import { useEffect, useMemo, useRef, useState } from "react";
import { ChevronRight, Home, Mail, Paperclip, RefreshCw } from "lucide-react";
import {
  Button,
  DismissibleAlert,
  ExplorerTree,
  LoadingIndicator,
  MessageDisplayPanel,
  formatDateTime,
  type ApiSettings
} from "@govoplan/core-webui";
import {
  getMailboxMessage,
  listMailboxFolders,
  listMailboxMessages,
  listMailServerProfiles,
  type MailImapFolderResponse,
  type MailMailboxMessageDetail,
  type MailMailboxMessageSummary,
  type MailServerProfile
} from "../../api/mail";

type MailFolderNode = {
  id: string;
  label: string;
  folderName: string | null;
  flags: string[];
  children: MailFolderNode[];
};

export default function MailboxPage({ settings }: { settings: ApiSettings }) {
  const [profiles, setProfiles] = useState<MailServerProfile[]>([]);
  const [selectedProfileId, setSelectedProfileId] = useState("");
  const [folders, setFolders] = useState<MailImapFolderResponse[]>([]);
  const [selectedFolder, setSelectedFolder] = useState("INBOX");
  const [foldersLoadedForProfile, setFoldersLoadedForProfile] = useState("");
  const [expandedFolders, setExpandedFolders] = useState<Set<string>>(() => new Set());
  const [messages, setMessages] = useState<MailMailboxMessageSummary[]>([]);
  const [messageTotalCount, setMessageTotalCount] = useState<number | null>(null);
  const [selectedMessage, setSelectedMessage] = useState<MailMailboxMessageDetail | null>(null);
  const [pendingMessageKey, setPendingMessageKey] = useState("");
  const [loadingProfiles, setLoadingProfiles] = useState(true);
  const [loadingFolders, setLoadingFolders] = useState(false);
  const [loadingMessages, setLoadingMessages] = useState(false);
  const [loadingMessage, setLoadingMessage] = useState(false);
  const [error, setError] = useState("");
  const folderRequestRef = useRef(0);
  const messageListRequestRef = useRef(0);
  const messageDetailRequestRef = useRef(0);

  const selectedProfile = profiles.find((profile) => profile.id === selectedProfileId) ?? null;
  const imapProfiles = useMemo(() => profiles.filter((profile) => profile.is_active && profile.imap), [profiles]);
  const folderTree = useMemo(() => buildMailboxFolderTree(folders), [folders]);
  const selectedFolderNodeId = useMemo(() => findFolderNodeId(folderTree, selectedFolder) ?? "", [folderTree, selectedFolder]);
  const shellBusy = loadingProfiles || loadingFolders || loadingMessages;
  const noImapProfiles = !loadingProfiles && imapProfiles.length === 0;
  const foldersReady = Boolean(selectedProfileId) && foldersLoadedForProfile === selectedProfileId;
  const selectedMessageKey = selectedMessage ? mailboxMessageKey(selectedMessage.folder || selectedFolder, selectedMessage.uid) : pendingMessageKey;
  const messageCountLabel = messageListCountLabel(messages.length, messageTotalCount, loadingMessages, foldersReady);
  const folderEmptyText = noImapProfiles ? "No IMAP-enabled mail profiles." : loadingFolders ? "Loading folders..." : "No folders available.";
  const messageEmptyText = !selectedProfileId ? "Select an IMAP profile." : !foldersReady || loadingMessages ? "Loading messages..." : "No messages in this folder.";
  const previewEmptyText = loadingMessage ? "Loading message..." : "Select a message to inspect its content.";
  const loadingLabel = loadingProfiles ? "Loading mail profiles..." : loadingFolders ? "Loading folders..." : loadingMessages ? "Loading messages..." : "Loading message...";

  useEffect(() => { void loadProfiles(); }, [settings.apiBaseUrl, settings.apiKey, settings.accessToken]);
  useEffect(() => { if (selectedProfileId) void loadFolders(selectedProfileId); }, [selectedProfileId]);
  useEffect(() => { if (selectedProfileId && selectedFolder && foldersReady) void loadMessages(selectedProfileId, selectedFolder); }, [foldersReady, selectedProfileId, selectedFolder]);

