package cli

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"strings"

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

const BuildReceiptName = ".releasekit-build.json"

type ReceiptTarget struct {
	OS   string `json:"os"`
	Arch string `json:"arch"`
}

type ReceiptArtifact struct {
	Path     string        `json:"path"`
	Filename string        `json:"filename"`
	Target   ReceiptTarget `json:"target"`
	SHA256   string        `json:"sha256"`
}

// BuildReceipt is private local coordination data for generated binaries.
type BuildReceipt struct {
	RepositoryDir   string            `json:"repository_dir"`
	CandidateCommit string            `json:"candidate_commit"`
	SourceVerified  bool              `json:"source_verified"`
	Version         string            `json:"version"`
	MainPackage     string            `json:"main_package"`
	BinaryName      string            `json:"binary_name"`
	OutputDir       string            `json:"output_dir"`
	Targets         []ReceiptTarget   `json:"targets"`
	Compiler        string            `json:"compiler"`
	Artifacts       []ReceiptArtifact `json:"artifacts"`
}

func WriteBuildReceipt(outputDir string, receipt BuildReceipt) (string, error) {
	resolvedDir, err := filepath.Abs(outputDir)
	if err != nil {
		return "", fmt.Errorf("resolve build receipt directory: %w", err)
	}
	receipt.OutputDir = resolvedDir
	if err := validateBuildReceipt(receipt, true); err != nil {
		return "", err
	}
	contents, err := json.MarshalIndent(receipt, "", "  ")
	if err != nil {
		return "", fmt.Errorf("encode build receipt: %w", err)
	}
	contents = append(contents, '\n')
	temporary, err := os.CreateTemp(resolvedDir, ".releasekit-build-receipt-*")
	if err != nil {
		return "", fmt.Errorf("create temporary build receipt: %w", err)
	}
	temporaryPath := temporary.Name()
	defer os.Remove(temporaryPath)
	if _, err := temporary.Write(contents); err != nil {
		_ = temporary.Close()
		return "", fmt.Errorf("write build receipt: %w", err)
	}
	if err := temporary.Close(); err != nil {
		return "", fmt.Errorf("close build receipt: %w", err)
	}
	path := filepath.Join(resolvedDir, BuildReceiptName)
	if err := os.Rename(temporaryPath, path); err != nil {
		if _, statErr := os.Lstat(path); statErr != nil {
			return "", fmt.Errorf("install build receipt: %w", err)
		}
		if removeErr := os.Remove(path); removeErr != nil {
			return "", fmt.Errorf("replace prior build receipt: %w", removeErr)
		}
		if err := os.Rename(temporaryPath, path); err != nil {
			return "", fmt.Errorf("install build receipt: %w", err)
		}
	}
	return path, nil
}

func LoadBuildReceipt(path string) (BuildReceipt, error) {
	resolvedPath, err := filepath.Abs(path)
	if err != nil {
		return BuildReceipt{}, fmt.Errorf("resolve build receipt path: %w", err)
	}
	if filepath.Base(resolvedPath) != BuildReceiptName {
		return BuildReceipt{}, fmt.Errorf("build receipt filename must be %s", BuildReceiptName)
	}
	file, err := os.Open(resolvedPath)
	if err != nil {
		return BuildReceipt{}, fmt.Errorf("open build receipt: %w", err)
	}
	defer file.Close()
	var receipt BuildReceipt
	decoder := json.NewDecoder(file)
	decoder.DisallowUnknownFields()
	if err := decoder.Decode(&receipt); err != nil {
		return BuildReceipt{}, fmt.Errorf("decode build receipt: %w", err)
	}
	var extra any
	if err := decoder.Decode(&extra); !errors.Is(err, io.EOF) {
		if err == nil {
			return BuildReceipt{}, errors.New("decode build receipt: multiple JSON values")
		}
		return BuildReceipt{}, fmt.Errorf("decode build receipt: %w", err)
	}
	if err := validateBuildReceipt(receipt, true); err != nil {
		return BuildReceipt{}, err
	}
	if filepath.Clean(receipt.OutputDir) != filepath.Dir(resolvedPath) {
		return BuildReceipt{}, errors.New("build receipt output directory does not match its location")
	}
	return receipt, nil
}

func (receipt BuildReceipt) MatchesBuild(repositoryDir, commit, version string, settings BuildSettings) bool {
	resolvedRepo, err := filepath.Abs(repositoryDir)
	if err != nil || filepath.Clean(receipt.RepositoryDir) != filepath.Clean(resolvedRepo) {
		return false
	}
	if receipt.CandidateCommit != commit || receipt.Version != version || receipt.MainPackage != settings.MainPackage || receipt.BinaryName != settings.BinaryName {
		return false
	}
	want := normalizeReceiptTargets(settings.Targets)
	if len(want) != len(receipt.Targets) {
		return false
	}
	for i, target := range want {
		if target != receipt.Targets[i] {
			return false
		}
	}
	return true
}

