import { afterEach, describe, expect, it } from 'vitest';
import net from 'node:net';
import { findAvailablePort } from '../src/webui/port';

const HOST = '127.0.0.1';
const OTHER_HOST = '127.0.0.2';

const held: net.Server[] = [];

afterEach(async () => {
    await Promise.all(held.splice(0).map(closeServer));
});

function closeServer(server: net.Server): Promise<void> {
    return new Promise((resolve) => {
        server.close(() => resolve());
    });
}

function portOf(server: net.Server): number {
    const addr = server.address();

    if (!addr || typeof addr === 'string') {
        throw new Error('expected TCP AddressInfo');
    }

    return addr.port;
}

function hold(port: number, host = HOST): Promise<net.Server> {
    return new Promise((resolve, reject) => {
        const server = net.createServer();
        server.once('error', reject);
        server.listen({ port, host, exclusive: true }, () => {
            held.push(server);
            resolve(server);
        });
    });
}

async function release(server: net.Server): Promise<void> {
    const i = held.indexOf(server);

    if (i >= 0) {
        held.splice(i, 1);
    }

    await closeServer(server);
}

/** Bind an ephemeral port that still has a free successor on the same host. */
async function holdWithFreeNext(host = HOST): Promise<number> {
    for (let n = 0; n < 8; n++) {
        const server = await hold(0, host);
        const start = portOf(server);

        if (start >= 65535) {
            await release(server);
            continue;
        }

        try {
            await release(await hold(start + 1, host));
            return start;
        } catch {
            await release(server);
        }
    }

    throw new Error('no occupied port with a free successor');
}

describe('findAvailablePort', () => {
    it('returns start when that TCP port is free', async () => {
        const server = await hold(0);
        const start = portOf(server);
        await release(server);

        expect(await findAvailablePort(start)).toBe(start);
    });

    it('truncates a fractional start toward zero before probing', async () => {
        const server = await hold(0);
        const start = portOf(server);
        await release(server);

        expect(await findAvailablePort(start + 0.9, { maxTries: 1 })).toBe(start);
        expect(await findAvailablePort(start + 0.1, { maxTries: 1 })).toBe(start);
    });

    it('clamps a start above 65535 down to 65535', async () => {
        const probe = await hold(65535);
        expect(portOf(probe)).toBe(65535);
        await release(probe);

        expect(await findAvailablePort(65536, { maxTries: 1 })).toBe(65535);
        expect(await findAvailablePort(70000, { maxTries: 1 })).toBe(65535);
        expect(await findAvailablePort(65535.8, { maxTries: 1 })).toBe(65535);
        expect(await findAvailablePort(Number.POSITIVE_INFINITY, { maxTries: 1 })).toBe(65535);
    });

    it('returns the next port when start is already bound', async () => {
        const start = await holdWithFreeNext();
        expect(await findAvailablePort(start)).toBe(start + 1);
    });

    it('walks forward one port at a time after consecutive collisions', async () => {
        const start = await holdWithFreeNext();
        await hold(start + 1);
        const third = await hold(start + 2);
        await release(third);

        expect(await findAvailablePort(start, { maxTries: 3 })).toBe(start + 2);
    });

    it('throws when maxTries is exhausted on an occupied port', async () => {
        const start = await holdWithFreeNext();
        await expect(findAvailablePort(start, { maxTries: 1 })).rejects.toThrow(
            `No available TCP port found near ${start}`,
        );
    });

    it('throws without probing when maxTries is 0 and keeps the caller start in the message', async () => {
        await expect(findAvailablePort(4123, { maxTries: 0 })).rejects.toThrow(
            'No available TCP port found near 4123',
        );
        await expect(findAvailablePort(0, { maxTries: 0 })).rejects.toThrow(
            'No available TCP port found near 0',
        );
        await expect(findAvailablePort(-20, { maxTries: 0 })).rejects.toThrow(
            'No available TCP port found near -20',
        );
        await expect(findAvailablePort(70000, { maxTries: 0 })).rejects.toThrow(
            'No available TCP port found near 70000',
        );
    });

    it('stops at 65535 instead of wrapping after the last TCP port is taken', async () => {
        await hold(65535);

        await expect(findAvailablePort(65535, { maxTries: 10 })).rejects.toThrow(
            'No available TCP port found near 65535',
        );
        await expect(findAvailablePort(80000, { maxTries: 10 })).rejects.toThrow(
            'No available TCP port found near 80000',
        );
    });

    it('defaults host to 127.0.0.1', async () => {
        const start = await holdWithFreeNext();
        await expect(findAvailablePort(start, { maxTries: 1 })).rejects.toThrow(
            `No available TCP port found near ${start}`,
        );
    });

    it('probes only the requested host', async (ctx) => {
        const start = await holdWithFreeNext();

        try {
            await release(await hold(start, OTHER_HOST));
        } catch (error) {
            if ((error as NodeJS.ErrnoException).code === 'EADDRNOTAVAIL') {
                ctx.skip(`${OTHER_HOST} is not assigned on this machine`);
            }

            throw error;
        }

        expect(await findAvailablePort(start, { host: OTHER_HOST, maxTries: 1 })).toBe(start);
        await expect(findAvailablePort(start, { host: HOST, maxTries: 1 })).rejects.toThrow(
            `No available TCP port found near ${start}`,
        );
    });

    it('treats a listen failure as unavailable', async () => {
        await expect(
            findAvailablePort(43123, { host: '256.256.256.256', maxTries: 1 }),
        ).rejects.toThrow('No available TCP port found near 43123');
        await expect(findAvailablePort(Number.NaN, { maxTries: 1 })).rejects.toThrow(
            'No available TCP port found near NaN',
        );
    });

    it('returns a port that can actually be bound', async () => {
        const server = await hold(0);
        const start = portOf(server);
        await release(server);

        const found = await findAvailablePort(start, { maxTries: 5 });
        const bound = await hold(found);
        expect(portOf(bound)).toBe(found);
    });
});