// 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::cmp::{min, max};
use std::ops::Range;

use index::{Point, Column, RangeInclusive, Side, Linear, Line};
use grid::ToRange;

/// 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
#[derive(Debug, Clone)]
pub enum Selection {
    Simple {
        /// 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>,

        /// When beginning a semantic selection, the grid is searched around the
        /// initial point to find semantic escapes, and this initial expansion
        /// marks those points.
        initial_expansion: Range<Point>
    },
    Lines {
        /// The region representing start and end of cursor movement
        region: Range<Point>,

        /// The line under the initial point. This is always selected regardless
        /// of which way the cursor is moved.
        initial_line: Line
    }
}

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

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

/// A type that can expand a given point to a region
///
/// Usually this is implemented for some 2-D array type since
/// points are two dimensional indices.
pub trait SemanticSearch {
    /// Find the nearest semantic boundary _to the left_ of provided point.
    fn semantic_search_left(&self, _: Point) -> Point;
    /// Find the nearest semantic boundary _to the point_ of provided point.
    fn semantic_search_right(&self, _: Point) -> Point;
}

/// A type that has 2-dimensional boundaries
pub trait Dimensions {
    /// Get the size of the area
    fn dimensions(&self) -> Point;
}

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

    pub fn semantic<G: SemanticSearch>(point: Point, grid: &G) -> Selection {
        let (start, end) = (grid.semantic_search_left(point), grid.semantic_search_right(point));
        Selection::Semantic {
            region: Range {
                start: point,
                end: point,
            },
            initial_expansion: Range {
                start: start,
                end: end
            }
        }
    }

    pub fn lines(point: Point) -> Selection {
        Selection::Lines {
            region: Range {
                start: point,
                end: point
            },
            initial_line: point.line
        }
    }

    pub fn update(&mut self, location: Point, side: Side) {
        // Always update the `end`; can normalize later during span generation.
        match *self {
            Selection::Simple { ref mut region } => {
                region.end = Anchor::new(location, side);
            },
            Selection::Semantic { ref mut region, .. } |
                Selection::Lines { ref mut region, .. } =>
            {
                region.end = location;
            },
        }
    }

    pub fn to_span<G: SemanticSearch + Dimensions>(&self, grid: &G) -> Option<Span> {
        match *self {
            Selection::Simple { ref region } => {
                Selection::span_simple(grid, region)
            },
            Selection::Semantic { ref region, ref initial_expansion } => {
                Selection::span_semantic(grid, region, initial_expansion)
            },
            Selection::Lines { ref region, ref initial_line } => {
                Selection::span_lines(grid, region, initial_line)
            }
        }
    }
    fn span_semantic<G>(
        grid: &G,
        region: &Range<Point>,
        initial_expansion: &Range<Point>
    ) -> Option<Span>
        where G: SemanticSearch + Dimensions
    {
        let mut start = initial_expansion.start;
        let mut end = initial_expansion.end;

        // Normalize ordering of selected cells
        let (front, tail) = if region.start < region.end {
            (region.start, region.end)
        } else {
            (region.end, region.start)
        };

        // Update start of selection *if* front has moved beyond initial start
        if front < start {
            start = grid.semantic_search_left(front);
        }

        // Update end of selection *if* tail has moved beyond initial end.
        if tail > end {
            end = grid.semantic_search_right(tail);
        }

        Some(Span {
            cols: grid.dimensions().col,
            front: start,
            tail: end,
            ty: SpanType::Inclusive,
        })
    }

    fn span_lines<G>(grid: &G, region: &Range<Point>, initial_line: &Line) -> Option<Span>
        where G: Dimensions
    {
        // First, create start and end points based on initial line and the grid
        // dimensions.
        let mut start = Point {
            col: Column(0),
            line: *initial_line
        };
        let mut end = Point {
            col: grid.dimensions().col - 1,
            line: *initial_line
        };

        // Now, expand lines based on where cursor started and ended.
        if region.start.line < region.end.line {
            // Start is above end
            start.line = min(start.line, region.start.line);
            end.line = max(end.line, region.end.line);
        } else {
            // Start is below end
            start.line = min(start.line, region.end.line);
            end.line = max(end.line, region.start.line);
        }

        Some(Span {
            cols: grid.dimensions().col,
            front: start,
            tail: end,
            ty: SpanType::Inclusive
        })
    }

    fn span_simple<G: Dimensions>(grid: &G, region: &Range<Anchor>) -> Option<Span> {
        let start = region.start.point;
        let start_side = region.start.side;
        let end = region.end.point;
        let end_side = region.end.side;
        let cols = grid.dimensions().col;

        let (front, tail, front_side, tail_side) = if start > end {
            // Selected upward; start/end are swapped
            (end, start, end_side, start_side)
        } else {
            // Selected downward; no swapping
            (start, end, start_side, end_side)
        };

        debug_assert!(!(tail < front));

        // Single-cell selections are a special case
        if start == end {
            if start_side == end_side {
                return None;
            } else {
                return Some(Span {
                    cols,
                    ty: SpanType::Inclusive,
                    front,
                    tail,
                });
            }
        }

        // The other special case is two adjacent cells with no
        // selection: [ B][E ] or [ E][B ]
        let adjacent = tail.line == front.line && tail.col - front.col == Column(1);
        if adjacent && front_side == Side::Right && tail_side == Side::Left {
            return None;
        }

