//! # Goose
//!
//! Have you ever been attacked by a goose?
//!
//! Goose is a load testing tool inspired by [Locust](https://locust.io/).
//! User behavior is defined with standard Rust code.
//!
//! Goose load tests, called Goose Attacks, are built by creating an application
//! with Cargo, and declaring a dependency on the Goose library.
//!
//! Goose uses [`reqwest`](https://docs.rs/reqwest/) to provide a convenient HTTP
//! client.
//!
//! ## Creating and running a Goose load test
//!
//! ### Creating a simple Goose load test
//!
//! First create a new empty cargo application, for example:
//!
//! ```bash
//! $ cargo new loadtest
//!      Created binary (application) `loadtest` package
//! $ cd loadtest/
//! ```
//!
//! Add Goose as a dependency in `Cargo.toml`:
//!
//! ```toml
//! [dependencies]
//! goose = "0.8"
//! ```
//!
//! Add the following boilerplate `use` declaration at the top of your `src/main.rs`:
//!
//! ```rust
//! use goose::prelude::*;
//! ```
//!
//! Using the above prelude will automatically add the following `use` statements
//! necessary for your load test, so you don't need to manually add them:
//!
//! ```rust
//! use goose::{GooseAttack, task, taskset};
//! use goose::goose::{GooseTaskSet, GooseUser, GooseTask};
//! ```
//!
//! Below your `main` function (which currently is the default `Hello, world!`), add
//! one or more load test functions. The names of these functions are arbitrary, but it is
//! recommended you use self-documenting names. Load test functions must be async. Each load
//! test function must accept a GooseUser pointer. For example:
//!
//! ```rust
//! use goose::prelude::*;
//!
//! async fn loadtest_foo(user: &GooseUser) {
//!   let _response = user.get("/path/to/foo");
//! }   
//! ```
//!
//! In the above example, we're using the GooseUser helper method `get` to load a path
//! on the website we are load testing. This helper creates a Reqwest request builder, and
//! uses it to build and execute a request for the above path. If you want access to the
//! request builder object, you can instead use the `goose_get` helper, for example to
//! set a timout on this specific request:
//!
//! ```rust
//! use std::time;
//!
//! use goose::prelude::*;
//!
//! async fn loadtest_bar(user: &GooseUser) {
//!   let request_builder = user.goose_get("/path/to/bar").await;
//!   let _response = user.goose_send(request_builder.timeout(time::Duration::from_secs(3)), None).await;
//! }   
//! ```
//!
//! We pass the `request_builder` object to `goose_send` which builds and executes it, also
//! collecting useful statistics. The `.await` at the end is necessary as `goose_send` is an
//! async function.
//!
//! Once all our tasks are created, we edit the main function to initialize goose and register
//! the tasks. In this very simple example we only have two tasks to register, while in a real
//! load test you can have any number of task sets with any number of individual tasks.
//!
//! ```rust,no_run
//! use goose::prelude::*;
//!
//! GooseAttack::initialize()
//!     .register_taskset(taskset!("LoadtestTasks")
//!         .set_wait_time(0, 3)
//!         // Register the foo task, assigning it a weight of 10.
//!         .register_task(task!(loadtest_foo).set_weight(10))
//!         // Register the bar task, assigning it a weight of 2 (so it
//!         // runs 1/5 as often as bar). Apply a task name which shows up
//!         // in statistics.
//!         .register_task(task!(loadtest_bar).set_name("bar").set_weight(2))
//!     )
//!     // You could also set a default host here, for example:
//!     //.set_host("http://dev.local/")
//!     .execute();
//!
//! async fn loadtest_foo(user: &GooseUser) {
//!   let _response = user.get("/path/to/foo");
//! }   
//!
//! async fn loadtest_bar(user: &GooseUser) {
//!   let _response = user.get("/path/to/bar");
//! }   
//! ```
//!
//! Goose now spins up a configurable number of users, each simulating a user on your
//! website. Thanks to Reqwest, each user maintains its own web client state, handling
//! cookies and more so your "users" can log in, fill out forms, and more, as real users
//! on your sites would do.
//!
//! ### Running the Goose load test
//!
//! Attempts to run our example will result in an error, as we have not yet defined the
//! host against which this load test should be run. We intentionally do not hard code the
//! host in the individual tasks, as this allows us to run the test against different
//! environments, such as local and staging.
//!
//! ```bash
//! $ cargo run --release
//!    Compiling loadtest v0.1.0 (~/loadtest)
//!     Finished release [optimized] target(s) in 1.52s
//!      Running `target/release/loadtest`
//! 05:33:06 [ERROR] Host must be defined globally or per-TaskSet. No host defined for LoadtestTasks.
//! ```
//! Pass in the `-h` flag to see all available run-time options. For now, we'll use a few
//! options to customize our load test.
//!
//! ```bash
//! $ cargo run --release -- --host http://dev.local -t 30s -v
//! ```
//!
//! The first option we specified is `--host`, and in this case tells Goose to run the load test
//! against an 8-core VM on my local network. The `-t 30s` option tells Goose to end the load test
//! after 30 seconds (for real load tests you'll certainly want to run it longer, you can use `m` to
//! specify minutes and `h` to specify hours. For example, `-t 1h30m` would run the load test for 1
//! hour 30 minutes). Finally, the `-v` flag tells goose to display INFO and higher level logs to
//! stdout, giving more insight into what is happening. (Additional `-v` flags will result in
//! considerably more debug output, and are not recommended for running actual load tests; they're
//! only useful if you're trying to debug Goose itself.)
//!
//! Running the test results in the following output (broken up to explain it as it goes):
//!
//! ```bash
//!    Finished release [optimized] target(s) in 0.05s
//!     Running `target/release/loadtest --host 'http://dev.local' -t 30s -v`
//! 05:56:30 [ INFO] Output verbosity level: INFO
//! 05:56:30 [ INFO] Logfile verbosity level: INFO
//! 05:56:30 [ INFO] Writing to log file: goose.log

