use std::error::Error;
use std::ffi::OsStr;
use std::fmt::{Display, Formatter};
use std::io::ErrorKind;
use std::path::{Path, PathBuf};
use std::path::Component::Normal;
use futures::{stream, TryStreamExt};
use log::{debug, info, warn};
use reqwest::Client;
use sha1_smol::Sha1;
use tokio::{fs, io};
use tokio::fs::File;
use tokio_stream::StreamExt;
use crate::assets::{Asset, AssetIndex};
use crate::launcher::download::{MultiDownloader, VerifiedDownload};
use crate::util;
use crate::util::{FileVerifyError, IntegrityError};
use crate::version::DownloadInfo;

const INDEX_PATH: &'static str = "indexes";
const OBJECT_PATH: &'static str = "objects";

pub struct AssetRepository {
    online: bool,
    home: PathBuf
}

#[derive(Debug)]
pub enum AssetError {
    InvalidId(Option<String>),
    IO { what: &'static str, error: io::Error },
    IndexParse(serde_json::Error),
    Offline,
    MissingURL,
    DownloadIndex(reqwest::Error),
    Integrity(IntegrityError),
    AssetObjectDownload,
    AssetVerifyError(FileVerifyError),
    AssetNameError(&'static str)
}

impl Display for AssetError {
    fn fmt(&self, f: &mut Formatter<'_>) -> std::fmt::Result {
        match self {
            AssetError::InvalidId(None) => f.write_str("missing asset index id"),
            AssetError::InvalidId(Some(id)) => write!(f, "invalid asset index id: {}", id),
            AssetError::IO { what, error } => write!(f, "i/o error ({}): {}", what, error),
            AssetError::IndexParse(error) => write!(f, "error parsing asset index: {}", error),
            AssetError::Offline => f.write_str("cannot download asset index while offline"),
            AssetError::MissingURL => f.write_str("missing asset index URL"),
            AssetError::DownloadIndex(e) => write!(f, "error downloading asset index: {}", e),
            AssetError::Integrity(e) => write!(f, "asset index integrity error: {}", e),
            AssetError::AssetObjectDownload => f.write_str("asset object download failed"),
            AssetError::AssetVerifyError(e) => write!(f, "error verifying asset object: {e}"),
            AssetError::AssetNameError(e) => write!(f, "invalid asset name: {e}")
        }
    }
}

impl Error for AssetError {
    fn source(&self) -> Option<&(dyn Error + 'static)> {
        match self {
            AssetError::IO { error, .. } => Some(error),
            AssetError::IndexParse(error) => Some(error),
            AssetError::DownloadIndex(error) => Some(error),
            AssetError::Integrity(error) => Some(error),
            AssetError::AssetVerifyError(error) => Some(error),
            _ => None
        }
    }
}

impl From<(&'static str, io::Error)> for AssetError {
    fn from((what, error): (&'static str, io::Error)) -> Self {
        AssetError::IO { what, error }
    }
}

impl AssetRepository {
    pub async fn new(online: bool, home: impl AsRef<Path>) -> Result<AssetRepository, io::Error> {
        let home = home.as_ref().to_owned();

        match fs::create_dir_all(&home).await {
            Ok(_) => (),
            Err(e) => match e.kind() {
                ErrorKind::AlreadyExists => (),
                _ => return Err(e)
            }
        };

        Ok(AssetRepository {
            online,
            home
        })
    }
    
    pub fn get_home(&self) -> &Path {
        self.home.as_path()
    }

    fn get_index_path(&self, id: &str) -> Result<PathBuf, AssetError> {
        let mut indexes_path: PathBuf = [self.home.as_ref(), OsStr::new(INDEX_PATH)].iter().collect();
        let Some(Normal(path)) = Path::new(id).components().last() else {
            return Err(AssetError::InvalidId(Some(id.into())));
        };

        let path = path.to_str().ok_or(AssetError::InvalidId(Some(path.to_string_lossy().into())))?;

        // FIXME: change this once "add_extension" is stabilized
        indexes_path.push(format!("{}.json", path));

