// backend/devices.go

package main

import (
	"context"
	"errors"
	"net/http"
	"strings"
	"time"

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

type Device struct {
	ID              string        `json:"id"`
	InventoryNumber string        `json:"inventoryNumber"`
	Manufacturer    string        `json:"manufacturer"`
	Model           string        `json:"model"`
	SerialNumber    string        `json:"serialNumber"`
	MacAddress      string        `json:"macAddress"`
	Location        string        `json:"location"`
	LoanStatus      string        `json:"loanStatus"`
	Comment         string        `json:"comment"`
	RelatedDevices  []DeviceShort `json:"relatedDevices"`
	CreatedAt       time.Time     `json:"createdAt"`
	UpdatedAt       time.Time     `json:"updatedAt"`
}

type DeviceShort struct {
	ID              string `json:"id"`
	InventoryNumber string `json:"inventoryNumber"`
	Manufacturer    string `json:"manufacturer"`
	Model           string `json:"model"`
}

type CreateDeviceRequest struct {
	InventoryNumber  string   `json:"inventoryNumber"`
	Manufacturer     string   `json:"manufacturer"`
	Model            string   `json:"model"`
	SerialNumber     string   `json:"serialNumber"`
	MacAddress       string   `json:"macAddress"`
	Location         string   `json:"location"`
	LoanStatus       string   `json:"loanStatus"`
	Comment          string   `json:"comment"`
	RelatedDeviceIDs []string `json:"relatedDeviceIds"`
}

type UpdateDeviceRequest = CreateDeviceRequest

var errDeviceNotFound = errors.New("device does not exist")

func (s *Server) handleDevices(w http.ResponseWriter, r *http.Request) {
	switch r.Method {
	case http.MethodGet:
		s.handleListDevices(w, r)
	case http.MethodPost:
		s.handleCreateDevice(w, r)
	default:
		writeError(w, http.StatusMethodNotAllowed, "Method not allowed")
	}
}

func (s *Server) handleListDevices(w http.ResponseWriter, r *http.Request) {
	rows, err := s.db.Query(
		r.Context(),
		`
		SELECT
			id,
			inventory_number,
			manufacturer,
			model,
			serial_number,
			mac_address,
			location,
			loan_status,
			comment,
			created_at,
			updated_at
		FROM devices
		ORDER BY inventory_number ASC
		`,
	)

	if err != nil {
		writeError(w, http.StatusInternalServerError, "Could not load devices")
		return
	}
	defer rows.Close()

	devices := make([]Device, 0)
	deviceMap := map[string]*Device{}

	for rows.Next() {
		var device Device

		if err := rows.Scan(
			&device.ID,
			&device.InventoryNumber,
			&device.Manufacturer,
			&device.Model,
			&device.SerialNumber,
			&device.MacAddress,
			&device.Location,
			&device.LoanStatus,
			&device.Comment,
			&device.CreatedAt,
			&device.UpdatedAt,
		); err != nil {
			writeError(w, http.StatusInternalServerError, "Could not read devices")
			return
		}

		device.RelatedDevices = []DeviceShort{}

		devices = append(devices, device)
		deviceMap[device.ID] = &devices[len(devices)-1]
	}

	if err := rows.Err(); err != nil {
		writeError(w, http.StatusInternalServerError, "Could not read devices")
		return
	}

	relationRows, err := s.db.Query(
		r.Context(),
		`
		SELECT
			device_relations.device_id,
			related_devices.id,
			related_devices.inventory_number,
			related_devices.manufacturer,
			related_devices.model
		FROM device_relations
		INNER JOIN devices AS related_devices
			ON related_devices.id = device_relations.related_device_id
		ORDER BY related_devices.inventory_number ASC
		`,
	)

	if err != nil {
		writeError(w, http.StatusInternalServerError, "Could not load device relations")
		return
	}
	defer relationRows.Close()

	for relationRows.Next() {
		var deviceID string
		var relatedDevice DeviceShort

		if err := relationRows.Scan(
			&deviceID,
			&relatedDevice.ID,
			&relatedDevice.InventoryNumber,
			&relatedDevice.Manufacturer,
			&relatedDevice.Model,
		); err != nil {
			writeError(w, http.StatusInternalServerError, "Could not read device relations")
			return
		}

		device, exists := deviceMap[deviceID]
		if exists {
			device.RelatedDevices = append(device.RelatedDevices, relatedDevice)
		}
	}

	if err := relationRows.Err(); err != nil {
		writeError(w, http.StatusInternalServerError, "Could not read device relations")
		return
	}

	writeJSON(w, http.StatusOK, map[string]any{
		"devices": devices,
	})
}

func (s *Server) handleCreateDevice(w http.ResponseWriter, r *http.Request) {
	var input CreateDeviceRequest

	if err := readJSON(r, &input); err != nil {
		writeError(w, http.StatusBadRequest, "Invalid JSON")
		return
	}

