use rustc_ast::{MetaItem, NestedMetaItem};
use rustc_attr as attr;
use rustc_data_structures::fx::FxHashMap;
use rustc_errors::{struct_span_err, ErrorGuaranteed};
use rustc_hir::def_id::DefId;
use rustc_middle::ty::{self, GenericParamDefKind, TyCtxt};
use rustc_parse_format::{ParseMode, Parser, Piece, Position};
use rustc_span::symbol::{kw, sym, Symbol};
use rustc_span::{Span, DUMMY_SP};

use crate::errors::{
    EmptyOnClauseInOnUnimplemented, InvalidOnClauseInOnUnimplemented, NoValueInOnUnimplemented,
};

#[derive(Clone, Debug)]
pub struct OnUnimplementedFormatString(Symbol);

#[derive(Debug)]
pub struct OnUnimplementedDirective {
    pub condition: Option<MetaItem>,
    pub subcommands: Vec<OnUnimplementedDirective>,
    pub message: Option<OnUnimplementedFormatString>,
    pub label: Option<OnUnimplementedFormatString>,
    pub note: Option<OnUnimplementedFormatString>,
    pub parent_label: Option<OnUnimplementedFormatString>,
    pub append_const_msg: Option<Option<Symbol>>,
}

#[derive(Default)]
pub struct OnUnimplementedNote {
    pub message: Option<String>,
    pub label: Option<String>,
    pub note: Option<String>,
    pub parent_label: Option<String>,
    /// Append a message for `~const Trait` errors. `None` means not requested and
    /// should fallback to a generic message, `Some(None)` suggests using the default
    /// appended message, `Some(Some(s))` suggests use the `s` message instead of the
    /// default one..
    pub append_const_msg: Option<Option<Symbol>>,
}

impl<'tcx> OnUnimplementedDirective {
    fn parse(
        tcx: TyCtxt<'tcx>,
        item_def_id: DefId,
        items: &[NestedMetaItem],
        span: Span,
        is_root: bool,
    ) -> Result<Self, ErrorGuaranteed> {
        let mut errored = None;
        let mut item_iter = items.iter();

        let parse_value = |value_str| {
            OnUnimplementedFormatString::try_parse(tcx, item_def_id, value_str, span).map(Some)
        };

        let condition = if is_root {
            None
        } else {
            let cond = item_iter
                .next()
                .ok_or_else(|| tcx.sess.emit_err(EmptyOnClauseInOnUnimplemented { span }))?
                .meta_item()
                .ok_or_else(|| tcx.sess.emit_err(InvalidOnClauseInOnUnimplemented { span }))?;
            attr::eval_condition(cond, &tcx.sess.parse_sess, Some(tcx.features()), &mut |cfg| {
                if let Some(value) = cfg.value && let Err(guar) = parse_value(value) {
                    errored = Some(guar);
                }
                true
            });
            Some(cond.clone())
        };

        let mut message = None;
        let mut label = None;
        let mut note = None;
        let mut parent_label = None;
        let mut subcommands = vec![];
        let mut append_const_msg = None;

        for item in item_iter {
            if item.has_name(sym::message) && message.is_none() {
                if let Some(message_) = item.value_str() {
                    message = parse_value(message_)?;
                    continue;
                }
            } else if item.has_name(sym::label) && label.is_none() {
                if let Some(label_) = item.value_str() {
                    label = parse_value(label_)?;
                    continue;
                }
            } else if item.has_name(sym::note) && note.is_none() {
                if let Some(note_) = item.value_str() {
                    note = parse_value(note_)?;
                    continue;
                }
            } else if item.has_name(sym::parent_label) && parent_label.is_none() {
                if let Some(parent_label_) = item.value_str() {
                    parent_label = parse_value(parent_label_)?;
                    continue;
                }
            } else if item.has_name(sym::on)
                && is_root
                && message.is_none()
                && label.is_none()
                && note.is_none()
            {
                if let Some(items) = item.meta_item_list() {
                    match Self::parse(tcx, item_def_id, &items, item.span(), false) {
                        Ok(subcommand) => subcommands.push(subcommand),
                        Err(reported) => errored = Some(reported),
                    };
                    continue;
                }
            } else if item.has_name(sym::append_const_msg) && append_const_msg.is_none() {
                if let Some(msg) = item.value_str() {
                    append_const_msg = Some(Some(msg));
                    continue;
                } else if item.is_word() {
                    append_const_msg = Some(None);
                    continue;
                }
            }

