package webingress

import (
	"context"
	"encoding/json"
	"io"
	"net/http"
	"strings"
	"time"
)

type RuntimeConfig struct {
	ServiceType    string
	Scope          string
	ServiceClasses []string
	TLSMode        string
	HTTPSPort      int
}

type Runtime struct {
	Config RuntimeConfig
	Binder FabricBinder
	Now    func() time.Time
}

type FabricBinder interface {
	Forward(ctx context.Context, request FabricRequest) (FabricResponse, error)
}

type FabricRequest struct {
	SchemaVersion string
	Method        string
	Path          string
	Query         string
	Host          string
	ServiceType   string
	Scope         string
	ServiceClass  string
	Headers       http.Header
	Body          []byte
	ObservedAt    time.Time
}

type FabricResponse struct {
	StatusCode int
	Headers    http.Header
	Body       []byte
}

type Response struct {
	SchemaVersion string   `json:"schema_version"`
	Status        string   `json:"status"`
	Reason        string   `json:"reason,omitempty"`
	ServiceType   string   `json:"service_type,omitempty"`
	Scope         string   `json:"scope,omitempty"`
	ServiceClass  string   `json:"service_class,omitempty"`
	Allowed       []string `json:"allowed_service_classes,omitempty"`
	ObservedAt    string   `json:"observed_at"`
}

func (r Runtime) HTTPSHandler() http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, req *http.Request) {
		if req.URL.Path == "/healthz" || req.URL.Path == "/readyz" {
			writeJSON(w, http.StatusOK, r.response("ready", "https_runtime_ready", ""))
			return
		}
		serviceClass := strings.TrimSpace(req.Header.Get("X-RAP-Service-Class"))
		if serviceClass == "" {
			serviceClass = serviceClassFromPath(req.URL.Path)
		}
		if serviceClass == "" {
			writeJSON(w, http.StatusBadRequest, r.response("blocked", "service_class_required", ""))
			return
		}
		if !contains(r.Config.ServiceClasses, serviceClass) {
			writeJSON(w, http.StatusForbidden, r.response("blocked", "service_class_not_allowed", serviceClass))
			return
		}
		if r.Binder == nil {
			writeJSON(w, http.StatusNotImplemented, r.response("blocked", "fabric_service_channel_binding_not_implemented", serviceClass))
			return
		}
		scope := scopeForServiceClass(serviceClass, req.URL.Path, r.Config.Scope)
		body, err := io.ReadAll(http.MaxBytesReader(w, req.Body, 1<<20))
		if err != nil {
			writeJSON(w, http.StatusRequestEntityTooLarge, r.response("blocked", "request_body_too_large", serviceClass))
			return
		}
		now := time.Now().UTC()
		if r.Now != nil {
			now = r.Now().UTC()
		}
		fabricResponse, err := r.Binder.Forward(req.Context(), FabricRequest{
			SchemaVersion: "rap.web_ingress.fabric_request.v1",
			Method:        req.Method,
			Path:          req.URL.Path,
			Query:         req.URL.RawQuery,
			Host:          req.Host,
			ServiceType:   strings.TrimSpace(r.Config.ServiceType),
			Scope:         scope,
			ServiceClass:  serviceClass,
			Headers:       cloneSafeHeaders(req.Header),
			Body:          body,
			ObservedAt:    now,
		})
		if err != nil {
			writeJSON(w, http.StatusBadGateway, r.response("blocked", "fabric_service_channel_forward_failed", serviceClass))
			return
		}
		writeFabricResponse(w, fabricResponse)
	})
}

func (r Runtime) response(status, reason, serviceClass string) Response {
	now := time.Now().UTC()
	if r.Now != nil {
		now = r.Now().UTC()
	}
	return Response{
		SchemaVersion: "rap.web_ingress.runtime_response.v1",
		Status:        status,
		Reason:        reason,
		ServiceType:   strings.TrimSpace(r.Config.ServiceType),
		Scope:         strings.TrimSpace(r.Config.Scope),
		ServiceClass:  serviceClass,
		Allowed:       append([]string{}, r.Config.ServiceClasses...),
		ObservedAt:    now.Format(time.RFC3339Nano),
	}
}

func scopeForServiceClass(serviceClass string, path string, fallback string) string {
	path = strings.Trim(strings.ToLower(path), "/")
	switch strings.TrimSpace(serviceClass) {
	case "admin-ingress":
		if strings.HasPrefix(path, "clusters/") {
			return "cluster"
		}
		return firstNonEmpty(strings.TrimSpace(fallback), "platform")
	case "public-ingress":
		if strings.HasPrefix(path, "users/") {
			return "user"
		}
		return firstNonEmpty(strings.TrimSpace(fallback), "organization")
	default:
		return strings.TrimSpace(fallback)
	}
}

func firstNonEmpty(value string, fallback string) string {
	if strings.TrimSpace(value) != "" {
		return strings.TrimSpace(value)
	}
	return strings.TrimSpace(fallback)
}

func serviceClassFromPath(path string) string {
	path = strings.Trim(strings.ToLower(path), "/")
	switch {
	case strings.HasPrefix(path, "admin/"), strings.HasPrefix(path, "platform/"), strings.HasPrefix(path, "clusters/"):
		return "admin-ingress"
	case strings.HasPrefix(path, "public/"), strings.HasPrefix(path, "organizations/"), strings.HasPrefix(path, "users/"):
		return "public-ingress"
	default:
		return ""
	}
}

func writeJSON(w http.ResponseWriter, status int, payload Response) {
	w.Header().Set("Content-Type", "application/json")
	w.Header().Set("Cache-Control", "no-store")
	w.WriteHeader(status)
	_ = json.NewEncoder(w).Encode(payload)
}

func writeFabricResponse(w http.ResponseWriter, payload FabricResponse) {
	for key, values := range payload.Headers {
		if !safeResponseHeader(key) {
			continue
		}
		for _, value := range values {
			w.Header().Add(key, value)
		}
	}
	w.Header().Set("Cache-Control", "no-store")
	status := payload.StatusCode
	if status < 100 || status > 599 {
		status = http.StatusOK
	}
	w.WriteHeader(status)
	_, _ = w.Write(payload.Body)
}

func cloneSafeHeaders(headers http.Header) http.Header {
	out := http.Header{}
	for key, values := range headers {
		if !safeRequestHeader(key) {
			continue
		}
		for _, value := range values {
			out.Add(key, value)
		}
	}
	return out
}

func safeRequestHeader(key string) bool {
	switch strings.ToLower(strings.TrimSpace(key)) {
	case "authorization", "cookie", "set-cookie", "x-rap-service-channel-token":
		return false
	default:
		return true
	}
}

func safeResponseHeader(key string) bool {
	switch strings.ToLower(strings.TrimSpace(key)) {
	case "set-cookie", "transfer-encoding", "connection":
		return false
	default:
		return true
	}
}

func contains(values []string, needle string) bool {
	for _, value := range values {
		if value == needle {
			return true
		}
	}
	return false
}