import "package:flutter/material.dart";
import "package:intl/intl.dart";

import "i18n.dart";
import "main.dart";
import "models.dart";
import "theme.dart";

/// The languages intl actually ships symbols for. It throws rather than falling
/// back on the rest, and the API only validates a locale's *shape*
/// (`^[a-z]{2}-[A-Z]{2}$`), so an unsupported tag can legitimately arrive here —
/// set from the web, which has the browser's full ICU data behind it. Guarding
/// once keeps that from throwing out of every date on screen.
final _supportedLanguages = DateFormat.allLocalesWithSymbols().toSet();

/// The user's locale when intl can render it, else a safe default. Only the
/// language subtag is checked: intl resolves an unknown *region* by falling back
/// to the language ("en-PL" formats as "en"), but an unknown language throws.
String get _locale =>
    _supportedLanguages.contains(appSettings.language) ? appSettings.locale : "en-US";

/// Every number we render goes through here so the grouping separator follows
/// the user's chosen region rather than the device's own locale — otherwise the
/// odometer disagrees with the dates and costs beside it.
String _num(num value) => NumberFormat.decimalPattern(_locale).format(value);

/// Formats a date per the signed-in user's chosen date format (appSettings),
/// mirroring the web app's format.js. Month names follow the locale's language.
String formatDate(DateTime? d) {
  if (d == null) return "—";
  final pattern = switch (appSettings.dateFormat) {
    "DMY_NUM" => "dd-MM-yyyy",
    "DMY" => "dd MMM yyyy",
    "MDY" => "MMM dd, yyyy",
    _ => "yyyy-MM-dd", // YMD
  };
  return DateFormat(pattern, _locale).format(d);
}

/// A timestamp: the user's chosen date format with the wall clock beside it.
/// Only the provider snapshot needs one — everything else in the app is
/// date-only — but it follows the same settings as [formatDate] so the two never
/// disagree on screen.
String formatDateTime(DateTime? d) {
  if (d == null) return "—";
  return "${formatDate(d)} ${DateFormat.Hm(_locale).format(d)}";
}

// 0 km is a reading — a car collected new — not a blank. See format.js.
String formatKm(int? km) => km == null ? "—" : "${_num(km)} km";

// The fuel figures. The server sends null for anything it could not derive (a
// window with a missed fill, a first-ever tank), which reads as "—" rather than
// a misleading zero.
String formatLiters(double? value) => value == null ? "—" : "${value.toStringAsFixed(2)} L";

/// Amounts are stored as plain numbers; the user's currency setting only decides
/// how they are displayed. Nothing is converted — a figure entered as 40 reads as
/// 40 in whichever currency is selected.
///
/// No explicit fraction digits: the currency's own minor unit pins them, which
/// keeps the 2 decimals the fuel figures were written for while still rendering
/// yen without phantom sen.
String formatMoney(double? value) {
  if (value == null) return "—";
  return NumberFormat.simpleCurrency(locale: _locale, name: appSettings.currency).format(value);
}

/// One decimal: the interesting differences between tanks live in tenths, and
/// rounding to whole litres collapses a best of 6.8 and a worst of 7.0 into the
/// same number.
String formatConsumption(double? value) =>
    value == null ? "—" : "${value.toStringAsFixed(1)} L/100km";

String formatKmPerLiter(double? value) =>
    value == null ? "—" : "${value.toStringAsFixed(2)} km/L";

/// The charging figures. Same rule as the fuel ones: null is "could not be
/// derived", which reads as "—" rather than a misleading zero.
String formatKwh(double? value) => value == null ? "—" : "${value.toStringAsFixed(2)} kWh";

String formatKwhConsumption(double? value) =>
    value == null ? "—" : "${value.toStringAsFixed(1)} kWh/100km";

String formatKmPerKwh(double? value) =>
    value == null ? "—" : "${value.toStringAsFixed(2)} km/kWh";

const int _kmSoon = 1000;

enum StatusKey { unknown, ok, soon, overdue }

class Status {
  final StatusKey key;
  final String label;
  const Status(this.key, this.label);

  /// Soft tint background for the status pill — DriverVault semantic colours,
  /// re-cut for dark surfaces.
  Color bg(bool dark) => switch (key) {
        StatusKey.overdue => dark ? DriverVault.dangerSoftDark : DriverVault.dangerSoft,
        StatusKey.soon => dark ? DriverVault.warningSoftDark : DriverVault.warningSoft,
        StatusKey.ok => dark ? DriverVault.successSoftDark : DriverVault.successSoft,
        StatusKey.unknown => dark ? DriverVault.darkSunken : DriverVault.ink50,
      };
  Color fg(bool dark) => switch (key) {
        StatusKey.overdue => DriverVault.danger,
        StatusKey.soon => DriverVault.warning,
        StatusKey.ok => DriverVault.success,
        StatusKey.unknown => dark ? DriverVault.darkTextMuted : DriverVault.ink500,
      };
}

int _rank(StatusKey k) => switch (k) {
      StatusKey.unknown => 0,
      StatusKey.ok => 1,
      StatusKey.soon => 2,
      StatusKey.overdue => 3,
    };

