package PAGI::FastAPI;

use v5.36;
use experimental qw/try for_list/;
use version;

our $VERSION   = qv('v0.0.1');
our $AUTHORITY = 'cpan:MANWAR';

use Future::AsyncAwait;
use JSON::PP qw(encode_json decode_json);
use Scalar::Util qw(blessed);
use PAGI::FastAPI::Context;
use PAGI::FastAPI::Depends qw(Depends);

=encoding utf-8

=head1 NAME

PAGI::FastAPI - Asynchronous, Type-Safe Micro-Framework with Dependency Injection and OpenAPI & Swagger UI

=head1 VERSION

Version v0.0.1

=head1 SYNOPSIS

    use v5.36;
    use PAGI::FastAPI;
    use PAGI::FastAPI::Depends qw(Depends);
    use Types::Standard qw(Int Str);
    use Future::AsyncAwait;

    my $app = PAGI::FastAPI->new(
        title   => 'Store Microservice',
        version => '1.0.0',
    );

    # 1. Add CORS Support
    $app->add_cors(
        allow_origins => ['https://example.com'],
        allow_methods => ['GET', 'POST'],
    );

    # 2. Add Authentication Middleware Hook
    $app->add_middleware(async sub ($c, $next) {
        my $auth = $c->header('Authorization') // '';
        if ($auth ne 'Bearer secret_token') {
            $c->status(401);
            return { detail => 'Unauthorized' };
        }
        $c->stash->{user_id} = 42;
        return await $next->($c);
    });

    # 3. Register Lifespan Handlers
    $app->on_startup(async sub {
        warn "Connecting to database connection pool...\n";
    });

    $app->on_shutdown(async sub {
        warn "Closing database connections...\n";
    });

    # 4. Declare Async Dependencies
    my $get_db = async sub ($c) {
        return { db_name => 'production_db' };
    };

    my $get_current_user = async sub ($c) {
        my $token = $c->header('Authorization') // '';
        unless ($token eq 'Bearer secret_token') {
            $c->status(401);
            return { detail => 'Invalid credentials' };
        }
        return { user_id => 42, role => 'admin' };
    };

    # 5. Route using HashRef Dependency Map
    $app->get('/profile',
        dependencies => {
            db   => $get_db,
            user => $get_current_user,
        },
        handler => async sub ($c) {
            my $db   = $c->stash->{db};
            my $user = $c->stash->{user};
            return { user => $user, db => $db->{db_name} };
        }
    );

    # 6. Route using Depends() Array Spec
    $app->get('/admin',
        dependencies => [
            Depends($get_current_user, key => 'user'),
            async sub ($c) {
                if ($c->stash->{user}{role} ne 'admin') {
                    $c->status(403);
                    return { detail => 'Admin privileges required' };
                }
            }
        ],
        handler => async sub ($c) {
            return { message => 'Welcome to admin panel' };
        }
    );

    # 7. Non-blocking GET route with path parameter & query validation
    $app->get('/items/{id}',
        query   => { limit => Int },
        handler => async sub ($c) {
            return {
                item_id => $c->param('id'),
                limit   => $c->param('limit'),
                status  => 'active',
            };
        }
    );

    # 8. Non-blocking POST route with JSON payload validation
    $app->post('/items',
        body    => { name => Str, price => Int },
        handler => async sub ($c) {
            return {
                created => 1,
                name    => $c->body('name'),
                price   => $c->body('price'),
            };
        }
    );

    my $pagi_app = $app->to_app;

=head1 DESCRIPTION

C<PAGI::FastAPI> is an asynchronous micro-framework for modern Perl (5.36+) inspired by Python's FastAPI.

It combines non-blocking async execution via L<Future::AsyncAwait> on the
L<PAGI> (Perl Asynchronous Gateway Interface) specification with request
parameter validation via L<Type::Tiny> and automatic interactive
documentation generation.

=head2 Key Features

=over 4

=item * B<PAGI Protocol Engine:> Asynchronous and non-blocking natively, built for scalable web applications.

