use crate::symbols::Symbol;
use async_trait::async_trait;
use std::error::Error;
use std::fs::{metadata, File};
use std::io::copy;
use std::marker::PhantomData;
use std::path::Path;

#[derive(Debug)]
pub struct Concat<S, D, I> {
  target: D,
  sources: S,
  source_item: PhantomData<I>,
}

impl<S, D, I> Concat<S, D, I> {
  pub fn new(sources: S, target: D) -> Self {
    Self {
      target,
      sources,
      source_item: PhantomData::default(),
    }
  }
}

#[async_trait(?Send)]
impl<S: AsRef<[I]>, D: AsRef<Path>, I: AsRef<Path>> Symbol for Concat<S, D, I> {
  async fn target_reached(&self) -> Result<bool, Box<dyn Error>> {
    let target = self.target.as_ref();
    if !target.exists() {
      return Ok(false);
    }
    let target_date = metadata(target)?.modified()?;
    for source in self.sources.as_ref() {
      if metadata(source)?.modified()? > target_date {
        return Ok(false);
      }
    }
    Ok(true)
  }

  async fn execute(&self) -> Result<(), Box<dyn Error>> {
    let mut file = File::create(self.target.as_ref())?;
    for source in self.sources.as_ref() {
      copy(&mut File::open(source)?, &mut file)?;
    }
    Ok(())
  }
}