#![deny(unused_must_use)]

use std::collections::HashSet;

use proc_macro2::{Ident, Span, TokenStream};
use quote::{format_ident, quote, quote_spanned};
use syn::parse::ParseStream;
use syn::spanned::Spanned;
use syn::{Attribute, LitStr, Meta, Path, Token, Type};
use synstructure::{BindingInfo, Structure, VariantInfo};

use super::utils::SubdiagnosticVariant;
use crate::diagnostics::error::{
    DiagnosticDeriveError, span_err, throw_invalid_attr, throw_span_err,
};
use crate::diagnostics::message::Message;
use crate::diagnostics::utils::{
    FieldInfo, FieldInnerTy, FieldMap, SetOnce, SpannedOption, SubdiagnosticKind,
    build_field_mapping, is_doc_comment, report_error_if_not_applied_to_span, report_type_error,
    should_generate_arg, type_is_bool, type_is_unit, type_matches_path,
};

pub(crate) fn each_variant<'s, F>(structure: &mut Structure<'s>, f: F) -> TokenStream
where
    F: for<'v> Fn(DiagnosticDeriveVariantBuilder, &VariantInfo<'v>) -> TokenStream,
{
    let ast = structure.ast();
    let span = ast.span().unwrap();
    match ast.data {
        syn::Data::Struct(..) | syn::Data::Enum(..) => (),
        syn::Data::Union(..) => {
            span_err(span, "diagnostic derives can only be used on structs and enums").emit();
        }
    }

    if matches!(ast.data, syn::Data::Enum(..)) {
        for attr in &ast.attrs {
            span_err(attr.span().unwrap(), "unsupported type attribute for diagnostic derive enum")
                .emit();
        }
    }

    structure.bind_with(|_| synstructure::BindStyle::Move);
    let variants = structure.each_variant(|variant| {
        let span = match structure.ast().data {
            syn::Data::Struct(..) => span,
            // There isn't a good way to get the span of the variant, so the variant's
            // name will need to do.
            _ => variant.ast().ident.span().unwrap(),
        };
        let builder = DiagnosticDeriveVariantBuilder {
            span,
            field_map: build_field_mapping(variant),
            formatting_init: TokenStream::new(),
            message: None,
            code: None,
            used_fields: HashSet::new(),
        };
        f(builder, variant)
    });

    quote! {
        match self {
            #variants
        }
    }
}

/// Tracks persistent information required for a specific variant when building up individual calls
/// to diagnostic methods for generated diagnostic derives.
pub(crate) struct DiagnosticDeriveVariantBuilder {
    /// Initialization of format strings for code suggestions.
    pub formatting_init: TokenStream,

    /// Span of the struct or the enum variant.
    pub span: proc_macro::Span,

    /// Store a map of field name to its corresponding field. This is built on construction of the
    /// derive builder.
    pub field_map: FieldMap,

    /// Message is a mandatory part of the struct attribute as corresponds to the Fluent message that
    /// has the actual diagnostic message.
    pub message: Option<Message>,

    /// Error codes are a optional part of the struct attribute - this is only set to detect
    /// multiple specifications.
    pub code: SpannedOption<()>,

    pub used_fields: HashSet<proc_macro2::Ident>,
}

impl DiagnosticDeriveVariantBuilder {
    pub(crate) fn primary_message(&self) -> Option<&Message> {
        match self.message.as_ref() {
            None => {
                span_err(self.span, "diagnostic message not specified")
                    .help(
                        "specify the message as the first argument to the `#[diag(...)]` \
                            attribute, such as `#[diag(\"Example error\")]`",
                    )
                    .emit();
                None
            }
            Some(msg) => Some(msg),
        }
    }

    /// Generates calls to `code` and similar functions based on the attributes on the type or
    /// variant.
    pub(crate) fn preamble(&mut self, variant: &VariantInfo<'_>) -> TokenStream {
        let ast = variant.ast();
        let attrs = &ast.attrs;
        let preamble = attrs.iter().map(|attr| {
            self.generate_structure_code_for_attr(attr).unwrap_or_else(|v| v.to_compile_error())
        });

        quote! {
            #(#preamble)*;
        }
    }

    /// Generates calls to `span_label` and similar functions based on the attributes on fields or
    /// calls to `arg` when no attributes are present.
    pub(crate) fn body(&mut self, variant: &VariantInfo<'_>) -> TokenStream {
        let mut body = quote! {};
        let mut second_part = quote! {};

