package configgen

import (
	"crypto/rand"
	"encoding/hex"
	"fmt"
	"time"

	"gitea.dooplex.hu/admin/felhom-hub/internal/store"
	"gopkg.in/yaml.v3"
)

// Generate takes the template YAML and a customer config,
// then produces a complete controller.yaml with customer-specific values
// merged in. The returned string is valid YAML ready for deployment.
func Generate(templateYAML string, cfg *store.CustomerConfig) (string, error) {
	// Parse template into generic map
	var base map[string]interface{}
	if err := yaml.Unmarshal([]byte(templateYAML), &base); err != nil {
		return "", fmt.Errorf("parsing template YAML: %w", err)
	}
	if base == nil {
		base = make(map[string]interface{})
	}

	// Parse customer config_json overrides
	var overrides map[string]interface{}
	if cfg.ConfigJSON != "" && cfg.ConfigJSON != "{}" {
		if err := yaml.Unmarshal([]byte(cfg.ConfigJSON), &overrides); err != nil {
			return "", fmt.Errorf("parsing config overrides: %w", err)
		}
	}

	// Apply config_json overrides first (deep merge)
	if len(overrides) > 0 {
		base = deepMerge(base, overrides)
	}

	// Apply programmatic overrides — these always win over config_json
	setNested(base, []string{"customer", "id"}, cfg.CustomerID)
	setNested(base, []string{"customer", "name"}, cfg.CustomerName)
	setNested(base, []string{"customer", "domain"}, cfg.Domain)
	setNested(base, []string{"customer", "email"}, cfg.Email)

	setNested(base, []string{"hub", "enabled"}, true)
	setNested(base, []string{"hub", "url"}, "https://hub.felhom.eu")
	setNested(base, []string{"hub", "api_key"}, cfg.APIKey)

	// Generate session secret
	sessionSecret, err := RandomHex(32)
	if err != nil {
		return "", fmt.Errorf("generating session secret: %w", err)
	}
	setNested(base, []string{"web", "session_secret"}, sessionSecret)

	// Marshal back to YAML
	out, err := yaml.Marshal(base)
	if err != nil {
		return "", fmt.Errorf("marshaling YAML: %w", err)
	}

	// Add header comment
	header := fmt.Sprintf(
		"# Felhom Controller Configuration\n# Generated by Felhom Hub for %q on %s\n# Download URL: https://hub.felhom.eu/api/v1/config/%s\n\n",
		cfg.CustomerID,
		time.Now().UTC().Format(time.RFC3339),
		cfg.CustomerID,
	)

	return header + string(out), nil
}

// deepMerge recursively merges overlay into base.
// When both base and overlay have a map at the same key, they are merged recursively.
// Otherwise, the overlay value wins.
func deepMerge(base, overlay map[string]interface{}) map[string]interface{} {
	result := make(map[string]interface{}, len(base))
	for k, v := range base {
		result[k] = v
	}
	for k, v := range overlay {
		if baseMap, ok := result[k].(map[string]interface{}); ok {
			if overlayMap, ok := v.(map[string]interface{}); ok {
				result[k] = deepMerge(baseMap, overlayMap)
				continue
			}
		}
		result[k] = v
	}
	return result
}

// setNested sets a value at a nested path in a map, creating intermediate maps as needed.
func setNested(m map[string]interface{}, path []string, value interface{}) {
	for i, key := range path {
		if i == len(path)-1 {
			m[key] = value
			return
		}
		sub, ok := m[key].(map[string]interface{})
		if !ok {
			sub = make(map[string]interface{})
			m[key] = sub
		}
		m = sub
	}
}

// RandomHex generates n random bytes and returns them as a hex string.
func RandomHex(n int) (string, error) {
	b := make([]byte, n)
	if _, err := rand.Read(b); err != nil {
		return "", err
	}
	return hex.EncodeToString(b), nil
}
