import { ANSI, isTTY, parseKey } from './ansi';

export interface MenuItem<T = string> {
  label: string;
  value: T;
  hint?: string;
  disabled?: boolean;
  separator?: boolean;
  /** Non-selectable label row (section heading). */
  kind?: 'heading';
  color?: 'red' | 'green' | 'yellow' | 'cyan';
}

export interface SelectOptions {
  message: string;
  subtitle?: string;
  /** Override the help line shown at the bottom of the menu. */
  help?: string;
  /**
   * Clear the terminal before each render (opt-in).
   * Useful for nested flows where previous logs make menus feel cluttered.
   */
  clearScreen?: boolean;
}

const ESCAPE_TIMEOUT_MS = 50;

const ANSI_REGEX = new RegExp("\\x1b\\[[0-9;]*m", "g");
const ANSI_LEADING_REGEX = new RegExp("^\\x1b\\[[0-9;]*m");

function stripAnsi(input: string): string {
  return input.replace(ANSI_REGEX, '');
}

function truncateAnsi(input: string, maxVisibleChars: number): string {
  if (maxVisibleChars <= 0) return '';

  const visible = stripAnsi(input);
  if (visible.length <= maxVisibleChars) return input;

  const suffix = maxVisibleChars >= 3 ? '...' : '.'.repeat(maxVisibleChars);
  const keep = Math.max(0, maxVisibleChars - suffix.length);

  let out = '';
  let i = 0;
  let kept = 0;

  while (i < input.length && kept < keep) {
    // Preserve ANSI sequences without counting them.
    if (input[i] === '\x1b') {
      const m = input.slice(i).match(ANSI_LEADING_REGEX);
      if (m) {
        out += m[0];
        i += m[0].length;
        continue;
      }
    }

    out += input[i];
    i += 1;
    kept += 1;
  }

  if (out.includes('\x1b[')) {
    return `${out}${ANSI.reset}${suffix}`;
  }

  return out + suffix;
}

function getColorCode(color: MenuItem['color']): string {
  switch (color) {
    case 'red': return ANSI.red;
    case 'green': return ANSI.green;
    case 'yellow': return ANSI.yellow;
    case 'cyan': return ANSI.cyan;
    default: return '';
  }
}

export async function select<T>(
  items: MenuItem<T>[],
  options: SelectOptions
): Promise<T | null> {
  if (!isTTY()) {
    throw new Error('Interactive select requires a TTY terminal');
  }

  if (items.length === 0) {
    throw new Error('No menu items provided');
  }

  const isSelectable = (i: MenuItem<T>) => !i.disabled && !i.separator && i.kind !== 'heading';
  const enabledItems = items.filter(isSelectable);
  if (enabledItems.length === 0) {
    throw new Error('All items disabled');
  }

  if (enabledItems.length === 1) {
    return enabledItems[0]!.value;
  }

  const { message, subtitle } = options;
  const { stdin, stdout } = process;

  let cursor = items.findIndex(isSelectable);
  if (cursor === -1) cursor = 0; // Fallback, though validation above should prevent this
  let escapeTimeout: ReturnType<typeof setTimeout> | null = null;
  let isCleanedUp = false;
  let renderedLines = 0;

  const render = () => {
    const columns = stdout.columns ?? 80;
    const rows = stdout.rows ?? 24;
    const shouldClearScreen = options.clearScreen === true;
    const previousRenderedLines = renderedLines;

    if (shouldClearScreen) {
      stdout.write(ANSI.clearScreen + ANSI.moveTo(1, 1));
    } else if (previousRenderedLines > 0) {
      stdout.write(ANSI.up(previousRenderedLines));
    }

    let linesWritten = 0;
    const writeLine = (line: string) => {
      stdout.write(`${ANSI.clearLine}${line}\n`);
      linesWritten += 1;
    };

    // Subtitle renders as 3 lines:
    // 1) blank "│" spacer, 2) subtitle line, 3) blank line. Header is counted separately.
    const subtitleLines = subtitle ? 3 : 0;
    const fixedLines = 1 + subtitleLines + 2; // header + subtitle + (help + bottom)
    // Keep a small safety margin so the final newline doesn't scroll the terminal.
    const maxVisibleItems = Math.max(1, Math.min(items.length, rows - fixedLines - 1));

    // If the menu is taller than the viewport, only render a window around the cursor.
    // This prevents terminal scrollback spam (e.g. repeated headers when pressing arrows).
    let windowStart = 0;
    let windowEnd = items.length;
    if (items.length > maxVisibleItems) {
      windowStart = cursor - Math.floor(maxVisibleItems / 2);
      windowStart = Math.max(0, Math.min(windowStart, items.length - maxVisibleItems));
      windowEnd = windowStart + maxVisibleItems;
    }

    const visibleItems = items.slice(windowStart, windowEnd);
    const headerMessage = truncateAnsi(message, Math.max(1, columns - 4));
    writeLine(`${ANSI.dim}┌  ${ANSI.reset}${headerMessage}`);
    
