/**
 * 每个 editor 的临时交互会话：多个 view 各自保存选择/视口/工具/mode，共用一份已提交文档。
 * 同时至多存在一个节点或连线手势；baseline/preview 均是短生命周期状态，不写 history/ledger。
 * pointerup 时才通过 editor 提交净修改；取消仅清预览，不回写旧整节点，因此不会撤掉晚到资源 ACK。
 */
import type { Editor } from './editor.ts';
import type { Availability, Capability, ElementRecord, Geometry, Id, Json, Result, Target } from './types.ts';
import { geometryValid, targetElement } from './document.ts';
import {createGesturePlacementReader} from './gesture-placement.ts';
import { clone, equal, fault, freeze, readMap, readSet, reject, validJson } from './values.ts';

/** 单视图状态：selection/modes 指向元素 ID，viewport 是画布 pan/zoom，均不属于持久模型。 */
export type ViewState = { readonly id: Id; readonly canvasId: Id; readonly selection: ReturnType<typeof readSet<Id>>; readonly viewport: { readonly x: number; readonly y: number; readonly zoom: number }; readonly tool: 'select' | 'pan'; readonly modes: ReadonlyMap<Id, string> };
/** 节点手势：token 区分先后两次手势，targets 带 incarnation，preview 只存几何。 */
export type GestureState = { readonly token: number; readonly viewId: Id; readonly targets: readonly Target[]; readonly preview: ReadonlyMap<Id, Geometry>; readonly phase: 'active' | 'committing' };
/** 连线路径预览与 committed path 分开；committing 阶段避免自己的提交被观察者当外部变化取消。 */
export type ConnectionGesture = { readonly token: number; readonly viewId: Id; readonly target: Target; readonly path: Json; readonly phase: 'active' | 'committing' };
/** 只读会话快照；lastCancelReason 解释取消原因，不代表持久任务失败或撤销。 */
export type SessionSnapshot = { readonly views: ReadonlyMap<Id, ViewState>; readonly gesture: GestureState | null; readonly connectionGesture: ConnectionGesture | null; readonly lastCancelReason: string | null };

/** Transient interaction state belongs to views; no pointer event enters the ledger. */
/** 创建会话管理器并订阅 editor，随发布清理失效选中项/mode、取消失效手势；dispose 时解除订阅。 */
export function createSessions(editor: Editor) {
  let snapshot: SessionSnapshot = Object.freeze({ views: readMap(new Map<Id, ViewState>()), gesture: null, connectionGesture: null, lastCancelReason: null });
  // 开始手势时捕获原记录，用它计算净几何差；提交时仍以 editor 当前数据为准，不恢复整条记录。
  let baseline = new Map<Id, ElementRecord>(), connectionBaseline: ElementRecord | undefined, disposed = false, nextGestureToken = 0;
  // Compare adjacent published identities without duplicating the per-view mode table.
  let publishedDocument=editor.getSnapshot().document;
  const listeners = new Set<() => void>();
  /** 对监听列表做副本迭代并隔离异常，renderer 出错不能影响已提交模型。 */
  const notify = () => { for (const listener of [...listeners]) try { listener(); } catch { /* A renderer cannot invalidate model commits. */ } };
  /** 一次发布 views；若被中断的是手势拥有者，同时清 baseline 和预览，只通知一次。 */
  function publishViews(views:Map<Id,ViewState>,cancelOwnedView?:Id,reason='view_interrupted'){
    const owned=cancelOwnedView!==undefined&&(snapshot.gesture?.viewId===cancelOwnedView||snapshot.connectionGesture?.viewId===cancelOwnedView);
    if(owned){baseline.clear();connectionBaseline=undefined;}
    snapshot=Object.freeze({...snapshot,views:readMap(views),...(owned?{gesture:null,connectionGesture:null,lastCancelReason:reason}:{})});notify();
  }
  /** 复制视图表并替换一项，可在同一发布中带上切工具/切 canvas 等取消原因。 */
  function setView(view: ViewState,cancelOwnedReason?:string) { const views = new Map(snapshot.views); views.set(view.id, view); publishViews(views,cancelOwnedReason?view.id:undefined,cancelOwnedReason); }
  /** 幂等取消当前手势，保留 committed 文档及资源状态；重复 cancel 不重复通知。 */
  function cancel(reason = 'canceled') {
    if (!snapshot.gesture && !snapshot.connectionGesture) return;
    baseline.clear(); connectionBaseline = undefined; snapshot = Object.freeze({ ...snapshot, gesture: null, connectionGesture: null, lastCancelReason: reason }); notify();
  }
  // 文档/运行时发布后重新检查临时状态：模式与代次、owner、组件版本绑定，不能跟随同 ID 复活。
  const detachEditor = editor.subscribe(() => {
    const document = editor.getSnapshot().document,beforeDocument=publishedDocument;publishedDocument=document;