//! ```
//!
//! By default Goose will write a log file with INFO and higher level logs into the same directory
//! as you run the test from.
//!
//! ```bash
//! 05:56:30 [ INFO] run_time = 30
//! 05:56:30 [ INFO] concurrent users defaulted to 8 (number of CPUs)
//! ```
//!
//! Goose will default to launching 1 user per available CPU core, and will launch them all in
//! one second. You can change how many users are launched with the `-u` option, and you can
//! change how many users are launched per second with the `-r` option. For example, `-u 30 -r 2`
//! would launch 30 users over 15 seconds, or two users per second.
//!
//! ```bash
//! 05:56:30 [ INFO] global host configured: http://dev.local
//! 05:56:30 [ INFO] launching user 1 from LoadtestTasks...
//! 05:56:30 [ INFO] launching user 2 from LoadtestTasks...
//! 05:56:30 [ INFO] launching user 3 from LoadtestTasks...
//! 05:56:30 [ INFO] launching user 4 from LoadtestTasks...
//! 05:56:30 [ INFO] launching user 5 from LoadtestTasks...
//! 05:56:30 [ INFO] launching user 6 from LoadtestTasks...
//! 05:56:30 [ INFO] launching user 7 from LoadtestTasks...
//! 05:56:31 [ INFO] launching user 8 from LoadtestTasks...
//! 05:56:31 [ INFO] launched 8 users...
//! ```
//!
//! Each user is launched in its own thread with its own user state. Goose is able to make
//! very efficient use of server resources.
//!
//! ```bash
//! 05:56:46 [ INFO] printing running statistics after 15 seconds...
//! ------------------------------------------------------------------------------
//!  Name                    | # reqs         | # fails        | req/s  | fail/s
//!  -----------------------------------------------------------------------------
//!  GET /path/to/foo        | 15,795         | 0 (0%)         | 1,053  | 0    
//!  GET bar                 | 3,161          | 0 (0%)         | 210    | 0    
//!  ------------------------+----------------+----------------+--------+---------
//!  Aggregated              | 18,956         | 0 (0%)         | 1,263  | 0    
//! ------------------------------------------------------------------------------
//! ```
//!
//! When printing statistics, by default Goose will display running values approximately
//! every 15 seconds. Running statistics are broken into two tables. The first, above,
//! shows how many requests have been made, how many of them failed (non-2xx response),
//! and the corresponding per-second rates.
//!
//! Note that Goose respected the per-task weights we set, and `foo` (with a weight of
//! 10) is being loaded five times as often as `bar` (with a weight of 2). Also notice
//! that because we didn't name the `foo` task by default we see the URL loaded in the
//! statistics, whereas we did name the `bar` task so we see the name in the statistics.
//!
//! ```bash
//!  Name                    | Avg (ms)   | Min        | Max        | Mean      
//!  -----------------------------------------------------------------------------
//!  GET /path/to/foo        | 67         | 31         | 1351       | 53      
//!  GET bar                 | 60         | 33         | 1342       | 53      
//!  ------------------------+------------+------------+------------+-------------
//!  Aggregated              | 66         | 31         | 1351       | 56      
//! ```
//!
//! The second table in running statistics provides details on response times. In our
//! example (which is running over wifi from my development laptop), on average each
//! page is returning within `66` milliseconds. The quickest page response was for
//! `foo` in `31` milliseconds. The slowest page response was also for `foo` in `1351`
//! milliseconds.
//!
//!
//! ```bash
//! 05:37:10 [ INFO] stopping after 30 seconds...
//! 05:37:10 [ INFO] waiting for users to exit
//! ```
//!
//! Our example only runs for 30 seconds, so we only see running statistics once. When
//! the test completes, we get more detail in the final summary. The first two tables
//! are the same as what we saw earlier, however now they include all statistics for the
//! entire load test:
//!
//! ```bash
//! ------------------------------------------------------------------------------
//!  Name                    | # reqs         | # fails        | req/s  | fail/s
//!  -----------------------------------------------------------------------------
//!  GET bar                 | 6,050          | 0 (0%)         | 201    | 0    
//!  GET /path/to/foo        | 30,257         | 0 (0%)         | 1,008  | 0    
//!  ------------------------+----------------+----------------+--------+----------
//!  Aggregated              | 36,307         | 0 (0%)         | 1,210  | 0    
//! -------------------------------------------------------------------------------
//!  Name                    | Avg (ms)   | Min        | Max        | Mean      
//!  -----------------------------------------------------------------------------
//!  GET bar                 | 66         | 32         | 1388       | 53      
//!  GET /path/to/foo        | 68         | 31         | 1395       | 53      
//!  ------------------------+------------+------------+------------+-------------
//!  Aggregated              | 67         | 31         | 1395       | 50      
//! -------------------------------------------------------------------------------
//! ```
//!
//! The ratio between `foo` and `bar` remained 5:2 as expected. As the test ran,
//! however, we saw some slower page loads, with the slowest again `foo` this time
//! at 1395 milliseconds.
//!
//! ```bash
//! Slowest page load within specified percentile of requests (in ms):
//! ------------------------------------------------------------------------------
//! Name                    | 50%    | 75%    | 98%    | 99%    | 99.9%  | 99.99%
//! -----------------------------------------------------------------------------
//! GET bar                 | 53     | 66     | 217   | 537     | 1872   | 12316
//! GET /path/to/foo        | 53     | 66     | 265   | 1060    | 1800   | 10732
//! ------------------------+--------+--------+-------+---------+--------+-------
//! Aggregated              | 53     | 66     | 237   | 645     | 1832   | 10818
//! ```
//!
//! A new table shows additional information, breaking down response-time by
//! percentile. This shows that the slowest page loads only happened in the
//! slowest .001% of page loads, so were very much an edge case. 99.9% of the time
//! page loads happened in less than 2 seconds.
//!
//! ## License
//!
//! Copyright 2020 Jeremy Andrews
//!
//! Licensed under the Apache License, Version 2.0 (the "License");
//! you may not use this file except in compliance with the License.
//! You may obtain a copy of the License at
//!
//! http://www.apache.org/licenses/LICENSE-2.0
//!
//! Unless required by applicable law or agreed to in writing, software
//! distributed under the License is distributed on an "AS IS" BASIS,
//! WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
//! See the License for the specific language governing permissions and
//! limitations under the License.

#[macro_use]
extern crate log;

extern crate structopt;

pub mod goose;

#[cfg(feature = "gaggle")]
mod manager;
pub mod prelude;
mod stats;
mod user;
mod util;
#[cfg(feature = "gaggle")]
mod worker;

use lazy_static::lazy_static;
#[cfg(feature = "gaggle")]
use nng::Socket;
use serde::{Deserialize, Serialize};
use serde_json::json;
use simplelog::*;
use std::collections::hash_map::DefaultHasher;
use std::collections::{BTreeMap, HashMap};
use std::f32;
use std::hash::{Hash, Hasher};
use std::path::PathBuf;
use std::sync::{
    atomic::{AtomicBool, AtomicUsize, Ordering},
    Arc,
};
use std::time;
use structopt::StructOpt;
use tokio::fs::File;
use tokio::io::BufWriter;
use tokio::prelude::*;
use tokio::sync::mpsc;
use url::Url;

use crate::goose::{
    GooseRawRequest, GooseRequest, GooseTask, GooseTaskSet, GooseUser, GooseUserCommand,
};

/// Constant defining how often statistics should be displayed while load test is running.
const RUNNING_STATS_EVERY: usize = 15;

/// Constant defining Goose's default port when running a Gaggle.
const DEFAULT_PORT: &str = "5115";

// WORKER_ID is only used when running a gaggle (a distributed load test).
lazy_static! {
    static ref WORKER_ID: AtomicUsize = AtomicUsize::new(0);
}

/// Worker ID to aid in tracing logs when running a Gaggle.
pub fn get_worker_id() -> usize {
    WORKER_ID.load(Ordering::Relaxed)
}

#[cfg(not(feature = "gaggle"))]
#[derive(Debug)]
/// Socket used for coordinating a Gaggle, a distributed load test.
pub struct Socket {}

