// Package apt implements the persistent Debian-family APT Target.
package apt

import (
	"bufio"
	"context"
	"errors"
	"fmt"
	"io/fs"
	"net"
	"net/url"
	"os"
	"os/exec"
	"path/filepath"
	"sort"
	"strings"

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

const (
	overlayName   = "99proxyctl"
	overlayHeader = "// Generated by proxyctl. Do not edit.\n"
)

// Configuration names the Debian marker and the isolated APT configuration
// fragment. TrustedRoot anchors all mutations and is injectable for tests.
type Configuration struct {
	DebianVersionFile string
	ConfigDirectory   string
	OverlayFile       string
	TrustedRoot       string
}

func DefaultConfiguration() Configuration {
	return Configuration{
		DebianVersionFile: "/etc/debian_version",
		ConfigDirectory:   "/etc/apt/apt.conf.d",
		OverlayFile:       "/etc/apt/apt.conf.d/" + overlayName,
		TrustedRoot:       "/",
	}
}

// FileSystem is the mutation seam used by the Adapter. Availability probes are
// read-only os.Stat calls, while writes remain descriptor-anchored in securefs.
type FileSystem interface {
	ReadFile(string) ([]byte, error)
	AtomicWrite(string, []byte, os.FileMode) error
	Remove(string) error
}

type OSFileSystem struct{ TrustedRoot string }

func NewOSFileSystem(trustedRoot string) OSFileSystem { return OSFileSystem{TrustedRoot: trustedRoot} }
func (f OSFileSystem) store() securefs.Store          { return securefs.Store{TrustedRoot: f.TrustedRoot} }
func (f OSFileSystem) ReadFile(path string) ([]byte, error) {
	return f.store().ReadFile(path)
}
func (f OSFileSystem) AtomicWrite(path string, data []byte, mode os.FileMode) error {
	return f.store().AtomicWrite(path, data, mode)
}
func (f OSFileSystem) Remove(path string) error { return f.store().Remove(path) }

// Runner isolates apt-config discovery and execution from adapter tests.
type Runner interface {
	LookPath(string) (string, error)
	Output(context.Context, string, ...string) ([]byte, error)
}

type systemRunner struct{}

func (systemRunner) LookPath(name string) (string, error) { return exec.LookPath(name) }
func (systemRunner) Output(ctx context.Context, name string, args ...string) ([]byte, error) {
	return exec.CommandContext(ctx, name, args...).Output()
}

type Adapter struct {
	configuration Configuration
	files         FileSystem
	runner        Runner
}

func New(configuration Configuration, files FileSystem, runner Runner) *Adapter {
	defaults := DefaultConfiguration()
	if configuration.DebianVersionFile == "" {
		configuration.DebianVersionFile = defaults.DebianVersionFile
	}
	if configuration.ConfigDirectory == "" {
		configuration.ConfigDirectory = defaults.ConfigDirectory
	}
	if configuration.OverlayFile == "" {
		configuration.OverlayFile = filepath.Join(configuration.ConfigDirectory, overlayName)
	}
	if configuration.TrustedRoot == "" {
		configuration.TrustedRoot = defaults.TrustedRoot
	}
	if files == nil {
		files = NewOSFileSystem(configuration.TrustedRoot)
	}
	if runner == nil {
		runner = systemRunner{}
	}
	return &Adapter{configuration: configuration, files: files, runner: runner}
}

func (a *Adapter) ID() string { return "apt" }
func (a *Adapter) Description() target.Description {
	return target.Description{
		Name:    "APT",
		Summary: "Persistently configures APT proxying across Shell and privilege boundaries.",
		Details: "APT supports proxy environment variables; this Target affects persistent APT package operations across Shell and privilege boundaries; it does not change Shell, desktop, Docker, or other application proxy settings. proxyctl owns only an isolated apt.conf.d overlay, leaving earlier configuration underneath so disabling restores any External setting. Writing /etc/apt normally requires pre-existing root authority; proxyctl never escalates privileges, and no service restart is performed.",
	}
}

func (a *Adapter) Confirmation(bool) string { return "" }

func (a *Adapter) Availability(ctx context.Context) target.Availability {
	marker, err := os.Stat(a.configuration.DebianVersionFile)
	if err != nil || !marker.Mode().IsRegular() {
		return target.Availability{Evidence: "Debian-family marker /etc/debian_version was not detected"}
	}
	directory, err := os.Stat(a.configuration.ConfigDirectory)
	if err != nil || !directory.IsDir() {
		return target.Availability{Evidence: "APT configuration directory apt.conf.d was not detected"}
	}
	command, err := a.runner.LookPath("apt-config")
	if err != nil {
		return target.Availability{Evidence: "Debian APT tool apt-config was not detected"}
	}
	if _, err := a.runner.Output(ctx, command, "dump"); err != nil {
		return target.Availability{Evidence: "apt-config could not inspect effective APT configuration"}
	}
	return target.Availability{Available: true, Evidence: "Debian marker, apt-config, and apt.conf.d configuration capability detected"}
}

