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use serde::{Deserialize, Serialize};
use std::ops::{Index, IndexMut};

pub const REGISTER_HI: usize = 32;
pub const REGISTER_LO: usize = 33;
pub const REGISTER_CURRENT_IP: usize = 34;
pub const REGISTER_NEXT_IP: usize = 35;
pub const REGISTER_HEAP_POINTER: usize = 36;
pub const REGISTER_PREIMAGE_KEY_START: usize = 37;
pub const REGISTER_PREIMAGE_KEY_END: usize = REGISTER_PREIMAGE_KEY_START + 8 /* 37 + 8 = 45 */;
pub const REGISTER_PREIMAGE_OFFSET: usize = 45;

pub const NUM_REGISTERS: usize = 46;

/// This represents the internal state of the virtual machine.
#[derive(Clone, Default, Debug, Serialize, Deserialize)]
pub struct Registers<T> {
    pub general_purpose: [T; 32],
    pub hi: T,
    pub lo: T,
    pub current_instruction_pointer: T,
    pub next_instruction_pointer: T,
    pub heap_pointer: T,
    pub preimage_key: [T; 8],
    pub preimage_offset: T,
}

impl<T> Registers<T> {
    pub fn iter(&self) -> impl Iterator<Item = &T> {
        self.general_purpose
            .iter()
            .chain([
                &self.hi,
                &self.lo,
                &self.current_instruction_pointer,
                &self.next_instruction_pointer,
                &self.heap_pointer,
            ])
            .chain(self.preimage_key.iter())
            .chain([&self.preimage_offset])
    }
}

impl<T: Clone> Index<usize> for Registers<T> {
    type Output = T;

    fn index(&self, index: usize) -> &Self::Output {
        if index < 32 {
            &self.general_purpose[index]
        } else if index == REGISTER_HI {
            &self.hi
        } else if index == REGISTER_LO {
            &self.lo
        } else if index == REGISTER_CURRENT_IP {
            &self.current_instruction_pointer
        } else if index == REGISTER_NEXT_IP {
            &self.next_instruction_pointer
        } else if index == REGISTER_HEAP_POINTER {
            &self.heap_pointer
        } else if (REGISTER_PREIMAGE_KEY_START..REGISTER_PREIMAGE_KEY_END).contains(&index) {
            &self.preimage_key[index - REGISTER_PREIMAGE_KEY_START]
        } else if index == REGISTER_PREIMAGE_OFFSET {
            &self.preimage_offset
        } else {
            panic!("Index out of bounds");
        }
    }
}

impl<T: Clone> IndexMut<usize> for Registers<T> {
    fn index_mut(&mut self, index: usize) -> &mut Self::Output {
        if index < 32 {
            &mut self.general_purpose[index]
        } else if index == REGISTER_HI {
            &mut self.hi
        } else if index == REGISTER_LO {
            &mut self.lo
        } else if index == REGISTER_CURRENT_IP {
            &mut self.current_instruction_pointer
        } else if index == REGISTER_NEXT_IP {
            &mut self.next_instruction_pointer
        } else if index == REGISTER_HEAP_POINTER {
            &mut self.heap_pointer
        } else if (REGISTER_PREIMAGE_KEY_START..REGISTER_PREIMAGE_KEY_END).contains(&index) {
            &mut self.preimage_key[index - REGISTER_PREIMAGE_KEY_START]
        } else if index == REGISTER_PREIMAGE_OFFSET {
            &mut self.preimage_offset
        } else {
            panic!("Index out of bounds");
        }
    }
}