package main

import (
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"strings"
)

var (
	projectDir = func() string {
		// go run cmd/build/main.go — __file__ is in cmd/build/, project root is ../../
		exe, _ := os.Getwd()
		return exe
	}()
	buildDir  = filepath.Join(projectDir, ".build")
	vendorDir = filepath.Join(projectDir, "vendor")
	gav1dDir  = filepath.Join(buildDir, "dav1d")
	ffmpegDir = filepath.Join(buildDir, "ffmpeg")
)

func init() {
	github := os.Getenv("GITHUB_WORKSPACE")
	if github != "" {
		projectDir = github
		buildDir = filepath.Join(projectDir, ".build")
		vendorDir = filepath.Join(projectDir, "vendor")
		gav1dDir = filepath.Join(buildDir, "dav1d")
		ffmpegDir = filepath.Join(buildDir, "ffmpeg")
	}
}

type buildTarget struct {
	name            string
	goos            string
	goarch          string
	dav1dCrossFile  string
	ffmpegExtraArgs []string
}

func availableTargets() []buildTarget {
	switch runtime.GOOS {
	case "linux":
		return []buildTarget{
			{name: "linux_amd64", goos: "linux", goarch: "amd64"},
			{
				name:           "linux_arm64",
				goos:           "linux",
				goarch:         "arm64",
				dav1dCrossFile: "cross_linux_arm64.ini",
				ffmpegExtraArgs: []string{
					"--enable-cross-compile",
					"--arch=aarch64",
					"--target-os=linux",
					"--cross-prefix=aarch64-linux-gnu-",
				},
			},
			{
				name:           "windows_amd64",
				goos:           "windows",
				goarch:         "amd64",
				dav1dCrossFile: "cross_windows_amd64.ini",
				ffmpegExtraArgs: []string{
					"--enable-cross-compile",
					"--arch=x86_64",
					"--target-os=mingw32",
					"--cross-prefix=x86_64-w64-mingw32-",
				},
			},
		}
	case "darwin":
		return []buildTarget{
			{name: "darwin_arm64", goos: "darwin", goarch: "arm64"},
			{
				name:           "darwin_amd64",
				goos:           "darwin",
				goarch:         "amd64",
				dav1dCrossFile: "cross_darwin_amd64.ini",
				ffmpegExtraArgs: []string{
					"--enable-cross-compile",
					"--arch=x86_64",
					"--target-os=darwin",
				},
			},
		}
	case "windows":
		return []buildTarget{
			{name: "windows_amd64", goos: "windows", goarch: "amd64"},
		}
	}
	return nil
}

func isNative(t buildTarget) bool {
	return t.goos == runtime.GOOS && t.goarch == runtime.GOARCH
}

func checkTool(tool string) bool {
	_, err := exec.LookPath(tool)
	return err == nil
}

func checkBuildDeps(target buildTarget) []string {
	var missing []string
	cc := "gcc"
	if runtime.GOOS == "darwin" {
		cc = "clang"
	}
	tools := []string{cc, "meson", "ninja", "pkg-config"}
	if isNative(target) {
		tools = append(tools, "nasm")
	}
	for _, t := range tools {
		if !checkTool(t) {
			missing = append(missing, t)
		}
	}
	if !isNative(target) {
		switch target.name {
		case "linux_arm64":
			if !checkTool("aarch64-linux-gnu-gcc") {
				missing = append(missing, "aarch64-linux-gnu-gcc")
			}
		case "windows_amd64":
			if !checkTool("x86_64-w64-mingw32-gcc") {
				missing = append(missing, "x86_64-w64-mingw32-gcc")
			}
		}
	}
	return missing
}

func run(dir, name string, args ...string) error {
	cmd := exec.Command(name, args...)
	cmd.Dir = dir
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	cmd.Env = os.Environ()
	fmt.Printf("\n>>> %s %v (in %s)\n", name, args, dir)
	return cmd.Run()
}

