use std::collections::HashMap;

use super::compiler::{Command, CompiledReid, HeapID, VariableType};
use super::errors::RuntimePanic;

pub struct VirtualMachine {
    registry_stack: Vec<[Option<Value>; 8]>,
    registry: [Option<Value>; 8],

    stack: Vec<Value>,
    heap: HashMap<HeapID, AllocatedVar>,

    position: usize,
    compiled: CompiledReid,
}

impl VirtualMachine {
    pub fn from(compiled: CompiledReid) -> VirtualMachine {
        VirtualMachine {
            registry_stack: Vec::new(),
            registry: Default::default(),

            stack: Vec::new(),
            heap: HashMap::new(),

            position: 0,
            compiled,
        }
    }

    pub fn run(&mut self) -> Result<(), RuntimePanic> {
        let mut error = None;
        while error.is_none() {
            if let Some(command) = self.compiled.list.get(self.position).map(|v| v.clone()) {
                self.position += 1;
                if let Err(err) = self.execute(command.clone()) {
                    error = Some(err);
                }
                if self.remaining() == 0 {
                    break;
                }
            } else {
                error = Some(RuntimePanic::InvalidCommandIdx(self.position));
            }
        }

        if let Some(error) = error {
            Err(error)
        } else {
            Ok(())
        }
    }

    fn remaining(&self) -> usize {
        let len = self.compiled.list.len();
        len - self.position.max(0).min(len)
    }

    fn execute(&mut self, command: Command) -> Result<(), RuntimePanic> {
        match command {
            Command::InitializeVariable(heapid, vtype) => {
                self.heap.insert(heapid, AllocatedVar(vtype, None));
                dbg!("Initialized new variable to heap", &self.heap);
                Ok(())
            }
            Command::BeginScope => {
                self.registry_stack.push(self.registry.clone());
                self.registry = Default::default();
                dbg!("Begun new scope");
                Ok(())
            }
            Command::EndScope => {
                if let Some(reg) = self.registry_stack.pop() {
                    self.registry = reg;
                    dbg!("Scope ended");
                    Ok(())
                } else {
                    Err(RuntimePanic::ScopeStackUnderflow)
                }
            }
            Command::Pop(regid) => {
                if let Some(val) = self.stack.pop() {
                    self.registry[regid] = Some(val);
                    dbg!("Registry popped", regid, &self.stack, &self.registry);
                    Ok(())
                } else {
                    Err(RuntimePanic::StackUnderflow)
                }
            }
            Command::Push(regid) => {
                if let Some(reg) = &self.registry[regid] {
                    if self.stack.len() < usize::MAX {
                        self.stack.push(reg.clone());
                        dbg!("Registry pushed", regid, &self.stack);
                        Ok(())
                    } else {
                        Err(RuntimePanic::StackOverflow)
                    }
                } else {
                    Err(RuntimePanic::RegistryNotDefined)
                }
            }
            Command::AssignVariable(heapid, regid) => {
                if let Some(reg) = &self.registry[regid] {
                    if let Some(var) = self.heap.get_mut(&heapid) {
                        var.1 = Some(reg.clone());
                        dbg!("Variable assigned", heapid, regid, &self.heap);
                        Ok(())
                    } else {
                        Err(RuntimePanic::InvalidHeapAddress)
                    }
                } else {
                    Err(RuntimePanic::RegistryNotDefined)
                }
            }
            Command::VarToReg(heapid, regid) => {
                if let Some(var) = self.heap.get(&heapid) {
                    if let Some(val) = &var.1 {
                        self.registry[regid] = Some(val.clone());
                        dbg!("Variable pushed to registry", heapid, regid, &self.registry);
                        Ok(())
                    } else {
                        Err(RuntimePanic::ValueNotInitialized)
                    }
                } else {
                    Err(RuntimePanic::InvalidHeapAddress)
                }
            }
            Command::StringLit(string) => {
                if self.stack.len() < usize::MAX {
                    self.stack.push(Value::StringVal(string.clone()));
                    dbg!("String literal added to stack", string, &self.stack);
                    Ok(())
                } else {
                    Err(RuntimePanic::StackOverflow)
                }
            }
        }
    }
}

#[derive(Clone, Debug)]
struct AllocatedVar(VariableType, Option<Value>);

#[derive(Clone, Debug)]
enum Value {
    StringVal(String),
}