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use {
super::util::{find_word_start_backward, find_word_start_forward},
crate::widgets::textarea::core::widget::Viewport,
std::cmp,
};
/// Specify how to move the cursor.
#[derive(Clone, Copy, Debug, PartialEq, Eq)]
pub enum CursorMove {
/// Move cursor forward by one character. When the cursor is at the end of line, it moves to the
/// head of next line.
Forward,
/// Move cursor backward by one character. When the cursor is at the head of line, it moves to
/// the end of previous line.
Back,
/// Move cursor up by one line.
Up,
/// Move cursor down by one line.
Down,
/// Move cursor to the head of line. When the cursor is at the head of line, it moves to the end of previous line.
Head,
/// Move cursor to the end of line. When the cursor is at the end of line, it moves to the head of next line.
End,
/// Move cursor forward by one word. Word boundary appears at spaces, punctuations, and others. For example
/// `fn foo(a)` consists of words `fn`, `foo`, `(`, `a`, `)`. When the cursor is at the end of line, it moves to the
/// head of next line.
WordForward,
/// Move cursor backward by one word. Word boundary appears at spaces, punctuations, and others. For example
/// `fn foo(a)` consists of words `fn`, `foo`, `(`, `a`, `)`.When the cursor is at the head of line, it moves to
/// the end of previous line.
WordBack,
/// Move cursor to keep it within the viewport. For example, when a viewport displays line 8 to line 16:
///
/// - cursor at line 4 is moved to line 8
/// - cursor at line 20 is moved to line 16
/// - cursor at line 12 is not moved
///
/// This is useful when you moved a cursor but you don't want to move the viewport.
InViewport,
}
impl CursorMove {
pub(crate) fn next_cursor(
&self,
(row, col): (usize, usize),
lines: &[String],
viewport: &Viewport,
) -> Option<(usize, usize)> {
use CursorMove::*;
fn fit_col(col: usize, line: &str) -> usize {
cmp::min(col, line.chars().count())
}
match self {
Forward if col >= lines[row].chars().count() => {
(row + 1 < lines.len()).then(|| (row + 1, 0))
}
Forward => Some((row, col + 1)),
Back if col == 0 => {
let row = row.checked_sub(1)?;
Some((row, lines[row].chars().count()))
}
Back => Some((row, col - 1)),
Up => {
let row = row.checked_sub(1)?;
Some((row, fit_col(col, &lines[row])))
}
Down => Some((row + 1, fit_col(col, lines.get(row + 1)?))),
Head => Some((row, 0)),
End => Some((row, lines[row].chars().count())),
WordForward => {
if let Some(col) = find_word_start_forward(&lines[row], col) {
Some((row, col))
} else if row + 1 < lines.len() {
Some((row + 1, 0))
} else {
Some((row, lines[row].chars().count()))
}
}
WordBack => {
if let Some(col) = find_word_start_backward(&lines[row], col) {
Some((row, col))
} else if row > 0 {
Some((row - 1, lines[row - 1].chars().count()))
} else {
Some((row, 0))
}
}
InViewport => {
let (row_top, col_top, row_bottom, col_bottom) = viewport.position();
let row = row.clamp(row_top as usize, row_bottom as usize);
let row = cmp::min(row, lines.len() - 1);
let col = col.clamp(col_top as usize, col_bottom as usize);
let col = fit_col(col, &lines[row]);
Some((row, col))
}
}
}
}