// The `ctrl-k` command bar (docs/COMMAND-BAR.md): a query line over a result
// list. Sessions and commands rank together by default; `>` narrows to
// commands, `~` to directories. `tab` on a session drills into its action page.
//
// The bar picks an action and hands off — it never reimplements one. Each
// handler defaults to the event the flow that already implements it listens
// on, so the React bar and the legacy shell raise the same flows.

import { useCallback, useEffect, useMemo, useRef, useState } from "react";
import { createPortal } from "react-dom";

import {
  KILL_SESSION_EVENT,
  RENAME_SESSION_EVENT,
  SESSION_SELECT_EVENT,
  SPAWN_SIMILAR_EVENT,
} from "../../uiEvents.js";
import { publishedCommands, type Command } from "../../commands.js";
import { sessionName, type Session } from "../../types.js";
import { ActionPage } from "./ActionPage.js";
import { ResultList } from "./ResultList.js";
import {
  barGroups,
  barRows,
  commandBarCandidates,
  dirEntryPaths,
  directoryBarCandidates,
  isActionCandidate,
  listDirEntries as defaultListDirEntries,
  loadBarDirectories,
  parseBarQuery,
  probeDir,
  sessionActionCandidates,
  sessionBarCandidates,
  PLACEHOLDERS,
  type BarCandidate,
  type BarResult,
  type DirectoryBarCandidate,
  type SessionAction,
} from "./model.js";

/** Raised when Enter lands on a directory row and no handler was given. The
 *  bar picks the directory; the shell owns the spawn, which is the same
 *  fast-forward path `N` takes. */
export const SPAWN_DIRECTORY_EVENT = "cmdbar-spawn-directory";

export interface CommandBarProps {
  /** Sessions to build candidates from, as the store has them right now. */
  sessions: readonly Session[];
  /** The daemon's home dir, for the directory field's `~/…` abbreviation. */
  homeDir?: string;
  /** The command registry to list under `>`. Defaults to every bound command,
   * in registry order. */
  commands?: readonly Command[];
  /** The directory list behind `~`, fetched once on first use. */
  loadDirectories?: () => Promise<string[]>;
  /** One directory's subdirectories, for filling the list in as a path is
   * typed. Defaults to `GET /api/dirs`. */
  listDirEntries?: (dir: string) => Promise<string[]>;
  onOpenSession?(sessionId: string): void;
  onSpawnDirectory?(path: string): void;
  onKillSession?(session: Session): void;
  onRenameSession?(session: Session): void;
  onSpawnSimilar?(session: Session): void;
  /** Closing returns the keyboard to whatever held it when the bar opened. */
  onClose(): void;
}

function raise(name: string, detail: unknown): void {
  document.dispatchEvent(new CustomEvent(name, { detail }));
}

export function CommandBar(props: CommandBarProps) {
  const {
    sessions,
    homeDir,
    commands,
    loadDirectories = loadBarDirectories,
    listDirEntries = defaultListDirEntries,
    onClose,
  } = props;

  const inputRef = useRef<HTMLInputElement>(null);
  const panelRef = useRef<HTMLDivElement>(null);

  const [raw, setRaw] = useState("");
  const [highlighted, setHighlighted] = useState(0);
  // The action page: `page` is the session being acted on, `stashed` the
  // result-list query it was drilled into from — backing out restores it, so
  // the round trip costs the operator nothing.
  const [page, setPage] = useState<Session | null>(null);
  const [stashed, setStashed] = useState("");

  // `~`'s candidates: the recents-and-projects list, fetched once, plus
  // whatever `/api/dirs` has filled in for the directory being typed.
  const [directories, setDirectories] = useState<DirectoryBarCandidate[]>([]);
  const [probed, setProbed] = useState<DirectoryBarCandidate[]>([]);
  const requestedRef = useRef(false);
  const listingsRef = useRef(new Map<string, string[]>());

  // On the action page the query line is over the three actions, so there is
  // no sigil to read: `>` and `~` are ordinary characters there.
  const parsed = useMemo(() => (page ? { sigil: null, query: raw } : parseBarQuery(raw)), [page, raw]);

  const sessionCandidates = useMemo(
    () => sessionBarCandidates(sessions, homeDir),
    [sessions, homeDir],
  );
  const commandCandidates = useMemo(
    () => commandBarCandidates(commands ?? publishedCommands()),
    [commands],
  );