    const views = new Map(snapshot.views); let changed = false;
    for (const [id, view] of views) {
      // 当前 canvas 被删除时回到根；失效 selection 清理，模式还需检查相邻发布的元素身份。
      const canvasMissing = !document.canvases.has(view.canvasId);
      const selection = [...view.selection].filter(target => document.elements.has(target)), modes = new Map([...view.modes].filter(([target]) => {
        const before=beforeDocument.elements.get(target),after=document.elements.get(target);
        return !!before&&!!after&&before.incarnation===after.incarnation&&before.ownerCanvasId===after.ownerCanvasId&&before.structure===after.structure&&before.componentId===after.componentId&&before.dataVersion===after.dataVersion;
      }));
      if (canvasMissing || selection.length !== view.selection.size || modes.size !== view.modes.size) { views.set(id, freeze({ ...view, canvasId: canvasMissing ? [...document.canvases.values()].find(canvas => !canvas.parent)!.id : view.canvasId, selection: readSet(canvasMissing ? [] : selection), modes: readMap(canvasMissing ? new Map() : modes) })); changed = true; }
    }
    let cancelReason:string|undefined;
    // 只审查 active；committing 的自身发布由提交者负责清理，避免误判为外部干扰。
    const active=snapshot.gesture?.phase==='active'?snapshot.gesture:snapshot.connectionGesture?.phase==='active'?snapshot.connectionGesture:undefined;
    const activeView=active?snapshot.views.get(active.viewId):undefined;
    if(activeView&&!document.canvases.has(activeView.canvasId))cancelReason='canvas_changed';
    // 对比 view 内祖先入口链；只有目标 geometry 相同仍不够，父级旋转/缩放也会改变坐标上下文。
    const oldPlacement=activeView?createGesturePlacementReader(beforeDocument,activeView.canvasId,editor.registry):undefined,newPlacement=activeView?createGesturePlacementReader(document,activeView.canvasId,editor.registry):undefined;
    /** 同文档无需重算；旧/新链不再可读或值变化都按坐标上下文失效处理。 */
    const placementChanged=(owner:Id)=>{if(beforeDocument===document)return false;try{return !oldPlacement||!newPlacement||!equal(oldPlacement(owner),newPlacement(owner));}catch{return true;}};
    // 连线预览只依赖 path、身份、owner 和准入；普通内容或资源 ACK 不应自动取消它。
    if (!cancelReason&&snapshot.connectionGesture?.phase === 'active') {
      const current = document.elements.get(snapshot.connectionGesture.target.id), before = connectionBaseline;
      if (!current || current.structure !== 'connection' || before?.structure !== 'connection' || current.incarnation !== before.incarnation || current.ownerCanvasId !== before.ownerCanvasId || current.componentId!==before.componentId || current.dataVersion!==before.dataVersion || !equal(current.path, before.path)) cancelReason='target_changed';
      else if(placementChanged(current.ownerCanvasId))cancelReason='coordinate_context_changed';
      else if (!editor.can({ type: 'connection.path', target: snapshot.connectionGesture.target, path: current.path }).enabled) cancelReason='permission_changed';
    }
    // 节点几何预览同理：几何/身份变化优先取消；然后核对祖先上下文和当前命令权限。
    if (snapshot.gesture?.phase === 'active'&&!cancelReason) for (const target of snapshot.gesture.targets) {
      const before = baseline.get(target.id), current = document.elements.get(target.id);
      if (!current || current.structure !== 'node' || before?.structure !== 'node' || current.incarnation !== before.incarnation || current.ownerCanvasId !== before.ownerCanvasId || current.componentId!==before.componentId || current.dataVersion!==before.dataVersion || !equal(current.geometry, before.geometry)) { cancelReason='target_changed'; break; }
      if(placementChanged(current.ownerCanvasId)){cancelReason='coordinate_context_changed';break;}
      if (!editor.can({ type: 'element.geometry', target, patch: {} }).enabled) { cancelReason='permission_changed'; break; }
    }
    if(changed||cancelReason){
      if(cancelReason){baseline.clear();connectionBaseline=undefined;}
      snapshot=Object.freeze({...snapshot,...(changed?{views:readMap(views)}:{}),...(cancelReason?{gesture:null,connectionGesture:null,lastCancelReason:cancelReason}:{})});notify();
