import { GameState } from '../types/domain'
import { normalizeGameState } from '../engine/world'

export const CURRENT_SCHEMA = 2
export const APP_ID = 'cotyc'

export interface MigrationError {
  code: 'TOO_NEW' | 'UNKNOWN_VERSION'
  version: number
  message: string
}

/**
 * 迁移链：obj.from 升到 obj.to 逐级执行（任何一步失败即中断抛出，原状态不被写入）。
 * v1（≤0.1.8）→ v2（0.1.9）：补 stats/finance/annals 字段并打上 schema 版本戳。
 */
const MIGRATIONS: Array<{ from: number; to: number; fn: (s: GameState) => GameState }> = [
  {
    from: 1,
    to: 2,
    fn: (s) => {
      normalizeGameState(s)
      s.schemaVersion = 2
      return s
    }
  }
]

export function migrateIfNeeded(state: GameState): { ok: true; state: GameState } | { ok: false; error: MigrationError } {
  const version = typeof state.schemaVersion === 'number' ? state.schemaVersion : 1
  if (version > CURRENT_SCHEMA) {
    return {
      ok: false,
      error: { code: 'TOO_NEW', version, message: `存档版本 ${version} 高于当前游戏支持（${CURRENT_SCHEMA}），请升级游戏。` }
    }
  }
  let cur = state
  let v = version
  let guard = 0
  while (v < CURRENT_SCHEMA && guard < 20) {
    const step = MIGRATIONS.find((m) => m.from === v)
    if (!step) {
      return { ok: false, error: { code: 'UNKNOWN_VERSION', version: v, message: `未知存档版本 ${v}，无法迁移。` } }
    }
    try {
      cur = step.fn(cur)
    } catch (e) {
      return { ok: false, error: { code: 'UNKNOWN_VERSION', version: v, message: `迁移失败：${String(e)}` } }
    }
    v = step.to
    guard++
  }
  return { ok: true, state: cur }
}

export function exportEnvelope(state: GameState): string {
  return JSON.stringify({ app: APP_ID, schemaVersion: state.schemaVersion ?? CURRENT_SCHEMA, payload: state })
}

export function parseImportEnvelope(text: string): { ok: true; state: GameState } | { ok: false; error: string } {
  try {
    const raw = JSON.parse(text) as { app?: string; schemaVersion?: number; payload?: GameState; state?: GameState }
    if (raw.app !== undefined && raw.app !== APP_ID) return { ok: false, error: '非本作存档（app 标识不符）。' }
    const state = raw.payload ?? raw.state
    if (!state || typeof state !== 'object') return { ok: false, error: '存档内容为空或损坏。' }
    const migrated = migrateIfNeeded(state as GameState)
    if (migrated.ok) return { ok: true, state: migrated.state }
    return { ok: false, error: migrated.error.message }
  } catch (e) {
    return { ok: false, error: `解析失败：${String(e)}` }
  }
}