func (a *Adapter) OverlayPath() string { return a.configuration.OverlayFile }

func (a *Adapter) Inspect(ctx context.Context, active *profile.Profile) target.Inspection {
	inspection, _ := a.inspect(ctx, active)
	return inspection
}

func (a *Adapter) inspect(ctx context.Context, active *profile.Profile) (target.Inspection, error) {
	overlay, overlayErr := a.files.ReadFile(a.configuration.OverlayFile)
	managed := overlayErr == nil && isOwnedOverlay(overlay)
	if overlayErr != nil && !errors.Is(overlayErr, fs.ErrNotExist) {
		return target.Inspection{State: target.Drifted, Evidence: "managed APT overlay cannot be read"}, fmt.Errorf("read managed APT overlay: %w", overlayErr)
	}
	effective, dumpErr := a.dump(ctx)
	if dumpErr != nil {
		if managed {
			return target.Inspection{State: target.Drifted, Evidence: "managed APT overlay exists but effective configuration cannot be inspected"}, dumpErr
		}
		return target.Inspection{State: target.Disabled, Evidence: "effective APT configuration could not be positively inspected"}, dumpErr
	}
	effectiveValues := parseConfiguration(effective)
	if managed {
		managedValues := parseConfiguration(overlay)
		if len(managedValues) == 0 {
			return target.Inspection{State: target.Drifted, Evidence: "managed APT overlay contains no recognized proxy settings"}, nil
		}
		if active == nil {
			return target.Inspection{State: target.Drifted, Evidence: "managed APT overlay exists without an Active Profile"}, nil
		}
		desired, err := translate(*active)
		if err == nil {
			coverExistingHostRules(desired.settings, effectiveValues)
		}
		if err == nil && equalSettings(managedValues, desired.settings) && equalSettings(effectiveValues, desired.settings) {
			return target.Inspection{State: target.Enabled, Evidence: "effective managed APT values match the Active Profile"}, nil
		}
		return target.Inspection{State: target.Drifted, Evidence: "effective managed APT values do not match the Active Profile"}, nil
	}
	if key, ok := recognizedProxy(effectiveValues); ok {
		return target.Inspection{State: target.External, Evidence: "recognized non-managed APT proxy setting " + key + " is effective"}, nil
	}
	return target.Inspection{State: target.Disabled, Evidence: "no recognized effective APT proxy configuration detected"}, nil
}

func (a *Adapter) SetDesired(ctx context.Context, enabled bool, active *profile.Profile) target.OperationResult {
	if !a.Availability(ctx).Available {
		return target.OperationResult{Inspection: a.Inspect(ctx, active), Err: errors.New("APT Target is unavailable: Debian APT tooling or configuration capability 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 mutationErr error
	if enabled {
		if existing, err := a.files.ReadFile(a.configuration.OverlayFile); err == nil && !isOwnedOverlay(existing) {
			return target.OperationResult{Inspection: a.Inspect(ctx, active), Err: errors.New("APT overlay path already contains configuration not owned by proxyctl; no changes made")}
		} else if err != nil && !errors.Is(err, fs.ErrNotExist) {
			return target.OperationResult{Inspection: a.Inspect(ctx, active), Err: redactError(fmt.Errorf("inspect managed APT overlay before writing: %w", err), active)}
		}
		translated, err := translate(*active)
		if err != nil {
			return target.OperationResult{Inspection: a.Inspect(ctx, active), Err: redactError(err, active)}
		}
		effective, err := a.dump(ctx)
		if err != nil {
			return target.OperationResult{Inspection: a.Inspect(ctx, active), Err: redactError(fmt.Errorf("inspect effective APT configuration before mutation: %w", err), active)}
		}
		coverExistingHostRules(translated.settings, parseConfiguration(effective))
		translated.rendered = render(translated.settings)
		mutationErr = a.files.AtomicWrite(a.configuration.OverlayFile, translated.rendered, 0o600)
		if mutationErr != nil {
			mutationErr = fmt.Errorf("write managed APT overlay: %w", mutationErr)
		}
	} else {
		existing, err := a.files.ReadFile(a.configuration.OverlayFile)
		switch {
		case errors.Is(err, fs.ErrNotExist):
		case err != nil:
			mutationErr = fmt.Errorf("inspect managed APT overlay before removal: %w", err)
		case !isOwnedOverlay(existing):
			// A path collision is user-owned configuration, not managed state.
		default:
			if err := a.files.Remove(a.configuration.OverlayFile); err != nil && !errors.Is(err, fs.ErrNotExist) {
				mutationErr = fmt.Errorf("remove managed APT overlay: %w", err)
			}
		}
	}
	inspection, inspectErr := a.inspect(ctx, active)
	if mutationErr == nil && inspectErr != nil {
		mutationErr = fmt.Errorf("re-inspect effective APT configuration after mutation: %w", inspectErr)
	}
	if mutationErr == nil && enabled && inspection.State != target.Enabled {
		mutationErr = errors.New("managed APT overlay was written but did not become the effective Active Profile configuration")
	}
	if mutationErr == nil && !enabled && inspection.State == target.Drifted {
		mutationErr = errors.New("managed APT overlay removal did not complete")
	}
	return target.OperationResult{Inspection: inspection, Err: redactError(mutationErr, active)}
}