    }
  });
  /** 读取已挂载且管理器仍开放的 view，不让旧组件回调操作已销毁的会话。 */
  function view(id: Id) { const found = snapshot.views.get(id); if (!found || disposed) throw fault('view_detached', [id]); return found; }
  /** 更新节点预览：校验手势所有权，将 patch 交给 capability handler，最后仅发布 session。 */
  function update(viewId: Id, target: Target, patch: Partial<Geometry>): Availability {
    try {
      view(viewId);
      if (snapshot.gesture?.viewId !== viewId || !snapshot.gesture.targets.some(value => value.id === target.id && value.incarnation === target.incarnation)) throw fault('gesture_not_owned', [target.id]);
      const original = targetElement(editor.getSnapshot().document, target);
      if (original.structure !== 'node') throw fault('unsupported_capability', [target.id]);
      if (Object.keys(patch).some(key => !['x', 'y', 'width', 'height', 'rotation'].includes(key))) throw fault('invalid_geometry_patch', [target.id]);
      // 以最新 committed 记录合并已有预览几何，保留其余最新字段，不用开始时的旧内容覆盖。
      let element: ElementRecord = freeze({ ...original, geometry: snapshot.gesture.preview.get(target.id) || original.geometry });
      const parts: [Capability, Partial<Geometry>][] = [
        ['geometry.move', Object.fromEntries(Object.entries(patch).filter(([key]) => key === 'x' || key === 'y'))],
        ['geometry.resize', Object.fromEntries(Object.entries(patch).filter(([key]) => key === 'width' || key === 'height'))],
        ['geometry.rotate', Object.fromEntries(Object.entries(patch).filter(([key]) => key === 'rotation'))],
      ];
      // move/resize/rotate 依次读取上一步预览结果；handler 只能给同目标生成合法 geometry。
      for (const [capability, value] of parts) if (Object.keys(value).length) {
        if (!editor.registry.supports(element, capability)) throw fault('unsupported_capability', [target.id]);
        const changes = editor.registry.handlers.get(element.componentId)!.get(capability)!({ element, input: freeze({ patch: value }) });
        for (const change of changes) {
          if (change.field !== 'geometry' || change.target.id !== target.id || change.target.incarnation !== target.incarnation) throw fault('invalid_handler_change', [target.id]);
          const geometry = change.after as Geometry;
          if (!geometryValid(geometry)) throw fault('invalid_geometry', [target.id]);
          element = freeze({ ...element, geometry });
        }
      }
      // 更新 preview 不触发 editor 命令，所以 pointermove 不制造 history 或出站请求。
      const preview = new Map(snapshot.gesture.preview); preview.set(target.id, (element as ElementRecord & { structure: 'node' }).geometry);
      snapshot = Object.freeze({ ...snapshot, gesture: freeze({ ...snapshot.gesture, preview: readMap(preview) }) }); notify();
      return { enabled: true };
    } catch (error) { const result = reject(error); return { enabled: false, code: result.code, targets: result.targets }; }
  }
  return Object.freeze({
    /** 外部订阅读取当前只读会话，不能直接修改内部 Map/Set。 */
    getSnapshot: () => snapshot,
    /** 创建独立 view，返回带 attached 标记的幂等卸载函数；只释放这个 view 与其手势。 */
    attach(id: Id, canvasId = [...editor.getSnapshot().document.canvases.values()].find(canvas => !canvas.parent)!.id) {
      if (disposed || snapshot.views.has(id)) throw fault('duplicate_view', [id]);
      if (!editor.getSnapshot().document.canvases.has(canvasId)) throw fault('canvas_missing', [canvasId]);
      setView(freeze({ id, canvasId, selection: readSet<Id>([]), viewport: { x: 0, y: 0, zoom: 1 }, tool: 'select', modes: readMap(new Map<Id, string>()) }));
      let attached=true;return () => { if(!attached)return;attached=false;if(!snapshot.views.has(id))return;const views=new Map(snapshot.views);views.delete(id);publishViews(views,id,'view_detached'); };
    },
    /** 切换查看的 canvas，清 selection/modes，并取消属于该 view 的旧坐标手势。 */
    canvas(id: Id, canvasId: Id) {
      const current = view(id);
