import React, { useCallback, useEffect, useId, useMemo, useRef, useState } from "react";
import { Box, Button, Chip, Paper, Stack, TextField, Typography } from "@mui/material";
import { api, getApiErrorMessage } from "../api";
import { CreatedSuggestedGmailJobResult, GmailManualSyncResult, GmailReviewQueueResponse, GmailSuggestedJobsResponse } from "../types";
import { useToast } from "../toast";
import { useNavigate } from "react-router-dom";
import { useI18n } from "../i18n/I18nProvider";
import type { TranslationKey } from "../i18n/translations";
import type { ViewResourceError } from "../hooks/useViewResource";
import ViewStateNotice from "../components/ViewStateNotice";
import { PageHeader, PageSection } from "../layout/PageLayout";

type ReviewRequestError = { response?: { status?: number; data?: { code?: string } } };

function noticeError(cause: unknown, fallback: string): ViewResourceError {
  const status = (cause as ReviewRequestError)?.response?.status;
  const unauthorized = status === 401 || status === 403;
  return { kind: unauthorized ? "unauthorized" : !status || status >= 500 ? "unavailable" : "error", status, retryable: !unauthorized, message: getApiErrorMessage(cause, fallback) };
}

export default function GmailReviewPage({ embedded = false, active = true }: { embedded?: boolean; active?: boolean }) {
  const { toast } = useToast();
  const { t } = useI18n();
  const navigate = useNavigate();
  const [data, setData] = useState<GmailReviewQueueResponse | null>(null);
  const [suggestions, setSuggestions] = useState<GmailSuggestedJobsResponse | null>(null);
  const [loading, setLoading] = useState(false);
  const [readError, setReadError] = useState<unknown | null>(null);
  const [writeError, setWriteError] = useState<{ cause: unknown; key: TranslationKey } | null>(null);
  const [operation, setOperation] = useState<{ kind: "decision" | "sync" | "create"; threadId?: string } | null>(null);
  const [createdJobs, setCreatedJobs] = useState<Record<string, number>>({});
  const [routingFilter, setRoutingFilter] = useState<"all" | "auto-link" | "review" | "unmatched" | "suggested" | "linked" | "rejected">("all");
  const [notes, setNotes] = useState<Record<string, string>>({});
  const sectionId = useId();
  const bodyRef = useRef<HTMLDivElement>(null);
  const mountedRef = useRef(false);
  const activeRef = useRef(active);
  const viewSequence = useRef(0);
  const readSequence = useRef(0);
  const loadingRef = useRef(false);
  const mutationRef = useRef(false);
  const tRef = useRef(t);
  activeRef.current = active;
  tRef.current = t;
  const isCurrentView = useCallback((view: number) => mountedRef.current && activeRef.current && view === viewSequence.current, []);
  const routeLabel = (value: string) => {
    if (value === "auto-link") return t("gmailReviewRouteAutoLink");
    if (value === "review") return t("gmailReviewRouteReview");
    if (value === "unmatched") return t("gmailReviewRouteUnmatched");
    if (value === "suggested") return t("gmailReviewRouteSuggested");
    if (value === "linked") return t("gmailReviewRouteLinked");
    if (value === "rejected") return t("gmailReviewRouteRejected");
    return t("gmailReviewRouteAll");
  };

  const load = useCallback(async () => {
    if (!mountedRef.current || !activeRef.current || loadingRef.current) return false;
    const view = viewSequence.current;
    const request = ++readSequence.current;
    loadingRef.current = true;
    setLoading(true);
    try {
      const [reviewRes, suggestedRes] = await Promise.all([
        api.get<GmailReviewQueueResponse>("/gmail/review-candidates"),
        api.get<GmailSuggestedJobsResponse>("/gmail/suggested-jobs"),
      ]);
      if (!isCurrentView(view) || request !== readSequence.current) return false;
      setData(reviewRes.data);
      setSuggestions(suggestedRes.data);
      setReadError(null);
      setNotes((prev) => {
        const next = { ...prev };
        for (const thread of reviewRes.data.threads) {
          if (next[thread.threadId] === undefined) next[thread.threadId] = thread.decisionNote || "";
        }
        return next;
      });
      return true;
    } catch (error) {
      if (isCurrentView(view) && request === readSequence.current) setReadError(error);
      return false;
    } finally {
      if (mountedRef.current && request === readSequence.current) {
        loadingRef.current = false;
        setLoading(false);
      }
    }
  }, [isCurrentView]);

  useEffect(() => {
    mountedRef.current = true;
    return () => {
      mountedRef.current = false;
      readSequence.current += 1;
      viewSequence.current += 1;
    };
  }, []);

