package usecase

import (
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"strings"
	"sync"
	"time"

	redislib "gateway/internal/library/redis"
	permission "gateway/internal/model/permission/domain"
	"gateway/internal/model/permission/domain/entity"
	"gateway/internal/model/permission/domain/enum"
	domrepo "gateway/internal/model/permission/domain/repository"
	dom "gateway/internal/model/permission/domain/usecase"

	"github.com/casbin/casbin/v2"
	casbinmodel "github.com/casbin/casbin/v2/model"
	"github.com/zeromicro/go-zero/core/logx"
)

// RBACUseCaseParam injects all repos + Redis Pub/Sub client. ModelPath
// must point at etc/rbac.conf; CasbinModelText overrides ModelPath when
// non-empty (used by tests / embedded resources).
type RBACUseCaseParam struct {
	Roles           domrepo.RoleRepository
	Permissions     domrepo.PermissionRepository
	RolePermissions domrepo.RolePermissionRepository
	UserRoles       domrepo.UserRoleRepository
	Redis           *redislib.Client
	ModelPath       string
	CasbinModelText string
	ReloadChannel   string
}

// reloadEvent is the JSON payload published on the reload channel.
type reloadEvent struct {
	TenantID string `json:"tenant_id"`
	TS       int64  `json:"ts"`
}

type rbacUseCase struct {
	roles     domrepo.RoleRepository
	perms     domrepo.PermissionRepository
	rolePerms domrepo.RolePermissionRepository
	userRoles domrepo.UserRoleRepository
	redis     *redislib.Client

	enforcerMu sync.RWMutex
	enforcers  map[string]*casbin.SyncedEnforcer

	model    casbinmodel.Model
	modelMu  sync.Mutex
	modelTxt string

	reloadChannel string
	stopSubscribe context.CancelFunc
	stopMu        sync.Mutex
}

// NewRBACUseCase wires the Casbin enforcer with the persistence layer.
// Returns ErrCasbinNotConfigured when Redis is missing — Casbin's Redis
// adapter and Pub/Sub require Redis to function.
func NewRBACUseCase(param RBACUseCaseParam) (dom.RBACUseCase, error) {
	if param.Redis == nil || param.Redis.Zero() == nil {
		return nil, permission.ErrCasbinNotConfigured
	}
	channel := strings.TrimSpace(param.ReloadChannel)
	if channel == "" {
		channel = permission.PolicyReloadChannel
	}
	uc := &rbacUseCase{
		roles:         param.Roles,
		perms:         param.Permissions,
		rolePerms:     param.RolePermissions,
		userRoles:     param.UserRoles,
		redis:         param.Redis,
		enforcers:     make(map[string]*casbin.SyncedEnforcer),
		modelTxt:      strings.TrimSpace(param.CasbinModelText),
		reloadChannel: channel,
	}
	if uc.modelTxt == "" && param.ModelPath != "" {
		mdl, err := casbinmodel.NewModelFromFile(param.ModelPath)
		if err != nil {
			return nil, fmt.Errorf("permission: load casbin model: %w", err)
		}
		uc.model = mdl
	}
	return uc, nil
}

// Check enforces (tenant, uid → role keys) ∩ policy. Multiple roles use
// any-allow semantics: the first matching role short-circuits with
// allow=true. The `r.role == p.role` matcher means we must call EnforceEx
// once per role; that is acceptable because a member typically has 1–3
// roles and the call is in-memory.
func (uc *rbacUseCase) Check(ctx context.Context, req *dom.CheckRequest) (*dom.CheckResult, error) {
	if req == nil || req.TenantID == "" || req.UID == "" || req.Path == "" || req.Method == "" {
		return nil, permission.ErrInvalidCheckRequest
	}
	enforcer, err := uc.enforcerFor(ctx, req.TenantID)
	if err != nil {
		return nil, err
	}
	roleKeys, err := uc.roleKeysOf(ctx, req.TenantID, req.UID)
	if err != nil {
		return nil, err
	}
	if len(roleKeys) == 0 {
		return &dom.CheckResult{Allow: false}, nil
	}
	for _, key := range roleKeys {
		ok, matched, err := enforcer.EnforceEx(req.TenantID, key, req.Path, req.Method)
		if err != nil {
			return nil, fmt.Errorf("permission: enforce: %w", err)
		}
		if ok {
			return &dom.CheckResult{
				Allow:            true,
				MatchedRoleKey:   key,
				MatchedPolicyRow: append([]string{permission.CasbinPolicyType}, matched...),
			}, nil
		}
	}
	return &dom.CheckResult{Allow: false}, nil
}

// LoadPolicy materialises role_permissions for a single tenant into
// Casbin policy rules and atomically saves them via the Redis adapter.
func (uc *rbacUseCase) LoadPolicy(ctx context.Context, tenantID string) error {
	rules, err := uc.buildRules(ctx, tenantID)
	if err != nil {
		return err
	}
	enforcer, err := uc.enforcerFor(ctx, tenantID)
	if err != nil {
		return err
	}
	enforcer.ClearPolicy()
	if len(rules) > 0 {
		if _, err := enforcer.AddPolicies(rules); err != nil {
			return fmt.Errorf("permission: add policies: %w", err)
		}
	}
	if err := uc.saveAdapter(ctx, tenantID, rules); err != nil {
		logx.WithContext(ctx).Errorf("permission: save adapter tenant=%s: %v", tenantID, err)
	}
	return nil
}

