use {
    crate::{
        instrs, lexer, log,
        parser::{self, Expr},
    },
    std::rc::Rc,
};

type LabelId = u32;
type Reg = u8;
type MaskElem = u64;
type Type = u32;

mod bt {
    use super::*;

    const fn builtin_type(id: u32) -> Type {
        Type::MAX - id
    }

    macro_rules! builtin_type {
        ($($name:ident;)*) => {$(
            pub const $name: Type = builtin_type(${index(0)});
        )*};
    }

    builtin_type! {
        INT;
        BOOL;
        MAX;
    }
}

enum TypeKind {
    Builtin(Type),
    Struct(Type),
}

impl TypeKind {
    fn from_ty(ty: Type) -> Self {
        if ty > bt::MAX {
            Self::Builtin(ty)
        } else {
            Self::Struct(ty)
        }
    }
}

const STACK_PTR: Reg = 254;
const ZERO: Reg = 0;
const RET_ADDR: Reg = 31;
const ELEM_WIDTH: usize = std::mem::size_of::<MaskElem>() * 8;

struct Frame {
    label:       LabelId,
    prev_relocs: usize,
    offset:      u32,
}

struct Reloc {
    id: LabelId,
    offset: u32,
    instr_offset: u16,
    size: u16,
}

struct StackReloc {
    offset: u32,
    size:   u16,
}

#[derive(Default)]
pub struct Func {
    code:   Vec<u8>,
    relocs: Vec<Reloc>,
}

impl Func {
    pub fn extend(&mut self, bytes: &[u8]) {
        self.code.extend_from_slice(bytes);
    }

    pub fn offset(&mut self, id: LabelId, instr_offset: u16, size: u16) {
        self.relocs.push(Reloc {
            id,
            offset: self.code.len() as u32,
            instr_offset,
            size,
        });
    }

    fn encode(&mut self, (len, instr): (usize, [u8; instrs::MAX_SIZE])) {
        let name = instrs::NAMES[instr[0] as usize];
        log::dbg!(
            "{:08x}: {}: {}",
            self.code.len(),
            name,
            instr
                .iter()
                .take(len)
                .skip(1)
                .map(|b| format!("{:02x}", b))
                .collect::<String>()
        );
        self.code.extend_from_slice(&instr[..len]);
    }

    fn push(&mut self, value: Reg, size: usize) {
        self.subi64(STACK_PTR, STACK_PTR, size as _);
        self.encode(instrs::st(value, STACK_PTR, 0, size as _));
    }

    fn pop(&mut self, value: Reg, size: usize) {
        self.encode(instrs::ld(value, STACK_PTR, 0, size as _));
        self.encode(instrs::addi64(STACK_PTR, STACK_PTR, size as _));
    }

    fn subi64(&mut self, dest: Reg, src: Reg, imm: u64) {
        self.encode(instrs::addi64(dest, src, imm.wrapping_neg()));
    }

    fn call(&mut self, func: LabelId) {
        self.offset(func, 3, 4);
        self.encode(instrs::jal(RET_ADDR, ZERO, 0));
    }

    fn ret(&mut self) {
        self.pop(RET_ADDR, 8);
        self.encode(instrs::jala(ZERO, RET_ADDR, 0));
    }

    fn prelude(&mut self, entry: LabelId) {
        self.call(entry);
        self.encode(instrs::tx());
    }

    fn relocate(&mut self, labels: &[FnLabel], shift: i64) {
        for reloc in self.relocs.drain(..) {
            let label = &labels[reloc.id as usize];
            let offset = if reloc.size == 8 {
                reloc.offset as i64
            } else {
                label.offset as i64 - reloc.offset as i64
            } + shift;

            log::dbg!(
                label.name.as_ref(),
                offset,
                reloc.size,
                reloc.instr_offset,
                reloc.offset,
                shift,
                label.offset
            );

            let dest = &mut self.code[reloc.offset as usize + reloc.instr_offset as usize..]
                [..reloc.size as usize];
            match reloc.size {
                2 => dest.copy_from_slice(&(offset as i16).to_le_bytes()),
                4 => dest.copy_from_slice(&(offset as i32).to_le_bytes()),
                8 => dest.copy_from_slice(&(offset as i64).to_le_bytes()),
                _ => unreachable!(),
            };
        }
    }
}

