package imageprocessor

import (
	"bytes"
	"image"
	"image/color"
	"image/png"
	"testing"
)

// TestImageProcessor_FitCoverServesThinSource verifies that FitCover serves
// a thin source at the requested size. A source of 8192x64 or 8192x1 scaled
// to cover 8192x8192 is 128 or 8192 times as long as the output on its long
// side. The centre of an 8192x1 source with the proportions of 1x8192 is
// 1/8192 of a pixel wide. Each case is also turned on its side.
func TestImageProcessor_FitCoverServesThinSource(t *testing.T) {
	t.Parallel()

	tests := []struct {
		name                    string
		inputWidth, inputHeight int
		size                    Size
	}{
		{"8192x64 at 8192x8192", 8192, 64, Size{Width: 8192, Height: 8192}},
		{"8192x1 at 8192x8192", 8192, 1, Size{Width: 8192, Height: 8192}},
		{"8192x1 at 1x8192", 8192, 1, Size{Width: 1, Height: 8192}},
		{"64x8192 at 8192x8192", 64, 8192, Size{Width: 8192, Height: 8192}},
		{"1x8192 at 8192x8192", 1, 8192, Size{Width: 8192, Height: 8192}},
		{"1x8192 at 8192x1", 1, 8192, Size{Width: 8192, Height: 1}},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			input := createTestJPEG(t, tt.inputWidth, tt.inputHeight)

			result, err := New(Params{}).Process(t.Context(),
				bytes.NewReader(input),
				&Request{Size: tt.size, Format: FormatJPEG, FitMode: FitCover})
			if err != nil {
				t.Fatalf("Process() error = %v", err)
			}

			defer func() { _ = result.Content.Close() }()

			t.Logf("Process() made %dx%d", result.Width, result.Height)

			if result.Width != tt.size.Width || result.Height != tt.size.Height {
				t.Errorf("Process() made %dx%d, want %dx%d",
					result.Width, result.Height, tt.size.Width, tt.size.Height)
			}
		})
	}
}

// createBandsPNG creates a PNG of three equal bands, red, green and blue,
// side by side when it is wider than tall and top to bottom otherwise.
func createBandsPNG(t *testing.T, width, height int) []byte {
	t.Helper()

	bands := []color.RGBA{
		{R: 255, A: 255},
		{G: 255, A: 255},
		{B: 255, A: 255},
	}

	img := image.NewRGBA(image.Rect(0, 0, width, height))
	for y := range height {
		for x := range width {
			band := 3 * y / height
			if width > height {
				band = 3 * x / width
			}

			img.Set(x, y, bands[band])
		}
	}

	return encodePNG(t, img)
}

// TestImageProcessor_FitCoverCropsTheCentre verifies that FitCover keeps the
// centre of the source: a 300x100 source of red, green and blue bands side
// by side, or a 100x300 one with them top to bottom, comes out at 50x50 as
// its green band.
func TestImageProcessor_FitCoverCropsTheCentre(t *testing.T) {
	t.Parallel()

	tests := []struct {
		name                    string
		inputWidth, inputHeight int
	}{
		{"bands side by side", 300, 100},
		{"bands top to bottom", 100, 300},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			t.Parallel()

			input := createBandsPNG(t, tt.inputWidth, tt.inputHeight)

			result, err := New(Params{}).Process(t.Context(),
				bytes.NewReader(input),
				&Request{
					Size:    Size{Width: 50, Height: 50},
					Format:  FormatPNG,
					FitMode: FitCover,
				})
			if err != nil {
				t.Fatalf("Process() error = %v", err)
			}

			defer func() { _ = result.Content.Close() }()

			output, err := png.Decode(result.Content)
			if err != nil {
				t.Fatalf("failed to decode output: %v", err)
			}

			bounds := output.Bounds()
			t.Logf("Process() made %dx%d", bounds.Dx(), bounds.Dy())

			if bounds.Dx() != 50 || bounds.Dy() != 50 {
				t.Fatalf("Process() made %dx%d, want 50x50",
					bounds.Dx(), bounds.Dy())
			}

			// Resampling may blend a little of the bands beside the
			// green one into the output's edges.
			for y := bounds.Min.Y; y < bounds.Max.Y; y++ {
				for x := bounds.Min.X; x < bounds.Max.X; x++ {
					r, g, b, _ := output.At(x, y).RGBA()
					if r>>8 > 64 || g>>8 < 192 || b>>8 > 64 {
						t.Fatalf("output pixel %d,%d is %d,%d,%d, want green",
							x, y, r>>8, g>>8, b>>8)
					}
				}
			}
		})
	}
}