/// Internal global state for load test.
#[derive(Clone)]
pub struct GooseAttack {
    /// An optional task to run one time before starting users and running task sets.
    test_start_task: Option<GooseTask>,
    /// An optional task to run one time after users have finished running task sets.
    test_stop_task: Option<GooseTask>,
    /// A vector containing one copy of each GooseTaskSet that will run during this load test.
    task_sets: Vec<GooseTaskSet>,
    /// A checksum of the task_sets vector to be sure all workers are running the same load test.
    task_sets_hash: u64,
    /// A weighted vector containing a GooseUser object for each user that will run during this load test.
    weighted_users: Vec<GooseUser>,
    /// An optional default host to run this load test against.
    host: Option<String>,
    /// Configuration object managed by StructOpt.
    configuration: GooseConfiguration,
    /// By default launch 1 user per number of CPUs.
    number_of_cpus: usize,
    /// Track how long the load test should run.
    run_time: usize,
    /// Track total number of users to run for this load test.
    users: usize,
    /// Track how many users are already loaded.
    active_users: usize,
    /// All requests statistics merged together.
    merged_requests: HashMap<String, GooseRequest>,
}
/// Goose's internal global state.
impl GooseAttack {
    /// Load configuration from command line and initialize a GooseAttack.
    ///
    /// # Example
    /// ```rust,no_run
    ///     use goose::prelude::*;
    ///
    ///     let mut goose_attack = GooseAttack::initialize();
    /// ```
    pub fn initialize() -> GooseAttack {
        let goose_attack = GooseAttack {
            test_start_task: None,
            test_stop_task: None,
            task_sets: Vec::new(),
            task_sets_hash: 0,
            weighted_users: Vec::new(),
            host: None,
            configuration: GooseConfiguration::from_args(),
            number_of_cpus: num_cpus::get(),
            run_time: 0,
            users: 0,
            active_users: 0,
            merged_requests: HashMap::new(),
        };
        goose_attack.setup()
    }

    /// Initialize a GooseAttack with an already loaded configuration.
    /// This should only be called by worker instances.
    ///
    /// # Example
    /// ```rust,no_run
    ///     use goose::{GooseAttack, GooseConfiguration};
    ///     use structopt::StructOpt;
    ///
    ///     let configuration = GooseConfiguration::from_args();
    ///     let mut goose_attack = GooseAttack::initialize_with_config(configuration);
    /// ```
    pub fn initialize_with_config(config: GooseConfiguration) -> GooseAttack {
        GooseAttack {
            test_start_task: None,
            test_stop_task: None,
            task_sets: Vec::new(),
            task_sets_hash: 0,
            weighted_users: Vec::new(),
            host: None,
            configuration: config,
            number_of_cpus: num_cpus::get(),
            run_time: 0,
            users: 0,
            active_users: 0,
            merged_requests: HashMap::new(),
        }
    }

    pub fn initialize_logger(&self) {
        // Allow optionally controlling debug output level
        let debug_level;
        match self.configuration.verbose {
            0 => debug_level = LevelFilter::Warn,
            1 => debug_level = LevelFilter::Info,
            2 => debug_level = LevelFilter::Debug,
            _ => debug_level = LevelFilter::Trace,
        }

        // Allow optionally controlling log level
        let log_level;
        match self.configuration.log_level {
            0 => log_level = LevelFilter::Info,
            1 => log_level = LevelFilter::Debug,
            _ => log_level = LevelFilter::Trace,
        }

        let log_file = PathBuf::from(&self.configuration.log_file);

        match CombinedLogger::init(vec![
            match TermLogger::new(debug_level, Config::default(), TerminalMode::Mixed) {
                Some(t) => t,
                None => {
                    eprintln!("failed to initialize TermLogger");
                    return;
                }
            },
            WriteLogger::new(
                log_level,
                Config::default(),
                std::fs::File::create(&log_file).unwrap(),
            ),
        ]) {
            Ok(_) => (),
            Err(e) => {
                info!("failed to initialize CombinedLogger: {}", e);
            }
        }
        info!("Output verbosity level: {}", debug_level);
        info!("Logfile verbosity level: {}", log_level);
        info!("Writing to log file: {}", log_file.display());
    }

    pub fn setup(mut self) -> Self {
        self.initialize_logger();

        // Collecting statistics is required for the following options.
        if self.configuration.no_stats {
            // Don't allow overhead of collecting statistics unless we're printing them.
            if self.configuration.status_codes {
                error!("You must not enable --no-stats when enabling --status-codes.");
                std::process::exit(1);
            }

            // Don't allow overhead of collecting statistics unless we're printing them.
            if self.configuration.only_summary {
                error!("You must not enable --no-stats when enabling --only-summary.");
                std::process::exit(1);
            }

            // There is nothing to log if statistics are disabled.
            if !self.configuration.stats_log_file.is_empty() {
                error!("You must not enable --no-stats when enabling --stats-log-file.");
                std::process::exit(1);
            }

            // There is nothing to log if statistics are disabled.
            if !self.configuration.stats_log_file.is_empty() {
                error!("You must not enable --no-stats when enabling --stats-log-format.");
                std::process::exit(1);
            }
        }

        if self.configuration.stats_log_format != "json" {
            // Log format isn't relevant if log not enabled.
            if self.configuration.stats_log_file.is_empty() {
                error!("You must enable --stats-log-file when setting --stats-log-format.");
                std::process::exit(1);
            }

            // All of these options must be defined below, search for formatted_log.
            let options = vec!["json", "csv", "raw"];
            if !options.contains(&self.configuration.stats_log_format.as_str()) {
                error!(
                    "The --stats-log-format must be set to one of: {}.",
                    options.join(", ")
                );
                std::process::exit(1);
            }
        }

        // Configure maximum run time if specified, otherwise run until canceled.
        if self.configuration.worker {
            if self.configuration.run_time != "" {
                error!("The --run-time option is only available to the manager.");
                std::process::exit(1);
            }
            self.run_time = 0;
        } else if self.configuration.run_time != "" {
            self.run_time = util::parse_timespan(&self.configuration.run_time);
            info!("run_time = {}", self.run_time);
        } else {
            self.run_time = 0;
        }

        // Configure number of user threads to launch, default to the number of CPU cores available.
        self.users = match self.configuration.users {
            Some(u) => {
                if u == 0 {
                    if self.configuration.worker {
                        error!("At least 1 user is required.");
                        std::process::exit(1);
                    } else {
                        0
                    }
                } else {
                    if self.configuration.worker {
                        error!("The --users option is only available to the manager.");
                        std::process::exit(1);
                    }
                    u
                }
            }
            None => {
                let u = self.number_of_cpus;
                if !self.configuration.manager && !self.configuration.worker {
                    info!("concurrent users defaulted to {} (number of CPUs)", u);
                }
                u
            }
        };

        if !self.configuration.manager && !self.configuration.worker {
            debug!("users = {}", self.users);
        }

        self
    }

    /// A load test must contain one or more `GooseTaskSet`s. Each task set must
    /// be registered into Goose's global state with this method for it to run.
    ///
    /// # Example
    /// ```rust,no_run
    ///     use goose::prelude::*;
    ///
    ///     GooseAttack::initialize()
    ///         .register_taskset(taskset!("ExampleTasks")
    ///             .register_task(task!(example_task))
    ///         )
    ///         .register_taskset(taskset!("OtherTasks")
    ///             .register_task(task!(other_task))
    ///         );
    ///
    ///     async fn example_task(user: &GooseUser) {
    ///       let _response = user.get("/foo");
    ///     }
    ///
    ///     async fn other_task(user: &GooseUser) {
    ///       let _response = user.get("/bar");
    ///     }
    /// ```
    pub fn register_taskset(mut self, mut taskset: GooseTaskSet) -> Self {
        taskset.task_sets_index = self.task_sets.len();
        self.task_sets.push(taskset);
        self
    }