        Ok(indexes_path)
    }

    pub async fn load_index(&self, index: &DownloadInfo, id: Option<&str>) -> Result<AssetIndex, AssetError> {
        let Some(id) = id else {
            return Err(AssetError::InvalidId(None));
        };

        info!("Loading asset index {}", id);

        let path = self.get_index_path(id)?;
        debug!("Asset index {} is located at {}", id, path.display());

        match util::verify_file(&path, index.size, index.sha1).await {
            Ok(_) => {
                debug!("Asset index {} verified on disk. Loading it.", id);
                let idx_data = fs::read_to_string(&path).await.map_err(|e| AssetError::IO {
                    what: "reading asset index",
                    error: e
                })?;

                return Ok(serde_json::from_str(&idx_data).map_err(|e| AssetError::IndexParse(e))?);
            },
            Err(FileVerifyError::Open(_, e)) => match e.kind() {
                ErrorKind::NotFound => {
                    debug!("Asset index {} not found on disk. Must download it.", id);
                },
                _ => return Err(("opening asset index", e).into())
            },
            Err(FileVerifyError::Integrity(_, e)) => {
                info!("Asset index {} has mismatched integrity: {}, must download it.", id, e);
                let _ = fs::remove_file(&path).await.map_err(|e| warn!("Error deleting modified index {}: {} (ignored)", id, e));
            },
            Err(FileVerifyError::Read(_, e)) => return Err(("reading asset index", e).into())
        }

        if !self.online {
            warn!("Must download asset index {}, but the launcher is in offline mode. Please try again in online mode.", id);
            return Err(AssetError::Offline);
        }

        let Some(url) = index.url.as_ref() else {
            return Err(AssetError::MissingURL);
        };

        debug!("Downloading asset index {} from {}", id, url);

        if let Some(parent) = path.parent() {
            fs::create_dir_all(parent).await.map_err(|e| AssetError::IO {
                what: "creating asset index folder",
                error: e
            })?;
        }

        let idx_text = reqwest::get(url).await
            .map_err(|e| AssetError::DownloadIndex(e))?
            .text().await
            .map_err(|e| AssetError::DownloadIndex(e))?;

        if index.size.is_some_and(|s| s != idx_text.len()) {
            return Err(AssetError::Integrity(IntegrityError::SizeMismatch {
                expect: index.size.unwrap(),
                actual: idx_text.len()
            }));
        }

        if let Some(expect) = index.sha1 {
            let actual = Sha1::from(&idx_text).digest();

            if actual != expect {
                return Err(AssetError::Integrity(IntegrityError::Sha1Mismatch { expect, actual }));
            }
        }

        debug!("Saving downloaded asset index to {}", path.display());
        fs::write(&path, &idx_text).await.map_err(|e| AssetError::IO {
            what: "writing asset index",
            error: e
        })?;

        Ok(serde_json::from_str(&idx_text).map_err(|e| AssetError::IndexParse(e))?)
    }

    fn get_object_url(obj: &Asset) -> String {
        format!("{}{:02x}/{}", super::constants::URL_RESOURCE_BASE, obj.hash.bytes()[0], obj.hash)
    }

    pub fn get_object_path(&self, obj: &Asset) -> PathBuf {
        let hex_digest = obj.hash.to_string();
        [self.home.as_ref(), OsStr::new(OBJECT_PATH), OsStr::new(&hex_digest[..2]), OsStr::new(&hex_digest)].iter().collect()
    }

    async fn ensure_dir(path: impl AsRef<Path>) -> Result<(), io::Error> {
        match fs::create_dir(path).await {
            Ok(_) => Ok(()),
            Err(e) if e.kind() == ErrorKind::AlreadyExists => Ok(()),
            Err(e) => Err(e)
        }
    }

    pub async fn ensure_assets(&self, index: &AssetIndex) -> Result<(), AssetError> {
        let mut downloads = Vec::new();
        let objects_path = [self.home.as_ref(), OsStr::new(OBJECT_PATH)].iter().collect::<PathBuf>();

        Self::ensure_dir(&objects_path).await.map_err(|e| AssetError::IO {
            what: "creating objects directory",
            error: e
        })?;

        for object in index.objects.values() {
            let path = self.get_object_path(object);

