package engine

import (
	"errors"
	"fmt"
	"io"
	"io/fs"
	"os"
	"path/filepath"
	"slices"
	"strconv"
	"strings"
)

const (
	secretsEntryLimit   = 1024
	secretFileByteLimit = int64(1 << 20)
	secretsByteLimit    = int64(8 << 20)
)

// SecretFileStatus describes the outcome for one file considered by
// LoadSecretsDir.
type SecretFileStatus string

const (
	SecretFileLoaded          SecretFileStatus = "loaded"
	SecretFileSkippedExisting SecretFileStatus = "skipped_existing"
	SecretFileNotApplied      SecretFileStatus = "not_applied"
	SecretFileFailed          SecretFileStatus = "failed"
)

// SecretFileResult is the safe, value-free bootstrap result for one directory
// entry. ExistingEmpty is meaningful when Status is SecretFileSkippedExisting.
type SecretFileResult struct {
	Name          string
	Path          string
	Status        SecretFileStatus
	ExistingEmpty bool
}

// SecretsReport is a detached snapshot of an explicit secrets-directory
// bootstrap. It does not retain file contents or environment values.
type SecretsReport struct {
	entries []SecretFileResult
}

// Entries returns a copy of the report's filename-ordered entries.
func (r *SecretsReport) Entries() []SecretFileResult {
	if r == nil {
		return nil
	}
	return slices.Clone(r.entries)
}

// WriteTo renders one safe, deterministic line per entry. Names and paths are
// quoted so control characters cannot affect terminal output.
func (r *SecretsReport) WriteTo(output io.Writer) (int64, error) {
	if output == nil {
		return 0, errors.New("configkit: secrets report output is nil")
	}
	if r == nil {
		return 0, nil
	}
	var total int64
	for _, entry := range r.entries {
		line := "status=" + strconv.Quote(string(entry.Status)) +
			" name=" + strconv.Quote(entry.Name) +
			" path=" + strconv.Quote(entry.Path) +
			" existing_empty=" + strconv.FormatBool(entry.ExistingEmpty) + "\n"
		written, err := io.WriteString(output, line)
		total += int64(written)
		if err != nil {
			return total, err
		}
		if written != len(line) {
			return total, io.ErrShortWrite
		}
	}
	return total, nil
}

// SecretsError reports safe structured diagnostics for a failed explicit
// secrets-directory bootstrap. It intentionally does not unwrap filesystem or
// environment errors.
type SecretsError struct {
	diagnostics []Diagnostic
}

// Error implements error without rendering filenames, paths, or file contents.
func (e *SecretsError) Error() string {
	if e == nil {
		return "configkit: secrets bootstrap failed"
	}
	count := 0
	for _, diagnostic := range e.diagnostics {
		if diagnostic.Severity == SeverityError {
			count++
		}
	}
	if count == 1 {
		return "configkit: secrets bootstrap failed with 1 error"
	}
	return fmt.Sprintf("configkit: secrets bootstrap failed with %d errors", count)
}

// Diagnostics returns a deep copy of the bootstrap diagnostics.
func (e *SecretsError) Diagnostics() []Diagnostic {
	if e == nil {
		return nil
	}
	return cloneDiagnostics(e.diagnostics)
}

type secretsEnvironment struct {
	lookup func(string) (string, bool)
	set    func(string, string) error
}

type secretsAccess struct {
	openDirectory func(string) (*os.File, error)
	lstat         func(string) (fs.FileInfo, error)
	openFile      func(string) (*os.File, error)
}

type stagedSecret struct {
	entry int
	value string
}

// LoadSecretsDir explicitly loads immediate regular files from directory into
// previously unset process environment variables. Applications should call it
// once during startup, before concurrent work; Load never calls it.
func LoadSecretsDir(directory string) (*SecretsReport, error) {
	return loadSecretsDir(directory, secretsEnvironment{lookup: os.LookupEnv, set: os.Setenv}, secretsAccess{
		openDirectory: os.Open,
		lstat:         os.Lstat,
		openFile:      os.Open,
	})
}

