import type {Document,Id} from '../canvas-core/types.ts';
import {equal,fault} from '../canvas-core/values.ts';
import type {projectCanvas} from './projection.ts';

type Projection=ReturnType<typeof projectCanvas>;
type Retained<T>={incarnation:number;ownerCanvasId:Id;value:T};
/** View-owned rendering cache, never a document store. Keep unchanged React Flow input identities. */
export function createProjectionCache(){
  let scope:object|undefined,projectId:Id|undefined,canvasId:Id|undefined;
  let nodes=new Map<Id,Retained<Projection['nodes'][number]>>(),edges=new Map<Id,Retained<Projection['edges'][number]>>();
  function retain<T extends{id:Id}>(document:Document,values:T[],previous:Map<Id,Retained<T>>){
    const next=new Map<Id,Retained<T>>();
    for(let index=0;index<values.length;index++){
      const value=values[index],record=document.elements.get(value.id);if(!record)throw fault('projection_identity_missing',[value.id]);
      const old=previous.get(value.id),retained=old&&old.incarnation===record.incarnation&&old.ownerCanvasId===record.ownerCanvasId&&equal(old.value,value)?old.value:value;
      values[index]=retained;next.set(value.id,{incarnation:record.incarnation,ownerCanvasId:record.ownerCanvasId,value:retained});
    }
    return next;
  }
  return Object.freeze({
    reuse(owner:object,document:Document,viewCanvasId:Id,projection:Projection):Projection{
      if(scope!==owner||projectId!==document.projectId||canvasId!==viewCanvasId){nodes.clear();edges.clear();scope=owner;projectId=document.projectId;canvasId=viewCanvasId;}
      nodes=retain(document,projection.nodes,nodes);edges=retain(document,projection.edges,edges);
      return projection;
    },
    getNode(id:Id){return nodes.get(id)?.value;},
    canRetainMeasurement(owner:object,document:Document,viewCanvasId:Id,value:Projection['nodes'][number]){
      const old=nodes.get(value.id),record=document.elements.get(value.id);
      return scope===owner&&projectId===document.projectId&&canvasId===viewCanvasId&&!!old&&!!record&&old.incarnation===record.incarnation&&old.ownerCanvasId===record.ownerCanvasId&&old.value.type===value.type&&old.value.width===value.width&&old.value.height===value.height&&equal(old.value.data,value.data);
    },
    clear(){nodes.clear();edges.clear();scope=undefined;projectId=undefined;canvasId=undefined;},
  });
}