        // Subdiagnostic additions.
        for binding in variant.bindings().iter().filter(|bi| !should_generate_arg(bi.ast())) {
            second_part.extend(self.generate_field_attrs_code(binding));
        }
        // Generate `arg` calls first..
        for binding in variant.bindings().iter().filter(|bi| should_generate_arg(bi.ast())) {
            if self.is_used_in_message(binding) {
                body.extend(self.generate_field_code(binding));
            }
        }
        body.extend(second_part);
        body
    }

    fn is_used_in_message(&self, binding: &BindingInfo<'_>) -> bool {
        binding.ast().ident.as_ref().is_some_and(|ident| self.used_fields.contains(ident))
    }

    /// Parse a `SubdiagnosticKind` from an `Attribute`.
    fn parse_subdiag_attribute(
        &mut self,
        attr: &Attribute,
    ) -> Result<Option<(SubdiagnosticKind, Message, bool)>, DiagnosticDeriveError> {
        let Some(subdiag) =
            SubdiagnosticVariant::from_attr(attr, &self.field_map, &mut self.used_fields)?
        else {
            // Some attributes aren't errors - like documentation comments - but also aren't
            // subdiagnostics.
            return Ok(None);
        };

        if let SubdiagnosticKind::MultipartSuggestion { .. } = subdiag.kind {
            throw_invalid_attr!(attr, |diag| diag
                .help("consider creating a `Subdiagnostic` instead"));
        }

        let Some(message) = subdiag.message else {
            throw_invalid_attr!(attr, |diag| diag.help("subdiagnostic message is missing"))
        };

        Ok(Some((subdiag.kind, message, false)))
    }

    /// Establishes state in the `DiagnosticDeriveBuilder` resulting from the struct
    /// attributes like `#[diag(..)]`, such as the message and error code. Generates
    /// diagnostic builder calls for setting error code and creating note/help messages.
    fn generate_structure_code_for_attr(
        &mut self,
        attr: &Attribute,
    ) -> Result<TokenStream, DiagnosticDeriveError> {
        // Always allow documentation comments.
        if is_doc_comment(attr) {
            return Ok(quote! {});
        }

        let name = attr.path().segments.last().unwrap().ident.to_string();
        let name = name.as_str();

        if name == "diag" {
            let mut tokens = TokenStream::new();
            attr.parse_args_with(|input: ParseStream<'_>| {
                if input.peek(LitStr) {
                    // Parse an inline message
                    let message = input.parse::<LitStr>()?;
                    if !message.suffix().is_empty() {
                        span_err(
                            message.span().unwrap(),
                            "Inline message is not allowed to have a suffix",
                        )
                        .emit();
                    }
                    let message = Message::new(
                        attr.span(),
                        message.span(),
                        message.value(),
                        &self.field_map,
                        &mut self.used_fields,
                    );
                    self.message = Some(message);
                }

                // Parse arguments
                while !input.is_empty() {
                    input.parse::<Token![,]>()?;
                    // Allow trailing comma
                    if input.is_empty() {
                        break;
                    }
                    let arg_name: Path = input.parse::<Path>()?;
                    if input.peek(Token![,]) {
                        span_err(
                            arg_name.span().unwrap(),
                            "diagnostic message must be the first argument",
                        )
                        .emit();
                        continue;
                    }
                    let arg_name = arg_name.require_ident()?;
                    input.parse::<Token![=]>()?;
                    let arg_value = input.parse::<syn::Expr>()?;
                    match arg_name.to_string().as_str() {
                        "code" => {
                            self.code.set_once((), arg_name.span().unwrap());
                            tokens.extend(quote! {
                                diag.code(#arg_value);
                            });
                        }
                        _ => {
                            span_err(arg_name.span().unwrap(), "unknown argument")
                                .note("only the `code` parameter is valid after the message")
                                .emit();
                        }
                    }
                }
                Ok(())
            })?;

            return Ok(tokens);
        }

        let Some((subdiag, message, _no_span)) = self.parse_subdiag_attribute(attr)? else {
            // Some attributes aren't errors - like documentation comments - but also aren't
            // subdiagnostics.
            return Ok(quote! {});
        };
        let fn_ident = format_ident!("{}", subdiag);
        match subdiag {
            SubdiagnosticKind::Note
            | SubdiagnosticKind::NoteOnce
            | SubdiagnosticKind::Help
            | SubdiagnosticKind::HelpOnce
            | SubdiagnosticKind::Warn => Ok(self.add_subdiagnostic(&fn_ident, message)),
            SubdiagnosticKind::Label | SubdiagnosticKind::Suggestion { .. } => {
                throw_invalid_attr!(attr, |diag| diag
                    .help("`#[label]` and `#[suggestion]` can only be applied to fields"));
            }
            SubdiagnosticKind::MultipartSuggestion { .. } => unreachable!(),
        }
    }