    if (subtitle) {
      writeLine(`${ANSI.dim}│${ANSI.reset}`);
      const sub = truncateAnsi(subtitle, Math.max(1, columns - 4));
      writeLine(`${ANSI.cyan}◆${ANSI.reset}  ${sub}`);
      writeLine("");
    }

    for (let i = 0; i < visibleItems.length; i++) {
      const itemIndex = windowStart + i;
      const item = visibleItems[i];
      if (!item) continue;

      if (item.separator) {
        writeLine(`${ANSI.dim}│${ANSI.reset}`);
        continue;
      }

      if (item.kind === 'heading') {
        const heading = truncateAnsi(`${ANSI.dim}${ANSI.bold}${item.label}${ANSI.reset}`, Math.max(1, columns - 6));
        writeLine(`${ANSI.cyan}│${ANSI.reset}  ${heading}`);
        continue;
      }

      const isSelected = itemIndex === cursor;
      const colorCode = getColorCode(item.color);

      let labelText: string;
      if (item.disabled) {
        labelText = `${ANSI.dim}${item.label} (unavailable)${ANSI.reset}`;
      } else if (isSelected) {
        labelText = colorCode ? `${colorCode}${item.label}${ANSI.reset}` : item.label;
        if (item.hint) labelText += ` ${ANSI.dim}${item.hint}${ANSI.reset}`;
      } else {
        labelText = colorCode 
          ? `${ANSI.dim}${colorCode}${item.label}${ANSI.reset}` 
          : `${ANSI.dim}${item.label}${ANSI.reset}`;
        if (item.hint) labelText += ` ${ANSI.dim}${item.hint}${ANSI.reset}`;
      }

      // Prevent wrapping: cursor positioning relies on a fixed line count.
      labelText = truncateAnsi(labelText, Math.max(1, columns - 8));

      if (isSelected) {
        writeLine(`${ANSI.cyan}│${ANSI.reset}  ${ANSI.green}●${ANSI.reset} ${labelText}`);
      } else {
        writeLine(`${ANSI.cyan}│${ANSI.reset}  ${ANSI.dim}○${ANSI.reset} ${labelText}`);
      }
    }

    const windowHint = items.length > visibleItems.length
      ? ` (${windowStart + 1}-${windowEnd}/${items.length})`
      : '';
    const helpText = options.help ?? `Up/Down to select | Enter: confirm | Esc: back${windowHint}`;
    const help = truncateAnsi(helpText, Math.max(1, columns - 6));
    writeLine(`${ANSI.cyan}│${ANSI.reset}  ${ANSI.dim}${help}${ANSI.reset}`);
    writeLine(`${ANSI.cyan}└${ANSI.reset}`);

    if (!shouldClearScreen && previousRenderedLines > linesWritten) {
      const extra = previousRenderedLines - linesWritten;
      for (let i = 0; i < extra; i++) {
        writeLine("");
      }
    }

    renderedLines = linesWritten;
  };

  return new Promise((resolve) => {
    const wasRaw = stdin.isRaw ?? false;

    const cleanup = () => {
      if (isCleanedUp) return;
      isCleanedUp = true;

      if (escapeTimeout) {
        clearTimeout(escapeTimeout);
        escapeTimeout = null;
      }

      try {
        stdin.removeListener('data', onKey);
        stdin.setRawMode(wasRaw);
        stdin.pause();
        stdout.write(ANSI.show);
      } catch {
        // Intentionally ignored - cleanup is best-effort
      }

      process.removeListener('SIGINT', onSignal);
      process.removeListener('SIGTERM', onSignal);
    };

    const onSignal = () => {
      cleanup();
      resolve(null);
    };

    const finishWithValue = (value: T | null) => {
      cleanup();
      resolve(value);
    };

    const findNextSelectable = (from: number, direction: 1 | -1): number => {
      if (items.length === 0) return from;
      
      let next = from;
      do {
        next = (next + direction + items.length) % items.length;
      } while (items[next]?.disabled || items[next]?.separator || items[next]?.kind === 'heading');
      return next;
    };

    const onKey = (data: Buffer) => {
      if (escapeTimeout) {
        clearTimeout(escapeTimeout);
        escapeTimeout = null;
      }

      const action = parseKey(data);

      switch (action) {
        case 'up':
          cursor = findNextSelectable(cursor, -1);
          render();
          return;
        case 'down':
          cursor = findNextSelectable(cursor, 1);
          render();
          return;
        case 'enter':
          finishWithValue(items[cursor]?.value ?? null);
          return;
        case 'escape':
          finishWithValue(null);
          return;
        case 'escape-start':
          // Bare escape byte - wait to see if more bytes coming (arrow key sequence)
          escapeTimeout = setTimeout(() => {
            finishWithValue(null);
          }, ESCAPE_TIMEOUT_MS);
          return;
        default:
          // Unknown key - ignore
          return;
      }
    };

    process.once('SIGINT', onSignal);
    process.once('SIGTERM', onSignal);

    try {
      stdin.setRawMode(true);
    } catch {
      // Failed to enable raw mode - cleanup and return null
      cleanup();
      resolve(null);
      return;
    }

    stdin.resume();
    stdout.write(ANSI.hide);
    render();

    stdin.on('data', onKey);
  });
}