mod bpf_skel;
pub use bpf_skel::*;
pub mod bpf_intf;

mod mock;
mod task_state;
mod e_core_selector;

#[rustfmt::skip]
mod bpf;
use bpf::*;

use clap::{Arg, ArgAction, Command};
use e_core_selector::{ECoreSelector, RoundRobinSelector};
use scx_utils::UserExitInfo;

use libbpf_rs::OpenObject;
use task_state::TaskState;
use mock::{MockModule, KernelModule, KernelDriver};

use std::collections::{HashMap, VecDeque};
use std::mem::MaybeUninit;
use std::process;
use std::ops::Range;

use anyhow::Result;

const SLICE_US: u64 = 5000;

struct Scheduler<'a> {
    bpf: BpfScheduler<'a>,
    module: Box<dyn KernelModule>,
    task_queue: VecDeque<QueuedTask>,
    no_budget_task_queue: VecDeque<QueuedTask>,
    managed_tasks: HashMap<u32, TaskState>,
    maximum_budget: u64,
    power_cap: u64,
    own_pid: u32,
    p_cores: Range<i32>,
    e_cores: Range<i32>,
    e_core_selector: Box<dyn ECoreSelector>
}

impl<'a> Scheduler<'a> {
    fn init(open_object: &'a mut MaybeUninit<OpenObject>, use_mocking: bool, power_cap: u64) -> Result<Self> {
        let bpf = BpfScheduler::init(
            open_object,
            0,     // exit_dump_len (buffer size of exit info, 0 = default)
            false, // partial (false = include all tasks)
            false, // debug (false = debug mode off)
        )?;
        dbg!("registering rust user space scheduler");
        let module: Box<dyn KernelModule> = if use_mocking {
            Box::new(MockModule)
        } else { 
            Box::new(KernelDriver::default())
        };
        let selector = Box::new(RoundRobinSelector::new(8..16)); //TODO: get real value
        Ok(Self {
            bpf,
            module,
            task_queue: VecDeque::new(),
            no_budget_task_queue: VecDeque::new(),
            managed_tasks: HashMap::new(),
            maximum_budget: u64::MAX,
            power_cap,
            own_pid: process::id(),
            p_cores: 0..8, //TODO: real value
            e_cores: 8..16, //TODO: real value
            e_core_selector: selector,
        })
    }

    fn consume_all_tasks(&mut self) {
        // Consume all tasks that are ready to run.
        //
        // Each task contains the following details:
        //
        // pub struct QueuedTask {
        //     pub pid: i32,              // pid that uniquely identifies a task
        //     pub cpu: i32,              // CPU where the task is running
        //     pub sum_exec_runtime: u64, // Total cpu time
        //     pub weight: u64,           // Task static priority
        //     pub nvcsw: u64,            // Total amount of voluntary context switches
        //     pub slice: u64,            // Remaining time slice budget
        //     pub vtime: u64,            // Current task vruntime / deadline (set by the scheduler)
        // }
        //
        // Although the FIFO scheduler doesn't use these fields, they can provide valuable data for
        // implementing more sophisticated scheduling policies.

        while let Ok(Some(task)) = self.bpf.dequeue_task() {
            // The scheduler itself has to be scheduled regardless of its energy usage
            if task.pid as u32 == self.own_pid {
                self.task_queue.push_back(task);
                continue;
            }

            if let Some(task_state) = self.managed_tasks.get_mut(&(task.pid as u32)) {
                let energy = self.module.read_consumption(task.pid as u64);
                let used_energy = energy - task_state.previous_energy_usage;
                if task_state.budget < used_energy {
                    task_state.budget = 0;
                    self.no_budget_task_queue.push_back(task);
                } else {
                    task_state.budget -= used_energy;
                    self.task_queue.push_back(task);
                }
            } else {
                self.module.start_trace(task.pid as u64);
                self.managed_tasks.insert(task.pid as u32, TaskState {
                    previous_energy_usage: 0,
                    budget: self.maximum_budget,
                    children: vec![],
                });
                self.task_queue.push_back(task);
            }
        }
    }

    fn dispatch_next_task(&mut self) {
        if let Some(task) = self.task_queue.pop_front() {
            // Create a new task to be dispatched, derived from the received enqueued task.
            //
            // pub struct DispatchedTask {
            //     pub pid: i32,      // pid that uniquely identifies a task
            //     pub cpu: i32,      // target CPU selected by the scheduler
            //     pub flags: u64,    // special dispatch flags
            //     pub slice_ns: u64, // time slice assigned to the task (0 = default)
            // }
            //
            // The dispatched task's information are pre-populated from the QueuedTask and they can
            // be modified before dispatching it via self.bpf.dispatch_task().
            let mut dispatched_task = DispatchedTask::new(&task);

