"""tui.py — minimal curses filter-select picker for CLI prompts.

Exposed surface:

  filter_select(items, *, title="", tty_path="/dev/tty") -> str | None

Opens /dev/tty directly so the picker works even when stdout/stdin are
redirected.  Returns the selected item or None on cancel.
"""

from __future__ import annotations

import curses
import os
import sys
from typing import Any, Optional


def filter_select(
    items: list[str],
    *,
    title: str = "",
    tty_path: str = "/dev/tty",
) -> Optional[str]:
    """Render a filter-select picker over *items*.

    Returns the selected item string, or ``None`` if the user cancelled
    (Esc / ``q`` / Ctrl-C / Ctrl-D) or if the terminal is too small.

    The picker opens *tty_path* directly so it works even when
    stdout/stdin are redirected.
    """
    if not items:
        return None

    try:
        tty_fd = open(tty_path, "r+b", buffering=0)
    except OSError:
        return None

    try:
        result = _run_picker(items, title=title, tty_fd=tty_fd.fileno())
    finally:
        tty_fd.close()

    return result


# ---------------------------------------------------------------------------
# Internal implementation
# ---------------------------------------------------------------------------

_KEY_ESC = 27
_KEY_CTRL_C = 3
_KEY_CTRL_D = 4
_KEY_BACKSPACE_WIN = 8
_KEY_ENTER_ALT = 10

_CANCEL_KEYS = frozenset([_KEY_ESC, _KEY_CTRL_C, _KEY_CTRL_D, ord("q")])


def _run_picker(items: list[str], *, title: str, tty_fd: int) -> Optional[str]:
    """Drive a curses session on *tty_fd* and return the picked item."""
    # newterm lets us run curses on an arbitrary fd rather than the
    # process's controlling tty / stdout — crucial when stdout is piped.
    os.environ.setdefault("TERM", "xterm-256color")

    # Save / restore the real stdin/stdout so curses newterm can use tty_fd.
    orig_stdin = sys.__stdin__
    orig_stdout = sys.__stdout__

    try:
        import io
        tty_text = io.TextIOWrapper(io.FileIO(tty_fd, mode='r+'), write_through=True)
        sys.__stdin__ = tty_text   # type: ignore[assignment]
        sys.__stdout__ = tty_text  # type: ignore[assignment]

        # curses.wrapper calls initscr which honours sys.__stdin__ / __stdout__
        # on some builds; use newterm where available.
        screen = curses.initscr()
        curses.noecho()
        curses.cbreak()
        screen.keypad(True)

        try:
            result = _picker_loop(screen, items, title=title)
        finally:
            screen.keypad(False)
            curses.nocbreak()
            curses.echo()
            curses.endwin()
    except Exception:  # noqa: W0718 — curses can raise many error types
        return None
    finally:
        sys.__stdin__ = orig_stdin    # type: ignore[assignment]
        sys.__stdout__ = orig_stdout  # type: ignore[assignment]

    return result


def _picker_loop(screen: Any, items: list[str], *, title: str) -> Optional[str]:
    query = ""
    cursor = 0

    while True:
        filtered = _filter_items(items, query)

        # Clamp cursor into the visible list.
        if not filtered:
            cursor = 0
        elif cursor >= len(filtered):
            cursor = len(filtered) - 1

        try:
            _render(screen, filtered, cursor, query=query, title=title)
        except curses.error:
            # Terminal too small or write error — bail out.
            return None

        try:
            key = screen.getch()
        except KeyboardInterrupt:
            return None

        if key in _CANCEL_KEYS:
            return None

        if key in (curses.KEY_ENTER, _KEY_ENTER_ALT, ord("\r")):
            return filtered[cursor] if filtered else None

        if key in (curses.KEY_UP, ord("k")):
            if cursor > 0:
                cursor -= 1

        elif key in (curses.KEY_DOWN, ord("j")):
            if cursor < len(filtered) - 1:
                cursor += 1

        elif key in (curses.KEY_BACKSPACE, _KEY_BACKSPACE_WIN, 127):
            query = query[:-1]
            # After narrowing the filter, keep cursor in range.
            new_filtered = _filter_items(items, query)
            if cursor >= len(new_filtered):
                cursor = max(0, len(new_filtered) - 1)

        elif 32 <= key <= 126:
            # Printable ASCII — append to query and reset cursor so the
            # top of the newly-filtered list is selected.
            query += chr(key)
            cursor = 0


def _filter_items(items: list[str], query: str) -> list[str]:
    if not query:
        return list(items)
    q = query.lower()
    return [i for i in items if q in i.lower()]


def _render(screen: Any, filtered: list[str], cursor: int, *, query: str, title: str) -> None:
    screen.erase()
    rows, cols = screen.getmaxyx()
    min_rows = 5

    if rows < min_rows:
        raise curses.error("terminal too small")

    row = 0

    if title and row < rows - 1:
        _addstr_safe(screen, row, 0, title[:cols - 1], curses.A_BOLD)
        row += 1

    filter_label = f"Filter: {query}"
    if row < rows - 1:
        _addstr_safe(screen, row, 0, filter_label[:cols - 1])
        row += 1

    sep = "─" * min(cols - 1, 40)
    if row < rows - 1:
        _addstr_safe(screen, row, 0, sep)
        row += 1

    list_start = row
    # Reserve two rows for separator + help line at bottom.
    list_rows = rows - list_start - 2
    if list_rows < 1:
        return

    # Scroll window: keep cursor visible.
    scroll = max(0, cursor - list_rows + 1)
    visible = filtered[scroll: scroll + list_rows]

    for idx, item in enumerate(visible):
        abs_idx = scroll + idx
        attr = curses.A_REVERSE if abs_idx == cursor else curses.A_NORMAL
        prefix = "> " if abs_idx == cursor else "  "
        line = (prefix + item)[:cols - 1]
        if row < rows - 1:
            _addstr_safe(screen, row, 0, line, attr)
        row += 1

    if row < rows - 1:
        _addstr_safe(screen, row, 0, sep)
        row += 1

    help_line = "[↑↓/jk] move  [Enter] select  [Esc/q] cancel"
    if row < rows:
        _addstr_safe(screen, min(rows - 1, row), 0, help_line[:cols - 1])

    screen.refresh()


def _addstr_safe(screen: Any, row: int, col: int, text: str, attr: int = curses.A_NORMAL) -> None:
    try:
        screen.addstr(row, col, text, attr)
    except curses.error:
        pass