use super::widget::Viewport;
use super::word::{
    find_word_inclusive_end_forward, find_word_start_backward, find_word_start_forward,
};
use std::cmp;

/// Specify how to move the cursor.
///
/// This type is marked as `#[non_exhaustive]` since more variations may be supported in the future.
#[non_exhaustive]
#[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.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// let mut textarea = TextArea::from(["abc"]);
    ///
    /// textarea.move_cursor(CursorMove::Forward);
    /// assert_eq!(textarea.cursor(), (0, 1));
    /// textarea.move_cursor(CursorMove::Forward);
    /// assert_eq!(textarea.cursor(), (0, 2));
    /// ```
    Forward,
    /// Move cursor backward by one character. When the cursor is at the head of line, it moves to the end of previous
    /// line.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// let mut textarea = TextArea::from(["abc"]);
    ///
    /// textarea.move_cursor(CursorMove::Forward);
    /// textarea.move_cursor(CursorMove::Forward);
    /// textarea.move_cursor(CursorMove::Back);
    /// assert_eq!(textarea.cursor(), (0, 1));
    /// ```
    Back,
    /// Move cursor up by one line.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// let mut textarea = TextArea::from(["a", "b", "c"]);
    ///
    /// textarea.move_cursor(CursorMove::Down);
    /// textarea.move_cursor(CursorMove::Down);
    /// textarea.move_cursor(CursorMove::Up);
    /// assert_eq!(textarea.cursor(), (1, 0));
    /// ```
    Up,
    /// Move cursor down by one line.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// let mut textarea = TextArea::from(["a", "b", "c"]);
    ///
    /// textarea.move_cursor(CursorMove::Down);
    /// assert_eq!(textarea.cursor(), (1, 0));
    /// textarea.move_cursor(CursorMove::Down);
    /// assert_eq!(textarea.cursor(), (2, 0));
    /// ```
    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.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// let mut textarea = TextArea::from(["abc"]);
    ///
    /// textarea.move_cursor(CursorMove::Forward);
    /// textarea.move_cursor(CursorMove::Forward);
    /// textarea.move_cursor(CursorMove::Head);
    /// assert_eq!(textarea.cursor(), (0, 0));
    /// ```
    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.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// let mut textarea = TextArea::from(["abc"]);
    ///
    /// textarea.move_cursor(CursorMove::End);
    /// assert_eq!(textarea.cursor(), (0, 3));
    /// ```
    End,
    /// Move cursor to the top of lines.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// let mut textarea = TextArea::from(["a", "b", "c"]);
    ///
    /// textarea.move_cursor(CursorMove::Down);
    /// textarea.move_cursor(CursorMove::Down);
    /// textarea.move_cursor(CursorMove::Top);
    /// assert_eq!(textarea.cursor(), (0, 0));
    /// ```
    Top,
    /// Move cursor to the bottom of lines.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// let mut textarea = TextArea::from(["a", "b", "c"]);
    ///
    /// textarea.move_cursor(CursorMove::Bottom);
    /// assert_eq!(textarea.cursor(), (2, 0));
    /// ```
    Bottom,
    /// 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.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// let mut textarea = TextArea::from(["aaa bbb ccc"]);
    ///
    /// textarea.move_cursor(CursorMove::WordForward);
    /// assert_eq!(textarea.cursor(), (0, 4));
    /// textarea.move_cursor(CursorMove::WordForward);
    /// assert_eq!(textarea.cursor(), (0, 8));
    /// ```
    WordForward,
    /// Move cursor forward to the next end of 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
    /// end of the first word of the next line. This is similar to the 'e' mapping of Vim in normal mode.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// let mut textarea = TextArea::from([
    ///     "aaa bbb [[[ccc]]]",
    ///     "",
    ///     " ddd",