func loadSecretsDir(directory string, environment secretsEnvironment, access secretsAccess) (*SecretsReport, error) {
	report := &SecretsReport{}
	if strings.TrimSpace(directory) == "" {
		return report, secretsFailure(CodeSecretsInvalidPath, "secrets directory path is required")
	}

	canonical, err := canonicalExistingPath(directory)
	if err != nil {
		return report, secretsFailure(classifySecretsFilesystemError(err), "secrets directory could not be canonicalized: "+strconv.Quote(cleanAbsolutePath(directory)))
	}
	info, err := os.Stat(canonical)
	if err != nil {
		return report, secretsFailure(classifySecretsFilesystemError(err), "secrets directory could not be inspected: "+strconv.Quote(canonical))
	}
	if !info.IsDir() {
		return report, secretsFailure(CodeSecretsInvalidPath, "secrets directory is not a directory: "+strconv.Quote(canonical))
	}

	directoryFile, err := access.openDirectory(canonical)
	if err != nil {
		return report, secretsFailure(classifySecretsFilesystemError(err), "secrets directory could not be opened: "+strconv.Quote(canonical))
	}
	entries, readErr := readSecretsEntries(directoryFile)
	closeErr := directoryFile.Close()
	if readErr != nil {
		return report, secretsFailure(classifySecretsFilesystemError(readErr), "secrets directory could not be enumerated: "+strconv.Quote(canonical))
	}
	if closeErr != nil {
		return report, secretsFailure(CodeSecretsRead, "secrets directory could not be closed: "+strconv.Quote(canonical))
	}
	slices.SortFunc(entries, func(left, right fs.DirEntry) int { return strings.Compare(left.Name(), right.Name()) })
	report.entries = make([]SecretFileResult, len(entries))
	for index, entry := range entries {
		name := entry.Name()
		report.entries[index] = SecretFileResult{Name: name, Path: filepath.Join(canonical, name), Status: SecretFileNotApplied}
	}
	if len(entries) > secretsEntryLimit {
		return report, secretsFailure(CodeSecretsLimitExceeded, "secrets directory exceeds the 1024-entry limit: "+strconv.Quote(canonical))
	}

	for index := range report.entries {
		entry := &report.entries[index]
		if !validEnvironmentName(entry.Name) {
			entry.Status = SecretFileFailed
			return report, secretsFailure(CodeSecretsInvalidName, "secret filename is not a valid environment name: "+strconv.Quote(entry.Path))
		}
		info, err := access.lstat(entry.Path)
		if err != nil {
			entry.Status = SecretFileFailed
			return report, secretsFailure(classifySecretsFilesystemError(err), "secret file could not be inspected: "+strconv.Quote(entry.Path))
		}
		if info.Mode()&fs.ModeSymlink != 0 || !info.Mode().IsRegular() {
			entry.Status = SecretFileFailed
			return report, secretsFailure(CodeSecretsNotRegular, "secret entry is not a regular file: "+strconv.Quote(entry.Path))
		}
	}

	staged := make([]stagedSecret, 0, len(report.entries))
	var consumed int64
	for index := range report.entries {
		entry := &report.entries[index]
		if existing, present := environment.lookup(entry.Name); present {
			entry.Status = SecretFileSkippedExisting
			entry.ExistingEmpty = existing == ""
			continue
		}
		remaining := secretsByteLimit - consumed
		value, used, err := readSecretValue(entry.Path, remaining, access)
		if err != nil {
			entry.Status = SecretFileFailed
			return report, secretsFailure(secretReadCode(err), secretReadMessage(err)+": "+strconv.Quote(entry.Path))
		}
		consumed += used
		staged = append(staged, stagedSecret{entry: index, value: value})
	}

	for _, secret := range staged {
		entry := &report.entries[secret.entry]
		if existing, present := environment.lookup(entry.Name); present {
			entry.Status = SecretFileSkippedExisting
			entry.ExistingEmpty = existing == ""
			continue
		}
		if err := environment.set(entry.Name, secret.value); err != nil {
			entry.Status = SecretFileFailed
			return report, secretsFailure(CodeSecretsApplyFailed, "secret environment variable could not be set for file: "+strconv.Quote(entry.Path))
		}
		entry.Status = SecretFileLoaded
	}
	return report, nil
}

