/**
 * history 的可逆增量记录：保存两栈 ID 顺序，以及历史项发生变化的数组区间。
 * 与 history.ts 的区别：这里恢复“历史元数据”，不执行文档修改或发送请求。
 * journal/恢复与资源 pin 扫描使用这些记录，既能回放，也保留被清 redo/淘汰的旧内容。
 */
import type { Change, HistoryEntry, HistoryState, Id } from './types.ts';
import { equal, fault, freeze, readMap, validJson } from './values.ts';

/** 数组区间补丁：共同前缀后的 offset、两边总长度与替换前后区间；共同后缀不重复保存。 */
type Splice<T>={readonly offset:number;readonly beforeLength:number;readonly afterLength:number;readonly before:readonly T[];readonly after:readonly T[]};
/** 历史项的展示/分组元数据；变化数组和 operation IDs 分开描述。 */
type Meta={readonly label:string;readonly groupId?:Id};
/** 同一 entry 的元数据与两个数组补丁；null 表示该侧不存在这个历史项。 */
type EntryPatch={readonly id:Id;readonly before:Meta|null;readonly after:Meta|null;readonly changes:Splice<Change>;readonly operationIds:Splice<Id>};
/** version 控制解释器兼容性，rootRevision 关联发布版本；不等同于服务端版本号。 */
export type HistoryTransition={readonly version:1;readonly rootRevision:number;readonly entryId?:Id;readonly before:{readonly undo:readonly Id[];readonly redo:readonly Id[]};readonly after:{readonly undo:readonly Id[];readonly redo:readonly Id[]};readonly entries:readonly EntryPatch[]};
// Resource scans revisit the same transition across many durability cuts. Cache
// only its flattened changes, never registry-dependent references or callbacks.
const transitionChanges=new WeakMap<HistoryTransition,readonly Change[]>();
const immutableData=new WeakSet<object>();
/** 检查缓存候选的冻结数据描述符与普通原型，最多递归 64 层；不是单独的 JSON/schema 校验器。
 * 冻结的 getter 仍可能返回不同值，稀疏数组也不是完整区间，因此都不允许缓存。 */
function immutablePlainData(value:unknown,depth=0):boolean{
  if(depth>64)return false;
  if(value===null||typeof value!=='object')return typeof value!=='function';
  // 只记住已遍历成功的对象身份；祖先链若太深仍会先被 depth 条件拒绝。
  if(immutableData.has(value))return true;
  if(!Object.isFrozen(value)||Object.getPrototypeOf(value)!==(Array.isArray(value)?Array.prototype:Object.prototype))return false;
  if(Array.isArray(value))for(let i=0;i<value.length;i++)if(!Object.hasOwn(value,i))return false;
  // Inspect every own descriptor, including non-enumerable properties. A frozen
  // getter or a shallow-frozen container cannot establish reusable data.
