"use client";

import Link from "next/link";
import { useParams, useRouter } from "next/navigation";
import { type MouseEvent, useCallback, useEffect, useRef, useState } from "react";
import {
  ArrowLeft,
  ChevronDown,
  ChevronRight,
  Printer,
  Redo2,
  RefreshCw,
  Undo2,
} from "lucide-react";
import {
  ApiRequestError,
  getEstimateBalance,
  getEstimateComparison,
  getProject,
  getProjectHistory,
  isRevisionConflictError,
  redoProjectCommand,
  undoProjectCommand,
  updateEstimateBalance,
} from "../../../../../frontend/utils/api";
import type {
  EstimateBalanceDto,
  EstimateComparisonDto,
  ProjectDto,
  ProjectHistoryStateDto,
} from "../../../../../frontend/types";
import type { EstimateGroupSnapshot } from "../../../../../shared/estimate-balance/estimate-balance";
import { GzfPickerModal } from "../../../../../frontend/components/gzf-picker-modal";
import {
  addEstimateGroup,
  estimateBalanceFingerprint,
  estimateTextLimits,
  normalizeEstimateSortOrder,
  toSaveableEstimateBalance,
  updateEstimateGroup,
  updateEstimateRow,
  validateEstimateBalance,
} from "../../../../../frontend/estimate-balance/estimate-balance-document";
import { formatIsoDateGerman } from "../../../../../frontend/estimate-balance/estimate-balance-format";
import {
  EstimateBalanceSheet,
  type EstimateBalanceUpdate,
} from "../../../../../frontend/estimate-balance/estimate-balance-sheet";
import { EstimateComparisonTable } from "../../../../../frontend/estimate-balance/estimate-comparison-table";
import { DraftInput } from "../../../../../frontend/estimate-balance/estimate-draft-input";
import { EstimatePrintHeader } from "../../../../../frontend/estimate-balance/estimate-print-header";
import {
  EstimateGroupModal,
  type EstimateGroupFormValues,
} from "../../../../../frontend/estimate-balance/estimate-group-modal";

const AUTOSAVE_DELAY_MS = 800;
const CONFLICT_MESSAGE = "Die Bilanz wurde zwischenzeitlich geändert und neu geladen.";

type SaveStatus = "saved" | "pending" | "saving" | "error" | "invalid";

type GroupDialog = { group: EstimateGroupSnapshot | null };

function errorMessage(error: unknown, fallback: string) {
  return error instanceof Error && error.message ? error.message : fallback;
}

function isNotFoundError(error: unknown) {
  return error instanceof ApiRequestError && error.status === 404;
}

export default function EstimateBalanceEditorPage() {
  const params = useParams<{ projectId: string; balanceId: string }>();
  const { projectId, balanceId } = params;
  const router = useRouter();

  const [project, setProject] = useState<ProjectDto | null>(null);
  const [draft, setDraft] = useState<EstimateBalanceDto | null>(null);
  const [history, setHistory] = useState<ProjectHistoryStateDto | null>(null);
  const [comparison, setComparison] = useState<EstimateComparisonDto | null>(null);
  const [comparisonError, setComparisonError] = useState<string | null>(null);
  const [isComparisonOpen, setIsComparisonOpen] = useState(false);
  const [saveStatus, setSaveStatus] = useState<SaveStatus>("saved");
  const [saveError, setSaveError] = useState<string | null>(null);
  const [error, setError] = useState<string | null>(null);
  const [notice, setNotice] = useState<string | null>(null);
  const [isLoading, setIsLoading] = useState(true);
  const [isMissing, setIsMissing] = useState(false);
  const [isHistoryBusy, setIsHistoryBusy] = useState(false);
  const [invalidFieldKeys, setInvalidFieldKeys] = useState<ReadonlySet<string>>(
    () => new Set()
  );
  const [groupDialog, setGroupDialog] = useState<GroupDialog | null>(null);
  const [gzfTarget, setGzfTarget] = useState<{ groupId: string; rowId: string } | null>(
    null
  );

