// Package shell implements the Bash and Zsh Shell Target.
package shell

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

	"proxyctl/internal/profile"
	"proxyctl/internal/securefs"
	"proxyctl/internal/target"
)

const (
	integrationStart     = "# >>> proxyctl shell integration >>>"
	integrationEnd       = "# <<< proxyctl shell integration <<<"
	shellRecoveryVersion = 1
)

var proxyVariables = []string{
	"HTTP_PROXY", "http_proxy", "HTTPS_PROXY", "https_proxy",
	"ALL_PROXY", "all_proxy", "NO_PROXY", "no_proxy",
}

type Configuration struct {
	Shell           string
	StartupFile     string
	EnvironmentFile string
	RecoveryFile    string
	OwnFiles        bool
	UID             int
	GID             int
	TrustedRoots    []string
}

// ResolveConfiguration keeps user Shell effects with the invoking user under sudo.
func ResolveConfiguration(environment profile.IdentityEnvironment) (Configuration, error) {
	profileConfiguration, err := profile.ResolveConfiguration(environment)
	if err != nil {
		return Configuration{}, err
	}
	owner := profileConfiguration.Owner
	current, err := environment.CurrentUser()
	if err != nil {
		return Configuration{}, fmt.Errorf("identify effective user: %w", err)
	}
	invokingUser := current.Username != owner.Username
	configDirectory := filepath.Dir(profileConfiguration.Path)
	stateDirectory := ""
	if value, ok := environment.LookupEnv("XDG_STATE_HOME"); ok && filepath.IsAbs(value) {
		if !invokingUser || pathWithin(value, owner.HomeDir) {
			stateDirectory = value
		}
	}
	if stateDirectory == "" {
		stateDirectory = filepath.Join(owner.HomeDir, ".local", "state")
	}
	shellPath, _ := environment.LookupEnv("SHELL")
	startupFile := ""
	switch filepath.Base(shellPath) {
	case "bash":
		startupFile = filepath.Join(owner.HomeDir, ".bashrc")
	case "zsh":
		startupFile = filepath.Join(owner.HomeDir, ".zshrc")
	}
	stateRoot := owner.HomeDir
	if !pathWithin(stateDirectory, owner.HomeDir) {
		stateRoot = stateDirectory
	}
	return Configuration{
		Shell: shellPath, StartupFile: startupFile,
		EnvironmentFile: filepath.Join(configDirectory, "shell.env"),
		RecoveryFile:    filepath.Join(stateDirectory, "proxyctl", "shell.json"),
		OwnFiles:        true, UID: owner.UID, GID: owner.GID,
		TrustedRoots: []string{owner.HomeDir, profileConfiguration.TrustedRoot, stateRoot},
	}, nil
}

func ResolveConfigurationForCurrentProcess() (Configuration, error) {
	return ResolveConfiguration(systemEnvironment{})
}

type systemEnvironment struct{}

func (systemEnvironment) CurrentUser() (profile.UserIdentity, error) {
	return profile.SystemCurrentUser()
}
func (systemEnvironment) LookupUser(name string) (profile.UserIdentity, error) {
	return profile.SystemLookupUser(name)
}
func (systemEnvironment) LookupEnv(name string) (string, bool) { return os.LookupEnv(name) }

func pathWithin(path, parent string) bool {
	relative, err := filepath.Rel(parent, path)
	return err == nil && relative != ".." && !strings.HasPrefix(relative, ".."+string(filepath.Separator))
}

type Environment interface{ LookupEnv(string) (string, bool) }
type MapEnvironment map[string]string

func (m MapEnvironment) LookupEnv(name string) (string, bool) { value, ok := m[name]; return value, ok }

type Ownership struct{ UID, GID int }

type FileSystem interface {
	ReadFile(string) ([]byte, error)
	FileMode(string) (os.FileMode, error)
	AtomicWrite(string, []byte, os.FileMode, *Ownership) error
	Remove(string) error
}