        Some(match (front_side, tail_side) {
            // [FX][XX][XT]
            (Side::Left, Side::Right) => Span {
                cols,
                front,
                tail,
                ty: SpanType::Inclusive
            },
            // [ F][XX][T ]
            (Side::Right, Side::Left) => Span {
                cols,
                front,
                tail,
                ty: SpanType::Exclusive
            },
            // [FX][XX][T ]
            (Side::Left, Side::Left) => Span {
                cols,
                front,
                tail,
                ty: SpanType::ExcludeTail
            },
            // [ F][XX][XT]
            (Side::Right, Side::Right) => Span {
                cols,
                front,
                tail,
                ty: SpanType::ExcludeFront
            },
        })
    }
}

/// How to interpret the locations of a Span.
#[derive(Debug, Eq, PartialEq)]
pub enum SpanType {
    /// Includes the beginning and end locations
    Inclusive,

    /// Exclude both beginning and end
    Exclusive,

    /// Excludes last cell of selection
    ExcludeTail,

    /// Excludes first cell of selection
    ExcludeFront,
}

/// Represents a span of selected cells
#[derive(Debug, Eq, PartialEq)]
pub struct Span {
    front: Point,
    tail: Point,
    cols: Column,

    /// The type says whether ends are included or not.
    ty: SpanType,
}

impl Span {
    pub fn to_locations(&self) -> (Point, Point) {
        match self.ty {
            SpanType::Inclusive => (self.front, self.tail),
            SpanType::Exclusive => {
                (Span::wrap_start(self.front, self.cols), Span::wrap_end(self.tail, self.cols))
            },
            SpanType::ExcludeFront => (Span::wrap_start(self.front, self.cols), self.tail),
            SpanType::ExcludeTail => (self.front, Span::wrap_end(self.tail, self.cols))
        }
    }

    fn wrap_start(mut start: Point, cols: Column) -> Point {
        if start.col == cols - 1 {
            Point {
                line: start.line + 1,
                col: Column(0),
            }
        } else {
            start.col += 1;
            start
        }
    }

    fn wrap_end(end: Point, cols: Column) -> Point {
        if end.col == Column(0) && end.line != Line(0) {
            Point {
                line: end.line - 1,
                col: cols
            }
        } else {
            Point {
                line: end.line,
                col: end.col - 1
            }
        }
    }

    #[inline]
    fn exclude_start(start: Linear) -> Linear {
        start + 1
    }

    #[inline]
    fn exclude_end(end: Linear) -> Linear {
        if end > Linear(0) {
            end - 1
        } else {
            end
        }
    }
}

impl ToRange for Span {
    fn to_range(&self) -> RangeInclusive<Linear> {
        let cols = self.cols;
        let start = Linear(self.front.line.0 * cols.0 + self.front.col.0);
        let end = Linear(self.tail.line.0 * cols.0 + self.tail.col.0);

        let (start, end) = match self.ty {
            SpanType::Inclusive => (start, end),
            SpanType::Exclusive => (Span::exclude_start(start), Span::exclude_end(end)),
            SpanType::ExcludeFront => (Span::exclude_start(start), end),
            SpanType::ExcludeTail => (start, Span::exclude_end(end))
        };

        RangeInclusive::new(start, end)
    }
}

/// 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 index::{Line, Column, Side, Point};
    use super::{Selection, Span, SpanType};

    struct Dimensions(Point);
    impl super::Dimensions for Dimensions {
        fn dimensions(&self) -> Point {
            self.0
        }
    }

    impl Dimensions {
        pub fn new(line: usize, col: usize) -> Self {
            Dimensions(Point {
                line: Line(line),
                col: Column(col)
            })
        }
    }

    impl super::SemanticSearch for Dimensions {
        fn semantic_search_left(&self, _: Point) -> Point { unimplemented!(); }
        fn semantic_search_right(&self, _: Point) -> Point { unimplemented!(); }
    }

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

        assert_eq!(selection.to_span(&Dimensions::new(1, 1)).unwrap(), Span {
            cols: Column(1),
            ty: SpanType::Inclusive,
            front: location,
            tail: location
        });
    }

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

        assert_eq!(selection.to_span(&Dimensions::new(1, 1)).unwrap(), Span {
            cols: Column(1),
            ty: SpanType::Inclusive,
            front: location,
            tail: location
        });
    }

    /// 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(Line(0), Column(0)), Side::Right);
        selection.update(Point::new(Line(0), Column(1)), Side::Left);

        assert_eq!(selection.to_span(&Dimensions::new(1, 2)), 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(Line(0), Column(1)), Side::Left);
        selection.update(Point::new(Line(0), Column(0)), Side::Right);

        assert_eq!(selection.to_span(&Dimensions::new(1, 2)), None);
    }

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

        assert_eq!(selection.to_span(&Dimensions::new(2, 5)).unwrap(), Span {
            cols: Column(5),
            front: Point::new(Line(0), Column(1)),
            tail: Point::new(Line(1), Column(1)),
            ty: SpanType::ExcludeFront
        });
    }

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

        assert_eq!(selection.to_span(&Dimensions::new(2, 5)).unwrap(), Span {
            cols: Column(5),
            front: Point::new(Line(0), Column(1)),
            tail: Point::new(Line(1), Column(0)),
            ty: SpanType::ExcludeFront
        });
    }
}