use std::fmt;

use crate::sharry;

pub struct Chunk<'t> {
    file_id: sharry::FileID,
    offset: u64,
    data: &'t [u8],
}

impl fmt::Debug for Chunk<'_> {
    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
        f.debug_struct("Chunk")
            .field("file_id", &self.file_id)
            .field("offset", &self.offset)
            .field("data.len()", &self.data.len())
            .finish_non_exhaustive()
    }
}

impl<'t> Chunk<'t> {
    pub(super) fn new_direct(file_id: sharry::FileID, offset: u64, data: &'t [u8]) -> Self {
        Self {
            file_id,
            offset,
            data,
        }
    }

    pub fn get_file_id(&self) -> &sharry::FileID {
        &self.file_id
    }

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

    pub fn get_data(&self) -> &[u8] {
        self.data
    }

    pub fn get_length(&self) -> u64 {
        let len = self.data.len();

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

#[cfg(test)]
mod tests {
    use crate::test_util::{
        check_trait,
        data::{DATA_LENGTHS_BAD, cases_with},
    };

    use super::*;

    #[test]
    fn basic_tests() {
        for (data, len, mock_offset) in cases_with(DATA_LENGTHS_BAD) {
            let fid = sharry::FileID::default();
            let chunk = Chunk::new_direct(fid, mock_offset, data);

            let repr_expect = format!(
                "Chunk {{ file_id: {:?}, offset: {:?}, data.len(): {:?}, .. }}",
                chunk.file_id,
                chunk.offset,
                chunk.data.len()
            );
            check_trait(format!("{chunk:?}"), repr_expect, "Debug", "Chunk");

            assert_eq!(chunk.get_file_id().to_string(), "fid");
            assert_eq!(chunk.get_offset(), mock_offset);
            assert_eq!(chunk.get_data(), data);
            assert_eq!(chunk.get_length(), len);
        }
    }
}