termdash/private/area/area.go

// Copyright 2018 Google Inc.
//
// 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.

// Package area provides functions working with image areas.
package area

import (
	"fmt"
	"image"

	"github.com/mum4k/termdash/private/numbers"
)

// Size returns the size of the provided area.
func Size(area image.Rectangle) image.Point {
	return image.Point{
		area.Dx(),
		area.Dy(),
	}
}

// FromSize returns the corresponding area for the provided size.
func FromSize(size image.Point) (image.Rectangle, error) {
	if size.X < 0 || size.Y < 0 {
		return image.Rectangle{}, fmt.Errorf("cannot convert zero or negative size to an area, got: %+v", size)
	}
	return image.Rect(0, 0, size.X, size.Y), nil
}

// HSplit returns two new areas created by splitting the provided area at the
// specified percentage of its width. The percentage must be in the range
// 0 <= heightPerc <= 100.
// Can return zero size areas.
func HSplit(area image.Rectangle, heightPerc int) (top image.Rectangle, bottom image.Rectangle, err error) {
	if min, max := 0, 100; heightPerc < min || heightPerc > max {
		return image.ZR, image.ZR, fmt.Errorf("invalid heightPerc %d, must be in range %d <= heightPerc <= %d", heightPerc, min, max)
	}
	height := area.Dy() * heightPerc / 100
	top = image.Rect(area.Min.X, area.Min.Y, area.Max.X, area.Min.Y+height)
	if top.Dy() == 0 {
		top = image.ZR
	}
	bottom = image.Rect(area.Min.X, area.Min.Y+height, area.Max.X, area.Max.Y)
	if bottom.Dy() == 0 {
		bottom = image.ZR
	}
	return top, bottom, nil
}

// VSplit returns two new areas created by splitting the provided area at the
// specified percentage of its width. The percentage must be in the range
// 0 <= widthPerc <= 100.
// Can return zero size areas.
func VSplit(area image.Rectangle, widthPerc int) (left image.Rectangle, right image.Rectangle, err error) {
	if min, max := 0, 100; widthPerc < min || widthPerc > max {
		return image.ZR, image.ZR, fmt.Errorf("invalid widthPerc %d, must be in range %d <= widthPerc <= %d", widthPerc, min, max)
	}
	width := area.Dx() * widthPerc / 100
	left = image.Rect(area.Min.X, area.Min.Y, area.Min.X+width, area.Max.Y)
	if left.Dx() == 0 {
		left = image.ZR
	}
	right = image.Rect(area.Min.X+width, area.Min.Y, area.Max.X, area.Max.Y)
	if right.Dx() == 0 {
		right = image.ZR
	}
	return left, right, nil
}

// VSplitCells returns two new areas created by splitting the provided area
// after the specified amount of cells of its width. The number of cells must
// be a zero or a positive integer. Providing a zero returns left=image.ZR,
// right=area. Providing a number equal or larger to area's width returns
// left=area, right=image.ZR.
func VSplitCells(area image.Rectangle, cells int) (left image.Rectangle, right image.Rectangle, err error) {
	if min := 0; cells < min {
		return image.ZR, image.ZR, fmt.Errorf("invalid cells %d, must be a positive integer", cells)
	}
	if cells == 0 {
		return image.ZR, area, nil
	}

	width := area.Dx()
	if cells >= width {
		return area, image.ZR, nil
	}

	left = image.Rect(area.Min.X, area.Min.Y, area.Min.X+cells, area.Max.Y)
	right = image.Rect(area.Min.X+cells, area.Min.Y, area.Max.X, area.Max.Y)
	return left, right, nil
}

// HSplitCells returns two new areas created by splitting the provided area
// after the specified amount of cells of its height. The number of cells must
// be a zero or a positive integer. Providing a zero returns top=image.ZR,
// bottom=area. Providing a number equal or larger to area's height returns
// top=area, bottom=image.ZR.
func HSplitCells(area image.Rectangle, cells int) (top image.Rectangle, bottom image.Rectangle, err error) {
	if min := 0; cells < min {
		return image.ZR, image.ZR, fmt.Errorf("invalid cells %d, must be a positive integer", cells)
	}
	if cells == 0 {
		return image.ZR, area, nil
	}

	height := area.Dy()
	if cells >= height {
		return area, image.ZR, nil
	}

	top = image.Rect(area.Min.X, area.Min.Y, area.Max.X, area.Min.Y+cells)
	bottom = image.Rect(area.Min.X, area.Min.Y+cells, area.Max.X, area.Max.Y)
	return top, bottom, nil
}

