use proc_macro2::{Ident, Span, TokenStream};
use quote::{ToTokens, TokenStreamExt};
use syn::{
    punctuated::Punctuated, spanned::Spanned, Data, DeriveInput, Expr, Lit, Meta, Token, UnOp,
};

#[derive(Debug)]
pub(crate) enum DiscriminantType {
    ISize,
    I8,
    I16,
    I32,
    I64,
    I128,
    USize,
    U8,
    U16,
    U32,
    U64,
    U128,
}

impl DiscriminantType {
    #[inline]
    pub(crate) fn parse_str<S: AsRef<str>>(s: S) -> Option<Self> {
        match s.as_ref() {
            "i8" => Some(Self::I8),
            "i16" => Some(Self::I16),
            "i32" => Some(Self::I32),
            "i64" => Some(Self::I64),
            "i128" => Some(Self::I128),
            "isize" => Some(Self::ISize),
            "u8" => Some(Self::U8),
            "u16" => Some(Self::U16),
            "u32" => Some(Self::U32),
            "u64" => Some(Self::U64),
            "u128" => Some(Self::U128),
            "usize" => Some(Self::USize),
            _ => None,
        }
    }

    #[inline]
    pub(crate) const fn as_str(&self) -> &'static str {
        match self {
            Self::ISize => "isize",
            Self::I8 => "i8",
            Self::I16 => "i16",
            Self::I32 => "i32",
            Self::I64 => "i64",
            Self::I128 => "i128",
            Self::USize => "usize",
            Self::U8 => "u8",
            Self::U16 => "u16",
            Self::U32 => "u32",
            Self::U64 => "u64",
            Self::U128 => "u128",
        }
    }
}

impl ToTokens for DiscriminantType {
    #[inline]
    fn to_tokens(&self, tokens: &mut TokenStream) {
        tokens.append(Ident::new(self.as_str(), Span::call_site()));
    }
}

impl DiscriminantType {
    pub(crate) fn from_ast(ast: &DeriveInput) -> syn::Result<Self> {
        if let Data::Enum(data) = &ast.data {
            for attr in ast.attrs.iter() {
                if attr.path().is_ident("repr") {
                    // #[repr(u8)], #[repr(u16)], ..., etc.
                    if let Meta::List(list) = &attr.meta {
                        let result =
                            list.parse_args_with(Punctuated::<Ident, Token![,]>::parse_terminated)?;

                        if let Some(value) = result.into_iter().next() {
                            if let Some(t) = Self::parse_str(value.to_string()) {
                                return Ok(t);
                            }
                        }
                    }
                }
            }

            let mut min = i128::MAX;
            let mut max = i128::MIN;
            let mut counter = 0i128;

            for variant in data.variants.iter() {
                if let Some((_, exp)) = variant.discriminant.as_ref() {
                    match exp {
                        Expr::Lit(lit) => {
                            if let Lit::Int(lit) = &lit.lit {
                                counter = lit
                                    .base10_parse()
                                    .map_err(|error| syn::Error::new(lit.span(), error))?;
                            } else {
                                return Err(syn::Error::new(lit.span(), "not an integer"));
                            }
                        },
                        Expr::Unary(unary) => {
                            if let UnOp::Neg(_) = unary.op {
                                if let Expr::Lit(lit) = unary.expr.as_ref() {
                                    if let Lit::Int(lit) = &lit.lit {
                                        match lit.base10_parse::<i128>() {
                                            Ok(i) => {
                                                counter = -i;
                                            },
                                            Err(error) => {
                                                // overflow
                                                if lit.base10_digits()
                                                    == "170141183460469231731687303715884105728"
                                                {
                                                    counter = i128::MIN;
                                                } else {
                                                    return Err(syn::Error::new(lit.span(), error));
                                                }
                                            },
                                        }
                                    } else {
                                        return Err(syn::Error::new(lit.span(), "not an integer"));
                                    }
                                } else {
                                    return Err(syn::Error::new(
                                        unary.expr.span(),
                                        "not a literal",
                                    ));
                                }
                            } else {
                                return Err(syn::Error::new(
                                    unary.op.span(),
                                    "this operation is not allow here",
                                ));
                            }
                        },
                        _ => return Err(syn::Error::new(exp.span(), "not a literal")),
                    }
                }

                if min > counter {
                    min = counter;
                }

                if max < counter {
                    max = counter;
                }

                counter = counter.saturating_add(1);
            }

            Ok(if min >= i8::MIN as i128 && max <= i8::MAX as i128 {
                Self::I8
            } else if min >= i16::MIN as i128 && max <= i16::MAX as i128 {
                Self::I16
            } else if min >= i32::MIN as i128 && max <= i32::MAX as i128 {
                Self::I32
            } else if min >= i64::MIN as i128 && max <= i64::MAX as i128 {
                Self::I64
            } else {
                Self::I128
            })
        } else {
            Err(syn::Error::new(ast.span(), "not an enum"))
        }
    }
}