=item * B<Automatic Type Validation:> Request query parameters and JSON payloads are checked against L<Type::Tiny> constraints before reaching route handlers.

=item * B<Automatic Interactive Docs:> Serves an interactive Swagger UI interface at C</docs> and machine-readable OpenAPI 3.1 JSON at C</openapi.json>.

=item * B<HTTP 422 Interception:> Automatically intercepts invalid or missing parameters and returns formatted JSON errors with an C<HTTP 422 Unprocessable Entity> status code.

=back

=head1 METHODS

=head2 C<new(%options)>

    my $app = PAGI::FastAPI->new(
        title   => 'My API',
        version => '1.2.3',
    );

Instantiates a new C<PAGI::FastAPI> instance. Acceptable options:

=over 4

=item * C<title> - (Optional) Title string for the application and OpenAPI specification. Default: C<'PAGI::FastAPI Application'>.

=item * C<version> - (Optional) Version string for the OpenAPI specification. Default: C<'$VERSION'>.

=back

=head2 C<get($path, %options)>

=head2 C<post($path, %options)>

=head2 C<put($path, %options)>

=head2 C<patch($path, %options)>

=head2 C<delete($path, %options)>

Registers a route for the specified HTTP verb. Options include:

=over 4

=item * C<query> - (Optional) HashRef mapping query string keys to L<Type::Tiny> type constraints.

=item * C<body> - (Optional) HashRef mapping JSON request body keys to L<Type::Tiny> type constraints.

=item * C<dependencies> - (Optional) HashRef or ArrayRef of dependency code blocks or L<PAGI::FastAPI::Depends> specs.

=item * C<handler> - (Required) An C<async sub ($c)> code reference executing business logic. Receives a L<PAGI::FastAPI::Context> instance.

=back

=cut

sub new ($class, %args) {
    return bless {
        title          => $args{title}   // 'PAGI::FastAPI Application',
        version        => $args{version} // $VERSION,
        routes         => [],
        middlewares    => [],
        event_handlers => {
            startup  => [],
            shutdown => [],
        },
        openapi => {
            openapi => '3.1.0',
            info    => {
                title   => $args{title}   // 'PAGI::FastAPI Application',
                version => $args{version} // $VERSION,
            },
            paths => {},
        }
    }, $class;
}

sub get    ($self, $path, %opts) { $self->_register_route('GET',    $path, \%opts) }
sub post   ($self, $path, %opts) { $self->_register_route('POST',   $path, \%opts) }
sub put    ($self, $path, %opts) { $self->_register_route('PUT',    $path, \%opts) }
sub patch  ($self, $path, %opts) { $self->_register_route('PATCH',  $path, \%opts) }
sub delete ($self, $path, %opts) { $self->_register_route('DELETE', $path, \%opts) }

=head2 C<on_startup($code_ref)>

=head2 C<on_shutdown($code_ref)>

=head2 C<on_event($event_type, $code_ref)>

Registers async callbacks for PAGI Lifespan Protocol events (C<'startup'> or C<'shutdown'>).

=cut

sub on_event ($self, $event_type, $code) {
    die "Event type must be 'startup' or 'shutdown'"
        unless $event_type =~ /^(?:startup|shutdown)$/;
    die "Event handler must be a CODE reference"
        unless ref $code eq 'CODE';
    push @{$self->{event_handlers}{$event_type}}, $code;
}

sub on_startup  ($self, $code) { $self->on_event('startup',  $code) }
sub on_shutdown ($self, $code) { $self->on_event('shutdown', $code) }

=head2 C<add_middleware($code_ref)>

Registers an asynchronous middleware with the application. Signature:

    $app->add_middleware(async sub ($c, $next) {
        # Pre-processing...
        my $res = await $next->($c);
        # Post-processing...
        return $res;
    });

=head2 C<add_cors(%options)>

Enables Cross-Origin Resource Sharing (CORS) with automatic handling of
C<OPTIONS> preflight requests. Options include:

=over 4

=item * C<allow_origins> - ArrayRef or string of allowed origins (default: C<['*']>).