    /// ]);
    ///
    ///
    /// textarea.move_cursor(CursorMove::WordEnd);
    /// assert_eq!(textarea.cursor(), (0, 2));      // At the end of 'aaa'
    /// textarea.move_cursor(CursorMove::WordEnd);
    /// assert_eq!(textarea.cursor(), (0, 6));      // At the end of 'bbb'
    /// textarea.move_cursor(CursorMove::WordEnd);
    /// assert_eq!(textarea.cursor(), (0, 10));     // At the end of '[[['
    /// textarea.move_cursor(CursorMove::WordEnd);
    /// assert_eq!(textarea.cursor(), (0, 13));     // At the end of 'ccc'
    /// textarea.move_cursor(CursorMove::WordEnd);
    /// assert_eq!(textarea.cursor(), (0, 16));     // At the end of ']]]'
    /// textarea.move_cursor(CursorMove::WordEnd);
    /// assert_eq!(textarea.cursor(), (2, 3));      // At the end of 'ddd'
    /// ```
    WordEnd,
    /// 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.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// let mut textarea = TextArea::from(["aaa bbb ccc"]);
    ///
    /// textarea.move_cursor(CursorMove::End);
    /// textarea.move_cursor(CursorMove::WordBack);
    /// assert_eq!(textarea.cursor(), (0, 8));
    /// textarea.move_cursor(CursorMove::WordBack);
    /// assert_eq!(textarea.cursor(), (0, 4));
    /// textarea.move_cursor(CursorMove::WordBack);
    /// assert_eq!(textarea.cursor(), (0, 0));
    /// ```
    WordBack,
    /// Move cursor down by one paragraph. Paragraph is a chunk of non-empty lines. Cursor moves to the first line of paragraph.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// // aaa
    /// //
    /// // bbb
    /// //
    /// // ccc
    /// // ddd
    /// let mut textarea = TextArea::from(["aaa", "", "bbb", "", "ccc", "ddd"]);
    ///
    /// textarea.move_cursor(CursorMove::ParagraphForward);
    /// assert_eq!(textarea.cursor(), (2, 0));
    /// textarea.move_cursor(CursorMove::ParagraphForward);
    /// assert_eq!(textarea.cursor(), (4, 0));
    /// ```
    ParagraphForward,
    /// Move cursor up by one paragraph. Paragraph is a chunk of non-empty lines. Cursor moves to the first line of paragraph.
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// // aaa
    /// //
    /// // bbb
    /// //
    /// // ccc
    /// // ddd
    /// let mut textarea = TextArea::from(["aaa", "", "bbb", "", "ccc", "ddd"]);
    ///
    /// textarea.move_cursor(CursorMove::Bottom);
    /// textarea.move_cursor(CursorMove::ParagraphBack);
    /// assert_eq!(textarea.cursor(), (4, 0));
    /// textarea.move_cursor(CursorMove::ParagraphBack);
    /// assert_eq!(textarea.cursor(), (2, 0));
    /// textarea.move_cursor(CursorMove::ParagraphBack);
    /// assert_eq!(textarea.cursor(), (0, 0));
    /// ```
    ParagraphBack,
    /// Move cursor to (row, col) position. When the position points outside the text, the cursor position is made fit
    /// within the text. Note that row and col are 0-based. (0, 0) means the first character of the first line.
    ///
    /// When there are 10 lines, jumping to row 15 moves the cursor to the last line (row is 9 in the case). When there
    /// are 10 characters in the line, jumping to col 15 moves the cursor to end of the line (col is 10 in the case).
    /// ```
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// let mut textarea = TextArea::from(["aaaa", "bbbb", "cccc"]);
    ///
    /// textarea.move_cursor(CursorMove::Jump(1, 2));
    /// assert_eq!(textarea.cursor(), (1, 2));
    ///
    /// textarea.move_cursor(CursorMove::Jump(10,  10));
    /// assert_eq!(textarea.cursor(), (2, 4));
    /// ```
    Jump(u16, u16),
    /// 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.
    /// ```
    /// # use ratatui::buffer::Buffer;
    /// # use ratatui::layout::Rect;
    /// # use ratatui::widgets::Widget as _;
    /// use bookokrat::vendored::tui_textarea::{TextArea, CursorMove};
    ///
    /// // Let's say terminal height is 8.
    ///
    /// // Create textarea with 20 lines "0", "1", "2", "3", ...
