import {validateCanvasElementCounts,type CanvasElementCounts} from '../canvas-runtime/scope-counts.ts';
import type { CanvasRecord, ElementRecord, Id, Registry } from '../canvas-core/types.ts';
import { createDocument, validateDocument } from '../canvas-core/document.ts';
import { fault, freeze, readMap, validJson } from '../canvas-core/values.ts';
import type { CanonicalReadUpdate } from '../canvas-runtime/contracts.ts';

export const modelStreamType = 'application/vnd.foundry.canvas-model+ndjson;version=1';
const maxBytes=64*1024*1024,maxLine=8*1024*1024,maxLines=4096;
const uuid=/^[a-f\d]{8}-[a-f\d]{4}-[a-f\d]{4}-[a-f\d]{4}-[a-f\d]{12}$/i;
const object=(value:unknown):Record<string,unknown>=>{if(!value||typeof value!=='object'||Array.isArray(value)||!validJson(value))throw fault('invalid_model_stream');return value as Record<string,unknown>;};
/** Bounded NDJSON framing. EOF is required even after a terminal record. */
async function* lines(source:AsyncIterable<Uint8Array>,signal:AbortSignal){
 const decoder=new TextDecoder('utf-8',{fatal:true});
 const decode=(bytes?:Uint8Array,stream=false)=>{try{return decoder.decode(bytes,{stream});}catch{throw fault('invalid_model_stream');}};
 let pending='',total=0,lineBytes=0,count=0;
 for await(const bytes of source){
  signal.throwIfAborted();if(!(bytes instanceof Uint8Array))throw fault('invalid_model_stream');total+=bytes.byteLength;if(total>maxBytes)throw fault('model_stream_budget');
  let start=0;
  for(let index=0;index<bytes.length;index++)if(bytes[index]===10){
   lineBytes+=index-start;if(lineBytes>maxLine)throw fault('model_stream_budget');
   pending+=decode(bytes.subarray(start,index),true);pending+=decode();if(++count>maxLines||!pending)throw fault('invalid_model_stream');
   let raw:unknown;try{raw=JSON.parse(pending);}catch{throw fault('invalid_model_stream');}
   yield{raw,byteLength:lineBytes+1};pending='';lineBytes=0;start=index+1;
  }
  lineBytes+=bytes.length-start;if(lineBytes>maxLine)throw fault('model_stream_budget');pending+=decode(bytes.subarray(start),true);
 }
 signal.throwIfAborted();pending+=decode();if(pending||lineBytes)throw fault('incomplete_model_stream');
}
export async function* decodeModelStream(source:AsyncIterable<Uint8Array>,canvasId:Id,registry:Registry,signal:AbortSignal){
 let sequence=0,token='',projectId='',expected=0,ended=false;
 let terminal: {sequence:number;snapshotToken:string;projectId:string;versions:ReadonlyMap<Id,number>;complete:boolean;byteLength:number;coverage:string[];value:CanonicalReadUpdate}|undefined;
 let canvases:CanvasRecord[]=[],versions:ReadonlyMap<Id,number>=new Map(),tombstones:ReadonlyMap<Id,number>=new Map();
 let canvasElementCounts:CanvasElementCounts|undefined;const ownerCounts=new Map<Id,number>();
 const elements:ElementRecord[]=[],ids=new Set<Id>(),canvasIds=new Set<Id>();
 for await(const line of lines(source,signal)){
  const raw=object(line.raw);
  if(ended||raw.streamVersion!==1||raw.sequence!==sequence++||typeof raw.snapshotToken!=='string'||!raw.snapshotToken||raw.snapshotToken.length>256)throw fault('invalid_model_stream');
  if(sequence===1){
   if(raw.kind!=='header'||raw.documentFormatVersion!==1||typeof raw.projectId!=='string'||!uuid.test(raw.projectId)||!Number.isSafeInteger(raw.elementCount)||(raw.elementCount as number)<0||!Array.isArray(raw.canvases)||raw.canvases.length>256)throw fault('invalid_model_stream');
   token=raw.snapshotToken;projectId=raw.projectId;expected=raw.elementCount as number;canvases=raw.canvases as CanvasRecord[];