func writeFile(path, content string) error {
	if err := os.MkdirAll(filepath.Dir(path), 0755); err != nil {
		return err
	}
	return os.WriteFile(path, []byte(content), 0644)
}

func copyFile(src, dst string) error {
	s, err := os.Open(src)
	if err != nil {
		return fmt.Errorf("open %s: %w", src, err)
	}
	defer s.Close()
	if err := os.MkdirAll(filepath.Dir(dst), 0755); err != nil {
		return err
	}
	d, err := os.Create(dst)
	if err != nil {
		return fmt.Errorf("create %s: %w", dst, err)
	}
	defer d.Close()
	if _, err := io.Copy(d, s); err != nil {
		return fmt.Errorf("copy %s -> %s: %w", src, dst, err)
	}
	fmt.Printf("  %s -> %s\n", filepath.Base(src), dst)
	return nil
}

func artifactExists(target buildTarget) bool {
	dest := filepath.Join(vendorDir, target.name)
	for _, lib := range []string{"libavcodec.a", "libavformat.a", "libavutil.a", "libswresample.a", "libdav1d.a"} {
		if _, err := os.Stat(filepath.Join(dest, lib)); err != nil {
			return false
		}
	}
	return true
}

func cloneIfMissing(dir, url string) error {
	if _, err := os.Stat(dir); os.IsNotExist(err) {
		fmt.Printf("cloning %s into %s...\n", url, dir)
		if err := os.MkdirAll(filepath.Dir(dir), 0755); err != nil {
			return err
		}
		return run(filepath.Dir(dir), "git", "clone", "--depth", "1", url, dir)
	}
	fmt.Printf("already exists: %s\n", dir)
	return nil
}

func buildDav1d(target buildTarget) error {
	name := target.name
	fmt.Printf("\n=== dav1d %s ===\n", name)

	targetBuildDir := filepath.Join(gav1dDir, "build_"+name)
	installDir := filepath.Join(buildDir, "dav1d_install_"+name)
	_ = os.RemoveAll(targetBuildDir)

	args := []string{
		"setup", targetBuildDir,
		"--default-library=static",
		"--buildtype=release",
		"-Denable_tools=false",
		"-Denable_tests=false",
		"--prefix=" + installDir,
	}
	if isNative(target) {
		args = append(args, "-Denable_asm=true")
	} else {
		args = append(args, "-Denable_asm=false")
	}
	if target.dav1dCrossFile != "" {
		args = append(args, "--cross-file="+filepath.Join(buildDir, target.dav1dCrossFile))
	}

	if err := run(gav1dDir, "meson", args...); err != nil {
		return fmt.Errorf("meson setup dav1d %s: %w", name, err)
	}
	if err := run(gav1dDir, "ninja", "-C", targetBuildDir); err != nil {
		return fmt.Errorf("ninja dav1d %s: %w", name, err)
	}
	if err := run(gav1dDir, "ninja", "-C", targetBuildDir, "install"); err != nil {
		return fmt.Errorf("ninja install dav1d %s: %w", name, err)
	}
	return copyFile(
		filepath.Join(installDir, "lib", "libdav1d.a"),
		filepath.Join(vendorDir, name, "libdav1d.a"),
	)
}

func buildFFmpeg(target buildTarget) error {
	name := target.name
	fmt.Printf("\n=== ffmpeg %s ===\n", name)

	installDir := filepath.Join(buildDir, "ffmpeg_install_"+name)
	dav1dInstall := filepath.Join(buildDir, "dav1d_install_"+name)
	if err := os.MkdirAll(installDir, 0755); err != nil {
		return err
	}

	run(ffmpegDir, "make", "distclean")

	extraCFlags := "-I" + filepath.Join(dav1dInstall, "include")
	extraLDFlags := "-L" + filepath.Join(dav1dInstall, "lib")
	if target.goos == "darwin" && target.goarch == "amd64" {
		extraCFlags += " -arch x86_64"
		extraLDFlags += " -arch x86_64"
	}

