use crate::{error::UploadError, safe_save_file, to_ext, ACCEPTED_MIMES};
use actix_web::web;
use futures::stream::{Stream, StreamExt};
use sha2::Digest;
use std::{path::PathBuf, pin::Pin, sync::Arc};

#[derive(Clone)]
pub struct UploadManager {
    inner: Arc<UploadManagerInner>,
}

struct UploadManagerInner {
    hasher: sha2::Sha256,
    image_dir: PathBuf,
    db: sled::Db,
}

type UploadStream = Pin<Box<dyn Stream<Item = Result<bytes::Bytes, actix_form_data::Error>>>>;

enum Dup {
    Exists,
    New,
}

impl Dup {
    fn exists(&self) -> bool {
        match self {
            Dup::Exists => true,
            _ => false,
        }
    }
}

impl UploadManager {
    /// Get the image directory
    pub(crate) fn image_dir(&self) -> PathBuf {
        self.inner.image_dir.clone()
    }

    /// Create a new UploadManager
    pub(crate) async fn new(mut root_dir: PathBuf) -> Result<Self, UploadError> {
        let mut sled_dir = root_dir.clone();
        sled_dir.push("db");
        // sled automatically creates it's own directories
        //
        // This is technically a blocking operation but it's fine because it happens before we
        // start handling requests
        let db = sled::open(sled_dir)?;

        root_dir.push("files");

        // Ensure file dir exists
        actix_fs::create_dir_all(root_dir.clone()).await?;

        Ok(UploadManager {
            inner: Arc::new(UploadManagerInner {
                hasher: sha2::Sha256::new(),
                image_dir: root_dir,
                db,
            }),
        })
    }

    /// Upload the file, discarding bytes if it's already present, or saving if it's new
    pub(crate) async fn upload(
        &self,
        _filename: String,
        content_type: mime::Mime,
        mut stream: UploadStream,
    ) -> Result<Option<PathBuf>, UploadError> {
        if ACCEPTED_MIMES.iter().all(|valid| *valid != content_type) {
            return Err(UploadError::ContentType(content_type));
        }

        // -- READ IN BYTES FROM CLIENT --
        let mut bytes = bytes::BytesMut::new();

        while let Some(res) = stream.next().await {
            bytes.extend(res?);
        }

        let bytes = bytes.freeze();

        // -- DUPLICATE CHECKS --

        // Cloning bytes is fine because it's actually a pointer
        let hash = self.hash(bytes.clone()).await?;

        let (dup, path) = self.check_duplicate(hash, content_type).await?;

        // bail early with path to existing file if this is a duplicate
        if dup.exists() {
            return Ok(Some(path));
        }

        // TODO: validate image before saving

        // -- WRITE NEW FILE --
        safe_save_file(path.clone(), bytes).await?;

        Ok(Some(path))
    }

    // produce a sh256sum of the uploaded file
    async fn hash(&self, bytes: bytes::Bytes) -> Result<Vec<u8>, UploadError> {
        let mut hasher = self.inner.hasher.clone();
        let hash = web::block(move || {
            hasher.input(&bytes);
            Ok(hasher.result().to_vec()) as Result<_, UploadError>
        })
        .await?;

        Ok(hash)
    }

    // check for an already-uploaded image with this hash, returning the path to the target file
    async fn check_duplicate(
        &self,
        hash: Vec<u8>,
        content_type: mime::Mime,
    ) -> Result<(Dup, PathBuf), UploadError> {
        let mut path = self.inner.image_dir.clone();
        let db = self.inner.db.clone();

        let filename = self.next_file(content_type).await?;

        let filename2 = filename.clone();
        let res = web::block(move || {
            db.compare_and_swap(hash, None as Option<sled::IVec>, Some(filename2.as_bytes()))
        })
        .await?;

        if let Err(sled::CompareAndSwapError {
            current: Some(ivec),
            ..
        }) = res
        {
            let name = String::from_utf8(ivec.to_vec())?;
            path.push(name);

            return Ok((Dup::Exists, path));
        }

        path.push(filename);

        Ok((Dup::New, path))
    }

    // generate a short filename that isn't already in-use
    async fn next_file(&self, content_type: mime::Mime) -> Result<String, UploadError> {
        let image_dir = self.inner.image_dir.clone();
        use rand::distributions::{Alphanumeric, Distribution};
        let mut limit: usize = 10;
        let rng = rand::thread_rng();
        loop {
            let mut path = image_dir.clone();
            let s: String = Alphanumeric.sample_iter(rng).take(limit).collect();

            let filename = format!("{}{}", s, to_ext(content_type.clone()));

            path.push(filename.clone());

            if let Err(e) = actix_fs::metadata(path).await {
                if e.kind() == Some(std::io::ErrorKind::NotFound) {
                    return Ok(filename);
                }
                return Err(e.into());
            }

            limit += 1;
        }
    }
}