// pest. The Elegant Parser

// Copyright (c) 2018 Dragoș Tiselice

//

// Licensed under the Apache License, Version 2.0

// <LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0> or the MIT

// license <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your

// option. All files in the project carrying such notice may not be copied,

// modified, or distributed except according to those terms.

use std::collections::HashMap;

use crate::ast::*;

pub fn skip(rule: Rule, map: &HashMap<String, Expr>) -> Rule {

    fn populate_choices(

        expr: Expr,

        map: &HashMap<String, Expr>,

        mut choices: Vec<String>,

    ) -> Option<Expr> {

        match expr {

            Expr::Choice(lhs, rhs) => {

                if let Expr::Str(string) = *lhs {

                    choices.push(string);

                    populate_choices(*rhs, map, choices)

                } else if let Expr::Ident(name) = *lhs {

                    // Try inlining rule in choices

                    if let Some(Expr::Skip(mut inlined_choices)) = map

                        .get(&name)

                        .and_then(|expr| populate_choices(expr.clone(), map, vec![]))

                    {

                        choices.append(&mut inlined_choices);

                        populate_choices(*rhs, map, choices)

                    } else {

                        None

                    }

                } else {

                    None

                }

            }

            Expr::Str(string) => {

                choices.push(string);

                Some(Expr::Skip(choices))

            }

            // Try inlining single rule

            Expr::Ident(name) => map

                .get(&name)

                .and_then(|expr| populate_choices(expr.clone(), map, choices)),

            _ => None,

        }

    }

    let Rule { name, ty, expr } = rule;

    Rule {

        name,

        ty,

        expr: if ty == RuleType::Atomic {

            expr.map_top_down(|expr| {

                if let Expr::Rep(expr) = expr.clone() {

                    if let Expr::Seq(lhs, rhs) = *expr {

                        if let (Expr::NegPred(expr), Expr::Ident(ident)) = (*lhs, *rhs) {

                            if ident == "ANY" {

                                if let Some(expr) = populate_choices(*expr, map, vec![]) {

                                    return expr;

                                }

                            }

                        }

                    }

                };

                expr

            })

        } else {

            expr

        },

    }

}