guise-ui 1.5.2

//! Pure sort and selection logic for [`TableView`](super::TableView).
//!
//! Sorting produces a *display order* — a stable permutation of source-row
//! indices — so the source data is never reordered. Selection is a set of
//! source indices, which is why it survives resorting unchanged.
//!
//! ```ignore
//! let order = sorted_order(&rows, SortDir::Asc, &|a, b| a.name.cmp(&b.name));
//! let mut sel = SelectionState::default();
//! sel.click(SelectionMode::Multi, &order, 0, false, false);
//! sel.click(SelectionMode::Multi, &order, 3, false, true); // shift: rows 0..=3
//! ```

use std::cmp::Ordering;
use std::collections::BTreeSet;

/// Sort direction of a table column.
#[derive(Debug, Clone, Copy, PartialEq, Eq)]
pub enum SortDir {
  Asc,
  Desc,
}

/// How rows respond to clicks and arrow keys.
#[derive(Debug, Clone, Copy, PartialEq, Eq, Default)]
pub enum SelectionMode {
  /// Rows are not selectable.
  #[default]
  None,
  /// At most one row selected at a time.
  Single,
  /// Many rows: cmd-click toggles, shift-click selects a range.
  Multi,
}

/// Header-click cycling: none → asc → desc → none on the same column; a click
/// on a different column starts fresh at ascending.
pub fn cycle_sort(current: Option<(usize, SortDir)>, column: usize) -> Option<(usize, SortDir)> {
  match current {
    Some((col, SortDir::Asc)) if col == column => Some((column, SortDir::Desc)),
    Some((col, SortDir::Desc)) if col == column => None,
    _ => Some((column, SortDir::Asc)),
  }
}

/// The unsorted display order: `0..len`.
pub fn identity_order(len: usize) -> Vec<usize> {
  (0..len).collect()
}

/// A stable sort of row indices by `cmp`; the source slice is never mutated.
/// `Desc` flips the comparator arguments (rather than reversing the result),
/// so equal rows keep their source order in both directions.
pub fn sorted_order<T>(rows: &[T], dir: SortDir, cmp: &dyn Fn(&T, &T) -> Ordering) -> Vec<usize> {
  let mut order = identity_order(rows.len());
  order.sort_by(|&a, &b| match dir {
    SortDir::Asc => cmp(&rows[a], &rows[b]),
    SortDir::Desc => cmp(&rows[b], &rows[a]),
  });
  order
}

/// Where `source` currently sits in the display order.
fn position_of(order: &[usize], source: usize) -> Option<usize> {
  order.iter().position(|&s| s == source)
}

/// Row selection over **source** indices. The shift anchor and keyboard cursor
/// are also source indices, mapped through the display order at use, so all
/// three survive resorting.
#[derive(Debug, Clone, Default)]
pub struct SelectionState {
  selected: BTreeSet<usize>,
  anchor: Option<usize>,
  cursor: Option<usize>,
}

impl SelectionState {
  /// The selected source indices, ascending.
  pub fn selected(&self) -> Vec<usize> {
    self.selected.iter().copied().collect()
  }

  pub fn is_selected(&self, source: usize) -> bool {
    self.selected.contains(&source)
  }

  /// The keyboard cursor (a source index), if any.
  pub fn cursor(&self) -> Option<usize> {
    self.cursor
  }

  /// Drop everything. Returns whether the selected set changed.
  pub fn clear(&mut self) -> bool {
    self.anchor = None;
    self.cursor = None;
    if self.selected.is_empty() {
      return false;
    }
    self.selected.clear();
    true
  }

  /// Prune indices that fell off the end after a row-count change. Returns
  /// whether the selected set changed.
  pub fn retain_below(&mut self, len: usize) -> bool {
    let before = self.selected.len();
    self.selected.retain(|&s| s < len);
    self.anchor = self.anchor.filter(|&s| s < len);
    self.cursor = self.cursor.filter(|&s| s < len);
    self.selected.len() != before
  }

  /// A mouse click on the row at `display` position. `toggle` is cmd-click,
  /// `range` is shift-click (range wins when both are held).
  pub fn click(
    &mut self,
    mode: SelectionMode,
    order: &[usize],
    display: usize,
    toggle: bool,
    range: bool,
  ) {
    let Some(&source) = order.get(display) else {
      return;
    };
    match mode {
      SelectionMode::None => {}
      SelectionMode::Single => {
        if toggle && self.selected.contains(&source) {
          self.selected.clear();
        } else {
          self.selected.clear();
          self.selected.insert(source);
        }
        self.anchor = Some(source);
        self.cursor = Some(source);
      }
      SelectionMode::Multi => {
        if range {
          let from = match self.anchor.and_then(|a| position_of(order, a)) {
            Some(pos) => pos,
            // No live anchor (first interaction, or its row is
            // gone): this click starts and anchors the range.
            None => {
              self.anchor = Some(source);
              display
            }
          };
          self.select_span(order, from, display);
        } else if toggle {
          if !self.selected.remove(&source) {
            self.selected.insert(source);
          }
          self.anchor = Some(source);
        } else {
          self.selected.clear();
          self.selected.insert(source);
          self.anchor = Some(source);
        }
        self.cursor = Some(source);
      }
    }
  }

