use darling::{FromDeriveInput, FromField, FromVariant};
use proc_macro2::TokenStream;
use quote::{format_ident, quote, quote_spanned};
use syn::{parse_macro_input, spanned::Spanned, Data, DeriveInput};

#[derive(Default, FromMeta)]
struct DisplayFieldOpts {
    /// Skip formatting this field or variant
    #[darling(default)]
    skip: bool,
    /// Use this field when formatting extra data
    #[darling(default)]
    extra: bool,
}

#[derive(Default, FromMeta)]
struct DisplayVariantOpts {
    /// Value to use as extra format instead of the variant name
    #[darling(default)]
    extra: Option<String>,
}

#[derive(FromField)]
#[darling(attributes(lang_util))]
struct NodeDisplayField {
    ident: Option<syn::Ident>,
    #[darling(default)]
    display: DisplayFieldOpts,
}

#[derive(FromVariant)]
#[darling(attributes(lang_util))]
struct NodeDisplayVariant {
    ident: syn::Ident,
    fields: darling::ast::Fields<NodeDisplayField>,
    #[darling(default)]
    display: DisplayVariantOpts,
}

fn is_unit_enum(en: &syn::DataEnum) -> bool {
    en.variants.iter().all(|variant| {
        NodeDisplayVariant::from_variant(variant)
            .map(|dv| dv.fields.style == darling::ast::Style::Unit)
            .unwrap_or(false)
    })
}

#[derive(Default, FromMeta)]
#[darling(default)]
struct NodeDisplay {
    leaf: bool,
}

#[derive(FromDeriveInput)]
#[darling(attributes(lang_util))]
pub(crate) struct NodeDisplayOpts {
    ident: syn::Ident,
    generics: syn::Generics,
    #[darling(default)]
    display: NodeDisplay,
}

pub(crate) fn node_display(input: proc_macro::TokenStream) -> proc_macro::TokenStream {
    // Parse the input tokens into a syntax tree
    let input = parse_macro_input!(input as DeriveInput);

    // Find out struct-level options
    let opts = NodeDisplayOpts::from_derive_input(&input).expect("failed to parse options");

    // Add anonymous lifetimes as needed
    let lifetimes: Vec<_> = opts.generics.lifetimes().map(|_| quote! { '_ }).collect();

    // Generate the name of the target for usage in impl targets
    let base_ident = &opts.ident;
    let struct_name = if lifetimes.is_empty() {
        quote! { #base_ident }
    } else {
        quote! { #base_ident<#(#lifetimes),*> }
    };

    // Is this a "Data" node?
    let raw_name = base_ident
        .to_string()
        .strip_suffix("Data")
        .map(|id| format_ident!("{}", id));

    // The node name for the NodeDisplay impl
    let node_name = raw_name.unwrap_or_else(|| base_ident.clone()).to_string();

    let display_quoted = {
        let display_extra_impl = {
            let mut ts = TokenStream::new();

            // TODO: Support `extra` on variant struct fields
            match &input.data {
                Data::Struct(st) => {
                    for (i, field) in st.fields.iter().enumerate() {
                        let df = NodeDisplayField::from_field(field)
                            .expect("failed to parse field attributes");

                        let ident = if let Some(id) = &df.ident {
                            quote! { #id }
                        } else {
                            let i = syn::Index::from(i);
                            quote! { #i }
                        };

                        if df.display.extra {
                            ts.extend(quote_spanned! {
                                field.span() =>
                                    write!(f, " `{}`", self.#ident)?;
                            });
                        }
                    }
                }
                Data::Enum(en) => {
                    let mut match_body = TokenStream::new();

                    // Are the variants all units?
                    for variant in &en.variants {
                        let dv = NodeDisplayVariant::from_variant(variant)
                            .expect("failed to parse variant attributes");

                        let name = &dv.ident;

                        // Find out how to display the enum variant
                        let vs = dv
                            .display
                            .extra
                            .clone()
                            .unwrap_or_else(|| dv.ident.to_string());

                        // Fields pattern
                        let fields = match dv.fields.style {
                            darling::ast::Style::Unit => None,
                            darling::ast::Style::Tuple => {
                                let mut v = Vec::with_capacity(dv.fields.fields.len());
                                let ident = format_ident!("_");
                                for _ in 0..dv.fields.fields.len() {
                                    v.push(ident.clone());
                                }
                                Some(quote! { (#(#v),*) })
                            }
                            darling::ast::Style::Struct => Some(quote! { { .. } }),
                        };

