// ASG IR template parsing
//
//  Copyright (C) 2014-2023 Ryan Specialty, LLC.
//
//  This file is part of TAME.
//
//  This program is free software: you can redistribute it and/or modify
//  it under the terms of the GNU General Public License as published by
//  the Free Software Foundation, either version 3 of the License, or
//  (at your option) any later version.
//
//  This program is distributed in the hope that it will be useful,
//  but WITHOUT ANY WARRANTY; without even the implied warranty of
//  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
//  GNU General Public License for more details.
//
//  You should have received a copy of the GNU General Public License
//  along with this program.  If not, see <http://www.gnu.org/licenses/>.

//! AIR template parser.
//!
//! See the [parent module](super) for more information.

use super::{
    super::{graph::object::Tpl, Asg, AsgError, ObjectIndex},
    ir::AirTemplatable,
    AirAggregateCtx, AirExprAggregate,
};
use crate::{
    asg::graph::object::{Meta, ObjectIndexRelTo},
    diagnose::Annotate,
    diagnostic_todo,
    fmt::{DisplayWrapper, TtQuote},
    parse::prelude::*,
    span::Span,
};

/// Template parser and token aggregator.
///
/// A template consists of
///
///   - Metadata about the template,
///       including its parameters; and
///   - A collection of [`AirTemplatable`] tokens representing the body of
///       the template that will be expanded into the application site when
///       the template is applied.
///
/// This contains an embedded [`AirExprAggregate`] parser for handling
///   expressions just the same as [`super::AirAggregate`] does with
///   packages.
#[derive(Debug, PartialEq)]
pub enum AirTplAggregate {
    /// Ready for a template,
    ///   defined as part of the given package.
    ///
    /// This state also includes the template header;
    ///   unlike NIR,
    ///     AIR has no restrictions on when template header tokens are
    ///     provided,
    ///       which simplifies AIR generation.
    Ready,

    /// Toplevel template context.
    ///
    /// Conceptually,
    ///   tokens that are received in this state are interpreted as directly
    ///   applying to the template itself,
    ///     or creating an object directly owned by the template.
    Toplevel(TplState),

    /// Defining a template metavariable.
    TplMeta(TplState, ObjectIndex<Meta>),

    /// Aggregating tokens into a template.
    TplExpr(TplState, AirExprAggregate),
}

impl Display for AirTplAggregate {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match self {
            Self::Ready => write!(f, "ready for template definition"),

            Self::Toplevel(tpl) => write!(f, "building {tpl} at toplevel"),

            Self::TplExpr(tpl, expr) => {
                write!(f, "building {tpl} with {expr}")
            }

            Self::TplMeta(tpl, _) => {
                write!(f, "building {tpl} metavariable")
            }
        }
    }
}

/// The current reachability status of the template.
#[derive(Debug, PartialEq, Eq, Clone, Copy)]
pub enum TplState {
    /// Template is dangling and cannot be referenced by anything else.
    Dangling(ObjectIndex<Tpl>),

    /// Template is anonymous and is not reachable by an identifier,
    ///   but is reachable in the current context.
    AnonymousReachable(ObjectIndex<Tpl>),

    /// Template is reachable via an identifier.
    ///
    /// This uses an [`SPair`] as evidence for that assertion rather than an
    ///   [`ObjectIndex`] so that it provides useful output via [`Display`]
    ///   in parser traces.
    Identified(ObjectIndex<Tpl>, SPair),
}

impl TplState {
    fn oi(&self) -> ObjectIndex<Tpl> {
        match self {
            TplState::Dangling(oi)
            | TplState::AnonymousReachable(oi)
            | TplState::Identified(oi, _) => *oi,
        }
    }

    fn identify(self, id: SPair) -> Self {
        Self::Identified(self.oi(), id)
    }

    fn anonymous_reachable(self) -> Self {
        Self::AnonymousReachable(self.oi())
    }

