package Test::Stream::Mock;
use strict;
use warnings;

use Scalar::Util qw/weaken reftype blessed/;

use Carp qw/croak confess/;
our @CARP_NOT = (__PACKAGE__, 'Test::Stream::Mock', 'Test::Stream::Workflow');

use Test::Stream::Util qw/parse_symbol slot_to_sig pkg_to_file/;

use Test::Stream::HashBase(
    accessors => [qw/class parent child _purge_on_destroy _blocked_load _symbols/],
    no_new    => 1,
);

sub new {
    my $class = shift;

    croak "Called new() on a blessed instance, did you mean to call \$control->class->new()?"
        if blessed($class);

    my $self = bless({}, $class);

    my @sets;
    while (my $arg = shift @_) {
        my $val = shift @_;

        if ($class->can(uc($arg))) {
            $self->{$arg} = $val;
            next;
        }

        push @sets => [$arg, $val];
    }

    croak "The 'class' field is required"
        unless $self->{+CLASS};

    for my $set (@sets) {
        my ($meth, $val) = @$set;
        my $type = reftype($val);

        confess "'$meth' is not a valid constructor argument for $class"
            unless $self->can($meth);

        if (!$type) {
            $self->$meth($val);
        }
        elsif($type eq 'HASH') {
            $self->$meth(%$val);
        }
        elsif($type eq 'ARRAY') {
            $self->$meth(@$val);
        }
        else {
            croak "'$val' is not a valid argument for '$meth'"
        }
    }

    return $self;
}

sub _check {
    return unless $_[0]->{+CHILD};
    croak "There is an active child controller, cannot proceed";
}

sub purge_on_destroy {
    my $self = shift;
    ($self->{+_PURGE_ON_DESTROY}) = @_ if @_;
    return $self->{+_PURGE_ON_DESTROY};
}

sub stash {
    my $self = shift;
    my $class = $self->{+CLASS};

    no strict 'refs';
    return \%{"${class}\::"};
}

sub file {
    my $self = shift;
    my $file = $self->class;
    return pkg_to_file($self->class);
}

sub block_load {
    my $self = shift;
    $self->_check();

    my $file = $self->file;

    croak "Cannot block the loading of module '" . $self->class . "', already loaded in file $INC{$file}"
        if $INC{$file};

    $INC{$file} = __FILE__;

    $self->{+_BLOCKED_LOAD} = 1;
}

my %NEW = (
    hash => sub {
        my ($class, %params) = @_;
        return bless \%params, $class;
    },
    array => sub {
        my ($class, @params) = @_;
        return bless \@params, $class;
    },
    ref => sub {
        my ($class, $params) = @_;
        return bless $params, $class;
    },
    ref_copy => sub {
        my ($class, $params) = @_;
        my $type = reftype($params);

        return bless {%$params}, $class
            if $type eq 'HASH';

        return bless [@$params], $class
            if $type eq 'ARRAY';

        croak "Not sure how to construct an '$class' from '$params'";
    },
);

sub override_constructor {
    my $self = shift;
    my ($name, $type) = @_;
    $self->_check();

    my $sub = $NEW{$type}
        || croak "'$type' is not a known constructor type";

    $self->override($name => $sub);
}

sub add_constructor {
    my $self = shift;
    my ($name, $type) = @_;
    $self->_check();

    my $sub = $NEW{$type}
        || croak "'$type' is not a known constructor type";

    $self->add($name => $sub);
}

sub autoload {
    my $self = shift;
    $self->_check();
    my $class = $self->class;
    my $stash = $self->stash;

    croak "Class '$class' already has an AUTOLOAD"
        if $stash->{AUTOLOAD} && *{$stash->{AUTOLOAD}}{CODE};