func (a *Adapter) dump(ctx context.Context) ([]byte, error) {
	command, err := a.runner.LookPath("apt-config")
	if err != nil {
		return nil, fmt.Errorf("locate apt-config: %w", err)
	}
	output, err := a.runner.Output(ctx, command, "dump")
	if err != nil {
		return nil, fmt.Errorf("run apt-config dump: %w", err)
	}
	return output, nil
}

type translation struct {
	settings map[string]string
	rendered []byte
}

func translate(input profile.Profile) (translation, error) {
	p, err := profile.ValidateAndNormalize(input)
	if err != nil {
		return translation{}, err
	}
	httpValue, httpsValue := p.HTTPURL, p.HTTPSURL
	if httpValue == "" {
		httpValue = p.AllURL
	}
	if httpsValue == "" {
		httpsValue = p.AllURL
	}
	for _, candidate := range []struct {
		field, value string
	}{{"HTTP proxy", p.HTTPURL}, {"HTTPS proxy", p.HTTPSURL}, {"ALL/SOCKS proxy", p.AllURL}} {
		if candidate.value == "" {
			continue
		}
		parsed, _ := url.Parse(candidate.value)
		if parsed.Scheme != "http" && parsed.Scheme != "https" && parsed.Scheme != "socks5h" {
			return translation{}, fmt.Errorf("APT cannot translate %s value %q: proxy scheme %q is incompatible", candidate.field, profile.ObscureURL(candidate.value), parsed.Scheme)
		}
	}
	settings := map[string]string{
		"Acquire::http::Proxy":  valueOrDirect(httpValue),
		"Acquire::https::Proxy": valueOrDirect(httpsValue),
	}
	for _, bypass := range p.Bypass {
		if strings.HasPrefix(bypass, ".") || strings.Contains(bypass, "/") || strings.Contains(bypass, ":") {
			return translation{}, fmt.Errorf("APT cannot translate Bypass entry %q; only exact hostnames and IPv4 addresses are supported", bypass)
		}
		if net.ParseIP(bypass) == nil && strings.ContainsAny(bypass, " \t\r\n;\"") {
			return translation{}, fmt.Errorf("APT cannot translate Bypass entry %q", bypass)
		}
		settings["Acquire::http::Proxy::"+bypass] = "DIRECT"
		settings["Acquire::https::Proxy::"+bypass] = "DIRECT"
	}
	return translation{settings: settings, rendered: render(settings)}, nil
}

func valueOrDirect(value string) string {
	if value == "" {
		return "DIRECT"
	}
	return value
}

var settingOrder = []string{"Acquire::http::Proxy", "Acquire::https::Proxy"}

func render(settings map[string]string) []byte {
	var output strings.Builder
	output.WriteString(overlayHeader)
	for _, key := range settingOrder {
		if value, ok := settings[key]; ok {
			fmt.Fprintf(&output, "%s \"%s\";\n", key, aptQuote(value))
		}
	}
	for _, protocol := range []string{"http", "https"} {
		prefix := "Acquire::" + protocol + "::Proxy::"
		var keys []string
		for key := range settings {
			if strings.HasPrefix(key, prefix) {
				keys = append(keys, key)
			}
		}
		sort.Strings(keys)
		for _, key := range keys {
			fmt.Fprintf(&output, "%s \"%s\";\n", key, aptQuote(settings[key]))
		}
	}
	return []byte(output.String())
}