// LoadAllPolicies refreshes policies for every tenant. Used by the
// 5-minute cron fallback (see plan §6.11).
func (uc *rbacUseCase) LoadAllPolicies(ctx context.Context) error {
	// Tenant list comes from the member module via Casbin keys; here we
	// scan the role collection's distinct tenant_id. For simplicity we
	// reload only tenants that have at least one role.
	roles, err := uc.allTenantsWithRoles(ctx)
	if err != nil {
		return err
	}
	for _, tenantID := range roles {
		if err := uc.LoadPolicy(ctx, tenantID); err != nil {
			logx.WithContext(ctx).Errorf("permission: reload tenant=%s: %v", tenantID, err)
		}
	}
	return nil
}

// BroadcastReload publishes a tenant-scoped reload event over Redis
// Pub/Sub. Other pods (and this pod itself) consume it to re-LoadPolicy.
func (uc *rbacUseCase) BroadcastReload(ctx context.Context, tenantID string) error {
	if uc.redis == nil || uc.redis.Zero() == nil {
		return nil
	}
	if tenantID == "" {
		tenantID = permission.PolicyReloadAllToken
	}
	payload, err := json.Marshal(reloadEvent{TenantID: tenantID, TS: time.Now().UnixMilli()})
	if err != nil {
		return err
	}
	_, err = uc.redis.Zero().PublishCtx(ctx, uc.reloadChannel, string(payload))
	return err
}

// StartReloadSubscriber spins a goroutine that reads from the Redis
// Pub/Sub channel and calls LoadPolicy for each event. Idempotent: a
// second call replaces the prior subscription.
func (uc *rbacUseCase) StartReloadSubscriber(ctx context.Context) error {
	uc.StopReloadSubscriber()
	pubsub := uc.redis.PubSubClient()
	if pubsub == nil {
		return nil
	}
	subCtx, cancel := context.WithCancel(ctx)
	uc.stopMu.Lock()
	uc.stopSubscribe = cancel
	uc.stopMu.Unlock()

	sub := pubsub.Subscribe(subCtx, uc.reloadChannel)
	if _, err := sub.Receive(subCtx); err != nil {
		cancel()
		return fmt.Errorf("permission: subscribe reload channel: %w", err)
	}
	ch := sub.Channel()
	go func() {
		defer func() { _ = sub.Close() }()
		for {
			select {
			case <-subCtx.Done():
				return
			case msg, ok := <-ch:
				if !ok {
					return
				}
				uc.handleReload(subCtx, msg.Payload)
			}
		}
	}()
	return nil
}

// StopReloadSubscriber cancels the subscriber goroutine (best-effort).
func (uc *rbacUseCase) StopReloadSubscriber() {
	uc.stopMu.Lock()
	defer uc.stopMu.Unlock()
	if uc.stopSubscribe != nil {
		uc.stopSubscribe()
		uc.stopSubscribe = nil
	}
}

func (uc *rbacUseCase) handleReload(ctx context.Context, payload string) {
	var ev reloadEvent
	if err := json.Unmarshal([]byte(payload), &ev); err != nil {
		logx.WithContext(ctx).Errorf("permission: invalid reload payload: %s", payload)
		return
	}
	if ev.TenantID == permission.PolicyReloadAllToken || ev.TenantID == "" {
		if err := uc.LoadAllPolicies(ctx); err != nil {
			logx.WithContext(ctx).Errorf("permission: reload all: %v", err)
		}
		return
	}
	if err := uc.LoadPolicy(ctx, ev.TenantID); err != nil {
		logx.WithContext(ctx).Errorf("permission: reload tenant=%s: %v", ev.TenantID, err)
	}
}

func (uc *rbacUseCase) enforcerFor(ctx context.Context, tenantID string) (*casbin.SyncedEnforcer, error) {
	uc.enforcerMu.RLock()
	if e, ok := uc.enforcers[tenantID]; ok {
		uc.enforcerMu.RUnlock()
		return e, nil
	}
	uc.enforcerMu.RUnlock()

	uc.enforcerMu.Lock()
	defer uc.enforcerMu.Unlock()
	if e, ok := uc.enforcers[tenantID]; ok {
		return e, nil
	}
	mdl, err := uc.cloneModel()
	if err != nil {
		return nil, err
	}
	enforcer, err := casbin.NewSyncedEnforcer(mdl)
	if err != nil {
		return nil, fmt.Errorf("permission: new enforcer: %w", err)
	}
	enforcer.EnableAutoSave(false)
	uc.enforcers[tenantID] = enforcer

	rules, err := uc.buildRules(ctx, tenantID)
	if err != nil {
		return nil, err
	}
	if len(rules) > 0 {
		if _, err := enforcer.AddPolicies(rules); err != nil {
			return nil, fmt.Errorf("permission: seed policies: %w", err)
		}
	}
	return enforcer, nil
}