	args := []string{
		"--prefix=" + installDir,
		"--disable-everything",
		"--disable-programs",
		"--disable-doc",
		"--disable-network",
		"--disable-avdevice",
		"--disable-avfilter",
		"--disable-swscale",
		"--disable-vaapi",
		"--disable-vdpau",
		"--disable-bzlib",
		"--disable-xlib",
		"--disable-libdrm",
		"--disable-hwaccels",
		"--enable-libdav1d",
		"--enable-avcodec",
		"--enable-avformat",
		"--enable-avutil",
		"--enable-swresample",
		"--enable-static",
		"--disable-shared",
		"--enable-pic",
		"--enable-decoder=h264,hevc,libdav1d,vp9,vp8,mpeg4,mp3,aac,opus,vorbis,flac,pcm_s16le,pcm_s16be,pcm_f32le",
		"--enable-demuxer=mov,mp4,matroska,webm,avi,flv,ogg,mp3,aac,flac,ivf,h264,hevc,mpegts",
		"--enable-parser=h264,hevc,av1,vp9,vp8,mpeg4video,mp3,aac,opus,vorbis,flac",
		"--enable-protocol=file,pipe",
		"--enable-bsf=h264_mp4toannexb,hevc_mp4toannexb,extract_extradata",
		"--pkg-config=pkg-config",
		"--pkg-config-flags=--static",
		"--extra-cflags=" + extraCFlags,
		"--extra-ldflags=" + extraLDFlags,
	}
	args = append(args, target.ffmpegExtraArgs...)

	pkgPath := filepath.Join(dav1dInstall, "lib", "pkgconfig")
	filtered := []string{}
	for _, e := range os.Environ() {
		if !strings.HasPrefix(e, "PKG_CONFIG_PATH=") &&
			!strings.HasPrefix(e, "PKG_CONFIG_LIBDIR=") {
			filtered = append(filtered, e)
		}
	}

	cmd := exec.Command(filepath.Join(ffmpegDir, "configure"), args...)
	cmd.Dir = ffmpegDir
	cmd.Stdout = os.Stdout
	cmd.Stderr = os.Stderr
	cmd.Env = append(filtered,
		"PKG_CONFIG_PATH="+pkgPath,
		"PKG_CONFIG_LIBDIR="+pkgPath,
	)
	fmt.Printf("\n>>> ./configure ... (in %s)\n", ffmpegDir)
	if err := cmd.Run(); err != nil {
		return fmt.Errorf("configure ffmpeg %s: %w", name, err)
	}

	nproc := fmt.Sprintf("%d", runtime.NumCPU())
	if err := run(ffmpegDir, "make", "-j"+nproc); err != nil {
		return fmt.Errorf("make ffmpeg %s: %w", name, err)
	}
	if err := run(ffmpegDir, "make", "install"); err != nil {
		return fmt.Errorf("make install ffmpeg %s: %w", name, err)
	}

	dest := filepath.Join(vendorDir, name)
	for _, lib := range []string{"libavcodec.a", "libavformat.a", "libavutil.a", "libswresample.a"} {
		if err := copyFile(filepath.Join(installDir, "lib", lib), filepath.Join(dest, lib)); err != nil {
			return err
		}
	}
	return nil
}

func firstBuiltTarget() string {
	for _, t := range availableTargets() {
		if artifactExists(t) {
			return t.name
		}
	}
	return availableTargets()[0].name
}

func copyHeaders() error {
	fmt.Println("\n=== copying headers ===")
	first := firstBuiltTarget()

	src := filepath.Join(buildDir, "ffmpeg_install_"+first, "include")
	dst := filepath.Join(vendorDir, "include")
	filepath.Walk(src, func(path string, info os.FileInfo, err error) error {
		if err != nil || info.IsDir() {
			return nil
		}
		rel, _ := filepath.Rel(src, path)
		return copyFile(path, filepath.Join(dst, rel))
	})

