/**
 * https://github.com/kawanet/git-cat-file
 */

import {promises as fs} from "fs"
import type {GCF} from "../types/git-cat-file.d.ts"
import {longCache} from "./cache.ts"
import type {ObjStore} from "./obj-store.ts"
import {readPackIndex} from "./pack-idx.ts"
import {readPackedObject} from "./pack-obj.ts"

export class Pack {
    protected readonly path: string

    constructor(path: string) {
        this.path = path
    }

    private getIndex = longCache(() => readPackIndex(this.path))

    private getList = longCache(() => this.getIndex().then(index => Object.keys(index).sort()))

    async findAll(object_id: string): Promise<string[]> {
        const list = await this.getList()
        const index: {[oid: string]: 1} = {}
        const {length} = object_id

        for (const oid of await list) {
            if (oid.slice(0, length) === object_id) {
                index[oid] = 1
            }
        }

        return Object.keys(index)
    }

    async getObject(object_id: string, store: ObjStore): Promise<GCF.IObject> {
        const index = await this.getIndex()
        const offset = index[object_id]
        if (!offset) return

        // console.warn(`open: ${this.path}`);
        const fh = await fs.open(this.path, "r")
        const obj = await readPackedObject(fh, offset, store)
        await fh.close()
        const {type, data} = obj
        return {oid: object_id, type, data}
    }
}