type OSFileSystem struct{ TrustedRoots []string }

func NewOSFileSystem(configuration Configuration) OSFileSystem {
	return OSFileSystem{TrustedRoots: append([]string(nil), configuration.TrustedRoots...)}
}
func (f OSFileSystem) store(path string, owner *Ownership) securefs.Store {
	root := ""
	if len(f.TrustedRoots) == 0 {
		root = string(filepath.Separator)
	}
	for _, candidate := range f.TrustedRoots {
		if pathWithin(path, candidate) && (root == "" || len(filepath.Clean(candidate)) > len(filepath.Clean(root))) {
			root = candidate
		}
	}
	var secureOwner *securefs.Owner
	if owner != nil {
		secureOwner = &securefs.Owner{UID: owner.UID, GID: owner.GID}
	}
	return securefs.Store{TrustedRoot: root, Owner: secureOwner}
}
func (f OSFileSystem) ReadFile(path string) ([]byte, error) { return f.store(path, nil).ReadFile(path) }
func (f OSFileSystem) Remove(path string) error             { return f.store(path, nil).Remove(path) }
func (f OSFileSystem) FileMode(path string) (os.FileMode, error) {
	return f.store(path, nil).FileMode(path)
}
func (f OSFileSystem) AtomicWrite(path string, data []byte, mode os.FileMode, owner *Ownership) error {
	return f.store(path, owner).AtomicWrite(path, data, mode)
}

type recovery struct {
	Version        int               `json:"version"`
	Original       map[string]string `json:"original"`
	OriginalScript *string           `json:"originalScript,omitempty"`
	Fingerprint    string            `json:"fingerprint"`
}

type Adapter struct {
	configuration Configuration
	files         FileSystem
	environment   Environment
}

func New(configuration Configuration, files FileSystem, environment Environment) *Adapter {
	if files == nil {
		configured := NewOSFileSystem(configuration)
		files = configured
	}
	if environment == nil {
		environment = MapEnvironment{}
	}
	return &Adapter{configuration: configuration, files: files, environment: environment}
}

func (a *Adapter) ID() string { return "shell" }
func (a *Adapter) Description() target.Description {
	return target.Description{
		Name:        "Shell",
		Summary:     "Exports proxy variables for commands started by integrated Bash and Zsh sessions.",
		Scope:       "future commands in the integrated Shell; not services, desktop settings, or existing processes",
		Permissions: "write access to the user's Shell files",
		Ownership:   "generated environment fragment; the one-time startup hook remains when management is disabled",
		RestartRisk: "none; the installed wrapper reloads exports into the parent Shell after proxyctl exits",
		Details:     "Affects commands started by the integrated Shell; it does not configure system services, desktop settings, or already-running processes. proxyctl owns a generated environment fragment while its one-time startup hook remains in the user's Shell file. User-file write permission is required; after proxyctl exits, the installed wrapper reloads exports and unsets into the parent Shell.",
	}
}
func (a *Adapter) Availability(context.Context) target.Availability {
	switch filepath.Base(a.configuration.Shell) {
	case "bash":
		return target.Availability{Available: true, Evidence: "Bash detected"}
	case "zsh":
		return target.Availability{Available: true, Evidence: "Zsh detected"}
	default:
		return target.Availability{Evidence: "Shell Target requires Bash or Zsh; neither was detected"}
	}
}
func (a *Adapter) Confirmation(bool) string { return "" }
func (a *Adapter) EnvironmentPath() string  { return a.configuration.EnvironmentFile }
func (a *Adapter) RecoveryPath() string     { return a.configuration.RecoveryFile }
func (a *Adapter) StartupPath() string      { return a.configuration.StartupFile }

// DiagnosticChecks performs no writes or command execution.
func (a *Adapter) DiagnosticChecks(_ context.Context, _ *profile.Profile) []target.Check {
	return []target.Check{
		{Name: "required commands", OK: true, Evidence: "Shell Target requires no external commands"},
		target.ReadOnlyWriteAuthority(a.configuration.EnvironmentFile, a.configuration.RecoveryFile),
	}
}

func (a *Adapter) Detect(ctx context.Context, active *profile.Profile) target.Detection {
	inspection, err := a.inspect(active)
	return target.Detection{Availability: a.Availability(ctx), Inspection: inspection, Err: redactError(err, active)}
}

// Inspect retains the maintenance contract: it always returns the safest
// state supported by the evidence. Detect adds the suppressed read error so an
// interactive check cannot present unreadable state as a successful result.
func (a *Adapter) Inspect(_ context.Context, active *profile.Profile) target.Inspection {
	inspection, _ := a.inspect(active)
	return inspection
}

