package saas

import (
	"context"
	"errors"
	"fmt"
	"strings"
	"time"

	"data-terminal-cloud/internal/audit"
	"data-terminal-cloud/internal/database"
	"data-terminal-cloud/internal/identity"

	"github.com/jackc/pgx/v5"
)

const (
	DeviceBindingActionUnbind   = "unbind"
	DeviceBindingActionTransfer = "transfer"
)

type DeviceBindingImpact struct {
	DeviceID                string    `json:"device_id"`
	BindingID               string    `json:"binding_id"`
	Action                  string    `json:"action"`
	SourceHouseholdID       string    `json:"source_household_id"`
	SourceSubjectID         string    `json:"source_subject_id"`
	SourceSubjectName       string    `json:"source_subject_name"`
	TargetHouseholdID       *string   `json:"target_household_id,omitempty"`
	TargetSubjectID         *string   `json:"target_subject_id,omitempty"`
	TargetSubjectName       *string   `json:"target_subject_name,omitempty"`
	ActiveConversationID    *string   `json:"active_conversation_id,omitempty"`
	PendingCommandCount     int       `json:"pending_command_count"`
	ActiveFirmwareTaskCount int       `json:"active_firmware_task_count"`
	Allowed                 bool      `json:"allowed"`
	Blockers                []string  `json:"blockers"`
	EvaluatedAt             time.Time `json:"evaluated_at"`
}

type ChangeDeviceBindingInput struct {
	Action            string
	ExpectedBindingID string
	TargetSubjectID   string
	Reason            string
	Acknowledged      bool
}

type DeviceBindingChangeResult struct {
	DeviceID          string    `json:"device_id"`
	Action            string    `json:"action"`
	PreviousBindingID string    `json:"previous_binding_id"`
	BindingID         *string   `json:"binding_id,omitempty"`
	HouseholdID       *string   `json:"household_id,omitempty"`
	SubjectID         *string   `json:"subject_id,omitempty"`
	ChangedAt         time.Time `json:"changed_at"`
}

func (s *Service) GetDeviceBindingImpact(ctx context.Context, principal identity.Principal, devicePublicID, action, targetSubjectPublicID string) (DeviceBindingImpact, error) {
	access, device, err := resolveDevice(ctx, s.pool, principal, devicePublicID, identity.CapabilityDeviceManage, false)
	if err != nil {
		return DeviceBindingImpact{}, err
	}
	return s.readDeviceBindingImpact(ctx, s.pool, principal, access, device, action, targetSubjectPublicID)
}

func (s *Service) ChangeDeviceBinding(ctx context.Context, principal identity.Principal, devicePublicID, requestID string, input ChangeDeviceBindingInput) (DeviceBindingChangeResult, error) {
	var result DeviceBindingChangeResult
	err := database.Transact(ctx, s.pool, func(tx pgx.Tx) error {
		access, device, err := resolveDevice(ctx, tx, principal, devicePublicID, identity.CapabilityDeviceManage, true)
		if err != nil {
			return err
		}
		var bindingID string
		if err := tx.QueryRow(ctx, `SELECT public_id::text FROM device_binding WHERE device_id=$1::uuid AND tenant_id=$2::uuid AND unbound_at IS NULL FOR UPDATE`, access.deviceID, access.tenantID).Scan(&bindingID); errors.Is(err, pgx.ErrNoRows) {
			return ErrDeviceBindingStale
		} else if err != nil {
			return fmt.Errorf("lock active device binding: %w", err)
		}
		if bindingID != input.ExpectedBindingID {
			return ErrDeviceBindingStale
		}
		impact, err := s.readDeviceBindingImpact(ctx, tx, principal, access, device, input.Action, input.TargetSubjectID)
		if err != nil {
			return err
		}
		if !impact.Allowed {
			return ErrDeviceBindingBlocked
		}
		now := time.Now().UTC()
		if _, err := tx.Exec(ctx, `UPDATE device_binding SET unbound_at=$1,unbound_by=$2::uuid,reason=$3 WHERE public_id=$4::uuid AND unbound_at IS NULL`, now, access.userID, input.Action+":"+strings.TrimSpace(input.Reason), bindingID); err != nil {
			return fmt.Errorf("close active device binding: %w", err)
		}
		result = DeviceBindingChangeResult{DeviceID: devicePublicID, Action: input.Action, PreviousBindingID: bindingID, ChangedAt: now}
		if input.Action == DeviceBindingActionTransfer {
			targetAccess, _, err := resolveSubject(ctx, tx, principal, input.TargetSubjectID, identity.CapabilityDeviceManage, true)
			if err != nil || targetAccess.tenantID != access.tenantID {
				return ErrAccessDenied
			}
			var newBindingID string
			if err := tx.QueryRow(ctx, `
				INSERT INTO device_binding (tenant_id,device_id,household_id,subject_id,bound_by,reason,bound_at)
				VALUES ($1::uuid,$2::uuid,$3::uuid,$4::uuid,$5::uuid,$6,$7)
				RETURNING public_id::text`, access.tenantID, access.deviceID, targetAccess.householdID, targetAccess.subjectID, access.userID, "transfer:"+strings.TrimSpace(input.Reason), now).Scan(&newBindingID); err != nil {
				return fmt.Errorf("create transferred device binding: %w", err)
			}
			result.BindingID = &newBindingID
			result.HouseholdID = &targetAccess.householdPublicID
			result.SubjectID = &input.TargetSubjectID
		}
		return s.audit.Record(ctx, tx, audit.Event{
			TenantID: strPtr(access.tenantID), ActorType: "user", ActorPublicID: strPtr(access.userPublicID),
			Action: "device.binding." + input.Action, ResourceType: "device", ResourceID: strPtr(devicePublicID),
			RequestID: requestID, Result: "success", Detail: map[string]any{
				"previous_binding_id": bindingID, "new_binding_id": result.BindingID, "target_household_id": result.HouseholdID,
				"target_subject_id": result.SubjectID, "reason": strings.TrimSpace(input.Reason),
			},
		})
	})
	return result, err
}

