use epub::doc::EpubDoc;
use pile_config::Label;
use std::{
	collections::HashMap,
	sync::{Arc, OnceLock},
};
use tracing::trace;

use crate::{
	extract::traits::ObjectExtractor,
	value::{Item, PileValue, SyncReadBridge},
};

pub struct EpubMetaExtractor {
	item: Item,
	output: OnceLock<HashMap<Label, PileValue>>,
}

impl EpubMetaExtractor {
	pub fn new(item: &Item) -> Self {
		Self {
			item: item.clone(),
			output: OnceLock::new(),
		}
	}

	async fn get_inner(&self) -> Result<&HashMap<Label, PileValue>, std::io::Error> {
		if let Some(x) = self.output.get() {
			return Ok(x);
		}

		let key = self.item.key();
		let ext = key.as_str().rsplit('.').next();
		if !matches!(ext, Some("epub")) {
			return Ok(self.output.get_or_init(HashMap::new));
		}

		let reader = SyncReadBridge::new_current(self.item.read().await?);
		let raw_meta = tokio::task::spawn_blocking(move || {
			let doc = EpubDoc::from_reader(reader)
				.map_err(|e| std::io::Error::new(std::io::ErrorKind::InvalidData, e.to_string()))?;

			let fields: &[&'static str] = &[
				"title",
				"creator",
				"description",
				"language",
				"publisher",
				"date",
				"subject",
				"identifier",
			];

			let meta: Vec<(&'static str, Option<String>)> =
				fields.iter().map(|&key| (key, doc.mdata(key))).collect();

			Ok::<_, std::io::Error>(meta)
		})
		.await
		.map_err(std::io::Error::other)?;

		let raw_meta = match raw_meta {
			Ok(x) => x,
			Err(error) => {
				trace!(message = "Could not process epub", ?error, key = ?self.item.key());
				return Ok(self.output.get_or_init(HashMap::new));
			}
		};

		let mut output: HashMap<Label, PileValue> = HashMap::new();

		#[expect(clippy::unwrap_used)]
		for (key, val) in raw_meta {
			let label = Label::new(key).unwrap();
			let value = match val {
				Some(s) => PileValue::String(Arc::new(s.into())),
				None => PileValue::Null,
			};
			output.insert(label, value);
		}

		return Ok(self.output.get_or_init(|| output));
	}
}

#[async_trait::async_trait]
impl ObjectExtractor for EpubMetaExtractor {
	async fn field(&self, name: &Label) -> Result<Option<PileValue>, std::io::Error> {
		Ok(self.get_inner().await?.get(name).cloned())
	}

	async fn fields(&self) -> Result<Vec<Label>, std::io::Error> {
		Ok(self.get_inner().await?.keys().cloned().collect())
	}
}