/**
 * Session history management
 * @module nopy.history
 */

import fs from 'node:fs';
import path from 'node:path';
import { describeSession, type NopySession } from './nopy.session.js';

/** Default number of sessions to keep in history */
export const DEFAULT_HISTORY_SIZE = 10;

/** History file name */
export const HISTORY_FILE = '.nopy.history.json';

/**
 * A session entry in history
 */
export interface HistoryEntry {
  /** Unique identifier (timestamp-based) */
  id: string;
  /** Human-readable name (timestamp + cube names) */
  name: string;
  /** ISO timestamp when session was executed */
  timestamp: string;
  /** The full session data */
  session: NopySession;
}

/**
 * History file structure
 */
export interface SessionHistory {
  /** Array of session entries, newest first */
  entries: HistoryEntry[];
}

/**
 * Gets the path to the history file
 */
export function getHistoryPath(): string {
  return path.resolve(process.cwd(), HISTORY_FILE);
}

/**
 * Loads the session history from disk
 *
 * @returns The session history or empty history if file doesn't exist
 */
export function loadHistory(): SessionHistory {
  const historyPath = getHistoryPath();

  if (!fs.existsSync(historyPath)) {
    return { entries: [] };
  }

  try {
    const content = fs.readFileSync(historyPath, 'utf-8');
    return JSON.parse(content) as SessionHistory;
  } catch {
    return { entries: [] };
  }
}

/**
 * Saves the session history to disk
 *
 * @param history - The history to save
 */
export function saveHistory(history: SessionHistory): void {
  const historyPath = getHistoryPath();
  fs.writeFileSync(historyPath, JSON.stringify(history, null, 2), 'utf-8');
}

/**
 * Generates a unique ID for a history entry
 */
function generateEntryId(): string {
  return Date.now().toString(36) + Math.random().toString(36).substring(2, 7);
}

/**
 * Adds a session to the history
 *
 * @param session - The session to add
 * @param maxEntries - Maximum number of entries to keep
 * @returns The created history entry
 */
export function addToHistory(
  session: NopySession,
  maxEntries: number = DEFAULT_HISTORY_SIZE
): HistoryEntry {
  const history = loadHistory();
  const timestamp = new Date().toISOString();

  const entry: HistoryEntry = {
    id: generateEntryId(),
    name: describeSession(session, timestamp),
    timestamp,
    session,
  };

  // Add to beginning (newest first)
  history.entries.unshift(entry);

  // Trim to max size
  if (history.entries.length > maxEntries) {
    history.entries = history.entries.slice(0, maxEntries);
  }

  saveHistory(history);
  return entry;
}

/**
 * Gets the most recent session from history
 *
 * @returns The last session or undefined if history is empty
 */
export function getLastSession(): HistoryEntry | undefined {
  const history = loadHistory();
  return history.entries[0];
}

/**
 * Gets a session by ID
 *
 * @param id - The session ID
 * @returns The session entry or undefined
 */
export function getSessionById(id: string): HistoryEntry | undefined {
  const history = loadHistory();
  return history.entries.find((e) => e.id === id);
}

/**
 * Lists all sessions in history
 *
 * @returns Array of history entries, newest first
 */
export function listHistory(): HistoryEntry[] {
  const history = loadHistory();
  return history.entries;
}

/**
 * Clears all session history
 */
export function clearHistory(): void {
  saveHistory({ entries: [] });
}

/**
 * Removes a specific session from history
 *
 * @param id - The session ID to remove
 * @returns true if removed, false if not found
 */
export function removeFromHistory(id: string): boolean {
  const history = loadHistory();
  const initialLength = history.entries.length;
  history.entries = history.entries.filter((e) => e.id !== id);

  if (history.entries.length < initialLength) {
    saveHistory(history);
    return true;
  }
  return false;
}

/**
 * Formats history entries for display
 *
 * @param entries - History entries to format
 * @returns Formatted string for console output
 */
export function formatHistoryList(entries: HistoryEntry[]): string {
  if (entries.length === 0) {
    return 'No sessions in history.';
  }

  const lines = ['', 'Session History:', ''];

  entries.forEach((entry, index) => {
    const marker = index === 0 ? '→' : ' ';
    lines.push(`  ${marker} [${index + 1}] ${entry.name}`);
    lines.push(`       ID: ${entry.id}`);
  });

  lines.push('');
  lines.push(`Total: ${entries.length} session(s)`);
  lines.push('');

  return lines.join('\n');
}