            // nothing found
            tcx.sess.emit_err(NoValueInOnUnimplemented { span: item.span() });
        }

        if let Some(reported) = errored {
            Err(reported)
        } else {
            Ok(OnUnimplementedDirective {
                condition,
                subcommands,
                message,
                label,
                note,
                parent_label,
                append_const_msg,
            })
        }
    }

    pub fn of_item(tcx: TyCtxt<'tcx>, item_def_id: DefId) -> Result<Option<Self>, ErrorGuaranteed> {
        let Some(attr) = tcx.get_attr(item_def_id, sym::rustc_on_unimplemented) else {
            return Ok(None);
        };

        let result = if let Some(items) = attr.meta_item_list() {
            Self::parse(tcx, item_def_id, &items, attr.span, true).map(Some)
        } else if let Some(value) = attr.value_str() {
            Ok(Some(OnUnimplementedDirective {
                condition: None,
                message: None,
                subcommands: vec![],
                label: Some(OnUnimplementedFormatString::try_parse(
                    tcx,
                    item_def_id,
                    value,
                    attr.span,
                )?),
                note: None,
                parent_label: None,
                append_const_msg: None,
            }))
        } else {
            let reported =
                tcx.sess.delay_span_bug(DUMMY_SP, "of_item: neither meta_item_list nor value_str");
            return Err(reported);
        };
        debug!("of_item({:?}) = {:?}", item_def_id, result);
        result
    }

    pub fn evaluate(
        &self,
        tcx: TyCtxt<'tcx>,
        trait_ref: ty::TraitRef<'tcx>,
        options: &[(Symbol, Option<String>)],
    ) -> OnUnimplementedNote {
        let mut message = None;
        let mut label = None;
        let mut note = None;
        let mut parent_label = None;
        let mut append_const_msg = None;
        info!("evaluate({:?}, trait_ref={:?}, options={:?})", self, trait_ref, options);

        let options_map: FxHashMap<Symbol, String> =
            options.iter().filter_map(|(k, v)| v.as_ref().map(|v| (*k, v.to_owned()))).collect();

        for command in self.subcommands.iter().chain(Some(self)).rev() {
            if let Some(ref condition) = command.condition && !attr::eval_condition(
                condition,
                &tcx.sess.parse_sess,
                Some(tcx.features()),
                &mut |cfg| {
                    let value = cfg.value.map(|v| {
                        OnUnimplementedFormatString(v).format(tcx, trait_ref, &options_map)
                    });

                    options.contains(&(cfg.name, value))
                },
            ) {
                debug!("evaluate: skipping {:?} due to condition", command);
                continue;
            }
            debug!("evaluate: {:?} succeeded", command);
            if let Some(ref message_) = command.message {
                message = Some(message_.clone());
            }

            if let Some(ref label_) = command.label {
                label = Some(label_.clone());
            }

            if let Some(ref note_) = command.note {
                note = Some(note_.clone());
            }

            if let Some(ref parent_label_) = command.parent_label {
                parent_label = Some(parent_label_.clone());
            }

            append_const_msg = command.append_const_msg;
        }

        OnUnimplementedNote {
            label: label.map(|l| l.format(tcx, trait_ref, &options_map)),
            message: message.map(|m| m.format(tcx, trait_ref, &options_map)),
            note: note.map(|n| n.format(tcx, trait_ref, &options_map)),
            parent_label: parent_label.map(|e_s| e_s.format(tcx, trait_ref, &options_map)),
            append_const_msg,
        }
    }
}

impl<'tcx> OnUnimplementedFormatString {
    fn try_parse(
        tcx: TyCtxt<'tcx>,
        item_def_id: DefId,
        from: Symbol,
        err_sp: Span,
    ) -> Result<Self, ErrorGuaranteed> {
        let result = OnUnimplementedFormatString(from);
        result.verify(tcx, item_def_id, err_sp)?;
        Ok(result)
    }