  useEffect(() => {
    const ancestorIds = folderAncestorIds(folderTree, selectedFolder);
    if (ancestorIds.length === 0) return;
    setExpandedFolders((current) => {
      const next = new Set(current);
      ancestorIds.forEach((id) => next.add(id));
      return next;
    });
  }, [folderTree, selectedFolder]);

  async function loadProfiles() {
    setLoadingProfiles(true);
    setError("");
    try {
      const loaded = await listMailServerProfiles(settings);
      const usable = loaded.filter((profile) => profile.is_active && profile.imap);
      setProfiles(loaded);
      setSelectedProfileId((current) => current && usable.some((profile) => profile.id === current) ? current : usable[0]?.id ?? "");
      if (usable.length === 0) {
        setFolders([]);
        setFoldersLoadedForProfile("");
        setMessages([]);
        setMessageTotalCount(null);
        setSelectedMessage(null);
        setPendingMessageKey("");
      }
    } catch (err) {
      setError(errorText(err));
    } finally {
      setLoadingProfiles(false);
    }
  }

  async function loadFolders(profileId = selectedProfileId) {
    if (!profileId) return;
    const requestId = ++folderRequestRef.current;
    messageListRequestRef.current += 1;
    messageDetailRequestRef.current += 1;
    setLoadingFolders(true);
    setFoldersLoadedForProfile("");
    setMessageTotalCount(null);
    setPendingMessageKey("");
    setError("");
    try {
      const response = await listMailboxFolders(settings, profileId);
      if (requestId !== folderRequestRef.current) return;
      if (!response.ok) throw new Error(response.message || "Mailbox folders could not be loaded.");
      const loaded = response.folders?.length ? response.folders : [{ name: "INBOX", flags: [] }];
      setFolders(loaded);
      setExpandedFolders(new Set());
      let nextFolder = selectedFolder;
      if (!nextFolder || !loaded.some((folder) => folder.name === nextFolder)) {
        nextFolder = loaded.some((folder) => folder.name === "INBOX") ? "INBOX" : response.detected_sent_folder || loaded[0]?.name || "INBOX";
      }
      setSelectedFolder(nextFolder);
      setFoldersLoadedForProfile(profileId);
    } catch (err) {
      if (requestId !== folderRequestRef.current) return;
      setError(errorText(err));
      setFolders([]);
      setFoldersLoadedForProfile("");
      setMessages([]);
      setMessageTotalCount(null);
      setSelectedMessage(null);
      setPendingMessageKey("");
    } finally {
      if (requestId === folderRequestRef.current) setLoadingFolders(false);
    }
  }

  async function loadMessages(profileId = selectedProfileId, folder = selectedFolder) {
    if (!profileId || !folder) return;
    const requestId = ++messageListRequestRef.current;
    messageDetailRequestRef.current += 1;
    setLoadingMessages(true);
    setMessageTotalCount(null);
    setSelectedMessage(null);
    setPendingMessageKey("");
    setError("");
    try {
      const response = await listMailboxMessages(settings, profileId, folder, 50);
      if (requestId !== messageListRequestRef.current) return;
      const loaded = response.messages ?? [];
      setMessages(loaded);
      setMessageTotalCount(response.total_count ?? loaded.length);
      setSelectedMessage(null);
    } catch (err) {
      if (requestId !== messageListRequestRef.current) return;
      setError(errorText(err));
      setMessages([]);
      setMessageTotalCount(null);
      setSelectedMessage(null);
      setPendingMessageKey("");
    } finally {
      if (requestId === messageListRequestRef.current) setLoadingMessages(false);
    }
  }

  async function openMessage(message: MailMailboxMessageSummary) {
    if (!selectedProfileId) return;
    const folderName = message.folder || selectedFolder;
    const requestId = ++messageDetailRequestRef.current;
    setPendingMessageKey(mailboxMessageKey(folderName, message.uid));
    setSelectedMessage(null);
    setLoadingMessage(true);
    setError("");
    try {
      const response = await getMailboxMessage(settings, selectedProfileId, folderName, message.uid);
      if (requestId !== messageDetailRequestRef.current) return;
      setSelectedMessage(response.message);
      setPendingMessageKey("");
    } catch (err) {
      if (requestId !== messageDetailRequestRef.current) return;
      setError(errorText(err));
      setPendingMessageKey("");
    } finally {
      if (requestId === messageDetailRequestRef.current) setLoadingMessage(false);
    }
  }