=item * C<allow_methods> - ArrayRef or string of allowed HTTP methods (default: C<['*']>).

=item * C<allow_headers> - ArrayRef or string of allowed HTTP headers (default: C<['*']>).

=item * C<allow_credentials> - Boolean enabling credentials support (default: C<0>).

=item * C<max_age> - Preflight cache max age in seconds (default: C<600>).

=back

=cut

sub add_middleware ($self, $code_ref) {
    push @{$self->{middlewares}}, $code_ref;
}

sub add_cors ($self, %opts) {
    my $allow_origins     = $opts{allow_origins}     // ['*'];
    my $allow_methods     = $opts{allow_methods}     // ['*'];
    my $allow_headers     = $opts{allow_headers}     // ['*'];
    my $allow_credentials = $opts{allow_credentials} // 0;
    my $max_age           = $opts{max_age}           // 600;

    my $origins_str = ref $allow_origins eq 'ARRAY' ? join(', ', @$allow_origins) : $allow_origins;
    my $methods_str = ref $allow_methods eq 'ARRAY' ? join(', ', @$allow_methods) : $allow_methods;
    my $headers_str = ref $allow_headers eq 'ARRAY' ? join(', ', @$allow_headers) : $allow_headers;

    $self->add_middleware(async sub ($ctx, $next) {
        my $origin = $ctx->header('origin');

        if ($origin) {
            $ctx->set_header('Access-Control-Allow-Origin'  => $origins_str eq '*' ? '*' : $origin);
            $ctx->set_header('Access-Control-Allow-Methods' => $methods_str);
            $ctx->set_header('Access-Control-Allow-Headers' => $headers_str);
            if ($allow_credentials) {
                $ctx->set_header('Access-Control-Allow-Credentials' => 'true');
            }
        }

        if (uc($ctx->scope->{method} // '') eq 'OPTIONS') {
            $ctx->set_header('Access-Control-Max-Age' => $max_age);
            $ctx->status(204);
            return '';
        }

        return await $next->($ctx);
    });
}

=head2 C<to_app()>

    my $pagi_closure = $app->to_app;

Generates and returns an asynchronous code reference conforming to the PAGI
protocol specification: C<sub ($scope, $receive, $send)>. This closure can
be served directly via C<pagi-server>.

=cut

sub to_app ($self) {
    return async sub ($scope, $receive, $send) {

        # Handle PAGI Lifespan Protocol (startup & shutdown)
        if ($scope->{type} eq 'lifespan') {
            while (1) {
                my $event = await $receive->();
                if ($event->{type} eq 'lifespan.startup') {
                    try {
                        for my $cb (@{$self->{event_handlers}{startup}}) {
                            await $cb->();
                        }
                        await $send->({ type => 'lifespan.startup.complete' });
                    }
                    catch ($err) {
                        await $send->({ type => 'lifespan.startup.failed', message => "$err" });
                        return;
                    }
                }
                elsif ($event->{type} eq 'lifespan.shutdown') {
                    try {
                        for my $cb (@{$self->{event_handlers}{shutdown}}) {
                            await $cb->();
                        }
                        await $send->({ type => 'lifespan.shutdown.complete' });
                    }
                    catch ($err) {
                        await $send->({ type => 'lifespan.shutdown.failed', message => "$err" });
                    }
                    last;
                }
            }
            return;
        }

        die "Unsupported type: $scope->{type}" unless $scope->{type} eq 'http';

        my $path   = $scope->{path} // '/';
        my $method = uc($scope->{method} // 'GET');

        if ($path eq '/docs') {
            await $send->({ type => 'http.response.start', status => 200, headers => [['content-type', 'text/html; charset=utf-8']] });
            await $send->({ type => 'http.response.body',  body => $self->_swagger_ui_html });
            return;
        }

        if ($path eq '/openapi.json') {
            await $send->({ type => 'http.response.start', status => 200, headers => [['content-type', 'application/json']] });
            await $send->({ type => 'http.response.body',  body => encode_json($self->{openapi}) });
            return;
        }

