// Package deploymentconfig loads the daemon's explicit local deployment configuration.
// It never infers deployment type, executable paths, unit names, slot paths, or endpoints.
package deploymentconfig

import (
	"bytes"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"sort"
	"strings"

	"github.com/pelletier/go-toml/v2"
)

const (
	// DefaultPath is the only default location used by the daemon entrypoint.
	DefaultPath = "/etc/yms-daemon/yms-daemon.toml"

	BackendTypeNative = "native"

	BackendPort8080 = 8080
	BackendPort8081 = 8081
)

const (
	nativeReleaseDir    = "/home/yms/lib/releases"
	nativeActiveJAR     = "/home/yms/lib/glory-soft-yms.jar"
	nativeUnit8080      = "yms-backend@8080.service"
	nativeUnit8081      = "yms-backend@8081.service"
	nativeSlotJAR8080   = "/home/yms/lib/glory-soft-yms-8080.jar"
	nativeSlotJAR8081   = "/home/yms/lib/glory-soft-yms-8081.jar"
	nativeHealthURL8080 = "http://127.0.0.1:8080/yms/actuator/health"
	nativeHealthURL8081 = "http://127.0.0.1:8081/yms/actuator/health"
)

// Config is the complete local deployment configuration currently understood by the daemon.
type Config struct {
	Backend Backend `toml:"backend"`
}

// Backend describes the explicitly selected backend runtime and its native blue/green slots.
type Backend struct {
	Type          string       `toml:"type"`
	ReleaseDir    string       `toml:"release_dir"`
	ActiveJAR     string       `toml:"active_jar"`
	SystemctlPath string       `toml:"systemctl_path"`
	Slot          BackendSlots `toml:"slot"`
}

// BackendSlots lists the only native backend ports supported by the current deployment contract.
type BackendSlots struct {
	Port8080 BackendSlot `toml:"8080"`
	Port8081 BackendSlot `toml:"8081"`
}

// BackendSlot contains values that are passed to the native backend executor without derivation.
type BackendSlot struct {
	Unit           string `toml:"unit"`
	JAR            string `toml:"jar"`
	HealthEndpoint string `toml:"health_endpoint"`
}

// Load opens path, performs strict TOML decoding, and validates the native backend contract.
func Load(path string) (Config, error) {
	if err := validateAbsolutePath("deployment configuration", path); err != nil {
		return Config{}, err
	}

	file, err := os.Open(path)
	if err != nil {
		return Config{}, fmt.Errorf("open deployment configuration %s: %w", path, err)
	}
	defer file.Close()

	info, err := file.Stat()
	if err != nil {
		return Config{}, fmt.Errorf("inspect deployment configuration %s: %w", path, err)
	}
	if !info.Mode().IsRegular() {
		return Config{}, fmt.Errorf("deployment configuration is not a regular file: %s", path)
	}

	document, err := io.ReadAll(file)
	if err != nil {
		return Config{}, fmt.Errorf("read deployment configuration %s: %w", path, err)
	}
	if err := validateExactDocumentKeys(document); err != nil {
		return Config{}, fmt.Errorf("decode deployment configuration %s: %w", path, err)
	}

	var config Config
	if err := toml.NewDecoder(bytes.NewReader(document)).DisallowUnknownFields().Decode(&config); err != nil {
		return Config{}, fmt.Errorf("decode deployment configuration %s: %w", path, err)
	}
	if err := config.Validate(); err != nil {
		return Config{}, fmt.Errorf("validate deployment configuration %s: %w", path, err)
	}
	return config, nil
}

