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use csv::StringRecordIter;
use std::cmp::PartialEq;
use std::collections::HashMap;
use std::collections::hash_map::DefaultHasher;
use std::hash::{Hash, Hasher};
use crate::Row;
/// A structure for keeping relationship between the headers and their positions
#[derive(Debug, Clone, PartialEq)]
pub struct Headers {
indexes: HashMap<String, usize>,
names: Row,
}
impl Headers {
pub fn from_row(row: Row) -> Headers {
let mut indexes = HashMap::new();
for (index, entry) in row.iter().enumerate() {
indexes.insert(entry.to_string(), index);
}
Headers {
indexes,
names: row,
}
}
/// Retrieves a field from a row given it's header name
///
/// ```rust
/// use csvsc::{Headers, Row};
///
/// let headers = Headers::from_row(Row::from(vec!["id", "val"]));
/// let row = Row::from(vec!["1", "40"]);
///
/// assert_eq!(headers.get_field(&row, "id"), Some("1"));
/// assert_eq!(headers.get_field(&row, "val"), Some("40"));
/// assert_eq!(headers.get_field(&row, "foo"), None);
/// ```
pub fn get_field<'r>(&self, row: &'r Row, field: &str) -> Option<&'r str> {
self.index(field).and_then(|i| row.get(i))
}
/// Creates a hash for the row given as first argument only considering the
/// columns specified by the second argument.
///
/// ```rust
/// use csvsc::{Headers, Row};
///
/// let headers = Headers::from_row(Row::from(vec!["id", "name", "val"]));
/// let row = Row::from(vec!["1", "juan", "40"]);
///
/// dbg!(headers.hash(&row, &["id".to_string(), "name".to_string()]));
/// ```
///
/// If no columns are specified, a random hash is chosen. If a column is not
/// found its name is returned as String wrapped in the Err variant of the
/// return value
pub fn hash(&self, row: &Row, columns: &[String]) -> Result<u64, String> {
if columns.len() == 0 {
return Ok(rand::random());
}
let mut hasher = DefaultHasher::new();
for col in columns {
match self.get_field(row, col) {
Some(field) => field.hash(&mut hasher),
None => return Err(col.to_string()),
}
}
Ok(hasher.finish())
}
/// Adds a new header. It'll fail if the header is already present
///
/// ```rust
/// use csvsc::{Headers, Row};
///
/// let mut h = Headers::from_row(Row::from(vec!["name"]));
///
/// h.add("value").unwrap();
///
/// assert_eq!(h, Headers::from_row(Row::from(vec!["name", "value"])));
///
/// assert_eq!(h.add("name"), Err(()));
/// assert_eq!(h, Headers::from_row(Row::from(vec!["name", "value"])));
/// ```
pub fn add(&mut self, colname: &str) -> Result<(), ()> {
if self.indexes.contains_key(colname) {
return Err(());
}
self.names.push_field(colname);
self.indexes
.insert(colname.to_string(), self.names.len() - 1);
Ok(())
}
pub fn len(&self) -> usize {
self.names.len()
}
pub fn as_row(&self) -> &Row {
&self.names
}
/// Obtains the index of the given field in the headers
pub fn index(&self, field: &str) -> Option<usize> {
self.indexes.get(field).map(|u| *u)
}
pub fn contains_key(&self, field: &str) -> bool {
self.indexes.contains_key(field)
}
pub fn iter(&self) -> StringRecordIter {
self.names.iter()
}
}
impl PartialEq<Headers> for Row {
fn eq(&self, other: &Headers) -> bool {
self == other.as_row()
}
}
#[cfg(test)]
mod tests {
use super::Headers;
use crate::Row;
#[test]
fn test_hash() {
let header = Headers::from_row(Row::from(vec!["a", "b"]));
let data = Row::from(vec!["1", "2"]);
let cols = vec!["a".to_string()];
assert_eq!(
header.hash(&data, &cols).unwrap(),
16569625464242099095
);
let header = Headers::from_row(Row::from(vec!["a", "b"]));
let data = Row::from(vec!["1", "2"]);
let cols = vec!["a".to_string(), "b".to_string()];
assert_eq!(
header.hash(&data, &cols).unwrap(),
15633344752900483833
);
let header = Headers::from_row(Row::from(vec!["a", "b"]));
let data = Row::from(vec!["1", "2"]);
let cols = vec!["d".to_string()];
assert_eq!(
header.hash(&data, &cols),
Err("d".to_string())
);
}
}