    # Weaken this reference so that AUTOLOAD does not prevent its own
    # destruction.
    weaken(my $c = $self);

    my ($file, $line) = (__FILE__, __LINE__ + 3);
    my $sub = eval <<EOT || die $@;
package $class;
#line $line "$file (Generated AUTOLOAD)"
our \$AUTOLOAD;
    sub {
        my (\$self) = \@_;
        my (\$pkg, \$name) = (\$AUTOLOAD =~ m/^(.*)::([^:]+)\$/g);
        \$AUTOLOAD = undef;

        return if \$name eq 'DESTROY';
        my \$sub = Test::Stream::HashBase->gen_accessor(\$name);

        \$c->add(\$name => \$sub);
        goto &\$sub;
    }
EOT

    $self->add(AUTOLOAD => $sub);
}

sub before {
    my $self = shift;
    my ($name, $sub) = @_;
    $self->_check();
    my $orig = $self->current($name);
    $self->_inject(0, $name => sub { $sub->(@_); $orig->(@_) });
}

sub after {
    my $self = shift;
    my ($name, $sub) = @_;
    $self->_check();
    my $orig = $self->current($name);
    $self->_inject(0, $name => sub {
        my @out;

        my $want = wantarray;

        if ($want) {
            @out = $orig->(@_);
        }
        elsif(defined $want) {
            $out[0] = $orig->(@_);
        }
        else {
            $orig->(@_);
        }

        $sub->(@_);

        return @out    if $want;
        return $out[0] if defined $want;
        return;
    });
}

sub around {
    my $self = shift;
    my ($name, $sub) = @_;
    $self->_check();
    my $orig = $self->current($name);
    $self->_inject(0, $name => sub { $sub->($orig, @_) });
}

sub add {
    my $self = shift;
    $self->_check();
    $self->_inject(1, @_);
}

sub override {
    my $self = shift;
    $self->_check();
    $self->_inject(0, @_);
}

sub current {
    my $self = shift;
    my ($sym) = @_;

    my $class = $self->{+CLASS};
    my ($name, $type) = parse_symbol($sym);

    my $stash = $self->stash;
    return unless $stash->{$name};

    no strict 'refs';
    return *{"$class\::$name"}{$type};
}

sub orig {
    my $self = shift;
    my ($sym) = @_;

    $sym = "&$sym" unless $sym =~ m/^[&\$\%\@]/;

    my $syms = $self->{+_SYMBOLS}
        or croak "No symbols have been mocked yet";

    my $ref = $syms->{$sym};

    croak "Symbol '$sym' is not mocked"
        unless $ref && @$ref;

    my ($orig) = @$ref;

    return $orig;
}

sub _parse_inject {
    my $self = shift;
    my ($param, $arg) = @_;

    if ($param =~ m/^-(.*)$/) {
        my $sym = $1;
        my $sig = slot_to_sig(reftype($arg));
        my $ref = $arg;
        return ($sig, $sym, $ref);
    }

    return ('&', $param, $arg)
        if ref($arg) && reftype($arg) eq 'CODE';

    my ($is, $field, $val);

    if (!ref($arg)) {
        $is    = $arg if $arg =~ m/^(rw|ro|wo)$/;
        $field = $param;
    }
    elsif (reftype($arg) eq 'HASH') {
        $field = delete $arg->{field} || $param;

        $val = delete $arg->{val};
        $is  = delete $arg->{is};

        croak "Cannot specify 'is' and 'val' together" if $val && $is;

        $is ||= $val ? 'val' : 'rw';

        croak "The following keys are not valid when defining a mocked sub with a hashref: " . join(", " => keys %$arg)
            if keys %$arg;
    }

    confess "'$arg' is not a valid argument when defining a mocked sub"
        unless $is;

    my $sub;
    if ($is eq 'rw') {
        $sub = Test::Stream::HashBase->gen_accessor($field);
    }
    elsif ($is eq 'ro') {
        $sub = Test::Stream::HashBase->gen_getter($field);
    }
    elsif ($is eq 'wo') {
        $sub = Test::Stream::HashBase->gen_setter($field);
    }
    else { # val
        $sub = sub { $val };
    }

    return ('&', $param, $sub);
}

sub _inject {
    my $self = shift;
    my ($add, @pairs) = @_;

    my $class = $self->{+CLASS};