  function selectProfile(profileId: string) {
    folderRequestRef.current += 1;
    messageListRequestRef.current += 1;
    messageDetailRequestRef.current += 1;
    setSelectedProfileId(profileId);
    setFolders([]);
    setFoldersLoadedForProfile("");
    setMessages([]);
    setMessageTotalCount(null);
    setSelectedMessage(null);
    setPendingMessageKey("");
    setExpandedFolders(new Set());
    setLoadingFolders(false);
    setLoadingMessages(false);
    setLoadingMessage(false);
  }

  function openFolderNode(node: MailFolderNode) {
    if (node.folderName) {
      if (node.folderName === selectedFolder && foldersReady) void loadMessages(selectedProfileId, node.folderName);
      else setSelectedFolder(node.folderName);
      return;
    }
    toggleFolderNode(node);
  }

  function toggleFolderNode(node: MailFolderNode) {
    setExpandedFolders((current) => {
      const next = new Set(current);
      if (next.has(node.id)) next.delete(node.id);
      else next.add(node.id);
      return next;
    });
  }

  return (
    <div className="workspace-data-page module-entry-page file-manager-page file-manager-fullscreen mailbox-page">
      {error && <DismissibleAlert tone="danger" resetKey={error} floating>{error}</DismissibleAlert>}

      <div className={`file-manager-shell mailbox-shell ${shellBusy ? "is-loading" : ""}`}>
        <aside className="file-tree-panel" aria-label="Mailbox folders">
          <div className="file-tree-heading">Folders</div>
          <div className="file-tree-list">
            {folderTree.length === 0 && <p className="muted small-text mailbox-tree-empty">{folderEmptyText}</p>}
            <ExplorerTree
              nodes={folderTree}
              getNodeId={(node) => node.id}
              getNodeLabel={(node) => node.label}
              getNodeChildren={(node) => node.children}
              activeId={selectedFolderNodeId}
              expandedIds={expandedFolders}
              onOpen={openFolderNode}
              onToggle={toggleFolderNode}
              disabled={shellBusy}
              renderNodeContent={(node) => {
                const flagText = folderFlagLabel(node.flags);
                const showCount = foldersReady && node.folderName === selectedFolder && messageTotalCount !== null;
                return (
                  <span className="mailbox-tree-node-label">
                    <span className="mailbox-tree-node-main">
                      <span>{node.label}</span>
                      {showCount && <small className="mailbox-folder-count">{messageTotalCount}</small>}
                    </span>
                    {flagText && <small>{flagText}</small>}
                  </span>
                );
              }}
            />
          </div>
        </aside>

        <section className="file-list-panel mailbox-message-list-panel" aria-label="Mailbox messages">
          <div className="file-list-sticky">
            <div className="file-manager-toolbar mailbox-toolbar" aria-label="Mail actions">
              <label className="mailbox-profile-field">
                <span>IMAP profile</span>
                <select value={selectedProfileId} disabled={shellBusy || imapProfiles.length === 0} onChange={(event) => selectProfile(event.target.value)}>
                  {imapProfiles.length === 0 && <option value="">No IMAP profiles available</option>}
                  {imapProfiles.map((profile) => <option key={profile.id} value={profile.id}>{profile.name}</option>)}
                </select>
              </label>
              <span className="mailbox-toolbar-meta">{selectedProfile?.imap ? transportLabel(selectedProfile) : "No IMAP profile selected"}</span>
              <div className="mailbox-toolbar-actions">
                <Button onClick={() => void loadProfiles()} disabled={shellBusy} title="Reload IMAP profiles">
                  <RefreshCw size={16} aria-hidden="true" />
                  Profiles
                </Button>
                <Button onClick={() => void loadFolders(selectedProfileId)} disabled={!selectedProfileId || shellBusy} title="Refresh mailbox folders">
                  <RefreshCw size={16} aria-hidden="true" />
                  Folders
                </Button>
                <Button onClick={() => void loadMessages(selectedProfileId, selectedFolder)} disabled={!selectedProfileId || !selectedFolder || !foldersReady || shellBusy} title="Refresh messages in the current folder">
                  <RefreshCw size={16} aria-hidden="true" />
                  Messages
                </Button>
              </div>
            </div>

