// Package build compiles versioned application binaries for explicit targets.
package build

import (
	"context"
	"crypto/sha256"
	"encoding/hex"
	"errors"
	"fmt"
	"io"
	"os"
	"os/exec"
	"path/filepath"
	"sort"
	"strings"

	"gitea.maximumdirect.net/eric/ReleaseKit/internal/candidate"
	"gitea.maximumdirect.net/eric/ReleaseKit/internal/versioncontract"
)

type Target struct {
	OS   string
	Arch string
}

type Spec struct {
	MainPackage string
	BinaryName  string
	Targets     []Target
}

type Request struct {
	RepositoryDir string
	Version       string
	Spec          Spec
	OutputDir     string
	Output        io.Writer
}

type Artifact struct {
	Path     string
	Filename string
	Target   Target
	SHA256   string
}

type Result struct {
	RepositoryDir   string
	CandidateCommit string
	SourceVerified  bool
	Version         string
	MainPackage     string
	BinaryName      string
	OutputDir       string
	Targets         []Target
	Artifacts       []Artifact
	Compiler        string
}

func Build(ctx context.Context, request Request) (Result, error) {
	result := Result{
		Version:     request.Version,
		MainPackage: request.Spec.MainPackage,
		BinaryName:  request.Spec.BinaryName,
		Targets:     normalizeTargets(request.Spec.Targets),
	}
	if !versioncontract.ValidStableVersion(request.Version) {
		return result, fmt.Errorf("%w: %q", candidate.ErrInvalidVersion, request.Version)
	}
	if request.RepositoryDir == "" {
		return result, errors.New("build requires a repository directory")
	}
	if len(result.Targets) != 0 {
		if request.Spec.MainPackage == "" {
			return result, errors.New("build requires a main package when targets are selected")
		}
		if !safeComponent(request.Spec.BinaryName) {
			return result, fmt.Errorf("unsafe binary name %q", request.Spec.BinaryName)
		}
		for _, target := range result.Targets {
			if !safeComponent(target.OS) || !safeComponent(target.Arch) {
				return result, fmt.Errorf("unsafe target %q/%q", target.OS, target.Arch)
			}
		}
	}
	if err := ctx.Err(); err != nil {
		return result, fmt.Errorf("build canceled: %w", err)
	}
	repositoryDir, err := filepath.Abs(request.RepositoryDir)
	if err != nil {
		return result, fmt.Errorf("resolve repository directory: %w", err)
	}
	result.RepositoryDir = repositoryDir
	commit, err := gitCommit(ctx, repositoryDir)
	if err != nil {
		return result, err
	}
	result.CandidateCommit = commit
	cleanBefore, err := cleanSource(ctx, repositoryDir)
	if err != nil {
		return result, err
	}

	if len(result.Targets) == 0 {
		result.OutputDir = resolvedOutputDir(repositoryDir, request.OutputDir)
		return result, nil
	}

	result.OutputDir = resolvedOutputDir(repositoryDir, request.OutputDir)
	filenames := make([]string, 0, len(result.Targets))
	for _, target := range result.Targets {
		filenames = append(filenames, artifactFilename(request.Spec.BinaryName, request.Version, target))
	}
	if err := os.MkdirAll(result.OutputDir, 0o755); err != nil {
		return result, fmt.Errorf("create build output directory %q: %w", result.OutputDir, err)
	}

	compiler, err := runGo(ctx, repositoryDir, nil, "version")
	if err != nil {
		return result, fmt.Errorf("identify Go compiler: %w", err)
	}
	result.Compiler = strings.TrimSpace(string(compiler))
	host, err := hostTarget(ctx, repositoryDir)
	if err != nil {
		return result, fmt.Errorf("identify Go host: %w", err)
	}

