// Copyright 2016 Joe Wilm, The Alacritty Project Contributors
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
//     http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.

//! State management for a selection in the grid
//!
//! A selection should start when the mouse is clicked, and it should be
//! finalized when the button is released. The selection should be cleared
//! when text is added/removed/scrolled on the screen. The selection should
//! also be cleared if the user clicks off of the selection.
use std::convert::TryFrom;
use std::mem;
use std::ops::Range;

use crate::index::{Column, Point, Side};
use crate::term::cell::Flags;
use crate::term::{Search, Term};

/// A Point and side within that point.
#[derive(Debug, Clone, PartialEq)]
pub struct Anchor {
    point: Point<usize>,
    side: Side,
}

impl Anchor {
    fn new(point: Point<usize>, side: Side) -> Anchor {
        Anchor { point, side }
    }
}

/// Represents a range of selected cells.
#[derive(Copy, Clone, Debug, Eq, PartialEq)]
pub struct SelectionRange<L = usize> {
    /// Start point, top left of the selection.
    pub start: Point<L>,
    /// End point, bottom right of the selection.
    pub end: Point<L>,
    /// Whether this selection is a block selection.
    pub is_block: bool,
}

impl<L> SelectionRange<L> {
    pub fn new(start: Point<L>, end: Point<L>, is_block: bool) -> Self {
        Self { start, end, is_block }
    }

    pub fn contains(&self, col: Column, line: L) -> bool
    where
        L: PartialEq + PartialOrd,
    {
        self.start.line <= line
            && self.end.line >= line
            && (self.start.col <= col || (self.start.line != line && !self.is_block))
            && (self.end.col >= col || (self.end.line != line && !self.is_block))
    }
}

/// Describes a region of a 2-dimensional area.
///
/// Used to track a text selection. There are three supported modes, each with its own constructor:
/// [`simple`], [`semantic`], and [`lines`]. The [`simple`] mode precisely tracks which cells are
/// selected without any expansion. [`semantic`] mode expands the initial selection to the nearest
/// semantic escape char in either direction. [`lines`] will always select entire lines.
///
/// Calls to [`update`] operate different based on the selection kind. The [`simple`] mode does
/// nothing special, simply tracks points and sides. [`semantic`] will continue to expand out to
/// semantic boundaries as the selection point changes. Similarly, [`lines`] will always expand the
/// new point to encompass entire lines.
///
/// [`simple`]: enum.Selection.html#method.simple
/// [`semantic`]: enum.Selection.html#method.semantic
/// [`lines`]: enum.Selection.html#method.lines
/// [`update`]: enum.Selection.html#method.update
#[derive(Debug, Clone, PartialEq)]
pub enum Selection {
    Simple {
        /// The region representing start and end of cursor movement.
        region: Range<Anchor>,
    },
    Block {
        /// The region representing start and end of cursor movement.
        region: Range<Anchor>,
    },
    Semantic {
        /// The region representing start and end of cursor movement.
        region: Range<Point<usize>>,
    },
    Lines {
        /// The region representing start and end of cursor movement.
        region: Range<Point<usize>>,
    },
}

impl Selection {
    pub fn simple(location: Point<usize>, side: Side) -> Selection {
        Selection::Simple {
            region: Range { start: Anchor::new(location, side), end: Anchor::new(location, side) },
        }
    }

    pub fn block(location: Point<usize>, side: Side) -> Selection {
        Selection::Block {
            region: Range { start: Anchor::new(location, side), end: Anchor::new(location, side) },
        }
    }

    pub fn semantic(point: Point<usize>) -> Selection {
        Selection::Semantic { region: Range { start: point, end: point } }
    }

    pub fn lines(point: Point<usize>) -> Selection {
        Selection::Lines { region: Range { start: point, end: point } }
    }

    pub fn update(&mut self, location: Point<usize>, side: Side) {
        let (_, end) = self.points_mut();
        *end = location;

        if let Some((_, end_side)) = self.sides_mut() {
            *end_side = side;
        }
    }

    pub fn rotate(&mut self, offset: isize) {
        let (start, end) = self.points_mut();
        start.line = usize::try_from(start.line as isize + offset).unwrap_or(0);
        end.line = usize::try_from(end.line as isize + offset).unwrap_or(0);
    }

    pub fn is_empty(&self) -> bool {
        match self {
            Selection::Simple { ref region } => {
                let (start, end) =
                    if Selection::points_need_swap(region.start.point, region.end.point) {
                        (&region.end, &region.start)
                    } else {
                        (&region.start, &region.end)
                    };

