// wget ftp://ftp.ncbi.nlm.nih.gov/refseq/H_sapiens/mRNA_Prot/human.6.rna.gbff.gz

import fs from 'fs'
import readline from 'readline'
import { Buffer } from 'buffer'
import genbankParser from 'genbank-parser'

const line$ = (path: string) => readline.createInterface({
    input: fs.createReadStream(path),
    crlfDelay: Infinity
});

const readOffset = (path: string, from:number, to:number) => {
    return new Promise<string>(async (resolve, reject) => {
        const size = to - from
        const buffer = Buffer.alloc(size);
        let filehandle = null;
        try {
            filehandle = await fs.promises.open(path, 'r+');
            await filehandle.read(buffer, 0, buffer.length, from);
        } finally {
            if (filehandle) {
                await filehandle.close()
                resolve(buffer.toString())
            }
        }
    })
}

/*
 * strings -a -t d human.1.rna.gbff | grep LOCUS | awk '{print $1"\t"$3}' > human.1.rna.gbff.index
 * 
 */
const makeGbffIndex = async (filePath: string, lineSize = 80, indexPath?: string) => {
    interface entry {
        filePath: string;
        value   : string;
        from    : number;
        to     ?: number;
    }
    indexPath = indexPath || filePath + '.jsi'
    let entries = [] as entry[]
    let lineN   = 0
    let byteAcc = 0
    for await (const line of line$(filePath)) {
        if(line.match(/^LOCUS/)) {
            entries.push({
                filePath,
                value   : line.split(/\s+/)[1],
                from    : byteAcc
            })
            if(lineN !== 0) {
                entries[entries.length - 2]["to"] = byteAcc 
                await fs.promises.appendFile(indexPath, [
                    entries[entries.length - 2]["value"],
                    entries[entries.length - 2]["from"],
                    entries[entries.length - 2]["to"]].join('\t') + '\n')
                entries = entries.splice(1)
            }
        }
        byteAcc += (line.length + 1)
        lineN++
    }
    entries[entries.length - 1]["to"] = byteAcc
    
    await fs.promises.appendFile(indexPath, [
        entries[entries.length - 1]["value"],
        entries[entries.length - 1]["from"],
        entries[entries.length - 1]["to"]].join('\t'))
    return entries
}

const getOffset = async (indexPath: string, acc: string) => {
    let res
    for await (const line of line$(indexPath)) {
        const tmp = line.split('\t')
        if (tmp[0] === acc) {
            res = [indexPath.split('.jsi')[0], tmp[1], tmp[2]]
            break
        }
    }
    return res
}

const getFromAcc = async (acc: string, dbPath: string | string[], indexPath?: string | string[]) => {
    dbPath = Array.isArray(dbPath) ? dbPath : [dbPath]
    if (!indexPath) {
        indexPath = []
        for (const p of dbPath) {
            const iP = p + '.jsi'
            if (!fs.existsSync(iP)) {
                console.log('Writing index: ' + iP);
                await makeGbffIndex(p)
            }
            indexPath.push(iP)
        }
    } else {
        indexPath = Array.isArray(indexPath) ? indexPath : [indexPath]
        if (indexPath.length !== dbPath.length) throw 'Error'
    }
    let i = 0
    let res
    for (const p of dbPath) {
        res = await getOffset(indexPath[i], acc)
        if (res) break
        i++
    }
    if (res) {
        const rr = await readOffset(res[0], Number(res[1]), Number(res[2]))
        res = genbankParser(rr)[0]
    }
    return res
}

export { getFromAcc }