    /// Optionally define a task to run before users are started and all task sets
    /// start running. This is would generally be used to set up anything required
    /// for the load test.
    ///
    /// When running in a distributed Gaggle, this task is only run one time by the
    /// Manager.
    ///
    /// # Example
    /// ```rust,no_run
    ///     use goose::prelude::*;
    ///
    ///     GooseAttack::initialize()
    ///         .test_start(task!(setup));
    ///
    ///     async fn setup(user: &GooseUser) {
    ///         // do stuff to set up load test ...
    ///     }
    /// ```
    pub fn test_start(mut self, task: GooseTask) -> Self {
        self.test_start_task = Some(task);
        self
    }

    /// Optionally define a task to run after all users have finished running
    /// all defined task sets. This would generally be used to clean up anything
    /// that was specifically set up for the load test.
    ///
    /// When running in a distributed Gaggle, this task is only run one time by the
    /// Manager.
    ///
    /// # Example
    /// ```rust,no_run
    ///     use goose::prelude::*;
    ///
    ///     GooseAttack::initialize()
    ///         .test_stop(task!(teardown));
    ///
    ///     async fn teardown(user: &GooseUser) {
    ///         // do stuff to tear down the load test ...
    ///     }
    /// ```
    pub fn test_stop(mut self, task: GooseTask) -> Self {
        self.test_stop_task = Some(task);
        self
    }

    /// Optionally configure a default host for the load test. This is used if
    /// no per-GooseTaskSet host is defined, no `--host` CLI option is configurared,
    /// and if the GooseTask itself doesn't hard-code the host in its request. The
    /// host is prepended on all requests.
    ///
    /// For example, your load test may default to running against your local development
    /// container, and the `--host` option could be used to override host to run the load
    /// test against production.
    ///
    /// # Example
    /// ```rust,no_run
    ///     use goose::prelude::*;
    ///
    ///     GooseAttack::initialize()
    ///         .set_host("local.dev");
    /// ```
    pub fn set_host(mut self, host: &str) -> Self {
        trace!("set_host: {}", host);
        // Host validation happens in main() at startup.
        self.host = Some(host.to_string());
        self
    }

    /// Allocate a vector of weighted GooseUser.
    fn weight_task_set_users(&mut self) -> Vec<GooseUser> {
        trace!("weight_task_set_users");

        let mut u: usize = 0;
        let mut v: usize;
        for task_set in &self.task_sets {
            if u == 0 {
                u = task_set.weight;
            } else {
                v = task_set.weight;
                trace!("calculating greatest common denominator of {} and {}", u, v);
                u = util::gcd(u, v);
                trace!("inner gcd: {}", u);
            }
        }
        // 'u' will always be the greatest common divisor
        debug!("gcd: {}", u);

        // Build a weighted lists of task sets (identified by index)
        let mut weighted_task_sets = Vec::new();
        for (index, task_set) in self.task_sets.iter().enumerate() {
            // divide by greatest common divisor so vector is as short as possible
            let weight = task_set.weight / u;
            trace!(
                "{}: {} has weight of {} (reduced with gcd to {})",
                index,
                task_set.name,
                task_set.weight,
                weight
            );
            let mut weighted_sets = vec![index; weight];
            weighted_task_sets.append(&mut weighted_sets);
        }

        // Allocate a state for each user that will be spawned.
        info!("initializing user states...");
        let mut weighted_users = Vec::new();
        let mut user_count = 0;
        let config = self.configuration.clone();
        loop {
            for task_sets_index in &weighted_task_sets {
                let base_url = goose::get_base_url(
                    Some(config.host.to_string()),
                    self.task_sets[*task_sets_index].host.clone(),
                    self.host.clone(),
                );
                weighted_users.push(GooseUser::new(
                    self.task_sets[*task_sets_index].task_sets_index,
                    base_url,
                    self.task_sets[*task_sets_index].min_wait,
                    self.task_sets[*task_sets_index].max_wait,
                    &config,
                    self.task_sets_hash,
                ));
                user_count += 1;
                if user_count >= self.users {
                    trace!("created {} weighted_users", user_count);
                    return weighted_users;
                }
            }
        }
    }

    /// Execute the load test.
    ///
    /// # Example
    /// ```rust,no_run
    ///     use goose::prelude::*;
    ///
    ///     GooseAttack::initialize()
    ///         .register_taskset(taskset!("ExampleTasks")
    ///             .register_task(task!(example_task).set_weight(2))
    ///             .register_task(task!(another_example_task).set_weight(3))
    ///         )
    ///         .execute();
    ///
    ///     async fn example_task(user: &GooseUser) {
    ///       let _response = user.get("/foo");
    ///     }
    ///
    ///     async fn another_example_task(user: &GooseUser) {
    ///       let _response = user.get("/bar");
    ///     }
    /// ```
    pub fn execute(mut self) {
        // At least one task set is required.
        if self.task_sets.is_empty() {
            error!("No task sets defined.");
            std::process::exit(1);
        }

        if self.configuration.list {
            // Display task sets and tasks, then exit.
            println!("Available tasks:");
            for task_set in self.task_sets {
                println!(" - {} (weight: {})", task_set.name, task_set.weight);
                for task in task_set.tasks {
                    println!("    o {} (weight: {})", task.name, task.weight);
                }
            }
            std::process::exit(0);
        }

        // Manager mode.
        if self.configuration.manager {
            // @TODO: support running in both manager and worker mode.
            if self.configuration.worker {
                error!("You can only run in manager or worker mode, not both.");
                std::process::exit(1);
            }

            if self.configuration.expect_workers < 1 {
                error!("You must set --expect-workers to 1 or more.");
                std::process::exit(1);
            }
            if self.configuration.expect_workers as usize > self.users {
                error!(
                    "You must enable at least as many users ({}) as workers ({}).",
                    self.users, self.configuration.expect_workers
                );
                std::process::exit(1);
            }
        }