#[derive(Default)]
pub struct RegAlloc {
    free: Vec<Reg>,
    // TODO:use 256 bit mask instead
    used: Vec<Reg>,
}

impl RegAlloc {
    fn init_callee(&mut self) {
        self.clear();
        self.free.extend(32..=253);
    }

    fn clear(&mut self) {
        self.free.clear();
        self.used.clear();
    }

    fn allocate(&mut self) -> Reg {
        let reg = self.free.pop().expect("TODO: we need to spill");
        if self.used.binary_search_by_key(&!reg, |&r| !r).is_err() {
            self.used.push(reg);
        }
        reg
    }

    fn free(&mut self, reg: Reg) {
        self.free.push(reg);
    }
}

struct FnLabel {
    offset: u32,
    // TODO: use different stile of identifier that does not allocate, eg. index + length into a
    // file
    name:   Rc<str>,
}

struct Variable<'a> {
    name:   Rc<str>,
    offset: u64,
    ty:     Expr<'a>,
}

struct RetReloc {
    offset:       u32,
    instr_offset: u16,
    size:         u16,
}

struct Loop {
    offset: u32,
    relocs: Vec<RetReloc>,
}

struct Struct {
    name:   Rc<str>,
    fields: Vec<(Rc<str>, Type)>,
}

pub struct Codegen<'a> {
    path: &'a std::path::Path,
    ret: Expr<'a>,
    gpa: RegAlloc,
    code: Func,
    temp: Func,
    labels: Vec<FnLabel>,
    stack_size: u64,
    vars: Vec<Variable<'a>>,
    stack_relocs: Vec<StackReloc>,
    ret_relocs: Vec<RetReloc>,
    loops: Vec<Loop>,
    records: Vec<Struct>,
}

impl<'a> Codegen<'a> {
    pub fn new() -> Self {
        Self {
            path:       std::path::Path::new(""),
            ret:        Expr::Return { val: None, pos: 0 },
            gpa:        Default::default(),
            code:       Default::default(),
            temp:       Default::default(),
            labels:     Default::default(),
            stack_size: 0,
            vars:       Default::default(),

            stack_relocs: Default::default(),
            ret_relocs:   Default::default(),
            loops:        Default::default(),
            records:      Default::default(),
        }
    }

    pub fn file(
        &mut self,
        path: &'a std::path::Path,
        exprs: &'a [parser::Expr<'a>],
    ) -> std::fmt::Result {
        self.path = path;
        for expr in exprs {
            self.expr(expr, None);
        }
        Ok(())
    }

    fn loc_to_reg(&mut self, loc: Loc) -> Reg {
        match loc {
            Loc::Reg(reg) => reg,
            Loc::Imm(imm) => {
                let reg = self.gpa.allocate();
                self.code.encode(instrs::li64(reg, imm));
                reg
            }
            Loc::Stack(offset) => {
                let reg = self.gpa.allocate();
                self.load_stack(reg, offset, 8);
                reg
            }
        }
    }

    fn alloc_stack(&mut self, size: u32) -> u64 {
        let offset = self.stack_size;
        self.stack_size += size as u64;
        offset
    }

    fn store_stack(&mut self, reg: Reg, offset: u64, size: u16) {
        self.stack_relocs.push(StackReloc {
            offset: self.code.code.len() as u32 + 3,
            size,
        });
        self.code.encode(instrs::st(reg, STACK_PTR, offset, size));
    }

    fn load_stack(&mut self, reg: Reg, offset: u64, size: u16) {
        self.stack_relocs.push(StackReloc {
            offset: self.code.code.len() as u32 + 3,
            size,
        });
        self.code.encode(instrs::ld(reg, STACK_PTR, offset, size));
    }

    fn reloc_stack(&mut self, stack_height: u64) {
        for reloc in self.stack_relocs.drain(..) {
            let dest = &mut self.code.code[reloc.offset as usize..][..reloc.size as usize];
            let value = u64::from_ne_bytes(dest.try_into().unwrap());
            let offset = stack_height - value;
            dest.copy_from_slice(&offset.to_ne_bytes());
        }
    }

    fn reloc_rets(&mut self) {
        let len = self.code.code.len() as i32;
        for reloc in self.ret_relocs.drain(..) {
            let dest = &mut self.code.code[reloc.offset as usize + reloc.instr_offset as usize..]
                [..reloc.size as usize];
            debug_assert!(dest.iter().all(|&b| b == 0));
            let offset = len - reloc.offset as i32;
            dest.copy_from_slice(&offset.to_ne_bytes());
        }
    }

