mod checked;
mod chunk;
mod uploading;

use std::{ffi::OsStr, fs, io::Read, path::Path};

use base64::prelude::{BASE64_STANDARD_NO_PAD as BASE64, Engine};
use blake2b_simd::Params as Blake2b;

pub use checked::Checked;
pub use chunk::Chunk;
use log::{debug, warn};
pub use uploading::Uploading;

/// how many bytes to hash at once (default: 4 MiB)
const HASH_CHUNK_SIZE: usize = 4 * 1024 * 1024;

/// compute hash for a file given its path.
/// Hash function: BLAKE2b, 512 bit
///
/// # Params
///
/// - `path` to the file to hash
/// - `size` of that file
/// - `on_progress` will be called for each processed chunk (max. `HASH_CHUNK_SIZE`)
///
/// # Errors
///
/// - from `fs::File::open` and `fs::File::read`
/// - Mismatch if given `size` does not match the file's size
fn compute_hash(path: &Path, size: u64, mut on_progress: impl FnMut(u64)) -> crate::Result<String> {
    let mut file = fs::File::open(path)?;

    // Blake2b-512 hasher (64 * 8 bit)
    let mut hasher = Blake2b::new().hash_length(64).to_state();

    // buffer
    let mut buffer = vec![0; HASH_CHUNK_SIZE];
    let mut bytes_read = 0;

    loop {
        let n = file.read(&mut buffer)?;
        if n == 0 {
            break;
        }
        hasher.update(&buffer[..n]);

        // `buf` size must be < 2 EiB
        bytes_read += n as u64;
        on_progress(n as u64);
    }

    if bytes_read != size {
        return Err(crate::Error::mismatch(size, bytes_read));
    }

    let result = BASE64.encode(hasher.finalize());
    debug!("hashed {:?}: {result:?}", path.display());
    Ok(result)
}

/// check hash for a file given its path, return Ok(()) on success
///
/// # Params
///
/// - `path` to the file to hash
/// - `size` of that file
/// - optional known `hash`
/// - `on_progress` will be called for each processed chunk (max. `HASH_CHUNK_SIZE`)
///
/// # Errors
///
/// - from `file::compute_hash`
/// - Mismatch if `hash` is `None`
/// - Mismatch if given `hash` does not match the computed hash
fn check_hash(
    path: &Path,
    size: u64,
    hash: Option<&str>,
    on_progress: impl FnMut(u64),
) -> crate::Result<()> {
    // check if hash is None
    let Some(expected) = hash else {
        return Err(crate::Error::mismatch("hash", path.display()));
    };

    // compute and check new hash
    let actual = &compute_hash(path, size, on_progress)?;

    if expected == actual {
        debug!("hash matches {expected:?}");
        Ok(())
    } else {
        warn!("hash mismatch for file {:?}", path.display());
        Err(crate::Error::mismatch(expected, actual))
    }
}

pub trait FileTrait {
    /// extract the filename part of a `Path` reference
    ///
    /// # Panics
    ///
    /// Expects `path::Path::file_name` and `ffi::OsStr::to_str` to succeed on the given path
    fn extract_file_name(p: &Path) -> &str {
        p.file_name()
            .and_then(OsStr::to_str)
            .expect("bad file name")
    }

    /// get a reference to the file's name
    ///
    /// Uses `file::FileTrait::extract_file_name`, which may **panic**!
    fn get_name(&self) -> &str;

    /// get the file's size
    fn get_size(&self) -> u64;

    /// check this file's hash, return Ok(()) on success
    ///
    /// # Errors
    ///
    /// - from `file::check_hash`
    fn check_hash(&self, on_progress: impl FnMut(u64)) -> crate::Result<()>;
}

#[cfg(test)]
mod tests {
    use std::io::Write;

    use tempfile::NamedTempFile;

    use super::*;

    /// Helper to create a temp file from `data`
    fn create_file(data: &[u8]) -> NamedTempFile {
        let mut tmp = NamedTempFile::new().expect("creating temp file");
        tmp.write_all(data).expect("writing to tempfile");
        tmp
    }

    static CASES: [(&[u8], u64); 8] = [
        (b"The quick brown fox jumps over the lazy dog", 43), // common pangram
        (b"hello world", 11),                                 // simple greeting
        (b"", 0),                                             // empty slice
        (b"x", 1),                                            // single-byte
        (b"0123456789", 10),                                  // numeric ASCII
        (b"!@#$%^&*()_+-=[]{};':,.<>/?", 27),                 // punctuation
        (b"RustLang1337", 12),                                // mixed alphanumeric
        (b"foo\0bar\0baz", 11),                               // embedded nulls
    ];