                // Simple selection is empty when the points are identical
                // or two adjacent cells have the sides right -> left
                start == end
                    || (start.side == Side::Right
                        && end.side == Side::Left
                        && (start.point.line == end.point.line)
                        && start.point.col + 1 == end.point.col)
            },
            Selection::Block { region: Range { ref start, ref end } } => {
                // Block selection is empty when the points' columns and sides are identical
                // or two cells with adjacent columns have the sides right -> left,
                // regardless of their lines
                (start.point.col == end.point.col && start.side == end.side)
                    || (start.point.col + 1 == end.point.col
                        && start.side == Side::Right
                        && end.side == Side::Left)
                    || (end.point.col + 1 == start.point.col
                        && start.side == Side::Left
                        && end.side == Side::Right)
            },
            Selection::Semantic { .. } | Selection::Lines { .. } => false,
        }
    }

    /// Convert selection to grid coordinates.
    pub fn to_range<T>(&self, term: &Term<T>) -> Option<SelectionRange> {
        let grid = term.grid();
        let num_cols = grid.num_cols();

        // Get selection boundaries
        let points = self.points();
        let (start, end) = (*points.0, *points.1);

        // Get selection sides, falling back to `Side::Left` if it will not be used
        let sides = self.sides().unwrap_or((&Side::Left, &Side::Left));
        let (start_side, end_side) = (*sides.0, *sides.1);

        // Order start above the end
        let (start, end) = if Self::points_need_swap(start, end) {
            (Anchor { point: end, side: end_side }, Anchor { point: start, side: start_side })
        } else {
            (Anchor { point: start, side: start_side }, Anchor { point: end, side: end_side })
        };

        // Clamp to inside the grid buffer
        let (start, end) = Self::grid_clamp(start, end, self.is_block(), grid.len()).ok()?;

        let range = match self {
            Self::Simple { .. } => self.range_simple(start, end, num_cols),
            Self::Block { .. } => self.range_block(start, end),
            Self::Semantic { .. } => Self::range_semantic(term, start.point, end.point),
            Self::Lines { .. } => Self::range_lines(term, start.point, end.point),
        };

        // Expand selection across fullwidth cells
        range.map(|range| Self::range_expand_fullwidth(term, range))
    }

    /// Expand the start/end of the selection range to account for fullwidth glyphs.
    fn range_expand_fullwidth<T>(term: &Term<T>, mut range: SelectionRange) -> SelectionRange {
        let grid = term.grid();
        let num_cols = grid.num_cols();

        // Helper for checking if cell at `point` contains `flag`
        let flag_at = |point: Point<usize>, flag: Flags| -> bool {
            grid[point.line][point.col].flags.contains(flag)
        };

        // Include all double-width cells and placeholders at top left of selection
        if range.start.col < num_cols {
            // Expand from wide char spacer to wide char
            if range.start.line + 1 != grid.len() || range.start.col.0 != 0 {
                let prev = range.start.sub(num_cols.0, 1, true);
                if flag_at(range.start, Flags::WIDE_CHAR_SPACER) && flag_at(prev, Flags::WIDE_CHAR)
                {
                    range.start = prev;
                }
            }

            // Expand from wide char to wide char spacer for linewrapping
            if range.start.line + 1 != grid.len() || range.start.col.0 != 0 {
                let prev = range.start.sub(num_cols.0, 1, true);
                if (prev.line + 1 != grid.len() || prev.col.0 != 0)
                    && flag_at(prev, Flags::WIDE_CHAR_SPACER)
                    && !flag_at(prev.sub(num_cols.0, 1, true), Flags::WIDE_CHAR)
                {
                    range.start = prev;
                }
            }
        }

        // Include all double-width cells and placeholders at bottom right of selection
        if range.end.line != 0 || range.end.col < num_cols {
            // Expand from wide char spacer for linewrapping to wide char
            if (range.end.line + 1 != grid.len() || range.end.col.0 != 0)
                && flag_at(range.end, Flags::WIDE_CHAR_SPACER)
                && !flag_at(range.end.sub(num_cols.0, 1, true), Flags::WIDE_CHAR)
            {
                range.end = range.end.add(num_cols.0, 1, true);
            }

            // Expand from wide char to wide char spacer
            if flag_at(range.end, Flags::WIDE_CHAR) {
                range.end = range.end.add(num_cols.0, 1, true);
            }
        }

        range
    }

    // Bring start and end points in the correct order
    fn points_need_swap(start: Point<usize>, end: Point<usize>) -> bool {
        start.line < end.line || start.line == end.line && start.col > end.col
    }