  // Closing returns the keyboard to whatever held it when the bar opened: a
  // round trip through the bar never silently moves focus.
  useEffect(() => {
    const previouslyFocused = document.activeElement as HTMLElement | null;
    inputRef.current?.focus();
    return () => {
      if (previouslyFocused?.isConnected) previouslyFocused.focus();
    };
  }, []);

  // The recents-and-projects list, the first time `~` is used. No directories
  // is a shorter list, not an error state.
  useEffect(() => {
    if (parsed.sigil !== "~" || requestedRef.current) return;
    requestedRef.current = true;
    let live = true;
    loadDirectories()
      .then((paths) => {
        if (live) setDirectories(directoryBarCandidates(paths, homeDir));
      })
      .catch(() => {});
    return () => {
      live = false;
    };
  }, [parsed.sigil, loadDirectories, homeDir]);

  // Fill the list in from `GET /api/dirs` once the query looks like a path: the
  // directory it names is listed and its children join the candidates, so `~`
  // reaches a directory that was never spawned in.
  const dir = parsed.sigil === "~" ? probeDir(parsed.query) : "";
  useEffect(() => {
    if (dir === "") {
      setProbed([]);
      return;
    }
    const cached = listingsRef.current.get(dir);
    if (cached) {
      setProbed(directoryBarCandidates(dirEntryPaths(dir, cached), homeDir));
      return;
    }
    let live = true;
    setProbed([]);
    listDirEntries(dir)
      .then((entries) => {
        listingsRef.current.set(dir, entries);
        if (live) setProbed(directoryBarCandidates(dirEntryPaths(dir, entries), homeDir));
      })
      .catch(() => {
        /* an unreadable directory contributes nothing */
      });
    return () => {
      live = false;
    };
  }, [dir, listDirEntries, homeDir]);

  /** What the matcher sees for the query line as it stands. With no sigil the
   *  list is mixed — sessions and commands together — except on an empty query,
   *  where the bar is a session switcher. */
  const candidates: BarCandidate[] = useMemo(() => {
    if (page) return sessionActionCandidates();
    switch (parsed.sigil) {
      case ">":
        return [...commandCandidates];
      case "~": {
        const seen = new Set<string>();
        return [...directories, ...probed].filter((c) =>
          seen.has(c.path) ? false : (seen.add(c.path), true),
        );
      }
      default:
        return parsed.query === ""
          ? [...sessionCandidates]
          : [...sessionCandidates, ...commandCandidates];
    }
  }, [page, parsed.sigil, parsed.query, sessionCandidates, commandCandidates, directories, probed]);

  const groups = useMemo(
    () => barGroups(barRows(parsed.query, candidates)),
    [parsed.query, candidates],
  );
  // Grouping is a rendering of the ranking, so the flattened groups are the
  // rows in the order they appear — which is the order the highlight walks and
  // Enter acts on.
  const rows: BarResult[] = useMemo(() => groups.flatMap((g) => g.results), [groups]);

  // The highlight starts on the globally best row every time the list changes:
  // an old index would point at a different result.
  useEffect(() => {
    setHighlighted(0);
  }, [rows]);

  /** The highlight does not wrap: it stops at the first and last row. */
  const move = useCallback(
    (delta: number) => {
      setHighlighted((at) => Math.min(rows.length - 1, Math.max(0, at + delta)));
    },
    [rows.length],
  );

  const runAction = useCallback(
    (action: SessionAction, session: Session) => {
      onClose();
      switch (action.id) {
        case "kill":
          (props.onKillSession ?? ((s: Session) => raise(KILL_SESSION_EVENT, s)))(session);
          return;
        case "rename":
          (props.onRenameSession ?? ((s: Session) => raise(RENAME_SESSION_EVENT, s)))(session);
          return;
        case "spawn-similar":
          (props.onSpawnSimilar ?? ((s: Session) => raise(SPAWN_SIMILAR_EVENT, s)))(session);
          return;
      }
    },
    [onClose, props.onKillSession, props.onRenameSession, props.onSpawnSimilar],
  );