    $self->{+_SYMBOLS} ||= {};
    my $syms = $self->{+_SYMBOLS};

    while (my $param = shift @pairs) {
        my $arg = shift @pairs;
        my ($sig, $sym, $ref) = $self->_parse_inject($param, $arg);
        my $orig = $self->current("$sig$sym");

        croak "Cannot override '$sig$class\::$sym', symbol is not already defined"
            unless $orig || $add;

        # Cannot be too sure about scalars in globs
        croak "Cannot add '$sig$class\::$sym', symbol is already defined"
            if $add && $orig
            && (reftype($orig) ne 'SCALAR' || defined($$orig));

        $syms->{"$sig$sym"} ||= [];
        push @{$syms->{"$sig$sym"}} => $orig; # Might be undef, thats expected

        no strict 'refs';
        no warnings 'redefine';
        *{"$class\::$sym"} = $ref;
    }

    return;
}

sub _set_or_unset {
    my $self = shift;
    my ($sym, $set) = @_;

    my $class = $self->{+CLASS};
    my ($name, $type) = parse_symbol($sym);

    if (defined $set) {
        no strict 'refs';
        no warnings 'redefine';
        return *{"$class\::$name"} = $set;
    }

    # Damn, need to clear it, this gets complicated :-(
    my $stash = $self->stash;
    local *__ORIG__ = do { no strict 'refs'; *{"$class\::$name"} };
    delete $stash->{$name};

    for my $slot (qw/CODE SCALAR HASH ARRAY/) {
        next if $slot eq $type;
        no strict 'refs';
        no warnings 'redefine';
        *{"$class\::$name"} = *__ORIG__{$slot} if defined(*__ORIG__{$slot});
    }

    return undef;
}

sub restore {
    my $self = shift;
    my ($sym) = @_;
    $self->_check();

    $sym = "&$sym" unless $sym =~ m/^[&\$\%\@]/;

    my $syms = $self->{+_SYMBOLS}
        or croak "No symbols are mocked";

    my $ref = $syms->{$sym};

    croak "Symbol '$sym' is not mocked"
        unless $ref && @$ref;

    my $old = pop @$ref;
    delete $syms->{$sym} unless @$ref;

    return $self->_set_or_unset($sym, $old);
}

sub reset {
    my $self = shift;
    my ($sym) = @_;
    $self->_check();

    $sym = "&$sym" unless $sym =~ m/^[&\$\%\@]/;

    my $syms = $self->{+_SYMBOLS}
        or croak "No symbols are mocked";

    my $ref = delete $syms->{$sym};

    croak "Symbol '$sym' is not mocked"
        unless $ref && @$ref;

    my ($old) = @$ref;

    return $self->_set_or_unset($sym, $old);
}

sub reset_all {
    my $self = shift;
    $self->_check();

    my $syms = $self->{+_SYMBOLS} || return;

    $self->reset($_) for keys %$syms;

    delete $self->{+_SYMBOLS};
}

sub _purge {
    my $self = shift;
    my $stash = $self->stash;
    delete $stash->{$_} for keys %$stash;
}

sub DESTROY {
    my $self = shift;

    $self->reset_all if $self->{+_SYMBOLS};

    delete $INC{$self->file} if $self->{+_BLOCKED_LOAD};

    $self->_purge if $self->{+_PURGE_ON_DESTROY};
}

1;

__END__

=pod

=encoding UTF-8

=head1 NAME

Test::Stream::Mock - Module for managing mocked classes and instances.

=head1 EXPERIMENTAL CODE WARNING

B<This is an experimental release!> Test-Stream, and all its components are
still in an experimental phase. This dist has been released to cpan in order to
allow testers and early adopters the chance to write experimental new tools
with it, or to add experimental support for it into old tools.

