use std::ffi::{CStr, CString};

use thiserror::Error;

mod black_box;

#[derive(Error, Debug, PartialEq, Eq)]
pub enum ConfirmationIdError {
    #[error("Installation ID is too short.")]
    TooShort,
    #[error("Installation ID is too long.")]
    TooLarge,
    #[error("Invalid character in installation ID.")]
    InvalidCharacter,
    #[error("Installation ID checksum failed. Please check that it is typed correctly.")]
    InvalidCheckDigit,
    #[error("Unknown installation ID version.")]
    UnknownVersion,
    #[error("Unable to generate valid confirmation ID.")]
    Unlucky,
}

pub fn generate(installation_id: &str) -> Result<String, ConfirmationIdError> {
    if installation_id.len() < 54 {
        return Err(ConfirmationIdError::TooShort);
    }
    if installation_id.len() > 54 {
        return Err(ConfirmationIdError::TooLarge);
    }
    let inst_id = CString::new(installation_id).unwrap();
    let conf_id = [0u8; 49];
    let result = unsafe { black_box::generate(inst_id.as_ptr(), conf_id.as_ptr() as *mut i8) };
    match result {
        0 => {}
        1 => return Err(ConfirmationIdError::TooShort),
        2 => return Err(ConfirmationIdError::TooLarge),
        3 => return Err(ConfirmationIdError::InvalidCharacter),
        4 => return Err(ConfirmationIdError::InvalidCheckDigit),
        5 => return Err(ConfirmationIdError::UnknownVersion),
        6 => return Err(ConfirmationIdError::Unlucky),
        _ => panic!("Unknown error code: {}", result),
    }
    unsafe {
        Ok(CStr::from_ptr(conf_id.as_ptr() as *const i8)
            .to_str()
            .unwrap()
            .to_string())
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_generate() {
        assert_eq!(
            generate("334481558826870862843844566221823392794862457401103810").unwrap(),
            "110281-200130-887120-647974-697175-027544-252733"
        );
        assert!(
            generate("33448155882687086284384456622182339279486245740110381")
                .is_err_and(|err| err == ConfirmationIdError::TooShort),
        );
        assert!(
            generate("3344815588268708628438445662218233927948624574011038100")
                .is_err_and(|err| err == ConfirmationIdError::TooLarge),
        );
        assert!(
            generate("33448155882687086284384456622182339279486245740110381!")
                .is_err_and(|err| err == ConfirmationIdError::InvalidCharacter),
        );
        assert!(
            generate("334481558826870862843844566221823392794862457401103811")
                .is_err_and(|err| err == ConfirmationIdError::InvalidCheckDigit),
        );
    }
}