// SPDX-License-Identifier: MIT
// SPDX-FileCopyrightText: Copyright (C) 2023 Tsukasa OI <floss_ssdeep@irq.a4lg.com>.

#![cfg(all(feature = "std", feature = "easy-functions"))]

use std::fs::File;
use std::io::Read;
use std::path::Path;

use crate::generate::{Generator, GeneratorError};
use crate::hash::RawFuzzyHash;
use crate::macros::{optionally_unsafe, invariant};


/// The error type describing either a generator error or an I/O error.
///
/// This type contains either:
/// *   A fuzzy hash generator error ([`GeneratorError`]) or
/// *   An I/O error ([`std::io::Error`]).
#[derive(Debug)]
pub enum GeneratorOrIOError {
    /// An error caused by the fuzzy hash generator.
    GeneratorError(GeneratorError),
    /// An error caused by an internal I/O operation.
    IOError(std::io::Error),
}

impl core::fmt::Display for GeneratorOrIOError {
    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
        match self {
            GeneratorOrIOError::GeneratorError(err) => err.fmt(f),
            GeneratorOrIOError::IOError(err) => err.fmt(f),
        }
    }
}

impl From<GeneratorError> for GeneratorOrIOError {
    // For wrapping with the '?' operator
    fn from(value: GeneratorError) -> Self {
        GeneratorOrIOError::GeneratorError(value)
    }
}

impl From<std::io::Error> for GeneratorOrIOError {
    // For wrapping with the '?' operator
    fn from(value: std::io::Error) -> Self {
        GeneratorOrIOError::IOError(value)
    }
}

impl std::error::Error for GeneratorOrIOError {}


/// Constant temporary buffer size for "easy" functions.
const BUFFER_SIZE: usize = 32768;

/// Generates a fuzzy hash from a given reader stream.
///
/// This is an internal function to allow other functions to
/// prepare a [`Generator`] object.
#[inline]
fn hash_stream_common<R: Read>(
    generator: &mut Generator,
    reader: &mut R,
) -> Result<RawFuzzyHash, GeneratorOrIOError>
{
    let mut buffer = [0u8; BUFFER_SIZE];
    loop {
        let len = reader.read(&mut buffer)?; // grcov-excl-br-line:IO
        if len == 0 {
            break;
        }
        optionally_unsafe! {
            invariant!(len <= buffer.len());
        }
        generator.update(&buffer[0..len]);
    }
    Ok(generator.finalize()?)
}


/// Generates a fuzzy hash from a given reader stream.
///
/// # Example
///
/// ```
/// use std::error::Error;
/// use std::fs::File;
///
/// fn main() -> Result<(), ssdeep::GeneratorOrIOError> {
///     let mut stream = File::open("data/examples/hello.txt")?;
///     let fuzzy_hash = ssdeep::hash_stream(&mut stream)?;
///     let fuzzy_hash_str = fuzzy_hash.to_string();
///     assert_eq!(fuzzy_hash_str, "3:aaX8v:aV");
///     Ok(())
/// }
/// ```
pub fn hash_stream<R: Read>(reader: &mut R)
    -> Result<RawFuzzyHash, GeneratorOrIOError>
{
    let mut generator = Generator::new();
    hash_stream_common(&mut generator, reader)
}

/// Generates a fuzzy hash from a given file.
///
/// # Example
///
/// ```
/// use std::error::Error;
///
/// fn main() -> Result<(), ssdeep::GeneratorOrIOError> {
///     let fuzzy_hash = ssdeep::hash_file("data/examples/hello.txt")?;
///     let fuzzy_hash_str = fuzzy_hash.to_string();
///     assert_eq!(fuzzy_hash_str, "3:aaX8v:aV");
///     Ok(())
/// }
/// ```
///
/// # Note
///
/// This function expects that the file size does not change while
/// generating.  On normal use cases, you hash a fixed file to generate
/// a fuzzy hash to interchange information about the file with others.
/// So, this assumption should be safe for most users.
///
/// Also, failing to meet this requirement only causes this function to
/// return an error (incorrect result will not be produced).
/// So, this function is always safe.
///
/// If the file size could change while generating a fuzzy hash,
/// use [`hash_stream`] instead.
pub fn hash_file<P: AsRef<Path>>(path: P)
    -> Result<RawFuzzyHash, GeneratorOrIOError>
{
    let mut file = File::open(path)?;
    let mut generator = Generator::new();
    generator.set_fixed_input_size(file.metadata()?.len())?; // grcov-excl-br-line:IO
    hash_stream_common(&mut generator, &mut file)
}





// grcov-excl-br-start
#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_hash_file_ok() {
        let hash = hash_file("data/examples/hello.txt");
        assert!(hash.is_ok());
        assert_eq!(hash.unwrap().to_string(), "3:aaX8v:aV");
    }

    #[test]
    fn test_hash_file_noexist() {
        let err = hash_file("data/examples/nonexistent.bin");
        if let Err(GeneratorOrIOError::IOError(err)) = err {
            let str1 = format!("{}", err);
            let big_error = GeneratorOrIOError::IOError(err);
            let str2 = format!("{}", big_error);
            assert_eq!(str1, str2);
            // Test default Debug impltmentation for IOError
            assert!(format!("{:?}", big_error).starts_with("IOError("));
        }
        else {
            // grcov-excl-start
            panic!("The error must be an IOError and this line should not be reachable!");
            // grcov-excl-stop
        }
    }

    #[test]
    fn test_hash_stream_common() {
        let mut file = File::open("data/examples/hello.txt").unwrap();
        let hash = hash_stream(&mut file);
        assert!(hash.is_ok());
        assert_eq!(hash.unwrap().to_string(), "3:aaX8v:aV");
    }

    #[test]
    fn test_hash_stream_common_inconsistency() {
        let mut file = File::open("data/examples/hello.txt").unwrap();
        let mut generator = Generator::new();
        generator.set_fixed_input_size(0).unwrap(); // Give wrong size.
        let err = hash_stream_common(&mut generator, &mut file);
        if let Err(GeneratorOrIOError::GeneratorError(err)) = err { // grcov-excl-br-line
            let str1 = format!("{}", err);
            let big_error = GeneratorOrIOError::GeneratorError(err);
            let str2 = format!("{}", big_error);
            assert_eq!(str1, str2);
            assert_eq!(str1, "current state mismatches to the fixed size previously set.");
            // Test default Debug impltmentation for GeneratorError
            assert!(format!("{:?}", big_error).starts_with("GeneratorError("));
        }
        else {
            // grcov-excl-start
            panic!("The error must be an IOError and this line should not be reachable!");
            // grcov-excl-stop
        }
    }
}
// grcov-excl-br-stop