    /// Clamp selection inside grid to prevent OOB.
    fn grid_clamp(
        mut start: Anchor,
        end: Anchor,
        is_block: bool,
        lines: usize,
    ) -> Result<(Anchor, Anchor), ()> {
        // Clamp selection inside of grid to prevent OOB
        if start.point.line >= lines {
            // Remove selection if it is fully out of the grid
            if end.point.line >= lines {
                return Err(());
            }

            // Clamp to grid if it is still partially visible
            if !is_block {
                start.side = Side::Left;
                start.point.col = Column(0);
            }
            start.point.line = lines - 1;
        }

        Ok((start, end))
    }

    fn range_semantic<T>(
        term: &Term<T>,
        mut start: Point<usize>,
        mut end: Point<usize>,
    ) -> Option<SelectionRange> {
        if start == end {
            if let Some(matching) = term.bracket_search(start) {
                if (matching.line == start.line && matching.col < start.col)
                    || (matching.line > start.line)
                {
                    start = matching;
                } else {
                    end = matching;
                }

                return Some(SelectionRange { start, end, is_block: false });
            }
        }

        start = term.semantic_search_left(start);
        end = term.semantic_search_right(end);

        Some(SelectionRange { start, end, is_block: false })
    }

    fn range_lines<T>(
        term: &Term<T>,
        mut start: Point<usize>,
        mut end: Point<usize>,
    ) -> Option<SelectionRange> {
        start = term.line_search_left(start);
        end = term.line_search_right(end);

        Some(SelectionRange { start, end, is_block: false })
    }

    fn range_simple(
        &self,
        mut start: Anchor,
        mut end: Anchor,
        num_cols: Column,
    ) -> Option<SelectionRange> {
        if self.is_empty() {
            return None;
        }

        // Remove last cell if selection ends to the left of a cell
        if end.side == Side::Left && start.point != end.point {
            // Special case when selection ends to left of first cell
            if end.point.col == Column(0) {
                end.point.col = num_cols - 1;
                end.point.line += 1;
            } else {
                end.point.col -= 1;
            }
        }

        // Remove first cell if selection starts at the right of a cell
        if start.side == Side::Right && start.point != end.point {
            start.point.col += 1;
        }

        Some(SelectionRange { start: start.point, end: end.point, is_block: false })
    }

    fn range_block(&self, mut start: Anchor, mut end: Anchor) -> Option<SelectionRange> {
        if self.is_empty() {
            return None;
        }

        // Always go top-left -> bottom-right
        if start.point.col > end.point.col {
            mem::swap(&mut start.side, &mut end.side);
            mem::swap(&mut start.point.col, &mut end.point.col);
        }

        // Remove last cell if selection ends to the left of a cell
        if end.side == Side::Left && start.point != end.point && end.point.col.0 > 0 {
            end.point.col -= 1;
        }

        // Remove first cell if selection starts at the right of a cell
        if start.side == Side::Right && start.point != end.point {
            start.point.col += 1;
        }

        Some(SelectionRange { start: start.point, end: end.point, is_block: true })
    }

    fn points(&self) -> (&Point<usize>, &Point<usize>) {
        match self {
            Self::Simple { ref region } | Self::Block { ref region } => {
                (&region.start.point, &region.end.point)
            },
            Self::Semantic { ref region } | Self::Lines { ref region } => {
                (&region.start, &region.end)
            },
        }
    }

    fn points_mut(&mut self) -> (&mut Point<usize>, &mut Point<usize>) {
        match self {
            Self::Simple { ref mut region } | Self::Block { ref mut region } => {
                (&mut region.start.point, &mut region.end.point)
            },
            Self::Semantic { ref mut region } | Self::Lines { ref mut region } => {
                (&mut region.start, &mut region.end)
            },
        }
    }

    fn sides(&self) -> Option<(&Side, &Side)> {
        match self {
            Self::Simple { ref region } | Self::Block { ref region } => {
                Some((&region.start.side, &region.end.side))
            },
            Self::Semantic { .. } | Self::Lines { .. } => None,
        }
    }

    fn sides_mut(&mut self) -> Option<(&mut Side, &mut Side)> {
        match self {
            Self::Simple { ref mut region } | Self::Block { ref mut region } => {
                Some((&mut region.start.side, &mut region.end.side))
            },
            Self::Semantic { .. } | Self::Lines { .. } => None,
        }
    }

    fn is_block(&self) -> bool {
        match self {
            Self::Block { .. } => true,
            _ => false,
        }
    }
}

