// Package httpserver composes the Fiber app and its middleware stack.
//
// The actual route tree is registered by internal/pkg/openapi through the
// humafiber adapter, so this package only owns lifecycle: configuration,
// graceful start, graceful shutdown, and basic observability middleware.
package httpserver

import (
	"context"
	"fmt"
	"log/slog"
	"net/http"
	"time"

	"github.com/gofiber/fiber/v2"
	"github.com/gofiber/fiber/v2/middleware/recover"
	"github.com/gofiber/fiber/v2/middleware/requestid"

	"anchorage/internal/pkg/metrics"
)

// Options configures a Server.
type Options struct {
	Host         string
	Port         int
	ReadTimeout  time.Duration
	WriteTimeout time.Duration

	// MetricsACLCIDRs is the allowlist for /metrics. Nil → use the
	// metrics package default (loopback + RFC1918). Explicit empty
	// slice → no restriction (firewall-only).
	MetricsACLCIDRs []string
}

// Server wraps *fiber.App with lifecycle helpers.
type Server struct {
	App  *fiber.App
	opts Options
}

// New constructs a Server with the standard anchorage middleware stack.
//
// The returned *fiber.App is exposed on Server.App so callers can register
// routes before Start is called.
func New(opts Options) *Server {
	app := fiber.New(fiber.Config{
		AppName:               "anchorage",
		DisableStartupMessage: true,
		ReadTimeout:           opts.ReadTimeout,
		WriteTimeout:          opts.WriteTimeout,
		ErrorHandler: func(c *fiber.Ctx, err error) error {
			// Fiber default returns an HTML body; JSON is more useful
			// for our API clients.
			code := fiber.StatusInternalServerError
			if fe, ok := err.(*fiber.Error); ok {
				code = fe.Code
			}
			return c.Status(code).JSON(fiber.Map{
				"error":   http.StatusText(code),
				"message": err.Error(),
			})
		},
	})

	app.Use(recover.New())
	app.Use(requestid.New())
	app.Use(accessLog())

	// /metrics lives at root (NOT under /v1) so Prometheus scrapers
	// find it at the conventional path. Gated by a CIDR ACL — see
	// metrics.ACL and MetricsConfig.AllowCIDRs.
	if acl, err := metrics.ACL(opts.MetricsACLCIDRs); err != nil {
		slog.Error("httpserver: bad metrics ACL; /metrics disabled", "err", err)
	} else {
		app.Get("/metrics", acl, metrics.Handler())
	}

	return &Server{App: app, opts: opts}
}

// Start binds and listens. Returns only on listener error.
func (s *Server) Start(_ context.Context) error {
	addr := fmt.Sprintf("%s:%d", s.opts.Host, s.opts.Port)
	slog.Info("httpserver: listening", "addr", addr)
	return s.App.Listen(addr)
}

// Shutdown drains in-flight requests with a bounded grace period.
func (s *Server) Shutdown(ctx context.Context) error {
	return s.App.ShutdownWithContext(ctx)
}