/*
 * Veskslop daemon — Vesktop core process control.
 *
 * The daemon can start, stop, and restart the Electron client that hosts the
 * core bridge. Only a process started by this daemon instance is managed.
 *
 * On Linux without a DISPLAY, the daemon starts Xvfb and points the client at
 * it. Set VESKSLOP_XVFB=0 to disable that.
 */

import { spawn, type ChildProcess } from "node:child_process";
import { existsSync, statSync } from "node:fs";
import { join } from "node:path";
import { fileURLToPath } from "node:url";

const ROOT = fileURLToPath(new URL("../..", import.meta.url));

const DEFAULT_ARGS = "--no-sandbox --disable-gpu --disable-dev-shm-usage";
const XVFB_ARGS = "-screen 0 1280x720x24 -nolisten tcp";
const MAX_OUTPUT_LINES = 200;

/**
 * Warn when the built client bundle predates the core sources. Without this, a
 * new daemon paired with a stale client reports UNKNOWN_ACTION for new actions.
 */
export function staleBundleWarning(): string | null {
    const sources = [
        "src/renderer/puppet/actions.ts",
        "src/renderer/puppet/events.ts",
        "src/shared/puppetProtocol.ts",
        "src/main/puppetBridge.ts"
    ];
    const bundles = ["dist/js/renderer.js", "dist/js/main.js"];

    try {
        let newest = 0;
        for (const source of sources) newest = Math.max(newest, statSync(join(ROOT, source)).mtimeMs);

        let oldest = Number.POSITIVE_INFINITY;
        for (const bundle of bundles) oldest = Math.min(oldest, statSync(join(ROOT, bundle)).mtimeMs);

        if (oldest < newest) {
            return "the built client bundle is older than the core sources; run `pnpm build` and restart the client";
        }
    } catch {
        // A missing bundle is reported by the client start itself.
    }

    return null;
}

export interface CoreExit {
    code: number | null;
    signal: string | null;
    at: string;
}

export interface CoreProcessStatus {
    managed: boolean;
    running: boolean;
    pid: number | null;
    startedAt: string | null;
    command: string | null;
    lastExit: CoreExit | null;
    output: string[];
}

export interface CoreProcessOptions {
    tokenFile: string;
}

function prefixLines(prefix: string, chunk: Buffer): string {
    return chunk
        .toString()
        .split("\n")
        .map(line => (line ? `${prefix} ${line}` : line))
        .join("\n");
}

function sleep(ms: number): Promise<void> {
    return new Promise(resolve => setTimeout(resolve, ms));
}

function findFreeDisplay(): string {
    for (let number = 99; number < 110; number++) {
        if (!existsSync(`/tmp/.X11-unix/X${number}`)) return `:${number}`;
    }
    return ":99";
}

export class CoreProcess {
    private child?: ChildProcess;
    private startedAt?: number;
    private command?: string;
    private xvfb?: ChildProcess;
    private display?: string;
    private lastExit: CoreExit | null = null;
    private readonly output: string[] = [];
    private readonly exitListeners = new Set<() => void>();

    constructor(private readonly options: CoreProcessOptions) {}

    status(): CoreProcessStatus {
        const running = !!this.child && this.child.exitCode === null && !this.child.killed;
        return {
            managed: !!this.child,
            running,
            pid: this.child?.pid ?? null,
            startedAt: this.startedAt ? new Date(this.startedAt).toISOString() : null,
            command: this.command ?? null,
            lastExit: this.lastExit,
            output: [...this.output]
        };
    }

    onExit(listener: () => void) {
        this.exitListeners.add(listener);
        return () => this.exitListeners.delete(listener);
    }

    async start(forceToken = false): Promise<CoreProcessStatus> {
        if (this.child) return this.status();

        const override = process.env.VESKSLOP_CORE_CMD;
        const args = (process.env.VESKSLOP_CORE_ARGS ?? DEFAULT_ARGS).split(/\s+/).filter(Boolean);
        const display = await this.ensureDisplay();

        const env = {
            ...process.env,
            ...(display ? { DISPLAY: display } : {}),
            VESKSLOP_HEADLESS: process.env.VESKSLOP_HEADLESS ?? "1",
            VESKSLOP_TOKEN_FILE: this.options.tokenFile,
            ...(forceToken ? { VESKSLOP_FORCE_TOKEN: "1" } : {})
        };

        let command: string;
        let child: ChildProcess;