        # Safe Query String Parsing
        my %query_params;
        if (defined $scope->{query_string} && length $scope->{query_string}) {
            for my $pair (split '&', $scope->{query_string}) {
                my ($k, $v) = split '=', $pair, 2;
                $query_params{$k} = $v // '';
            }
        }

        my $body_data;
        if ($method eq 'POST' || $method eq 'PUT' || $method eq 'PATCH') {
            my $raw_body = '';
            while (1) {
                my $event = await $receive->();
                if ($event->{type} eq 'http.request') {
                    $raw_body .= $event->{body} // '';
                    last unless $event->{more_body};
                }
            }

            if (length $raw_body) {
                try {
                    $body_data = decode_json($raw_body);
                }
                catch ($err) {
                    await $send->({ type => 'http.response.start', status => 422, headers => [['content-type', 'application/json']] });
                    await $send->({ type => 'http.response.body',  body => encode_json({ detail => 'Invalid JSON body payload' }) });
                    return;
                }
            }
        }

        my $ctx = PAGI::FastAPI::Context->new(
            query_params => \%query_params,
            body         => $body_data,
            scope        => $scope,
        );

        my $dispatcher = async sub ($c) {
            for my $route (@{$self->{routes}}) {
                next unless $route->{method} eq $method;

                if (my @captures = ($path =~ $route->{regex})) {
                    my %path_params;
                    my %query_params_validated;

                    for my $i (0 .. $#{$route->{path_params}}) {
                        $path_params{$route->{path_params}[$i]} = $captures[$i];
                    }
                    $c->{path_params} = \%path_params;

                    for my ($param, $type) (%{$route->{query_types}}) {
                        my $val = $query_params{$param};
                        if (my $err = $type->validate($val)) {
                            $c->status(422);
                            return { detail => "Query param '$param' invalid: $err" };
                        }
                        my $t_name = eval { $type->name } // '';
                        $query_params_validated{$param} = $type->has_coercion ? $type->coerce($val) : (($t_name eq 'Int') ? $val + 0 : $val);
                    }
                    $c->{query_params} = \%query_params_validated;

                    if (defined $route->{body_spec}) {
                        my $spec = $route->{body_spec};

                        if (blessed($spec) && $spec->can('validate')) {
                            if (my $err = $spec->validate($c->body)) {
                                $c->status(422);
                                return { detail => "Body validation failed: $err" };
                            }
                            if ($spec->has_coercion) {
                                $c->{body} = $spec->coerce($c->body);
                            }
                        }
                        elsif (ref $spec eq 'HASH') {
                            unless (ref $c->body eq 'HASH') {
                                $c->status(422);
                                return { detail => 'Expected a JSON object in request body' };
                            }

                            for my ($field, $type) (%$spec) {
                                my $val = $c->body($field);
                                if (my $err = $type->validate($val)) {
                                    $c->status(422);
                                    return { detail => "Body field '$field' invalid: $err" };
                                }
                                if ($type->has_coercion) {
                                    $c->{body}{$field} = $type->coerce($val);
                                }
                            }
                        }
                    }

                    for my $dep (@{$route->{dependencies}}) {
                        my $dep_res = await $dep->{code}->($c);

                        if ($c->status >= 400) {
                            return $dep_res // { detail => 'Dependency execution failed' };
                        }