    /// Attempt to complete a template definition.
    ///
    /// If `self` is [`Self::Dangling`],
    ///   then an [`AsgError::DanglingTpl`] will be returned.
    ///
    /// This updates the span of the template to encompass the entire
    ///   definition,
    ///     even if an error occurs.
    fn close(self, asg: &mut Asg, close_span: Span) -> Result<(), AsgError> {
        let oi = self.oi().close(asg, close_span);

        match self {
            Self::Dangling(_) => {
                Err(AsgError::DanglingTpl(oi.resolve(asg).span()))
            }
            Self::AnonymousReachable(..) | Self::Identified(..) => Ok(()),
        }
    }
}

impl Display for TplState {
    fn fmt(&self, f: &mut std::fmt::Formatter) -> std::fmt::Result {
        match self {
            TplState::Dangling(_) => write!(f, "anonymous dangling template"),
            TplState::AnonymousReachable(_) => {
                write!(f, "anonymous reachable template")
            }
            TplState::Identified(_, id) => {
                write!(f, "identified template {}", TtQuote::wrap(id))
            }
        }
    }
}

impl ParseState for AirTplAggregate {
    type Token = AirTemplatable;
    type Object = ();
    type Error = AsgError;
    type Context = AirAggregateCtx;

    fn parse_token(
        self,
        tok: Self::Token,
        ctx: &mut Self::Context,
    ) -> TransitionResult<Self::Super> {
        use super::ir::{AirBind::*, AirTpl::*};
        use AirTemplatable::*;
        use AirTplAggregate::*;

        match (self, tok) {
            (Ready, AirTpl(TplStart(span))) => {
                let oi_tpl = ctx.asg_mut().create(Tpl::new(span));

                Transition(Toplevel(TplState::Dangling(oi_tpl))).incomplete()
            }

            (Toplevel(..), AirTpl(TplStart(span))) => diagnostic_todo!(
                vec![span.note("for this template")],
                "nested tpl open"
            ),

            (Toplevel(tpl), AirBind(BindIdent(id))) => {
                let oi_root = ctx.rooting_oi().expect("TODO");
                let asg = ctx.asg_mut();

                asg.lookup_global_or_missing(id)
                    .bind_definition(asg, id, tpl.oi())
                    .map(|oi_ident| oi_root.defines(asg, oi_ident))
                    .map(|_| ())
                    .transition(Toplevel(tpl.identify(id)))
            }

            (Toplevel(tpl), AirBind(RefIdent(id))) => {
                tpl.oi().apply_named_tpl(ctx.asg_mut(), id);
                Transition(Toplevel(tpl)).incomplete()
            }

            (Toplevel(tpl), AirTpl(TplMetaStart(span))) => {
                let oi_meta = ctx.asg_mut().create(Meta::new_required(span));
                Transition(TplMeta(tpl, oi_meta)).incomplete()
            }
            (TplMeta(tpl, oi_meta), AirTpl(TplMetaEnd(cspan))) => {
                oi_meta.close(ctx.asg_mut(), cspan);
                Transition(Toplevel(tpl)).incomplete()
            }

            (TplMeta(tpl, oi_meta), AirTpl(TplLexeme(lexeme))) => Transition(
                TplMeta(tpl, oi_meta.assign_lexeme(ctx.asg_mut(), lexeme)),
            )
            .incomplete(),

            (TplMeta(tpl, oi_meta), AirBind(BindIdent(name))) => {
                oi_meta.identify_as_tpl_param(ctx.asg_mut(), tpl.oi(), name);
                Transition(TplMeta(tpl, oi_meta)).incomplete()
            }

            (TplMeta(..), tok @ AirBind(RefIdent(..))) => {
                diagnostic_todo!(
                    vec![tok.note("this token")],
                    "AirBind in metavar context (param-value)"
                )
            }

            (TplMeta(..), tok @ AirExpr(..)) => {
                diagnostic_todo!(
                    vec![tok.note("this token")],
                    "AirExpr in metavar context (e.g. @values@)"
                )
            }

            (
                TplMeta(..),
                tok @ AirTpl(
                    TplStart(..) | TplMetaStart(..) | TplEnd(..)
                    | TplEndRef(..),
                ),
            ) => {
                diagnostic_todo!(vec![tok.note("this token")], "AirTpl variant")
            }

            (Toplevel(..), tok @ AirTpl(TplMetaEnd(..))) => {
                diagnostic_todo!(
                    vec![tok.note("this token")],
                    "unbalanced meta"
                )
            }