            <nav className="file-breadcrumbs" aria-label="Current mailbox folder">
              <span className="file-breadcrumb mailbox-breadcrumb-static"><Home size={15} aria-hidden="true" /> {selectedProfile?.name || "Mail"}</span>
              <span className="file-breadcrumb-segment"><ChevronRight size={14} aria-hidden="true" /><span className="file-breadcrumb mailbox-breadcrumb-static">{selectedFolder}</span></span>
            </nav>

            <div className="file-list-meta">
              <span>{messageCountLabel}</span>
              <span>{selectedFolder}</span>
              {shellBusy && <span>Working...</span>}
              {loadingMessage && <span>Loading preview...</span>}
            </div>

            <div className="file-list-table-head mailbox-message-head" role="row">
              <span>Subject</span>
              <span>Date</span>
              <span>Size</span>
            </div>
          </div>

          <div className="file-list-drop-target mailbox-message-scroll">
            <div className="file-list-table mailbox-message-table" role="table" aria-label="Mailbox messages">
              {messages.length === 0 && <div className="file-list-empty">{messageEmptyText}</div>}
              {messages.map((message) => {
                const key = mailboxMessageKey(message.folder || selectedFolder, message.uid);
                const selected = key === selectedMessageKey;
                const loadingSelected = loadingMessage && key === pendingMessageKey;
                return (
                  <div
                    key={message.uid}
                    className={`file-list-row file-row mailbox-message-row ${selected ? "is-selected" : ""} ${loadingSelected ? "is-loading-message" : ""}`}
                    role="row"
                    tabIndex={0}
                    onClick={() => void openMessage(message)}
                    onKeyDown={(event) => {
                      if (event.key === "Enter" || event.key === " ") {
                        event.preventDefault();
                        void openMessage(message);
                      }
                    }}
                  >
                    <div className="file-list-name-cell">
                      <div className="file-list-name">
                        <Mail className="file-row-icon" size={20} aria-hidden="true" />
                        <span>
                          <strong>{message.subject || "(no subject)"}</strong>
                          <small>{message.from_header || "-"}</small>
                        </span>
                      </div>
                    </div>
                    <span className="mailbox-message-date">{formatDateTime(message.date, { fallback: "-" })}</span>
                    <span className="file-row-tail mailbox-message-tail">
                      {message.attachment_count ? <span><Paperclip size={14} aria-hidden="true" /> {message.attachment_count}</span> : null}
                      <span>{formatBytes(message.size_bytes)}</span>
                    </span>
                  </div>
                );
              })}
            </div>
          </div>
        </section>

        <section className="mailbox-preview-panel" aria-label="Message preview">
          <div className="file-tree-heading">Preview</div>
          <div className="mailbox-preview-scroll">
            <MessageDisplayPanel
              title={selectedMessage?.subject}
              fields={selectedMessage ? [
                { label: "From", value: selectedMessage.from_header || "-" },
                { label: "To", value: selectedMessage.to_header || "-" },
                { label: "Cc", value: selectedMessage.cc_header || null },
                { label: "Date", value: formatDateTime(selectedMessage.date, { fallback: "-" }) }
              ] : []}
              bodyText={selectedMessage?.body_text}
              bodyHtml={selectedMessage?.body_html}
              bodyPreview={selectedMessage?.body_preview}
              headers={selectedMessage?.headers}
              attachments={selectedMessage?.attachments?.map((attachment) => ({
                filename: attachment.filename,
                contentType: attachment.content_type,
                sizeBytes: attachment.size_bytes
              }))}
              emptyText={previewEmptyText}
            />
          </div>
        </section>

