use std::collections::HashMap;
use std::sync::Arc;

use crate::asm::data::literal::{Addr, Label, RoutineName};
use crate::asm::instr::Op;
use crate::runtime::fault::Fault;

#[derive(Debug)]
pub struct Program {
    pub ops: Vec<Op>,
    routines: HashMap<RoutineName, Addr>,
    far_labels: HashMap<Label, Addr>,
    barriers: Vec<Addr>,
}

impl Program {
    pub fn new(ops: Vec<Op>) -> Arc<Self> {
        let mut p = Self {
            ops,
            routines: Default::default(),
            far_labels: Default::default(),
            barriers: Default::default(),
        };
        p.scan();
        Arc::new(p)
    }

    /// Find all the named things
    fn scan(&mut self) {
        for (pos, op) in self.ops.iter().enumerate() {
            match op {
                Op::FarLabel(name) => {
                    self.far_labels.insert(name.clone(), pos.into());
                }
                Op::Routine(name) => {
                    self.routines.insert(name.clone(), pos.into());
                }
                Op::Barrier(_) => {
                    self.barriers.push(pos.into());
                }
                _ => {}
            }
        }
    }

    /// Read a program instruction at address
    pub fn read(&self, addr: Addr) -> &Op {
        if addr.0 >= self.ops.len() as u64 {
            &Op::Nop
        } else {
            &self.ops[addr.0 as usize]
        }
    }

    /// Return error if any barrier is crossed during a jump / skip
    pub fn validate_jump(&self, mut from: Addr, mut to: Addr) -> Result<(), Fault> {
        if from > to {
            std::mem::swap(&mut from, &mut to);
        }

        for b in &self.barriers {
            if *b >= from && *b <= to {
                if let Op::Barrier(msg) = self.read(*b) {
                    return Err(Fault::JumpThroughBarrier {
                        msg: msg.clone().unwrap_or("No msg".into())
                    });
                } else {
                    unreachable!();
                }
            }
        }
        Ok(())
    }

    /// Find routine by name
    pub fn find_routine(&self, name: &RoutineName) -> Result<Addr, Fault> {
        self.routines.get(name).copied()
            .ok_or_else(|| Fault::NoSuchRoutine { routine: name.clone() })
    }

    /// Find far label by name
    pub fn find_far_label(&self, name: &Label) -> Result<Addr, Fault> {
        self.far_labels.get(name).copied()
            .ok_or_else(|| Fault::NoSuchLabel { label: name.clone() })
    }

    /// Find local label by name (label within a boundary-delimited region).
    /// If more than one such label exists, the outcome is undefined.
    pub fn find_local_label(&self, pc: Addr, name: &Label) -> Result<Addr, Fault> {
        // TODO more efficient impl with look-up

        for at in (0..=pc.0).rev() {
            match &self.ops[at as usize] {
                Op::Label(lbl) if lbl == name => {
                    return Ok(at.into());
                }
                Op::Barrier(_) => {
                    break;
                }
                _ => {}
            }
        }

        for at in pc.0..(self.ops.len() as u64) {
            match &self.ops[at as usize] {
                Op::Label(lbl) if lbl == name => {
                    return Ok(at.into());
                }
                Op::Barrier(_) => {
                    break;
                }
                _ => {}
            }
        }

        Err(Fault::NoSuchLabel { label: name.clone() })
    }
}