   for(const canvas of canvases){object(canvas);if(typeof canvas.id!=='string'||!uuid.test(canvas.id)||canvasIds.has(canvas.id))throw fault('invalid_model_stream');canvasIds.add(canvas.id);}
   if(!canvasIds.has(canvasId)||!canvasIds.has(projectId))throw fault('project_mismatch');
   const versionMap=new Map<Id,number>(),dead=new Map<Id,number>();
   for(const [id,value]of Object.entries(object(raw.versions))){if(!uuid.test(id)||!Number.isSafeInteger(value)||(value as number)<1)throw fault('invalid_canonical_version');versionMap.set(id,value as number);}
   if([...canvasIds].some(id=>!versionMap.has(id)))throw fault('invalid_model_stream');
   if(!Array.isArray(raw.removedCanvasIds)||new Set(raw.removedCanvasIds).size!==raw.removedCanvasIds.length||raw.removedCanvasIds.some(id=>typeof id!=='string'||canvasIds.has(id)||!versionMap.has(id))||versionMap.size!==canvasIds.size+raw.removedCanvasIds.length)throw fault('invalid_model_stream');
   for(const [id,value]of Object.entries(object(raw.tombstones))){if(!id||!Number.isSafeInteger(value)||(value as number)<1)throw fault('invalid_model_stream');dead.set(id,value as number);}
   versions=readMap(versionMap);tombstones=readMap(dead);
   if(Object.hasOwn(raw,'canvasElementCounts')){validateCanvasElementCounts(raw.canvasElementCounts,[...canvasIds],expected);canvasElementCounts=freeze({...raw.canvasElementCounts});}
   const value:CanonicalReadUpdate=freeze({status:'receiving',...(canvasElementCounts?{canvasElementCounts}:{}),projectId,canvases,elements:[],tombstones,versions,receivedElements:0,totalElements:expected});
   yield{sequence:0,snapshotToken:token,projectId,versions,complete:false,byteLength:line.byteLength,coverage:['model-header'],value};continue;
  }
  if(raw.snapshotToken!==token)throw fault('load_snapshot_changed');
  if(raw.kind==='elements'){
   if(!Array.isArray(raw.elements)||!raw.elements.length||raw.elements.length>64||elements.length+raw.elements.length>expected)throw fault('invalid_model_stream');
   for(const item of raw.elements){const element=object(item) as unknown as ElementRecord;if(typeof element.id!=='string'||!element.id||ids.has(element.id)||!canvasIds.has(element.ownerCanvasId))throw fault('invalid_model_stream');const count=(ownerCounts.get(element.ownerCanvasId)??0)+1;if(canvasElementCounts&&count>canvasElementCounts[element.ownerCanvasId])throw fault('invalid_model_coverage');ownerCounts.set(element.ownerCanvasId,count);ids.add(element.id);elements.push(element);}
   const value:CanonicalReadUpdate=freeze({status:'receiving',projectId,canvases:[],elements:raw.elements as ElementRecord[],tombstones:readMap(new Map()),versions,receivedElements:elements.length,totalElements:expected});
   yield{sequence:sequence-1,snapshotToken:token,projectId,versions,complete:false,byteLength:line.byteLength,coverage:raw.elements.map(item=>`element:${(item as ElementRecord).id}`),value};
  }else if(raw.kind==='complete'){
   if(raw.elementCount!==expected||elements.length!==expected)throw fault('incomplete_model_stream');
   const document=createDocument(projectId,canvases,elements,tombstones);validateDocument(document,registry);ended=true;
   const value:CanonicalReadUpdate=Object.freeze({status:'ready',document,versions});
   terminal={sequence:sequence-1,snapshotToken:token,projectId,versions,complete:true,byteLength:line.byteLength,coverage:[...canvasIds].map(id=>`canvas:${id}`),value};
  }else throw fault('invalid_model_stream');
 }
 if(!ended||!terminal)throw fault('incomplete_model_stream');
 yield terminal;
}