      if (!editor.getSnapshot().document.canvases.has(canvasId)) throw fault('canvas_missing', [canvasId]);
      setView(freeze({ ...current, canvasId, selection: readSet<Id>([]), modes: readMap(new Map<Id, string>()) }),'canvas_changed');
    },
    /** 捕获有效元素 ID 为只读选择集合；这是会话选择，不是文档命令。 */
    select(id: Id, ids: readonly Id[]) {
      const current = view(id), document = editor.getSnapshot().document;
      for (const target of ids) if (!document.elements.has(target)) throw fault('element_missing', [target]);
      setView(freeze({ ...current, selection: readSet(ids) }));
    },
    /** 保存有限 pan 和正 zoom；改变观察视口不修改元素几何或 history。 */
    viewport(id: Id, viewport: ViewState['viewport']) {
      if (![viewport.x, viewport.y, viewport.zoom].every(Number.isFinite) || viewport.zoom <= 0) throw fault('invalid_viewport');
      setView(freeze({ ...view(id), viewport: { ...viewport } }));
    },
    /** select/pan 切换会取消本 view 的手势；重复设置相同工具不发通知。 */
    tool(id: Id, tool: ViewState['tool']) { const current=view(id);if(tool!=='select'&&tool!=='pan')throw fault('invalid_tool');if(current.tool===tool)return;setView(freeze({ ...current, tool }),'tool_changed'); },
    /** 保存某元素的临时编辑模式；空值移除，不创建持久的业务字段。 */
    mode(id: Id, target: Id, mode: string | null) { const current = view(id);if(mode!==null&&typeof mode!=='string')throw fault('invalid_mode');if(mode&&!editor.getSnapshot().document.elements.has(target))throw fault('element_missing',[target]);if((current.modes.get(target)??null)===(mode||null))return;const modes = new Map(current.modes); if (mode) modes.set(target, mode); else modes.delete(target); setView(freeze({ ...current, modes: readMap(modes) })); },
    /** 节点手势准入：select 工具、无其它手势、目标去重/版本支持、可见拥有链及 policy 全部通过。
     * 先把整组选区检查完再替换 baseline，拒绝不会留下半组手势。 */
    begin(viewId: Id, targets: readonly Target[]): Availability {
      try {
        if(view(viewId).tool!=='select')throw fault('tool_not_select');
        if (snapshot.gesture || snapshot.connectionGesture || !targets.length || new Set(targets.map(target => target.id)).size !== targets.length) throw fault('gesture_busy');
        const placement=createGesturePlacementReader(editor.getSnapshot().document,view(viewId).canvasId,editor.registry);
        const plannedBaseline = new Map(targets.map(target => { const element = targetElement(editor.getSnapshot().document, target); if (element.structure !== 'node' || editor.registry.resolve(element) !== 'known') throw fault('unsupported_component', [target.id]); return [target.id, element]; }));
        for (const target of targets) { placement(plannedBaseline.get(target.id)!.ownerCanvasId);const allowed = editor.can({ type: 'element.geometry', target, patch: {} }); if (!allowed.enabled) throw fault(allowed.code, allowed.targets); }
        // 成功时分配新 token 并清取消原因；初始 preview 为空，尚无任何文档变化。
        baseline=plannedBaseline;
        snapshot = Object.freeze({ ...snapshot, lastCancelReason: null, gesture: freeze({ token: ++nextGestureToken, viewId, targets: targets.map(target => ({ ...target })), preview: readMap(new Map<Id, Geometry>()), phase: 'active' as const }) }); notify();
        return { enabled: true };
      } catch (error) { const result = reject(error); return { enabled: false, code: result.code, targets: result.targets }; }
    },
    /** 开始连线编辑，保存当前 path/身份与可见坐标链，通过 editor.can 后才建立会话。 */
    beginConnection(viewId: Id, target: Target): Availability {
      try {
        if(view(viewId).tool!=='select')throw fault('tool_not_select');
        if (snapshot.gesture || snapshot.connectionGesture) throw fault('gesture_busy');
        const element = targetElement(editor.getSnapshot().document, target);
        if (element.structure !== 'connection') throw fault('unsupported_capability', [target.id]);
        createGesturePlacementReader(editor.getSnapshot().document,view(viewId).canvasId,editor.registry)(element.ownerCanvasId);
        const allowed = editor.can({ type: 'connection.path', target, path: element.path });