  // Refs carry the latest values into timers, unload handlers and chained
  // async saves without re-creating them.
  const draftRef = useRef<EstimateBalanceDto | null>(null);
  const revisionRef = useRef<number | null>(null);
  const savedFingerprintRef = useRef<string | null>(null);
  const saveInFlightRef = useRef<Promise<boolean> | null>(null);
  const saveTimerRef = useRef<ReturnType<typeof setTimeout> | null>(null);

  useEffect(() => {
    draftRef.current = draft;
  }, [draft]);

  const applyServerBalance = useCallback((balance: EstimateBalanceDto) => {
    const normalized = normalizeEstimateSortOrder(balance);
    savedFingerprintRef.current = estimateBalanceFingerprint(normalized);
    draftRef.current = normalized;
    setDraft(normalized);
    setSaveStatus("saved");
    setSaveError(null);
  }, []);

  const reloadComparison = useCallback(async () => {
    try {
      setComparison(await getEstimateComparison(projectId, balanceId));
      setComparisonError(null);
    } catch (err) {
      setComparisonError(
        errorMessage(err, "Der Vergleich konnte nicht geladen werden.")
      );
    }
  }, [balanceId, projectId]);

  /** Reloads project, document and history; replaces the local draft. */
  const reloadAll = useCallback(async () => {
    const balanceRequest = getEstimateBalance(projectId, balanceId);
    // Handled below; avoids an "unhandled rejection" while project/history load.
    balanceRequest.catch(() => undefined);
    // Project and history are applied even when the balance is missing, so
    // Redo stays available after its creation was undone.
    const [currentProject, currentHistory] = await Promise.all([
      getProject(projectId),
      getProjectHistory(projectId).catch(() => null),
    ]);
    setProject(currentProject);
    revisionRef.current = currentHistory?.currentRevision ?? currentProject.currentRevision;
    setHistory(currentHistory);
    const balance = await balanceRequest;
    applyServerBalance(balance);
    setIsMissing(false);
    void reloadComparison();
  }, [applyServerBalance, balanceId, projectId, reloadComparison]);

  const handleReloadError = useCallback((err: unknown) => {
    if (isNotFoundError(err)) {
      setIsMissing(true);
      setDraft(null);
      draftRef.current = null;
      return;
    }
    setError(errorMessage(err, "Die grobe Leistungsbilanz konnte nicht geladen werden."));
  }, []);

  useEffect(() => {
    if (!projectId || !balanceId) {
      return;
    }
    setIsLoading(true);
    reloadAll()
      .then(() => setError(null))
      .catch(handleReloadError)
      .finally(() => setIsLoading(false));
  }, [balanceId, handleReloadError, projectId, reloadAll]);

  const clearSaveTimer = useCallback(() => {
    if (saveTimerRef.current) {
      clearTimeout(saveTimerRef.current);
      saveTimerRef.current = null;
    }
  }, []);

  /**
   * Saves the current draft if it differs from the last saved state. Saves
   * never overlap: a save requested while another runs waits for it and then
   * saves whatever changed in the meantime. Resolves to false when the draft
   * could not be saved.
   */
  const saveNow = useCallback(async (): Promise<boolean> => {
    clearSaveTimer();
    while (saveInFlightRef.current) {
      await saveInFlightRef.current;
    }
    const current = draftRef.current;
    const revision = revisionRef.current;
    if (!current || revision === null) {
      return true;
    }
    const fingerprint = estimateBalanceFingerprint(current);
    if (fingerprint === savedFingerprintRef.current) {
      setSaveStatus("saved");
      return true;
    }
    const problems = validateEstimateBalance(current);
    if (problems.length) {
      setSaveStatus("invalid");
      setSaveError(problems.join(" "));
      return false;
    }
    const body = toSaveableEstimateBalance(current);