func isOwnedOverlay(data []byte) bool { return strings.HasPrefix(string(data), overlayHeader) }

func aptQuote(value string) string {
	return strings.NewReplacer("\\", "\\\\", "\"", "\\\"").Replace(value)
}

func parseConfiguration(data []byte) map[string]string {
	settings := make(map[string]string)
	scanner := bufio.NewScanner(strings.NewReader(string(data)))
	for scanner.Scan() {
		line := strings.TrimSpace(scanner.Text())
		if line == "" || strings.HasPrefix(line, "//") || strings.HasPrefix(line, "#") {
			continue
		}
		key, rest, ok := strings.Cut(line, " ")
		if !ok {
			key, rest, ok = strings.Cut(line, "\t")
		}
		key, recognized := canonicalKey(key)
		if !ok || !recognized {
			continue
		}
		rest = strings.TrimSpace(rest)
		if len(rest) < 3 || rest[0] != '"' || rest[len(rest)-1] != ';' {
			continue
		}
		quoted := strings.TrimSpace(rest[:len(rest)-1])
		if len(quoted) < 2 || quoted[len(quoted)-1] != '"' {
			continue
		}
		settings[key] = aptUnquote(quoted[1 : len(quoted)-1])
	}
	return settings
}

func canonicalKey(key string) (string, bool) {
	parts := strings.Split(key, "::")
	if len(parts) < 3 || !strings.EqualFold(parts[0], "Acquire") ||
		(!strings.EqualFold(parts[1], "http") && !strings.EqualFold(parts[1], "https")) ||
		!strings.EqualFold(parts[2], "Proxy") {
		return "", false
	}
	canonical := "Acquire::" + strings.ToLower(parts[1]) + "::Proxy"
	if len(parts) == 3 {
		return canonical, true
	}
	host := strings.Join(parts[3:], "::")
	if host == "" {
		return "", false
	}
	return canonical + "::" + strings.ToLower(host), true
}

func recognizedProxy(settings map[string]string) (string, bool) {
	keys := make([]string, 0, len(settings))
	for key := range settings {
		keys = append(keys, key)
	}
	sort.Strings(keys)
	for _, key := range keys {
		value := settings[key]
		if value != "" && !strings.EqualFold(value, "DIRECT") && !strings.EqualFold(value, "false") {
			return key, true
		}
	}
	return "", false
}

func aptUnquote(value string) string {
	var output strings.Builder
	escaped := false
	for _, r := range value {
		if escaped {
			output.WriteRune(r)
			escaped = false
		} else if r == '\\' {
			escaped = true
		} else {
			output.WriteRune(r)
		}
	}
	if escaped {
		output.WriteByte('\\')
	}
	return output.String()
}

func coverExistingHostRules(desired, effective map[string]string) {
	for key := range effective {
		var protocol, prefix string
		switch {
		case strings.HasPrefix(key, "Acquire::http::Proxy::"):
			protocol, prefix = "http", "Acquire::http::Proxy::"
		case strings.HasPrefix(key, "Acquire::https::Proxy::"):
			protocol, prefix = "https", "Acquire::https::Proxy::"
		default:
			continue
		}
		if _, alreadyCovered := desired[key]; alreadyCovered {
			continue
		}
		value := desired["Acquire::"+protocol+"::Proxy"]
		if value == "" {
			value = "DIRECT"
		}
		// A later fragment can shadow a more-specific earlier host rule only by
		// repeating that host key. The earlier file itself remains untouched and
		// becomes effective again when the owned overlay is removed.
		desired[prefix+strings.TrimPrefix(key, prefix)] = value
	}
}

func equalSettings(left, right map[string]string) bool {
	if len(left) != len(right) {
		return false
	}
	for key, value := range left {
		if right[key] != value {
			return false
		}
	}
	return true
}

type redactedError struct {
	message string
	class   error
}

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

func redactError(err error, active *profile.Profile) error {
	if err == nil {
		return nil
	}
	message := profile.RedactText(err.Error())
	if active != nil {
		for _, raw := range []string{active.SingleURL, active.HTTPURL, active.HTTPSURL, active.AllURL} {
			if raw != "" {
				message = strings.ReplaceAll(message, raw, profile.ObscureURL(raw))
			}
		}
	}
	var class error
	for _, safe := range []error{os.ErrPermission, fs.ErrNotExist, fs.ErrExist, context.Canceled, context.DeadlineExceeded} {
		if errors.Is(err, safe) {
			class = safe
			break
		}
	}
	return &redactedError{message: message, class: class}
}