NAME
    CHI::Cascade - a cache dependencies (cache and like 'make' utility
    concept)

SYNOPSIS
        use CHI;
        use CHI::Cascade;

        $cascade = CHI::Cascade->new(chi => CHI->new(...));

        $cascade->rule(
            target  => 'unique_name',
            depends => ['unique_name_other1', 'unique_name_other2'],
            code    => sub {
                my ($rule, $target_name, $values_of_depends) = @_;

                # $values_of_depends == {
                #     unique_name_other1 => $value_1,
                #     unique_name_other2 => $value_2
                # }
                # $rule->target     eq      $target_name
                # $rule->depends    ===     ['unique_name_other1', 'unique_name_other2']
                # $rule->dep_values ==      $values_of_depends
                # $rule->params     ==      { a => 1, b => 2 }

                # Now we can calcualte $value
                return $value;
            },
            params  => { a => 1, b => 2 }
        );

        $cascade->rule(
            target  => 'unique_name_other1',
            depends => 'unique_name_other3',
            code    => sub {
                my ($rule, $target_name, $values_of_depends) = @_;

                # $values_of_depends == {
                #     unique_name_other3 => $value_3
                # }

                # computing here
                return $value;
            }
        );

        $value_of_this_target = $cascade->run('unique_name');

DESCRIPTION
    This module is the attempt to use a benefits of caching and 'make'
    concept. If we have many an expensive tasks and want to cache it we can
    split its to small expsnsive tasks and to describe dependencies for
    cache items.

    This module is experimental yet. I plan to improve it near time but some
    things already work. You can take a look for t/* tests as examples.

CONSTRUCTOR
    $cascade = CHI::Cascade->new( %options )

    This method constructs a new "CHI::Cascade" object and returns it.
    Key/value pair arguments may be provided to set up the initial state.
    Options are:

    chi Required. Instance of CHI object. The CHI::Cascade doesn't construct
        this object for you. Please create instance of "CHI" yourself.

    busy_lock
        Optional. Default is *never*. *This is not "busy_lock" option of
        CHI!* This is amount of time (to see "DURATION EXPRESSIONS" in CHI)
        until all target locks expire. When a target is recomputed it is
        locked. If process is to be recomputing target and it will die or OS
        will be hangs up we can dead locks and locked target will never
        recomputed again. This option helps to avoid it. You can set up a
        special busy_lock for rules too.

METHODS
    rule( %options )
        To add new rule to "CHI::Cascade" object. All rules should be added
        before first "run" method

        The keys of %options are:

        target
            Required. A target for "run" and for searching of "depends". It
            can be as scalar text or "Regexp" object created through "qr//"

        depends
            Optional. The scalar, arrayref or coderef values of
            dependencies. This is the definition of target(s) from which
            this current rule is dependent. If *depends* is:

            scalar
                It should be plain text of single dependence of this target.

            arrayref
                An each item of list can be scalar value (exactly matched
                target) or code reference. If item is coderef it will be
                executed as $coderef->( $rule, $rule->qr_params ) and should
                return a scalar value as current dependence for this target
                at runtime (the API for coderef parameters was changed since
                v0.16)

            coderef
                This subroutine will be executed every time inside *run*
                method if necessary and with parameters as: $coderef->(
                $rule, $rule->qr_params ) (API was changed since v0.16). It
                should return scalar or arrayref. The returned value is
                *scalar* it will be considered as single dependence of this
                target and the behavior will be exactly as described for
                *scalar* in this paragraph. If the returned value is
                *arrayref* it will be considered as list of dependencies for
                this target and the behavior will be exactly as described
                for *arrayref* in this paragraph.

        code
            Required. The code reference for computing a value of this
            target (a recompute code). Will be executed if no value in cache
            for this target or any dependence or dependences of dependences
            and so on will be recomputed. Will be executed as "$code->(
            $rule, $target, $hashref_to_value_of_dependencies )" *(The API
            of running this code was changed since v0.10)*

            If you want to terminate a code and to return immediately from
            run method and don't want to save a value in cache you can throw
            an exception from code of type CHI::Cascade::Value. Your
            instance of CHI::Cascade::Value can have a value or cannot (a
            valid value can be even "undef"!). A run method returns either a
            value is set by you (through CHI::Cascade::Value::value method)
            or value from cache or "undef" in other cases. Please to see
            CHI::Cascade::Value

            $rule
                An instance of CHI::Cascade::Rule object. You can use it
                object as accessor for some current executed target data
                (plain text of target, for getting of parameters and so on).
                Please to see CHI::Cascade::Rule

            $target
                A current target as plain text (what a target the $cascade
                got from run method)

            $hashref_to_value_of_dependencies
                A hash reference of values of all dependencies for current
                target. Keys in this hash are flat strings of dependecies
                and values are computed or cached ones.