            Self::ensure_dir(path.parent().unwrap()).await.map_err(|error| AssetError::IO { error, what: "creating directory for object" })?;

            downloads.push(VerifiedDownload::new(&Self::get_object_url(object), &path, Some(object.size), Some(object.hash)));
        }

        if self.online {
            info!("Downloading {} asset objects...", downloads.len());
            let client = Client::new();
            MultiDownloader::with_concurrent(downloads.iter_mut(), 32).perform(&client).await
                .inspect_err(|e| warn!("asset download failed: {e}"))
                .try_fold((), |_, _| async {Ok(())})
                .await
                .map_err(|_| AssetError::AssetObjectDownload)?;
        } else {
            info!("Verifying {} asset objects...", downloads.len());
            super::download::verify_files(downloads.iter_mut()).await.map_err(|e| AssetError::AssetVerifyError(e))?;
        }

        Ok(())
    }

    pub async fn reconstruct_assets(&self, index: &AssetIndex, instance_path: &Path, index_id: Option<&str>) -> Result<Option<PathBuf>, AssetError> {
        let target_path: PathBuf;
        let Some(index_id) = index_id else {
            return Err(AssetError::InvalidId(None));
        };

        if index.virtual_assets {
            target_path = [self.home.as_ref(), OsStr::new("virtual"), OsStr::new(index_id)].iter().collect();
        } else if index.map_to_resources {
            target_path = [instance_path, Path::new("resources")].iter().collect();
        } else {
            info!("This asset index does not request a virtual assets folder. Nothing to be done.");
            return Ok(None);
        }

        info!("Reconstructing virtual assets for {}", index_id);

        fs::create_dir_all(&target_path).await.map_err(|e| AssetError::from(("creating virtual assets directory", e)))?;

        stream::iter(index.objects.values()
            .map(|object| {
                let obj_path = util::check_path(object.name.as_str()).map_err(AssetError::AssetNameError)?;
                let obj_path = target_path.join(obj_path);

                Ok((object, obj_path))
            }))
            .try_filter_map(|(object, obj_path)| async move {
                match util::verify_file(&obj_path, Some(object.size), Some(object.hash)).await {
                    Ok(_) => {
                        debug!("Not copying asset {}, integrity matches.", object.name);
                        Ok(None)
                    }
                    Err(FileVerifyError::Open(_, e)) if e.kind() == ErrorKind::NotFound => {
                        debug!("Copying asset {}, file does not exist.", object.name);
                        Ok(Some((object, obj_path)))
                    },
                    Err(FileVerifyError::Integrity(_, e)) => {
                        debug!("Copying asset {}: {}", object.name, e);
                        Ok(Some((object, obj_path)))
                    },
                    Err(e) => {
                        debug!("Error while reconstructing assets: {e}");
                        Err(AssetError::AssetVerifyError(e))
                    }
                }
            })
            .try_for_each_concurrent(32, |(object, obj_path)| async move {
                if let Some(parent) = obj_path.parent() {
                    fs::create_dir_all(parent).await
                        .inspect_err(|e| debug!("Error creating directory for asset object {}: {e}", object.name))
                        .map_err(|e| AssetError::from(("creating asset object directory", e)))?;
                }

                let mut fromfile = File::open(self.get_object_path(object)).await
                    .map_err(|e| AssetError::from(("opening source object", e)))?;
                let mut tofile = File::create(&obj_path).await
                    .map_err(|e| AssetError::from(("creating target object", e)))?;

                io::copy(&mut fromfile, &mut tofile).await.map_err(|e| AssetError::from(("copying asset object", e)))?;
                debug!("Copied object {} to {}.", object.name, obj_path.display());
                Ok(())
            }).await.map(|_| Some(target_path))
    }
}

mod tests {
    use super::*;

    #[test]
    fn test_it() {
        let digest_str = "ad1115931887a73cd596300f2c93f84adf39521d";
        assert_eq!(AssetRepository::get_object_url(&Asset {
            name: String::from("test"),
            hash: digest_str.parse().unwrap(),
            size: 0usize
        }), "https://resources.download.minecraft.net/ad/ad1115931887a73cd596300f2c93f84adf39521d");
    }
}