  useEffect(() => {
    viewSequence.current += 1;
    readSequence.current += 1;
    loadingRef.current = false;
    setLoading(false);
    if (active && !mutationRef.current) void load();
  }, [active, load]);

  const beginOperation = useCallback((kind: "decision" | "sync" | "create", threadId?: string) => {
    if (!mountedRef.current || !activeRef.current || mutationRef.current || loadingRef.current || readError) return null;
    bodyRef.current?.focus();
    mutationRef.current = true;
    setOperation({ kind, threadId });
    setWriteError(null);
    return viewSequence.current;
  }, [readError]);

  const finishOperation = useCallback((view: number) => {
    mutationRef.current = false;
    if (!mountedRef.current) return;
    setOperation(null);
    if (activeRef.current && view !== viewSequence.current) void load();
  }, [load]);

  const saveDecision = useCallback(async (threadId: string, decision: "linked" | "rejected" | "review" | "suggested", jobApplicationId?: number) => {
    const view = beginOperation("decision", threadId);
    if (view === null) return;
    try {
      await api.post("/gmail/review-decision", {
        threadId,
        decision,
        jobApplicationId: decision === "linked" ? jobApplicationId ?? null : null,
        note: notes[threadId]?.trim() || null,
      });
      if (!isCurrentView(view)) return;
      await load();
      if (!isCurrentView(view)) return;
      toast(
        decision === "linked"
          ? tRef.current("gmailReviewLinked")
          : decision === "rejected"
            ? tRef.current("gmailReviewRejected")
            : decision === "suggested"
              ? tRef.current("gmailReviewKeptSuggested")
              : tRef.current("gmailReviewReturned"),
        "success",
      );
    } catch (error) {
      if (isCurrentView(view)) setWriteError({ cause: error, key: "gmailReviewSaveFailed" });
    } finally {
      finishOperation(view);
    }
  }, [beginOperation, finishOperation, isCurrentView, load, notes, toast]);

  const runManualSync = useCallback(async () => {
    const view = beginOperation("sync");
    if (view === null) return;
    try {
      const res = await api.post<GmailManualSyncResult>("/gmail/manual-sync", {
        lookbackDays: 365,
        maxResultsPerQuery: 8,
        autoImportHighConfidence: true,
        includeSpamTrash: false,
      });
      if (!isCurrentView(view)) return;
      await load();
      if (!isCurrentView(view)) return;
      toast(
        tRef.current("gmailReviewSyncFinished", { linked: res.data.importedThreads, review: res.data.reviewThreadCount, unmatched: res.data.unmatchedThreadCount }),
        "success",
      );
    } catch (error) {
      if (isCurrentView(view)) setWriteError({ cause: error, key: "gmailReviewSyncFailed" });
    } finally {
      finishOperation(view);
    }
  }, [beginOperation, finishOperation, isCurrentView, load, toast]);

  const createSuggestedJob = useCallback(async (threadId: string) => {
    const suggestion = suggestions?.items.find((item) => item.threadId === threadId);
    if (!suggestion || createdJobs[threadId]) return;

    const view = beginOperation("create", threadId);
    if (view === null) return;
    try {
      const res = await api.post<CreatedSuggestedGmailJobResult>("/gmail/create-suggested-job", {
        threadId,
        companyName: suggestion.companyName || t("gmailReviewUnknownCompany"),
        jobTitle: suggestion.suggestedJobTitle || suggestion.subject || t("gmailReviewSuggestedRole"),
        recruiterName: suggestion.recruiterName || null,
        recruiterEmail: suggestion.recruiterEmail || null,
        notes: notes[threadId]?.trim() || suggestion.preview || null,
        status: "Applied",
      });
      if (!mountedRef.current) return;
      // Keep a successful creation identity even if the owner changes views before it settles.
      setCreatedJobs((prev) => ({ ...prev, [threadId]: res.data.jobApplicationId }));
      if (!isCurrentView(view)) return;
      const refreshed = await load();
      if (!isCurrentView(view)) return;
      toast(tRef.current(res.data.imported === 1 ? "gmailReviewCreatedImportedMessage" : "gmailReviewCreatedImportedMessages", { count: res.data.imported }), "success");
      if (refreshed) navigate(`/jobs/${res.data.jobApplicationId}?section=communication`);
    } catch (error) {
      if (isCurrentView(view)) setWriteError({ cause: error, key: "gmailReviewCreateFailed" });
    } finally {
      finishOperation(view);
    }
  }, [beginOperation, createdJobs, finishOperation, isCurrentView, load, navigate, notes, suggestions?.items, t, toast]);

  const filteredThreads = useMemo(() => {
    const threads = data?.threads ?? [];
    return routingFilter === "all" ? threads : threads.filter((thread) => thread.routing === routingFilter);
  }, [data?.threads, routingFilter]);