  /// Move the cursor by `delta` display positions (arrow keys), selecting
  /// the row it lands on. `extend` (shift) grows the range from the anchor
  /// in `Multi` mode. Returns the new cursor's display position so the
  /// caller can scroll it into view.
  pub fn step(
    &mut self,
    mode: SelectionMode,
    order: &[usize],
    delta: isize,
    extend: bool,
  ) -> Option<usize> {
    if matches!(mode, SelectionMode::None) || order.is_empty() {
      return None;
    }
    let last = order.len() - 1;
    let display = match self.cursor.and_then(|c| position_of(order, c)) {
      Some(pos) => (pos as isize + delta).clamp(0, last as isize) as usize,
      // Nothing focused yet: Down enters at the top, Up at the bottom.
      None if delta < 0 => last,
      None => 0,
    };
    let source = order[display];
    if extend && matches!(mode, SelectionMode::Multi) {
      let from = match self.anchor.and_then(|a| position_of(order, a)) {
        Some(pos) => pos,
        // No live anchor yet: the row this step lands on anchors the
        // range, so further shift-steps grow from it.
        None => {
          self.anchor = Some(source);
          display
        }
      };
      self.select_span(order, from, display);
    } else {
      self.selected.clear();
      self.selected.insert(source);
      self.anchor = Some(source);
    }
    self.cursor = Some(source);
    Some(display)
  }

  /// Select exactly the display range `a..=b` (either direction).
  fn select_span(&mut self, order: &[usize], a: usize, b: usize) {
    let (lo, hi) = if a <= b { (a, b) } else { (b, a) };
    self.selected.clear();
    self.selected.extend(order[lo..=hi].iter().copied());
  }
}

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

  #[test]
  fn sort_cycles_asc_desc_none() {
    let s1 = cycle_sort(None, 2);
    assert_eq!(s1, Some((2, SortDir::Asc)));
    let s2 = cycle_sort(s1, 2);
    assert_eq!(s2, Some((2, SortDir::Desc)));
    assert_eq!(cycle_sort(s2, 2), None);
  }

  #[test]
  fn sort_switching_column_restarts_ascending() {
    let current = Some((0, SortDir::Desc));
    assert_eq!(cycle_sort(current, 1), Some((1, SortDir::Asc)));
  }

  #[test]
  fn sorted_order_never_touches_the_source() {
    let rows = vec![3, 1, 2];
    let order = sorted_order(&rows, SortDir::Asc, &|a, b| a.cmp(b));
    assert_eq!(order, vec![1, 2, 0]);
    assert_eq!(rows, vec![3, 1, 2]);
  }

  #[test]
  fn sorted_order_is_stable_in_both_directions() {
    // Equal keys (by first tuple field) must keep source order.
    let rows = vec![(1, "a"), (0, "b"), (1, "c"), (0, "d")];
    let cmp = |a: &(i32, &str), b: &(i32, &str)| a.0.cmp(&b.0);
    assert_eq!(sorted_order(&rows, SortDir::Asc, &cmp), vec![1, 3, 0, 2]);
    assert_eq!(sorted_order(&rows, SortDir::Desc, &cmp), vec![0, 2, 1, 3]);
  }

  #[test]
  fn single_mode_holds_one_row_and_cmd_click_deselects() {
    let order = identity_order(4);
    let mut sel = SelectionState::default();
    sel.click(SelectionMode::Single, &order, 1, false, false);
    assert_eq!(sel.selected(), vec![1]);
    sel.click(SelectionMode::Single, &order, 3, false, false);
    assert_eq!(sel.selected(), vec![3]);
    sel.click(SelectionMode::Single, &order, 3, true, false);
    assert_eq!(sel.selected(), Vec::<usize>::new());
  }

  #[test]
  fn none_mode_ignores_clicks_and_steps() {
    let order = identity_order(3);
    let mut sel = SelectionState::default();
    sel.click(SelectionMode::None, &order, 0, false, false);
    assert!(sel.selected().is_empty());
    assert_eq!(sel.step(SelectionMode::None, &order, 1, false), None);
  }