    /**
     * Another command changed the project revision. When this document is
     * still unchanged on the server (e.g. an edit in a circuit list), the
     * draft is kept and saved again; otherwise the server state wins.
     */
    async function resolveConflict(): Promise<"retry" | "reloaded"> {
      const [currentProject, serverBalance, currentHistory] = await Promise.all([
        getProject(projectId),
        getEstimateBalance(projectId, balanceId),
        getProjectHistory(projectId).catch(() => null),
      ]);
      setProject(currentProject);
      setHistory(currentHistory);
      revisionRef.current = currentHistory?.currentRevision ?? currentProject.currentRevision;
      if (estimateBalanceFingerprint(serverBalance) === savedFingerprintRef.current) {
        return "retry";
      }
      applyServerBalance(serverBalance);
      setNotice(CONFLICT_MESSAGE);
      void reloadComparison();
      return "reloaded";
    }

    const run = (async () => {
      setSaveStatus("saving");
      for (let attempt = 0; ; attempt += 1) {
        try {
          const result = await updateEstimateBalance(
            projectId,
            body,
            attempt === 0 ? revision : revisionRef.current ?? revision
          );
          if (!("unchanged" in result)) {
            revisionRef.current = result.history.currentRevision;
            setHistory(result.history);
            setProject((currentProject) =>
              currentProject
                ? { ...currentProject, currentRevision: result.history.currentRevision }
                : currentProject
            );
          }
          // The sent document is the saved state; the local draft is kept so
          // typing is never interrupted by the server's copy.
          savedFingerprintRef.current = fingerprint;
          setSaveError(null);
          const latest = draftRef.current;
          if (latest && estimateBalanceFingerprint(latest) !== fingerprint) {
            setSaveStatus("pending");
          } else {
            setSaveStatus("saved");
          }
          void reloadComparison();
          return true;
        } catch (err) {
          if (isRevisionConflictError(err)) {
            try {
              if (attempt === 0 && (await resolveConflict()) === "retry") {
                continue;
              }
              if (attempt > 0) {
                await reloadAll();
                setNotice(CONFLICT_MESSAGE);
              }
            } catch (reloadError) {
              handleReloadError(reloadError);
            }
            return false;
          }
          if (isNotFoundError(err)) {
            handleReloadError(err);
            return false;
          }
          setSaveStatus("error");
          setSaveError(errorMessage(err, "Die Änderungen konnten nicht gespeichert werden."));
          return false;
        }
      }
    })();
    saveInFlightRef.current = run;
    try {
      return await run;
    } finally {
      saveInFlightRef.current = null;
    }
  }, [
    applyServerBalance,
    balanceId,
    clearSaveTimer,
    handleReloadError,
    projectId,
    reloadAll,
    reloadComparison,
  ]);

  // Debounced autosave after every change of the draft.
  useEffect(() => {
    if (!draft) {
      return;
    }
    if (estimateBalanceFingerprint(draft) === savedFingerprintRef.current) {
      return;
    }
    setSaveStatus((status) => (status === "saving" ? status : "pending"));
    clearSaveTimer();
    saveTimerRef.current = setTimeout(() => {
      saveTimerRef.current = null;
      void saveNow();
    }, AUTOSAVE_DELAY_MS);
    return clearSaveTimer;
  }, [clearSaveTimer, draft, saveNow]);

  // Save immediately when the tab is hidden; on unload/unmount send the last
  // change with keepalive so it survives the page.
  useEffect(() => {
    function hasUnsavedDraft() {
      const current = draftRef.current;
      return Boolean(
        current && estimateBalanceFingerprint(current) !== savedFingerprintRef.current
      );
    }
    function sendKeepalive(): boolean {
      const current = draftRef.current;
      const revision = revisionRef.current;
      if (
        !current ||
        revision === null ||
        saveInFlightRef.current ||
        validateEstimateBalance(current).length
      ) {
        return false;
      }
      savedFingerprintRef.current = estimateBalanceFingerprint(current);
      void updateEstimateBalance(projectId, toSaveableEstimateBalance(current), revision, {
        keepalive: true,
      }).catch(() => undefined);
      return true;
    }
    function handleVisibilityChange() {
      if (document.visibilityState === "hidden" && hasUnsavedDraft()) {
        void saveNow();
      }
    }
    function handleBeforeUnload(event: BeforeUnloadEvent) {
      if (!hasUnsavedDraft() || sendKeepalive()) {
        return;
      }
      // A save is still running or the draft is invalid: let the browser ask.
      event.preventDefault();
      event.returnValue = "";
    }
    document.addEventListener("visibilitychange", handleVisibilityChange);
    window.addEventListener("beforeunload", handleBeforeUnload);
    return () => {
      document.removeEventListener("visibilitychange", handleVisibilityChange);
      window.removeEventListener("beforeunload", handleBeforeUnload);
      // In-app navigation (e.g. sidebar) unmounts the editor.
      if (hasUnsavedDraft()) {
        sendKeepalive();
      }
    };
  }, [projectId, saveNow]);