	for index, target := range result.Targets {
		if err := ctx.Err(); err != nil {
			return result, fmt.Errorf("build canceled: %w", err)
		}
		filename := filenames[index]
		path := filepath.Join(result.OutputDir, filename)
		if request.Output != nil {
			fmt.Fprintf(request.Output, "building %s/%s as %s\n", target.OS, target.Arch, filename)
		}
		if err := buildTarget(ctx, repositoryDir, request.Spec.MainPackage, path, request.Version, target); err != nil {
			return result, fmt.Errorf("build target %s/%s: %w", target.OS, target.Arch, err)
		}
		artifact := Artifact{Path: path, Filename: filename, Target: target}
		result.Artifacts = append(result.Artifacts, artifact)
		if err := hashArtifact(&result.Artifacts[len(result.Artifacts)-1]); err != nil {
			return result, fmt.Errorf("hash build output %q: %w", path, err)
		}
	}

	var smokePath string
	for _, artifact := range result.Artifacts {
		if artifact.Target == host {
			smokePath = artifact.Path
			break
		}
	}
	if smokePath == "" {
		temporaryDir, err := os.MkdirTemp("", "releasekit-native-smoke-")
		if err != nil {
			return result, fmt.Errorf("create native smoke directory: %w", err)
		}
		defer os.RemoveAll(temporaryDir)
		smokePath = filepath.Join(temporaryDir, request.Spec.BinaryName)
		if host.OS == "windows" {
			smokePath += ".exe"
		}
		if request.Output != nil {
			fmt.Fprintf(request.Output, "building temporary version check for %s/%s\n", host.OS, host.Arch)
		}
		if err := buildTarget(ctx, repositoryDir, request.Spec.MainPackage, smokePath, request.Version, host); err != nil {
			return result, fmt.Errorf("build native version check: %w", err)
		}
	}
	if request.Output != nil {
		fmt.Fprintf(request.Output, "checking %s version output\n", request.Spec.BinaryName)
	}
	if err := checkVersion(ctx, smokePath, request.Spec.BinaryName, request.Version); err != nil {
		return result, err
	}
	commitAfter, err := gitCommit(ctx, repositoryDir)
	if err != nil {
		return result, err
	}
	cleanAfter, err := cleanSource(ctx, repositoryDir)
	if err != nil {
		return result, err
	}
	result.SourceVerified = cleanBefore && cleanAfter && commitAfter == commit
	return result, nil
}

func normalizeTargets(targets []Target) []Target {
	seen := make(map[Target]struct{}, len(targets))
	result := make([]Target, 0, len(targets))
	for _, target := range targets {
		if _, ok := seen[target]; ok {
			continue
		}
		seen[target] = struct{}{}
		result = append(result, target)
	}
	return result
}

func safeComponent(value string) bool {
	return value != "" && !strings.ContainsAny(value, "/\\\r\n")
}

func resolvedOutputDir(repositoryDir, outputDir string) string {
	if outputDir == "" {
		outputDir = filepath.Join(repositoryDir, "dist")
	} else if !filepath.IsAbs(outputDir) {
		outputDir = filepath.Join(repositoryDir, outputDir)
	}
	resolved, err := filepath.Abs(outputDir)
	if err != nil {
		return filepath.Clean(outputDir)
	}
	return resolved
}

func artifactFilename(binaryName, version string, target Target) string {
	filename := fmt.Sprintf("%s-%s-%s-%s", binaryName, version, target.OS, target.Arch)
	if target.OS == "windows" {
		filename += ".exe"
	}
	return filename
}

func gitCommit(ctx context.Context, repositoryDir string) (string, error) {
	command := exec.CommandContext(ctx, "git", "-C", repositoryDir, "rev-parse", "--verify", "HEAD^{commit}")
	output, err := command.Output()
	if err != nil {
		if ctx.Err() != nil {
			return "", fmt.Errorf("read source commit: %w", ctx.Err())
		}
		return "", fmt.Errorf("read source commit: %w", err)
	}
	return strings.TrimSpace(string(output)), nil
}

func hostTarget(ctx context.Context, repositoryDir string) (Target, error) {
	output, err := runGo(ctx, repositoryDir, nil, "env", "GOHOSTOS", "GOHOSTARCH")
	if err != nil {
		return Target{}, err
	}
	parts := strings.Fields(string(output))
	if len(parts) != 2 {
		return Target{}, fmt.Errorf("unexpected Go host response %q", output)
	}
	return Target{OS: parts[0], Arch: parts[1]}, nil
}

