// This file is part of yash, an extended POSIX shell.
// Copyright (C) 2020 WATANABE Yuki
//
// 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 <https://www.gnu.org/licenses/>.

//! Part of the lexer that parses operators.

use super::core::Lexer;
use super::core::Token;
use super::core::TokenId;
use crate::parser::core::Result;
use crate::syntax::Literal;
use crate::syntax::Unquoted;
use crate::syntax::Word;
use std::fmt;
use std::fmt::Write;
use std::future::Future;
use std::pin::Pin;

/// Operator token identifier.
#[derive(Clone, Copy, Debug, Eq, PartialEq)]
pub enum Operator {
    /// Newline
    Newline,
    /// `&`
    And,
    /// `&&`
    AndAnd,
    /// `(`
    OpenParen,
    /// `)`
    CloseParen,
    /// `;`
    Semicolon,
    /// `;;`
    SemicolonSemicolon,
    /// `<`
    Less,
    /// `<&`
    LessAnd,
    /// `<(`
    LessOpenParen,
    /// `<<`
    LessLess,
    /// `<<-`
    LessLessDash,
    /// `<<<`
    LessLessLess,
    /// `<>`
    LessGreater,
    /// `>`
    Greater,
    /// `>&`
    GreaterAnd,
    /// `>(`
    GreaterOpenParen,
    /// `>>`
    GreaterGreater,
    /// `>>|`
    GreaterGreaterBar,
    /// `>|`
    GreaterBar,
    /// `|`
    Bar,
    /// `||`
    BarBar,
}

impl Operator {
    /// Determines if this token can be a delimiter of a clause.
    ///
    /// This function returns `true` for `CloseParen` and `SemicolonSemicolon`,
    /// and `false` for others.
    pub fn is_clause_delimiter(self) -> bool {
        use Operator::*;
        match self {
            CloseParen | SemicolonSemicolon => true,
            Newline | And | AndAnd | OpenParen | Semicolon | Less | LessAnd | LessOpenParen
            | LessLess | LessLessDash | LessLessLess | LessGreater | Greater | GreaterAnd
            | GreaterOpenParen | GreaterGreater | GreaterGreaterBar | GreaterBar | Bar | BarBar => {
                false
            }
        }
    }
}

impl fmt::Display for Operator {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        use Operator::*;
        match self {
            Newline => f.write_char('\n'),
            And => f.write_char('&'),
            AndAnd => f.write_str("&&"),
            OpenParen => f.write_char('('),
            CloseParen => f.write_char(')'),
            Semicolon => f.write_char(';'),
            SemicolonSemicolon => f.write_str(";;"),
            Less => f.write_char('<'),
            LessAnd => f.write_str("<&"),
            LessOpenParen => f.write_str("<("),
            LessLess => f.write_str("<<"),
            LessLessDash => f.write_str("<<-"),
            LessLessLess => f.write_str("<<<"),
            LessGreater => f.write_str("<>"),
            Greater => f.write_char('>'),
            GreaterAnd => f.write_str(">&"),
            GreaterOpenParen => f.write_str(">("),
            GreaterGreater => f.write_str(">>"),
            GreaterGreaterBar => f.write_str(">>|"),
            GreaterBar => f.write_str(">|"),
            Bar => f.write_char('|'),
            BarBar => f.write_str("||"),
        }
    }
}

/// Trie data structure that defines a set of operator tokens.
///
/// This struct represents a node of the trie. A node is a sorted array of [`Edge`]s.
#[derive(Copy, Clone, Debug)]
pub struct Trie(&'static [Edge]);

/// Edge of a [`Trie`].
#[derive(Copy, Clone, Debug)]
pub struct Edge {
    /// Character value of this edge.
    pub key: char,
    /// Final operator token that is delimited after taking this edge if there are no longer
    /// matches.
    pub value: Option<Operator>,
    /// Sub-trie containing values for keys that have the common prefix.
    pub next: Trie,
}

impl Trie {
    /// Tests if this trie is empty.
    pub fn is_empty(&self) -> bool {
        self.0.is_empty()
    }

    /// Finds an edge for the given key.
    pub fn edge(&self, key: char) -> Option<&Edge> {
        self.0
            .binary_search_by_key(&key, |edge| edge.key)
            .ok()
            .map(|i| &self.0[i])
    }
}

/// Trie containing all the operators.
pub const OPERATORS: Trie = Trie(&[
    Edge {
        key: '\n',
        value: Some(Operator::Newline),
        next: NONE,
    },
    Edge {
        key: '&',
        value: Some(Operator::And),
        next: AND,
    },
    Edge {
        key: '(',
        value: Some(Operator::OpenParen),
        next: NONE,
    },
    Edge {
        key: ')',
        value: Some(Operator::CloseParen),
        next: NONE,
    },
    Edge {
        key: ';',
        value: Some(Operator::Semicolon),
        next: SEMICOLON,
    },
    Edge {
        key: '<',
        value: Some(Operator::Less),
        next: LESS,
    },
    Edge {
        key: '>',
        value: Some(Operator::Greater),
        next: GREATER,
    },
    Edge {
        key: '|',
        value: Some(Operator::Bar),
        next: BAR,
    },
]);