func readSecretsEntries(directory *os.File) ([]fs.DirEntry, error) {
	entries := make([]fs.DirEntry, 0)
	for len(entries) <= secretsEntryLimit {
		batch, err := directory.ReadDir(secretsEntryLimit + 1 - len(entries))
		entries = append(entries, batch...)
		if err == io.EOF {
			return entries, nil
		}
		if err != nil {
			return entries, err
		}
		if len(entries) > secretsEntryLimit {
			return entries, nil
		}
	}
	return entries, nil
}

type secretReadFailure int

const (
	secretReadFilesystem secretReadFailure = iota
	secretReadFileLimit
	secretReadTotalLimit
	secretReadNUL
)

type secretReadError struct {
	kind secretReadFailure
	err  error
}

func (e *secretReadError) Error() string { return "secret read failed" }

func readSecretValue(path string, remaining int64, access secretsAccess) (string, int64, error) {
	if remaining < 0 {
		return "", 0, &secretReadError{kind: secretReadTotalLimit}
	}
	limit := min(secretFileByteLimit, remaining)
	file, err := access.openFile(path)
	if err != nil {
		return "", 0, &secretReadError{kind: secretReadFilesystem, err: err}
	}
	data, readErr := io.ReadAll(io.LimitReader(file, limit+1))
	closeErr := file.Close()
	if readErr != nil {
		return "", 0, &secretReadError{kind: secretReadFilesystem, err: readErr}
	}
	if closeErr != nil {
		return "", 0, &secretReadError{kind: secretReadFilesystem, err: closeErr}
	}
	if int64(len(data)) > limit {
		kind := secretReadFileLimit
		if remaining < secretFileByteLimit {
			kind = secretReadTotalLimit
		}
		return "", 0, &secretReadError{kind: kind}
	}
	if slices.Contains(data, byte(0)) {
		return "", 0, &secretReadError{kind: secretReadNUL}
	}
	value := string(data)
	if strings.HasSuffix(value, "\r\n") {
		value = strings.TrimSuffix(value, "\r\n")
	} else {
		value = strings.TrimSuffix(value, "\n")
	}
	return value, int64(len(data)), nil
}

func validEnvironmentName(name string) bool {
	if name == "" || !asciiEnvironmentFirst(name[0]) {
		return false
	}
	for index := 1; index < len(name); index++ {
		character := name[index]
		if !asciiEnvironmentFirst(character) && (character < '0' || character > '9') {
			return false
		}
	}
	return true
}

func asciiEnvironmentFirst(character byte) bool {
	return character == '_' || character >= 'A' && character <= 'Z' || character >= 'a' && character <= 'z'
}

func cleanAbsolutePath(path string) string {
	absolute, err := filepath.Abs(path)
	if err != nil {
		return filepath.Clean(path)
	}
	return filepath.Clean(absolute)
}

func classifySecretsFilesystemError(err error) Code {
	switch {
	case errors.Is(err, fs.ErrNotExist):
		return CodeSecretsMissing
	case errors.Is(err, fs.ErrPermission):
		return CodeSecretsPermission
	default:
		return CodeSecretsRead
	}
}

func secretReadCode(err error) Code {
	var failure *secretReadError
	if errors.As(err, &failure) {
		switch failure.kind {
		case secretReadFileLimit, secretReadTotalLimit:
			return CodeSecretsLimitExceeded
		case secretReadNUL:
			return CodeSecretsInvalidValue
		case secretReadFilesystem:
			return classifySecretsFilesystemError(failure.err)
		}
	}
	return CodeSecretsRead
}

func secretReadMessage(err error) string {
	var failure *secretReadError
	if errors.As(err, &failure) {
		switch failure.kind {
		case secretReadFileLimit:
			return "secret file exceeds the 1 MiB limit"
		case secretReadTotalLimit:
			return "eligible secret files exceed the 8 MiB total limit"
		case secretReadNUL:
			return "secret file contains a NUL byte"
		}
	}
	return "secret file could not be read"
}

func secretsFailure(code Code, message string) *SecretsError {
	return &SecretsError{diagnostics: []Diagnostic{{Code: code, Severity: SeverityError, Message: message}}}
}