package Test::MockInputFile;

use strict;

# ---

my %file;

sub define_file_mocker {
    my ($name, $content) = @_;

    $content ||= '';

    $file{$name} = $content;
}

sub undefine_file_mocker {
    my ($name, $content) = @_;

    delete $file{$name};
}

# ---

sub import {
    my ($class, %arg) = @_;

    my $package = caller;

    _export_functions_to($package);

    my $module = defined $arg{module} ? $arg{module} : $package;

    _override_open_and_close_builtins_for($module);
}

# ---

sub _export_functions_to {
    my ($package) = @_;

    no strict 'refs';

    *{"$package\::define_file_mocker"} = \&define_file_mocker;

    *{"$package\::undefine_file_mocker"} = \&undefine_file_mocker;
}

# ---

sub _override_open_and_close_builtins_for {
    my ($module) = @_;

    no strict 'refs';

    *{"$module\::open"} = sub (\$$;$) {
        my ($fh, $mode, $name) = @_;

        if ($mode =~ /^<$/) {
        }
        elsif ($mode =~ /^<\s*([^<>].*)$/) {
            $name = $1;
        }
        else {
            $name = $mode;
        }

        # ---

        if (! defined $file{$name}) {
            # indicating; 'No such file or directory'
            $! = 2;

            return 0;
        }

        $$fh = Test::MockInputFile::Handler->new($name);

        return 1;
    };

    *{"$module\::close"} = sub (\$) {
        my ($fh) = @_;

        undef $$fh;
    };
}

# ---

{
    package Test::MockInputFile::Handler;

    use overload '<>' => \&next_line;

    sub new {
        my ($class, $name) = @_;

        bless {
            content => $file{$name},
        }, $class;
    }

    sub next_line {
        my ($self) = @_;

        if (! defined $self->{content}) {
            return undef;
        }

        my $line;

        if (! defined $/) {
            $line = $self->{content};
            $self->{content} = undef;
        }
        elsif ($self->{content} =~ m;(.+?$/);s) {
            $line = $1;
            $self->{content} = $';

            $self->{content} = undef if $self->{content} eq '';
        }
        else {
            $line = $self->{content};
            $self->{content} = undef;
        }

        return $line;
    }
}

# ---

1;
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