//! A small RFC 4180 reader for the `/csv` batch endpoint.
//!
//! Values may contain commas and are then double-quoted with `""` escaping,
//! which is why the batch cannot be split on `,`. The reader is deliberately
//! lenient: blank lines are skipped and a stray quote inside an unquoted field
//! is kept as data, because a malformed byte in one row must not cost the whole
//! batch.

/// Split CSV text into records, honouring quoting, `""` escapes, embedded
/// commas and newlines, CRLF and LF line endings, and a leading BOM.
pub(crate) fn parse(input: &str) -> Vec<Vec<String>> {
    let input = input.strip_prefix('\u{feff}').unwrap_or(input);

    let mut records: Vec<Vec<String>> = Vec::new();
    let mut record: Vec<String> = Vec::new();
    let mut field = String::new();
    let mut quoted = false;
    let mut chars = input.chars().peekable();

    while let Some(c) = chars.next() {
        if quoted {
            if c == '"' {
                if chars.peek() == Some(&'"') {
                    chars.next();
                    field.push('"');
                } else {
                    quoted = false;
                }
            } else {
                field.push(c);
            }
            continue;
        }

        match c {
            '"' if field.is_empty() => quoted = true,
            ',' => record.push(std::mem::take(&mut field)),
            '\n' | '\r' => {
                if c == '\r' && chars.peek() == Some(&'\n') {
                    chars.next();
                }
                record.push(std::mem::take(&mut field));
                records.push(std::mem::take(&mut record));
            }
            _ => field.push(c),
        }
    }

    if !field.is_empty() || !record.is_empty() {
        record.push(field);
        records.push(record);
    }

    records.retain(|r| r.iter().any(|f| !f.is_empty()));
    records
}

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

    #[test]
    fn splits_plain_rows() {
        let records = parse("a,b,c\n1,2,3\n");
        assert_eq!(records, vec![vec!["a", "b", "c"], vec!["1", "2", "3"]]);
    }

    #[test]
    fn keeps_empty_fields() {
        let records = parse("99999999,,,,,,,,,,,,\n");
        assert_eq!(records.len(), 1);
        assert_eq!(records[0].len(), 13);
    }

    #[test]
    fn reads_quoted_field_with_comma() {
        let records = parse("cep,logradouro\n01001000,\"Rua Um, Dois\"\n");
        assert_eq!(records[1][1], "Rua Um, Dois");
    }

    #[test]
    fn unescapes_doubled_quotes() {
        let records = parse("a\n\"say \"\"hi\"\"\"\n");
        assert_eq!(records[1][0], "say \"hi\"");
    }

    #[test]
    fn accepts_embedded_newline_and_crlf() {
        let records = parse("a,b\r\n\"line\nbreak\",2\r\n");
        assert_eq!(records[1][0], "line\nbreak");
        assert_eq!(records[1][1], "2");
    }

    #[test]
    fn ignores_bom_and_blank_lines() {
        let records = parse("\u{feff}a,b\n\n1,2");
        assert_eq!(records, vec![vec!["a", "b"], vec!["1", "2"]]);
    }
}