  const activate = useCallback(
    (index: number) => {
      const result = rows[index];
      if (!result) return;
      const candidate = result.candidate;
      if (isActionCandidate(candidate)) {
        // The page cannot be up without a session to act on.
        if (page) runAction(candidate.action, page);
        return;
      }
      onClose();
      switch (candidate.kind) {
        case "session":
          (props.onOpenSession ?? ((id: string) => raise(SESSION_SELECT_EVENT, id)))(
            candidate.session.id,
          );
          return;
        case "command":
          candidate.command.run();
          return;
        case "directory":
          (props.onSpawnDirectory ?? ((p: string) => raise(SPAWN_DIRECTORY_EVENT, p)))(
            candidate.path,
          );
          return;
      }
    },
    [rows, page, runAction, onClose, props.onOpenSession, props.onSpawnDirectory],
  );

  /** `tab`: drill into the highlighted session's action page. No effect on any
   *  other kind, and none on the page itself, which has no session rows. */
  const drillIn = useCallback(() => {
    const candidate = rows[highlighted]?.candidate;
    if (page || candidate?.kind !== "session") return;
    setPage(candidate.session);
    setStashed(raw);
    setRaw("");
  }, [rows, highlighted, page, raw]);

  /** Escape, or backspace at an empty query: back to the result list with the
   *  query the drill-in was made from. */
  const leavePage = useCallback(() => {
    setPage(null);
    setRaw(stashed);
    setStashed("");
  }, [stashed]);

  const onKeyDown = (e: React.KeyboardEvent<HTMLInputElement>) => {
    switch (e.key) {
      case "Escape":
        e.preventDefault();
        // On an action page Escape is one level up, not the way out.
        if (page) leavePage();
        else onClose();
        return;
      case "Tab":
        e.preventDefault();
        drillIn();
        return;
      case "Backspace":
        // Ordinary editing, except at an empty query on the action page.
        if (page && raw === "") {
          e.preventDefault();
          leavePage();
        }
        return;
      case "Enter":
        e.preventDefault();
        activate(highlighted);
        return;
      case "ArrowDown":
        e.preventDefault();
        move(1);
        return;
      case "ArrowUp":
        e.preventDefault();
        move(-1);
        return;
      case "n":
        if (e.ctrlKey) {
          e.preventDefault();
          move(1);
        }
        return;
      case "p":
        if (e.ctrlKey) {
          e.preventDefault();
          move(-1);
        }
        return;
    }
  };

  const activeRowId = rows.length > 0 ? `cmdbar-row-${highlighted}` : undefined;

  return createPortal(
    <div
      className="cmdbar-overlay fixed inset-0 z-modal flex items-start justify-center bg-bg/70 pt-[12vh] backdrop-blur-sm max-[600px]:items-end max-[600px]:pt-0"
      role="dialog"
      aria-modal="true"
      aria-label="Command bar"
      onMouseDown={(e) => {
        // A press on the scrim closes; one inside the panel is left alone.
        if (!panelRef.current?.contains(e.target as Node)) onClose();
      }}
    >
      <div
        ref={panelRef}
        className="cmdbar-panel flex w-full max-w-[560px] flex-col overflow-hidden rounded-r-3 border border-border bg-surface shadow-2 max-[600px]:max-w-none max-[600px]:rounded-b-none"
      >
        <input
          ref={inputRef}
          type="text"
          role="combobox"
          aria-expanded="true"
          aria-controls="cmdbar-results"
          aria-label="Search sessions, commands and directories"
          aria-activedescendant={activeRowId}
          autoComplete="off"
          spellCheck={false}
          className="cmdbar-input w-full border-b border-border bg-transparent px-sp-3 py-sp-2 text-fs-15 text-ink outline-none"
          placeholder={page ? `Act on ${sessionName(page)}…` : PLACEHOLDERS[parsed.sigil ?? "mixed"]}
          value={raw}
          onChange={(e) => setRaw(e.currentTarget.value)}
          onKeyDown={onKeyDown}
        />
        {page ? (
          <ActionPage
            session={page}
            groups={groups}
            highlighted={highlighted}
            onActivate={activate}
          />
        ) : (
          <ResultList
            groups={groups}
            // While a sigil is in force there is one kind, so the header is
            // dropped.
            showHeaders={parsed.sigil === null}
            highlighted={highlighted}
            onActivate={activate}
          />
        )}
      </div>
    </div>,
    document.body,
  );
}