// Package api wires HTTP routing, middleware, and JSON conventions on top
// of the stdlib ServeMux (Go 1.22+ method patterns and r.PathValue).
package api

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

	"git.k6n.net/mats/fullstack-template/internal/items"
)

// Pinger abstracts the database health check so tests can stub it.
type Pinger interface {
	PingContext(ctx context.Context) error
}

// Deps are the server's runtime collaborators, wired in cmd/api.
type Deps struct {
	Logger         *slog.Logger
	Items          *items.Service
	DB             Pinger
	AllowedOrigins []string
	RequestTimeout time.Duration // zero means the 30s default
	Auth           *AuthDeps     // nil disables OIDC: /api/auth answers 404, /api/v1 stays open
}

const defaultRequestTimeout = 30 * time.Second

// New builds the full handler: middleware chain around the route table.
// Middleware order (outermost first): logging → recover → cors → timeout
// → (requireAuth, only when OIDC is configured).
func New(deps Deps) http.Handler {
	if deps.RequestTimeout <= 0 {
		deps.RequestTimeout = defaultRequestTimeout
	}

	var authH *authHandler
	if deps.Auth != nil {
		if deps.Auth.SessionTTL <= 0 {
			deps.Auth.SessionTTL = defaultSessionTTL
		}
		authH = &authHandler{
			client:     deps.Auth.Client,
			signer:     deps.Auth.Signer,
			sessionTTL: deps.Auth.SessionTTL,
			logger:     deps.Logger,
		}
	}

	s := &server{
		logger: deps.Logger,
		db:     deps.DB,
		items:  &itemHandler{svc: deps.Items, logger: deps.Logger},
		auth:   authH,
	}

	mux := http.NewServeMux()

	// Liveness is "the process is up"; readiness is "it can serve real
	// traffic", here meaning the database answers.
	mux.HandleFunc("GET /healthz", s.health)
	mux.HandleFunc("GET /readyz", s.readiness)

	if s.auth != nil {
		mux.HandleFunc("GET /api/auth/session", s.auth.session)
		mux.HandleFunc("GET /api/auth/login", s.auth.login)
		mux.HandleFunc("GET /api/auth/callback", s.auth.callback)
		mux.HandleFunc("POST /api/auth/logout", s.auth.logout)
	}

	// Reference CRUD resource. Method-specific patterns make the mux
	// answer 405 with an Allow header for free; read segments with
	// r.PathValue("id").
	mux.HandleFunc("GET /api/v1/items", s.items.list)
	mux.HandleFunc("POST /api/v1/items", s.items.create)
	mux.HandleFunc("GET /api/v1/items/{id}", s.items.get)
	mux.HandleFunc("PATCH /api/v1/items/{id}", s.items.update)
	mux.HandleFunc("DELETE /api/v1/items/{id}", s.items.delete)

	// The wrapper keeps the mux's automatic 405 + Allow responses for
	// wrong-method requests and renders all unmatched routes as JSON 404s
	// (the mux default is plain text).
	mws := []middleware{
		logging(deps.Logger),
		recoverPanics(deps.Logger),
		cors(deps.AllowedOrigins),
		timeout(deps.RequestTimeout),
	}
	if s.auth != nil {
		mws = append(mws, requireAuth(deps.Auth.Signer))
	}
	return chain(jsonNotFounds(mux), mws...)
}

type server struct {
	logger *slog.Logger
	db     Pinger
	items  *itemHandler
	auth   *authHandler
}

// jsonNotFounds delegates to mux and turns its default plain-text responses
// for unmatched requests into the JSON error envelope. A registered "/" or
// catch-all route would swallow the mux's automatic 405s, so this checks
// mux.Handler instead: an empty pattern means nothing matched, and probing
// the registered methods distinguishes "wrong method" (405 + Allow) from
// "unknown route" (404). The probe runs only on the miss path.
func jsonNotFounds(mux *http.ServeMux) http.Handler {
	methods := []string{
		http.MethodGet, http.MethodPost, http.MethodPut,
		http.MethodPatch, http.MethodDelete,
	}
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if _, pattern := mux.Handler(r); pattern == "" {
			var allowed []string
			for _, m := range methods {
				probe := r.Clone(r.Context())
				probe.Method = m
				if _, pattern := mux.Handler(probe); pattern != "" {
					allowed = append(allowed, m)
				}
			}
			if len(allowed) > 0 {
				w.Header().Set("Allow", strings.Join(allowed, ", "))
				writeError(w, http.StatusMethodNotAllowed, "method_not_allowed",
					r.Method+" is not allowed for this route")
				return
			}
			writeError(w, http.StatusNotFound, "not_found", "route not found")
			return
		}
		mux.ServeHTTP(w, r)
	})
}

func (s *server) health(w http.ResponseWriter, _ *http.Request) {
	writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
}

func (s *server) readiness(w http.ResponseWriter, r *http.Request) {
	ctx, cancel := context.WithTimeout(r.Context(), 2*time.Second)
	defer cancel()
	if err := s.db.PingContext(ctx); err != nil {
		writeError(w, http.StatusServiceUnavailable, "unavailable", "database is not reachable")
		return
	}
	writeJSON(w, http.StatusOK, map[string]string{"status": "ready"})
}