	srcDav1d := filepath.Join(buildDir, "dav1d_install_"+first, "include", "dav1d")
	dstDav1d := filepath.Join(vendorDir, "include", "dav1d")
	filepath.Walk(srcDav1d, func(path string, info os.FileInfo, err error) error {
		if err != nil || info.IsDir() {
			return nil
		}
		rel, _ := filepath.Rel(srcDav1d, path)
		return copyFile(path, filepath.Join(dstDav1d, rel))
	})
	return nil
}

func writeCrossFiles() error {
	if runtime.GOOS == "darwin" {
		pkgConfigPath, _ := exec.LookPath("pkg-config")
		wrapperPath := filepath.Join(buildDir, "clang_x86_64.sh")
		if err := writeFile(wrapperPath, "#!/bin/sh\nexec clang -arch x86_64 \"$@\"\n"); err != nil {
			return err
		}
		if err := os.Chmod(wrapperPath, 0755); err != nil {
			return err
		}
		if err := writeFile(
			filepath.Join(buildDir, "cross_darwin_amd64.ini"),
			fmt.Sprintf(`[binaries]
c = '%s'
ar = 'ar'
strip = 'strip'
pkg-config = '%s'

[built-in options]
c_args = ['-arch', 'x86_64']
c_link_args = ['-arch', 'x86_64']

[host_machine]
system = 'darwin'
cpu_family = 'x86_64'
cpu = 'x86_64'
endian = 'little'
`, wrapperPath, pkgConfigPath)); err != nil {
			return err
		}
	}

	if err := writeFile(filepath.Join(buildDir, "cross_linux_arm64.ini"), `[binaries]
c = 'aarch64-linux-gnu-gcc'
ar = 'aarch64-linux-gnu-ar'
strip = 'aarch64-linux-gnu-strip'
pkgconfig = 'pkg-config'

[host_machine]
system = 'linux'
cpu_family = 'aarch64'
cpu = 'aarch64'
endian = 'little'
`); err != nil {
		return err
	}

	return writeFile(filepath.Join(buildDir, "cross_windows_amd64.ini"), `[binaries]
c = 'x86_64-w64-mingw32-gcc'
ar = 'x86_64-w64-mingw32-ar'
strip = 'x86_64-w64-mingw32-strip'
pkgconfig = 'pkg-config'

[host_machine]
system = 'windows'
cpu_family = 'x86_64'
cpu = 'x86_64'
endian = 'little'
`)
}

func main() {
	if err := os.MkdirAll(buildDir, 0755); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	if err := cloneIfMissing(ffmpegDir, "https://m8sh.su/x/ffmpeg"); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}
	if err := cloneIfMissing(gav1dDir, "https://m8sh.su/x/dav1d"); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	if err := writeCrossFiles(); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	var targetsToBuild []buildTarget
	for _, t := range availableTargets() {
		missing := checkBuildDeps(t)
		if len(missing) > 0 {
			fmt.Printf("SKIP %s (missing deps: %v)\n", t.name, missing)
			continue
		}
		targetsToBuild = append(targetsToBuild, t)
	}

	for _, t := range targetsToBuild {
		if artifactExists(t) {
			fmt.Printf("\nSKIP %s (artifacts already exist)\n", t.name)
			continue
		}
		if err := buildDav1d(t); err != nil {
			fmt.Fprintln(os.Stderr, err)
			os.Exit(1)
		}
		if err := buildFFmpeg(t); err != nil {
			fmt.Fprintln(os.Stderr, err)
			os.Exit(1)
		}
	}

	if err := copyHeaders(); err != nil {
		fmt.Fprintln(os.Stderr, err)
		os.Exit(1)
	}

	fmt.Println("\n=== all done ===")
}