        {shellBusy && (
          <div className="file-manager-loading-overlay" aria-live="polite" aria-busy="true">
            <div className="loading-frame-panel"><LoadingIndicator label={loadingLabel} /> <span>{loadingLabel}</span></div>
          </div>
        )}
      </div>
    </div>
  );
}

function buildMailboxFolderTree(folders: MailImapFolderResponse[]): MailFolderNode[] {
  const roots: MailFolderNode[] = [];
  const byId = new Map<string, MailFolderNode>();

  function ensureNode(parts: string[], index: number): MailFolderNode | null {
    if (index < 0 || index >= parts.length) return null;
    const id = parts.slice(0, index + 1).join("/");
    const existing = byId.get(id);
    if (existing) return existing;

    const node: MailFolderNode = { id, label: parts[index], folderName: null, flags: [], children: [] };
    byId.set(id, node);

    if (index === 0) {
      roots.push(node);
    } else {
      ensureNode(parts, index - 1)?.children.push(node);
    }
    return node;
  }

  for (const folder of folders) {
    const parts = folderParts(folder.name);
    const node = ensureNode(parts, parts.length - 1);
    if (node) {
      node.folderName = folder.name;
      node.flags = folder.flags ?? [];
    }
  }

  sortFolderNodes(roots);
  return roots;
}

function folderParts(folderName: string): string[] {
  const normalized = folderName.trim();
  if (!normalized) return [];
  if (normalized.includes("/")) return normalized.split("/").filter(Boolean);
  if (/^INBOX[.]/i.test(normalized)) return ["INBOX", ...normalized.slice(6).split(".").filter(Boolean)];
  return [normalized];
}

function sortFolderNodes(nodes: MailFolderNode[]) {
  nodes.sort((left, right) => folderSortKey(left.label).localeCompare(folderSortKey(right.label)));
  nodes.forEach((node) => sortFolderNodes(node.children));
}

function folderSortKey(label: string): string {
  return label.toUpperCase() === "INBOX" ? "0" : `1:${label.toLocaleLowerCase()}`;
}

function findFolderNodeId(nodes: MailFolderNode[], folderName: string): string | null {
  for (const node of nodes) {
    if (node.folderName === folderName) return node.id;
    const child = findFolderNodeId(node.children, folderName);
    if (child) return child;
  }
  return null;
}

function folderAncestorIds(nodes: MailFolderNode[], folderName: string, parents: string[] = []): string[] {
  for (const node of nodes) {
    const path = [...parents, node.id];
    if (node.folderName === folderName) return path;
    const child = folderAncestorIds(node.children, folderName, path);
    if (child.length > 0) return child;
  }
  return [];
}


function mailboxMessageKey(folder: string, uid: string): string {
  return `${folder || "INBOX"}::${uid}`;
}

function messageListCountLabel(visibleCount: number, totalCount: number | null, loading: boolean, ready: boolean): string {
  if (!ready) return "No folder loaded";
  if (loading) return "Loading messages";
  if (totalCount !== null && totalCount > visibleCount) return `${visibleCount} of ${totalCount} messages`;
  const count = totalCount ?? visibleCount;
  return `${count} message${count === 1 ? "" : "s"}`;
}

function folderFlagLabel(flags: string[]): string {
  const labels = flags.map(displayFolderFlag).filter((label): label is string => Boolean(label));
  return Array.from(new Set(labels)).join(" ");
}

function displayFolderFlag(flag: string): string | null {
  const normalized = flag.replace(/^\\/, "").toLowerCase();
  switch (normalized) {
    case "sent":
      return "Sent";
    case "drafts":
      return "Drafts";
    case "trash":
      return "Trash";
    case "archive":
      return "Archive";
    case "junk":
      return "Junk";
    case "flagged":
      return "Flagged";
    case "haschildren":
    case "hasnochildren":
    case "noselect":
      return null;
    default:
      return null;
  }
}

function transportLabel(profile: MailServerProfile): string {
  const imap = profile.imap;
  if (!imap?.host) return "IMAP not configured";
  return `${imap.host}:${imap.port ?? "?"} ${imap.security ?? ""}`.trim();
}

function formatBytes(value?: number | null): string {
  if (!value) return "-";
  if (value < 1024) return `${value} B`;
  if (value < 1024 * 1024) return `${(value / 1024).toFixed(1)} KB`;
  return `${(value / 1024 / 1024).toFixed(1)} MB`;
}

function errorText(error: unknown): string {
  return error instanceof Error ? error.message : String(error);
}