package config

import (
	"errors"
	"fmt"
	"os"
	"strings"

	"github.com/knadh/koanf/parsers/yaml"
	"github.com/knadh/koanf/providers/env/v2"
	"github.com/knadh/koanf/providers/file"
	"github.com/knadh/koanf/v2"
)

const envPrefix = "CDROP_"

type Config struct {
	AuthMode string `koanf:"auth_mode"`
	DevToken string `koanf:"dev_token"`

	DBPath string `koanf:"db_path"`
	Listen string `koanf:"listen"`

	// DeviceTTLHours is the maximum age of a row in `devices` before the
	// background sweeper deletes it. Brief §2 sets the refresh_token sliding
	// window at 196h (≈8 days) — devices must not outlive that. Default 196h.
	DeviceTTLHours int `koanf:"device_ttl_hours"`

	// OIDC settings. Generic OAuth/OIDC provider compatible (Casdoor included).
	OIDCAuthorizeURL string `koanf:"oidc_authorize_url"`
	OIDCTokenURL     string `koanf:"oidc_token_url"`
	OIDCJWKSURL      string `koanf:"oidc_jwks_url"`
	OIDCIssuer       string `koanf:"oidc_issuer"`
	// OIDCAudience accepts a comma-separated list. A token passes when its `aud`
	// matches any one entry — this lets one backend serve several OAuth clients
	// that carry different audiences (e.g. the web app and the desktop client).
	// Empty disables audience checking; a single value behaves as before.
	OIDCAudience     string `koanf:"oidc_audience"`
	OIDCClientID     string `koanf:"oidc_client_id"`
	OIDCClientSecret string `koanf:"oidc_client_secret"`
	OIDCRedirectURI  string `koanf:"oidc_redirect_uri"`
	OIDCScopes       string `koanf:"oidc_scopes"`

	HS256Secret string `koanf:"hs256_secret"`

	// Shortcut tokens：iOS 快捷指令用的长效 HS256 token。TTLDays 是签发有效期
	// （默认 365 天），MaxPerUser 是每用户未吊销且未过期的 token 上限（默认 10）。
	// 需配 HS256Secret 才启用，否则签发端点返回 503。
	ShortcutTokenTTLDays int `koanf:"shortcut_token_ttl_days"`
	ShortcutMaxPerUser   int `koanf:"shortcut_max_per_user"`

	// Cloudflare Realtime TURN (https://developers.cloudflare.com/realtime/turn/).
	// When both fields are set, /api/calls/credentials returns short-lived
	// TLS-capable TURN creds (turns:turn.cloudflare.com:5349); otherwise the
	// endpoint serves a STUN-only fallback so dev / no-CF deploys still work.
	CFTurnKeyID    string `koanf:"cf_turn_key_id"`
	CFTurnAPIToken string `koanf:"cf_turn_api_token"`

	// Clipboard：单条覆写式同步。MaxBytes 限制单次写入字节数；DebounceSec 是
	// 收到 PUT 后等待"无新写入稳定窗口"的秒数，到期才广播 SSE。同窗口内的
	// 后续 PUT 直接刷新 generation 让旧广播取消。
	ClipboardMaxBytes    int `koanf:"clipboard_max_bytes"`
	ClipboardDebounceSec int `koanf:"clipboard_debounce_sec"`
	// ClipboardTTLSec 是云剪贴板内容的存活秒数。因为无法可靠区分密码与普通
	// 文本（密码.app / 浏览器扩展复制都不打敏感标记），改以短 TTL 限制暴露面：
	// 内容超过 TTL 后 GET 返回空，后台 sweeper 亦清除其 content。0 = 不过期。
	ClipboardTTLSec int `koanf:"clipboard_ttl_sec"`
}

// Load reads config from optional ./config.yaml then overrides with CDROP_* env.
// Validates dev/prod invariants; returns error if invariants are violated.
func Load() (*Config, error) {
	k := koanf.New(".")

	k.Set("auth_mode", "prod")
	k.Set("db_path", "./cdrop.db")
	k.Set("listen", ":8080")
	k.Set("device_ttl_hours", 196)
	k.Set("oidc_scopes", "openid profile email")
	k.Set("clipboard_max_bytes", 65536)
	k.Set("clipboard_debounce_sec", 3)
	k.Set("shortcut_token_ttl_days", 365)
	k.Set("shortcut_max_per_user", 10)

	if _, err := os.Stat("config.yaml"); err == nil {
		if err := k.Load(file.Provider("config.yaml"), yaml.Parser()); err != nil {
			return nil, fmt.Errorf("load config.yaml: %w", err)
		}
	}

	envProvider := env.Provider(".", env.Opt{
		Prefix: envPrefix,
		TransformFunc: func(key, value string) (string, any) {
			return strings.ToLower(strings.TrimPrefix(key, envPrefix)), value
		},
	})
	if err := k.Load(envProvider, nil); err != nil {
		return nil, fmt.Errorf("load env: %w", err)
	}

	cfg := &Config{}
	if err := k.Unmarshal("", cfg); err != nil {
		return nil, fmt.Errorf("unmarshal config: %w", err)
	}

	if err := cfg.validate(); err != nil {
		return nil, err
	}
	return cfg, nil
}

func (c *Config) validate() error {
	switch c.AuthMode {
	case "dev":
		if c.DevToken == "" {
			return errors.New("CDROP_AUTH_MODE=dev requires CDROP_DEV_TOKEN; refusing to start")
		}
	case "prod":
		// Audience MUST be set in prod (R6). With it empty, RS256 audience
		// checking is skipped entirely, so ANY token the IdP mints for ANY
		// application sharing this JWKS would validate here — a user of a
		// sibling Casdoor app could impersonate a cdrop user. The web + desktop
		// client_ids go in CDROP_OIDC_AUDIENCE (comma-separated); refuse to boot
		// without it rather than run wide open.
		if c.OIDCAudience == "" {
			return errors.New(
				"CDROP_AUTH_MODE=prod requires CDROP_OIDC_AUDIENCE " +
					"(comma-separated OAuth client_ids); refusing to start")
		}
	default:
		return fmt.Errorf("CDROP_AUTH_MODE must be \"dev\" or \"prod\", got %q", c.AuthMode)
	}
	return nil
}