        // Worker mode.
        if self.configuration.worker {
            // @TODO: support running in both manager and worker mode.
            if self.configuration.manager {
                error!("You can only run in manager or worker mode, not both.");
                std::process::exit(1);
            }

            if self.configuration.expect_workers > 0 {
                error!("The --expect-workers option is only available to the manager");
                std::process::exit(1);
            }

            if self.configuration.host != "" {
                error!("The --host option is only available to the manager");
                std::process::exit(1);
            }

            if self.configuration.manager_bind_host != "0.0.0.0" {
                error!("The --manager-bind-host option is only available to the manager");
                std::process::exit(1);
            }

            let default_port: u16 = DEFAULT_PORT.to_string().parse().unwrap();
            if self.configuration.manager_bind_port != default_port {
                error!("The --manager-bind-port option is only available to the manager");
                std::process::exit(1);
            }

            if self.configuration.no_stats {
                error!("The --no-stats option is only available to the manager");
                std::process::exit(1);
            }

            if self.configuration.only_summary {
                error!("The --only-summary option is only available to the manager");
                std::process::exit(1);
            }

            if self.configuration.status_codes {
                error!("The --status-codes option is only available to the manager");
                std::process::exit(1);
            }

            if self.configuration.no_hash_check {
                error!("The --no-hash-check option is only available to the manager");
                std::process::exit(1);
            }
        }

        if !self.configuration.manager
            && !self.configuration.worker
            && self.configuration.no_hash_check
        {
            error!("The --no-hash-check option is only available when running in manager mode");
            std::process::exit(1);
        }

        // Configure number of user threads to launch per second, defaults to 1.
        let hatch_rate = self.configuration.hatch_rate;
        if hatch_rate < 1 {
            error!("Hatch rate must be greater than 0, or no users will launch.");
            std::process::exit(1);
        }
        if hatch_rate > 1 && self.configuration.worker {
            error!("The --hatch-rate option is only available to the manager");
            std::process::exit(1);
        }
        debug!("hatch_rate = {}", hatch_rate);

        // Confirm there's either a global host, or each task set has a host defined.
        if self.configuration.host.is_empty() {
            for task_set in &self.task_sets {
                match &task_set.host {
                    Some(h) => {
                        if is_valid_host(h) {
                            info!("host for {} configured: {}", task_set.name, h);
                        }
                    }
                    None => match &self.host {
                        Some(h) => {
                            if is_valid_host(h) {
                                info!("host for {} configured: {}", task_set.name, h);
                            }
                        }
                        None => {
                            if !self.configuration.worker {
                                error!("Host must be defined globally or per-TaskSet. No host defined for {}.", task_set.name);
                                std::process::exit(1);
                            }
                        }
                    },
                }
            }
        } else if is_valid_host(&self.configuration.host) {
            info!("global host configured: {}", self.configuration.host);
        }

        // Apply weights to tasks in each task set.
        for task_set in &mut self.task_sets {
            let (weighted_on_start_tasks, weighted_tasks, weighted_on_stop_tasks) =
                weight_tasks(&task_set);
            task_set.weighted_on_start_tasks = weighted_on_start_tasks;
            task_set.weighted_tasks = weighted_tasks;
            task_set.weighted_on_stop_tasks = weighted_on_stop_tasks;
            debug!(
                "weighted {} on_start: {:?} tasks: {:?} on_stop: {:?}",
                task_set.name,
                task_set.weighted_on_start_tasks,
                task_set.weighted_tasks,
                task_set.weighted_on_stop_tasks
            );
        }

        // Allocate a state for each of the users we are about to start.
        if !self.configuration.worker {
            self.weighted_users = self.weight_task_set_users();
        }

        // Calculate a unique hash for the current load test.
        let mut s = DefaultHasher::new();
        self.task_sets.hash(&mut s);
        self.task_sets_hash = s.finish();
        debug!("task_sets_hash: {}", self.task_sets_hash);

        // Our load test is officially starting.
        let started = time::Instant::now();
        // Spawn users at hatch_rate per second, or one every 1 / hatch_rate fraction of a second.
        let sleep_float = 1.0 / hatch_rate as f32;
        let sleep_duration = time::Duration::from_secs_f32(sleep_float);

        // Start goose in manager mode.
        if self.configuration.manager {
            #[cfg(feature = "gaggle")]
            {
                let mut rt = tokio::runtime::Runtime::new().unwrap();
                self = rt.block_on(manager::manager_main(self));
            }

            #[cfg(not(feature = "gaggle"))]
            {
                error!(
                    "goose must be recompiled with `--features gaggle` to start in manager mode"
                );
                std::process::exit(1);
            }
        }
        // Start goose in worker mode.
        else if self.configuration.worker {
            #[cfg(feature = "gaggle")]
            {
                let mut rt = tokio::runtime::Runtime::new().unwrap();
                self = rt.block_on(worker::worker_main(&self));
            }

            #[cfg(not(feature = "gaggle"))]
            {
                error!("goose must be recompiled with `--features gaggle` to start in worker mode");
                std::process::exit(1);
            }
        }
        // Start goose in single-process mode.
        else {
            let mut rt = tokio::runtime::Runtime::new().unwrap();
            self = rt.block_on(self.launch_users(started, sleep_duration, None));
        }

        if !self.configuration.no_stats && !self.configuration.worker {
            stats::print_final_stats(&self, started.elapsed().as_secs() as usize);
        }
    }

    /// Helper to wrap configured host in Option<> if set.
    fn get_configuration_host(&self) -> Option<String> {
        if self.configuration.host.is_empty() {
            None
        } else {
            Some(self.configuration.host.to_string())
        }
    }

    /// Helper to create CSV-formatted logs.
    fn prepare_csv(raw_request: &GooseRawRequest, header: &mut bool) -> String {
        let body = format!(
            // Put quotes around name, url and final_url as they are strings.
            "{},{:?},\"{}\",\"{}\",\"{}\",{},{},{},{},{},{}",
            raw_request.elapsed,
            raw_request.method,
            raw_request.name,
            raw_request.url,
            raw_request.final_url,
            raw_request.redirected,
            raw_request.response_time,
            raw_request.status_code,
            raw_request.success,
            raw_request.update,
            raw_request.user
        );
        // Concatenate the header before the body one time.
        if *header {
            *header = false;
            format!(
                // No quotes needed in header.
                "{},{},{},{},{},{},{},{},{},{},{}\n",
                "elapsed",
                "method",
                "name",
                "url",
                "final_url",
                "redirected",
                "response_time",
                "status_code",
                "success",
                "update",
                "user"
            ) + &body
        } else {
            body
        }
    }

    /// Called internally in local-mode and gaggle-mode.
    async fn launch_users(
        mut self,
        mut started: time::Instant,
        sleep_duration: time::Duration,
        socket: Option<Socket>,
    ) -> GooseAttack {
        trace!(
            "launch users: started({:?}) sleep_duration({:?}) socket({:?})",
            started,
            sleep_duration,
            socket
        );

        // Initilize per-user states.
        if !self.configuration.worker {
            // First run global test_start_task, if defined.
            match &self.test_start_task {
                Some(t) => {
                    info!("running test_start_task");
                    // Create a one-time-use User to run the test_start_task.
                    let base_url =
                        goose::get_base_url(self.get_configuration_host(), None, self.host.clone());
                    let user = GooseUser::single(base_url, &self.configuration);
                    let function = t.function;
                    function(&user).await;
                }
                // No test_start_task defined, nothing to do.
                None => (),
            }
        }

