use std::collections::VecDeque;

use nom::{
    branch::alt,
    character::complete::{anychar, char, none_of},
    combinator::{eof, map, recognize, value},
    multi::{many0_count, separated_list0},
    sequence::{preceded, separated_pair},
    IResult,
};

#[derive(PartialEq, Eq, Debug)]
pub struct ParseResult<'l> {
    pub commands: Vec<ParsedCommand<'l>>,
}

#[derive(PartialEq, Eq, Debug)]
pub struct ParsedCommand<'l> {
    pub arguments: VecDeque<&'l str>,
}

impl ParsedCommand<'_> {
    pub fn split_out_command(&self) -> Option<(&str, Self)> {
        let mut tmp_arguments = self.arguments.clone();
        loop {
            match tmp_arguments.pop_front() {
                None => return None,
                Some(head) => {
                    let trimmed_cmd = head.trim();
                    if !trimmed_cmd.is_empty() {
                        return Some((
                            trimmed_cmd,
                            Self {
                                arguments: tmp_arguments,
                            },
                        ));
                    }
                }
            }
        }
    }
}

fn parse_string(input: &str) -> IResult<&str, ()> {
    value(
        (),
        many0_count(alt((
            value((), preceded(char('\\'), anychar)),
            value((), none_of("\"")),
        ))),
    )(input)
}

fn parse_parenthetical(input: &str) -> IResult<&str, ()> {
    value(
        (),
        many0_count(alt((
            value((), preceded(char('\\'), anychar)),
            value(
                (),
                separated_pair(
                    char('{'),
                    parse_parenthetical,
                    alt((value((), eof), value((), char('}')))),
                ),
            ),
            value(
                (),
                separated_pair(
                    char('"'),
                    parse_string,
                    alt((value((), eof), value((), char('"')))),
                ),
            ),
            value((), none_of("}")),
        ))),
    )(input)
}

fn parse_argument(input: &str) -> IResult<&str, ()> {
    value(
        (),
        many0_count(alt((
            value((), preceded(char('\\'), anychar)),
            value(
                (),
                separated_pair(
                    char('{'),
                    parse_parenthetical,
                    alt((value((), eof), value((), char('}')))),
                ),
            ),
            value(
                (),
                separated_pair(
                    char('"'),
                    parse_string,
                    alt((value((), eof), value((), char('"')))),
                ),
            ),
            value((), none_of(" ;")),
        ))),
    )(input)
}

fn parse_command(input: &str) -> IResult<&str, ParsedCommand> {
    map(
        separated_list0(char(' '), recognize(parse_argument)),
        |arguments| ParsedCommand {
            arguments: arguments.into(),
        },
    )(input)
}

pub fn parse_commands(input: &str) -> ParseResult {
    // Note that the core parser doesn't do things like skipping multiple whitespace,
    separated_list0(preceded(char(';'), many0_count(char(' '))), parse_command)(input)
        .map(|(_, commands)| ParseResult { commands })
        .unwrap_or_else(|_| ParseResult { commands: vec![] })
}

#[cfg(test)]
mod tests {
    use super::*;
    #[test]
    fn test_parse_commands() {
        assert_eq!(
            parse_commands(""),
            ParseResult {
                commands: vec![ParsedCommand {
                    arguments: vec![""].into()
                }]
            }
        );
        assert_eq!(
            parse_commands("north"),
            ParseResult {
                commands: vec![ParsedCommand {
                    arguments: vec!["north"].into()
                }]
            }
        );
        assert_eq!(
            parse_commands("north "),
            ParseResult {
                commands: vec![ParsedCommand {
                    // This is deliberate, ensures we can reconstruct the input.
                    arguments: vec!["north", ""].into()
                }]
            }
        );
        assert_eq!(
            parse_commands("#blah {x = 1 + 2; y = 3}; #home"),
            ParseResult {
                commands: vec![
                    ParsedCommand {
                        arguments: vec!["#blah", "{x = 1 + 2; y = 3}"].into()
                    },
                    ParsedCommand {
                        arguments: vec!["#home"].into()
                    }
                ]
            }
        );
        assert_eq!(
            parse_commands("#blah {x = 1 + 2"),
            ParseResult {
                commands: vec![ParsedCommand {
                    arguments: vec!["#blah", "{x = 1 + 2"].into()
                },]
            }
        );
        assert_eq!(
            parse_commands("#blah {x = 1} {y = 1}"),
            ParseResult {
                commands: vec![ParsedCommand {
                    arguments: vec!["#blah", "{x = 1}", "{y = 1}"].into()
                }]
            }
        );
        assert_eq!(
            parse_commands("#blah \"hello\" \"world\""),
            ParseResult {
                commands: vec![ParsedCommand {
                    arguments: vec!["#blah", "\"hello\"", "\"world\""].into()
                }]
            }
        );
        assert_eq!(
            parse_commands("#blah {x = \"}\"} {y = 1}"),
            ParseResult {
                commands: vec![ParsedCommand {
                    arguments: vec!["#blah", "{x = \"}\"}", "{y = 1}"].into()
                }]
            }
        );
        assert_eq!(
            parse_commands("#blah {x = \"}\"; a = \"{\"; y = {}; z = 1;} { q = 5 };"),
            ParseResult {
                commands: vec![
                    ParsedCommand {
                        arguments: vec![
                            "#blah",
                            "{x = \"}\"; a = \"{\"; y = {}; z = 1;}",
                            "{ q = 5 }"
                        ]
                        .into()
                    },
                    ParsedCommand {
                        arguments: vec![""].into()
                    }
                ]
            }
        );
        assert_eq!(
            parse_commands("#blah {\\}\\}\\}} {y = 1}"),
            ParseResult {
                commands: vec![ParsedCommand {
                    arguments: vec!["#blah", "{\\}\\}\\}}", "{y = 1}"].into()
                }]
            }
        );
        assert_eq!(
            parse_commands("#blah \"This is a \\\"test\\\"\""),
            ParseResult {
                commands: vec![ParsedCommand {
                    arguments: vec!["#blah", "\"This is a \\\"test\\\"\""].into()
                }]
            }
        );
    }
}