gitech

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// Copyright 2021 The Gitea Authors. All rights reserved.
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// SPDX-License-Identifier: MIT
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// Copied and modified from https://github.com/issue9/identicon/ (MIT License)
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// Generate pseudo-random avatars by IP, E-mail, etc.
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package identicon
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import (
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	"crypto/sha256"
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	"fmt"
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	"image"
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	"image/color"
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)
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const minImageSize = 16
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// Identicon is used to generate pseudo-random avatars
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type Identicon struct {
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	foreColors []color.Color
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	backColor  color.Color
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	size       int
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	rect       image.Rectangle
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}
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// New returns an Identicon struct with the correct settings
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// size image size
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// back background color
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// fore all possible foreground colors. only one foreground color will be picked randomly for one image
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func New(size int, back color.Color, fore ...color.Color) (*Identicon, error) {
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	if len(fore) == 0 {
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		return nil, fmt.Errorf("foreground is not set")
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	}
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	if size < minImageSize {
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		return nil, fmt.Errorf("size %d is smaller than min size %d", size, minImageSize)
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	}
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	return &Identicon{
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		foreColors: fore,
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		backColor:  back,
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		size:       size,
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		rect:       image.Rect(0, 0, size, size),
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	}, nil
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}
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// Make generates an avatar by data
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func (i *Identicon) Make(data []byte) image.Image {
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	h := sha256.New()
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	h.Write(data)
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	sum := h.Sum(nil)
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	b1 := int(sum[0]+sum[1]+sum[2]) % len(blocks)
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	b2 := int(sum[3]+sum[4]+sum[5]) % len(blocks)
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	c := int(sum[6]+sum[7]+sum[8]) % len(centerBlocks)
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	b1Angle := int(sum[9]+sum[10]) % 4
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	b2Angle := int(sum[11]+sum[12]) % 4
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	foreColor := int(sum[11]+sum[12]+sum[15]) % len(i.foreColors)
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	return i.render(c, b1, b2, b1Angle, b2Angle, foreColor)
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}
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func (i *Identicon) render(c, b1, b2, b1Angle, b2Angle, foreColor int) image.Image {
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	p := image.NewPaletted(i.rect, []color.Color{i.backColor, i.foreColors[foreColor]})
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	drawBlocks(p, i.size, centerBlocks[c], blocks[b1], blocks[b2], b1Angle, b2Angle)
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	return p
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}
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/*
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# Algorithm
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Origin: An image is splitted into 9 areas
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```
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  -------------
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  | 1 | 2 | 3 |
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  -------------
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  | 4 | 5 | 6 |
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  -------------
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  | 7 | 8 | 9 |
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  -------------
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```
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Area 1/3/9/7 use a 90-degree rotating pattern.
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Area 1/3/9/7 use another 90-degree rotating pattern.
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Area 5 uses a random pattern.
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The Patched Fix: make the image left-right mirrored to get rid of something like "swastika"
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*/
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// draw blocks to the paletted
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// c: the block drawer for the center block
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// b1,b2: the block drawers for other blocks (around the center block)
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// b1Angle,b2Angle: the angle for the rotation of b1/b2
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func drawBlocks(p *image.Paletted, size int, c, b1, b2 blockFunc, b1Angle, b2Angle int) {
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	nextAngle := func(a int) int {
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		return (a + 1) % 4
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	}
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	padding := (size % 3) / 2 // in cased the size can not be aligned by 3 blocks.
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	blockSize := size / 3
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	twoBlockSize := 2 * blockSize
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	// center
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	c(p, blockSize+padding, blockSize+padding, blockSize, 0)
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	// left top (1)
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	b1(p, 0+padding, 0+padding, blockSize, b1Angle)
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	// center top (2)
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	b2(p, blockSize+padding, 0+padding, blockSize, b2Angle)
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	b1Angle = nextAngle(b1Angle)
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	b2Angle = nextAngle(b2Angle)
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	// right top (3)
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	// b1(p, twoBlockSize+padding, 0+padding, blockSize, b1Angle)
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	// right middle (6)
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	// b2(p, twoBlockSize+padding, blockSize+padding, blockSize, b2Angle)
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	b1Angle = nextAngle(b1Angle)
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	b2Angle = nextAngle(b2Angle)
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	// right bottom (9)
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	// b1(p, twoBlockSize+padding, twoBlockSize+padding, blockSize, b1Angle)
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	// center bottom (8)
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	b2(p, blockSize+padding, twoBlockSize+padding, blockSize, b2Angle)
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	b1Angle = nextAngle(b1Angle)
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	b2Angle = nextAngle(b2Angle)
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	// lef bottom (7)
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	b1(p, 0+padding, twoBlockSize+padding, blockSize, b1Angle)
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	// left middle (4)
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	b2(p, 0+padding, blockSize+padding, blockSize, b2Angle)
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	// then we make it left-right mirror, so we didn't draw 3/6/9 before
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	for x := 0; x < size/2; x++ {
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		for y := 0; y < size; y++ {
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			p.SetColorIndex(size-x, y, p.ColorIndexAt(x, y))
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		}
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	}
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}
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