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use std::collections::VecDeque;
use std::iter::{Chain, Iterator, Once};
use std::process::ExitStatus;
use std::rc::Rc;
use std::collections::vec_deque::Iter;
use std::sync::Arc;

use futures::future::join_all;
use futures::join;

use async_recursion::async_recursion;
use async_trait::async_trait;

#[async_trait]
pub trait Command {
    async fn run(&self, args: VarArgs) -> Result<ExitStatus, ()>;
}

pub type VarArgs = VecDeque<Arc<String>>;
#[derive(Debug)]
pub struct ScriptGroup<CommandGeneric: Command> {
    pub bail: bool,
    // Enforces that there's always at least 1 script
    pub first: Script<CommandGeneric>,
    pub rest: VecDeque<Script<CommandGeneric>>,
}

impl<CommandGeneric: Command> ScriptGroup<CommandGeneric> {
    fn iter(&self) -> Chain<Once<&'_ Script<CommandGeneric>>, Iter<'_, Script<CommandGeneric>>> {
        std::iter::once(&self.first).chain(self.rest.iter())
    }
}

/**
 * TODO: Choose a better name
 */
#[derive(Debug)]
pub enum CommandGroup<CommandGeneric: Command> {
    Parallel(ScriptGroup<CommandGeneric>),
    Series(ScriptGroup<CommandGeneric>),
}

fn merge_status(status1: ExitStatus, status2: ExitStatus) -> ExitStatus {
    if !status1.success() {
        return status2;
    }
    return status1;
}

impl<CommandGeneric: Command> CommandGroup<CommandGeneric> {
    async fn run(
        &self,
        parser: &impl ScriptParser<CommandGeneric>,
        args: VarArgs,
    ) -> Result<ExitStatus, ()> {
        // TODO: Figure out what to do with args
        match self {
            Self::Parallel(group) => {
                if group.bail {
                    println!("Warning: Bail in parallel groups are currently not supported");
                }

                let mut promises = Vec::<_>::new();

                let mut group_iter = group.iter();
                let mut command = group_iter.next().unwrap();

                while let Some(next_command) = group_iter.next() {
                    promises.push(command.run(parser, VecDeque::new()));

                    command = next_command;
                }

                let last_result = command.run(parser, args);
                let (results, last) = join!(
                    join_all(promises),
                    last_result
                );

                let final_status = results.into_iter().fold(
                    last.unwrap(),
                    |prev_exit_status, this_result| {
                        if let Ok(current_status) = this_result {
                            return merge_status(prev_exit_status, current_status);
                        } else {
                            // TODO: Do something with the error
                            return prev_exit_status;
                        }
                    },
                );

                return Ok(final_status);
            }
            Self::Series(group) => {               
                let mut rest_iter = group.rest.iter();
                if let Some(last_command) = rest_iter.next_back() {
                    let mut exit_status = group.first.run(parser, VecDeque::new()).await.unwrap();

                    for command in rest_iter {
                        exit_status = merge_status(exit_status, command.run(parser, VecDeque::new()).await.unwrap());
                    }

                    exit_status = merge_status(exit_status, last_command.run(parser, args).await.unwrap());

                    Ok(exit_status)
                } else {
                    Ok(group.first.run(parser, args).await.unwrap())
                }
            }
        }
    }
}

#[derive(Debug)]
pub struct Alias {
    pub task: String,
    pub args: VarArgs,
}

/**
 * TODO: Choose a better name
 */
#[derive(Debug)]
pub enum Script<CommandGeneric: Command> {
    Command(CommandGeneric),
    Group(Box<CommandGroup<CommandGeneric>>),
    Alias(Alias),
}

impl<CommandGeneric: Command> Script<CommandGeneric> {
    #[async_recursion(?Send)]
    pub async fn run(
        &self,
        parser: &impl ScriptParser<CommandGeneric>,
        args: VarArgs,
    ) -> Result<ExitStatus, ()> {
        match self {
            Script::Command(cmd) => cmd.run(args).await,
            Script::Group(group) => group.run(parser, args).await,
            Script::Alias(alias) => {
                let joined_args: VecDeque<Arc<String>> = alias
                    .args
                    .iter()
                    .into_iter()
                    .map(|arg| arg.clone())
                    .chain(args.into_iter())
                    .collect();

                parser
                    .parse(alias.task.as_str())
                    .unwrap()
                    .run(parser, joined_args)
                    .await
            }
        }
    }
}

pub trait ScriptParser<CommandGeneric: Command> {
    fn parse(&self, task: &str) -> Result<Rc<Script<CommandGeneric>>, ()>;
}