func (a *Adapter) inspect(active *profile.Profile) (target.Inspection, error) {
	metadata, managed, metadataErr := a.readRecovery()
	generated, generatedErr := a.files.ReadFile(a.configuration.EnvironmentFile)
	if managed || (metadataErr != nil && !errors.Is(metadataErr, fs.ErrNotExist)) {
		if metadataErr != nil {
			return target.Inspection{State: target.Drifted, Evidence: "managed Shell recovery metadata cannot be read"}, fmt.Errorf("inspect Shell recovery metadata: %w", metadataErr)
		}
		if generatedErr != nil {
			return target.Inspection{State: target.Drifted, Evidence: "managed Shell environment is missing or unreadable"}, fmt.Errorf("inspect managed Shell environment: %w", generatedErr)
		}
		if active != nil && fingerprint(generated) == metadata.Fingerprint && fingerprint(renderEnabled(*active)) == metadata.Fingerprint {
			return target.Inspection{State: target.Enabled, Evidence: "managed Shell environment matches the Active Profile"}, nil
		}
		return target.Inspection{State: target.Drifted, Evidence: "managed Shell environment does not match the Active Profile"}, nil
	}
	if generatedErr != nil && !errors.Is(generatedErr, fs.ErrNotExist) {
		return target.Inspection{State: target.Disabled, Evidence: "Shell environment could not be inspected"}, fmt.Errorf("inspect Shell environment: %w", generatedErr)
	}
	if generatedErr == nil && recognizesProxy(generated) {
		return target.Inspection{State: target.External, Evidence: "recognized proxy assignments exist in the Shell environment file"}, nil
	}
	for _, name := range proxyVariables {
		if value, ok := a.environment.LookupEnv(name); ok && value != "" {
			return target.Inspection{State: target.External, Evidence: "recognized proxy variable " + name + " exists"}, nil
		}
	}
	return target.Inspection{State: target.Disabled, Evidence: "no recognized Shell proxy configuration detected"}, nil
}

func (a *Adapter) SetDesired(ctx context.Context, enabled bool, active *profile.Profile) target.OperationResult {
	// Enabling requires a supported current Shell, but disabling must remain
	// available so reset can remove managed state after the user's Shell changes.
	if enabled && !a.Availability(ctx).Available {
		return target.OperationResult{Inspection: a.Inspect(ctx, active), Err: errors.New("Shell Target is unavailable: Bash or Zsh was not detected")}
	}
	if enabled && active == nil {
		return target.OperationResult{Inspection: a.Inspect(ctx, active), Err: errors.New("no Active Profile; open Profile management to create and activate one")}
	}
	var err error
	if enabled {
		err = a.enable(*active)
	} else {
		err = a.disable()
	}
	inspection := a.Inspect(ctx, active)
	if err != nil {
		err = redactError(err, active)
	}
	return target.OperationResult{Inspection: inspection, Err: err}
}

func (a *Adapter) enable(active profile.Profile) error {
	normalized, err := profile.ValidateAndNormalize(active)
	if err != nil {
		return err
	}
	metadata, managed, err := a.readRecovery()
	if err != nil && !errors.Is(err, fs.ErrNotExist) {
		return fmt.Errorf("read Shell recovery metadata: %w", err)
	}
	if !managed {
		metadata.Version = shellRecoveryVersion
		if existing, readErr := a.files.ReadFile(a.configuration.EnvironmentFile); readErr == nil && recognizesProxy(existing) {
			original := string(existing)
			metadata.OriginalScript = &original
		} else {
			metadata.Original = make(map[string]string)
			for _, name := range proxyVariables {
				if value, ok := a.environment.LookupEnv(name); ok {
					metadata.Original[name] = value
				}
			}
		}
	}
	generated := renderEnabled(normalized)
	metadata.Fingerprint = fingerprint(generated)
	data, err := json.MarshalIndent(metadata, "", "  ")
	if err != nil {
		return err
	}
	// The true original must be durable before the managed environment becomes
	// visible. A retry then reuses this metadata instead of snapshotting its own
	// partially applied output as External state.
	if err := a.writeOwned(a.configuration.RecoveryFile, append(data, '\n')); err != nil {
		return fmt.Errorf("persist Shell recovery metadata before changing environment: %w", err)
	}
	if err := a.writeOwned(a.configuration.EnvironmentFile, generated); err != nil {
		return fmt.Errorf("write Shell environment after recovery metadata persisted: %w", err)
	}
	return nil
}

func (a *Adapter) disable() error {
	metadata, managed, err := a.readRecovery()
	if errors.Is(err, fs.ErrNotExist) || !managed {
		return nil
	}
	if err != nil {
		return fmt.Errorf("read Shell recovery metadata: %w", err)
	}
	restored := renderRestored(metadata.Original)
	if metadata.OriginalScript != nil {
		restored = []byte(*metadata.OriginalScript)
	}
	if err := a.writeOwned(a.configuration.EnvironmentFile, restored); err != nil {
		return fmt.Errorf("restore Shell environment: %w", err)
	}
	if err := a.files.Remove(a.configuration.RecoveryFile); err != nil && !errors.Is(err, fs.ErrNotExist) {
		return fmt.Errorf("remove Shell recovery metadata after environment changed: %w", err)
	}
	return nil
}