        // Collect user threads in a vector for when we want to stop them later.
        let mut users = vec![];
        // Collect user thread channels in a vector so we can talk to the user threads.
        let mut user_channels = vec![];
        // Create a single channel allowing all Goose child threads to sync state back to parent
        let (all_threads_sender, mut parent_receiver): (
            mpsc::UnboundedSender<GooseRawRequest>,
            mpsc::UnboundedReceiver<GooseRawRequest>,
        ) = mpsc::unbounded_channel();
        // Spawn users, each with their own weighted task_set.
        for mut thread_user in self.weighted_users.clone() {
            // Stop launching threads if the run_timer has expired.
            if util::timer_expired(started, self.run_time) {
                break;
            }

            // Copy weighted tasks and weighted on start tasks into the user thread.
            thread_user.weighted_tasks = self.task_sets[thread_user.task_sets_index]
                .weighted_tasks
                .clone();
            thread_user.weighted_on_start_tasks = self.task_sets[thread_user.task_sets_index]
                .weighted_on_start_tasks
                .clone();
            thread_user.weighted_on_stop_tasks = self.task_sets[thread_user.task_sets_index]
                .weighted_on_stop_tasks
                .clone();
            // Remember which task group this user is using.
            thread_user.weighted_users_index = self.active_users;

            // Create a per-thread channel allowing parent thread to control child threads.
            let (parent_sender, thread_receiver): (
                mpsc::UnboundedSender<GooseUserCommand>,
                mpsc::UnboundedReceiver<GooseUserCommand>,
            ) = mpsc::unbounded_channel();
            user_channels.push(parent_sender);

            // Copy the user-to-parent sender channel, used by all threads.
            thread_user.parent = Some(all_threads_sender.clone());

            // Copy the appropriate task_set into the thread.
            let thread_task_set = self.task_sets[thread_user.task_sets_index].clone();

            // We number threads from 1 as they're human-visible (in the logs), whereas active_users starts at 0.
            let thread_number = self.active_users + 1;

            let is_worker = self.configuration.worker;

            // Launch a new user.
            let user = tokio::spawn(user::user_main(
                thread_number,
                thread_task_set,
                thread_user,
                thread_receiver,
                is_worker,
            ));

            users.push(user);
            self.active_users += 1;
            debug!("sleeping {:?} milliseconds...", sleep_duration);
            tokio::time::delay_for(sleep_duration).await;
        }
        // Restart the timer now that all threads are launched.
        started = time::Instant::now();
        if self.configuration.worker {
            info!(
                "[{}] launched {} users...",
                get_worker_id(),
                self.active_users
            );
        } else {
            info!("launched {} users...", self.active_users);
        }

        // Track whether or not we've (optionally) reset the statistics after all users started.
        let mut statistics_reset: bool = false;

        // Catch ctrl-c to allow clean shutdown to display statistics.
        let canceled = Arc::new(AtomicBool::new(false));
        util::setup_ctrlc_handler(&canceled);

        // Determine when to display running statistics (if enabled).
        let mut statistics_timer = time::Instant::now();
        let mut display_running_statistics = false;

        // Prepare an asynchronous buffered file writer for stats_log_file (if enabled).
        let mut stats_log_file = None;
        if !self.configuration.no_stats && !self.configuration.stats_log_file.is_empty() {
            stats_log_file = match File::create(&self.configuration.stats_log_file).await {
                Ok(f) => Some(BufWriter::new(f)),
                Err(e) => {
                    error!(
                        "failed to create stats_log_file ({}): {}",
                        self.configuration.stats_log_file, e
                    );
                    std::process::exit(1);
                }
            }
        }

        // If logging stats to CSV, use this flag to write header; otherwise it's ignored.
        let mut header = true;
        loop {
            // When displaying running statistics, sync data from user threads first.
            if !self.configuration.no_stats {
                // Synchronize statistics from user threads into parent.
                if util::timer_expired(statistics_timer, RUNNING_STATS_EVERY) {
                    statistics_timer = time::Instant::now();
                    if !self.configuration.only_summary {
                        display_running_statistics = true;
                    }
                }

                // Load messages from user threads until the receiver queue is empty.
                let mut received_message = false;
                let mut message = parent_receiver.try_recv();
                while message.is_ok() {
                    received_message = true;
                    let raw_request = message.unwrap();

                    // Options should appear above, search for formatted_log.
                    let formatted_log = match self.configuration.stats_log_format.as_str() {
                        // Use serde_json to create JSON.
                        "json" => json!(raw_request).to_string(),
                        // Manually create CSV, library doesn't support single-row string conversion.
                        "csv" => GooseAttack::prepare_csv(&raw_request, &mut header),
                        // Raw format is Debug output for GooseRawRequest structure.
                        "raw" => format!("{:?}", raw_request).to_string(),
                        _ => unreachable!(),
                    };

                    match stats_log_file.as_mut() {
                        Some(file) => {
                            match file.write(format!("{}\n", formatted_log).as_ref()).await {
                                Ok(_) => (),
                                Err(e) => {
                                    warn!(
                                        "failed to write statistics to {}: {}",
                                        &self.configuration.stats_log_file, e
                                    );
                                }
                            }
                        }
                        None => (),
                    }

                    let key = format!("{:?} {}", raw_request.method, raw_request.name);
                    let mut merge_request = match self.merged_requests.get(&key) {
                        Some(m) => m.clone(),
                        None => GooseRequest::new(&raw_request.name, raw_request.method, 0),
                    };
                    // Handle a statistics update.
                    if raw_request.update {
                        if raw_request.success {
                            merge_request.success_count += 1;
                            merge_request.fail_count -= 1;
                        } else {
                            merge_request.success_count -= 1;
                            merge_request.fail_count += 1;
                        }
                    }
                    // Store a new statistic.
                    else {
                        merge_request.set_response_time(raw_request.response_time);
                        merge_request.set_status_code(raw_request.status_code);
                        if raw_request.success {
                            merge_request.success_count += 1;
                        } else {
                            merge_request.fail_count += 1;
                        }
                    }

                    self.merged_requests.insert(key.to_string(), merge_request);
                    message = parent_receiver.try_recv();
                }

                // As worker, push statistics up to manager.
                if self.configuration.worker && received_message {
                    #[cfg(feature = "gaggle")]
                    {
                        // Push all statistics to manager process.
                        if !worker::push_stats_to_manager(
                            &socket.clone().unwrap(),
                            &self.merged_requests.clone(),
                            true,
                        ) {
                            // EXIT received, cancel.
                            canceled.store(true, Ordering::SeqCst);
                        }
                        // The manager has all our statistics, reset locally.
                        self.merged_requests = HashMap::new();
                    }
                }

                // Flush statistics collected prior to all user threads running
                if self.configuration.reset_stats && !statistics_reset {
                    info!("statistics reset...");
                    self.merged_requests = HashMap::new();
                    statistics_reset = true;
                }
            }

            if util::timer_expired(started, self.run_time) || canceled.load(Ordering::SeqCst) {
                if self.configuration.worker {
                    info!(
                        "[{}] stopping after {} seconds...",
                        get_worker_id(),
                        started.elapsed().as_secs()
                    );
                } else {
                    info!("stopping after {} seconds...", started.elapsed().as_secs());
                }
                for (index, send_to_user) in user_channels.iter().enumerate() {
                    match send_to_user.send(GooseUserCommand::EXIT) {
                        Ok(_) => {
                            debug!("telling user {} to exit", index);
                        }
                        Err(e) => {
                            info!("failed to tell user {} to exit: {}", index, e);
                        }
                    }
                }
                if self.configuration.worker {
                    info!("[{}] waiting for users to exit", get_worker_id());
                } else {
                    info!("waiting for users to exit");
                }
                futures::future::join_all(users).await;
                debug!("all users exited");

