// Copyright (c) 2025 taitep
// SPDX-License-Identifier: MIT
//
// This file is part of TRVE (https://gitea.taitep.se/taitep/trve)
// See LICENSE file in the project root for full license text.

use std::{collections::HashSet, sync::mpsc};

use crate::{
    consts::{Addr, RegId, RegValue},
    core::commands::CoreCmd,
    decode::Instruction,
    exceptions::ExceptionType,
    gdb::{self, DebugCommand, DebugStream, StopReason},
    instructions::find_and_exec,
    mem::MemConfig,
};

pub struct Core {
    pub(crate) x_regs: [RegValue; 32],
    pub(crate) pc: Addr,
    pub(crate) mem: MemConfig,
    command_stream: mpsc::Receiver<CoreCmd>,
}

pub mod commands;

impl Core {
    pub fn new(mem: MemConfig, command_stream: mpsc::Receiver<CoreCmd>) -> Self {
        Self {
            x_regs: [0; 32],
            pc: 0,
            mem,
            command_stream,
        }
    }

    pub fn run(&mut self) {
        loop {
            if let Ok(cmd) = self.command_stream.try_recv() {
                match cmd {
                    CoreCmd::EnterDbgMode(DebugStream(dbg_stream)) => {
                        let _ = self.debug_loop(dbg_stream);
                    }
                };
            }

            if let Err(e) = self.step() {
                self.throw_exception(e);
                break;
            }
        }
    }

    pub fn run_waiting_for_cmd(&mut self) {
        eprintln!("Waiting for any core command...");
        if let Ok(cmd) = self.command_stream.recv() {
            eprintln!("Recieved a command");
            match cmd {
                CoreCmd::EnterDbgMode(DebugStream(dbg_stream)) => {
                    let _ = self.debug_loop(dbg_stream);
                }
            };
        } else {
            eprintln!("Error recieving command, starting anyway");
        }

        eprintln!("Command processed");

        self.run();
    }

    fn debug_loop(&mut self, dbg_stream: mpsc::Receiver<gdb::DebugCommand>) -> anyhow::Result<()> {
        let mut breakpoints = HashSet::new();

        loop {
            match dbg_stream.recv()? {
                DebugCommand::GetRegs(sender) => sender.send(gdb::RegsResponse {
                    x_regs: self.x_regs.clone(),
                    pc: self.pc,
                })?,
                DebugCommand::ReadMem {
                    addr,
                    len,
                    responder,
                } => {
                    let data = (0..len)
                        .map(|offset| self.mem.read_byte(addr + offset))
                        .collect();

                    responder.send(data)?;
                }
                DebugCommand::SetBreakpoint(addr) => {
                    breakpoints.insert(addr);
                }
                DebugCommand::RemoveBreakpoint(addr) => {
                    breakpoints.remove(&addr);
                }
                DebugCommand::Step(responder) => {
                    responder.send(match self.step() {
                        Ok(_) => gdb::StopReason::Step,
                        Err(e) => {
                            self.throw_exception(e);
                            gdb::StopReason::Exception(e)
                        }
                    })?;
                }
                DebugCommand::Continue(responder, stopper) => {
                    responder.send(self.continue_loop(&breakpoints, stopper))?;
                }
                DebugCommand::ExitDebugMode => {
                    eprintln!("exitdbgmode");
                    break Ok(());
                }
            };
        }
    }

    fn continue_loop(
        &mut self,
        breakpoints: &HashSet<Addr>,
        stopper: oneshot::Receiver<()>,
    ) -> StopReason {
        loop {
            if breakpoints.contains(&self.pc) {
                return StopReason::Exception(ExceptionType::Breakpoint);
            }

            if let Ok(_) = stopper.try_recv() {
                return StopReason::Interrupted;
            }

            if let Err(e) = self.step() {
                self.throw_exception(e);
                return StopReason::Exception(e);
            }
        }
    }

    pub(crate) fn step(&mut self) -> Result<(), ExceptionType> {
        if !self.pc.is_multiple_of(4) {
            self.throw_exception(ExceptionType::InstructionAddressMisaligned);
        }

        let instr = match self.mem.read_word(self.pc) {
            Ok(i) => i,
            Err(e) => {
                return Err(e.to_exception_instr());
            }
        };

        if instr == 0 {
            return Err(ExceptionType::IllegalInstruction);
        }

        if instr & 3 != 3 {
            // Compressed instruction - (currently) unsupported
            return Err(ExceptionType::IllegalInstruction);
        }

        let instr = Instruction(instr);

        if let Err(e) = find_and_exec(instr, self) {
            eprintln!("instr: {:08x}", instr.0);
            return Err(e);
        }

        Ok(())
    }

    fn throw_exception(&mut self, exception_type: ExceptionType) {
        eprintln!("Exception: {exception_type:?}");
        dbg!(self.pc, self.x_regs);
    }

    pub fn reset(&mut self, pc: Addr) {
        self.pc = pc;
    }

    pub(crate) fn reg_read(&self, id: RegId) -> RegValue {
        self.x_regs[id as usize]
    }

    pub(crate) fn reg_write(&mut self, id: RegId, value: RegValue) {
        if id == 0 {
            return;
        }
        self.x_regs[id as usize] = value;
    }

    pub(crate) fn advance_pc(&mut self) {
        self.pc = self.pc.wrapping_add(4);
    }
}