// Package rosa provides Rosa OS toolchain artifacts and miscellaneous software.
package rosa

import (
	"log"
	"runtime"
	"slices"
	"strconv"
	"strings"

	"hakurei.app/container/fhs"
	"hakurei.app/internal/pkg"
)

const (
	// kindEtc is the kind of [pkg.Artifact] of cureEtc.
	kindEtc = iota + pkg.KindCustomOffset

	// kindBusyboxBin is the kind of [pkg.Artifact] of busyboxBin.
	kindBusyboxBin
)

// mustDecode is like [pkg.MustDecode], but replaces the zero value and prints
// a warning.
func mustDecode(s string) pkg.Checksum {
	var fallback = pkg.Checksum{}
	if s == "" {
		log.Println(
			"falling back to",
			pkg.Encode(fallback),
			"for unpopulated checksum",
		)
		return fallback
	}
	return pkg.MustDecode(s)
}

var (
	// AbsUsrSrc is the conventional directory to place source code under.
	AbsUsrSrc = fhs.AbsUsr.Append("src")

	// AbsSystem is the Rosa OS installation prefix.
	AbsSystem = fhs.AbsRoot.Append("system")
)

// linuxArch returns the architecture name used by linux corresponding to
// [runtime.GOARCH].
func linuxArch() string {
	switch runtime.GOARCH {
	case "amd64":
		return "x86_64"

	default:
		panic("unsupported target " + runtime.GOARCH)
	}
}

// triplet returns the Rosa OS host triple corresponding to [runtime.GOARCH].
func triplet() string {
	return linuxArch() + "-rosa-linux-musl"
}

const (
	// EnvTriplet holds the return value of triplet.
	EnvTriplet = "ROSA_TRIPLE"
	// EnvRefCFLAGS holds toolchain-specific reference CFLAGS.
	EnvRefCFLAGS = "ROSA_CFLAGS"
	// EnvRefCXXFLAGS holds toolchain-specific reference CXXFLAGS.
	EnvRefCXXFLAGS = "ROSA_CXXFLAGS"
)

// ldflags returns LDFLAGS corresponding to triplet.
func ldflags(static bool) string {
	s := "LDFLAGS=" +
		"-fuse-ld=lld " +
		"-L/system/lib -Wl,-rpath=/system/lib " +
		"-L/system/lib/" + triplet() + " " +
		"-Wl,-rpath=/system/lib/" + triplet() + " " +
		"-rtlib=compiler-rt " +
		"-unwindlib=libunwind " +
		"-Wl,--as-needed"
	if !static {
		s += " -Wl,--dynamic-linker=/system/lib/ld-musl-x86_64.so.1"
	}
	return s
}

// cflags is reference CFLAGS for the Rosa OS toolchain.
const cflags = "-Qunused-arguments " +
	"-isystem/system/include"

// cxxflags returns reference CXXFLAGS for the Rosa OS toolchain corresponding
// to [runtime.GOARCH].
func cxxflags() string {
	return "--start-no-unused-arguments " +
		"-stdlib=libc++ " +
		"--end-no-unused-arguments " +
		"-isystem/system/include/c++/v1 " +
		"-isystem/system/include/" + triplet() + "/c++/v1 " +
		"-isystem/system/include "
}

// Toolchain denotes the infrastructure to compile a [pkg.Artifact] on.
type Toolchain uintptr

const (
	// toolchainBusybox denotes a busybox installation from the busyboxBin
	// binary distribution. This is for decompressing unsupported formats.
	toolchainBusybox Toolchain = iota

	// toolchainStage3 denotes the Gentoo stage3 toolchain. Special care must be
	// taken to compile correctly against this toolchain.
	toolchainStage3
)

// lastIndexFunc is like [strings.LastIndexFunc] but for [slices].
func lastIndexFunc[S ~[]E, E any](s S, f func(E) bool) (i int) {
	if i = slices.IndexFunc(s, f); i < 0 {
		return
	}
	if i0 := lastIndexFunc[S](s[i+1:], f); i0 >= 0 {
		i = i0
	}
	return
}

// fixupEnviron fixes up PATH, prepends extras and returns the resulting slice.
func fixupEnviron(env, extras []string, paths ...string) []string {
	const pathPrefix = "PATH="
	pathVal := strings.Join(paths, ":")

	if i := lastIndexFunc(env, func(s string) bool {
		return strings.HasPrefix(s, pathPrefix)
	}); i < 0 {
		env = append(env, pathPrefix+pathVal)
	} else {
		if len(env[i]) == len(pathPrefix) {
			env[i] = pathPrefix + pathVal
		} else {
			env[i] += ":" + pathVal
		}
	}

	return append(extras, env...)
}

// absCureScript is the absolute pathname [Toolchain.New] places the fixed-up
// build script under.
var absCureScript = fhs.AbsUsrBin.Append(".cure-script")

// New returns a [pkg.Artifact] compiled on this toolchain.
func (t Toolchain) New(
	name string,
	extra []pkg.Artifact,
	checksum *pkg.Checksum,
	env []string,
	script string,

	paths ...pkg.ExecPath,
) pkg.Artifact {
	const lcMessages = "LC_MESSAGES=C.UTF-8"

	var (
		path    = AbsSystem.Append("bin", "busybox")
		args    = []string{"hush", absCureScript.String()}
		support []pkg.Artifact
	)
	switch t {
	case toolchainBusybox:
		support = slices.Concat([]pkg.Artifact{newBusyboxBin()}, extra)
		env = fixupEnviron(env, nil, "/system/bin")

	case toolchainStage3:
		const (
			version  = "20260111T160052Z"
			checksum = "c5_FwMnRN8RZpTdBLGYkL4RR8ampdaZN2JbkgrFLe8-QHQAVQy08APVvIL6eT7KW"
		)
		path = fhs.AbsRoot.Append("bin", "bash")
		args[0] = "bash"
		support = slices.Concat([]pkg.Artifact{
			cureEtc{},
			toolchainBusybox.New("stage3-"+version, nil, nil, nil, `
tar -C /work -xf /usr/src/stage3.tar.xz
rm -rf /work/dev/ /work/proc/
ln -vs ../usr/bin /work/bin
`, pkg.Path(AbsUsrSrc.Append("stage3.tar.xz"), false,
				pkg.NewHTTPGet(
					nil, "https://distfiles.gentoo.org/releases/"+
						runtime.GOARCH+"/autobuilds/"+version+
						"/stage3-"+runtime.GOARCH+"-musl-llvm-"+version+".tar.xz",
					mustDecode(checksum),
				),
			)),
		}, extra)
		env = fixupEnviron(env, []string{
			EnvTriplet + "=" + triplet(),
			lcMessages,

			EnvRefCFLAGS + "=" + cflags,
			EnvRefCXXFLAGS + "=" + cxxflags(),
			ldflags(true),
		}, "/system/bin",
			"/usr/bin",
			"/usr/lib/llvm/21/bin",
		)
	default:
		panic("unsupported toolchain " + strconv.Itoa(int(t)))
	}

	return pkg.NewExec(
		name, checksum, pkg.ExecTimeoutMax,
		fhs.AbsRoot, env,
		path, args,

		slices.Concat([]pkg.ExecPath{pkg.Path(
			fhs.AbsRoot, true,
			support...,
		), pkg.Path(
			absCureScript, false,
			pkg.NewFile(".cure-script", []byte("set -e\n"+script)),
		)}, paths)...,
	)
}