import { Injectable, Logger } from "@nestjs/common";
import { Cron } from "@nestjs/schedule";
import { PrismaService } from 'src/prisma/prisma.service';
import * as path from 'node:path';
import { promises as fsp } from 'node:fs';
import { resolveAttachmentsRoot } from "src/config/attachment.config";

@Injectable()
export class GarbargeCollectorService {
    private readonly logger = new Logger(GarbargeCollectorService.name);

    //.env refs
    private readonly batch_size = Number(process.env.GC_BATCH_SIZE || 500);
    private readonly cron_expression = process.env.GC_CRON || '15 4 * * *'; // everyday at 04:15 AM

    //fetchs root of storage
    private readonly root = resolveAttachmentsRoot();

    constructor(private readonly prisma: PrismaService) { }

    //planif for the Cronjob
    @Cron(function (this: GarbargeCollectorService) { return this.cron_expression; } as any)
    async runScheduled() {
        await this.collect();
    }

    //Manage Garbage collecting by batch of elements until a batch != full
    async collect() {
        let total = 0, round = 0;
        //infinit loop (;;) with break
        for (; ;) {
            round++;
            const num = await this.collectBatch();
            total += num;
            this.logger.log(`Garbage Collector round #${round} removed ${num}`);
            if (num < this.batch_size) break;     //breaks if not a full batch       
        }
        this.logger.log(`Garbage Collecting done: total removed ${total}`);
        return { removed: total };
    }

    //Manage a single lot of orphan blobs
    private async collectBatch(): Promise<number> {
        const blobs = await this.prisma.blobs.findMany({
            where: { refcount: { lte: 0 } },
            select: { sha256: true, storage_path: true },
            take: this.batch_size,
        });
        if (blobs.length === 0) return 0;

        // delete original file and all its variants <hash> in the same file
        await Promise.all(
            blobs.map(async (blob) => {
                const absolute_path = path.join(this.root, blob.storage_path);
                await this.deleteFileIfExists(absolute_path); //tries to delete original file if found

                const dir = path.dirname(absolute_path);
                const base = path.basename(absolute_path);
                try {
                    const entries = await fsp.readdir(dir, { withFileTypes: true });
                    const targets = entries.filter(entry => entry.isFile() && entry.name.startsWith(base + '.'))
                        .map(entry => path.join(dir, entry.name));
                    //deletes all variants
                    await Promise.all(targets.map(target => this.deleteFileIfExists(target)));
                } catch { }
            })
        );
        //deletes blobs lignes if file is deleted
        const hashes = blobs.map(blob => blob.sha256);
        await this.prisma.blobs.deleteMany({ where: { sha256: { in: hashes } } });
        return blobs.length;
    }

    //helper: deletes path if exists and ignore errors
    private async deleteFileIfExists(path: string) {
        try { await fsp.unlink(path); } catch { }
    }
}