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// Vesper: declarative human-readable structural language
//
// SPDX-License-Identifier: Apache-2.0
//
// Written in 2024 by
//     Dr Maxim Orlovsky <orlovsky@ubideco.org>
//
// Copyright (C) 2024 UBIDECO Institute, Switzerland
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

use std::fmt::{Display, Formatter};

use amplify::confinement::{SmallVec, TinyVec};
use strict_encoding::Ident;

pub trait Predicate: Clone + Eq {
    type Attr: Attribute;
}

pub trait Expression: Clone + Eq + Display {}

pub trait Attribute: Clone + Eq {
    type Expression: Expression;

    fn is_named(&self) -> bool { self.name().is_some() }
    fn name(&self) -> Option<Ident>;
    fn value(&self) -> AttrVal<Self::Expression>;
}

#[derive(Clone, Eq, PartialEq, Debug, Display)]
#[display(inner)]
pub enum AttrVal<E: Expression> {
    Ident(Ident),
    Expr(E),
}

#[derive(Clone, Eq, PartialEq, Debug)]
pub struct TExpr<P: Predicate> {
    pub subject: Ident,
    pub predicate: P,
    pub attributes: SmallVec<P::Attr>,
    pub content: TinyVec<Box<TExpr<P>>>,
    pub comment: Option<String>,
}

impl<P: Predicate> TExpr<P> {
    pub fn display(&self) -> TExprDisplay<P>
    where P: Display {
        TExprDisplay {
            expr: self,
            indent: 0,
            tab: s!("  "),
        }
    }
}

pub struct TExprDisplay<'expr, P: Predicate>
where P: Display
{
    expr: &'expr TExpr<P>,
    indent: usize,
    tab: String,
}

impl<'expr, P: Predicate> TExprDisplay<'expr, P>
where P: Display
{
    pub fn indented(parent: &Self, expr: &'expr TExpr<P>) -> TExprDisplay<'expr, P> {
        TExprDisplay {
            expr,
            indent: parent.indent + 1,
            tab: parent.tab.clone(),
        }
    }
}

impl<'expr, P: Predicate> Display for TExprDisplay<'expr, P>
where P: Display
{
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        const MAX_LINE_VARS: usize = 8;

        let expr = self.expr;
        let attrs = &expr.attributes;

        let indent = self.tab.repeat(self.indent);
        write!(f, "{indent}{} {}", expr.subject, expr.predicate)?;

        if attrs.len() > MAX_LINE_VARS {
            write!(f, " {{\n{indent}{}", self.tab)?;
        } else if !attrs.is_empty() {
            f.write_str(" ")?;
        }
        for (pos, attr) in expr.attributes.iter().enumerate() {
            if pos == 1 || (pos > 0 && pos % MAX_LINE_VARS != 1) {
                f.write_str(" ")?;
            }
            if let Some(name) = attr.name() {
                write!(f, "{name}=")?;
            }
            write!(f, "{}", attr.value())?;

            if pos > 0 && pos % MAX_LINE_VARS == 0 {
                write!(f, "\n{indent}{}", self.tab)?;
            }
        }
        if attrs.len() > MAX_LINE_VARS {
            write!(f, "\n{indent}}}")?;
        }

        if let Some(comment) = &expr.comment {
            write!(f, " -- {comment}")?;
        }
        writeln!(f)?;

        for expr in &expr.content {
            let display = TExprDisplay::indented(self, expr.as_ref());
            Display::fmt(&display, f)?;
        }
        Ok(())
    }
}