func (a *Adapter) readRecovery() (recovery, bool, error) {
	data, err := a.files.ReadFile(a.configuration.RecoveryFile)
	if err != nil {
		return recovery{}, false, err
	}
	var fields map[string]json.RawMessage
	if err := json.Unmarshal(data, &fields); err != nil {
		return recovery{}, true, err
	}
	if fields == nil {
		return recovery{}, true, errors.New("Shell recovery metadata must be a JSON object")
	}
	var value recovery
	if err := json.Unmarshal(data, &value); err != nil {
		return recovery{}, true, err
	}
	if err := validateRecovery(value, fields); err != nil {
		return recovery{}, true, err
	}
	return value, true, nil
}

func validateRecovery(value recovery, fields map[string]json.RawMessage) error {
	for _, name := range []string{"version", "original", "fingerprint"} {
		if _, present := fields[name]; !present {
			return fmt.Errorf("Shell recovery metadata is missing required field %q", name)
		}
	}
	if value.Version != shellRecoveryVersion {
		return fmt.Errorf("unsupported Shell recovery metadata version %d", value.Version)
	}
	decoded, err := hex.DecodeString(value.Fingerprint)
	if err != nil || len(decoded) != sha256.Size {
		return errors.New("Shell recovery metadata has an invalid fingerprint")
	}
	_, hasOriginalScript := fields["originalScript"]
	if hasOriginalScript {
		if value.OriginalScript == nil || value.Original != nil || len(*value.OriginalScript) == 0 || !recognizesProxy([]byte(*value.OriginalScript)) {
			return errors.New("Shell recovery metadata has inconsistent original script state")
		}
		return nil
	}
	if value.Original == nil {
		return errors.New("Shell recovery metadata is missing the original environment snapshot")
	}
	for name := range value.Original {
		known := false
		for _, candidate := range proxyVariables {
			known = known || name == candidate
		}
		if !known {
			return fmt.Errorf("Shell recovery metadata contains unsupported variable %q", name)
		}
	}
	return nil
}
func (a *Adapter) ownership() *Ownership {
	if !a.configuration.OwnFiles {
		return nil
	}
	return &Ownership{UID: a.configuration.UID, GID: a.configuration.GID}
}
func (a *Adapter) writeOwned(path string, data []byte) error {
	return a.files.AtomicWrite(path, data, 0o600, a.ownership())
}

func renderEnabled(p profile.Profile) []byte {
	values := map[string]string{"HTTP_PROXY": p.HTTPURL, "http_proxy": p.HTTPURL, "HTTPS_PROXY": p.HTTPSURL, "https_proxy": p.HTTPSURL, "ALL_PROXY": p.AllURL, "all_proxy": p.AllURL, "NO_PROXY": strings.Join(p.Bypass, ","), "no_proxy": strings.Join(p.Bypass, ",")}
	var output strings.Builder
	output.WriteString("# Generated by proxyctl. Do not edit.\n")
	for _, name := range proxyVariables {
		if value := values[name]; value != "" {
			fmt.Fprintf(&output, "export %s=%s\n", name, shellQuote(value))
		} else {
			fmt.Fprintf(&output, "unset %s\n", name)
		}
	}
	return []byte(output.String())
}
func renderRestored(original map[string]string) []byte {
	var output strings.Builder
	output.WriteString("# Generated by proxyctl. Restores the environment present before enable.\n")
	var unset []string
	for _, name := range proxyVariables {
		if value, ok := original[name]; ok {
			fmt.Fprintf(&output, "export %s=%s\n", name, shellQuote(value))
		} else {
			unset = append(unset, name)
		}
	}
	if len(unset) > 0 {
		fmt.Fprintf(&output, "unset %s\n", strings.Join(unset, " "))
	}
	return []byte(output.String())
}
func shellQuote(value string) string { return "'" + strings.ReplaceAll(value, "'", "'\\''") + "'" }
func fingerprint(data []byte) string { sum := sha256.Sum256(data); return hex.EncodeToString(sum[:]) }
func recognizesProxy(data []byte) bool {
	supported := make(map[string]bool, len(proxyVariables))
	for _, name := range proxyVariables {
		supported[name] = true
	}
	for _, raw := range strings.Split(string(data), "\n") {
		line := strings.TrimSpace(raw)
		if line == "" || strings.HasPrefix(line, "#") {
			continue
		}
		if strings.HasPrefix(line, "export") {
			if len(line) == len("export") || (line[len("export")] != ' ' && line[len("export")] != '\t') {
				continue
			}
			line = strings.TrimSpace(line[len("export"):])
		}
		name, _, found := strings.Cut(line, "=")
		if !found || strings.TrimSpace(name) != name || !supported[name] {
			continue
		}
		return true
	}
	return false
}