func validateBuildReceipt(receipt BuildReceipt, verifyFiles bool) error {
	if !versioncontract.ValidStableVersion(receipt.Version) {
		return fmt.Errorf("build receipt has invalid version %q", receipt.Version)
	}
	if !filepath.IsAbs(receipt.RepositoryDir) || !filepath.IsAbs(receipt.OutputDir) {
		return errors.New("build receipt repository and output directories must be absolute")
	}
	if !validCommitID(receipt.CandidateCommit) {
		return errors.New("build receipt has invalid candidate commit")
	}
	if receipt.MainPackage == "" || !safeReceiptComponent(receipt.BinaryName) || receipt.Compiler == "" {
		return errors.New("build receipt is missing build identity")
	}
	if len(receipt.Targets) == 0 || len(receipt.Artifacts) != len(receipt.Targets) {
		return errors.New("build receipt target and artifact counts do not match")
	}
	seenTargets := make(map[ReceiptTarget]bool, len(receipt.Targets))
	seenArtifacts := make(map[ReceiptTarget]bool, len(receipt.Artifacts))
	for _, target := range receipt.Targets {
		if !safeReceiptComponent(target.OS) || !safeReceiptComponent(target.Arch) {
			return fmt.Errorf("build receipt has unsafe target %q/%q", target.OS, target.Arch)
		}
		if seenTargets[target] {
			return fmt.Errorf("build receipt repeats target %s/%s", target.OS, target.Arch)
		}
		seenTargets[target] = true
	}
	for _, artifact := range receipt.Artifacts {
		if !seenTargets[artifact.Target] || seenArtifacts[artifact.Target] {
			return fmt.Errorf("build receipt has an unexpected artifact target %s/%s", artifact.Target.OS, artifact.Target.Arch)
		}
		seenArtifacts[artifact.Target] = true
		wantName := receiptArtifactFilename(receipt.BinaryName, receipt.Version, artifact.Target)
		if artifact.Filename != wantName || filepath.Base(artifact.Filename) != artifact.Filename {
			return fmt.Errorf("build receipt has invalid artifact filename %q", artifact.Filename)
		}
		wantPath := filepath.Join(receipt.OutputDir, artifact.Filename)
		if !filepath.IsAbs(artifact.Path) || filepath.Clean(artifact.Path) != filepath.Clean(wantPath) {
			return fmt.Errorf("build receipt artifact path does not match filename %q", artifact.Filename)
		}
		if !validSHA256(artifact.SHA256) {
			return fmt.Errorf("build receipt has invalid SHA-256 for %q", artifact.Filename)
		}
		if verifyFiles {
			if err := verifyReceiptArtifact(artifact); err != nil {
				return err
			}
		}
	}
	return nil
}

func verifyReceiptArtifact(artifact ReceiptArtifact) error {
	info, err := os.Lstat(artifact.Path)
	if err != nil {
		return fmt.Errorf("inspect build artifact %q: %w", artifact.Path, err)
	}
	if !info.Mode().IsRegular() {
		return fmt.Errorf("build artifact %q is not a regular file", artifact.Path)
	}
	file, err := os.Open(artifact.Path)
	if err != nil {
		return fmt.Errorf("open build artifact %q: %w", artifact.Path, err)
	}
	defer file.Close()
	hash := sha256.New()
	if _, err := io.Copy(hash, file); err != nil {
		return fmt.Errorf("hash build artifact %q: %w", artifact.Path, err)
	}
	if actual := hex.EncodeToString(hash.Sum(nil)); actual != artifact.SHA256 {
		return fmt.Errorf("build artifact %q hash changed: got %s, expected %s", artifact.Path, actual, artifact.SHA256)
	}
	return nil
}

func normalizeReceiptTargets(targets []string) []ReceiptTarget {
	seen := make(map[ReceiptTarget]bool, len(targets))
	result := make([]ReceiptTarget, 0, len(targets))
	for _, value := range targets {
		goos, goarch, ok := strings.Cut(value, "/")
		if !ok {
			continue
		}
		target := ReceiptTarget{OS: goos, Arch: goarch}
		if !seen[target] {
			seen[target] = true
			result = append(result, target)
		}
	}
	return result
}

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

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

func validCommitID(value string) bool {
	if len(value) != 40 && len(value) != 64 {
		return false
	}
	for _, char := range value {
		if !(char >= '0' && char <= '9' || char >= 'a' && char <= 'f') {
			return false
		}
	}
	return true
}

func validSHA256(value string) bool {
	if len(value) != sha256.Size*2 {
		return false
	}
	for _, char := range value {
		if !(char >= '0' && char <= '9' || char >= 'a' && char <= 'f') {
			return false
		}
	}
	return true
}

// RemoveBuildReceipt invalidates prior CLI coordination data after a rebuild.
func RemoveBuildReceipt(outputDir string) error {
	err := os.Remove(filepath.Join(outputDir, BuildReceiptName))
	if errors.Is(err, os.ErrNotExist) {
		return nil
	}
	if err != nil {
		return fmt.Errorf("invalidate prior build receipt: %w", err)
	}
	return nil
}