/// Tests for selection.
///
/// There are comments on all of the tests describing the selection. Pictograms
/// are used to avoid ambiguity. Grid cells are represented by a [  ]. Only
/// cells that are completely covered are counted in a selection. Ends are
/// represented by `B` and `E` for begin and end, respectively.  A selected cell
/// looks like [XX], [BX] (at the start), [XB] (at the end), [XE] (at the end),
/// and [EX] (at the start), or [BE] for a single cell. Partially selected cells
/// look like [ B] and [E ].
#[cfg(test)]
mod test {
    use std::mem;

    use super::{Selection, SelectionRange};
    use crate::clipboard::Clipboard;
    use crate::config::MockConfig;
    use crate::event::{Event, EventListener};
    use crate::grid::Grid;
    use crate::index::{Column, Line, Point, Side};
    use crate::term::cell::{Cell, Flags};
    use crate::term::{SizeInfo, Term};

    struct Mock;
    impl EventListener for Mock {
        fn send_event(&self, _event: Event) {}
    }

    fn term(width: usize, height: usize) -> Term<Mock> {
        let size = SizeInfo {
            width: width as f32,
            height: height as f32,
            cell_width: 1.0,
            cell_height: 1.0,
            padding_x: 0.0,
            padding_y: 0.0,
            dpr: 1.0,
        };
        Term::new(&MockConfig::default(), &size, Clipboard::new_nop(), Mock)
    }

    /// Test case of single cell selection.
    ///
    /// 1. [  ]
    /// 2. [B ]
    /// 3. [BE]
    #[test]
    fn single_cell_left_to_right() {
        let location = Point { line: 0, col: Column(0) };
        let mut selection = Selection::simple(location, Side::Left);
        selection.update(location, Side::Right);

        assert_eq!(selection.to_range(&term(1, 1)).unwrap(), SelectionRange {
            start: location,
            end: location,
            is_block: false
        });
    }

    /// Test case of single cell selection.
    ///
    /// 1. [  ]
    /// 2. [ B]
    /// 3. [EB]
    #[test]
    fn single_cell_right_to_left() {
        let location = Point { line: 0, col: Column(0) };
        let mut selection = Selection::simple(location, Side::Right);
        selection.update(location, Side::Left);

        assert_eq!(selection.to_range(&term(1, 1)).unwrap(), SelectionRange {
            start: location,
            end: location,
            is_block: false
        });
    }

    /// Test adjacent cell selection from left to right.
    ///
    /// 1. [  ][  ]
    /// 2. [ B][  ]
    /// 3. [ B][E ]
    #[test]
    fn between_adjacent_cells_left_to_right() {
        let mut selection = Selection::simple(Point::new(0, Column(0)), Side::Right);
        selection.update(Point::new(0, Column(1)), Side::Left);

        assert_eq!(selection.to_range(&term(2, 1)), None);
    }

    /// Test adjacent cell selection from right to left.
    ///
    /// 1. [  ][  ]
    /// 2. [  ][B ]
    /// 3. [ E][B ]
    #[test]
    fn between_adjacent_cells_right_to_left() {
        let mut selection = Selection::simple(Point::new(0, Column(1)), Side::Left);
        selection.update(Point::new(0, Column(0)), Side::Right);

        assert_eq!(selection.to_range(&term(2, 1)), None);
    }

    /// Test selection across adjacent lines.
    ///
    /// 1.  [  ][  ][  ][  ][  ]
    ///     [  ][  ][  ][  ][  ]
    /// 2.  [  ][ B][  ][  ][  ]
    ///     [  ][  ][  ][  ][  ]
    /// 3.  [  ][ B][XX][XX][XX]
    ///     [XX][XE][  ][  ][  ]
    #[test]
    fn across_adjacent_lines_upward_final_cell_exclusive() {
        let mut selection = Selection::simple(Point::new(1, Column(1)), Side::Right);
        selection.update(Point::new(0, Column(1)), Side::Right);

        assert_eq!(selection.to_range(&term(5, 2)).unwrap(), SelectionRange {
            start: Point::new(1, Column(2)),
            end: Point::new(0, Column(1)),
            is_block: false,
        });
    }