        if (!allowed.enabled) throw fault(allowed.code, allowed.targets);
        connectionBaseline = element;
        snapshot = Object.freeze({ ...snapshot, lastCancelReason: null, connectionGesture: freeze({ token: ++nextGestureToken, viewId, target: { ...target }, path: element.path, phase: 'active' as const }) }); notify();
        return { enabled: true };
      } catch (error) { const result = reject(error); return { enabled: false, code: result.code, targets: result.targets }; }
    },
    /** 捕获合法 JSON 路径预览；具体路径协议与当前权限仍在真正 editor 提交时重新校验。 */
    updateConnection(viewId: Id, path: Json): Availability {
      try {
        view(viewId);
        if (snapshot.connectionGesture?.viewId !== viewId) throw fault('gesture_not_owned');
        if (!validJson(path)) throw fault('invalid_connection_path');
        snapshot = Object.freeze({ ...snapshot, connectionGesture: freeze({ ...snapshot.connectionGesture, path: clone(path) }) }); notify();
        return { enabled: true };
      } catch (error) { const result = reject(error); return { enabled: false, code: result.code, targets: result.targets }; }
    },
    /** 连线结束只 dispatch 一次；先标 committing，结束后无论成功/拒绝都清预览。 */
    commitConnection(viewId: Id): Result {
      try {
        view(viewId);
        const gesture = snapshot.connectionGesture;
        if (!gesture || gesture.viewId !== viewId) throw fault('gesture_not_owned');
        snapshot = Object.freeze({ ...snapshot, connectionGesture: freeze({ ...gesture, phase: 'committing' as const }) });
        const result = editor.dispatch({ type: 'connection.path', target: gesture.target, path: gesture.path }, { label: 'Edit connection' });
        cancel(result.status === 'rejected' ? result.code : 'committed'); return result;
      } catch (error) { cancel('commit_failed'); return reject(error); }
    },
    update,
    /** 节点手势提交一个同步事务，把各目标相对 baseline 的净字段变化合成一个 Transform 历史项。 */
    commit(viewId: Id): Result {
      try {
        view(viewId);
        const gesture = snapshot.gesture;
        if (!gesture || gesture.viewId !== viewId) throw fault('gesture_not_owned');
        snapshot = Object.freeze({ ...snapshot, gesture: freeze({ ...gesture, phase: 'committing' as const }) });
        const result = editor.transaction(tx => {
          for (const [id, geometry] of gesture.preview) {
            const original = baseline.get(id);
            if (!original || original.structure !== 'node') throw fault('target_changed', [id]);
            // 只发送实际变化的几何键，避免覆盖未由此次手势修改的值；其余 data 从不回写。
            const patch = Object.fromEntries(Object.entries(geometry).filter(([key, value]) => !equal(original.geometry[key as keyof Geometry], value)));
            tx.dispatch({ type: 'element.geometry', target: { id, incarnation: original.incarnation }, patch });
          }
        }, { label: 'Transform' });
        cancel(result.status === 'rejected' ? result.code : 'committed');
        return result;
      } catch (error) { cancel('commit_failed'); return reject(error); }
    },
    cancel,
    /** 渲染时优先读取预览，否则读取最新 committed 几何；取消后自然显露最新模型。 */
    effectiveGeometry(id: Id): Geometry | undefined {
      const element = editor.getSnapshot().document.elements.get(id);
      return snapshot.gesture?.preview.get(id) || (element?.structure === 'node' ? element.geometry : undefined);
    },
    /** 订阅会话变化；退订只清监听，不负责取消持久上传或关闭整个 editor。 */
    subscribe(listener: () => void) { if (disposed) throw fault('sessions_disposed'); listeners.add(listener); return () => { listeners.delete(listener); }; },
    /** 幂等销毁：解绑 editor、清临时会话并通知一次，然后释放全部 session listener。 */
    dispose() { if(disposed)return;disposed = true;detachEditor();baseline.clear();connectionBaseline=undefined;snapshot = Object.freeze({ ...snapshot, views: readMap(new Map<Id, ViewState>()),gesture:null,connectionGesture:null,lastCancelReason:'disposed' }); notify();listeners.clear(); },
  });
}