B<PLEASE DO NOT COMPLETELY CONVERT OLD TOOLS YET>. This experimental release is
very likely to see a lot of code churn. API's may break at any time.
Test-Stream should NOT be depended on by any toolchain level tools until the
experimental phase is over.

=head1 DESCRIPTION

This module lets you add and override methods for any package temporarily. When
the instance is destroyed it will restore the package to its original state.

=head1 SYNOPSIS

    use Test::Stream::Mock;
    use MyClass;

    my $mock = Test::Stream::Mock->new(
        class => 'MyClass',
        override => [
            name => sub { 'fred' },
            ...
        ],
        add => [
            is_mocked => sub { 1 }
            ...
        ],
        ...
    );

    # Unmock the 'name' sub
    $mock->restore('name');

    ...

    $mock = undef; # Will remove all the mocking

=head1 CONSTRUCTION

=head1 METHODS

=over 4

=item $mock = $class->new(class => $CLASS, ...)

This will create a new instance of L<Test::Stream::Mock> that manages mocking
for the specified C<$CLASS>.

Any C<Test::Stream::Mock> method can be used as a constructor argument, each
should be followed by an arrayref of arguments to be used with the method. For
instance the 'add' method:

    my $mock = Test::Stream::Mock->new(
        class => 'AClass',
        add => [foo => sub { 'foo' }],
    );

is identical to this:

    my $mock = Test::Stream::Mock->new(
        class => 'AClass',
    );
    $mock->add(foo => sub { 'foo' });

=item $mock->add('symbol' => ..., 'synbol2' => ...)

=item $mock->override('symbol1' => ..., 'symbol2' => ...)

C<add()> and C<override()> are the primary ways to add/modify methods for a
class. Both accept the exact same type of arguments. The difference is that
C<override> will fail unless the symbol you are overriding already exists,
C<add> on the other hand will fail if the symbol does already exist.

B<Note:> Think of override as a push operation. If you call override on the
same symbol multiple times it will track that. You can use C<restore()> as a
pop operation to go back to the previous mock. C<reset> can be used to remove
all the mocking for a symbol.

Arguments must be a symbol name, with optional sigil, followed by a new
specification of the symbol. If no sigil is specified then '&' (sub) is
assumed. A simple example of overriding a sub:

    $mock->override(foo => sub { 'overridden foo' });
    my $val = $class->foo; # Runs our override
    # $val is now set to 'overridden foo'

You can also simply provide a value and it will be wrapped in a sub for you:

    $mock->override( foo => 'foo' );

The example above will generate a sub that always returns the string 'foo'.

There are 3 *special* values that can be used to generate accessors:

    $mock->add(
        name => 'rw',   # Generates a read/write accessor
        age  => 'ro',   # Generates a read only accessor
        size => 'wo',   # Generates a write only accessor
    );

If you want to have a sub that actually returns on of the 3 special strings, or
that returns a coderef, you can use a hashref as the spec:

    my $ref = sub { 'my sub' };
    $mock->add(
        rw_string => { val => 'rw' },
        ro_string => { val => 'ro' },
        wo_string => { val => 'wo' },
        coderef   => { val => $ref }, # the coderef method returns $ref each time
    );

You can also override/add other symbol types, such as hash:

    package Foo;
    ...

    $mock->add('%foo' => {a => 1});

    print $Foo::foo{a}; # prints '1'

You can also tell mock to deduce the symbol type for the add/override from the
reference, rules are similar to glob assignments:

    $mock->add(
        -foo => sub { 'foo' },     # Adds the &foo sub to the package
        -foo => { foo => 1 },      # Adds the %foo hash to the package
        -foo => [ 'f', 'o', 'o' ], # Adds the @foo array to the package
        -foo => \"foo",            # Adds the $foo scalar to the package
    );

=item $mock->restore($SYMBOL)

Restore the symbol to what it was before the last override. If the symbol was
recently added this will remove it. If the symbol has been overriden multiple
times this will ONLY restore it to the previous state. Think of override as a
push operation, this is the pop operation.