    /// // The viewport is displaying from line 1 to line 8.
    /// let mut textarea: TextArea = (0..20).into_iter().map(|i| i.to_string()).collect();
    /// # // Call `render` at least once to populate terminal size
    /// # let r = Rect { x: 0, y: 0, width: 24, height: 8 };
    /// # let mut b = Buffer::empty(r.clone());
    /// # textarea.render(r, &mut b);
    ///
    /// // Move cursor to the end of lines (line 20). It is outside the viewport (line 1 to line 8)
    /// textarea.move_cursor(CursorMove::Bottom);
    /// assert_eq!(textarea.cursor(), (19, 0));
    ///
    /// // Cursor is moved to line 8 to enter the viewport
    /// textarea.move_cursor(CursorMove::InViewport);
    /// assert_eq!(textarea.cursor(), (7, 0));
    /// ```
    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())),
            Top => Some((0, fit_col(col, &lines[0]))),
            Bottom => {
                let row = lines.len() - 1;
                Some((row, fit_col(col, &lines[row])))
            }
            WordEnd => {
                // `+ 1` for not accepting the current cursor position
                if let Some(col) = find_word_inclusive_end_forward(&lines[row], col + 1) {
                    Some((row, col))
                } else {
                    let mut row = row;
                    loop {
                        if row == lines.len() - 1 {
                            break Some((row, lines[row].chars().count()));
                        }
                        row += 1;
                        if let Some(col) = find_word_inclusive_end_forward(&lines[row], 0) {
                            break Some((row, col));
                        }
                    }
                }
            }
            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))
                }
            }
            ParagraphForward => {
                let mut prev_is_empty = lines[row].is_empty();
                for row in row + 1..lines.len() {
                    let line = &lines[row];
                    let is_empty = line.is_empty();
                    if !is_empty && prev_is_empty {
                        return Some((row, fit_col(col, line)));
                    }
                    prev_is_empty = is_empty;
                }
                let row = lines.len() - 1;
                Some((row, fit_col(col, &lines[row])))
            }
            ParagraphBack => {
                let row = row.checked_sub(1)?;
                let mut prev_is_empty = lines[row].is_empty();
                for row in (0..row).rev() {
                    let is_empty = lines[row].is_empty();
                    if is_empty && !prev_is_empty {
                        return Some((row + 1, fit_col(col, &lines[row + 1])));
                    }
                    prev_is_empty = is_empty;
                }
                Some((0, fit_col(col, &lines[0])))
            }
            Jump(row, col) => {
                let row = cmp::min(*row as usize, lines.len() - 1);
                let col = fit_col(*col as usize, &lines[row]);
                Some((row, col))
            }
            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))
            }
        }
    }
}

#[cfg(test)]
mod tests {
    #[test]
    fn in_viewport() {
        use super::super::textarea::TextArea;
        use super::CursorMove;
        use ratatui::buffer::Buffer;
        use ratatui::layout::Rect;
        use ratatui::widgets::Widget as _;

        let mut textarea: TextArea = (0..20).map(|i| i.to_string()).collect();
        let r = Rect {
            x: 0,
            y: 0,
            width: 24,
            height: 8,
        };
        let mut b = Buffer::empty(r);
        textarea.render(r, &mut b);

        textarea.move_cursor(CursorMove::Bottom);
        assert_eq!(textarea.cursor(), (19, 0));

        textarea.move_cursor(CursorMove::InViewport);
        assert_eq!(textarea.cursor(), (7, 0));
    }
}