	normalizeDeviceInput(&input)

	if input.InventoryNumber == "" {
		writeError(w, http.StatusBadRequest, "Inventur-Nr. ist erforderlich")
		return
	}

	user, ok := userFromContext(r.Context())
	if !ok {
		writeError(w, http.StatusUnauthorized, "Unauthorized")
		return
	}

	tx, err := s.db.Begin(r.Context())
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Could not create device")
		return
	}
	defer tx.Rollback(r.Context())

	var device Device

	err = tx.QueryRow(
		r.Context(),
		`
		INSERT INTO devices (
			inventory_number,
			manufacturer,
			model,
			serial_number,
			mac_address,
			location,
			loan_status,
			comment
		)
		VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
		RETURNING
			id,
			inventory_number,
			manufacturer,
			model,
			serial_number,
			mac_address,
			location,
			loan_status,
			comment,
			created_at,
			updated_at
		`,
		input.InventoryNumber,
		input.Manufacturer,
		input.Model,
		input.SerialNumber,
		input.MacAddress,
		input.Location,
		input.LoanStatus,
		input.Comment,
	).Scan(
		&device.ID,
		&device.InventoryNumber,
		&device.Manufacturer,
		&device.Model,
		&device.SerialNumber,
		&device.MacAddress,
		&device.Location,
		&device.LoanStatus,
		&device.Comment,
		&device.CreatedAt,
		&device.UpdatedAt,
	)

	if err != nil {
		var pgErr *pgconn.PgError

		if errors.As(err, &pgErr) && pgErr.Code == "23505" {
			writeError(w, http.StatusConflict, "Gerät mit dieser Inventur-Nr., Seriennummer oder MAC-Adresse existiert bereits")
			return
		}

		writeError(w, http.StatusInternalServerError, "Could not create device")
		return
	}

	if err := syncDeviceRelations(r.Context(), tx, device.ID, input.RelatedDeviceIDs); err != nil {
		if errors.Is(err, errDeviceNotFound) {
			writeError(w, http.StatusBadRequest, "Zugeordnetes Gerät wurde nicht gefunden")
			return
		}

		writeError(w, http.StatusInternalServerError, "Could not assign related device")
		return
	}

	changes, err := buildDeviceCreateHistoryChanges(r.Context(), tx, input)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Could not create device history")
		return
	}

	if err := recordDeviceHistory(r.Context(), tx, device.ID, user, "created", changes); err != nil {
		writeError(w, http.StatusInternalServerError, "Could not create device history")
		return
	}

	if err := tx.Commit(r.Context()); err != nil {
		writeError(w, http.StatusInternalServerError, "Could not create device")
		return
	}

	device.RelatedDevices = []DeviceShort{}

	writeJSON(w, http.StatusCreated, map[string]any{
		"device": device,
	})
}

func (s *Server) handleUpdateDevice(w http.ResponseWriter, r *http.Request) {
	deviceID := strings.TrimSpace(r.PathValue("id"))

	if deviceID == "" {
		writeError(w, http.StatusBadRequest, "Geräte-ID fehlt")
		return
	}

	var input UpdateDeviceRequest

	if err := readJSON(r, &input); err != nil {
		writeError(w, http.StatusBadRequest, "Invalid JSON")
		return
	}

	normalizeDeviceInput(&input)

	if input.InventoryNumber == "" {
		writeError(w, http.StatusBadRequest, "Inventur-Nr. ist erforderlich")
		return
	}

	user, ok := userFromContext(r.Context())
	if !ok {
		writeError(w, http.StatusUnauthorized, "Unauthorized")
		return
	}

	tx, err := s.db.Begin(r.Context())
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Could not update device")
		return
	}
	defer tx.Rollback(r.Context())

	oldDevice, oldRelatedDeviceIDs, err := getDeviceForHistory(r.Context(), tx, deviceID)
	if errors.Is(err, pgx.ErrNoRows) {
		writeError(w, http.StatusNotFound, "Gerät wurde nicht gefunden")
		return
	}

	if err != nil {
		writeError(w, http.StatusInternalServerError, "Could not load device history state")
		return
	}

	var device Device

	err = tx.QueryRow(
		r.Context(),
		`
		UPDATE devices
		SET
			inventory_number = $2,
			manufacturer = $3,
			model = $4,
			serial_number = $5,
			mac_address = $6,
			location = $7,
			loan_status = $8,
			comment = $9,
			updated_at = now()
		WHERE id = $1
		RETURNING
			id,
			inventory_number,
			manufacturer,
			model,
			serial_number,
			mac_address,
			location,
			loan_status,
			comment,
			created_at,
			updated_at
		`,
		deviceID,
		input.InventoryNumber,
		input.Manufacturer,
		input.Model,
		input.SerialNumber,
		input.MacAddress,
		input.Location,
		input.LoanStatus,
		input.Comment,
	).Scan(
		&device.ID,
		&device.InventoryNumber,
		&device.Manufacturer,
		&device.Model,
		&device.SerialNumber,
		&device.MacAddress,
		&device.Location,
		&device.LoanStatus,
		&device.Comment,
		&device.CreatedAt,
		&device.UpdatedAt,
	)