  const handleChange: EstimateBalanceUpdate = useCallback((update) => {
    setNotice(null);
    setDraft((current) => (current ? update(current) : current));
  }, []);

  const handleValidityChange = useCallback((fieldKey: string, isValid: boolean) => {
    setInvalidFieldKeys((current) => {
      if (isValid ? !current.has(fieldKey) : current.has(fieldKey)) {
        return current;
      }
      const next = new Set(current);
      if (isValid) {
        next.delete(fieldKey);
      } else {
        next.add(fieldKey);
      }
      return next;
    });
  }, []);

  async function handleHistory(direction: "undo" | "redo") {
    setError(null);
    setNotice(null);
    setIsHistoryBusy(true);
    try {
      // Pending edits are saved first so they become their own undo step.
      await saveNow();
      const revision = revisionRef.current;
      if (revision === null) {
        return;
      }
      const result =
        direction === "undo"
          ? await undoProjectCommand(projectId, revision)
          : await redoProjectCommand(projectId, revision);
      revisionRef.current = result.history.currentRevision;
      setHistory(result.history);
      await reloadAll();
    } catch (err) {
      if (isRevisionConflictError(err)) {
        await reloadAll().catch(handleReloadError);
        setNotice(CONFLICT_MESSAGE);
      } else if (isNotFoundError(err)) {
        handleReloadError(err);
      } else {
        setError(
          errorMessage(
            err,
            direction === "undo"
              ? "Die letzte Änderung konnte nicht rückgängig gemacht werden."
              : "Die letzte Änderung konnte nicht wiederholt werden."
          )
        );
      }
    } finally {
      setIsHistoryBusy(false);
    }
  }

  async function handleBackClick(event: MouseEvent<HTMLAnchorElement>) {
    const current = draftRef.current;
    if (!current || estimateBalanceFingerprint(current) === savedFingerprintRef.current) {
      return;
    }
    event.preventDefault();
    await saveNow();
    router.push(`/projects/${projectId}/grobbilanz`);
  }

  function handleSaveGroup(values: EstimateGroupFormValues) {
    const editingGroup = groupDialog?.group ?? null;
    handleChange((current) =>
      editingGroup
        ? updateEstimateGroup(current, editingGroup.id, values)
        : addEstimateGroup(current, values).balance
    );
    setGroupDialog(null);
  }

  function handleSelectGzf(value: number) {
    if (gzfTarget) {
      handleChange((current) =>
        updateEstimateRow(current, gzfTarget.groupId, gzfTarget.rowId, {
          simultaneityFactor: value,
        })
      );
    }
    setGzfTarget(null);
  }

  const isEditingDisabled = !draft || isHistoryBusy;
  const invalidCount = invalidFieldKeys.size;
  const listHref = `/projects/${projectId}/grobbilanz`;