    /// Test selection across adjacent lines.
    ///
    /// 1.  [  ][  ][  ][  ][  ]
    ///     [  ][  ][  ][  ][  ]
    /// 2.  [  ][  ][  ][  ][  ]
    ///     [  ][ B][  ][  ][  ]
    /// 3.  [  ][ E][XX][XX][XX]
    ///     [XX][XB][  ][  ][  ]
    /// 4.  [ E][XX][XX][XX][XX]
    ///     [XX][XB][  ][  ][  ]
    #[test]
    fn selection_bigger_then_smaller() {
        let mut selection = Selection::simple(Point::new(0, Column(1)), Side::Right);
        selection.update(Point::new(1, Column(1)), Side::Right);
        selection.update(Point::new(1, Column(0)), Side::Right);

        assert_eq!(selection.to_range(&term(5, 2)).unwrap(), SelectionRange {
            start: Point::new(1, Column(1)),
            end: Point::new(0, Column(1)),
            is_block: false,
        });
    }

    #[test]
    fn line_selection() {
        let mut selection = Selection::lines(Point::new(0, Column(1)));
        selection.update(Point::new(5, Column(1)), Side::Right);
        selection.rotate(7);

        assert_eq!(selection.to_range(&term(5, 10)).unwrap(), SelectionRange {
            start: Point::new(9, Column(0)),
            end: Point::new(7, Column(4)),
            is_block: false,
        });
    }

    #[test]
    fn semantic_selection() {
        let mut selection = Selection::semantic(Point::new(0, Column(3)));
        selection.update(Point::new(5, Column(1)), Side::Right);
        selection.rotate(7);

        assert_eq!(selection.to_range(&term(5, 10)).unwrap(), SelectionRange {
            start: Point::new(9, Column(0)),
            end: Point::new(7, Column(3)),
            is_block: false,
        });
    }

    #[test]
    fn simple_selection() {
        let mut selection = Selection::simple(Point::new(0, Column(3)), Side::Right);
        selection.update(Point::new(5, Column(1)), Side::Right);
        selection.rotate(7);

        assert_eq!(selection.to_range(&term(5, 10)).unwrap(), SelectionRange {
            start: Point::new(9, Column(0)),
            end: Point::new(7, Column(3)),
            is_block: false,
        });
    }

    #[test]
    fn block_selection() {
        let mut selection = Selection::block(Point::new(0, Column(3)), Side::Right);
        selection.update(Point::new(5, Column(1)), Side::Right);
        selection.rotate(7);

        assert_eq!(selection.to_range(&term(5, 10)).unwrap(), SelectionRange {
            start: Point::new(9, Column(2)),
            end: Point::new(7, Column(3)),
            is_block: true
        });
    }

    #[test]
    fn double_width_expansion() {
        let mut term = term(10, 1);
        let mut grid = Grid::new(Line(1), Column(10), 0, Cell::default());
        grid[Line(0)][Column(0)].flags.insert(Flags::WIDE_CHAR);
        grid[Line(0)][Column(1)].flags.insert(Flags::WIDE_CHAR_SPACER);
        grid[Line(0)][Column(8)].flags.insert(Flags::WIDE_CHAR);
        grid[Line(0)][Column(9)].flags.insert(Flags::WIDE_CHAR_SPACER);
        mem::swap(term.grid_mut(), &mut grid);

        let mut selection = Selection::simple(Point::new(0, Column(1)), Side::Left);
        selection.update(Point::new(0, Column(8)), Side::Right);

        assert_eq!(selection.to_range(&term).unwrap(), SelectionRange {
            start: Point::new(0, Column(0)),
            end: Point::new(0, Column(9)),
            is_block: false,
        });
    }

    #[test]
    fn simple_is_empty() {
        let mut selection = Selection::simple(Point::new(0, Column(0)), Side::Right);
        assert!(selection.is_empty());
        selection.update(Point::new(0, Column(1)), Side::Left);
        assert!(selection.is_empty());
        selection.update(Point::new(1, Column(0)), Side::Right);
        assert!(!selection.is_empty());
    }

    #[test]
    fn block_is_empty() {
        let mut selection = Selection::block(Point::new(0, Column(0)), Side::Right);
        assert!(selection.is_empty());
        selection.update(Point::new(0, Column(1)), Side::Left);
        assert!(selection.is_empty());
        selection.update(Point::new(0, Column(1)), Side::Right);
        assert!(!selection.is_empty());
        selection.update(Point::new(1, Column(0)), Side::Right);
        assert!(selection.is_empty());
        selection.update(Point::new(1, Column(1)), Side::Left);
        assert!(selection.is_empty());
        selection.update(Point::new(1, Column(1)), Side::Right);
        assert!(!selection.is_empty());
    }
}