func (s *Service) readDeviceBindingImpact(ctx context.Context, q queryRow, principal identity.Principal, access deviceAccess, device ManagedDevice, action, targetSubjectPublicID string) (DeviceBindingImpact, error) {
	if action != DeviceBindingActionUnbind && action != DeviceBindingActionTransfer {
		return DeviceBindingImpact{}, ErrNotFound
	}
	impact := DeviceBindingImpact{
		DeviceID: device.ID, BindingID: device.BindingID, Action: action,
		SourceHouseholdID: device.HouseholdID, SourceSubjectID: device.SubjectID, SourceSubjectName: device.SubjectName,
		Blockers: make([]string, 0), EvaluatedAt: time.Now().UTC(),
	}
	if action == DeviceBindingActionTransfer {
		if targetSubjectPublicID == "" || targetSubjectPublicID == device.SubjectID {
			impact.Blockers = append(impact.Blockers, "target_subject_required")
		} else {
			targetAccess, target, err := resolveSubject(ctx, q, principal, targetSubjectPublicID, identity.CapabilityDeviceManage, false)
			if err != nil || targetAccess.tenantID != access.tenantID {
				return DeviceBindingImpact{}, ErrAccessDenied
			}
			impact.TargetHouseholdID = &target.HouseholdID
			impact.TargetSubjectID = &target.ID
			impact.TargetSubjectName = &target.PreferredName
		}
	}
	var activeConversation string
	err := q.QueryRow(ctx, `SELECT public_id::text FROM conversation WHERE device_id=$1::uuid AND tenant_id=$2::uuid AND status NOT IN ('COMPLETED','FAILED','EXPIRED') ORDER BY created_at DESC LIMIT 1`, access.deviceID, access.tenantID).Scan(&activeConversation)
	if err == nil {
		impact.ActiveConversationID = &activeConversation
		impact.Blockers = append(impact.Blockers, "active_conversation")
	} else if !errors.Is(err, pgx.ErrNoRows) {
		return DeviceBindingImpact{}, fmt.Errorf("check active device conversation: %w", err)
	}
	if err := q.QueryRow(ctx, `SELECT count(*) FROM device_command WHERE device_id=$1::uuid AND tenant_id=$2::uuid AND status IN ('QUEUED','DELIVERED','ACKNOWLEDGED') AND expires_at>now()`, access.deviceID, access.tenantID).Scan(&impact.PendingCommandCount); err != nil {
		return DeviceBindingImpact{}, fmt.Errorf("count pending device commands: %w", err)
	}
	if impact.PendingCommandCount > 0 {
		impact.Blockers = append(impact.Blockers, "pending_device_commands")
	}
	if err := q.QueryRow(ctx, `SELECT count(*) FROM firmware_assignment WHERE device_id=$1::uuid AND tenant_id=$2::uuid AND status IN ('PENDING','COMMAND_QUEUED','DOWNLOADING','INSTALLING')`, access.deviceID, access.tenantID).Scan(&impact.ActiveFirmwareTaskCount); err != nil {
		return DeviceBindingImpact{}, fmt.Errorf("count active firmware assignments: %w", err)
	}
	if impact.ActiveFirmwareTaskCount > 0 {
		impact.Blockers = append(impact.Blockers, "active_firmware_task")
	}
	impact.Allowed = len(impact.Blockers) == 0
	return impact, nil
}