zig-pay/src/services/service_pool.zig

const std = @import("std");

const testing = std.testing;
const expect = testing.expect;

const HttpService = @import("http_service.zig").HttpService;

const s = @import("service.zig");
const ServiceTicket = s.ServiceTicket;

const ServicePoolError = error{ FullPoll, NoServiceAvailable };

pub const ServicePool = struct {
    services: [10]*HttpService = undefined,
    services_len: usize = 0,

    pub fn add(self: *ServicePool, service: *HttpService) ServicePoolError!void {
        if (service.connections.len == 0) {
            return;
        }

        if (self.services_len == self.services.len) {
            return ServicePoolError.FullPoll;
        }

        self.services[self.services_len] = service;
        self.services_len += 1;
    }

    pub fn dive(self: *ServicePool, message: []const u8) ServicePoolError!*ServiceTicket {
        var skip: [10]bool = .{false} ** 10;

        for (0..self.services_len) |_| {
            var best_service = self.findBestService(&skip);

            if (best_service == null) {
                return error.NoServiceAvailable;
            }

            const ticket = best_service.?.queue(message);

            if (ticket == null) {
                continue;
            }

            return ticket.?;
        }

        return error.NoServiceAvailable;
    }

    fn findBestService(self: *ServicePool, skip: []bool) ?*HttpService {
        var first_service_available_i: ?usize = null;
        var best_perfomance_i: ?usize = null;

        for (0..self.services_len) |i| {
            if (skip[i]) {
                continue;
            }

            const service = self.services[i];

            if (service.health == .unavailable or service.capacity >= 90) {
                continue;
            }

            if (first_service_available_i == null) {
                first_service_available_i = i;
            }

            if (best_perfomance_i == null or self.services[best_perfomance_i.?].response_time > service.response_time) {
                best_perfomance_i = i;
            }
        }

        if (best_perfomance_i != null) {
            skip[best_perfomance_i.?] = true;
            return self.services[best_perfomance_i.?];
        }

        if (first_service_available_i != null) {
            skip[first_service_available_i.?] = true;
            return self.services[first_service_available_i.?];
        }

        return null;
    }
};

test "expect error FullPoll if more then 10 service is added" {
    var service_pool = ServicePool{};

    for (0..10) |_| {
        var service = try HttpService.init(1, "default", "one.one.one.one", 53, 40, testing.allocator);
        defer service.deinit();
        try service_pool.add(&service);
    }

    var service = try HttpService.init(1, "default", "one.one.one.one", 53, 40, testing.allocator);
    defer service.deinit();

    service_pool.add(&service) catch |err| {
        try expect(err == ServicePoolError.FullPoll);
        return;
    };

    try expect(false);
}

test "expect NoServiceAvailable if no service has been add" {
    var service_pool = ServicePool{};

    _ = service_pool.dive("test") catch |err| {
        try expect(err == ServicePoolError.NoServiceAvailable);
        return;
    };

    try expect(false);
}

test "expect if NoServiceAvailable all sevice are unavailable" {
    var service_pool = ServicePool{};

    for (0..10) |_| {
        var service = try HttpService.init(1, "default", "one.one.one.one", 53, 40, testing.allocator);
        service.health = .unavailable;
        defer service.deinit();
        try service_pool.add(&service);
    }

    var service = try HttpService.init(2, "default", "one.one.one.one", 53, 40, testing.allocator);
    defer service.deinit();

    service_pool.add(&service) catch |err| {
        try expect(err == ServicePoolError.FullPoll);
        return;
    };

    try expect(false);
}

test "expect choice service with best perfomance" {
    var service_pool = ServicePool{};

    var service1 = try HttpService.init(1, "default", "one.one.one.one", 53, 40, testing.allocator);
    service1.health = .available;
    service1.response_time = 100;
    defer service1.deinit();
    try service_pool.add(&service1);

    var service2 = try HttpService.init(2, "fallback", "one.one.one.one", 53, 40, testing.allocator);
    service2.health = .available;
    service2.response_time = 10;
    defer service2.deinit();
    try service_pool.add(&service2);

    var skip: [10]bool = .{false} ** 10;
    const res = service_pool.findBestService(&skip);

    try expect(res.? == &service2);
    try expect(skip[1]);
}

test "expect choice service first service available if all has the same perfomance" {
    var service_pool = ServicePool{};

    var service1 = try HttpService.init(1, "default", "one.one.one.one", 53, 40, testing.allocator);
    service1.health = .available;
    service1.response_time = 10;
    defer service1.deinit();
    try service_pool.add(&service1);

    var service2 = try HttpService.init(2, "fallback", "one.one.one.one", 53, 40, testing.allocator);
    service2.health = .available;
    service2.response_time = 10;
    defer service2.deinit();
    try service_pool.add(&service2);

    var skip: [10]bool = .{false} ** 10;
    const res = service_pool.findBestService(&skip);

    try expect(res.? == &service1);
    try expect(skip[0]);
}

test "expect choice service with overloaded" {
    var service_pool = ServicePool{};

    var service1 = try HttpService.init(1, "default", "one.one.one.one", 53, 40, testing.allocator);
    service1.health = .available;
    service1.response_time = 10;
    service1.capacity = 90;
    defer service1.deinit();
    try service_pool.add(&service1);

    var service2 = try HttpService.init(2, "fallback", "one.one.one.one", 53, 40, testing.allocator);
    service2.health = .available;
    service2.response_time = 10;
    service2.capacity = 100;
    defer service2.deinit();
    try service_pool.add(&service2);

    var service3 = try HttpService.init(3, "fallback_fallback", "one.one.one.one", 53, 40, testing.allocator);
    service3.health = .available;
    service3.response_time = 10;
    service3.capacity = 50;
    defer service3.deinit();
    try service_pool.add(&service3);

    var skip: [10]bool = .{false} ** 10;
    const res = service_pool.findBestService(&skip);

    try expect(res.? == &service3);
    try expect(skip[2]);
}