# Define a few basic "interchange" classes tha

module Nodepile
    
# Caches the result of named calculations and their parameters and provides
# a crude flushing
class CrudeCalculationCache
    
    # Used to disable use of cache by all instances of this class.  Note that this
    # is extremely useful during testing.
    def self.global_disable_cache(flag) = @@universally_disable_cache = flag
    
    # @param disable_cache [Boolean] if truthy, then caching is never triggered
    #                        for this object
    def initialize(disable_cache: false)
       @h = Hash.new
       @disable_cache = disable_cache
    end
   
    # Empties the entire cache forcing recalculation of some or all entries
    # @param name [String,Symbol,nil] Name of the calculation or nil if all calculations
    #               are to be flushed
    # @param params [] If empty, all cached values for the given name will be flushed
    def flush_cache(name = nil, *params) 
        if key.nil?
            @h.clear
        elsif params.empty?
            @h.delete(name) # delete simple keys
            @h.delete{|(cname,*cparams)| cname == name }
        else
            @h.delete([key,*params])
        end
        return nil
    end
    
    def form_cache_key(sym,*parms) = parms.empty? ? sym : [sym,*parms]
    def stuff_cache(val,sym,*parms) = @h[form_cache_key(sym,*parms)] = val
    def has_cache?(sym,*parms) = @h.include?(form_cache_key(sym,*parms))
        
    def fetch_cache(sym,*parms)
        key = form_cache_key(sym,*parms)
        raise "This item is not in the cache #{key.inspect}" unless @h.include?(key)
        return @h[key]
    end
   
    # Will either retrieve the value matching these parameters from the cache
    # or will do the calculation, cache the value, and return the result
    def cache(sym,*parms)
        raise "Calculation block expected" unless block_given?
        key = form_cache_key(sym,*parms)
        if @h.include?(key) && !@disable_cache && !@@global_disable_cache
            return @h[key]
        else
            return @h[sym] = yield(*parms)
        end
    end

    @@global_disable_cache = false
end
    
end #module Nodepile