  #[test]
  fn multi_mode_cmd_click_toggles() {
    let order = identity_order(4);
    let mut sel = SelectionState::default();
    sel.click(SelectionMode::Multi, &order, 0, false, false);
    sel.click(SelectionMode::Multi, &order, 2, true, false);
    assert_eq!(sel.selected(), vec![0, 2]);
    sel.click(SelectionMode::Multi, &order, 0, true, false);
    assert_eq!(sel.selected(), vec![2]);
  }

  #[test]
  fn multi_mode_shift_click_selects_a_range_from_the_anchor() {
    let order = identity_order(6);
    let mut sel = SelectionState::default();
    sel.click(SelectionMode::Multi, &order, 1, false, false);
    sel.click(SelectionMode::Multi, &order, 4, false, true);
    assert_eq!(sel.selected(), vec![1, 2, 3, 4]);
    // Shift again re-ranges from the same anchor, upward this time.
    sel.click(SelectionMode::Multi, &order, 0, false, true);
    assert_eq!(sel.selected(), vec![0, 1]);
  }

  #[test]
  fn shift_click_first_establishes_the_anchor() {
    let order = identity_order(6);
    let mut sel = SelectionState::default();
    // Fresh table: a shift-click anchors at the clicked row...
    sel.click(SelectionMode::Multi, &order, 2, false, true);
    assert_eq!(sel.selected(), vec![2]);
    // ...so the next shift-click grows a range from it.
    sel.click(SelectionMode::Multi, &order, 5, false, true);
    assert_eq!(sel.selected(), vec![2, 3, 4, 5]);
  }

  #[test]
  fn shift_step_first_extends_from_the_entry_row() {
    let order = identity_order(4);
    let mut sel = SelectionState::default();
    // Fresh table: shift+down enters at the top and anchors there...
    assert_eq!(sel.step(SelectionMode::Multi, &order, 1, true), Some(0));
    assert_eq!(sel.selected(), vec![0]);
    // ...so the next shift+down extends instead of moving the selection.
    assert_eq!(sel.step(SelectionMode::Multi, &order, 1, true), Some(1));
    assert_eq!(sel.selected(), vec![0, 1]);
  }

  #[test]
  fn shift_range_follows_display_order_but_stores_source_indices() {
    // Display order reversed: display 0 shows source 3, etc.
    let order = vec![3, 2, 1, 0];
    let mut sel = SelectionState::default();
    sel.click(SelectionMode::Multi, &order, 0, false, false);
    assert_eq!(sel.selected(), vec![3]);
    sel.click(SelectionMode::Multi, &order, 2, false, true);
    assert_eq!(sel.selected(), vec![1, 2, 3]);
  }

  #[test]
  fn selection_survives_resorting() {
    let mut sel = SelectionState::default();
    sel.click(SelectionMode::Single, &identity_order(4), 2, false, false);
    assert_eq!(sel.selected(), vec![2]);
    // Order flips; source 2 is still the selected row.
    assert!(sel.is_selected(2));
    // Stepping down from it moves through the *new* display order.
    let order = vec![3, 2, 1, 0]; // source 2 is at display 1
    let display = sel.step(SelectionMode::Single, &order, 1, false);
    assert_eq!(display, Some(2));
    assert_eq!(sel.selected(), vec![1]);
  }

  #[test]
  fn step_enters_at_the_edges_and_clamps() {
    let order = identity_order(3);
    let mut sel = SelectionState::default();
    assert_eq!(sel.step(SelectionMode::Single, &order, 1, false), Some(0));
    assert_eq!(sel.step(SelectionMode::Single, &order, -1, false), Some(0));
    assert_eq!(sel.selected(), vec![0]);

    let mut sel = SelectionState::default();
    assert_eq!(sel.step(SelectionMode::Single, &order, -1, false), Some(2));
    assert_eq!(sel.selected(), vec![2]);
  }

  #[test]
  fn shift_step_extends_from_the_anchor() {
    let order = identity_order(5);
    let mut sel = SelectionState::default();
    sel.click(SelectionMode::Multi, &order, 2, false, false);
    sel.step(SelectionMode::Multi, &order, 1, true);
    sel.step(SelectionMode::Multi, &order, 1, true);
    assert_eq!(sel.selected(), vec![2, 3, 4]);
    // Un-extending walks the range back.
    sel.step(SelectionMode::Multi, &order, -1, true);
    assert_eq!(sel.selected(), vec![2, 3]);
  }

  #[test]
  fn clear_and_retain_report_changes() {
    let order = identity_order(4);
    let mut sel = SelectionState::default();
    assert!(!sel.clear());
    sel.click(SelectionMode::Multi, &order, 1, false, false);
    sel.click(SelectionMode::Multi, &order, 3, true, false);
    assert!(sel.retain_below(2)); // drops source 3
    assert_eq!(sel.selected(), vec![1]);
    assert!(!sel.retain_below(2));
    assert!(sel.clear());
    assert_eq!(sel.cursor(), None);
  }
}