  for(const key of Reflect.ownKeys(value)){
    const descriptor=Object.getOwnPropertyDescriptor(value,key)!;
    if(!Object.hasOwn(descriptor,'value')||!immutablePlainData(descriptor.value,depth+1))return false;
  }
  immutableData.add(value);return true;
}
/** 提取除 id/changes/operationIds 外的元数据，缺项用 null 表示，以便正反向校验。 */
const meta=(entry:HistoryEntry|undefined):Meta|null=>{if(!entry)return null;const{id:_id,changes:_changes,operationIds:_operations,...remaining}=entry;return remaining;};
/** 去掉相等的共同前缀、后缀，只保存真正变化的中间区间；后缀不能与前缀重叠。 */
function splice<T>(before:readonly T[],after:readonly T[]):Splice<T>{
  let offset=0,suffix=0;while(offset<before.length&&offset<after.length&&equal(before[offset],after[offset]))offset++;
  while(suffix<before.length-offset&&suffix<after.length-offset&&equal(before[before.length-suffix-1],after[after.length-suffix-1]))suffix++;
  return{offset,beforeLength:before.length,afterLength:after.length,before:before.slice(offset,before.length-suffix),after:after.slice(offset,after.length-suffix)};
}
/** Store changed ranges only. Clearing redo/eviction still retains the removed entry records needed to reverse that transition. */
/** 对比两份 history，记录新增、删除和修改的 entry 及两栈顺序。
 * 默认无变化不造记录；recordNoop 用于调用方显式需要记录发布边界的情形。
 * 来源应是不可变 history：两栈和区间内的 Change 沿用引用，最终 freeze 不等于任意外部输入的深复制。 */
export function describeHistoryTransition(before:HistoryState,after:HistoryState,rootRevision:number,entryId?:Id,recordNoop=false):HistoryTransition|undefined{
  const entries:EntryPatch[]=[];
  for(const id of new Set([...before.entries.keys(),...after.entries.keys()])){const a=before.entries.get(id),b=after.entries.get(id);if(equal(a,b))continue;entries.push({id,before:meta(a),after:meta(b),changes:splice(a?.changes??[],b?.changes??[]),operationIds:splice(a?.operationIds??[],b?.operationIds??[])});}
  if(!recordNoop&&!entries.length&&equal(before.undo,after.undo)&&equal(before.redo,after.redo))return undefined;
  return freeze({version:1,rootRevision,...(entryId?{entryId}:{}),before:{undo:before.undo,redo:before.redo},after:{undo:after.undo,redo:after.redo},entries});
}
/** 验证外部/恢复的增量 DTO，未知 version 明确要求其它解释器。
 * checkChanges 可由调用方注入更严格的 Change 校验；未传时只检查 DTO/区间形状，不解释每条 Change 的领域语义。
 * rootRevision 只在此检查非负整数，不在此证明 transition 属于哪次实际发布。 */
export function validateHistoryTransition(value:unknown,checkChanges?:(value:unknown)=>unknown):asserts value is HistoryTransition{
  // 四个局部校验器统一抛领域错误，分别约束非数组记录形状、非负整数、非空 ID 和 ID 数组。
  const object=(v:unknown):Record<string,unknown>=>{if(!v||typeof v!=='object'||Array.isArray(v))throw fault('invalid_history_transition');return v as Record<string,unknown>;};
  const integer=(v:unknown)=>{if(typeof v!=='number'||!Number.isSafeInteger(v)||v<0)throw fault('invalid_history_transition');};
  const id=(v:unknown)=>{if(typeof v!=='string'||!v)throw fault('invalid_history_transition');};
  const ids=(v:unknown):string[]=>{if(!Array.isArray(v))throw fault('invalid_history_transition');v.forEach(id);return v;};
  const raw=object(value);if(raw.version!==1)throw fault('history_transition_interpreter_unavailable');if(!validJson(value))throw fault('invalid_history_transition');integer(raw.rootRevision);if(raw.entryId!==undefined)id(raw.entryId);
  // 同一侧 undo/redo 中不允许重复 ID，避免同一项同时处于两个栈或重复出现。
  for(const side of [raw.before,raw.after]){const s=object(side),list=[...ids(s.undo),...ids(s.redo)];if(new Set(list).size!==list.length)throw fault('invalid_history_transition');}
  if(!Array.isArray(raw.entries))throw fault('invalid_history_transition');const seen=new Set<string>();
  for(const item of raw.entries){const p=object(item);id(p.id);if(seen.has(p.id as string))throw fault('invalid_history_transition');seen.add(p.id as string);
    for(const side of [p.before,p.after])if(side!==null){const m=object(side);if(typeof m.label!=='string'||['id','changes','operationIds'].some(key=>Object.hasOwn(m,key)))throw fault('invalid_history_transition');if(m.groupId!==undefined)id(m.groupId);}
