import { useEffect, useMemo, useState } from "react";
import { Save } from "lucide-react";
import { FormGrid, ContentGrid,
  Button,
  Card,
  DismissibleAlert,
  DocumentationHelpLink,
  FormField,
  ToggleSwitch,
  useUnsavedDraftGuard,
  type ApiSettings,
  type AuthInfo
} from "@govoplan/core-webui";
import {
  getCalendarViewPreferences,
  updateCalendarViewPreferences,
  type CalendarViewPreferences
} from "../../api/calendar";
import {
  CALENDAR_DOCUMENTATION,
  CALENDAR_I18N,
} from "./interfacePatterns";

type CalendarPreferenceDraft = Pick<
  CalendarViewPreferences,
  | "dim_weekends"
  | "dim_off_hours"
  | "workday_start_hour"
  | "workday_end_hour"
  | "continuous_virtualization"
  | "continuous_overscan_weeks"
  | "alternate_continuous_months"
>;

const FALLBACK_DRAFT: CalendarPreferenceDraft = {
  dim_weekends: true,
  dim_off_hours: true,
  workday_start_hour: 6,
  workday_end_hour: 20,
  continuous_virtualization: true,
  continuous_overscan_weeks: 6,
  alternate_continuous_months: true
};

export default function CalendarSettingsPanel({
  settings,
  auth
}: {
  settings: ApiSettings;
  auth: AuthInfo;
}) {
  const [loaded, setLoaded] = useState<CalendarPreferenceDraft | null>(null);
  const [draft, setDraft] = useState<CalendarPreferenceDraft>(FALLBACK_DRAFT);
  const [loading, setLoading] = useState(true);
  const [saving, setSaving] = useState(false);
  const [message, setMessage] = useState("");
  const [tone, setTone] = useState<"success" | "warning">("success");
  const dirty = useMemo(
    () => loaded !== null && JSON.stringify(loaded) !== JSON.stringify(draft),
    [draft, loaded]
  );

  useEffect(() => {
    void loadPreferences();
  }, [auth.user.id, settings.accessToken, settings.apiBaseUrl, settings.apiKey]);

  async function loadPreferences() {
    setLoading(true);
    setMessage("");
    try {
      const response = await getCalendarViewPreferences(settings);
      const next = preferenceDraft(response);
      setLoaded(next);
      setDraft(next);
    } catch (error) {
      setTone("warning");
      setMessage(errorText(error));
    } finally {
      setLoading(false);
    }
  }

  async function savePreferences(): Promise<boolean> {
    if (draft.workday_end_hour <= draft.workday_start_hour) {
      setTone("warning");
      setMessage("Workday end must be after workday start.");
      return false;
    }
    setSaving(true);
    setMessage("");
    try {
      const response = await updateCalendarViewPreferences(settings, draft);
      const next = preferenceDraft(response);
      setLoaded(next);
      setDraft(next);
      setTone("success");
      setMessage("Calendar preferences saved.");
      window.dispatchEvent(
        new CustomEvent("govoplan:calendar-preferences-changed")
      );
      return true;
    } catch (error) {
      setTone("warning");
      setMessage(errorText(error));
      return false;
    } finally {
      setSaving(false);
    }
  }

  const disabled = loading || saving;
  const saveDisabledReason = loading
    ? CALENDAR_I18N.loading
    : saving
      ? CALENDAR_I18N.saving
      : !dirty
        ? CALENDAR_I18N.noChanges
        : undefined;

  useUnsavedDraftGuard({
    dirty,
    onSave: savePreferences,
    onDiscard: () => setDraft(loaded ?? FALLBACK_DRAFT)
  });

  return (
    <ContentGrid columns={2} collapseAt="workspace" className="calendar-settings-panel">
      <Card title="Calendar display" titleHelp={<DocumentationHelpLink reference={CALENDAR_DOCUMENTATION} />}>
        <FormGrid columns={1} collapseAt="standard" className="">
          <ToggleSwitch
            label="Dim weekends"
            help="Use a quieter background for Saturday and Sunday in week views."
            checked={draft.dim_weekends}
            disabled={disabled}
            onChange={(dim_weekends) =>
              setDraft((current) => ({ ...current, dim_weekends }))
            }
          />
          <ToggleSwitch
            label="Dim hours outside the workday"
            checked={draft.dim_off_hours}
            disabled={disabled}
            onChange={(dim_off_hours) =>
              setDraft((current) => ({ ...current, dim_off_hours }))
            }
          />
          <FormGrid columns={2} gap="small" collapseAt="narrow">
            <FormField label="Workday starts">
              <input
                type="number"
                min={0}
                max={23}
                value={draft.workday_start_hour}
                disabled={disabled}
                onChange={(event) =>
                  setDraft((current) => ({
                    ...current,
                    workday_start_hour: Number(event.target.value)
                  }))
                }
              />
            </FormField>
            <FormField label="Workday ends">
              <input
                type="number"
                min={1}
                max={24}
                value={draft.workday_end_hour}
                disabled={disabled}
                onChange={(event) =>
                  setDraft((current) => ({
                    ...current,
                    workday_end_hour: Number(event.target.value)
                  }))
                }
              />
            </FormField>
          </FormGrid>
        </FormGrid>
      </Card>
      <Card title="Continuous view">
        <FormGrid columns={1} collapseAt="standard" className="">
          <ToggleSwitch
            label="Virtualize distant weeks"
            help="Keep the continuous calendar responsive by rendering only nearby weeks."
            checked={draft.continuous_virtualization}
            disabled={disabled}
            onChange={(continuous_virtualization) =>
              setDraft((current) => ({
                ...current,
                continuous_virtualization
              }))
            }
          />
          <FormField
            label="Overscan weeks"
            help="Additional weeks rendered above and below the viewport."
          >
            <input
              type="number"
              min={2}
              max={20}
              value={draft.continuous_overscan_weeks}
              disabled={disabled || !draft.continuous_virtualization}
              onChange={(event) =>
                setDraft((current) => ({
                  ...current,
                  continuous_overscan_weeks: Number(event.target.value)
                }))
              }
            />
          </FormField>
          <ToggleSwitch
            label="Alternate month backgrounds"
            checked={draft.alternate_continuous_months}
            disabled={disabled}
            onChange={(alternate_continuous_months) =>
              setDraft((current) => ({
                ...current,
                alternate_continuous_months
              }))
            }
          />
          <div className="button-row compact-actions">
            <Button
              type="button"
              variant="primary"
              disabled={Boolean(saveDisabledReason)}
              disabledReason={saveDisabledReason}
              onClick={() => void savePreferences()}
            >
              <Save size={16} /> {saving ? "Saving" : "Save preferences"}
            </Button>
          </div>
          {message && (
            <DismissibleAlert tone={tone} resetKey={message} floating>
              {message}
            </DismissibleAlert>
          )}
        </FormGrid>
      </Card>
    </ContentGrid>
  );
}

function preferenceDraft(
  preferences: CalendarViewPreferences
): CalendarPreferenceDraft {
  return {
    dim_weekends: preferences.dim_weekends,
    dim_off_hours: preferences.dim_off_hours,
    workday_start_hour: preferences.workday_start_hour,
    workday_end_hour: preferences.workday_end_hour,
    continuous_virtualization: preferences.continuous_virtualization,
    continuous_overscan_weeks: preferences.continuous_overscan_weeks,
    alternate_continuous_months: preferences.alternate_continuous_months
  };
}

function errorText(error: unknown): string {
  return error instanceof Error
    ? error.message
    : "Calendar preferences could not be loaded.";
}