//! Starting a manifest program: load it, hand it what the manifest says
//! and nothing else, run it.

use libkos::device::Device as BoardDevice;
use libkos::fs::Storage;
use libkos::syscall;
use types::address::StackPointer;
use types::badge::Badge;
use types::bounded::CapSlot;
use types::permission::{Permission, PermissionSet};

use crate::devices::Devices;
use crate::load::{self, LoadedProcess};
use crate::manifest::{Device, Program};
use crate::spawn::Spawner;

const USER_STACK_TOP: StackPointer = StackPointer::from_raw(0x10000);
const MAX_SERVED: usize = 8;

fn perms(list: &[Permission]) -> PermissionSet {
    list.iter().fold(PermissionSet::empty(), |s, p| s.with(*p))
}

pub(crate) struct Launcher<'a> {
    storage: &'a mut Storage,
    scratch: &'a mut [u8],
    devices: Devices,
    /// The endpoint of every server started so far, by name.
    served: [Option<(&'static str, CapSlot)>; MAX_SERVED],
    /// Init's own endpoint, for the spawn service.
    pub(crate) spawn_ep: CapSlot,
    /// Bound to init's thread: spawned children's deaths, a bit each.
    pub(crate) deaths: CapSlot,
    pub(crate) spawner: Spawner,
}

impl<'a> Launcher<'a> {
    pub(crate) fn new(
        storage: &'a mut Storage,
        scratch: &'a mut [u8],
        devices: Devices,
    ) -> Result<Self, &'static str> {
        let spawn_ep = syscall::create_endpoint().ok_or("no spawn endpoint")?;
        let deaths = syscall::create_notification().map_err(|_| "no death notification")?;
        Ok(Self { storage, scratch, devices, served: [None; MAX_SERVED], spawn_ep, deaths, spawner: Spawner::new() })
    }

    pub(crate) fn storage(&mut self) -> (&mut Storage, &mut [u8]) {
        (self.storage, self.scratch)
    }

    fn endpoint(&self, name: &str) -> Option<CapSlot> {
        self.served.iter().flatten().find(|(n, _)| *n == name).map(|(_, ep)| *ep)
    }

    /// What became of the program's device, if it has one.
    pub(crate) fn launch(&mut self, p: &Program) -> Result<&'static str, &'static str> {
        let loaded =
            load::load_binary(self.storage, self.scratch, p.file, p.limits).ok_or("cannot load")?;
        let child = loaded.process_cap;
        let ep = match p.serves {
            true => {
                let ep = syscall::create_endpoint().ok_or("no endpoint")?;
                // Read to receive on it; init keeps the original.
                let server = perms(&[Permission::Read, Permission::Execute]);
                syscall::delegate(ep, child, server).ok_or("cannot give its endpoint")?;
                Some(ep)
            }
            false => None,
        };
        // A client only calls: Execute, never Read, so it cannot pose as the
        // server and take other clients' requests.
        for name in p.uses {
            let ep = self.endpoint(name).ok_or("needs a server that is not running")?;
            syscall::delegate(ep, child, perms(&[Permission::Execute])).ok_or("cannot give an endpoint")?;
        }
        if let Some(allowance) = p.spawns {
            self.give_spawn(child, allowance)?;
        }
        if p.system_control {
            let control = crate::devices::system_control().ok_or("no SystemControl to give")?;
            syscall::delegate(control, child, perms(&[Permission::Execute])).ok_or("cannot give SystemControl")?;
        }
        let console = libkos::start::console()
            .filter(|_| p.console)
            .and_then(|c| syscall::delegate(c, child, perms(&[Permission::Write])));
        start(&loaded, console);

        let mut note = "";
        if let Some(ep) = ep {
            if let Some(free) = self.served.iter_mut().find(|s| s.is_none()) {
                *free = Some((p.name, ep));
            }
            if let Some(device) = p.device {
                note = self.give(device, ep);
            }
            if console.is_some() {
                hand_over_console(ep);
                note = ", console handed over";
            }
        }
        Ok(note)
    }

    /// A badged copy of init's endpoint: the badge names the client and so
    /// its allowance.
    fn give_spawn(&mut self, child: CapSlot, allowance: types::budget::Limits) -> Result<(), &'static str> {
        let badge: Badge = self.spawner.add_client(allowance).ok_or("too many spawn clients")?;
        let minted = perms(&[Permission::Execute, Permission::Delegate]);
        let copy = syscall::mint(self.spawn_ep, badge, minted).map_err(|_| "cannot mint")?;
        let given = syscall::delegate(copy, child, perms(&[Permission::Execute]));
        syscall::drop_cap(copy);
        given.map(|_| ()).ok_or("cannot give the spawn endpoint")
    }

    /// The driver waits for its device before serving, and runs without
    /// one (headless) if the board has none.
    fn give(&self, device: Device, ep: CapSlot) -> &'static str {
        let (dev, given, none): (BoardDevice, _, _) = match device {
            Device::Gpu => (self.devices.gpu, ", gpu handed over", ", no gpu"),
            Device::Input => (self.devices.input, ", input device handed over", ", no input device"),
        };
        match libkos::device::give_device(ep, dev).is_ok() && dev.mmio.is_some() {
            true => given,
            false => none,
        }
    }
}

/// From here on init prints through the log server, like everyone else,
/// and holds no console of its own.
fn hand_over_console(log: CapSlot) {
    if let Some(console) = libkos::start::console() {
        syscall::drop_cap(console);
    }
    libkos::start::set_console(None);
    libkos::start::set_log(Some(log));
}

/// Starts `program` with `console` and, once there is one, the log.
pub(crate) fn start(program: &LoadedProcess, console: Option<CapSlot>) {
    let log = libkos::start::log()
        .and_then(|l| syscall::delegate(l, program.process_cap, perms(&[Permission::Execute])));
    let arg = types::start_arg::encode(console, log);
    syscall::spawn_thread_in(program.process_cap, program.entry_point, USER_STACK_TOP, arg);
}