                        let quoted = quote_spanned! {
                            variant.span() =>
                                Self::#name #fields=> {
                                    write!(f, " `{}`", #vs)?;
                                }
                        };

                        match_body.extend(quoted);
                    }

                    ts.extend(quote_spanned! {
                        input.span() => match self {
                            #match_body
                        };
                    });
                }
                Data::Union(_) => ts.extend(quote_spanned! {
                    input.span() =>
                        compile_error!("Unions are not supported");
                }),
            };

            ts.extend(quote! { Ok(()) });
            ts
        };

        let display_children_impl = if opts.display.leaf {
            quote! { Ok(()) }
        } else {
            let mut ts = TokenStream::new();
            ts.extend(quote! { use ::lang_util::node::NodeDisplay; });

            match &input.data {
                Data::Struct(st) => {
                    for (i, field) in st.fields.iter().enumerate() {
                        let df = NodeDisplayField::from_field(field)
                            .expect("failed to parse field attributes");

                        let ident = if let Some(id) = &df.ident {
                            quote! { #id }
                        } else {
                            let i = syn::Index::from(i);
                            quote! { #i }
                        };

                        ts.extend(quote_spanned! {
                            field.span() =>
                                write!(f, "{}", self.#ident.display().set_level(level))?;
                        });
                    }
                }
                Data::Enum(en) => {
                    let mut match_body = TokenStream::new();

                    if !is_unit_enum(en) {
                        for variant in &en.variants {
                            let dv = NodeDisplayVariant::from_variant(variant)
                                .expect("failed to parse variant attributes");

                            let name = &dv.ident;

                            if let darling::ast::Style::Unit = dv.fields.style {
                                let vs = dv.ident.to_string();
                                let quoted = quote_spanned! {
                                    variant.span() =>
                                        Self::#name => {
                                            write!(f, "{}", ::lang_util::node::NodeDisplayWrapper::new(#vs, level))?;
                                        }
                                };

                                match_body.extend(quoted);
                            } else if let darling::ast::Style::Tuple = dv.fields.style {
                                let mut variant_body = TokenStream::new();
                                let mut field_names = Vec::new();

                                for (i, field) in dv.fields.fields.iter().enumerate() {
                                    // Add tuple identifier
                                    let ff = if field.display.skip {
                                        format_ident!("_")
                                    } else {
                                        format_ident!("tuple{}", i)
                                    };

                                    field_names.push(ff.clone());

                                    // Add code
                                    if !field.display.skip {
                                        variant_body.extend(quote! {
                                            write!(f, "{}", #ff.display().set_level(level))?;
                                        });
                                    }
                                }

                                match_body.extend(quote_spanned! {
                                    variant.span() =>
                                        Self::#name(#(#field_names),*) => {
                                            #variant_body
                                        }
                                });
                            } else {
                                let mut variant_body = TokenStream::new();
                                let mut field_names = Vec::new();

                                for field in &dv.fields.fields {
                                    // Add tuple identifier
                                    let ff = field.ident.as_ref().unwrap();
                                    field_names.push(ff.clone());

                                    // Add code
                                    if !field.display.skip {
                                        variant_body.extend(quote! {
                                            write!(f, "{}", #ff.display().set_level(level))?;
                                        });
                                    }
                                }

                                match_body.extend(quote_spanned! {
                                    variant.span() =>
                                        Self::#name { #(#field_names),* } => {
                                            #variant_body
                                        }
                                });
                            }
                        }

                        ts.extend(quote_spanned! {
                            input.span() => match self {
                                #match_body
                            };
                        });
                    }
                }
                Data::Union(_) => ts.extend(quote_spanned! {
                    input.span() =>
                        compile_error!("Unions are not supported");
                }),
            };

            ts.extend(quote! { Ok(()) });
            ts
        };

        quote! {
            #[automatically_derived]
            impl ::lang_util::node::NodeContentDisplay for #struct_name {
                fn name() -> Option<&'static str> {
                   Some(#node_name)
                }

                fn display_extra(&self, f: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result {
                    #display_extra_impl
                }

                fn display_children(&self, level: usize, f: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result {
                    #display_children_impl
                }
            }
        }
    };

    proc_macro::TokenStream::from(display_quoted)
}