Status _dateSignal(DateTime? nextDate) {
  if (nextDate == null) return Status(StatusKey.unknown, t("status.noData"));
  final today = DateTime.now();
  final days = DateTime(nextDate.year, nextDate.month, nextDate.day)
      .difference(DateTime(today.year, today.month, today.day))
      .inDays;
  if (days < 0) return Status(StatusKey.overdue, t("status.serviceOverdueDays", params: {"days": days.abs()}));
  if (days <= 30) return Status(StatusKey.soon, t("status.dueInDays", params: {"days": days}));
  return Status(StatusKey.ok, t("status.okDays", params: {"days": days}));
}

Status _kmSignal(int currentKm, int? nextKm) {
  if (nextKm == null) return Status(StatusKey.unknown, t("status.noKm"));
  final remaining = nextKm - currentKm;
  if (remaining < 0) return Status(StatusKey.overdue, t("status.serviceOverdueKm", params: {"km": _num(remaining.abs())}));
  if (remaining <= _kmSoon) return Status(StatusKey.soon, t("status.inKm", params: {"km": _num(remaining)}));
  return Status(StatusKey.ok, t("status.kmLeft", params: {"km": _num(remaining)}));
}

/// Maps the server's expiry/reminder state names onto the badge palette. The
/// client never re-derives the date maths — it only chooses the wording.
StatusKey _expiryKey(String state) => switch (state) {
      "expired" => StatusKey.overdue,
      "expiring_soon" => StatusKey.soon,
      "valid" => StatusKey.ok,
      _ => StatusKey.unknown, // no_expiry
    };

/// Renewal badge for a dated document or certificate, driven by the server's
/// expiry assessment.
Status expiryStatus(ExpiryAssessment e) {
  final days = e.days;
  final label = switch (e.state) {
    "expired" => t("status.expiredAgo", params: {"days": (days ?? 0).abs()}),
    "expiring_soon" => days == 0 ? t("status.expiresToday") : t("status.renewInDays", params: {"days": days}),
    "valid" => t("status.validDays", params: {"days": days}),
    _ => t("status.noExpiry"),
  };
  return Status(_expiryKey(e.state), label);
}

/// Reminder badge. The server has already picked the worse of the date and
/// odometer signals; this only chooses the wording, leading with whichever
/// trigger is actually closest to firing.
Status reminderStatus(Reminder r) {
  final key = switch (r.status) {
    "overdue" => StatusKey.overdue,
    "due_soon" => StatusKey.soon,
    "upcoming" => StatusKey.ok,
    _ => StatusKey.unknown, // done | no_trigger
  };

  final days = r.daysLeft;
  final km = r.kmLeft;
  if (r.status == "done") return Status(StatusKey.unknown, t("status.done"));
  if (r.status == "no_trigger") return Status(StatusKey.unknown, t("status.noTrigger"));

  final parts = <String>[];
  if (r.status == "overdue") {
    if (days != null && days < 0) parts.add(t("status.days", params: {"days": days.abs()}));
    if (km != null && km < 0) parts.add(t("status.km", params: {"km": _num(km.abs())}));
    return Status(key, parts.isEmpty ? t("status.overdue") : t("status.overdueBy", params: {"parts": parts.join(" · ")}));
  }

  if (days != null && days >= 0) parts.add(days == 0 ? t("status.today") : t("status.days", params: {"days": days}));
  if (km != null && km >= 0) parts.add(t("status.km", params: {"km": _num(km)}));
  return Status(key, parts.isEmpty ? t("status.upcoming") : t("status.dueIn", params: {"parts": parts.join(" · ")}));
}

/// Warranty badge for a maintenance entry. Unlike the others this one has no
/// server-side assessment — only the raw active/days-left pair — so the wording
/// is chosen from those directly.
Status? warrantyStatus(MaintenanceEntry m) {
  final days = m.warrantyDaysLeft;
  if (m.warrantyActive == null || days == null) return null;
  if (!m.warrantyActive!) return Status(StatusKey.unknown, t("status.warrantyExpiredAgo", params: {"days": days.abs()}));
  if (days <= 30) return Status(StatusKey.soon, t("status.warrantyEndsIn", params: {"days": days}));
  return Status(StatusKey.ok, t("status.underWarranty", params: {"days": days}));
}

/// Combines the date- and km-based signals, returning the worse of the two —
/// the same logic as the web app and the spreadsheet idea.
Status serviceStatus(ServiceRecord? latest, Car car) {
  final date = _dateSignal(latest?.nextServiceDate);
  final km = _kmSignal(car.currentKm, latest?.nextServiceKm);
  final worse = _rank(km.key) > _rank(date.key) ? km : date;
  if (date.key == StatusKey.unknown && km.key != StatusKey.unknown) return km;
  if (km.key == StatusKey.unknown && date.key != StatusKey.unknown) return date;
  return worse;
}