use crate::error::KernelError;

#[derive(Debug, Clone, Copy, PartialEq, Eq)]
#[repr(u8)]
pub enum ProcessState {
    Free = 0,
    Ready = 1,
    Running = 2,
    Blocked = 3,
    Dead = 4,
    Created = 5,
    Zombie = 6,
}

impl ProcessState {
    pub const ALL: [ProcessState; 7] = [
        Self::Free,
        Self::Ready,
        Self::Running,
        Self::Blocked,
        Self::Dead,
        Self::Created,
        Self::Zombie,
    ];

    pub fn is_valid_transition(from: ProcessState, to: ProcessState) -> bool {
        matches!(
            (from, to),
            (Self::Free, Self::Created)
                | (Self::Created, Self::Ready)
                | (Self::Ready, Self::Running)
                | (Self::Running, Self::Ready)
                | (Self::Running, Self::Blocked)
                | (Self::Blocked, Self::Ready)
                | (Self::Running, Self::Dead)
                | (Self::Ready, Self::Dead)
                | (Self::Blocked, Self::Dead)
                | (Self::Created, Self::Dead)
                | (Self::Dead, Self::Free)
                | (Self::Running, Self::Zombie)
                | (Self::Ready, Self::Zombie)
                | (Self::Blocked, Self::Zombie)
                | (Self::Created, Self::Zombie)
                | (Self::Zombie, Self::Free)
        )
    }

    pub fn transition(&mut self, to: ProcessState) -> Result<(), KernelError> {
        if Self::is_valid_transition(*self, to) {
            *self = to;
            Ok(())
        } else {
            Err(KernelError::BadState)
        }
    }
}