import fs from "fs"
import path from "path"
import { WebSocketServer } from "ws"

const DATA_DIR = path.resolve("./")
const DATA_FILE = path.join(DATA_DIR, "master.forms")

if (!fs.existsSync(DATA_DIR)) {
    fs.mkdirSync(DATA_DIR, { recursive: true })
}

if (!fs.existsSync(DATA_FILE)) {
    fs.writeFileSync(DATA_FILE, "")
}

class Kernel {
    port
    seq = 0
    clients = new Set()

    constructor(port = 10000) {
        this.port = port

        this._loadSeq()

        this.wss = new WebSocketServer({ port: this.port })
        this.wss.on("connection", ws => this._onConnection(ws))

        console.log(`[kernel] running on ws://localhost:${port}`)
    }

    _loadSeq() {
        const data = fs.readFileSync(DATA_FILE, "utf8")
        if (!data) return

        const lines = data.trim().split("\n")
        const last = lines[lines.length - 1]
        if (last) {
            const entry = JSON.parse(last)
            this.seq = entry.seq
        }
    }

    _onConnection(ws) {
        this.clients.add(ws)

        ws.on("message", msg => this._onMessage(ws, msg))
        ws.on("close", () => this.clients.delete(ws))

        ws.send(JSON.stringify({
            type: "hello",
            seq: this.seq
        }))
    }

    _onMessage(ws, raw) {
        let msg
        try {
            msg = JSON.parse(raw.toString())
        } catch {
            return
        }

        if (msg.op === "append") {
            this._append(msg.form, msg.data)
        }

        if (msg.op === "replay") {
            this._replay(ws, msg.form, msg.fromSeq)
        }
    }

    _append(form, data) {
        const entry = {
            seq: ++this.seq,
            time: Date.now(),
            form,
            data
        }

        fs.appendFileSync(DATA_FILE, JSON.stringify(entry) + "\n")

        const payload = JSON.stringify({
            type: "form:update",
            ...entry
        })

        for (const ws of this.clients) {
            if (ws.readyState === ws.OPEN) {
                ws.send(payload)
            }
        }
    }

    _replay(ws, form, fromSeq = 0) {
        const stream = fs.createReadStream(DATA_FILE, { encoding: "utf8" })
        let buffer = ""

        stream.on("data", chunk => {
            buffer += chunk
            let idx
            while ((idx = buffer.indexOf("\n")) >= 0) {
                const line = buffer.slice(0, idx)
                buffer = buffer.slice(idx + 1)

                if (!line) continue

                const entry = JSON.parse(line)
                if (entry.seq > fromSeq && entry.form === form) {
                    ws.send(JSON.stringify({
                        type: "form:update",
                        ...entry
                    }))
                }
            }
        })
    }
}

new Kernel()