/// Trie of the operators that start with `&`.
const AND: Trie = Trie(&[Edge {
    key: '&',
    value: Some(Operator::AndAnd),
    next: NONE,
}]);

/// Trie of the operators that start with `;`.
const SEMICOLON: Trie = Trie(&[Edge {
    key: ';',
    value: Some(Operator::SemicolonSemicolon),
    next: NONE,
}]);

/// Trie of the operators that start with `<`.
const LESS: Trie = Trie(&[
    Edge {
        key: '&',
        value: Some(Operator::LessAnd),
        next: NONE,
    },
    Edge {
        key: '(',
        value: Some(Operator::LessOpenParen),
        next: NONE,
    },
    Edge {
        key: '<',
        value: Some(Operator::LessLess),
        next: LESS_LESS,
    },
    Edge {
        key: '>',
        value: Some(Operator::LessGreater),
        next: NONE,
    },
]);

/// Trie of the operators that start with `<<`.
const LESS_LESS: Trie = Trie(&[
    Edge {
        key: '-',
        value: Some(Operator::LessLessDash),
        next: NONE,
    },
    Edge {
        key: '<',
        value: Some(Operator::LessLessLess),
        next: NONE,
    },
]);

/// Trie of the operators that start with `>`.
const GREATER: Trie = Trie(&[
    Edge {
        key: '&',
        value: Some(Operator::GreaterAnd),
        next: NONE,
    },
    Edge {
        key: '(',
        value: Some(Operator::GreaterOpenParen),
        next: NONE,
    },
    Edge {
        key: '>',
        value: Some(Operator::GreaterGreater),
        next: GREATER_GREATER,
    },
    Edge {
        key: '|',
        value: Some(Operator::GreaterBar),
        next: NONE,
    },
]);

/// Trie of the operators that start with `>>`.
const GREATER_GREATER: Trie = Trie(&[Edge {
    key: '|',
    value: Some(Operator::GreaterGreaterBar),
    next: NONE,
}]);

/// Trie of the operators that start with `|`.
const BAR: Trie = Trie(&[Edge {
    key: '|',
    value: Some(Operator::BarBar),
    next: NONE,
}]);

/// Trie containing nothing.
const NONE: Trie = Trie(&[]);

/// Tests whether the given character is the first character of an operator.
pub fn is_operator_char(c: char) -> bool {
    OPERATORS.edge(c).is_some()
}

/// Return type for [`Lexer::operator_tail`]
struct OperatorTail {
    pub operator: Operator,
    pub reversed_key: Vec<char>,
}

impl Lexer<'_> {
    /// Parses an operator that matches a key in the given trie, if any.
    fn operator_tail(
        &mut self,
        trie: Trie,
    ) -> Pin<Box<dyn Future<Output = Result<Option<OperatorTail>>> + '_>> {
        Box::pin(async move {
            if trie.is_empty() {
                return Ok(None);
            }

            let c = match self.peek_char().await? {
                None => return Ok(None),
                Some(c) => c,
            };
            let edge = match trie.edge(c) {
                None => return Ok(None),
                Some(edge) => edge,
            };

            let old_index = self.index();
            self.consume_char();

            if let Some(mut operator_tail) = self.operator_tail(edge.next).await? {
                operator_tail.reversed_key.push(c);
                return Ok(Some(operator_tail));
            }

            match edge.value {
                None => {
                    self.rewind(old_index);
                    Ok(None)
                }
                Some(operator) => Ok(Some(OperatorTail {
                    operator,
                    reversed_key: vec![c],
                })),
            }
        })
    }

    /// Parses an operator token.
    pub async fn operator(&mut self) -> Result<Option<Token>> {
        let index = self.index();
        self.operator_tail(OPERATORS).await.map(|o| {
            o.map(|ot| {
                let OperatorTail {
                    operator,
                    reversed_key,
                } = ot;
                let units = reversed_key
                    .into_iter()
                    .rev()
                    .map(|c| Unquoted(Literal(c)))
                    .collect::<Vec<_>>();
                let location = self.location_range(index..self.index());
                let word = Word { units, location };
                let id = TokenId::Operator(operator);
                Token { word, id, index }
            })
        })
    }
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::input::Context;
    use crate::input::Input;
    use crate::source::Source;
    use crate::syntax::TextUnit;
    use crate::syntax::WordUnit;
    use futures_executor::block_on;
    use std::num::NonZeroU64;

    fn ensure_sorted(trie: &Trie) {
        assert!(
            trie.0.windows(2).all(|pair| pair[0].key < pair[1].key),
            "The trie should be sorted: {:?}",
            trie
        );

        for edge in trie.0 {
            ensure_sorted(&edge.next);
        }
    }

    #[test]
    fn tries_are_sorted() {
        ensure_sorted(&OPERATORS);
    }

    #[test]
    fn lexer_operator_longest_match() {
        let mut lexer = Lexer::from_memory("<<-", Source::Unknown);

