace('T', 'U', $Sequence);
        }

        # Run checks on the input
        if (!in_array($SequenceType, ['DNA', 'RNA', 'PROTEIN'])) {
            throw new Exception("SequenceType must be one of [DNA, RNA, PROTEIN]. Got $SequenceType.");
        }

        # Check the alphabet used
        $SequenceRegex = '/[ATUGCYRSWKMBDHVNZ]/';
        $ProteinRegex = '/[ACDEFGHIKLMNPQRSTVWYUO*BXZ]/';

        # todo: Refactor this to detect $SequenceType from alphabet
        if ($SequenceType === 'DNA' || $SequenceType === 'RNA') {
            foreach (str_split($Sequence) as $Letter) {
                if (!preg_match($SequenceRegex, $Letter)) {
                    throw new Exception("Only letters ATUGCYRSWKMBDHVNZ are allowed for DNA/RNA. Got $Letter.");
                }
            }
        }

        /**
         * Selenocysteine (Sec; U) and pyrrolysine (Pyl; O) are added
         * in accordance with https://www.uniprot.org/help/sequences
         *
         * The release notes https://web.expasy.org/docs/relnotes/relstat.html
         * also state there are Asx (B), Glx (Z), and Xaa (X) amino acids,
         * so these are added in as well.
         */
        else {
            foreach (str_split($Sequence) as $Letter) {
                if (!preg_match($ProteinRegex, $Letter)) {
                    throw new Exception("Only letters ACDEFGHIKLMNPQRSTVWYUO*BXZ are allowed for proteins. Got $Letter.");
                }
            }
        }
    
        # There is no check for circular proteins since proteins can be circular
        if ($SequenceType === 'PROTEIN' && $DoubleStranded) {
            throw new Exception("Proteins can't be double stranded.");
        }

        # Gets deterministic sequence based off of metadata + sequence
        #switch ($Circular && $DoubleStranded) {
        switch ([$Circular, $DoubleStranded]) {
            #case (true && true):
            case [true, true]:
                $PotentialSequences = [
                    $this->rotateSequence($Sequence),
                    $this->rotateSequence($this->reverseComplement($Sequence)),
                ];
                $DeterministicSequence = sort($PotentialSequences)[0];
                break;

            #case (true && false):
            case [true, false]:
                $DeterministicSequence = $this->rotateSequence($Sequence);
                break;

            #case (false && true):
            case [false, true]:
                $PotentialSequences = [
                    $Sequence,
                    $this->reverseComplement($Sequence),
                ];
                $DeterministicSequence = sort($PotentialSequences)[0];
                break;

            #case (false && false):
            case [false, false]:
                $DeterministicSequence = $Sequence;
                break;

            default:
                break;
        }

        /**
         * Build 3 letter metadata
         */

        # Get first letter: D for DNA, R for RNA, and P for Protein
        switch ($SequenceType) {
            case 'DNA':
                $SequenceTypeLetter = 'D';
                break;
            
            case 'RNA':
                $SequenceTypeLetter = 'R';
                break;
            
            case 'PROTEIN':
                $SequenceTypeLetter = 'P';
                break;
                
            default:
                break;
            }

        # Get 2nd letter: C for circular, L for Linear
        if ($Circular) {
            $CircularLetter = 'C';
        } else {
            $CircularLetter = 'L';
        }

        # Get 3rd letter: D for Double stranded, S for Single stranded
        if ($DoubleStranded) {
            $DoubleStrandedLetter = 'D';
        } else {
            $DoubleStrandedLetter = 'S';
        }

        # php-blake3 returns hex by default,
        # binary if $rawOutput = true
        return
            'v1'
          . '_'
          . $SequenceTypeLetter
          . $CircularLetter
          . $DoubleStrandedLetter
          . '_'
          . blake3($DeterministicSequence);
    }


    /**
     * validate
     *
     * Validates a Seqhash's metadata.
     * Doesn't check the Blake3 hash itself,
     * because php-blake3 has no such feature.
     */
    public function validate(string $Seqhash)
    {
        $Parts = explode('_', $Seqhash);

        # Check version info
        if ($Parts[0] !== 'v1') {
            throw new Exception("Invalid version info. Got $Parts[0].");
        }

        # Check 3 letter metadata
        $Meta = str_split($Parts[1]);
        if (!in_array($Meta[0], ['D', 'R', 'P'])
         || !in_array($Meta[1], ['C', 'L'])
         || !in_array($Meta[2], ['D', 'S'])) {
            throw new Exception("Invalid metadata. Got $Parts[1].");
        }

        # Check Blake3 hex and hash length
        if (!ctype_xdigit($Parts[2]) || strlen($Parts[2] !== 64)) {
            throw new Exception("Invalid Blake3 hash. Expected a 64-character hex string.");
        }

        return true;
    }


    /**
     * gcContent
     *
     * Bonus feature!
     * Calculate GC content of a DNA sequence.
     * Shamelessly ripped from kennypavan/BioPHP.
     *
     * @see https://github.com/kennypavan/BioPHP/blob/master/BioPHP.php
     */
    public function gcContent(string $Sequence, int $Precision = 2)
    {
        $Sequence = strtoupper($Sequence);
        
        $G = substr_count($Sequence, 'G');
        $C = substr_count($Sequence, 'C');

        return number_format((($G + $C) / strlen($Sequence)) * 100, $Precision);
    }
}