                // If we're printing statistics, collect the final messages received from users.
                if !self.configuration.no_stats {
                    let mut message = parent_receiver.try_recv();
                    while message.is_ok() {
                        let raw_request = message.unwrap();
                        let key = format!("{:?} {}", raw_request.method, raw_request.name);
                        let mut merge_request = match self.merged_requests.get(&key) {
                            Some(m) => m.clone(),
                            None => GooseRequest::new(&raw_request.name, raw_request.method, 0),
                        };
                        merge_request.set_response_time(raw_request.response_time);
                        merge_request.set_status_code(raw_request.status_code);
                        if raw_request.success {
                            merge_request.success_count += 1;
                        } else {
                            merge_request.fail_count += 1;
                        }

                        self.merged_requests.insert(key.to_string(), merge_request);
                        message = parent_receiver.try_recv();
                    }
                }

                #[cfg(feature = "gaggle")]
                {
                    // As worker, push statistics up to manager.
                    if self.configuration.worker {
                        // Push all statistics to manager process.
                        worker::push_stats_to_manager(
                            &socket.clone().unwrap(),
                            &self.merged_requests.clone(),
                            true,
                        );
                        // No need to reset local stats, the worker is exiting.
                    }
                }

                // All users are done, exit out of loop for final cleanup.
                break;
            }

            // If enabled, display running statistics after sync
            if display_running_statistics {
                display_running_statistics = false;
                stats::print_running_stats(&self, started.elapsed().as_secs() as usize);
            }

            let one_second = time::Duration::from_secs(1);
            tokio::time::delay_for(one_second).await;
        }

        if !self.configuration.worker {
            // Run global test_stop_task, if defined.
            match &self.test_stop_task {
                Some(t) => {
                    info!("running test_stop_task");
                    let base_url =
                        goose::get_base_url(self.get_configuration_host(), None, self.host.clone());
                    // Create a one-time-use user to run the test_stop_task.
                    let user = GooseUser::single(base_url, &self.configuration);
                    let function = t.function;
                    function(&user).await;
                }
                // No test_stop_task defined, nothing to do.
                None => (),
            }
        }

        // If stats logging is enabled, flush all stats before we exit.
        match stats_log_file.as_mut() {
            Some(file) => {
                info!(
                    "flushing stats_log_file: {}",
                    &self.configuration.stats_log_file
                );
                match file.flush().await {
                    Ok(_) => (),
                    Err(_) => (),
                }
            }
            None => (),
        };

        self
    }
}

/// CLI options available when launching a Goose load test.
#[derive(StructOpt, Debug, Default, Clone, Serialize, Deserialize)]
#[structopt(name = "Goose")]
pub struct GooseConfiguration {
    /// Host to load test, for example: http://10.21.32.33
    #[structopt(short = "H", long, required = false, default_value = "")]
    pub host: String,

    /// Number of concurrent Goose users (defaults to available CPUs).
    #[structopt(short, long)]
    pub users: Option<usize>,

    /// How many users to spawn per second.
    #[structopt(short = "r", long, required = false, default_value = "1")]
    pub hatch_rate: usize,

    /// Stop after e.g. (300s, 20m, 3h, 1h30m, etc.).
    #[structopt(short = "t", long, required = false, default_value = "")]
    pub run_time: String,

    /// Don't print stats in the console
    #[structopt(long)]
    pub no_stats: bool,

    /// Includes status code counts in console stats
    #[structopt(long)]
    pub status_codes: bool,

    /// Only prints summary stats
    #[structopt(long)]
    pub only_summary: bool,

    /// Resets statistics once hatching has been completed
    #[structopt(long)]
    pub reset_stats: bool,

    /// Shows list of all possible Goose tasks and exits
    #[structopt(short, long)]
    pub list: bool,

    // The number of occurrences of the `v/verbose` flag
    /// Debug level (-v, -vv, -vvv, etc.)
    #[structopt(short = "v", long, parse(from_occurrences))]
    pub verbose: u8,

    // The number of occurrences of the `g/log-level` flag
    /// Log level (-g, -gg, -ggg, etc.)
    #[structopt(short = "g", long, parse(from_occurrences))]
    pub log_level: u8,

    /// Log file name
    #[structopt(long, default_value = "goose.log")]
    pub log_file: String,

    /// Statistics log file name
    #[structopt(short = "s", long, default_value = "")]
    pub stats_log_file: String,

    /// Statistics log format ('csv', 'json', or 'raw')
    #[structopt(long, default_value = "json")]
    pub stats_log_format: String,

    /// User follows redirect of base_url with subsequent requests
    #[structopt(long)]
    pub sticky_follow: bool,

    /// Enables manager mode
    #[structopt(long)]
    pub manager: bool,

    /// Ignore worker load test checksum
    #[structopt(long)]
    pub no_hash_check: bool,

    /// Required when in manager mode, how many workers to expect
    #[structopt(long, required = false, default_value = "0")]
    pub expect_workers: u16,

    /// Define host manager listens on, formatted x.x.x.x
    #[structopt(long, default_value = "0.0.0.0")]
    pub manager_bind_host: String,

    /// Define port manager listens on
    #[structopt(long, default_value=DEFAULT_PORT)]
    pub manager_bind_port: u16,

    /// Enables worker mode
    #[structopt(long)]
    pub worker: bool,

    /// Host manager is running on
    #[structopt(long, default_value = "127.0.0.1")]
    pub manager_host: String,

    /// Port manager is listening on
    #[structopt(long, default_value=DEFAULT_PORT)]
    pub manager_port: u16,
}

/// Returns a sequenced bucket of weighted usize pointers to Goose Tasks
fn weight_tasks(task_set: &GooseTaskSet) -> (Vec<Vec<usize>>, Vec<Vec<usize>>, Vec<Vec<usize>>) {
    trace!("weight_tasks for {}", task_set.name);