                        if (defined $dep->{key} && defined $dep_res) {
                            $c->stash->{$dep->{key}} = $dep_res;
                        }
                    }

                    return await $route->{handler}->($c);
                }
            }

            $c->status(404);
            return { detail => 'Not Found' };
        };

        my $pipeline = $dispatcher;
        for my $mw (reverse @{$self->{middlewares}}) {
            my $next_stage = $pipeline;
            $pipeline = async sub ($c) {
                return await $mw->($c, $next_stage);
            };
        }

        my $res = await $pipeline->($ctx);

        my $response_body_str = '';
        if (defined $res) {
            $response_body_str = ref $res ? encode_json($res) : "$res";
        }

        my @res_headers = (
            (ref $res ? (['content-type', 'application/json']) : ()),
            @{$ctx->res_headers}
        );

        await $send->({
            type    => 'http.response.start',
            status  => $ctx->status,
            headers => \@res_headers,
        });

        await $send->({
            type => 'http.response.body',
            body => $response_body_str,
        });
    };
}

# PRIVATE METHODS

sub _register_route ($self, $method, $path, $opts) {
    my $query_types = $opts->{query}   // {};
    my $body_spec   = $opts->{body};
    my $raw_deps    = $opts->{dependencies} // [];
    my $handler     = $opts->{handler} // async sub {};

    my @dependencies;
    if (ref $raw_deps eq 'HASH') {
        for my ($key, $code) (%$raw_deps) {
            push @dependencies, { key => $key, code => $code };
        }
    } elsif (ref $raw_deps eq 'ARRAY') {
        for my $dep (@$raw_deps) {
            if (blessed($dep) && $dep->isa('PAGI::FastAPI::Depends')) {
                push @dependencies, { key => $dep->key, code => $dep->code };
            } elsif (ref $dep eq 'CODE') {
                push @dependencies, { key => undef, code => $dep };
            }
        }
    }

    my @path_params;
    my $regex_path = $path;
    while ($regex_path =~ s/\{([a-zA-Z_]\w*)\}/([^\/]+)/) {
        push @path_params, $1;
    }
    $regex_path = "^$regex_path\$";

    my @parameters;
    for my $param (@path_params) {
        push @parameters, { name => $param, in => 'path', required => \1, schema => { type => 'string' } };
    }
    for my ($param, $type) (%$query_types) {
        my $t_name = eval { $type->name } // '';
        push @parameters, {
            name     => $param,
            in       => 'query',
            required => \1,
            schema   => { type => ($t_name eq 'Int' ? 'integer' : 'string') }
        };
    }

    my $route_doc = {
        summary    => "$method $path",
        parameters => \@parameters,
        responses  => {
            200 => { description => "Successful Response" },
            422 => { description => "Validation Error" },
        }
    };

    if ($body_spec) {
        my $properties = {};
        if (ref $body_spec eq 'HASH') {
            for my ($k, $t) (%$body_spec) {
                my $t_name = eval { $t->name } // '';
                $properties->{$k} = { type => ($t_name eq 'Int' ? 'integer' : 'string') };
            }
        }
        $route_doc->{requestBody} = {
            required => \1,
            content  => {
                'application/json' => {
                    schema => {
                        type       => 'object',
                        properties => $properties,
                    }
                }
            }
        };
    }

    $self->{openapi}{paths}{$path}{lc($method)} = $route_doc;

    push @{$self->{routes}}, {
        method       => $method,
        path         => $path,
        regex        => qr/$regex_path/,
        path_params  => \@path_params,
        query_types  => $query_types,
        body_spec    => $body_spec,
        dependencies => \@dependencies,
        handler      => $handler,
    };
}

sub _swagger_ui_html ($self) {
    return <<"HTML";
<!DOCTYPE html>
<html>
<head>
    <title>$self->{title} - Swagger UI</title>
    <link rel="stylesheet" href="https://unpkg.com/swagger-ui-dist\@5/swagger-ui.css" />
</head>
<body>
    <div id="swagger-ui"></div>
    <script src="https://unpkg.com/swagger-ui-dist\@5/swagger-ui-bundle.js"></script>
    <script>
        SwaggerUIBundle({ url: '/openapi.json', dom_id: '#swagger-ui' });
    </script>
</body>
</html>
HTML
}

=head1 AUTO-GENERATED ENDPOINTS

C<PAGI::FastAPI> automatically registers the following system endpoints:

=over 4

=item * C<GET /docs> - Serves an interactive Swagger UI web viewer in the browser.