    fn generate_field_code(&mut self, binding_info: &BindingInfo<'_>) -> TokenStream {
        let field = binding_info.ast();
        let mut field_binding = binding_info.binding.clone();
        field_binding.set_span(field.ty.span());

        let Some(ident) = field.ident.as_ref() else {
            span_err(field.span().unwrap(), "tuple structs are not supported").emit();
            return TokenStream::new();
        };
        let ident = format_ident!("{}", ident); // strip `r#` prefix, if present

        quote! {
            diag.arg(
                stringify!(#ident),
                #field_binding
            );
        }
    }

    fn generate_field_attrs_code(&mut self, binding_info: &BindingInfo<'_>) -> TokenStream {
        let field = binding_info.ast();
        let field_binding = &binding_info.binding;

        let inner_ty = FieldInnerTy::from_type(&field.ty);
        let mut seen_label = false;

        field
            .attrs
            .iter()
            .map(move |attr| {
                // Always allow documentation comments.
                if is_doc_comment(attr) {
                    return quote! {};
                }

                let name = attr.path().segments.last().unwrap().ident.to_string();

                if name == "primary_span" && seen_label {
                    span_err(attr.span().unwrap(), format!("`#[primary_span]` must be placed before labels, since it overwrites the span of the diagnostic")).emit();
                }
                if name == "label" {
                    seen_label = true;
                }

                let needs_clone =
                    name == "primary_span" && matches!(inner_ty, FieldInnerTy::Vec(_));
                let (binding, needs_destructure) = if needs_clone {
                    // `primary_span` can accept a `Vec<Span>` so don't destructure that.
                    (quote_spanned! {inner_ty.span()=> #field_binding.clone() }, false)
                } else {
                    (quote_spanned! {inner_ty.span()=> #field_binding }, true)
                };

                let generated_code = self
                    .generate_inner_field_code(
                        attr,
                        FieldInfo { binding: binding_info, ty: inner_ty, span: &field.span() },
                        binding,
                    )
                    .unwrap_or_else(|v| v.to_compile_error());

                if needs_destructure {
                    inner_ty.with(field_binding, generated_code)
                } else {
                    generated_code
                }
            })
            .collect()
    }

    fn generate_inner_field_code(
        &mut self,
        attr: &Attribute,
        info: FieldInfo<'_>,
        binding: TokenStream,
    ) -> Result<TokenStream, DiagnosticDeriveError> {
        let ident = &attr.path().segments.last().unwrap().ident;
        let name = ident.to_string();
        match (&attr.meta, name.as_str()) {
            (Meta::Path(_), "primary_span") => {
                report_error_if_not_applied_to_span(attr, &info)?;

                return Ok(quote! {
                    diag.span(#binding);
                });
            }
            (Meta::Path(_), "subdiagnostic") => {
                return Ok(quote! { diag.subdiagnostic(#binding); });
            }
            _ => (),
        }

        let Some((subdiag, message, _no_span)) = self.parse_subdiag_attribute(attr)? else {
            // Some attributes aren't errors - like documentation comments - but also aren't
            // subdiagnostics.
            return Ok(quote! {});
        };
        let fn_ident = format_ident!("{}", subdiag);
        match subdiag {
            SubdiagnosticKind::Label => {
                report_error_if_not_applied_to_span(attr, &info)?;
                Ok(self.add_spanned_subdiagnostic(binding, &fn_ident, message))
            }
            SubdiagnosticKind::Note
            | SubdiagnosticKind::NoteOnce
            | SubdiagnosticKind::Help
            | SubdiagnosticKind::HelpOnce
            | SubdiagnosticKind::Warn => {
                let inner = info.ty.inner_type();
                if type_matches_path(inner, &["rustc_span", "Span"])
                    || type_matches_path(inner, &["rustc_span", "MultiSpan"])
                {
                    Ok(self.add_spanned_subdiagnostic(binding, &fn_ident, message))
                } else if type_is_unit(inner)
                    || (matches!(info.ty, FieldInnerTy::Plain(_)) && type_is_bool(inner))
                {
                    Ok(self.add_subdiagnostic(&fn_ident, message))
                } else {
                    report_type_error(attr, "`Span`, `MultiSpan`, `bool` or `()`")?
                }
            }
            SubdiagnosticKind::Suggestion {
                suggestion_kind,
                applicability: static_applicability,
                code_field,
                code_init,
            } => {
                if let FieldInnerTy::Vec(_) = info.ty {
                    throw_invalid_attr!(attr, |diag| {
                        diag
                        .note("`#[suggestion(...)]` applied to `Vec` field is ambiguous")
                        .help("to show a suggestion consisting of multiple parts, use a `Subdiagnostic` annotated with `#[multipart_suggestion(...)]`")
                        .help("to show a variable set of suggestions, use a `Vec` of `Subdiagnostic`s annotated with `#[suggestion(...)]`")
                    });
                }