            (Toplevel(..), tok @ AirTpl(TplLexeme(..))) => {
                diagnostic_todo!(
                    vec![tok.note("this token")],
                    "err: TplLexeme outside of metavar"
                )
            }

            (Toplevel(tpl), AirTpl(TplEnd(span))) => {
                tpl.close(ctx.asg_mut(), span).transition(Ready)
            }

            (TplExpr(tpl, expr), AirTpl(TplEnd(span))) => {
                // TODO: duplicated with AirAggregate
                if expr.is_accepting(ctx) {
                    ctx.pop();
                    tpl.close(ctx.asg_mut(), span).transition(Ready)
                } else {
                    Transition(TplExpr(tpl, expr))
                        .err(AsgError::InvalidTplEndContext(span))
                }
            }

            (Toplevel(tpl), AirTpl(TplEndRef(span))) => {
                let oi_target = ctx.expansion_oi().expect("TODO");
                tpl.oi().expand_into(ctx.asg_mut(), oi_target);

                Transition(Toplevel(tpl.anonymous_reachable()))
                    .incomplete()
                    .with_lookahead(AirTpl(TplEnd(span)))
            }

            (TplExpr(tpl, expr_done), AirTpl(TplEndRef(span))) => {
                let oi_target = ctx.expansion_oi().expect("TODO");
                tpl.oi().expand_into(ctx.asg_mut(), oi_target);

                // TODO: We have to make sure the expression ended first!
                Transition(TplExpr(tpl.anonymous_reachable(), expr_done))
                    .incomplete()
                    .with_lookahead(AirTpl(TplEnd(span)))
            }

            (Toplevel(tpl), tok @ AirExpr(_)) => {
                ctx.push(Toplevel(tpl));

                Transition(TplExpr(tpl, AirExprAggregate::new()))
                    .incomplete()
                    .with_lookahead(tok)
            }

            (TplExpr(tpl, expr), AirExpr(etok)) => {
                Self::delegate_expr(ctx, tpl, expr, etok)
            }

            (TplExpr(tpl, expr), AirBind(etok)) => {
                Self::delegate_expr(ctx, tpl, expr, etok)
            }

            (TplExpr(..), AirTpl(TplStart(span))) => {
                diagnostic_todo!(
                    vec![span.note("for this token")],
                    "nested template (template-generated template)"
                )
            }

            (
                Ready | TplExpr(..),
                tok @ AirTpl(TplMetaStart(..) | TplLexeme(..) | TplMetaEnd(..)),
            ) => {
                diagnostic_todo!(
                    vec![tok.note("for this token")],
                    "metasyntactic token in non-tpl-toplevel context: {tok:?}"
                )
            }

            (st @ Ready, AirTpl(TplEnd(span) | TplEndRef(span))) => {
                Transition(st).err(AsgError::UnbalancedTpl(span))
            }

            (st @ Ready, tok @ (AirExpr(..) | AirBind(..))) => {
                Transition(st).dead(tok)
            }
        }
    }

    fn is_accepting(&self, _: &Self::Context) -> bool {
        matches!(self, Self::Ready)
    }
}

impl AirTplAggregate {
    pub(super) fn new() -> Self {
        Self::Ready
    }

    pub(super) fn active_tpl_oi(&self) -> Option<ObjectIndex<Tpl>> {
        use AirTplAggregate::*;

        match self {
            Ready => None,
            Toplevel(tplst) | TplMeta(tplst, _) | TplExpr(tplst, _) => {
                Some(tplst.oi())
            }
        }
    }

    /// Delegate to the expression parser [`AirExprAggregate`].
    fn delegate_expr(
        asg: &mut <Self as ParseState>::Context,
        tpl: TplState,
        expr: AirExprAggregate,
        etok: impl Into<<AirExprAggregate as ParseState>::Token>,
    ) -> TransitionResult<Self> {
        let tok = etok.into();

        expr.parse_token(tok, asg).branch_dead::<Self, _>(
            |_, ()| Transition(Self::Toplevel(tpl)).incomplete(),
            |expr, result, ()| {
                result
                    .map(ParseStatus::reflexivity)
                    .transition(Self::TplExpr(tpl, expr))
            },
            (),
        )
    }
}

#[cfg(test)]
mod test;