use std::sync::atomic::AtomicU32;
use crate::instr::{HLOp, Instr, Cond, Routine, Op};
use crate::error::{Error, AsmError};
use std::collections::HashMap;
use crate::data::literal::{Label, Value};
use crate::data::{Rd, SrcDisp};

/// A trait for something that can turn into multiple instructions
pub trait Flatten {
    fn flatten(self, label_num: &AtomicU32) -> Result<Vec<HLOp>, Error>;
}

impl Flatten for Instr {
    fn flatten(self, label_num: &AtomicU32) -> Result<Vec<HLOp>, Error> {
        let mut ops = vec![self.op];

        if let Some(branches) = self.branches {
            let labels = HashMap::<Cond, u32>::new();
            let branch_count = branches.len();
            let end_lbl = Label::unique(label_num);
            for (cnt, (cond, branch)) in branches.into_iter().enumerate() {
                if labels.contains_key(&cond) {
                    return Err(Error::Asm(AsmError::ConditionalAlreadyUsed(cond)));
                }

                let next_lbl = if cnt == branch_count - 1 {
                    end_lbl.clone()
                } else {
                    Label::unique(label_num)
                };
                ops.push(HLOp::JumpIf(!cond, next_lbl.clone()));

                for branch_instr in branch {
                    ops.extend(branch_instr.flatten(label_num)?);
                }

                if cnt != branch_count - 1 {
                    ops.push(HLOp::Jump(end_lbl.clone()));
                    ops.push(HLOp::Label(next_lbl));
                }
            }
            ops.push(HLOp::Label(end_lbl));
        }

        Ok(ops)
    }
}

impl Flatten for Routine {
    fn flatten(self, label_num: &AtomicU32) -> Result<Vec<HLOp>, Error> {
        let mut ops = vec![
            Op::Routine(self.name.clone()).into(),
        ];

        for instr in self.body {
            ops.extend(instr.flatten(label_num)?);
        }

        ops.push(Op::Barrier(Some(format!("Routine \"{}\" overrun", self.name).into())).into());
        Ok(ops)
    }
}

/// Convert jumps to relative skips
pub fn lower(ops: Vec<HLOp>) -> Result<Vec<Op>, Error> {
    let mut label_positions = HashMap::<Label, usize>::new();
    for (n, op) in ops.iter().enumerate() {
        if let HLOp::Label(name) = op {
            label_positions.insert(name.clone(), n - label_positions.len());
        }
    }

    let mut cleaned = vec![];
    let mut skipped = 0;
    for (n, op) in ops.into_iter().enumerate() {
        match op {
            HLOp::Label(_) => {
                skipped += 1;
            }
            HLOp::Jump(target) => {
                if let Some(dest) = label_positions.get(&target) {
                    let skip = *dest as isize - n as isize + skipped;
                    cleaned.push(Op::Skip(Rd::new(SrcDisp::Immediate(skip as Value))));
                } else {
                    return Err(Error::Asm(AsmError::LabelNotDefined(target)));
                }
            }
            HLOp::JumpIf(cond, target) => {
                if let Some(dest) = label_positions.get(&target) {
                    let skip = *dest as isize - n as isize + skipped;
                    cleaned.push(Op::SkipIf(cond, Rd::new(SrcDisp::Immediate(skip as Value))));
                } else {
                    return Err(Error::Asm(AsmError::LabelNotDefined(target)));
                }
            }
            HLOp::L(op) => {
                cleaned.push(op);
            }
        }
    }

    Ok(cleaned)
}