package models

import (
	"crypto/aes"
	"crypto/cipher"
	"crypto/rand"
	"crypto/sha256"
	"encoding/base64"
	"fmt"
	"time"
)

// SecretScope controls which resources a secret is visible to.
type SecretScope string

const (
	SecretScopeGlobal    SecretScope = "global"    // admin-only; available to all repos
	SecretScopeWorkspace SecretScope = "workspace"  // available to all repos in a workspace
	SecretScopeRepo      SecretScope = "repo"       // specific repository
	SecretScopeEnv       SecretScope = "env"        // specific environment (highest priority)
)

// Secret stores an AES-256-GCM encrypted key/value pair.
// Values are write-only: the API never returns the plaintext after creation.
// Uniqueness: (scope, scope_id, name) must be unique.
type Secret struct {
	ID             int64       `xorm:"'id' pk autoincr"                   json:"id"`
	Scope          SecretScope `xorm:"'scope' varchar(20) notnull"        json:"scope"`
	ScopeID        int64       `xorm:"'scope_id'"                         json:"scopeId"` // 0 for global
	Name           string      `xorm:"'name' varchar(255) notnull"        json:"name"`
	EncryptedValue string      `xorm:"'encrypted_value' text notnull"     json:"-"`        // never serialised
	CreatedAt      time.Time   `xorm:"'created_at' created"              json:"createdAt"`
	UpdatedAt      time.Time   `xorm:"'updated_at' updated"              json:"updatedAt"`
}

// ── Encryption helpers ────────────────────────────────────────────────────────

// deriveKey produces a 32-byte AES key from the session secret via SHA-256.
func deriveKey(sessionSecret string) []byte {
	h := sha256.Sum256([]byte(sessionSecret))
	return h[:]
}

// EncryptSecret encrypts plaintext with AES-256-GCM and returns a base64 string
// of the form: base64(nonce || ciphertext).
func EncryptSecret(plaintext, sessionSecret string) (string, error) {
	key := deriveKey(sessionSecret)
	block, err := aes.NewCipher(key)
	if err != nil {
		return "", fmt.Errorf("aes cipher: %w", err)
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", fmt.Errorf("gcm: %w", err)
	}
	nonce := make([]byte, gcm.NonceSize())
	if _, err := rand.Read(nonce); err != nil {
		return "", fmt.Errorf("nonce: %w", err)
	}
	sealed := gcm.Seal(nonce, nonce, []byte(plaintext), nil)
	return base64.StdEncoding.EncodeToString(sealed), nil
}

// DecryptSecret reverses EncryptSecret.
func DecryptSecret(encrypted, sessionSecret string) (string, error) {
	data, err := base64.StdEncoding.DecodeString(encrypted)
	if err != nil {
		return "", fmt.Errorf("base64: %w", err)
	}
	key := deriveKey(sessionSecret)
	block, err := aes.NewCipher(key)
	if err != nil {
		return "", fmt.Errorf("aes cipher: %w", err)
	}
	gcm, err := cipher.NewGCM(block)
	if err != nil {
		return "", fmt.Errorf("gcm: %w", err)
	}
	if len(data) < gcm.NonceSize() {
		return "", fmt.Errorf("ciphertext too short")
	}
	nonce, ct := data[:gcm.NonceSize()], data[gcm.NonceSize():]
	pt, err := gcm.Open(nil, nonce, ct, nil)
	if err != nil {
		return "", fmt.Errorf("decrypt: %w", err)
	}
	return string(pt), nil
}