    // 两边保留的前后缀长度必须一致；不存在的历史项不允许带非零原数组长度。
    for(const key of ['changes','operationIds']){const patch=object(p[key]);for(const field of ['offset','beforeLength','afterLength'])integer(patch[field]);if(!Array.isArray(patch.before)||!Array.isArray(patch.after))throw fault('invalid_history_transition');const{offset,beforeLength,afterLength}=patch as unknown as Splice<unknown>;if(offset+patch.before.length>beforeLength||offset+patch.after.length>afterLength||beforeLength-patch.before.length!==afterLength-patch.after.length)throw fault('invalid_history_transition');if(key==='operationIds'){ids(patch.before);ids(patch.after);}else{checkChanges?.(patch.before);checkChanges?.(patch.after);}
      if(p.before===null&&beforeLength!==0||p.after===null&&afterLength!==0)throw fault('invalid_history_transition');
    }
  }
}
/** Conditional metadata-only replay. A mismatch leaves the supplied history untouched. */
/** 先检查两栈，再逐 entry 检查元数据/数组区间并在私有副本上正向或反向回放。
 * 不改写输入两栈/entries 表；不能拿旧 journal 覆盖新的历史顺序。
 * history/transition 应已捕获：补丁内 Change 会沿用并冻结，不应把此接口当任意外部值的深隔离入口。 */
export function applyHistoryTransition(history:HistoryState,transition:HistoryTransition,direction:'forward'|'reverse'):HistoryState{
  validateHistoryTransition(transition);const reverse=direction==='reverse',source=reverse?transition.after:transition.before,destination=reverse?transition.before:transition.after;
  if(!equal({undo:history.undo,redo:history.redo},source))throw fault('history_transition_conflict');
  /** 按方向交换 expected/insert；同时比较总长度和旧区间，防止错位拼接。 */
  function apply<T>(current:readonly T[],patch:Splice<T>):readonly T[]{const expected=reverse?patch.after:patch.before,insert=reverse?patch.before:patch.after,length=reverse?patch.afterLength:patch.beforeLength;if(current.length!==length||!equal(current.slice(patch.offset,patch.offset+expected.length),expected))throw fault('history_transition_conflict');return[...current.slice(0,patch.offset),...insert,...current.slice(patch.offset+expected.length)];}
  // 各 entry 使用独立数组补丁，新增/删除也校验旧元数据，不直接拿整份快照覆盖。
  const entries=new Map(history.entries);
  for(const patch of transition.entries){const entry=entries.get(patch.id),expected=reverse?patch.after:patch.before,next=reverse?patch.before:patch.after;if(!equal(meta(entry),expected))throw fault('history_transition_conflict');const changes=apply(entry?.changes??[],patch.changes),operationIds=apply(entry?.operationIds??[],patch.operationIds);if(next)entries.set(patch.id,freeze({id:patch.id,...next,changes,operationIds}));else entries.delete(patch.id);}
  // 最终两栈必须精确覆盖 entries 表，不能留下孤立项或指向缺失 entry 的栈 ID。
  const ids=[...destination.undo,...destination.redo];if(ids.length!==entries.size||ids.some(id=>!entries.has(id)))throw fault('history_transition_conflict');
  return Object.freeze({undo:freeze([...destination.undo]),redo:freeze([...destination.redo]),entries:readMap(entries)});
}
/** 汇总增量两侧出现的 Change，供资源保留扫描使用；不执行这些修改。
 * 只有自有区间且整条 transition 深不可变时才缓存，否则每次重新计算。 */
export function historyTransitionChanges(transition:HistoryTransition):readonly Change[]{
  const cached=transitionChanges.get(transition);if(cached)return cached;
  validateHistoryTransition(transition);
  // 仅收集被记录的变化区间两侧，未重复保存的共同前后缀不在本结果中；它不是完整 history 的展开。
  const changes=transition.entries.flatMap(patch=>[...patch.changes.before,...patch.changes.after]);
  // 属性来自原型或 getter 时不可把一次结果当永久事实，避免错误释放资源 pin。
  const ownRanges=Object.hasOwn(transition,'entries')&&transition.entries.every(patch=>Object.hasOwn(patch,'changes')&&Object.hasOwn(patch.changes,'before')&&Object.hasOwn(patch.changes,'after'));
  if(!ownRanges||!immutablePlainData(transition))return changes;
  const result=Object.freeze(changes);transitionChanges.set(transition,result);return result;
}