=item $mock->reset($SYMBOL)

Remove all mocking of the symbol, restore the original symbol. If the symbol
was initially added then it will be completely removed.

=item $mock->orig($SYMBOL)

This will return the original symbol, before any mocking. For symbols that were
added this will return undef.

=item $mock->current($SYMBOL)

This will return the current symbol.

=item $mock->reset_all

Remove all added symbols, and restore all overriden symbols to their originals.

=item $mock->add_constructor($NAME => $TYPE)

=item $mock->override_constructor($NAME => $TYPE)

This can be used to inject constructors. The first argument should be the name
of the constructor. The second argument specifies the constructor type.

The C<hash> type is the most common, all arguments are used to create a new
hash that is blessed.

    hash => sub  {
        my ($class, %params) = @_;
        return bless \%params, $class;
    };

The C<array> type is similar to the hash type, but accepts a list instead of
key/value pairs:

    array => sub {
        my ($class, @params) = @_;
        return bless \@params, $class;
    };

The C<ref> type takes a reference and blesses it. This will modify your
original input argument.

    ref => sub {
        my ($class, $params) = @_;
        return bless $params, $class;
    };

The C<ref_copy> type will copy your reference and bless the copy:

    ref_copy => sub {
        my ($class, $params) = @_;
        my $type = reftype($params);

        return bless {%$params}, $class
            if $type eq 'HASH';

        return bless [@$params], $class
            if $type eq 'ARRAY';

        croak "Not sure how to construct an '$class' from '$params'";
    };

=item $mock->before($NAME, sub { ... })

This will replace the orignal sub C<$NAME> with a new sub that calls your
custom code just before calling the original method. The return from your
custom sub is ignored. Your sub and the original both get the unmodified
arguments.

=item $mock->after($NAME, sub { ... })

This is similar to before, except your callback runs after the original code.
The return from your callback is ignored. 

=item $mock->around($NAME, sub { ... })

This gives you the chance to wrap the original sub:

    $mock->around(foo => sub {
        my $orig = shift;
        my $self = shift;
        my (@args) = @_;

        ...
        $orig->(@args);
        ...

        return ...;
    });

The original sub is passed in as the first argument, even before C<$self>. You
are responsible for making sure your wrapper sub returns the correct thing.

=item $mock->autoload

This will inject an C<AUTOLOAD> sub into the class. This autoload will
automatically generate read-write accessors for any sub called that does not
already exist.

=item $mock->block_load

This will prevent the real class from loading until the mock is destroyed. This
will fail if the class is already loaded. This will let you mock a class
completely without loading the original module.

=item $pm_file = $mock->file

This returns the relative path to the file for the module. This corresponds to
the C<%INC> entry.

=item $bool = $mock->purge_on_destroy($bool)

When true, this will cause the package stash to be completely obliterated when
the mock object falls out of scope or is otherwise destroyed. You do not
normally want this.

=item $stash = $mock->stash

This returns the stash for the class being mocked. This is the equivelent of:

    my $stash = \%{"${class}\::"};

This saves you from needing to turn off strict.

=item $class = $mock->class

The class being mocked by this instance.

=item $p = $mock->parent

If you mock a class twice the first instance is the parent, the second is the
child. This prevents the parent from being destroyed before the child, which
would lead to a very unpleasant situation.

=item $c = $mock->child

Returns the child mock, if any.

=back

=head1 SOURCE

The source code repository for Test::Stream can be found at
F<http://github.com/Test-More/Test-Stream/>.

=head1 MAINTAINERS

=over 4

=item Chad Granum E<lt>exodist@cpan.orgE<gt>

=back

=head1 AUTHORS

=over 4

=item Chad Granum E<lt>exodist@cpan.orgE<gt>

=back

=head1 COPYRIGHT

Copyright 2015 Chad Granum E<lt>exodist7@gmail.comE<gt>.

This program is free software; you can redistribute it and/or
modify it under the same terms as Perl itself.

See F<http://www.perl.com/perl/misc/Artistic.html>

=cut