// ExcludeBorder returns a new area created by subtracting a border around the
// provided area. Return the zero area if there isn't enough space to exclude
// the border.
func ExcludeBorder(area image.Rectangle) image.Rectangle {
	// If the area dimensions are smaller than this, subtracting a point for the
	// border on each of its sides results in a zero area.
	const minDim = 2
	if area.Dx() < minDim || area.Dy() < minDim {
		return image.ZR
	}
	return image.Rect(
		numbers.Abs(area.Min.X+1),
		numbers.Abs(area.Min.Y+1),
		numbers.Abs(area.Max.X-1),
		numbers.Abs(area.Max.Y-1),
	)
}

// WithRatio returns the largest area that has the requested ratio but is
// either equal or smaller than the provided area. Returns zero area if the
// area or the ratio are zero, or if there is no such area.
func WithRatio(area image.Rectangle, ratio image.Point) image.Rectangle {
	ratio = numbers.SimplifyRatio(ratio)
	if area == image.ZR || ratio == image.ZP {
		return image.ZR
	}

	wFact := area.Dx() / ratio.X
	hFact := area.Dy() / ratio.Y

	var fact int
	if wFact < hFact {
		fact = wFact
	} else {
		fact = hFact
	}
	return image.Rect(
		area.Min.X,
		area.Min.Y,
		ratio.X*fact+area.Min.X,
		ratio.Y*fact+area.Min.Y,
	)
}

// Shrink returns a new area whose size is reduced by the specified amount of
// cells. Can return a zero area if there is no space left in the area.
// The values must be zero or positive integers.
func Shrink(area image.Rectangle, topCells, rightCells, bottomCells, leftCells int) (image.Rectangle, error) {
	for _, v := range []struct {
		name  string
		value int
	}{
		{"topCells", topCells},
		{"rightCells", rightCells},
		{"bottomCells", bottomCells},
		{"leftCells", leftCells},
	} {
		if min := 0; v.value < min {
			return image.ZR, fmt.Errorf("invalid %s(%d), must be in range %d <= value", v.name, v.value, min)
		}
	}

	shrunk := area
	shrunk.Min.X, _ = numbers.MinMaxInts([]int{shrunk.Min.X + leftCells, shrunk.Max.X})
	_, shrunk.Max.X = numbers.MinMaxInts([]int{shrunk.Max.X - rightCells, shrunk.Min.X})
	shrunk.Min.Y, _ = numbers.MinMaxInts([]int{shrunk.Min.Y + topCells, shrunk.Max.Y})
	_, shrunk.Max.Y = numbers.MinMaxInts([]int{shrunk.Max.Y - bottomCells, shrunk.Min.Y})

	if shrunk.Dx() == 0 || shrunk.Dy() == 0 {
		return image.ZR, nil
	}
	return shrunk, nil
}

// ShrinkPercent returns a new area whose size is reduced by percentage of its
// width or height. Can return a zero area if there is no space left in the area.
// The topPerc and bottomPerc indicate the percentage of area's height.
// The rightPerc and leftPerc indicate the percentage of area's width.
// The percentages must be in range 0 <= v <= 100.
func ShrinkPercent(area image.Rectangle, topPerc, rightPerc, bottomPerc, leftPerc int) (image.Rectangle, error) {
	for _, v := range []struct {
		name  string
		value int
	}{
		{"topPerc", topPerc},
		{"rightPerc", rightPerc},
		{"bottomPerc", bottomPerc},
		{"leftPerc", leftPerc},
	} {
		if min, max := 0, 100; v.value < min || v.value > max {
			return image.ZR, fmt.Errorf("invalid %s(%d), must be in range %d <= value <= %d", v.name, v.value, min, max)
		}
	}

	top := area.Dy() * topPerc / 100
	bottom := area.Dy() * bottomPerc / 100
	right := area.Dx() * rightPerc / 100
	left := area.Dx() * leftPerc / 100
	return Shrink(area, top, right, bottom, left)
}

// MoveUp returns a new area that is moved up by the specified amount of cells.
// Returns an error if the move would result in negative Y coordinates.
// The values must be zero or positive integers.
func MoveUp(area image.Rectangle, cells int) (image.Rectangle, error) {
	if min := 0; cells < min {
		return image.ZR, fmt.Errorf("cannot move area %v up by %d cells, must be in range %d <= value", area, cells, min)
	}

	if area.Min.Y < cells {
		return image.ZR, fmt.Errorf("cannot move area %v up by %d cells, would result in negative Y coordinate", area, cells)
	}

	moved := area
	moved.Min.Y -= cells
	moved.Max.Y -= cells
	return moved, nil
}

// MoveDown returns a new area that is moved down by the specified amount of
// cells.
// The values must be zero or positive integers.
func MoveDown(area image.Rectangle, cells int) (image.Rectangle, error) {
	if min := 0; cells < min {
		return image.ZR, fmt.Errorf("cannot move area %v down by %d cells, must be in range %d <= value", area, cells, min)
	}

	moved := area
	moved.Min.Y += cells
	moved.Max.Y += cells
	return moved, nil
}