  return (
    <main className="container-fluid py-4 estimate-print-root">
      {project && draft ? <EstimatePrintHeader balance={draft} project={project} /> : null}
      <div className="page-header estimate-page-header">
        <div className="d-flex align-items-start gap-3">
          <Link
            aria-label="Zurück zur Übersicht der Stände"
            className="btn btn-outline-secondary btn-sm structure-back-link estimate-no-print"
            href={listHref}
            onClick={(event) => void handleBackClick(event)}
            title="Zurück zur Übersicht der Stände"
          >
            <ArrowLeft aria-hidden="true" size={18} />
          </Link>
          <div>
            <div className="kicker">{project?.name ?? "Projekt"}</div>
            <h1>Grobe Leistungsbilanz{draft ? ` – ${draft.name}` : ""}</h1>
            <p className="text-secondary mb-0 estimate-no-print">
              Leistungsabschätzung nach Kostengruppen (DIN 276) für LPH 2/3.
            </p>
          </div>
        </div>
        <div className="estimate-toolbar estimate-no-print">
          <SaveStatusBadge
            error={saveError}
            invalidCount={invalidCount}
            onRetry={() => void saveNow()}
            status={saveStatus}
          />
          <div className="btn-group btn-group-sm" role="group" aria-label="Verlauf">
            <button
              aria-label="Rückgängig"
              className="btn btn-outline-secondary"
              disabled={isHistoryBusy || !history || history.undoDepth === 0}
              onClick={() => void handleHistory("undo")}
              title="Rückgängig (letzte Änderung im Projekt)"
              type="button"
            >
              <Undo2 aria-hidden="true" size={16} />
            </button>
            <button
              aria-label="Wiederholen"
              className="btn btn-outline-secondary"
              disabled={isHistoryBusy || !history || history.redoDepth === 0}
              onClick={() => void handleHistory("redo")}
              title="Wiederholen (im Projekt)"
              type="button"
            >
              <Redo2 aria-hidden="true" size={16} />
            </button>
          </div>
          <button
            aria-label="Drucken"
            className="btn btn-sm btn-outline-secondary"
            disabled={!draft}
            onClick={() => window.print()}
            title="Drucken"
            type="button"
          >
            <Printer aria-hidden="true" className="me-1" size={16} />
            Drucken
          </button>
        </div>
      </div>

      {notice ? (
        <div className="alert alert-info estimate-no-print" role="status">
          {notice}
        </div>
      ) : null}
      {error ? (
        <div className="alert alert-warning estimate-no-print" role="alert">
          {error}
        </div>
      ) : null}
      {isLoading ? (
        <p className="text-secondary" role="status">
          Grobe Leistungsbilanz wird geladen …
        </p>
      ) : null}
      {isMissing ? (
        <div className="alert alert-warning" role="alert">
          Dieser Stand existiert nicht (mehr), z. B. weil er gelöscht oder sein Anlegen
          rückgängig gemacht wurde.{" "}
          <Link href={listHref}>Zur Übersicht der Stände</Link>
        </div>
      ) : null}

      {draft && project ? (
        <>
          <section className="card shadow-sm mb-3 estimate-sheet-card">
            <div className="card-body">
              <div className="estimate-header-fields">
                <div className="estimate-header-field">
                  <span className="estimate-header-label">Projekt</span>
                  <span className="estimate-header-value">{project.name}</span>
                </div>
                <label className="estimate-header-field is-wide">
                  <span className="estimate-header-label">Stand</span>
                  <DraftInput
                    ariaLabel="Bezeichnung des Stands"
                    className="estimate-cell-input estimate-header-input"
                    disabled={isEditingDisabled}
                    format={(value: string) => value}
                    maxLength={estimateTextLimits.balanceName}
                    onCommit={(name) => handleChange((current) => ({ ...current, name }))}
                    onValidityChange={(isValid) =>
                      handleValidityChange("balance:name", isValid)
                    }
                    parse={(text) =>
                      text.trim()
                        ? { ok: true, value: text }
                        : { ok: false, error: "Die Bezeichnung darf nicht leer sein." }
                    }
                    value={draft.name}
                  />
                </label>
                <label className="estimate-header-field">
                  <span className="estimate-header-label">LPH</span>
                  <input
                    aria-label="Leistungsphase"
                    className="estimate-cell-input estimate-header-input"
                    disabled={isEditingDisabled}
                    maxLength={estimateTextLimits.workStage}
                    onChange={(event) =>
                      handleChange((current) => ({
                        ...current,
                        workStage: event.target.value,
                      }))
                    }
                    placeholder="z. B. LPH 3"
                    type="text"
                    value={draft.workStage ?? ""}
                  />
                  <span className="estimate-print-value">{draft.workStage ?? ""}</span>
                </label>
                <label className="estimate-header-field">
                  <span className="estimate-header-label">Datum</span>
                  <input
                    aria-label="Datum"
                    className="estimate-cell-input estimate-header-input"
                    disabled={isEditingDisabled}
                    onChange={(event) =>
                      handleChange((current) => ({
                        ...current,
                        dateIso: event.target.value || null,
                      }))
                    }
                    type="date"
                    value={draft.dateIso ?? ""}
                  />
                  <span className="estimate-print-value">
                    {formatIsoDateGerman(draft.dateIso)}
                  </span>
                </label>
              </div>
              <EstimateBalanceSheet
                balance={draft}
                disabled={isEditingDisabled}
                onAddGroup={() => setGroupDialog({ group: null })}
                onChange={handleChange}
                onEditGroup={(group) => setGroupDialog({ group })}
                onOpenGzfPicker={(groupId, rowId) => setGzfTarget({ groupId, rowId })}
                onValidityChange={handleValidityChange}
                threePhaseVoltageV={project.threePhaseVoltageV}
              />
            </div>
          </section>