    static HASHES: [&str; 8] = [
        "qK3Uvd39k+SHfSdG5igXsRY2Sh+nvBSNlQkLxzM7NnP4JAHPeqLkyx7NkCluPxTLVBP47Xe+cwRbE5FM3NapGA", // common pangram
        "Ahzth5kpbOylV4MquUGlC0oR+DR4zxQfUfkz9lOrn7zAWgN83b7QbjCb8zSULE5YzfGkbiN5EczX/Pl4fLx/0A", // simple greeting
        "eGoC90IBWQPGxv2FJVLScpEvR0DhWEdhiobiF/cfVBnSXhAxr+5YUxOJZESTTrBLkDpoWxRIt1XVb3Aa/pvizg", // empty slice
        "CQk3etNREMr7KQnhhWcrfyco0fUJT4rWjW+sYnS/H0mUhagOo2TATtAG0pRZ6jy3xgAoDi+D4DJSmQb4iuMNCg", // single-byte
        "UqCSwAW2Ib1X5QGgrtlQp2/vuwDQeqQ9rdb1NALMJUE3SfDTxi6MoKfbrjRIQa3qUdU/i2HZaaFdSmMYtXa4rA", // numeric ASCII
        "Sr91qmX4R/Ly4HsJh5eiG3S1tuO81kwV0KPfRpn1j4jjrQoGL2I+SeKfcGvpXu3l/rfhGdJHF8ei775ZzdgK3Q", // punctuation
        "Ox+zobaUmB8Ps410/TGOtjjLIJKaMUCwG/iFLNXjwRShuJAmtvQcK9Ahc9+SfD4Ci67HyPPorl7NGjN6LRrmlQ", // mixed alphanumeric
        "a3rsGWE2kfvN6e2sVhioWP9NOmwLK9trzjc/GKXTPvvsiagiRSHMjlg5jy+bMepip68Pv69dY8TvTSFZES5Jzw", // embedded nulls
    ];

    #[test]
    fn compute_hash_as_expected() {
        for (&(content, size), expected_hash) in CASES.iter().zip(HASHES) {
            // to capture progress updates from `compute_hash`
            let file = create_file(content);
            let mut read_total = 0;
            let callback = |n| read_total += n;

            let hash = compute_hash(file.path(), size, callback).expect("hash should succeed");

            assert_eq!(hash, expected_hash);
            assert_eq!(read_total, size);
        }
    }

    #[test]
    fn hash_size_mismatch() {
        let bad_sizes = [
            36, // common pangram
            12, // simple greeting
            1,  // empty slice
            0,  // single-byte
            9,  // numeric ASCII
            24, // punctuation
            13, // mixed alphanumeric
            10, // embedded nulls
        ];

        for (&(content, good_size), bad_size) in CASES.iter().zip(bad_sizes) {
            let file = create_file(content);
            let callback = drop;

            {
                let err = compute_hash(file.path(), bad_size, callback)
                    .expect_err("compute_hash should report a mismatch");

                // check error
                assert!(err.is_mismatch(bad_size.to_string(), good_size.to_string()));
            }

            {
                let err = check_hash(file.path(), bad_size, Some("foobar"), callback)
                    .expect_err("check_hash should report a mismatch");

                // check error
                assert!(err.is_mismatch(bad_size.to_string(), good_size.to_string()));
            }
        }
    }

    #[test]
    fn hash_value_none() {
        for (content, size) in CASES {
            let file = create_file(content);
            let callback = drop;

            let err = check_hash(file.path(), size, None, callback)
                .expect_err("check_hash should report a mismatch");

            // check error
            assert!(err.is_mismatch("hash", file.path().display().to_string()));
        }
    }

    #[test]
    fn hash_value_mismatch() {
        let bad_hashes = [
            "invalid9k+SHfSdG5igXsRY2Sh+nvBSNlQkLxzM7NnP4JAHPeqLkyx7NkCluPxTLVBP47Xe+cwRbE5FM3NapGA", // common pangram
            "", // simple greeting
            "eGoC90IBWQPGxv2FJVLScpEvR0DhWEdhiobiG/cfVBnSXhAxr+5YUxOJZESTTrBLkDpoWxRIt1XVb3Aa/pvizg", // empty slice
            "Hash", // single-byte
        ];

        for ((&(content, size), good_hash), bad_hash) in CASES.iter().zip(HASHES).zip(bad_hashes) {
            let file = create_file(content);
            let callback = drop;

            let err = check_hash(file.path(), size, Some(bad_hash), callback)
                .expect_err("check_hash should report a mismatch");

            // check error
            assert!(err.is_mismatch(bad_hash, good_hash));
        }
    }
}