  const disconnected = (readError as ReviewRequestError)?.response?.data?.code === "gmail_not_connected";
  const readTitle = t(disconnected ? "gmailReviewNotConnected" : "gmailReviewLoadFailed");
  const readNotice = readError ? noticeError(readError, readTitle) : null;
  if (disconnected && readNotice) readNotice.message = readTitle;
  const unavailable = disconnected || readNotice?.kind === "unauthorized";
  const controlsDisabled = !active || loading || operation !== null || readError !== null;
  const chipSx = { maxWidth: "100%", height: "auto", minHeight: 24, "& .MuiChip-label": { whiteSpace: "normal", overflowWrap: "anywhere", py: 0.5 } };
  const actions = <>
    <Button variant="contained" onClick={() => void runManualSync()} disabled={controlsDisabled}>
      {operation?.kind === "sync" ? t("gmailReviewSyncing") : t("gmailReviewRunSync")}
    </Button>
    <Button variant="outlined" onClick={() => { bodyRef.current?.focus(); void load(); }} disabled={!active || loading || operation !== null}>
      {loading ? t("loading") : t("correspondenceRefresh")}
    </Button>
    {!embedded ? <Button variant="text" disabled={!active || operation !== null} onClick={() => navigate("/correspondence")}>{t("gmailReviewBackToInbox")}</Button> : null}
  </>;
  const body = <Box ref={bodyRef} role="group" aria-label={t(embedded ? "gmailReviewEmbeddedTitle" : "gmailReviewTitle")} tabIndex={-1} sx={{ minWidth: 0 }}>
      <ViewStateNotice compact loading={loading || operation !== null} error={readNotice} title={readTitle} onRetry={() => { bodyRef.current?.focus(); void load(); }} />
      {writeError ? <ViewStateNotice compact title={t(writeError.key)} error={{ ...noticeError(writeError.cause, t(writeError.key)), retryable: false }} /> : null}

      <Box sx={{ display: "flex", gap: 1, flexWrap: "wrap", mb: 2 }}>
        <Chip label={t("gmailReviewFilter", { value: routeLabel(routingFilter) })} variant="outlined" sx={chipSx} />
        {(["all", "auto-link", "review", "unmatched", "suggested", "linked", "rejected"] as const).map((value) => (
          <Button key={value} size="small" aria-pressed={routingFilter === value} disabled={!active} variant={routingFilter === value ? "contained" : "text"} onClick={() => setRoutingFilter(value)}>
            {routeLabel(value)}
          </Button>
        ))}
      </Box>

      {!unavailable && data ? (
        <Box sx={{ display: "flex", gap: 1, flexWrap: "wrap", mb: 2 }}>
          <Chip label={t("gmailReviewCandidateThreads", { count: data.candidateThreadCount })} variant="outlined" sx={chipSx} />
          <Chip label={t("gmailReviewAutoLinkCount", { count: data.autoLinkThreadCount })} color="success" variant="outlined" sx={chipSx} />
          <Chip label={t("gmailReviewReviewCount", { count: data.reviewThreadCount })} color="warning" variant="outlined" sx={chipSx} />
          <Chip label={t("gmailReviewUnmatchedCount", { count: data.unmatchedThreadCount })} variant="outlined" sx={chipSx} />
          {suggestions?.count ? <Chip label={t("gmailReviewSuggestedJobsCount", { count: suggestions.count })} color="secondary" variant="outlined" sx={chipSx} /> : null}
        </Box>
      ) : null}

      {!loading && !readError && data && filteredThreads.length === 0 ? <Typography color="text.secondary">{t("gmailReviewNoCandidates")}</Typography> : null}

