// Copyright (c) Tailscale Inc & contributors
// SPDX-License-Identifier: BSD-3-Clause

// Package wasmbuild contains the shared build flags and manifest layout
// used to produce the @tailscale/connect NPM package's main.wasm. It is
// imported both by cmd/tsconnect (which does the build) and by tests
// that verify the produced pkg/main.wasm matches what the current
// source tree would build (see tstest/integration/jswasmtest).
package wasmbuild

import (
	"fmt"
	"os"
	"os/exec"
	"path/filepath"
	"runtime"
	"slices"
	"strings"

	"tailscale.com/feature/featuretags"
)

// baseTags are the non-featuretag build tags always set for the wasm
// build. Featuretag omits (ts_omit_*) are computed dynamically by
// [Tags] from [Keep] using the [featuretags] registry.
//
// Note: nethttpomithttp2 is intentionally NOT included: control/ts2021
// (since commit 1d93bdce2, Oct 2025) requires HTTP/2 from net/http's
// bundled implementation. Excluding it leaves the wasm client unable
// to negotiate with any control plane.
var baseTags = []string{
	"tailscale_go",
	"osusergo",
	"netgo",
	"omitidna",
	"omitpemdecrypt",
}

// Omit is the set of feature/featuretags tags excluded from the
// cmd/tsconnect/wasm build via their ts_omit_ build tag (computed by
// [Tags]). Everything else in [featuretags.Features] stays linked.
//
// Upstream uses the opposite polarity here — a small allow-list — because
// its wasm client is only an SSH/fetch-in-browser tool. This fork's JS
// bridge exposes Taildrop, Taildrive, Funnel/serve, ACME certs, exit node
// selection, service advertisement and the peerAPI, so an allow-list is
// the wrong default: a missing entry is not a compile error, it is a
// feature that silently stops working at runtime (an omitted extension
// simply never registers its hooks). Linking everything also matches how
// this build behaved before upstream introduced featuretags.
//
// The init() below panics if any entry is unknown to feature/featuretags,
// so a rename / removal in that registry fails loudly here.
//
// Trimming the bundle by omitting more features is worthwhile but should
// be done with measurements and per-feature runtime verification, not by
// assuming a feature is unreachable from the browser.
var Omit = []featuretags.FeatureTag{
	// feature/ace does not compile for GOOS=js: control/controlhttp only
	// installs HookMakeACEDialer on non-js platforms, so feature/ace's
	// reference to it is undefined here.
	"ace",
}

func init() {
	for _, ft := range Omit {
		if _, ok := featuretags.Features[ft]; !ok {
			panic(fmt.Sprintf("wasmbuild.Omit references unknown feature tag %q; "+
				"did feature/featuretags rename or remove it?", ft))
		}
	}
}

// ProdLDFlags is the -ldflags value used in production wasm builds.
// -s strips the symbol table, -w strips DWARF, both to shrink the
// shipped artifact.
const ProdLDFlags = "-s -w"

// BuildInfoFile is the basename of the JSON manifest that build-pkg
// writes alongside main.wasm, recording the sha256 of the raw
// (pre-wasm-opt) go-build output. Tests use this to detect a stale
// pkg/main.wasm without having to re-run wasm-opt themselves.
const BuildInfoFile = "build-info.json"

// BuildInfo is the JSON contents of [BuildInfoFile].
type BuildInfo struct {
	// RawWasmSHA256 is the lowercase hex sha256 of the wasm bytes as
	// they came out of `go build` (before wasm-opt was run in place).
	RawWasmSHA256 string `json:"raw_wasm_sha256"`
}

// Tags returns the joined -tags value for the wasm build: [baseTags]
// plus a ts_omit_<feature> for every entry in [Omit].
//
// The result is sorted so that the same source tree always produces
// the same string (and therefore the same wasm bytes, given identical
// inputs to `go build`).
func Tags() string {
	omit := map[featuretags.FeatureTag]bool{}
	for _, ft := range Omit {
		omit[ft] = true
	}
	tags := slices.Clone(baseTags)
	for ft := range featuretags.Features {
		if ft == "" || !ft.IsOmittable() {
			continue
		}
		if omit[ft] {
			tags = append(tags, ft.OmitTag())
		}
	}
	slices.Sort(tags)
	return strings.Join(tags, ",")
}

// ProdCommand returns an *exec.Cmd that runs `go build` for
// cmd/tsconnect/wasm with the production flags, writing the raw
// (pre-wasm-opt) wasm to outputPath. GOOS=js GOARCH=wasm is set in the
// command's environment. The caller is responsible for wiring
// Stdin/Stdout/Stderr and invoking Run.
//
// If goBin is empty, runtime.GOROOT()+"/bin/go" is used so that the
// build runs under the same toolchain that built the caller.
func ProdCommand(goBin, outputPath string) *exec.Cmd {
	if goBin == "" {
		goBin = filepath.Join(runtime.GOROOT(), "bin", "go")
	}
	cmd := exec.Command(goBin, "build",
		"-tags", Tags(),
		"-trimpath",
		"-ldflags", ProdLDFlags,
		"-o", outputPath,
		"tailscale.com/cmd/tsconnect/wasm",
	)
	cmd.Env = append(os.Environ(), "GOOS=js", "GOARCH=wasm")
	return cmd
}