=item * C<GET /openapi.json> - Serves the generated OpenAPI 3.1 schema.

=back

=head1 ERROR HANDLING

When a request fails parameter validation (either query string or JSON payload), C<PAGI::FastAPI> short-circuits handler execution and returns C<HTTP 422 Unprocessable Entity> with a JSON body:

    {
        "detail": "Query param 'priority' invalid: Undef did not pass type constraint"
    }

Unmatched routes return C<HTTP 404 Not Found> with C<{"detail": "Not Found"}>.

=head1 SEE ALSO

=over 4

=item * L<PAGI> - Perl Asynchronous Gateway Interface specification.

=item * L<PAGI::FastAPI::Context> - Context object passed to route handlers.

=item * L<PAGI::FastAPI::Depends> - Dependency injection helper.

=item * L<Type::Tiny> - Efficient Perl type constraint system.

=item * L<Future::AsyncAwait> - Async/Await syntax for Perl.

=back

=head1 AUTHOR

Mohammad Sajid Anwar, C<< <mohammad.anwar at yahoo.com> >>

=head1 REPOSITORY

L<https://github.com/manwar/PAGI-FastAPI>

=head1 BUGS

Please report any bugs or feature requests through the web interface at L<https://github.com/manwar/PAGI-FastAPI/issues>.
I will be notified and then you'll automatically be notified of progress on your
bug as I make changes.

=head1 SUPPORT

You can find documentation for this module with the perldoc command.

    perldoc PAGI::FastAPI

You can also look for information at:

=over 4

=item * BUG Report

L<https://github.com/manwar/PAGI-FastAPI/issues>

=item * CPAN Ratings

L<http://cpanratings.perl.org/d/PAGI-FastAPI>

=item * Search MetaCPAN

L<https://metacpan.org/dist/PAGI-FastAPI/>

=back

=head1 LICENSE AND COPYRIGHT

Copyright (C) 2026 Mohammad Sajid Anwar.

This program is free software; you can redistribute it and/or modify it under
the terms of the Artistic License (2.0). You may obtain a copy of the full
license at:

L<http://www.perlfoundation.org/artistic_license_2_0>

Any use, modification, and distribution of the Standard or Modified Versions is
governed by this Artistic License. By using, modifying or distributing the Package,
you accept this license. Do not use, modify, or distribute the Package, if you do
not accept this license.

If your Modified Version has been derived from a Modified Version made by someone
other than you, you are nevertheless required to ensure that your Modified Version
complies with the requirements of this license.

This license does not grant you the right to use any trademark, service mark,
tradename, or logo of the Copyright Holder.

This license includes the non-exclusive, worldwide, free-of-charge patent license
to make, have made, use, offer to sell, sell, import and otherwise transfer the
Package with respect to any patent claims licensable by the Copyright Holder that
are necessarily infringed by the Package. If you institute patent litigation
(including a cross-claim or counterclaim) against any party alleging that the
Package constitutes direct or contributory patent infringement, then this Artistic
License to you shall terminate on the date that such litigation is filed.

Disclaimer of Warranty: THE PACKAGE IS PROVIDED BY THE COPYRIGHT HOLDER AND
CONTRIBUTORS "AS IS" AND WITHOUT ANY EXPRESS OR IMPLIED WARRANTIES. THE IMPLIED
WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE, OR
NON-INFRINGEMENT ARE DISCLAIMED TO THE EXTENT PERMITTED BY YOUR LOCAL LAW. UNLESS
REQUIRED BY LAW, NO COPYRIGHT HOLDER OR CONTRIBUTOR WILL BE LIABLE FOR ANY DIRECT,
INDIRECT, INCIDENTAL, OR CONSEQUENTIAL DAMAGES ARISING IN ANY WAY OUT OF THE USE
OF THE PACKAGE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

=cut

1; # End of PAGI::FastAPI