    fn expr(&mut self, expr: &'a parser::Expr<'a>, expeted: Option<Expr<'a>>) -> Option<Value<'a>> {
        use {lexer::TokenKind as T, parser::Expr as E};
        match *expr {
            E::BinOp {
                left: E::Ident { name, .. },
                op: T::Decl,
                right: E::Closure {
                    ret, body, args, ..
                },
            } => {
                let frame = self.add_label(name);
                for (i, &(name, ty)) in args.iter().enumerate() {
                    let offset = self.alloc_stack(8);
                    self.decl_var(name, offset, ty);
                    self.store_stack(i as Reg + 2, offset, 8);
                }
                self.gpa.init_callee();
                self.ret = **ret;
                self.expr(body, None);
                self.vars.clear();
                let stack = std::mem::take(&mut self.stack_size);
                self.reloc_stack(stack);
                self.write_fn_prelude(frame);
                self.reloc_rets();
                self.ret();
                None
            }
            E::BinOp {
                left: E::Ident { name, .. },
                op: T::Decl,
                right,
            } => {
                let val = self.expr(right, None).unwrap();
                let reg = self.loc_to_reg(val.loc);
                let offset = self.alloc_stack(8);
                self.decl_var(name, offset, val.ty);
                self.store_stack(reg, offset, 8);
                None
            }
            E::Call {
                func: E::Ident { name, .. },
                args,
            } => {
                for (i, arg) in args.iter().enumerate() {
                    let arg = self.expr(arg, None).unwrap();
                    let reg = self.loc_to_reg(arg.loc);
                    self.code.encode(instrs::cp(i as Reg + 2, reg));
                }
                let func = self.get_or_reserve_label(name);
                self.code.call(func);
                let reg = self.gpa.allocate();
                self.code.encode(instrs::cp(reg, 1));
                Some(Value {
                    ty:  self.ret,
                    loc: Loc::Reg(reg),
                })
            }
            E::Ident { name, .. } => {
                let var = self.vars.iter().find(|v| v.name.as_ref() == name).unwrap();
                Some(Value {
                    ty:  var.ty,
                    loc: Loc::Stack(var.offset),
                })
            }
            E::Return { val, .. } => {
                if let Some(val) = val {
                    let val = self.expr(val, Some(self.ret)).unwrap();
                    if val.ty != self.ret {
                        panic!("expected {:?}, got {:?}", self.ret, val.ty);
                    }
                    self.assign(
                        Value {
                            ty:  self.ret,
                            loc: Loc::Reg(1),
                        },
                        val,
                    );
                }
                self.ret_relocs.push(RetReloc {
                    offset:       self.code.code.len() as u32,
                    instr_offset: 1,
                    size:         4,
                });
                self.code.encode(instrs::jmp(0));
                None
            }
            E::Block { stmts, .. } => {
                for stmt in stmts {
                    self.expr(stmt, None);
                }
                None
            }
            E::Number { value, .. } => Some(Value {
                ty:  expeted.unwrap_or(Expr::Ident {
                    name: "int",
                    pos:  0,
                }),
                loc: Loc::Imm(value),
            }),
            E::If {
                cond, then, else_, ..
            } => {
                let cond = self
                    .expr(
                        cond,
                        Some(Expr::Ident {
                            name: "bool",
                            pos:  0,
                        }),
                    )
                    .unwrap();
                let reg = self.loc_to_reg(cond.loc);
                let jump_offset = self.code.code.len() as u32;
                self.code.encode(instrs::jeq(reg, 0, 0));
                self.gpa.free(reg);

                self.expr(then, None);

                let jump;

                if let Some(else_) = else_ {
                    let else_jump_offset = self.code.code.len() as u32;
                    self.code.encode(instrs::jmp(0));

                    jump = self.code.code.len() as i16 - jump_offset as i16;

                    self.expr(else_, None);

                    let jump = self.code.code.len() as i32 - else_jump_offset as i32;
                    self.code.code[else_jump_offset as usize + 1..][..4]
                        .copy_from_slice(&jump.to_ne_bytes());
                } else {
                    jump = self.code.code.len() as i16 - jump_offset as i16;
                }

                self.code.code[jump_offset as usize + 3..][..2]
                    .copy_from_slice(&jump.to_ne_bytes());

                None
            }
            E::Loop { body, .. } => {
                let loop_start = self.code.code.len() as u32;
                self.loops.push(Loop {
                    offset: loop_start,
                    relocs: Default::default(),
                });
                self.expr(body, None);

                let loop_end = self.code.code.len();
                self.code
                    .encode(instrs::jmp(loop_start as i32 - loop_end as i32));
                let loop_end = self.code.code.len() as u32;

                let loop_ = self.loops.pop().unwrap();
                for reloc in loop_.relocs {
                    let dest = &mut self.code.code
                        [reloc.offset as usize + reloc.instr_offset as usize..]
                        [..reloc.size as usize];
                    let offset = loop_end as i32 - reloc.offset as i32;
                    dest.copy_from_slice(&offset.to_ne_bytes());
                }

