use std::{
    fmt, fs,
    io::{self, Read, Seek, SeekFrom},
    path::PathBuf,
};

use serde::{Deserialize, Serialize};

use super::{FileChecked, SharryFile};

#[derive(Serialize, Deserialize, Debug)]
pub struct FileUploading {
    path: PathBuf,
    size: u64,
    patch_uri: String,
    offset: u64,
}

impl fmt::Display for FileUploading {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        write!(
            f,
            "Uploading {:?} ({}/{})",
            self.path.display(),
            self.offset,
            self.size
        )
    }
}

impl FileUploading {
    pub fn new(file: FileChecked, patch_uri: String) -> Self {
        Self {
            path: file.path,
            size: file.size,
            patch_uri,
            offset: 0,
        }
    }

    pub fn get_patch_uri(&self) -> &str {
        &self.patch_uri
    }

    pub fn get_offset(&self) -> u64 {
        self.offset
    }

    pub fn read(&mut self, buf: &mut [u8]) -> io::Result<u64> {
        let mut f = fs::File::open(&self.path)?;

        f.seek(SeekFrom::Start(self.offset))?;
        let read_len = f.read(buf)?;

        // convert into `u64`
        //
        // BOOKMARK this might **panic** on platforms where `usize` has more than 64 bit.
        // Also, you're reading more than 2 EiB ... in ONE chunk.
        // Whoa! Maybe just chill?
        let read_len = u64::try_from(read_len)
            .unwrap_or_else(|e| panic!("usize={} did not fit into u64: {}", read_len, e));

        self.offset += read_len;

        Ok(read_len)
    }

    pub fn check_eof(self) -> Result<Self, PathBuf> {
        if self.offset < self.size {
            Ok(self)
        } else {
            Err(self.path)
        }
    }
}

impl<'t> SharryFile<'t> for FileUploading {
    /// get a reference to the file's name
    ///
    /// Uses `SharryFile::extract_file_name`, which may **panic**!
    fn get_name(&'t self) -> &'t str {
        <Self as SharryFile>::extract_file_name(&self.path)
    }

    fn get_size(&self) -> u64 {
        self.size
    }
}