// Copyright 2020 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 axes

// label.go contains code that calculates the positions of labels on the axes.

import (
	"fmt"
	"image"

	"github.com/mum4k/termdash/align"
	"github.com/mum4k/termdash/private/alignfor"
)

// Label is one text label on an axis.
type Label struct {
	// Label content.
	Text string

	// Position of the label within the canvas.
	Pos image.Point
}

// yLabels returns labels that should be placed next to the Y axis.
// The labelWidth is the width of the area from the left-most side of the
// canvas until the Y axis (not including the Y axis). This is the area where
// the labels will be placed and aligned.
// Labels are returned with Y coordinates in ascending order.
// Y coordinates grow down.
func yLabels(graphHeight, labelWidth int, stringLabels []string) ([]*Label, error) {
	if min := 2; graphHeight < min {
		return nil, fmt.Errorf("cannot place labels on a canvas with height %d, minimum is %d", graphHeight, min)
	}
	if min := 0; labelWidth < min {
		return nil, fmt.Errorf("cannot place labels in label area width %d, minimum is %d", labelWidth, min)
	}

	var labels []*Label
	for row, l := range stringLabels {
		label, err := rowLabel(row, l, labelWidth)
		if err != nil {
			return nil, err
		}

		labels = append(labels, label)
	}

	return labels, nil
}

// rowLabel returns one label for the specified row.
// The row is the Y coordinate of the row, Y coordinates grow down.
func rowLabel(row int, label string, labelWidth int) (*Label, error) {
	// The area available for the label
	ar := image.Rect(0, row, labelWidth, row+1)

	pos, err := alignfor.Text(ar, label, align.HorizontalRight, align.VerticalMiddle)
	if err != nil {
		return nil, fmt.Errorf("unable to align the label value: %v", err)
	}

	return &Label{
		Text: label,
		Pos:  pos,
	}, nil
}

// xLabels returns labels that should be placed under the X axis.
// Labels are returned with X coordinates in ascending order.
// X coordinates grow right.
func xLabels(yEnd image.Point, graphWidth int, stringLabels []string, cellWidth int) ([]*Label, error) {
	var ret []*Label

	length, index := paddedLabelLength(graphWidth, LongestString(stringLabels), cellWidth)

	for x := yEnd.X + 1; x <= graphWidth && index < len(stringLabels); x += length {
		ar := image.Rect(x, yEnd.Y, x+length, yEnd.Y+1)
		pos, err := alignfor.Text(ar, stringLabels[index], align.HorizontalCenter, align.VerticalMiddle)
		if err != nil {
			return nil, fmt.Errorf("unable to align the label value: %v", err)
		}

		l := &Label{
			Text: stringLabels[index],
			Pos:  pos,
		}
		index += length / cellWidth
		ret = append(ret, l)
	}

	return ret, nil
}

// paddedLabelLength calculates the length of the padded label and
// the column index corresponding to the label.
// For example, the longest label's length is 5, like '12:34', and the cell's width is 3.
// So in order to better display, every three cells will display a label,
// the label belongs to the middle column of the three columns,
// and the padded length is 3*3, which is 9.
func paddedLabelLength(graphWidth, longest, cellWidth int) (l, index int) {
	l, index = 0, 0
	for i := longest/cellWidth + 1; i < graphWidth/cellWidth; i++ {
		if (i*cellWidth-longest)%2 == 0 {
			l = i * cellWidth
			index = i / 2
			break
		}
	}
	return
}