package main

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

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

type DeviceHistoryEntry struct {
	ID              string                `json:"id"`
	DeviceID        string                `json:"deviceId"`
	UserID          string                `json:"userId"`
	UserDisplayName string                `json:"userDisplayName"`
	Action          string                `json:"action"`
	Changes         []DeviceHistoryChange `json:"changes"`
	CreatedAt       time.Time             `json:"createdAt"`
}

type DeviceHistoryChange struct {
	Field    string `json:"field"`
	Label    string `json:"label"`
	OldValue string `json:"oldValue"`
	NewValue string `json:"newValue"`
}

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

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

	rows, err := s.db.Query(
		r.Context(),
		`
		SELECT
			h.id,
			h.device_id,
			COALESCE(h.user_id::TEXT, ''),
			COALESCE(NULLIF(u.display_name, ''), NULLIF(u.username, ''), u.email, 'Unbekannt'),
			h.action,
			h.changes,
			h.created_at
		FROM device_history h
		LEFT JOIN users u ON u.id = h.user_id
		WHERE h.device_id = $1
		ORDER BY h.created_at DESC
		`,
		deviceID,
	)

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

	history := []DeviceHistoryEntry{}

	for rows.Next() {
		var entry DeviceHistoryEntry
		var changesRaw []byte

		if err := rows.Scan(
			&entry.ID,
			&entry.DeviceID,
			&entry.UserID,
			&entry.UserDisplayName,
			&entry.Action,
			&changesRaw,
			&entry.CreatedAt,
		); err != nil {
			writeError(w, http.StatusInternalServerError, "Could not read device history")
			return
		}

		if len(changesRaw) > 0 {
			if err := json.Unmarshal(changesRaw, &entry.Changes); err != nil {
				writeError(w, http.StatusInternalServerError, "Could not parse device history")
				return
			}
		}

		history = append(history, entry)
	}

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

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

func userFromContext(ctx context.Context) (User, bool) {
	user, ok := ctx.Value(userContextKey).(User)
	return user, ok
}

func recordDeviceHistory(
	ctx context.Context,
	tx pgx.Tx,
	deviceID string,
	user User,
	action string,
	changes []DeviceHistoryChange,
) error {
	changesJSON, err := json.Marshal(changes)
	if err != nil {
		return err
	}

	_, err = tx.Exec(
		ctx,
		`
		INSERT INTO device_history (
			device_id,
			user_id,
			action,
			changes
		)
		VALUES ($1, $2, $3, $4::JSONB)
		`,
		deviceID,
		user.ID,
		action,
		string(changesJSON),
	)

	return err
}

func getDeviceForHistory(ctx context.Context, tx pgx.Tx, deviceID string) (Device, []string, error) {
	var device Device

	err := tx.QueryRow(
		ctx,
		`
		SELECT
			id,
			inventory_number,
			manufacturer,
			model,
			serial_number,
			mac_address,
			location,
			loan_status,
			comment,
			created_at,
			updated_at
		FROM devices
		WHERE id = $1
		LIMIT 1
		`,
		deviceID,
	).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 {
		return device, nil, err
	}

	rows, err := tx.Query(
		ctx,
		`
		SELECT related_device_id
		FROM device_relations
		WHERE device_id = $1
		ORDER BY related_device_id ASC
		`,
		deviceID,
	)

	if err != nil {
		return device, nil, err
	}
	defer rows.Close()

	relatedDeviceIDs := []string{}

	for rows.Next() {
		var relatedDeviceID string

		if err := rows.Scan(&relatedDeviceID); err != nil {
			return device, nil, err
		}

		relatedDeviceIDs = append(relatedDeviceIDs, relatedDeviceID)
	}

	if err := rows.Err(); err != nil {
		return device, nil, err
	}

	return device, relatedDeviceIDs, nil
}

func buildDeviceCreateHistoryChanges(
	ctx context.Context,
	tx pgx.Tx,
	input CreateDeviceRequest,
) ([]DeviceHistoryChange, error) {
	changes := []DeviceHistoryChange{}

	changes = appendHistoryChange(changes, "inventoryNumber", "Inventur-Nr.", "", input.InventoryNumber)
	changes = appendHistoryChange(changes, "manufacturer", "Hersteller", "", input.Manufacturer)
	changes = appendHistoryChange(changes, "model", "Modell", "", input.Model)
	changes = appendHistoryChange(changes, "serialNumber", "Seriennummer", "", input.SerialNumber)
	changes = appendHistoryChange(changes, "macAddress", "MAC-Adresse", "", input.MacAddress)
	changes = appendHistoryChange(changes, "location", "Standort", "", input.Location)
	changes = appendHistoryChange(changes, "loanStatus", "Verleih-Status", "", input.LoanStatus)
	changes = appendHistoryChange(changes, "comment", "Kommentar", "", input.Comment)