        if (override) {
            command = override;
            child = spawn(override, { cwd: ROOT, env, shell: true, stdio: ["ignore", "pipe", "pipe"] });
        } else {
            const electron = join(
                ROOT,
                "node_modules",
                ".bin",
                process.platform === "win32" ? "electron.cmd" : "electron"
            );
            if (!existsSync(electron)) {
                throw new Error("electron is not installed; run pnpm install or set VESKSLOP_CORE_CMD");
            }
            command = `${electron} . ${args.join(" ")}`;
            child = spawn(electron, [".", ...args], { cwd: ROOT, env, stdio: ["ignore", "pipe", "pipe"] });
        }

        this.child = child;
        this.startedAt = Date.now();
        this.command = command;
        this.lastExit = null;
        this.output.length = 0;

        child.stdout?.on("data", chunk => {
            this.appendOutput(chunk);
            process.stdout.write(prefixLines("[core]", chunk));
        });
        child.stderr?.on("data", chunk => {
            this.appendOutput(chunk);
            process.stderr.write(prefixLines("[core]", chunk));
        });

        child.on("error", error => {
            console.error("[core] failed to start:", error.message);
            this.appendOutput(Buffer.from(error.message));
        });

        child.on("exit", (code, signal) => {
            console.log(`[core] exited (code ${code ?? "null"}${signal ? `, signal ${signal}` : ""})`);
            this.lastExit = { code, signal, at: new Date().toISOString() };
            this.child = undefined;
            this.startedAt = undefined;
            this.command = undefined;
            for (const listener of this.exitListeners) listener();
        });

        console.log(`[core] starting: ${command}${display ? ` (DISPLAY=${display})` : ""}`);
        return this.status();
    }

    async stop(timeoutMs = 8000): Promise<CoreProcessStatus> {
        const child = this.child;
        if (!child) return this.status();

        await new Promise<void>(resolve => {
            const timer = setTimeout(() => {
                try {
                    child.kill("SIGKILL");
                } catch {
                    // already gone
                }
            }, timeoutMs);

            child.once("exit", () => {
                clearTimeout(timer);
                resolve();
            });

            try {
                child.kill("SIGTERM");
            } catch {
                clearTimeout(timer);
                resolve();
            }
        });

        return this.status();
    }

    async restart(forceToken = false): Promise<CoreProcessStatus> {
        await this.stop();
        return this.start(forceToken);
    }

    /** Stop the core and any Xvfb that this daemon started. */
    async dispose(timeoutMs = 4000): Promise<void> {
        await this.stop(timeoutMs);
        this.stopXvfb();
    }

    private appendOutput(chunk: Buffer) {
        for (const line of chunk.toString().split("\n")) {
            if (!line.trim()) continue;
            this.output.push(line);
            if (this.output.length > MAX_OUTPUT_LINES) this.output.shift();
        }
    }

    private async ensureDisplay(): Promise<string | undefined> {
        if (process.env.DISPLAY) return process.env.DISPLAY;
        if (process.platform !== "linux" || process.env.VESKSLOP_XVFB === "0") return undefined;
        if (this.xvfb && this.xvfb.exitCode === null) return this.display;

        const display = findFreeDisplay();
        const child = spawn("Xvfb", [display, ...XVFB_ARGS.split(" ")], { stdio: ["ignore", "ignore", "pipe"] });

        child.stderr?.on("data", chunk => process.stderr.write(prefixLines("[xvfb]", chunk)));
        child.on("error", error => {
            console.warn(`[core] Xvfb is not available: ${error.message}`);
            this.xvfb = undefined;
            this.display = undefined;
        });
        child.on("exit", () => {
            this.xvfb = undefined;
            this.display = undefined;
        });

        this.xvfb = child;
        this.display = display;

        // Wait for the X socket so Electron does not race the server startup.
        const socket = `/tmp/.X11-unix/X${display.slice(1)}`;
        for (let attempt = 0; attempt < 30 && !existsSync(socket); attempt++) await sleep(100);
        if (!existsSync(socket)) console.warn(`[core] Xvfb socket ${socket} did not appear; continuing anyway`);

        console.log(`[core] Xvfb on ${display} (pid ${child.pid})`);
        return display;
    }

    private stopXvfb() {
        const child = this.xvfb;
        this.xvfb = undefined;
        this.display = undefined;

        if (child && child.exitCode === null) {
            try {
                child.kill("SIGTERM");
            } catch {
                // already gone
            }
        }
    }
}