package camera

import (
	"strings"
	"testing"
)

// TestBuildCaptureArgsForOS 驗證三平台各自用正確的 ffmpeg input device（indev）：
// macOS→avfoundation、Windows→dshow、Linux→v4l2。這是 ADR-020 的核心修復：
// 原本 Linux 會誤落 default 分支用 avfoundation → 必壞。
func TestBuildCaptureArgsForOS(t *testing.T) {
	const (
		width  = 640
		height = 480
		fps    = 30
		index  = 0
	)

	tests := []struct {
		name       string
		goos       string
		cameraName string
		// wantInputFlag 是預期的 "-f <indev>" 值
		wantIndev string
		// wantInputArg 是 "-i" 後面的值
		wantInputArg string
	}{
		{
			name:         "macOS uses avfoundation with index:none",
			goos:         "darwin",
			wantIndev:    "avfoundation",
			wantInputArg: "0:none",
		},
		{
			name:         "Windows uses dshow with video=name",
			goos:         "windows",
			cameraName:   "Integrated Camera",
			wantIndev:    "dshow",
			wantInputArg: "video=Integrated Camera",
		},
		{
			name:         "Linux uses v4l2 with /dev/video path",
			goos:         "linux",
			wantIndev:    "v4l2",
			wantInputArg: "/dev/video0",
		},
	}

	for _, tt := range tests {
		t.Run(tt.name, func(t *testing.T) {
			args := buildCaptureArgsForOS(tt.goos, index, tt.cameraName, width, height, fps)

			gotIndev := valueAfterFlag(args, "-f") // 第一個 -f 是 input format
			if gotIndev != tt.wantIndev {
				t.Errorf("indev = %q, want %q\nargs: %v", gotIndev, tt.wantIndev, args)
			}

			gotInput := valueAfterFlag(args, "-i")
			if gotInput != tt.wantInputArg {
				t.Errorf("input = %q, want %q\nargs: %v", gotInput, tt.wantInputArg, args)
			}

			// 三平台後段皆須為 image2pipe / mjpeg，MJPEG pipe 架構共用。
			if !containsSeq(args, "-f", "image2pipe") {
				t.Errorf("missing image2pipe output, args: %v", args)
			}
			if !containsSeq(args, "-vcodec", "mjpeg") {
				t.Errorf("missing mjpeg vcodec, args: %v", args)
			}
			if args[len(args)-1] != "-" {
				t.Errorf("last arg should be stdout '-', got %q", args[len(args)-1])
			}
		})
	}
}

// TestBuildCaptureArgsForOS_LinuxIndexToDevicePath 驗證 Linux 的 cameraIndex 正確
// 對應到 /dev/video<N> 節點路徑。
func TestBuildCaptureArgsForOS_LinuxIndexToDevicePath(t *testing.T) {
	for _, idx := range []int{0, 1, 2, 10} {
		args := buildCaptureArgsForOS("linux", idx, "", 640, 480, 30)
		want := "/dev/video" + itoa(idx)
		if got := valueAfterFlag(args, "-i"); got != want {
			t.Errorf("index %d → input %q, want %q", idx, got, want)
		}
	}
}

// TestBuildCaptureArgsForOS_LinuxNotAVFoundation 是 ADR-020 的回歸鎖：Linux 絕不能
// 用 avfoundation（macOS 專用）。若未來有人把 Linux case 拿掉、讓它落回 default，
// 這個測試會抓到。
func TestBuildCaptureArgsForOS_LinuxNotAVFoundation(t *testing.T) {
	args := buildCaptureArgsForOS("linux", 0, "", 640, 480, 30)
	joined := strings.Join(args, " ")
	if strings.Contains(joined, "avfoundation") {
		t.Fatalf("Linux must NOT use avfoundation (macOS-only), args: %v", args)
	}
	if !strings.Contains(joined, "v4l2") {
		t.Fatalf("Linux must use v4l2, args: %v", args)
	}
}

// TestParseV4L2Devices 驗證 /dev/video* 路徑清單解析成 CameraInfo，且依 index 數值
// 排序（video10 排在 video2 之後、而非字典序）。
func TestParseV4L2Devices(t *testing.T) {
	paths := []string{
		"/dev/video10",
		"/dev/video2",
		"/dev/video0",
		"/dev/video-not-a-number", // 應被略過
		"/dev/videoX",             // 應被略過
	}

	got := parseV4L2Devices(paths)

	wantIndexes := []int{0, 2, 10}
	if len(got) != len(wantIndexes) {
		t.Fatalf("got %d devices, want %d: %+v", len(got), len(wantIndexes), got)
	}
	for i, want := range wantIndexes {
		if got[i].Index != want {
			t.Errorf("device[%d].Index = %d, want %d", i, got[i].Index, want)
		}
		if got[i].Name != "/dev/video"+itoa(want) {
			t.Errorf("device[%d].Name = %q, want /dev/video%d", i, got[i].Name, want)
		}
	}
}

// TestParseV4L2Devices_Empty 驗證無裝置時回 nil/空。
func TestParseV4L2Devices_Empty(t *testing.T) {
	if got := parseV4L2Devices(nil); len(got) != 0 {
		t.Errorf("expected no devices, got %+v", got)
	}
}

// TestV4L2Index 驗證從路徑取 index。
func TestV4L2Index(t *testing.T) {
	cases := map[string]int{
		"/dev/video0":  0,
		"/dev/video12": 12,
		"/dev/video":   -1,
		"/dev/videoab": -1,
		"videoX":       -1,
	}
	for path, want := range cases {
		if got := v4l2Index(path); got != want {
			t.Errorf("v4l2Index(%q) = %d, want %d", path, got, want)
		}
	}
}

// --- helpers ---

// valueAfterFlag 回傳 args 中第一個等於 flag 的元素的下一個值。
func valueAfterFlag(args []string, flag string) string {
	for i := 0; i < len(args)-1; i++ {
		if args[i] == flag {
			return args[i+1]
		}
	}
	return ""
}

// containsSeq 判斷 args 是否包含連續的 a b 兩個元素。
func containsSeq(args []string, a, b string) bool {
	for i := 0; i < len(args)-1; i++ {
		if args[i] == a && args[i+1] == b {
			return true
		}
	}
	return false
}

func itoa(n int) string {
	if n == 0 {
		return "0"
	}
	neg := n < 0
	if neg {
		n = -n
	}
	var buf []byte
	for n > 0 {
		buf = append([]byte{byte('0' + n%10)}, buf...)
		n /= 10
	}
	if neg {
		buf = append([]byte{'-'}, buf...)
	}
	return string(buf)
}