func validateExactDocumentKeys(document []byte) error {
	var root map[string]any
	if err := toml.Unmarshal(document, &root); err != nil {
		return err
	}
	if err := rejectUnknownKeys(root, "", "backend"); err != nil {
		return err
	}
	backend, err := exactTable(root, "", "backend")
	if err != nil {
		return err
	}
	if err := rejectUnknownKeys(backend, "backend", "type", "release_dir", "active_jar", "systemctl_path", "slot"); err != nil {
		return err
	}
	slots, err := exactTable(backend, "backend", "slot")
	if err != nil {
		return err
	}
	if err := rejectUnknownKeys(slots, "backend.slot", "8080", "8081"); err != nil {
		return err
	}
	for _, port := range []string{"8080", "8081"} {
		slot, err := exactTable(slots, "backend.slot", port)
		if err != nil {
			return err
		}
		if err := rejectUnknownKeys(slot, "backend.slot."+port, "unit", "jar", "health_endpoint"); err != nil {
			return err
		}
	}
	return nil
}

func exactTable(table map[string]any, parent string, key string) (map[string]any, error) {
	value, found := table[key]
	field := key
	if parent != "" {
		field = parent + "." + key
	}
	if !found {
		return nil, fmt.Errorf("%s table is required", field)
	}
	nested, ok := value.(map[string]any)
	if !ok {
		return nil, fmt.Errorf("%s must be a table", field)
	}
	return nested, nil
}

func rejectUnknownKeys(table map[string]any, parent string, allowed ...string) error {
	known := make(map[string]struct{}, len(allowed))
	for _, key := range allowed {
		known[key] = struct{}{}
	}
	keys := make([]string, 0, len(table))
	for key := range table {
		keys = append(keys, key)
	}
	sort.Strings(keys)
	for _, key := range keys {
		if _, found := known[key]; found {
			continue
		}
		field := key
		if parent != "" {
			field = parent + "." + key
		}
		return fmt.Errorf("unknown deployment configuration field %s", field)
	}
	return nil
}

// Validate rejects incomplete or altered local deployment identifiers.
func (c Config) Validate() error {
	if c.Backend.Type != BackendTypeNative {
		return fmt.Errorf("backend.type must be %q", BackendTypeNative)
	}
	if c.Backend.ReleaseDir != nativeReleaseDir {
		return fmt.Errorf("backend.release_dir must be %q", nativeReleaseDir)
	}
	if c.Backend.ActiveJAR != nativeActiveJAR {
		return fmt.Errorf("backend.active_jar must be %q", nativeActiveJAR)
	}
	if err := validateAbsolutePath("backend.systemctl_path", c.Backend.SystemctlPath); err != nil {
		return err
	}
	if err := validateSlot("backend.slot.8080", c.Backend.Slot.Port8080, nativeUnit8080, nativeSlotJAR8080, nativeHealthURL8080); err != nil {
		return err
	}
	if err := validateSlot("backend.slot.8081", c.Backend.Slot.Port8081, nativeUnit8081, nativeSlotJAR8081, nativeHealthURL8081); err != nil {
		return err
	}
	return nil
}

// Slot returns the exact configuration for one supported backend port.
func (b Backend) SlotForPort(port int) (BackendSlot, error) {
	switch port {
	case BackendPort8080:
		return b.Slot.Port8080, nil
	case BackendPort8081:
		return b.Slot.Port8081, nil
	default:
		return BackendSlot{}, fmt.Errorf("unsupported native backend port: %d", port)
	}
}

func validateSlot(field string, slot BackendSlot, unit string, jar string, endpoint string) error {
	if slot.Unit != unit {
		return fmt.Errorf("%s.unit must be %q", field, unit)
	}
	if slot.JAR != jar {
		return fmt.Errorf("%s.jar must be %q", field, jar)
	}
	if slot.HealthEndpoint != endpoint {
		return fmt.Errorf("%s.health_endpoint must be %q", field, endpoint)
	}
	return nil
}

func validateAbsolutePath(field string, value string) error {
	if value == "" {
		return fmt.Errorf("%s is required", field)
	}
	if strings.TrimSpace(value) != value {
		return fmt.Errorf("%s must not contain surrounding whitespace", field)
	}
	if !filepath.IsAbs(value) {
		return fmt.Errorf("%s must be an absolute path", field)
	}
	if filepath.Clean(value) != value {
		return fmt.Errorf("%s must be a clean absolute path", field)
	}
	if strings.ContainsRune(value, '\x00') {
		return errors.New(field + " contains a NUL byte")
	}
	return nil
}