	relatedDevices, err := formatRelatedDeviceLabels(ctx, tx, input.RelatedDeviceIDs)
	if err != nil {
		return nil, err
	}

	changes = appendHistoryChange(changes, "relatedDeviceIds", "Zugeordnete Geräte / Zubehör", "", relatedDevices)

	return changes, nil
}

func buildDeviceUpdateHistoryChanges(
	ctx context.Context,
	tx pgx.Tx,
	oldDevice Device,
	oldRelatedDeviceIDs []string,
	input UpdateDeviceRequest,
) ([]DeviceHistoryChange, error) {
	changes := []DeviceHistoryChange{}

	changes = appendHistoryChange(changes, "inventoryNumber", "Inventur-Nr.", oldDevice.InventoryNumber, input.InventoryNumber)
	changes = appendHistoryChange(changes, "manufacturer", "Hersteller", oldDevice.Manufacturer, input.Manufacturer)
	changes = appendHistoryChange(changes, "model", "Modell", oldDevice.Model, input.Model)
	changes = appendHistoryChange(changes, "serialNumber", "Seriennummer", oldDevice.SerialNumber, input.SerialNumber)
	changes = appendHistoryChange(changes, "macAddress", "MAC-Adresse", oldDevice.MacAddress, input.MacAddress)
	changes = appendHistoryChange(changes, "location", "Standort", oldDevice.Location, input.Location)
	changes = appendHistoryChange(changes, "loanStatus", "Verleih-Status", oldDevice.LoanStatus, input.LoanStatus)
	changes = appendHistoryChange(changes, "comment", "Kommentar", oldDevice.Comment, input.Comment)

	oldRelatedDevices, err := formatRelatedDeviceLabels(ctx, tx, oldRelatedDeviceIDs)
	if err != nil {
		return nil, err
	}

	newRelatedDevices, err := formatRelatedDeviceLabels(ctx, tx, input.RelatedDeviceIDs)
	if err != nil {
		return nil, err
	}

	changes = appendHistoryChange(
		changes,
		"relatedDeviceIds",
		"Zugeordnete Geräte / Zubehör",
		oldRelatedDevices,
		newRelatedDevices,
	)

	return changes, nil
}

func appendHistoryChange(
	changes []DeviceHistoryChange,
	field string,
	label string,
	oldValue string,
	newValue string,
) []DeviceHistoryChange {
	oldValue = strings.TrimSpace(oldValue)
	newValue = strings.TrimSpace(newValue)

	if oldValue == newValue {
		return changes
	}

	return append(changes, DeviceHistoryChange{
		Field:    field,
		Label:    label,
		OldValue: displayHistoryValue(oldValue),
		NewValue: displayHistoryValue(newValue),
	})
}

func displayHistoryValue(value string) string {
	value = strings.TrimSpace(value)

	if value == "" {
		return "-"
	}

	return value
}

func formatRelatedDeviceLabels(ctx context.Context, tx pgx.Tx, deviceIDs []string) (string, error) {
	normalizedDeviceIDs := normalizeDeviceIDs(deviceIDs)

	if len(normalizedDeviceIDs) == 0 {
		return "-", nil
	}

	labels := []string{}

	for _, deviceID := range normalizedDeviceIDs {
		var label string

		err := tx.QueryRow(
			ctx,
			`
			SELECT TRIM(CONCAT_WS(' ', inventory_number, NULLIF(manufacturer, ''), NULLIF(model, '')))
			FROM devices
			WHERE id = $1
			LIMIT 1
			`,
			deviceID,
		).Scan(&label)

		if errors.Is(err, pgx.ErrNoRows) {
			return "", errDeviceNotFound
		}

		if err != nil {
			return "", err
		}

		label = strings.TrimSpace(label)

		if label == "" {
			label = deviceID
		}

		labels = append(labels, label)
	}

	return strings.Join(labels, ", "), nil
}

func normalizeDeviceIDs(deviceIDs []string) []string {
	seen := map[string]bool{}
	result := []string{}

	for _, deviceID := range deviceIDs {
		deviceID = strings.TrimSpace(deviceID)

		if deviceID == "" {
			continue
		}

		if seen[deviceID] {
			continue
		}

		seen[deviceID] = true
		result = append(result, deviceID)
	}

	return result
}