      <Stack spacing={1.25}>
        {!unavailable && filteredThreads.map((thread) => {
          const suggestion = (suggestions?.items ?? []).find((item) => item.threadId === thread.threadId);
          const headingId = `${sectionId}-${encodeURIComponent(thread.threadId)}`;
          return (
            <Paper key={thread.threadId} component="article" aria-labelledby={headingId} variant="outlined" sx={{ p: "var(--app-card-padding)", borderRadius: 1, minWidth: 0 }}>
              <Box sx={{ display: "flex", justifyContent: "space-between", gap: 2, flexWrap: "wrap", alignItems: "flex-start" }}>
                <Box sx={{ minWidth: 0, flex: "1 1 420px" }}>
                  <Typography id={headingId} component={embedded ? "h3" : "h2"} variant="subtitle1" sx={{ fontWeight: 700, overflowWrap: "anywhere" }}>{thread.subject}</Typography>
                  <Typography variant="body2" sx={{ color: "text.secondary" }}>
                    {t("gmailReviewThreadSummary", { count: thread.messageCount, route: routeLabel(thread.routing) })}
                  </Typography>
                  <Box sx={{ display: "flex", gap: 0.75, flexWrap: "wrap", mt: 0.75 }}>
                    {thread.matchedQueries.slice(0, 3).map((query) => (
                      <Chip key={query} size="small" label={query} variant="outlined" sx={chipSx} />
                    ))}
                    {thread.hasImportedMessages ? <Chip size="small" label={t("gmailReviewHasImported")} color="success" variant="outlined" sx={chipSx} /> : null}
                  </Box>
                  <TextField
                    label={t("gmailReviewNotes")}
                    value={notes[thread.threadId] ?? ""}
                    onChange={(event) => {
                      if (!activeRef.current || mutationRef.current) return;
                      setNotes((prev) => ({ ...prev, [thread.threadId]: event.target.value }));
                    }}
                    disabled={!active || operation !== null}
                    size="small"
                    fullWidth
                    multiline
                    minRows={2}
                    sx={{ mt: 1.25 }}
                    placeholder={t("gmailReviewNotesPlaceholder")}
                  />
                  {suggestion ? (
                    <Typography variant="body2" sx={{ color: "text.secondary", mt: 1 }}>
                      {t("gmailReviewSuggestedJob", { company: suggestion.companyName || t("gmailReviewUnknownCompany"), role: suggestion.suggestedJobTitle || t("gmailReviewUnknownRole") })}
                    </Typography>
                  ) : null}
                </Box>
                <Box sx={{ display: "flex", gap: 0.75, flexWrap: "wrap", justifyContent: "flex-end", minWidth: 0, maxWidth: "100%", "& .MuiButton-root": { maxWidth: "100%", whiteSpace: "normal", overflowWrap: "anywhere" } }}>
                  {thread.jobCandidates.slice(0, 2).map((candidate) => (
                    <Chip
                      key={candidate.jobApplicationId}
                      label={`${candidate.companyName} • ${candidate.jobTitle} (${candidate.score})`}
                      variant="outlined"
                      sx={chipSx}
                      color={candidate.confidence === "high" ? "success" : candidate.confidence === "medium" ? "warning" : "default"}
                    />
                  ))}
                  {thread.jobCandidates[0] ? (
                    <Button size="small" variant="text" disabled={!active || operation !== null} onClick={() => navigate(`/jobs/${thread.jobCandidates[0].jobApplicationId}?section=communication`)}>
                      {t("gmailReviewOpenTopJob")}
                    </Button>
                  ) : null}
                  {thread.jobCandidates[0] ? (
                    <Button
                      size="small"
                      variant="contained"
                      disabled={controlsDisabled}
                      onClick={() => void saveDecision(thread.threadId, "linked", thread.jobCandidates[0].jobApplicationId)}
                    >
                      {t("gmailReviewLinkTopJob")}
                    </Button>
                  ) : null}
                  <Button
                    size="small"
                    variant="outlined"
                    color="warning"
                    disabled={controlsDisabled}
                    onClick={() => void saveDecision(thread.threadId, "review")}
                  >
                    {t("gmailReviewKeepInReview")}
                  </Button>
                  <Button
                    size="small"
                    variant="outlined"
                    color="secondary"
                    disabled={controlsDisabled}
                    onClick={() => void saveDecision(thread.threadId, "suggested")}
                  >
                    {t("gmailReviewSuggestedJobAction")}
                  </Button>
                  {createdJobs[thread.threadId] ? <Button size="small" variant="outlined" disabled={!active || operation !== null} onClick={() => navigate(`/jobs/${createdJobs[thread.threadId]}?section=communication`)}>{t("emailInboxOpenJob")}</Button> : suggestion ? (
                    <Button
                      size="small"
                      variant="outlined"
                      disabled={controlsDisabled}
                      onClick={() => void createSuggestedJob(thread.threadId)}
                    >
                      {operation?.kind === "create" && operation.threadId === thread.threadId ? t("gmailReviewCreating") : t("createJob")}
                    </Button>
                  ) : null}
                  <Button
                    size="small"
                    variant="outlined"
                    color="error"
                    disabled={controlsDisabled}
                    onClick={() => void saveDecision(thread.threadId, "rejected")}
                  >
                    {t("gmailReviewReject")}
                  </Button>
                </Box>
              </Box>
            </Paper>
          );
        })}
      </Stack>
    </Box>;

  return embedded ? <PageSection title={t("gmailReviewEmbeddedTitle")} description={t("gmailReviewSubtitle")} actions={actions}>{body}</PageSection> :
    <Box component="section" aria-labelledby={sectionId} sx={{ minWidth: 0, display: "grid", gap: 2 }}>
      <PageHeader title={t("gmailReviewTitle")} titleId={sectionId} description={t("gmailReviewSubtitle")} actions={actions} />
      {body}
    </Box>;
}