xplr/src/directory_buffer.rs

use crate::node::Node;
use serde::{Deserialize, Serialize};
use std::cmp::Ordering;
use time::OffsetDateTime;

#[derive(Debug, Clone, Copy, Eq, PartialEq, Serialize, Deserialize)]
pub struct ScrollState {
    pub current_focus: usize,
    pub last_focus: Option<usize>,
    pub skipped_rows: usize,
    /* The number of visible next lines when scrolling towards either ends of the view port */
    pub initial_preview_cushion: usize,

    pub vimlike_scrolling: bool,
}

impl ScrollState {
    pub fn new(current_focus: usize, total: usize, vimlike_scrolling: bool) -> Self {
        let initial_preview_cushion = 5;
        Self {
            current_focus,
            last_focus: None,
            skipped_rows: 0,
            initial_preview_cushion,
            vimlike_scrolling,
        }
        .update_skipped_rows(initial_preview_cushion + 1, total)
    }

    pub fn set_focus(mut self, current_focus: usize) -> Self {
        self.last_focus = Some(self.current_focus);
        self.current_focus = current_focus;
        self
    }

    pub fn update_skipped_rows(self, height: usize, total: usize) -> Self {
        if self.vimlike_scrolling {
            self.update_skipped_rows_vimlike(height, total)
        } else {
            self.update_skipped_rows_paginated(height)
        }
    }

    pub fn update_skipped_rows_paginated(mut self, height: usize) -> Self {
        self.skipped_rows = height * (self.current_focus / height.max(1));
        self
    }

    pub fn update_skipped_rows_vimlike(mut self, height: usize, total: usize) -> Self {
        let preview_cushion = if height >= self.initial_preview_cushion * 3 {
            self.initial_preview_cushion
        } else if height >= 9 {
            3
        } else if height >= 3 {
            1
        } else {
            0
        };

        let current_focus = self.current_focus;
        let last_focus = self.last_focus;
        let first_visible_row = self.skipped_rows;

        // Calculate the cushion rows at the start and end of the view port
        let start_cushion_row = first_visible_row + preview_cushion;
        let end_cushion_row = (first_visible_row + height)
            .saturating_sub(preview_cushion + 1)
            .min(total.saturating_sub(preview_cushion + 1));

        self.skipped_rows = if current_focus == 0 {
            // When focus goes to first node
            0
        } else if current_focus == total.saturating_sub(1) {
            // When focus goes to last node
            total.saturating_sub(height)
        } else if current_focus > start_cushion_row && current_focus <= end_cushion_row {
            // If within cushioned area; do nothing
            first_visible_row
        } else if let Some(last_focus) = last_focus {
            match current_focus.cmp(&last_focus) {
                Ordering::Greater => {
                    // When scrolling down the cushioned area
                    if current_focus > total.saturating_sub(preview_cushion + 1) {
                        // When focusing the last nodes; always view the full last page
                        total.saturating_sub(height)
                    } else {
                        // When scrolling down the cushioned area without reaching the last nodes
                        current_focus
                            .saturating_sub(height.saturating_sub(preview_cushion + 1))
                    }
                }

                Ordering::Less => {
                    // When scrolling up the cushioned area
                    if current_focus < preview_cushion {
                        // When focusing the first nodes; always view the full first page
                        0
                    } else if current_focus > end_cushion_row {
                        // When scrolling up from the last rows; do nothing
                        first_visible_row
                    } else {
                        // When scrolling up the cushioned area without reaching the first nodes
                        current_focus.saturating_sub(preview_cushion)
                    }
                }
                Ordering::Equal => {
                    // Do nothing
                    first_visible_row
                }
            }
        } else {
            // Just entered dir
            first_visible_row
        };
        self
    }
}

#[derive(Debug, Clone, Eq, PartialEq, Serialize, Deserialize)]
pub struct DirectoryBuffer {
    pub parent: String,
    pub nodes: Vec<Node>,
    pub total: usize,
    pub focus: usize,

    #[serde(skip, default = "now")]
    pub explored_at: OffsetDateTime,
}

impl DirectoryBuffer {
    pub fn new(parent: String, nodes: Vec<Node>, focus: usize) -> Self {
        let total = nodes.len();
        Self {
            parent,
            nodes,
            total,
            focus,
            explored_at: now(),
        }
    }

    pub fn focused_node(&self) -> Option<&Node> {
        self.nodes.get(self.focus)
    }
}

fn now() -> OffsetDateTime {
    OffsetDateTime::now_local()
        .ok()
        .unwrap_or_else(OffsetDateTime::now_utc)
}

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

    #[test]
    fn test_update_skipped_rows_paginated() {
        let state = ScrollState {
            current_focus: 10,
            last_focus: Some(8),
            skipped_rows: 0,
            initial_preview_cushion: 5,
            vimlike_scrolling: false,
        };

        let height = 5;
        let total = 100;

        let state = state.update_skipped_rows(height, total);
        assert_eq!(
            state.skipped_rows,
            height * (state.current_focus / height.max(1))
        );
    }

    #[test]
    fn test_update_skipped_rows_entered_directory() {
        let state = ScrollState {
            current_focus: 100,
            last_focus: None,
            skipped_rows: 0,
            initial_preview_cushion: 5,
            vimlike_scrolling: true,
        };

        let height = 5;
        let total = 200;

        let result = state.update_skipped_rows(height, total).skipped_rows;
        assert_eq!(result, 0);
    }

    #[test]
    fn test_calc_skipped_rows_top_of_directory() {
        let state = ScrollState {
            current_focus: 0,
            last_focus: Some(8),
            skipped_rows: 5,
            initial_preview_cushion: 5,
            vimlike_scrolling: true,
        };

        let height = 5;
        let total = 20;

        let result = state.update_skipped_rows(height, total).skipped_rows;
        assert_eq!(result, 0);
    }

    #[test]
    fn test_calc_skipped_rows_bottom_of_directory() {
        let state = ScrollState {
            current_focus: 19,
            last_focus: Some(18),
            skipped_rows: 15,
            initial_preview_cushion: 5,
            vimlike_scrolling: true,
        };

        let height = 5;
        let total = 20;

        let result = state.update_skipped_rows(height, total).skipped_rows;
        assert_eq!(result, 15);
    }

    #[test]
    fn test_calc_skipped_rows_scrolling_down() {
        let state = ScrollState {
            current_focus: 12,
            last_focus: Some(10),
            skipped_rows: 10,
            initial_preview_cushion: 5,
            vimlike_scrolling: true,
        };

        let height = 5;
        let total = 20;

        let result = state.update_skipped_rows(height, total).skipped_rows;
        assert_eq!(result, 10);
    }

    #[test]
    fn test_calc_skipped_rows_scrolling_up() {
        let state = ScrollState {
            current_focus: 8,
            last_focus: Some(10),
            skipped_rows: 10,
            initial_preview_cushion: 5,
            vimlike_scrolling: true,
        };

        let height = 5;
        let total = 20;

        let result = state.update_skipped_rows(height, total).skipped_rows;
        assert_eq!(result, 7);
    }

    // Add more tests for other scenarios...
}