func buildTarget(ctx context.Context, repositoryDir, mainPackage, outputPath, version string, target Target) error {
	ldflags := "-s -w -X " + versioncontract.InjectedVersionLinkerSymbol + "=" + version
	_, err := runGo(ctx, repositoryDir, map[string]string{"GOOS": target.OS, "GOARCH": target.Arch},
		"build", "-o", outputPath, "-mod=readonly", "-trimpath", "-buildvcs=false", "-ldflags", ldflags, mainPackage)
	return err
}

func runGo(ctx context.Context, directory string, target map[string]string, args ...string) ([]byte, error) {
	commandArgs := append([]string(nil), args...)
	command := exec.CommandContext(ctx, "go", commandArgs...)
	command.Dir = directory
	command.Env = goEnvironment(target)
	output, err := command.CombinedOutput()
	if err == nil {
		return output, nil
	}
	if ctx.Err() != nil {
		err = fmt.Errorf("%w: %v", ctx.Err(), err)
	}
	if len(output) != 0 {
		return output, fmt.Errorf("go %s: %w: %s", strings.Join(commandArgs, " "), err, strings.TrimSpace(string(output)))
	}
	return output, fmt.Errorf("go %s: %w", strings.Join(commandArgs, " "), err)
}

func goEnvironment(target map[string]string) []string {
	controlled := map[string]bool{
		"GOWORK": true, "GOPROXY": true, "GONOPROXY": true, "GOSUMDB": true,
		"GOTOOLCHAIN": true, "GOFLAGS": true, "CGO_ENABLED": true, "GOOS": true, "GOARCH": true,
	}
	for key := range target {
		controlled[key] = true
	}
	environment := make([]string, 0, len(os.Environ())+len(controlled))
	for _, entry := range os.Environ() {
		key, _, ok := strings.Cut(entry, "=")
		if !ok || !controlled[key] {
			environment = append(environment, entry)
		}
	}
	values := map[string]string{
		"GOWORK": "off", "GOPROXY": "off", "GONOPROXY": "none", "GOSUMDB": "off",
		"GOTOOLCHAIN": "local", "GOFLAGS": "-mod=readonly", "CGO_ENABLED": "0",
	}
	for key, value := range target {
		values[key] = value
	}
	keys := make([]string, 0, len(values))
	for key := range values {
		keys = append(keys, key)
	}
	sort.Strings(keys)
	for _, key := range keys {
		environment = append(environment, key+"="+values[key])
	}
	return environment
}

func hashArtifact(artifact *Artifact) error {
	file, err := os.Open(artifact.Path)
	if err != nil {
		return err
	}
	defer file.Close()
	hash := sha256.New()
	if _, err := io.Copy(hash, file); err != nil {
		return err
	}
	artifact.SHA256 = hex.EncodeToString(hash.Sum(nil))
	return nil
}

func checkVersion(ctx context.Context, binaryPath, binaryName, version string) error {
	command := exec.CommandContext(ctx, binaryPath, "version")
	command.Env = goEnvironment(nil)
	output, err := command.CombinedOutput()
	if err != nil {
		if ctx.Err() != nil {
			return fmt.Errorf("run native version check: %w", ctx.Err())
		}
		return fmt.Errorf("run native version check: %w: %s", err, strings.TrimSpace(string(output)))
	}
	want := binaryName + " " + version + "\n"
	if string(output) != want {
		return fmt.Errorf("native version output = %q, want %q", output, want)
	}
	return nil
}

func cleanSource(ctx context.Context, repositoryDir string) (bool, error) {
	command := exec.CommandContext(ctx, "git", "-C", repositoryDir, "status", "--porcelain", "--untracked-files=all")
	output, err := command.Output()
	if err != nil {
		return false, fmt.Errorf("inspect build source: %w", err)
	}
	return len(output) == 0, nil
}