/**
 * Session Management Service
 * Handles creation, storage, and retrieval of chat sessions
 */

const STORAGE_KEY = 'light-chat-sessions'
const CONFIG_KEY = 'light-chat-config'

/**
 * Generate unique session ID
 * @returns {string}
 */
function generateId() {
  return Date.now().toString(36) + Math.random().toString(36).substr(2)
}

/**
 * Default session structure
 */
function createSession(endpoint = '', systemPrompt = '') {
  return {
    id: generateId(),
    name: `Session ${new Date().toLocaleTimeString()}`,
    endpoint,
    systemPrompt,
    messages: [],
    createdAt: Date.now(),
    updatedAt: Date.now()
  }
}

/**
 * Load all sessions from storage
 * @returns {Array}
 */
export function loadSessions() {
  try {
    const data = localStorage.getItem(STORAGE_KEY)
    return data ? JSON.parse(data) : []
  } catch (error) {
    console.error('Failed to load sessions:', error)
    return []
  }
}

/**
 * Save sessions to storage
 * @param {Array} sessions
 */
export function saveSessions(sessions) {
  try {
    localStorage.setItem(STORAGE_KEY, JSON.stringify(sessions))
  } catch (error) {
    console.error('Failed to save sessions:', error)
  }
}

/**
 * Load API configuration
 * @returns {Object} { endpoint, systemPrompt }
 */
export function loadConfig() {
  try {
    const data = localStorage.getItem(CONFIG_KEY)
    return data ? JSON.parse(data) : { endpoint: '', systemPrompt: '' }
  } catch (error) {
    console.error('Failed to load config:', error)
    return { endpoint: '', systemPrompt: '' }
  }
}

/**
 * Save API configuration
 * @param {Object} config
 */
export function saveConfig(config) {
  try {
    localStorage.setItem(CONFIG_KEY, JSON.stringify(config))
  } catch (error) {
    console.error('Failed to save config:', error)
  }
}

/**
 * Add a new session
 * @param {Object} options
 * @returns {Object} new session
 */
export function addSession(options = {}) {
  const sessions = loadSessions()
  const newSession = createSession(
    options.endpoint,
    options.systemPrompt
  )
  sessions.push(newSession)
  saveSessions(sessions)
  return newSession
}

/**
 * Delete a session
 * @param {string} sessionId
 * @returns {boolean}
 */
export function deleteSession(sessionId) {
  const sessions = loadSessions()
  const filtered = sessions.filter(s => s.id !== sessionId)
  if (filtered.length === sessions.length) {
    return false
  }
  saveSessions(filtered)
  return true
}

/**
 * Update a session
 * @param {string} sessionId
 * @param {Object} updates
 * @returns {Object|null} updated session or null
 */
export function updateSession(sessionId, updates) {
  const sessions = loadSessions()
  const index = sessions.findIndex(s => s.id === sessionId)

  if (index === -1) {
    return null
  }

  sessions[index] = {
    ...sessions[index],
    ...updates,
    updatedAt: Date.now()
  }

  // Update name if messages exist and name is default
  if (sessions[index].messages.length > 0 && sessions[index].name.startsWith('Session')) {
    sessions[index].name = `Chat ${new Date(sessions[index].createdAt).toLocaleDateString()}`
  }

  saveSessions(sessions)
  return sessions[index]
}

/**
 * Get a specific session
 * @param {string} sessionId
 * @returns {Object|null}
 */
export function getSession(sessionId) {
  const sessions = loadSessions()
  return sessions.find(s => s.id === sessionId) || null
}

/**
 * Add message to a session
 * @param {string} sessionId
 * @param {Object} message - { role: 'user'|'assistant', content: string }
 * @returns {Object|null} updated session
 */
export function addMessage(sessionId, message) {
  const session = getSession(sessionId)

  if (!session) {
    return null
  }

  session.messages.push(message)
  return updateSession(sessionId, { messages: session.messages })
}