                This module should guarantee that values of dependencies
                will be valid values even if value is "undef". This code can
                return "undef" value as a valid code return but author
                doesn't recommend it. If "CHI::Cascade" could not get a
                valid values of all dependencies of current target before
                execution of this code the last will not be executed (The
                "run" will return "undef").

        params
            You can pass in your code any additional parameters by this
            option. These parameters are accessed in your code through
            params method of CHI::Cascade::Rule instance object.

        busy_lock
            Optional. Default is "busy_lock" of constructor or *never* if
            first is not defined. *This is not "busy_lock" option of CHI!*
            This is amount of time (to see "DURATION EXPRESSIONS" in CHI)
            until target lock expires. When a target is recomputed it is
            locked. If process is to be recomputing target and it will die
            or OS will be hangs up we can dead locks and locked target will
            never recomputed again. This option helps to avoid it.

        recomputed
            Optional. This is a recomputed callback (coderef). If target of
            this rule was recomputed this callback will be executed right
            away after recomputed value has been saved in cache. The
            callback will be executed as $coderef->( $rule, $target, $value
            ) where are:

            $rule
                An instance of CHI::Cascade::Rule class. This instance is
                recreated for every target searching and recomputing if
                need.

            $target
                A current target as string

            $value
                The instance of CHI::Cascade::Value class. You can use a
                recomputed value as $value->value

            For example you can use this callback for notifying of other
            sites that your target's value has been changed and is already
            in cache.

    run( $target )
        This method makes a cascade computing if need and returns value for
        this target If any dependence of this target of any dependencies of
        dependencies were recomputed this target will be recomputed too.

    touch( $target )
        This method refreshes the time of this target. Here is analogy with
        touch utility of Unix and behaviour as make after it. After "touch"
        all targets are dependent from this target will be recomputed at
        next "run" with an appropriate ones.

    target_remove ( $target )
        It's like a removing of target file in make. You can force to
        recompute target by this method. It will remove target marker if one
        exists and once when cascade will need target value it will be
        recomputed. In a during recomputing of course cascade will return an
        old value if one exists in cache.

STATUS
    This module is experimental and not finished for new features ;-) Please
    send me issues through <https://github.com/Perlover/CHI-Cascade> page

ANALOGIES WITH make
    Here simple example how it works. Here is a direct analogy to Unix make
    utility:

        In CHI::Cascade:            In make:

        rule                        rule
        depends                     prerequisites
        code                        commands
        run( rule_name )            make target_name

FEATURES
    The features of this module are following:

    Computing inside process
        If module needs to compute item for cache we compute inside process
        (no forks) For web applications it means that one process for one
        request could take a some time for computing. But other processes
        will not wait and will get either old previous computed value or
        *undef* value.

    Non-blocking computing for concurrent processes
        If other process want to get data from cache we should not block it.
        So concurrent process can get an old data if new computing is run or
        can get *undef* value. A concurrent process should decide itself
        what it should do after it - try again after few time or print some
        message like 'Please wait and try again' to user.

    Each target is splitted is two items in cache
        For optimization this module keeps target's info by separately from
        value item. A target item has lock & timestamp fields. A value item
        has a computed value.

EXAMPLE
    For example please to see the SYNOPSIS

    When we prepared a rules and a depends we can:

    If unique_name_other1 and/or unique_name_other2 are(is) more newer than
    unique_name the unique_name will be recomputed. If in this example
    unique_name_other1 and unique_name_other2 are older than unique_name but
    the unique_name_other3 is newer than unique_name_other1 then
    unique_name_other1 will be recomputed and after the unique_name will be
    recomputed.

    And even we can have a same rule:

        $cascade->rule(
            target  => qr/^unique_name_(.*)$/,
            depends => sub { 'unique_name_other_' . $_[1] },
            code    => sub {
                my ($rule, $target_name, $values_of_depends) = @_;

                # $rule->qr_params          === ( 3 )
                # $target_name              == 'unique_name_3' if $cascade->run('unique_name_3') was
                # $values_of_depends        == {
                #     unique_name_other_3   => $value_ref_3
                # }
            }
        );

        $cascade->rule(
            target  => qr/unique_name_other_(.*)/,
            code    => sub {
                my ($rule, $target_name, $values_of_depends) = @_;
                ...
            }
        );

    When we will do:

        $cascade->run('unique_name_52');

    $cascade will find rule with qr/^unique_name_(.*)$/, will make =~ and
    will find a depend as unique_name_other_52

AUTHOR
    This module has been written by Perlover <perlover@perlover.com>

LICENSE
    This module is free software and is published under the same terms as
    Perl itself.

SEE ALSO
    CHI::Cascade::Rule
        An instance of this object can be used in your target codes.

    CHI This object is used for cache.

    CHI::Driver::Memcached::Fast
        Recommended if you have the Memcached

    CHI::Driver::File
        Recommended if you want to use the file caching instead the
        Memcached for example

