nsv 0.0.12

NSV (Newline-Separated Values) format parser and encoder
Documentation 
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//! Utility functions for NSV structural operations.
//!
//! Encoding: `spill('\n') ∘ spill("") ∘ escape_seqseq`
//! Decoding: `unescape_seqseq ∘ unspill("") ∘ unspill('\n')`

use crate::{escape, unescape};

/// Apply NSV escaping at depth 2: map(map(escape)).
pub fn escape_seqseq(seqseq: &[Vec<String>]) -> Vec<Vec<String>> {
    seqseq
        .iter()
        .map(|row| row.iter().map(|cell| escape(cell).into_owned()).collect())
        .collect()
}

/// Apply NSV unescaping at depth 2: map(map(unescape)).
pub fn unescape_seqseq(seqseq: &[Vec<String>]) -> Vec<Vec<String>> {
    seqseq
        .iter()
        .map(|row| row.iter().map(|cell| unescape(cell).into_owned()).collect())
        .collect()
}

/// Collapse a dimension by spilling termination markers into the flat sequence.
pub fn spill<T: Clone>(seqseq: &[Vec<T>], marker: T) -> Vec<T> {
    let mut seq = Vec::new();
    for row in seqseq {
        for item in row {
            seq.push(item.clone());
        }
        seq.push(marker.clone());
    }
    seq
}

/// Recover a dimension by picking up termination markers. Incomplete rows discarded.
pub fn unspill<T: Clone + PartialEq>(seq: &[T], marker: &T) -> Vec<Vec<T>> {
    let mut seqseq = Vec::new();
    let mut row = Vec::new();
    for item in seq {
        if item != marker {
            row.push(item.clone());
        } else {
            seqseq.push(row);
            row = Vec::new();
        }
    }
    seqseq
}

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

    #[test]
    fn test_escape_unescape_seqseq() {
        let original = vec![
            vec!["normal".into(), "with\nnewline".into(), "with\\backslash".into()],
            vec!["".into(), "both\n\\".into()],
        ];
        let escaped = escape_seqseq(&original);
        assert_eq!(escaped[0][1], "with\\nnewline");
        assert_eq!(escaped[1][0], "\\");
        assert_eq!(unescape_seqseq(&escaped), original);
    }

    #[test]
    fn test_spill_unspill_invertibility() {
        let cases: Vec<Vec<Vec<String>>> = vec![
            vec![],
            vec![vec![]],
            vec![vec![], vec![]],
            vec![vec!["a".into()]],
            vec![vec!["a".into(), "b".into()], vec!["c".into()]],
            vec![vec!["a".into()], vec![], vec!["b".into()]],
        ];
        for seqseq in cases {
            let spilled = spill(&seqseq, String::new());
            assert_eq!(unspill(&spilled, &String::new()), seqseq);
        }

        let ints: Vec<Vec<i32>> = vec![vec![1, 2], vec![3]];
        assert_eq!(spill(&ints, -1), vec![1, 2, -1, 3, -1]);
    }

    #[test]
    fn test_unspill_discards_incomplete() {
        let input = vec!["a".into(), "b".into()];
        assert!(unspill(&input, &String::new()).is_empty());
    }

    #[test]
    fn test_composition() {
        let samples: Vec<Vec<Vec<String>>> = vec![
            vec![],
            vec![vec![]],
            vec![vec![], vec![], vec![]],
            vec![vec!["a".into(), "b".into()], vec!["c".into(), "d".into()]],
            vec![vec!["".into(), "x".into(), "".into()]],
            vec![vec!["field\\with\\backslashes".into(), "field\nwith\nnewlines".into()]],
            vec![vec!["\\n".into(), "\\\n".into()], vec!["\\\\".into(), "\n\n".into()]],
        ];
        for original in &samples {
            let escaped = escape_seqseq(original);
            let flat = spill(&escaped, String::new());
            let chars: Vec<char> = spill(&flat.iter().map(|s| s.chars().collect()).collect::<Vec<Vec<char>>>(), '\n');
            let encoded: String = chars.into_iter().collect();
            assert_eq!(crate::encode(original), encoded);

            let decoded_chars: Vec<Vec<char>> = unspill(&crate::encode(original).chars().collect::<Vec<_>>(), &'\n');
            let decoded_strings: Vec<String> = decoded_chars.into_iter().map(|cs| cs.into_iter().collect()).collect();
            let decoded_rows = unspill(&decoded_strings, &String::new());
            assert_eq!(*original, unescape_seqseq(&decoded_rows));
        }
    }

    #[test]
    fn test_large_dataset_composition() {
        let original: Vec<Vec<String>> = (0..10_000)
            .map(|i| vec![format!("row{}", i), format!("col\n{}", i), format!("back\\{}", i)])
            .collect();

        let escaped = escape_seqseq(&original);
        let flat = spill(&escaped, String::new());
        let chars: Vec<char> = spill(&flat.iter().map(|s| s.chars().collect()).collect::<Vec<Vec<char>>>(), '\n');
        let encoded: String = chars.into_iter().collect();

        assert!(encoded.len() > 64 * 1024);
        assert_eq!(crate::encode(&original), encoded);
        assert_eq!(crate::decode(&encoded), original);
    }
}