    // A BTreeMap of Vectors allows us to group and sort tasks per sequence value.
    let mut sequenced_tasks: BTreeMap<usize, Vec<GooseTask>> = BTreeMap::new();
    let mut sequenced_on_start_tasks: BTreeMap<usize, Vec<GooseTask>> = BTreeMap::new();
    let mut sequenced_on_stop_tasks: BTreeMap<usize, Vec<GooseTask>> = BTreeMap::new();
    let mut unsequenced_tasks: Vec<GooseTask> = Vec::new();
    let mut unsequenced_on_start_tasks: Vec<GooseTask> = Vec::new();
    let mut unsequenced_on_stop_tasks: Vec<GooseTask> = Vec::new();
    let mut u: usize = 0;
    let mut v: usize;
    // Handle ordering of tasks.
    for task in &task_set.tasks {
        if task.sequence > 0 {
            if task.on_start {
                if let Some(sequence) = sequenced_on_start_tasks.get_mut(&task.sequence) {
                    // This is another task with this order value.
                    sequence.push(task.clone());
                } else {
                    // This is the first task with this order value.
                    sequenced_on_start_tasks.insert(task.sequence, vec![task.clone()]);
                }
            }
            // Allow a task to be both on_start and on_stop.
            if task.on_stop {
                if let Some(sequence) = sequenced_on_stop_tasks.get_mut(&task.sequence) {
                    // This is another task with this order value.
                    sequence.push(task.clone());
                } else {
                    // This is the first task with this order value.
                    sequenced_on_stop_tasks.insert(task.sequence, vec![task.clone()]);
                }
            }
            if !task.on_start && !task.on_stop {
                if let Some(sequence) = sequenced_tasks.get_mut(&task.sequence) {
                    // This is another task with this order value.
                    sequence.push(task.clone());
                } else {
                    // This is the first task with this order value.
                    sequenced_tasks.insert(task.sequence, vec![task.clone()]);
                }
            }
        } else {
            if task.on_start {
                unsequenced_on_start_tasks.push(task.clone());
            }
            if task.on_stop {
                unsequenced_on_stop_tasks.push(task.clone());
            }
            if !task.on_start && !task.on_stop {
                unsequenced_tasks.push(task.clone());
            }
        }
        // Look for lowest common divisor amongst all tasks of any weight.
        if u == 0 {
            u = task.weight;
        } else {
            v = task.weight;
            trace!("calculating greatest common denominator of {} and {}", u, v);
            u = util::gcd(u, v);
            trace!("inner gcd: {}", u);
        }
    }
    // 'u' will always be the greatest common divisor
    debug!("gcd: {}", u);

    // Apply weight to sequenced tasks.
    let mut weighted_tasks: Vec<Vec<usize>> = Vec::new();
    for (_sequence, tasks) in sequenced_tasks.iter() {
        let mut sequence_weighted_tasks = Vec::new();
        for task in tasks {
            // divide by greatest common divisor so bucket is as small as possible
            let weight = task.weight / u;
            trace!(
                "{}: {} has weight of {} (reduced with gcd to {})",
                task.tasks_index,
                task.name,
                task.weight,
                weight
            );
            let mut tasks = vec![task.tasks_index; weight];
            sequence_weighted_tasks.append(&mut tasks);
        }
        weighted_tasks.push(sequence_weighted_tasks);
    }
    // Apply weight to unsequenced tasks.
    trace!("created weighted_tasks: {:?}", weighted_tasks);
    let mut weighted_unsequenced_tasks = Vec::new();
    for task in unsequenced_tasks {
        // divide by greatest common divisor so bucket is as small as possible
        let weight = task.weight / u;
        trace!(
            "{}: {} has weight of {} (reduced with gcd to {})",
            task.tasks_index,
            task.name,
            task.weight,
            weight
        );
        let mut tasks = vec![task.tasks_index; weight];
        weighted_unsequenced_tasks.append(&mut tasks);
    }
    // Unsequenced tasks come last.
    if !weighted_unsequenced_tasks.is_empty() {
        weighted_tasks.push(weighted_unsequenced_tasks);
    }

    // Apply weight to on_start sequenced tasks.
    let mut weighted_on_start_tasks: Vec<Vec<usize>> = Vec::new();
    for (_sequence, tasks) in sequenced_on_start_tasks.iter() {
        let mut sequence_on_start_weighted_tasks = Vec::new();
        for task in tasks {
            // divide by greatest common divisor so bucket is as small as possible
            let weight = task.weight / u;
            trace!(
                "{}: {} has weight of {} (reduced with gcd to {})",
                task.tasks_index,
                task.name,
                task.weight,
                weight
            );
            let mut tasks = vec![task.tasks_index; weight];
            sequence_on_start_weighted_tasks.append(&mut tasks);
        }
        weighted_on_start_tasks.push(sequence_on_start_weighted_tasks);
    }
    // Apply weight to unsequenced on_start tasks.
    trace!("created weighted_on_start_tasks: {:?}", weighted_tasks);
    let mut weighted_on_start_unsequenced_tasks = Vec::new();
    for task in unsequenced_on_start_tasks {
        // divide by greatest common divisor so bucket is as small as possible
        let weight = task.weight / u;
        trace!(
            "{}: {} has weight of {} (reduced with gcd to {})",
            task.tasks_index,
            task.name,
            task.weight,
            weight
        );
        let mut tasks = vec![task.tasks_index; weight];
        weighted_on_start_unsequenced_tasks.append(&mut tasks);
    }
    // Unsequenced tasks come lost.
    weighted_on_start_tasks.push(weighted_on_start_unsequenced_tasks);

    // Apply weight to on_stop sequenced tasks.
    let mut weighted_on_stop_tasks: Vec<Vec<usize>> = Vec::new();
    for (_sequence, tasks) in sequenced_on_stop_tasks.iter() {
        let mut sequence_on_stop_weighted_tasks = Vec::new();
        for task in tasks {
            // divide by greatest common divisor so bucket is as small as possible
            let weight = task.weight / u;
            trace!(
                "{}: {} has weight of {} (reduced with gcd to {})",
                task.tasks_index,
                task.name,
                task.weight,
                weight
            );
            let mut tasks = vec![task.tasks_index; weight];
            sequence_on_stop_weighted_tasks.append(&mut tasks);
        }
        weighted_on_stop_tasks.push(sequence_on_stop_weighted_tasks);
    }
    // Apply weight to unsequenced on_stop tasks.
    trace!("created weighted_on_stop_tasks: {:?}", weighted_tasks);
    let mut weighted_on_stop_unsequenced_tasks = Vec::new();
    for task in unsequenced_on_stop_tasks {
        // divide by greatest common divisor so bucket is as small as possible
        let weight = task.weight / u;
        trace!(
            "{}: {} has weight of {} (reduced with gcd to {})",
            task.tasks_index,
            task.name,
            task.weight,
            weight
        );
        let mut tasks = vec![task.tasks_index; weight];
        weighted_on_stop_unsequenced_tasks.append(&mut tasks);
    }
    // Unsequenced tasks come last.
    weighted_on_stop_tasks.push(weighted_on_stop_unsequenced_tasks);

    (
        weighted_on_start_tasks,
        weighted_tasks,
        weighted_on_stop_tasks,
    )
}

fn is_valid_host(host: &str) -> bool {
    match Url::parse(host) {
        Ok(_) => true,
        Err(e) => {
            error!("invalid host '{}': {}", host, e);
            std::process::exit(1);
        }
    }
}
#[cfg(test)]
mod test {
    use super::*;

    #[test]
    fn valid_host() {
        // We can only test valid domains, as we exit on failure.
        // @TODO: rework so we don't exit on failure
        assert_eq!(is_valid_host("http://example.com"), true);
        assert_eq!(is_valid_host("http://example.com/"), true);
        assert_eq!(is_valid_host("https://www.example.com/and/with/path"), true);
        assert_eq!(is_valid_host("foo://example.com"), true);
        assert_eq!(is_valid_host("file:///path/to/file"), true);
    }
}