                None
            }
            E::Break { .. } => {
                let loop_ = self.loops.last_mut().unwrap();
                let offset = self.code.code.len() as u32;
                self.code.encode(instrs::jmp(0));
                loop_.relocs.push(RetReloc {
                    offset,
                    instr_offset: 1,
                    size: 4,
                });
                None
            }
            E::Continue { .. } => {
                let loop_ = self.loops.last().unwrap();
                let offset = self.code.code.len() as u32;
                self.code
                    .encode(instrs::jmp(loop_.offset as i32 - offset as i32));
                None
            }
            E::BinOp { left, op, right } => {
                let left = self.expr(left, expeted).unwrap();
                let right = self.expr(right, Some(left.ty)).unwrap();

                let lhs = self.loc_to_reg(left.loc);
                let rhs = self.loc_to_reg(right.loc);

                let op = match op {
                    T::Plus => instrs::add64,
                    T::Minus => instrs::sub64,
                    T::Star => instrs::mul64,
                    T::Le => {
                        self.code.encode(instrs::cmpu(lhs, lhs, rhs));
                        self.gpa.free(rhs);
                        self.code.encode(instrs::cmpui(lhs, lhs, 1));
                        return Some(Value {
                            ty:  Expr::Ident {
                                name: "bool",
                                pos:  0,
                            },
                            loc: Loc::Reg(lhs),
                        });
                    }
                    T::Eq => {
                        self.code.encode(instrs::cmpu(lhs, lhs, rhs));
                        self.gpa.free(rhs);
                        self.code.encode(instrs::cmpui(lhs, lhs, 0));
                        self.code.encode(instrs::not(lhs, lhs));
                        return Some(Value {
                            ty:  Expr::Ident {
                                name: "bool",
                                pos:  0,
                            },
                            loc: Loc::Reg(lhs),
                        });
                    }
                    T::FSlash => |reg0, reg1, reg2| instrs::diru64(reg0, ZERO, reg1, reg2),
                    T::Assign => return self.assign(left, right),
                    _ => unimplemented!("{:#?}", op),
                };

                self.code.encode(op(lhs, lhs, rhs));
                self.gpa.free(rhs);

                Some(Value {
                    ty:  left.ty,
                    loc: Loc::Reg(lhs),
                })
            }
            ast => unimplemented!("{:#?}", ast),
        }
    }

    fn assign(&mut self, left: Value<'a>, right: Value<'a>) -> Option<Value<'a>> {
        let rhs = self.loc_to_reg(right.loc);
        match left.loc {
            Loc::Reg(reg) => self.code.encode(instrs::cp(reg, rhs)),
            Loc::Stack(offset) => self.store_stack(rhs, offset, 8),
            _ => unimplemented!(),
        }
        self.gpa.free(rhs);
        Some(left)
    }

    fn get_or_reserve_label(&mut self, name: &str) -> LabelId {
        if let Some(label) = self.labels.iter().position(|l| l.name.as_ref() == name) {
            label as u32
        } else {
            self.labels.push(FnLabel {
                offset: 0,
                name:   name.into(),
            });
            self.labels.len() as u32 - 1
        }
    }

    fn add_label(&mut self, name: &str) -> Frame {
        let offset = self.code.code.len() as u32;
        let label = if let Some(label) = self.labels.iter().position(|l| l.name.as_ref() == name) {
            self.labels[label].offset = offset;
            label as u32
        } else {
            self.labels.push(FnLabel {
                offset,
                name: name.into(),
            });
            self.labels.len() as u32 - 1
        };

        Frame {
            label,
            prev_relocs: self.code.relocs.len(),
            offset,
        }
    }

    fn get_label(&self, name: &str) -> LabelId {
        self.labels
            .iter()
            .position(|l| l.name.as_ref() == name)
            .unwrap() as _
    }

    fn write_fn_prelude(&mut self, frame: Frame) {
        self.temp.push(RET_ADDR, 8);
        for &reg in self.gpa.used.clone().iter() {
            self.temp.push(reg, 8);
        }
        self.temp.subi64(STACK_PTR, STACK_PTR, self.stack_size as _);

        for reloc in &mut self.code.relocs[frame.prev_relocs..] {
            reloc.offset += self.temp.code.len() as u32;
        }

        for reloc in &mut self.ret_relocs {
            reloc.offset += self.temp.code.len() as u32;
        }

        self.code.code.splice(
            frame.offset as usize..frame.offset as usize,
            self.temp.code.drain(..),
        );
    }