type redactedError struct {
	message string
	class   error
}

func (e *redactedError) Error() string        { return e.message }
func (e *redactedError) Is(target error) bool { return e.class != nil && errors.Is(e.class, target) }

func redactError(err error, active *profile.Profile) error {
	if err == nil {
		return nil
	}
	message := profile.RedactText(err.Error())
	class := classifySafeError(err)
	if active == nil {
		return &redactedError{message: message, class: class}
	}
	for _, raw := range []string{active.SingleURL, active.HTTPURL, active.HTTPSURL, active.AllURL} {
		if raw == "" {
			continue
		}
		message = strings.ReplaceAll(message, raw, profile.ObscureURL(raw))
		if parsed, parseErr := url.Parse(raw); parseErr == nil && parsed.User != nil {
			if password, ok := parsed.User.Password(); ok && password != "" {
				message = strings.ReplaceAll(message, password, "REDACTED")
			}
		}
	}
	return &redactedError{message: message, class: class}
}

func classifySafeError(err error) error {
	for _, safe := range []error{os.ErrPermission, fs.ErrNotExist, fs.ErrExist, context.Canceled, context.DeadlineExceeded} {
		if errors.Is(err, safe) {
			return safe
		}
	}
	return nil
}

func (a *Adapter) Install(_ context.Context, executable string) error {
	contents, err := a.files.ReadFile(a.configuration.StartupFile)
	if err != nil && !errors.Is(err, fs.ErrNotExist) {
		return fmt.Errorf("read Shell startup file: %w", err)
	}
	cleaned := removeIntegration(string(contents))
	if strings.Contains(cleaned, integrationStart) || strings.Contains(cleaned, integrationEnd) {
		return errors.New("Shell startup file contains malformed proxyctl integration markers; no changes made")
	}
	if cleaned != "" && !strings.HasSuffix(cleaned, "\n") {
		cleaned += "\n"
	}
	block := integrationStart + "\n" +
		"[ -r " + shellQuote(a.configuration.EnvironmentFile) + " ] && . " + shellQuote(a.configuration.EnvironmentFile) + "\n" +
		"proxyctl() {\n" +
		"  command " + shellQuote(executable) + " \"$@\"\n" +
		"  proxyctl_status=$?\n" +
		"  [ -r " + shellQuote(a.configuration.EnvironmentFile) + " ] && . " + shellQuote(a.configuration.EnvironmentFile) + "\n" +
		"  return $proxyctl_status\n" +
		"}\n" + integrationEnd + "\n"
	mode := os.FileMode(0o644)
	if existingMode, modeErr := a.files.FileMode(a.configuration.StartupFile); modeErr == nil {
		mode = existingMode
	}
	if err := a.files.AtomicWrite(a.configuration.StartupFile, []byte(cleaned+block), mode, a.ownership()); err != nil {
		return fmt.Errorf("install Shell integration: %w", err)
	}
	return nil
}
func (a *Adapter) Uninstall(_ context.Context) error {
	contents, err := a.files.ReadFile(a.configuration.StartupFile)
	if errors.Is(err, fs.ErrNotExist) {
		return nil
	}
	if err != nil {
		return fmt.Errorf("read Shell startup file: %w", err)
	}
	cleaned := removeIntegration(string(contents))
	if strings.Contains(cleaned, integrationStart) || strings.Contains(cleaned, integrationEnd) {
		return errors.New("Shell startup file contains malformed proxyctl integration markers; no changes made")
	}
	if cleaned == string(contents) {
		return nil
	}
	mode := os.FileMode(0o644)
	if existingMode, modeErr := a.files.FileMode(a.configuration.StartupFile); modeErr == nil {
		mode = existingMode
	}
	if err := a.files.AtomicWrite(a.configuration.StartupFile, []byte(cleaned), mode, a.ownership()); err != nil {
		return fmt.Errorf("uninstall Shell integration: %w", err)
	}
	return nil
}
func removeIntegration(contents string) string {
	for {
		start := strings.Index(contents, integrationStart)
		if start < 0 {
			return contents
		}
		endRelative := strings.Index(contents[start:], integrationEnd)
		if endRelative < 0 {
			return contents
		}
		end := start + endRelative + len(integrationEnd)
		if end < len(contents) && contents[end] == '\n' {
			end++
		}
		contents = contents[:start] + contents[end:]
	}
}