func (uc *rbacUseCase) cloneModel() (casbinmodel.Model, error) {
	uc.modelMu.Lock()
	defer uc.modelMu.Unlock()
	if uc.modelTxt != "" {
		return casbinmodel.NewModelFromString(uc.modelTxt)
	}
	if uc.model == nil {
		return nil, errors.New("permission: casbin model not loaded")
	}
	// casbin/model is not safe for concurrent enforcers in some versions;
	// dump+parse keeps each enforcer isolated.
	return casbinmodel.NewModelFromString(uc.model.ToText())
}

func (uc *rbacUseCase) buildRules(ctx context.Context, tenantID string) ([][]string, error) {
	roles, err := uc.roles.ListByTenant(ctx, tenantID)
	if err != nil {
		return nil, wrapRepoErr(err)
	}
	if len(roles) == 0 {
		return nil, nil
	}
	roleByID := make(map[string]*entity.Role, len(roles))
	roleIDs := make([]string, 0, len(roles))
	for _, role := range roles {
		if role.Status != enum.StatusOpen {
			continue
		}
		roleByID[role.ID.Hex()] = role
		roleIDs = append(roleIDs, role.ID.Hex())
	}
	rps, err := uc.rolePerms.ListByRoles(ctx, tenantID, roleIDs)
	if err != nil {
		return nil, wrapRepoErr(err)
	}
	if len(rps) == 0 {
		return nil, nil
	}
	permIDSet := make(map[string]struct{}, len(rps))
	for _, rp := range rps {
		permIDSet[rp.PermissionID] = struct{}{}
	}
	ids := make([]string, 0, len(permIDSet))
	for id := range permIDSet {
		ids = append(ids, id)
	}
	perms, err := uc.perms.GetByIDs(ctx, ids)
	if err != nil {
		return nil, wrapRepoErr(err)
	}
	permByID := make(map[string]*entity.Permission, len(perms))
	for _, perm := range perms {
		permByID[perm.ID.Hex()] = perm
	}
	rules := make([][]string, 0, len(rps))
	for _, rp := range rps {
		role, ok := roleByID[rp.RoleID]
		if !ok {
			continue
		}
		perm, ok := permByID[rp.PermissionID]
		if !ok || !perm.IsLeaf() || perm.Status != enum.StatusOpen {
			continue
		}
		rules = append(rules, []string{
			tenantID,
			role.Key,
			perm.HTTPPath,
			perm.HTTPMethods,
			perm.Name,
		})
	}
	return rules, nil
}

func (uc *rbacUseCase) allTenantsWithRoles(ctx context.Context) ([]string, error) {
	// Casbin reload is best-effort across pods; we use the Redis cluster
	// to remember which tenant keys exist. Empty set ⇒ nothing to do.
	if uc.redis == nil || uc.redis.Zero() == nil {
		return nil, nil
	}
	keys, err := uc.redis.Zero().KeysCtx(ctx, permission.CasbinRulesRedisKey.String()+":*")
	if err != nil {
		return nil, err
	}
	prefix := permission.CasbinRulesRedisKey.String() + ":"
	tenantIDs := make([]string, 0, len(keys))
	for _, key := range keys {
		tenantIDs = append(tenantIDs, strings.TrimPrefix(key, prefix))
	}
	return tenantIDs, nil
}

func (uc *rbacUseCase) saveAdapter(ctx context.Context, tenantID string, rules [][]string) error {
	adapter, err := newRedisAdapterFromClient(uc.redis)
	if err != nil || adapter == nil {
		return err
	}
	return adapter.SaveAll(ctx, tenantID, rules)
}

// newRedisAdapterFromClient is implemented in casbin_adapter_bridge.go to
// keep the import surface narrow (avoid pulling repository into usecase).
func newRedisAdapterFromClient(client *redislib.Client) (domrepo.CasbinPolicyAdapter, error) {
	return RedisAdapterFactory(client)
}

// RedisAdapterFactory is plugged in by module.go (DI seam). Tests can
// override by assigning a stub.
var RedisAdapterFactory = func(_ *redislib.Client) (domrepo.CasbinPolicyAdapter, error) {
	return nil, nil
}

func (uc *rbacUseCase) roleKeysOf(ctx context.Context, tenantID, uid string) ([]string, error) {
	urs, err := uc.userRoles.ListByUser(ctx, tenantID, uid)
	if err != nil {
		return nil, wrapRepoErr(err)
	}
	if len(urs) == 0 {
		return nil, nil
	}
	roleIDs := make([]string, 0, len(urs))
	for _, ur := range urs {
		roleIDs = append(roleIDs, ur.RoleID)
	}
	roles, err := uc.roles.ListByTenantAndIDs(ctx, tenantID, roleIDs)
	if err != nil {
		return nil, wrapRepoErr(err)
	}
	out := make([]string, 0, len(roles))
	for _, role := range roles {
		if role.Status != enum.StatusOpen {
			continue
		}
		out = append(out, role.Key)
	}
	return out, nil
}

var _ dom.RBACUseCase = (*rbacUseCase)(nil)