Simple PHP class that handles a simple key value store, It uses flat textfiles for this. You can store values of string, Array, Objects. Etc.

EyeKeyValueStore.php

<?PHP
namespace EyeDentify\Tools;

class EyeKeyValueStore {
    
    /*
        EyeKeyValueStore class v1.1
        author: Magnus Bonnevier.
        e-mail: magnus.bonnevier@gmail.com
        website: www.magnusbonnevier.se
                
        Simple class that handles simple key value store.
        It uses flat textfiles for this.
        A default path to a directory for the files are provided,
        change this for your needs.
        
        The directory needs to be writable ofcourse.
        
        default key value files is created like this:
        _keyname.php
        
        You can change Prefix and Suffix to your needs.
        
        Code is free to use, you are not obligated to 
        reference me, but it would be appreciated.
    */
        
    /* init vars */
    protected $storePath = 'key_value_store/';
    protected $filePrefix = '_';
    protected $fileSuffix = '.php';
        
    /* init class constructor */
    public function __construct($path = null) {
                
        /* if key value store path supplied then override the default one */
        if(!$path == '') {
            
            if(!is_string($path)) {
                exit('Error __construct(), you must supply a path string!');
            }
            
            $this->storePath = $path;
        }
        
        /* return this for chainability */
        return $this;
    }
    
    /* set the filename prefix */
    public function setFilePrefix ($prefixStr = null) {
        
        if(!$prefixStr == '') {
            
            if(!is_string($prefixStr)) {
                exit('Error setFilePrefix(), you must supply a string!');
            }
            $this->filePrefix = $prefixStr;    
        }
                
        return $this;
    }
        
    /* set the filename suffix */
    public function setFileSuffix ($suffixStr = null) {
        
        if(!$suffixStr == '') {
            
            if(!is_string($suffixStr)) {
                exit('Error setFileSuffix(), you must supply a string!');
            }
            $this->fileSuffix = $suffixStr;
        }
        
        return $this;
    }
    
    /* check if key exists */
    public function keyExists($key = null) {
    
        /* construct the file name to get the value from */
        $keyValueFile = $this->filePrefix . $key . $this->fileSuffix;
                        
        /* do the associated key value file exist? */
        if(!file_exists($this->storePath . $keyValueFile)) {
            
            /* key do not exist return false */
            return FALSE;
            
        } else {
            
            /* Yes!!! key exists so return true */
            return TRUE;
            
        }        
        
    }
    
    /* add data to a new key or overwrite existing */
    public function add($key = null, $value = null) {
        
        if(!is_string($key)) {
            exit('Error add(), you must supply a key string to value: ' . $value . '' . PHP_EOL);
        }
        
        /* construct the file name to store the value in */
        $keyValueFile = $this->filePrefix . $key . $this->fileSuffix;
                
        /* encode the data to JSON */
        $data = json_encode($value);
        
        /* save the json data to a flat file */
        $result = file_put_contents($this->storePath . $keyValueFile, $data);
        
        if($result === FALSE) {
            exit('Error key could not be saved and written to file!');
        }
        
        return $this;
    }
    
    /* update a key value (overwrite existing value) */
    public function update($key = null, $value) {
        
        if(!is_string($key)) {
            exit('Error update(), you must supply a key string to value: ' . $value . '' . PHP_EOL);
        }
        
        /* use the add() method, because it simply overwrites existing value if key exists */
        $this->add($key, $value);
    }    
    
    /* get data from the stored key value file and return it */
    public function get($key = null) {
        
        if(!is_string($key)) {
            exit('Error get(), you must supply a key string!');
        }
        
        /* construct the file name to get the value from */
        $keyValueFile = $this->filePrefix . $key . $this->fileSuffix;
                        
        /* read the json data from flat file */
        if(file_exists($this->storePath . $keyValueFile)) {
            $data = file_get_contents($this->storePath . $keyValueFile);
        } else {
            exit('Error key does not exist in store.');
        }
        
        /* decode JSON data into a Array, String or object depending of what was saved */
        $data = json_decode($data);
        
        /* return key value data */
        return $data;
    }
    
    /* get a list of keys stored */
    public function getKeys() {
        
        /* init vars */
        $path = $this->storePath;
        $prefix = $this->filePrefix;
        $suffix = $this->fileSuffix;
        
        /* list all key value files in store directory */
        foreach (glob("{$path}{$prefix}*{$suffix}") as $fileName) {
            
            /* get path info filename */
            $pathInfo = pathinfo($fileName);
                    
            /* do replace */
            $keyValue = ltrim($pathInfo['basename'], $this->filePrefix);
            $keyValue = rtrim($keyValue, $this->fileSuffix);
            
            /* save the key value */
            $keyValues[] = $keyValue;
        }
                    
        return $keyValues;
    }
    
    /* get a list of the filenames used for key values */
    public function getKeyFiles() {
        
        /* init vars */
        $path = $this->storePath;
        $prefix = $this->filePrefix;
        $suffix = $this->fileSuffix;
        
        /* list all key value files in store directory */
        foreach (glob("{$path}{$prefix}*{$suffix}") as $fileName) {
            
            /* get path info filename */
            $pathInfo = pathinfo($fileName);
                        
            /* save the key value filename */
            $keyValues[] = $pathInfo['basename'];
        }
                    
        return $keyValues;
    }
        
    /* remove key value file based on key name */
    public function remove($key = null) {
        
        if(!is_string($key)) {
            exit('Error remove(), you must supply a key string!');
        }
        
        /* construct the file name to remove */
        $keyValueFile = $this->filePrefix . $key . $this->fileSuffix;
                    
        /* remove key value file if it exists */
        if(file_exists($this->storePath . $keyValueFile)) {
            
            /* returns TRUE if successfull or FALSE if not */
            $removeResult = unlink($this->storePath . $keyValueFile);
            
            return $removeResult;
            
        } else {
            
            /* if file does not exist then give a error also return FALSE */
            exit('Error key does not exist in store.');
            return FALSE;
        }
                
    }        
}
?>