use status::StatusFlags;

use crate::asm::data::{DstDisp, Rd, Register, SrcDisp, Wr};
use crate::asm::data::literal::{Addr, Value};

use super::fault::Fault;

mod status;

pub const REG_COUNT: usize = 8;

pub type CallStack = Vec<StackFrame>;

#[derive(Default, Clone, Debug)]
pub struct StackFrame {
    /// Program counter, address of the executed instruction
    pub pc: Addr,
    /// Status flags
    pub status: StatusFlags,
    /// Argument registers
    pub arg: [Value; REG_COUNT],
    /// Result registers
    pub res: [Value; REG_COUNT],
    /// General purpose registers
    pub gen: [Value; REG_COUNT],
}

impl StackFrame {
    /// Create a new stack frame at a given address
    pub fn new(addr: Addr, args: &[Value]) -> Self {
        let mut sf = StackFrame::default();
        sf.pc = addr;
        for n in 0..(args.len().min(REG_COUNT)) {
            sf.arg[n] = args[n];
        }
        sf
    }

    pub fn set_retvals(&mut self, vals: &[Value]) {
        for n in 0..(vals.len().min(REG_COUNT)) {
            self.res[n] = vals[n];
        }
    }

    pub fn read(&mut self, rd: Rd) -> Result<Value, Fault> {
        match rd.d() {
            SrcDisp::Immediate(v) => Ok(v),
            SrcDisp::ImmediatePtr(_) => {
                unimplemented!("Immediate ptr")
            }
            SrcDisp::Register(Register::Res(rn)) => {
                if rn >= REG_COUNT as u8 {
                    Err(Fault::RegisterNotExist { reg: Register::Res(rn) }) // TODO use match after @ when stabilized https://github.com/rust-lang/rust/issues/65490
                } else {
                    trace!("Rd {:?} = {}", rd, self.res[rn as usize]);
                    Ok(self.res[rn as usize])
                }
            }
            SrcDisp::Register(Register::Arg(rn)) => {
                if rn >= REG_COUNT as u8 {
                    Err(Fault::RegisterNotExist { reg: Register::Arg(rn) })
                } else {
                    trace!("Rd {:?} = {}", rd, self.arg[rn as usize]);
                    Ok(self.arg[rn as usize])
                }
            }
            SrcDisp::Register(Register::Gen(rn)) => {
                if rn >= REG_COUNT as u8 {
                    Err(Fault::RegisterNotExist { reg: Register::Gen(rn) })
                } else {
                    trace!("Rd {:?} = {}", rd, self.gen[rn as usize]);
                    Ok(self.gen[rn as usize])
                }
            }
            SrcDisp::RegisterPtr(_) => {
                unimplemented!("Register ptr")
            }
        }
    }

    pub fn write(&mut self, wr: Wr, val: Value) -> Result<(), Fault> {
        trace!("WR {:?} := {}", wr, val);

        match wr.d() {
            DstDisp::ImmediatePtr(_) => {
                unimplemented!("Immediate ptr")
            }
            DstDisp::Discard => {
                /* Discard */
                Ok(())
            }
            DstDisp::Register(Register::Res(rn)) => {
                if rn >= REG_COUNT as u8 {
                    Err(Fault::RegisterNotExist { reg: Register::Res(rn) }) // TODO use match after @ when stabilized https://github.com/rust-lang/rust/issues/65490
                } else {
                    Err(Fault::RegisterNotWritable { reg: Register::Res(rn) })
                }
            }
            DstDisp::Register(Register::Arg(rn)) => {
                if rn >= REG_COUNT as u8 {
                    Err(Fault::RegisterNotExist { reg: Register::Arg(rn) })
                } else {
                    Err(Fault::RegisterNotWritable { reg: Register::Res(rn) })
                }
            }
            DstDisp::Register(Register::Gen(rn)) => {
                if rn >= REG_COUNT as u8 {
                    Err(Fault::RegisterNotExist { reg: Register::Gen(rn) })
                } else {
                    self.gen[rn as usize] = val;
                    Ok(())
                }
            }
            DstDisp::RegisterPtr(_) => {
                unimplemented!("Register ptr")
            }
        }
    }
}