export const CURRENT_DESKTOP_PERSISTENCE_SCHEMA_VERSION = 1
export const DESKTOP_PERSISTENCE_VERSION_KEY = 'cc-haha.persistence.schemaVersion'

type DesktopMigrationReport = {
  migratedKeys: string[]
}

type StorageLike = Pick<Storage, 'getItem' | 'setItem' | 'removeItem'>

const TAB_STORAGE_KEY = 'cc-haha-open-tabs'
const SESSION_RUNTIME_STORAGE_KEY = 'cc-haha-session-runtime'
const THEME_STORAGE_KEY = 'cc-haha-theme'
const LOCALE_STORAGE_KEY = 'cc-haha-locale'

function readJson(storage: StorageLike, key: string): unknown {
  const raw = storage.getItem(key)
  if (!raw) return null
  return JSON.parse(raw)
}

function isRecord(value: unknown): value is Record<string, unknown> {
  return !!value && typeof value === 'object' && !Array.isArray(value)
}

function writeJson(storage: StorageLike, key: string, value: unknown): void {
  storage.setItem(key, JSON.stringify(value))
}

function migrateTabs(storage: StorageLike, report: DesktopMigrationReport): void {
  const raw = storage.getItem(TAB_STORAGE_KEY)
  if (!raw) return

  try {
    const parsed = readJson(storage, TAB_STORAGE_KEY)
    const rawTabs = Array.isArray(parsed)
      ? parsed
      : isRecord(parsed) && Array.isArray(parsed.openTabs)
        ? parsed.openTabs
        : []
    const openTabs = rawTabs
      .filter((tab): tab is Record<string, unknown> => isRecord(tab))
      .filter((tab) => typeof tab.sessionId === 'string' && typeof tab.title === 'string')
      .filter((tab) => tab.type !== 'terminal' && !String(tab.sessionId).startsWith('__terminal__'))
      .map((tab) => ({
        sessionId: tab.sessionId as string,
        title: tab.title as string,
        type: tab.type === 'settings' || tab.type === 'scheduled' ? tab.type : 'session',
      }))
    const activeTabId =
      isRecord(parsed) &&
      typeof parsed.activeTabId === 'string' &&
      openTabs.some((tab) => tab.sessionId === parsed.activeTabId)
        ? parsed.activeTabId
        : (openTabs[0]?.sessionId ?? null)

    if (openTabs.length === 0) {
      storage.removeItem(TAB_STORAGE_KEY)
    } else {
      writeJson(storage, TAB_STORAGE_KEY, { openTabs, activeTabId })
    }
  } catch {
    storage.removeItem(TAB_STORAGE_KEY)
  }
  report.migratedKeys.push(TAB_STORAGE_KEY)
}

function migrateSessionRuntime(storage: StorageLike, report: DesktopMigrationReport): void {
  const raw = storage.getItem(SESSION_RUNTIME_STORAGE_KEY)
  if (!raw) return

  try {
    const parsed = readJson(storage, SESSION_RUNTIME_STORAGE_KEY)
    if (!isRecord(parsed)) {
      storage.removeItem(SESSION_RUNTIME_STORAGE_KEY)
      report.migratedKeys.push(SESSION_RUNTIME_STORAGE_KEY)
      return
    }

    const next = Object.fromEntries(
      Object.entries(parsed).filter(([, selection]) => (
        isRecord(selection) &&
        typeof selection.modelId === 'string' &&
        (selection.providerId === null || typeof selection.providerId === 'string')
      )),
    )

    if (Object.keys(next).length === 0) {
      storage.removeItem(SESSION_RUNTIME_STORAGE_KEY)
    } else {
      writeJson(storage, SESSION_RUNTIME_STORAGE_KEY, next)
    }

    if (JSON.stringify(next) !== JSON.stringify(parsed)) {
      report.migratedKeys.push(SESSION_RUNTIME_STORAGE_KEY)
    }
  } catch {
    storage.removeItem(SESSION_RUNTIME_STORAGE_KEY)
    report.migratedKeys.push(SESSION_RUNTIME_STORAGE_KEY)
  }
}

function normalizeEnumKey(
  storage: StorageLike,
  key: string,
  allowedValues: string[],
  report: DesktopMigrationReport,
): void {
  const value = storage.getItem(key)
  if (value !== null && !allowedValues.includes(value)) {
    storage.removeItem(key)
    report.migratedKeys.push(key)
  }
}

function runMigrationStep(
  report: DesktopMigrationReport,
  fallbackKey: string,
  step: () => void,
): void {
  try {
    step()
  } catch {
    report.migratedKeys.push(fallbackKey)
  }
}

function getDefaultStorage(): StorageLike | null {
  try {
    return globalThis.localStorage ?? null
  } catch {
    return null
  }
}

export function runDesktopPersistenceMigrations(storage: StorageLike | null = getDefaultStorage()): DesktopMigrationReport {
  const report: DesktopMigrationReport = { migratedKeys: [] }
  if (!storage) return report

  runMigrationStep(report, TAB_STORAGE_KEY, () => migrateTabs(storage, report))
  runMigrationStep(report, SESSION_RUNTIME_STORAGE_KEY, () => migrateSessionRuntime(storage, report))
  runMigrationStep(report, THEME_STORAGE_KEY, () => normalizeEnumKey(storage, THEME_STORAGE_KEY, ['light', 'dark'], report))
  runMigrationStep(report, LOCALE_STORAGE_KEY, () => normalizeEnumKey(storage, LOCALE_STORAGE_KEY, ['zh', 'en'], report))
  try {
    storage.setItem(DESKTOP_PERSISTENCE_VERSION_KEY, String(CURRENT_DESKTOP_PERSISTENCE_SCHEMA_VERSION))
  } catch {
    report.migratedKeys.push(DESKTOP_PERSISTENCE_VERSION_KEY)
  }

  return report
}