    fn verify(
        &self,
        tcx: TyCtxt<'tcx>,
        item_def_id: DefId,
        span: Span,
    ) -> Result<(), ErrorGuaranteed> {
        let trait_def_id = if tcx.is_trait(item_def_id) {
            item_def_id
        } else {
            tcx.trait_id_of_impl(item_def_id)
                .expect("expected `on_unimplemented` to correspond to a trait")
        };
        let trait_name = tcx.item_name(trait_def_id);
        let generics = tcx.generics_of(item_def_id);
        let s = self.0.as_str();
        let parser = Parser::new(s, None, None, false, ParseMode::Format);
        let mut result = Ok(());
        for token in parser {
            match token {
                Piece::String(_) => (), // Normal string, no need to check it
                Piece::NextArgument(a) => match a.position {
                    Position::ArgumentNamed(s) => {
                        match Symbol::intern(s) {
                            // `{Self}` is allowed
                            kw::SelfUpper => (),
                            // `{ThisTraitsName}` is allowed
                            s if s == trait_name => (),
                            // `{from_method}` is allowed
                            sym::from_method => (),
                            // `{from_desugaring}` is allowed
                            sym::from_desugaring => (),
                            // `{ItemContext}` is allowed
                            sym::ItemContext => (),
                            // `{integral}` and `{integer}` and `{float}` are allowed
                            sym::integral | sym::integer_ | sym::float => (),
                            // So is `{A}` if A is a type parameter
                            s => match generics.params.iter().find(|param| param.name == s) {
                                Some(_) => (),
                                None => {
                                    let reported = struct_span_err!(
                                        tcx.sess,
                                        span,
                                        E0230,
                                        "there is no parameter `{}` on {}",
                                        s,
                                        if trait_def_id == item_def_id {
                                            format!("trait `{}`", trait_name)
                                        } else {
                                            "impl".to_string()
                                        }
                                    )
                                    .emit();
                                    result = Err(reported);
                                }
                            },
                        }
                    }
                    // `{:1}` and `{}` are not to be used
                    Position::ArgumentIs(..) | Position::ArgumentImplicitlyIs(_) => {
                        let reported = struct_span_err!(
                            tcx.sess,
                            span,
                            E0231,
                            "only named substitution parameters are allowed"
                        )
                        .emit();
                        result = Err(reported);
                    }
                },
            }
        }

        result
    }

    pub fn format(
        &self,
        tcx: TyCtxt<'tcx>,
        trait_ref: ty::TraitRef<'tcx>,
        options: &FxHashMap<Symbol, String>,
    ) -> String {
        let name = tcx.item_name(trait_ref.def_id);
        let trait_str = tcx.def_path_str(trait_ref.def_id);
        let generics = tcx.generics_of(trait_ref.def_id);
        let generic_map = generics
            .params
            .iter()
            .filter_map(|param| {
                let value = match param.kind {
                    GenericParamDefKind::Type { .. } | GenericParamDefKind::Const { .. } => {
                        trait_ref.substs[param.index as usize].to_string()
                    }
                    GenericParamDefKind::Lifetime => return None,
                };
                let name = param.name;
                Some((name, value))
            })
            .collect::<FxHashMap<Symbol, String>>();
        let empty_string = String::new();

        let s = self.0.as_str();
        let parser = Parser::new(s, None, None, false, ParseMode::Format);
        let item_context = (options.get(&sym::ItemContext)).unwrap_or(&empty_string);
        parser
            .map(|p| match p {
                Piece::String(s) => s,
                Piece::NextArgument(a) => match a.position {
                    Position::ArgumentNamed(s) => {
                        let s = Symbol::intern(s);
                        match generic_map.get(&s) {
                            Some(val) => val,
                            None if s == name => &trait_str,
                            None => {
                                if let Some(val) = options.get(&s) {
                                    val
                                } else if s == sym::from_desugaring || s == sym::from_method {
                                    // don't break messages using these two arguments incorrectly
                                    &empty_string
                                } else if s == sym::ItemContext {
                                    &item_context
                                } else if s == sym::integral {
                                    "{integral}"
                                } else if s == sym::integer_ {
                                    "{integer}"
                                } else if s == sym::float {
                                    "{float}"
                                } else {
                                    bug!(
                                        "broken on_unimplemented {:?} for {:?}: \
                                      no argument matching {:?}",
                                        self.0,
                                        trait_ref,
                                        s
                                    )
                                }
                            }
                        }
                    }
                    _ => bug!("broken on_unimplemented {:?} - bad format arg", self.0),
                },
            })
            .collect()
    }
}