    fn ret(&mut self) {
        self.code
            .encode(instrs::addi64(STACK_PTR, STACK_PTR, self.stack_size as _));
        for reg in self.gpa.used.clone().iter().rev() {
            self.code.pop(*reg, 8);
        }
        self.code.ret();
    }

    pub fn dump(mut self, out: &mut impl std::io::Write) -> std::io::Result<()> {
        self.temp.prelude(self.get_label("main"));
        self.temp
            .relocate(&self.labels, self.temp.code.len() as i64);

        self.code.relocate(&self.labels, 0);
        out.write_all(&self.temp.code)?;
        out.write_all(&self.code.code)
    }

    fn decl_var(&mut self, name: &str, offset: u64, ty: Expr<'a>) {
        self.vars.push(Variable {
            name: name.into(),
            offset,
            ty,
        });
    }
}

pub struct Value<'a> {
    ty:  Expr<'a>,
    loc: Loc,
}

#[derive(Clone, Copy)]
pub enum Loc {
    Reg(Reg),
    Imm(u64),
    Stack(u64),
}

#[cfg(test)]
mod tests {
    use crate::{instrs, log};

    struct TestMem;

    impl hbvm::mem::Memory for TestMem {
        #[inline]
        unsafe fn load(
            &mut self,
            addr: hbvm::mem::Address,
            target: *mut u8,
            count: usize,
        ) -> Result<(), hbvm::mem::LoadError> {
            log::dbg!(
                "read: {:x} {} {:?}",
                addr.get(),
                count,
                core::slice::from_raw_parts(target, count)
                    .iter()
                    .rev()
                    .skip_while(|&&b| b == 0)
                    .map(|&b| format!("{:02x}", b))
                    .collect::<String>()
            );
            unsafe { core::ptr::copy(addr.get() as *const u8, target, count) }
            Ok(())
        }

        #[inline]
        unsafe fn store(
            &mut self,
            addr: hbvm::mem::Address,
            source: *const u8,
            count: usize,
        ) -> Result<(), hbvm::mem::StoreError> {
            log::dbg!("write: {:x} {}", addr.get(), count);
            unsafe { core::ptr::copy(source, addr.get() as *mut u8, count) }
            Ok(())
        }

        #[inline]
        unsafe fn prog_read<T: Copy>(&mut self, addr: hbvm::mem::Address) -> T {
            log::dbg!(
                "read-typed: {:x} {} {:?}",
                addr.get(),
                std::any::type_name::<T>(),
                if core::mem::size_of::<T>() == 1 {
                    instrs::NAMES[std::ptr::read(addr.get() as *const u8) as usize].to_string()
                } else {
                    core::slice::from_raw_parts(addr.get() as *const u8, core::mem::size_of::<T>())
                        .iter()
                        .map(|&b| format!("{:02x}", b))
                        .collect::<String>()
                }
            );
            unsafe { core::ptr::read(addr.get() as *const T) }
        }
    }

    fn generate(input: &'static str, output: &mut String) {
        let path = std::path::Path::new("test");
        let arena = crate::parser::Arena::default();
        let mut buffer = Vec::new();
        let mut parser = super::parser::Parser::new(input, path, &arena, &mut buffer);
        let exprs = parser.file();
        let mut codegen = super::Codegen::new();
        codegen.file(path, &exprs).unwrap();
        let mut out = Vec::new();
        codegen.dump(&mut out).unwrap();

        std::fs::write("test.bin", &out).unwrap();
        use std::fmt::Write;

        let mut stack = [0_u64; 1024];

        let mut vm = unsafe {
            hbvm::Vm::<TestMem, 0>::new(TestMem, hbvm::mem::Address::new(out.as_ptr() as u64))
        };

        vm.write_reg(
            super::STACK_PTR,
            unsafe { stack.as_mut_ptr().add(stack.len()) } as u64,
        );

        let stat = loop {
            match vm.run() {
                Ok(hbvm::VmRunOk::End) => break Ok(()),
                Ok(ev) => writeln!(output, "ev: {:?}", ev).unwrap(),
                Err(e) => break Err(e),
            }
        };

        writeln!(output, "ret: {:?}", vm.read_reg(1).0).unwrap();
        writeln!(output, "status: {:?}", stat).unwrap();
    }

    crate::run_tests! { generate:
        example => include_str!("../examples/main_fn.hb");
        arithmetic => include_str!("../examples/arithmetic.hb");
        variables => include_str!("../examples/variables.hb");
        functions => include_str!("../examples/functions.hb");
        if_statements => include_str!("../examples/if_statement.hb");
        loops => include_str!("../examples/loops.hb");
    }
}