          <section
            className={
              isComparisonOpen
                ? "card shadow-sm estimate-comparison-card"
                : "card shadow-sm estimate-comparison-card estimate-no-print"
            }
          >
            <div className="card-header d-flex justify-content-between align-items-center gap-2">
              <button
                aria-controls="estimate-comparison-body"
                aria-expanded={isComparisonOpen}
                className="estimate-collapse-toggle"
                onClick={() => setIsComparisonOpen((open) => !open)}
                type="button"
              >
                {isComparisonOpen ? (
                  <ChevronDown aria-hidden="true" size={16} />
                ) : (
                  <ChevronRight aria-hidden="true" size={16} />
                )}
                Vergleich mit detaillierter Bilanz
              </button>
              {isComparisonOpen ? (
                <button
                  aria-label="Vergleich neu laden"
                  className="btn btn-sm btn-outline-secondary structure-icon-button estimate-no-print"
                  onClick={() => void reloadComparison()}
                  title="Vergleich neu laden"
                  type="button"
                >
                  <RefreshCw aria-hidden="true" size={14} />
                </button>
              ) : null}
            </div>
            {isComparisonOpen ? (
              <div className="card-body" id="estimate-comparison-body">
                {comparisonError ? (
                  <div className="alert alert-warning" role="alert">
                    {comparisonError}
                  </div>
                ) : null}
                {comparison ? <EstimateComparisonTable comparison={comparison} /> : null}
                <p className="text-secondary small mt-2 mb-0">
                  Detailliert = Summe der Gerätezeilen aller Stromkreislisten (Anzahl ×
                  Leistung × Geräte-GZF), zugeordnet über die Kostengruppe; ohne
                  Verteiler-GZF.
                </p>
              </div>
            ) : null}
          </section>
        </>
      ) : null}

      {groupDialog ? (
        <EstimateGroupModal
          group={groupDialog.group}
          onClose={() => setGroupDialog(null)}
          onSave={handleSaveGroup}
        />
      ) : null}
      {gzfTarget ? (
        <GzfPickerModal onClose={() => setGzfTarget(null)} onSelect={handleSelectGzf} />
      ) : null}
    </main>
  );
}

function SaveStatusBadge({
  error,
  invalidCount,
  onRetry,
  status,
}: {
  error: string | null;
  invalidCount: number;
  onRetry: () => void;
  status: SaveStatus;
}) {
  const label =
    status === "saving"
      ? "Wird gespeichert …"
      : status === "pending"
        ? "Ungespeicherte Änderungen"
        : status === "error"
          ? "Nicht gespeichert – Fehler"
          : status === "invalid"
            ? "Nicht gespeichert – ungültige Eingaben"
            : "Gespeichert";
  const tone =
    status === "error" || status === "invalid"
      ? "is-error"
      : status === "saved"
        ? "is-saved"
        : "is-busy";
  return (
    <div className="estimate-save-status" role="status" aria-live="polite">
      <span className={`estimate-save-badge ${tone}`} title={error ?? undefined}>
        {label}
      </span>
      {invalidCount ? (
        <span className="estimate-save-hint">
          {invalidCount === 1
            ? "1 ungültige Eingabe wird nicht gespeichert"
            : `${invalidCount} ungültige Eingaben werden nicht gespeichert`}
        </span>
      ) : null}
      {status === "error" ? (
        <button className="btn btn-link btn-sm p-0" onClick={onRetry} type="button">
          Erneut versuchen
        </button>
      ) : null}
    </div>
  );
}