                let (span_field, mut applicability) = self.span_and_applicability_of_ty(info)?;

                if let Some((static_applicability, span)) = static_applicability {
                    applicability.set_once(quote! { #static_applicability }, span);
                }

                let message = message.diag_message();
                let applicability = applicability
                    .value()
                    .unwrap_or_else(|| quote! { rustc_errors::Applicability::Unspecified });
                let style = suggestion_kind.to_suggestion_style();

                self.formatting_init.extend(code_init);
                Ok(quote! {
                    diag.span_suggestions_with_style(
                        #span_field,
                        #message,
                        #code_field,
                        #applicability,
                        #style
                    );
                })
            }
            SubdiagnosticKind::MultipartSuggestion { .. } => unreachable!(),
        }
    }

    /// Adds a spanned subdiagnostic by generating a `diag.span_$kind` call with the current message
    /// and `fluent_attr_identifier`.
    fn add_spanned_subdiagnostic(
        &self,
        field_binding: TokenStream,
        kind: &Ident,
        message: Message,
    ) -> TokenStream {
        let fn_name = format_ident!("span_{}", kind);
        let message = message.diag_message();
        quote! {
            diag.#fn_name(
                #field_binding,
                #message
            );
        }
    }

    /// Adds a subdiagnostic by generating a `diag.span_$kind` call with the current message
    /// and `fluent_attr_identifier`.
    fn add_subdiagnostic(&self, kind: &Ident, message: Message) -> TokenStream {
        let message = message.diag_message();
        quote! {
            diag.#kind(#message);
        }
    }

    fn span_and_applicability_of_ty(
        &self,
        info: FieldInfo<'_>,
    ) -> Result<(TokenStream, SpannedOption<TokenStream>), DiagnosticDeriveError> {
        match &info.ty.inner_type() {
            // If `ty` is `Span` w/out applicability, then use `Applicability::Unspecified`.
            ty @ Type::Path(..) if type_matches_path(ty, &["rustc_span", "Span"]) => {
                let binding = &info.binding.binding;
                Ok((quote!(#binding), None))
            }
            // If `ty` is `(Span, Applicability)` then return tokens accessing those.
            Type::Tuple(tup) => {
                let mut span_idx = None;
                let mut applicability_idx = None;

                fn type_err(span: &Span) -> Result<!, DiagnosticDeriveError> {
                    span_err(span.unwrap(), "wrong types for suggestion")
                        .help(
                            "`#[suggestion(...)]` on a tuple field must be applied to fields \
                             of type `(Span, Applicability)`",
                        )
                        .emit();
                    Err(DiagnosticDeriveError::ErrorHandled)
                }

                for (idx, elem) in tup.elems.iter().enumerate() {
                    if type_matches_path(elem, &["rustc_span", "Span"]) {
                        span_idx.set_once(syn::Index::from(idx), elem.span().unwrap());
                    } else if type_matches_path(elem, &["rustc_errors", "Applicability"]) {
                        applicability_idx.set_once(syn::Index::from(idx), elem.span().unwrap());
                    } else {
                        type_err(&elem.span())?;
                    }
                }

                let Some((span_idx, _)) = span_idx else {
                    type_err(&tup.span())?;
                };
                let Some((applicability_idx, applicability_span)) = applicability_idx else {
                    type_err(&tup.span())?;
                };
                let binding = &info.binding.binding;
                let span = quote!(#binding.#span_idx);
                let applicability = quote!(#binding.#applicability_idx);

                Ok((span, Some((applicability, applicability_span))))
            }
            // If `ty` isn't a `Span` or `(Span, Applicability)` then emit an error.
            _ => throw_span_err!(info.span.unwrap(), "wrong field type for suggestion", |diag| {
                diag.help(
                    "`#[suggestion(...)]` should be applied to fields of type `Span` or \
                     `(Span, Applicability)`",
                )
            }),
        }
    }
}
