// Copyright ©2021 The Gonum Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

package text

import (
	"image/color"
	"math"

	"gonum.org/v1/plot/font"
	"gonum.org/v1/plot/vg"
)

// Handler parses, formats and renders text.
type Handler interface {
	// Cache returns the cache of fonts used by the text handler.
	Cache() *font.Cache

	// Extents returns the Extents of a font.
	Extents(fnt font.Font) font.Extents

	// Lines splits a given block of text into separate lines.
	Lines(txt string) []string

	// Box returns the bounding box of the given non-multiline text where:
	//  - width is the horizontal space from the origin.
	//  - height is the vertical space above the baseline.
	//  - depth is the vertical space below the baseline, a positive number.
	Box(txt string, fnt font.Font) (width, height, depth vg.Length)

	// Draw renders the given text with the provided style and position
	// on the canvas.
	Draw(c vg.Canvas, txt string, sty Style, pt vg.Point)
}

// XAlignment specifies text alignment in the X direction. Three preset
// options are available, but an arbitrary alignment
// can also be specified using XAlignment(desired number).
type XAlignment float64

const (
	// XLeft aligns the left edge of the text with the specified location.
	XLeft XAlignment = 0
	// XCenter aligns the horizontal center of the text with the specified location.
	XCenter XAlignment = -0.5
	// XRight aligns the right edge of the text with the specified location.
	XRight XAlignment = -1
)

// YAlignment specifies text alignment in the Y direction. Three preset
// options are available, but an arbitrary alignment
// can also be specified using YAlignment(desired number).
type YAlignment float64

const (
	// YTop aligns the top of of the text with the specified location.
	YTop YAlignment = -1
	// YCenter aligns the vertical center of the text with the specified location.
	YCenter YAlignment = -0.5
	// YBottom aligns the bottom of the text with the specified location.
	YBottom YAlignment = 0
)

// Position specifies the text position.
const (
	PosLeft   = -1
	PosBottom = -1
	PosCenter = 0
	PosTop    = +1
	PosRight  = +1
)

// Style describes what text will look like.
type Style struct {
	// Color is the text color.
	Color color.Color

	// Font is the font description.
	Font font.Font

	// Rotation is the text rotation in radians, performed around the axis
	// defined by XAlign and YAlign.
	Rotation float64

	// XAlign and YAlign specify the alignment of the text.
	XAlign XAlignment
	YAlign YAlignment

	// Handler parses and formats text according to a given
	// dialect (Markdown, LaTeX, plain, ...)
	// The default is a plain text handler.
	Handler Handler
}

// FontExtents returns the extents of this Style's font.
func (s Style) FontExtents() font.Extents {
	return s.Handler.Extents(s.Font)
}

// Width returns the width of lines of text
// when using the given font before any text rotation is applied.
func (s Style) Width(txt string) (max vg.Length) {
	w, _ := s.box(txt)
	return w
}

// Height returns the height of the text when using
// the given font before any text rotation is applied.
func (s Style) Height(txt string) vg.Length {
	_, h := s.box(txt)
	return h
}

// box returns the bounding box of a possibly multi-line text.
func (s Style) box(txt string) (w, h vg.Length) {
	var (
		lines   = s.Handler.Lines(txt)
		e       = s.FontExtents()
		linegap = (e.Height - e.Ascent - e.Descent)
	)
	for i, line := range lines {
		ww, hh, dd := s.Handler.Box(line, s.Font)
		if ww > w {
			w = ww
		}
		h += hh + dd
		if i > 0 {
			h += linegap
		}
	}

	return w, h
}

// Rectangle returns a rectangle giving the bounds of
// this text assuming that it is drawn at (0, 0).
func (s Style) Rectangle(txt string) vg.Rectangle {
	e := s.Handler.Extents(s.Font)
	w, h := s.box(txt)
	desc := vg.Length(e.Height - e.Ascent) // descent + linegap
	xoff := vg.Length(s.XAlign) * w
	yoff := vg.Length(s.YAlign)*h - desc

	// lower left corner
	p1 := rotatePoint(s.Rotation, vg.Point{X: xoff, Y: yoff})
	// upper left corner
	p2 := rotatePoint(s.Rotation, vg.Point{X: xoff, Y: h + yoff})
	// lower right corner
	p3 := rotatePoint(s.Rotation, vg.Point{X: w + xoff, Y: yoff})
	// upper right corner
	p4 := rotatePoint(s.Rotation, vg.Point{X: w + xoff, Y: h + yoff})

	return vg.Rectangle{
		Max: vg.Point{
			X: max(p1.X, p2.X, p3.X, p4.X),
			Y: max(p1.Y, p2.Y, p3.Y, p4.Y),
		},
		Min: vg.Point{
			X: min(p1.X, p2.X, p3.X, p4.X),
			Y: min(p1.Y, p2.Y, p3.Y, p4.Y),
		},
	}
}

// rotatePoint applies rotation theta (in radians) about the origin to point p.
func rotatePoint(theta float64, p vg.Point) vg.Point {
	if theta == 0 {
		return p
	}
	x := float64(p.X)
	y := float64(p.Y)

	sin, cos := math.Sincos(theta)

	return vg.Point{
		X: vg.Length(x*cos - y*sin),
		Y: vg.Length(y*cos + x*sin),
	}
}

func max(d ...vg.Length) vg.Length {
	o := vg.Length(math.Inf(-1))
	for _, dd := range d {
		if dd > o {
			o = dd
		}
	}
	return o
}

func min(d ...vg.Length) vg.Length {
	o := vg.Length(math.Inf(1))
	for _, dd := range d {
		if dd < o {
			o = dd
		}
	}
	return o
}