use crate::{obj::prelude::*, vm::consts::*};
use shredder::EmptyScan;

#[derive(Debug, PartialEq, Clone, Copy)]
pub enum Inst {
    /// Push a literal symbol object to the stack.
    PushSym(Sym),

    /// Push a const value reference to the stack.
    PushConst(ConstHandle),

    /// Looks up and pushes a local value.
    LoadLocal(Name),

    /// Looks up and pushes a global value.
    LoadGlobal(Name),

    /// Pop a value from the stack, possibly into a local symbol.
    PopLocal(Option<Name>),

    /// Pop a value from the stack, possibly into a global symbol.
    PopGlobal(Option<Name>),

    /// Pops a symbol value and an object reference.
    ///
    /// This will get an attr from the object reference pointed to by the symbol.
    GetAttr(Sym),

    /// Pops a target reference and a source reference from the stack.
    ///
    /// The target reference will have the given symbol attribute assigned to the source.
    ///
    /// In code, it would look like this:
    ///
    /// `target.symbol = source`
    ///
    SetAttr(Sym),

    /// Jump to a given address in the current function unconditionally.
    Jump(usize),

    /// Jump to a given address in the current function if the condition flag is true.
    ///
    /// The condition flag may be set by an internal function.
    JumpTrue(usize),

    /// Calls a function with the supplied number of arguments.
    ///
    /// The stack, from bottom to top, should contain the function followed by the arguments.
    ///
    /// After the function has returned, the VM will have popped the arguments and function
    /// pointer, and the return value will be on top of the stack.
    Call(usize),

    /// Indexes a value, e.g. a list or a dict.
    ///
    /// The stack, from bottom to top, should have the expression being indexed, and then the
    /// indexed value.
    Index,

    /// Pops the top value from the stack, and returns from the function, using the popped value as
    /// a return value.
    Return,

    /// Replaces the top stack value with its negation applied.
    UnNeg,

    /// Replaces the top stack value with its absolute value applied.
    UnPos,

    /// Pops the top two items off of the stack, and applies the binary addition operator to them,
    /// pushing the result to the stack.
    BinPlus,

    /// Pops the top two items off of the stack, and applies the binary subtraction operator to
    /// them, pushing the result to the stack.
    BinMinus,

    /// Pops the top two items off of the stack, and applies the binary multiplication operator to
    /// them, pushing the result to the stack.
    BinMul,

    /// Pops the top two items off of the stack, and applies the binary division operator to them,
    /// pushing the result to the stack.
    BinDiv,

    /// Pops the top two items off of the stack, and applies the boolean equality operator to them,
    /// pushing the result to the stack.
    BinEq,

    /// Pops the top two items off of the stack, and applies the boolean inequality operator to
    /// them, pushing the result to the stack.
    BinNeq,

    /// Pops the top two items off of the stack, and applies the boolean less-than operator to
    /// them, pushing the result to the stack.
    BinLt,

    /// Pops the top two items off of the stack, and applies the binary less-than or equals
    /// operator to them, pushing the result to the stack.
    BinLe,

    /// Pops the top two items off of the stack, and applies the boolean greater-than operator to
    /// them, pushing the result to the stack.
    BinGt,

    /// Pops the top two items off of the stack, and applies the binary greater-than or equals
    /// operator to them, pushing the result to the stack.
    BinGe,

    /// Pops the top two items off of the stack, and applies the boolean and operator to them,
    /// pushing the result to the stack.
    BinAnd,

    /// Pops the top two items off of the stack, and applies the boolean or operator to them,
    /// pushing the result to the stack.
    BinOr,
}

//
// impl Inst
//
impl Inst {
    pub fn name(&self) -> &'static str {
        match self {
            Inst::PushSym(_) => "PUSH_SYM",
            Inst::PushConst(_) => "PUSH_CONST",
            Inst::LoadLocal(_) => "LOAD_LOCAL",
            Inst::LoadGlobal(_) => "LOAD_GLOBAL",
            Inst::PopLocal(_) => "POP_LOCAL",
            Inst::PopGlobal(_) => "POP_GLOBAL",
            Inst::GetAttr(_) => "GET_ATTR",
            Inst::SetAttr(_) => "SET_ATTR",
            Inst::Jump(_) => "JUMP",
            Inst::JumpTrue(_) => "JUMP_TRUE",
            Inst::Call(_) => "CALL",
            Inst::Index => "INDEX",
            Inst::Return => "RETURN",
            Inst::UnNeg => "UN_NEG",
            Inst::UnPos => "UN_POS",
            Inst::BinPlus => "BIN_PLUS",
            Inst::BinMinus => "BIN_MINUS",
            Inst::BinMul => "BIN_MUL",
            Inst::BinDiv => "BIN_DIV",
            Inst::BinEq => "BIN_EQ",
            Inst::BinNeq => "BIN_NEQ",
            Inst::BinLt => "BIN_LT",
            Inst::BinLe => "BIN_LE",
            Inst::BinGt => "BIN_GT",
            Inst::BinGe => "BIN_GE",
            Inst::BinAnd => "BIN_AND",
            Inst::BinOr => "BIN_OR",
        }
    }
}

impl EmptyScan for Inst {}