	if errors.Is(err, pgx.ErrNoRows) {
		writeError(w, http.StatusNotFound, "Gerät wurde nicht gefunden")
		return
	}

	if err != nil {
		var pgErr *pgconn.PgError

		if errors.As(err, &pgErr) && pgErr.Code == "23505" {
			writeError(w, http.StatusConflict, "Gerät mit dieser Inventur-Nr., Seriennummer oder MAC-Adresse existiert bereits")
			return
		}

		writeError(w, http.StatusInternalServerError, "Could not update device")
		return
	}

	if err := syncDeviceRelations(r.Context(), tx, device.ID, input.RelatedDeviceIDs); err != nil {
		if errors.Is(err, errDeviceNotFound) {
			writeError(w, http.StatusBadRequest, "Zugeordnetes Gerät wurde nicht gefunden")
			return
		}

		writeError(w, http.StatusInternalServerError, "Could not update device relations")
		return
	}

	changes, err := buildDeviceUpdateHistoryChanges(r.Context(), tx, oldDevice, oldRelatedDeviceIDs, input)
	if err != nil {
		writeError(w, http.StatusInternalServerError, "Could not create device history")
		return
	}

	if len(changes) > 0 {
		if err := recordDeviceHistory(r.Context(), tx, device.ID, user, "updated", changes); err != nil {
			writeError(w, http.StatusInternalServerError, "Could not create device history")
			return
		}
	}

	if err := tx.Commit(r.Context()); err != nil {
		writeError(w, http.StatusInternalServerError, "Could not update device")
		return
	}

	device.RelatedDevices = []DeviceShort{}

	writeJSON(w, http.StatusOK, map[string]any{
		"device": device,
	})
}

func ensureDeviceExists(ctx context.Context, tx pgx.Tx, deviceID string) error {
	var exists bool

	err := tx.QueryRow(
		ctx,
		`
		SELECT EXISTS(
			SELECT 1
			FROM devices
			WHERE id = $1
		)
		`,
		deviceID,
	).Scan(&exists)

	if err != nil {
		return err
	}

	if !exists {
		return errDeviceNotFound
	}

	return nil
}

func normalizeDeviceInput(input *CreateDeviceRequest) {
	input.InventoryNumber = strings.TrimSpace(input.InventoryNumber)
	input.Manufacturer = strings.TrimSpace(input.Manufacturer)
	input.Model = strings.TrimSpace(input.Model)
	input.SerialNumber = strings.TrimSpace(input.SerialNumber)
	input.MacAddress = strings.TrimSpace(input.MacAddress)
	input.Location = strings.TrimSpace(input.Location)
	input.LoanStatus = strings.TrimSpace(input.LoanStatus)
	input.Comment = strings.TrimSpace(input.Comment)

	if input.LoanStatus == "" {
		input.LoanStatus = "Verfügbar"
	}
}

func syncDeviceRelations(ctx context.Context, tx pgx.Tx, deviceID string, relatedDeviceIDs []string) error {
	_, err := tx.Exec(
		ctx,
		`
		DELETE FROM device_relations
		WHERE device_id = $1 OR related_device_id = $1
		`,
		deviceID,
	)

	if err != nil {
		return err
	}

	seen := map[string]bool{}

	for _, relatedDeviceID := range relatedDeviceIDs {
		relatedDeviceID = strings.TrimSpace(relatedDeviceID)

		if relatedDeviceID == "" || relatedDeviceID == deviceID {
			continue
		}

		if seen[relatedDeviceID] {
			continue
		}

		seen[relatedDeviceID] = true

		if err := ensureDeviceExists(ctx, tx, relatedDeviceID); err != nil {
			return err
		}

		if err := assignRelatedDevice(ctx, tx, deviceID, relatedDeviceID); err != nil {
			return err
		}

		if err := assignRelatedDevice(ctx, tx, relatedDeviceID, deviceID); err != nil {
			return err
		}
	}

	return nil
}

func assignRelatedDevice(ctx context.Context, tx pgx.Tx, deviceID string, relatedDeviceID string) error {
	_, err := tx.Exec(
		ctx,
		`
		INSERT INTO device_relations (
			device_id,
			related_device_id
		)
		VALUES ($1, $2)
		ON CONFLICT (device_id, related_device_id) DO NOTHING
		`,
		deviceID,
		relatedDeviceID,
	)

	return err
}

type deviceTransaction interface {
	QueryRow(ctx context.Context, sql string, args ...any) pgx.Row
	Exec(ctx context.Context, sql string, args ...any) (pgconn.CommandTag, error)
}