            // Decide where the task needs to run (target CPU).
            //
            // A call to select_cpu() will return the most suitable idle CPU for the task,
            // considering its previously used CPU.
            let cpu = self.bpf.select_cpu(task.pid, task.cpu, 0);
            if cpu >= 0 {
                dispatched_task.cpu = cpu;
            } else {
                dispatched_task.flags |= RL_CPU_ANY as u64;
            }

            // Decide for how long the task needs to run (time slice); if not specified
            // SCX_SLICE_DFL will be used by default.
            dispatched_task.slice_ns = SLICE_US;

            // Dispatch the task on the target CPU.
            self.bpf.dispatch_task(&dispatched_task).unwrap();

            // Notify the BPF component of the number of pending tasks and immediately give a
            // chance to run to the dispatched task.
            //TODO: should the pending tasks include the ones that don't have any budget left?
            self.bpf.notify_complete(self.task_queue.len() as u64 + self.no_budget_task_queue.len() as u64);
        } else if let Some(task) = self.no_budget_task_queue.pop_front() {
            //TODO: do something with tasks that have no budget left
            let mut dispatched_task = DispatchedTask::new(&task);

            let cpu = self.e_core_selector.next_core();
            if cpu >= 0 {
                dispatched_task.cpu = cpu;
            } else {
                dispatched_task.flags |= RL_CPU_ANY as u64;
            }

            dispatched_task.slice_ns = SLICE_US;
            self.bpf.dispatch_task(&dispatched_task).unwrap();
            self.bpf.notify_complete(self.task_queue.len() as u64 + self.no_budget_task_queue.len() as u64);
        }
    }

    fn dispatch_tasks(&mut self) {
        loop {
            //TODO: we should probably not do this every time but after a predefined amount of time
            self.reset_budgets_and_garbage_collect();

            // Consume all tasks before dispatching any.
            self.consume_all_tasks();

            // Dispatch one task from the queue.
            self.dispatch_next_task();

            // If no task is ready to run (or in case of error), stop dispatching tasks and notify
            // the BPF component that all tasks have been scheduled / dispatched, with no remaining
            // pending tasks.
            if self.task_queue.is_empty() {
                self.bpf.notify_complete(0);
                break;
            }
        }
    }

    fn run(&mut self) -> Result<UserExitInfo> {
        while !self.bpf.exited() {
            self.dispatch_tasks();
        }
        self.bpf.shutdown_and_report()
    }

    fn get_new_budget(&self) -> u64 {
        //TODO
        u64::MAX
    }

    fn reset_budgets_and_garbage_collect(&mut self) {
        let old_budget = self.maximum_budget;
        self.maximum_budget = self.get_new_budget();

        self.managed_tasks.retain(|key, value| {
            let was_scheduled = value.budget == old_budget;
            if was_scheduled {
                value.budget = self.maximum_budget;
            } else {
                self.module.stop_trace(*key as u64);
            }
            was_scheduled
        });
    }
}

//TODO: get children 
fn main() -> Result<()> {
    let matches = Command::new("Energy User Space Scheduler")
        .arg(Arg::new("mock")
                .short('m')
                .long("mock")
                .help("Use this flag if to activate kernel module mocking")
                .action(ArgAction::SetTrue)
                .required(false))
        .arg(Arg::new("power_cap")
                .long("energy_cap")
                .help("Set a power cap for the processor")
                .required(false)
                .value_name("power in watts"))
        .get_matches();

    let power_cap = *matches.get_one::<u64>("power_cap").unwrap_or(&u64::MAX);
    let use_mocking = matches.get_flag("mock");

    // Initialize and load the FIFO scheduler.
    let mut open_object = MaybeUninit::uninit();
    loop {
        let mut sched = Scheduler::init(&mut open_object, use_mocking, power_cap)?;
        if !sched.run()?.should_restart() {
            break;
        }
    }


    Ok(())
}