import sharp from 'sharp';
import {createHash} from 'node:crypto';
import {mkdir,readFile,writeFile,rename,stat,readdir,unlink,realpath} from 'node:fs/promises';
import {resolve,sep,join} from 'node:path';
import {tmpdir} from 'node:os';
export const previewWidths=[240,480,960,1280];
export function previewWidth(value:unknown,profile?:unknown){const n=Number(value||480);return profile==='export'?(n===2160?n:null):profile===undefined&&previewWidths.includes(n)?n:null;}
export function staticPreviewPath(source:string,root:string){if(!source.startsWith('/')||source.startsWith('//')||source.includes('\\')||!/^\/(?:[^?]+)\.(png|jpe?g|webp)$/i.test(source))throw Error('Invalid source');const file=resolve(root,'.'+source);if(!file.startsWith(resolve(root)+sep))throw Error('Invalid source');return file;}
let active=0;const waiting:(()=>void)[]=[];
async function limited<T>(work:()=>Promise<T>){if(active>=3){if(waiting.length>=24)throw Error('Preview busy');await new Promise<void>(done=>waiting.push(done));}else active++;try{return await work()}finally{const next=waiting.shift();if(next)next();else active--;}}
const pending=new Map<string,Promise<Buffer>>();const cache=join(tmpdir(),'prompt-previews-v1');let writes=0;
export async function compressPreview(input:Buffer,width:number){const max=width<=480?100_000:220_000;let size=width,quality=72;let output:Buffer;do{output=await sharp(input,{limitInputPixels:40_000_000,animated:false}).rotate().resize({width:size,withoutEnlargement:true}).webp({quality,effort:3}).toBuffer();if(output.length<=max)return output;size=Math.max(240,Math.floor(size*.8));quality=Math.max(30,quality-10);}while(size>240||quality>30);return sharp(input,{limitInputPixels:40_000_000}).rotate().resize({width:240,withoutEnlargement:true}).webp({quality:30}).toBuffer();}
export async function cachedPreview(identity:string,width:number,load:()=>Promise<Buffer>,quality=false){const key=createHash('sha256').update(identity+':'+width+(quality?':export-v1':':webp-v1')).digest('hex');const file=join(cache,key+'.webp');try{return {bytes:await readFile(file),etag:'"'+key+'"'};}catch{/* cache miss */}let task=pending.get(key);if(!task){task=limited(async()=>{await mkdir(cache,{recursive:true});const input=await load();const bytes=quality?await sharp(input,{limitInputPixels:40_000_000,animated:false}).rotate().resize({width,withoutEnlargement:true}).webp({quality:95,effort:4}).toBuffer():await compressPreview(input,width);const temp=file+'.'+process.pid+'.tmp';await writeFile(temp,bytes);await rename(temp,file);if(++writes%32===0){const files=await readdir(cache);if(files.length>1024){const dates=await Promise.all(files.map(async name=>({name,time:(await stat(join(cache,name)).catch(()=>({mtimeMs:0}))).mtimeMs})));await Promise.all(dates.sort((a,b)=>a.time-b.time).slice(0,files.length-1024).map(f=>unlink(join(cache,f.name)).catch(()=>{})));}}return bytes;});pending.set(key,task);}try{return {bytes:await task,etag:'"'+key+'"'};}finally{pending.delete(key);}}
export async function loadStaticPreview(source:string){const root=await realpath(join(process.cwd(),'public'));const file=await realpath(staticPreviewPath(source,root));if(!file.startsWith(root+sep))throw Error('Invalid source');const info=await stat(file);if(info.size>64*1024*1024)throw Error('Image too large');return {identity:file+':'+info.mtimeMs,load:()=>readFile(file)};}