        let t = block_on(lexer.operator()).unwrap().unwrap();
        assert_eq!(t.word.units.len(), 3);
        assert_eq!(t.word.units[0], WordUnit::Unquoted(TextUnit::Literal('<')));
        assert_eq!(t.word.units[1], WordUnit::Unquoted(TextUnit::Literal('<')));
        assert_eq!(t.word.units[2], WordUnit::Unquoted(TextUnit::Literal('-')));
        assert_eq!(*t.word.location.code.value.borrow(), "<<-");
        assert_eq!(t.word.location.code.start_line_number.get(), 1);
        assert_eq!(t.word.location.code.source, Source::Unknown);
        assert_eq!(t.word.location.range, 0..3);
        assert_eq!(t.id, TokenId::Operator(Operator::LessLessDash));

        assert_eq!(block_on(lexer.peek_char()), Ok(None));
    }

    #[test]
    fn lexer_operator_delimited_by_another_operator() {
        let mut lexer = Lexer::from_memory("<<>", Source::Unknown);

        let t = block_on(lexer.operator()).unwrap().unwrap();
        assert_eq!(t.word.units.len(), 2);
        assert_eq!(t.word.units[0], WordUnit::Unquoted(TextUnit::Literal('<')));
        assert_eq!(t.word.units[1], WordUnit::Unquoted(TextUnit::Literal('<')));
        assert_eq!(*t.word.location.code.value.borrow(), "<<>");
        assert_eq!(t.word.location.code.start_line_number.get(), 1);
        assert_eq!(t.word.location.code.source, Source::Unknown);
        assert_eq!(t.word.location.range, 0..2);
        assert_eq!(t.id, TokenId::Operator(Operator::LessLess));

        assert_eq!(block_on(lexer.location()).unwrap().range, 2..3);
    }

    #[test]
    fn lexer_operator_delimited_by_eof() {
        let mut lexer = Lexer::from_memory("<<", Source::Unknown);

        let t = block_on(lexer.operator()).unwrap().unwrap();
        assert_eq!(t.word.units.len(), 2);
        assert_eq!(t.word.units[0], WordUnit::Unquoted(TextUnit::Literal('<')));
        assert_eq!(t.word.units[1], WordUnit::Unquoted(TextUnit::Literal('<')));
        assert_eq!(*t.word.location.code.value.borrow(), "<<");
        assert_eq!(t.word.location.code.start_line_number.get(), 1);
        assert_eq!(t.word.location.code.source, Source::Unknown);
        assert_eq!(t.word.location.range, 0..2);
        assert_eq!(t.id, TokenId::Operator(Operator::LessLess));

        assert_eq!(block_on(lexer.peek_char()), Ok(None));
    }

    #[test]
    fn lexer_operator_containing_line_continuations() {
        let mut lexer = Lexer::from_memory("\\\n\\\n<\\\n<\\\n>", Source::Unknown);

        let t = block_on(lexer.operator()).unwrap().unwrap();
        assert_eq!(t.word.units.len(), 2);
        assert_eq!(t.word.units[0], WordUnit::Unquoted(TextUnit::Literal('<')));
        assert_eq!(t.word.units[1], WordUnit::Unquoted(TextUnit::Literal('<')));
        assert_eq!(*t.word.location.code.value.borrow(), "\\\n\\\n<\\\n<\\\n>");
        assert_eq!(t.word.location.code.start_line_number.get(), 1);
        assert_eq!(t.word.location.code.source, Source::Unknown);
        assert_eq!(t.word.location.range, 0..10);
        assert_eq!(t.id, TokenId::Operator(Operator::LessLess));

        assert_eq!(block_on(lexer.peek_char()), Ok(Some('>')));
    }

    #[test]
    fn lexer_operator_none() {
        let mut lexer = Lexer::from_memory("\\\n ", Source::Unknown);

        let r = block_on(lexer.operator()).unwrap();
        assert!(r.is_none(), "Unexpected success: {:?}", r);
    }

    #[test]
    fn lexer_operator_should_not_peek_beyond_newline() {
        struct OneLineInput(Option<String>);
        #[async_trait::async_trait(?Send)]
        impl Input for OneLineInput {
            async fn next_line(&mut self, _: &Context) -> crate::input::Result {
                if let Some(line) = self.0.take() {
                    Ok(line)
                } else {
                    panic!("The second line should not be read")
                }
            }
        }

        let line_number = NonZeroU64::new(1).unwrap();
        let mut lexer = Lexer::new(
            Box::new(OneLineInput(Some("\n".to_owned()))),
            line_number,
            Source::Unknown,
        );

        let t = block_on(lexer.operator()).unwrap().unwrap();
        assert_eq!(t.word.units, [WordUnit::Unquoted(TextUnit::Literal('\n'))]);
        assert_eq!(*t.word.location.code.value.borrow(), "\n");
        assert_eq!(t.word.location.code.start_line_number.get(), 1);
        assert_eq!(t.word.location.code.source, Source::Unknown);
        assert_eq!(t.word.location.range, 0..1);
        assert_eq!(t.id, TokenId::Operator(Operator::Newline));
    }
}