package config

import (
	"fmt"
	"os"
	"strings"
	"time"

	"github.com/BurntSushi/toml"
)

// Config is the top-level configuration for the gosearch service.
type Config struct {
	Server      ServerConfig   `toml:"server"`
	Upstream    UpstreamConfig `toml:"upstream"`
	Engines     EnginesConfig  `toml:"engines"`
	Cache       CacheConfig    `toml:"cache"`
	CORS        CORSConfig     `toml:"cors"`
	RateLimit   RateLimitConfig `toml:"rate_limit"`
}

type ServerConfig struct {
	Port        int    `toml:"port"`
	HTTPTimeout string `toml:"http_timeout"`
	BaseURL     string `toml:"base_url"` // Public URL for OpenSearch XML (e.g. "https://search.example.com")
}

type UpstreamConfig struct {
	URL string `toml:"url"`
}

type EnginesConfig struct {
	LocalPorted []string    `toml:"local_ported"`
	Brave       BraveConfig `toml:"brave"`
	Qwant       QwantConfig `toml:"qwant"`
}

// CacheConfig holds Valkey/Redis cache settings.
type CacheConfig struct {
	Address    string `toml:"address"`     // Valkey server address (e.g. "localhost:6379")
	Password   string `toml:"password"`    // Auth password (empty = none)
	DB         int    `toml:"db"`          // Database index (default 0)
	DefaultTTL string `toml:"default_ttl"` // Cache TTL (e.g. "5m", default "5m")
}

// CORSConfig holds CORS middleware settings.
type CORSConfig struct {
	AllowedOrigins []string `toml:"allowed_origins"`
	AllowedMethods []string `toml:"allowed_methods"`
	AllowedHeaders []string `toml:"allowed_headers"`
	ExposedHeaders []string `toml:"exposed_headers"`
	MaxAge         int      `toml:"max_age"`
}

// RateLimitConfig holds per-IP rate limiting settings.
type RateLimitConfig struct {
	Requests        int    `toml:"requests"`          // Max requests per window (default: 30)
	Window          string `toml:"window"`            // Time window (e.g. "1m", default: "1m")
	CleanupInterval string `toml:"cleanup_interval"`  // Stale entry cleanup interval (default: "5m")
}

type BraveConfig struct {
	APIKey       string `toml:"api_key"`
	AccessToken  string `toml:"access_token"`
}

type QwantConfig struct {
	Category       string `toml:"category"`
	ResultsPerPage int    `toml:"results_per_page"`
}

// Load reads configuration from the given TOML file path.
// If the file does not exist, it returns defaults (empty values where applicable).
// Environment variables are used as fallbacks for any zero-value fields.
func Load(path string) (*Config, error) {
	cfg := defaultConfig()

	if _, err := os.Stat(path); err == nil {
		if _, err := toml.DecodeFile(path, &cfg); err != nil {
			return nil, fmt.Errorf("parse config %s: %w", path, err)
		}
	}

	applyEnvOverrides(cfg)
	return cfg, nil
}

func defaultConfig() *Config {
	return &Config{
		Server: ServerConfig{
			Port:        8080,
			HTTPTimeout: "10s",
		},
		Upstream: UpstreamConfig{},
		Engines: EnginesConfig{
			LocalPorted: []string{"wikipedia", "arxiv", "crossref", "braveapi", "qwant", "duckduckgo", "github", "reddit", "bing"},
			Qwant: QwantConfig{
				Category:       "web-lite",
				ResultsPerPage: 10,
			},
		},
		Cache: CacheConfig{
			DB:         0,
			DefaultTTL: "5m",
		},
		RateLimit: RateLimitConfig{
			Window:          "1m",
			CleanupInterval: "5m",
		},
	}
}

// applyEnvOverrides fills any zero-value fields from environment variables.
// This preserves backward compatibility: existing deployments using env vars
// continue to work without a config file.
func applyEnvOverrides(cfg *Config) {
	if v := os.Getenv("PORT"); v != "" {
		fmt.Sscanf(v, "%d", &cfg.Server.Port)
	}
	if v := os.Getenv("HTTP_TIMEOUT"); v != "" {
		cfg.Server.HTTPTimeout = v
	}
	if v := os.Getenv("UPSTREAM_SEARXNG_URL"); v != "" {
		cfg.Upstream.URL = v
	}
	if v := os.Getenv("LOCAL_PORTED_ENGINES"); v != "" {
		parts := splitCSV(v)
		if len(parts) > 0 {
			cfg.Engines.LocalPorted = parts
		}
	}
	if v := os.Getenv("BRAVE_API_KEY"); v != "" {
		cfg.Engines.Brave.APIKey = v
	}
	if v := os.Getenv("BRAVE_ACCESS_TOKEN"); v != "" {
		cfg.Engines.Brave.AccessToken = v
	}
	if v := os.Getenv("VALKEY_ADDRESS"); v != "" {
		cfg.Cache.Address = v
	}
	if v := os.Getenv("VALKEY_PASSWORD"); v != "" {
		cfg.Cache.Password = v
	}
	if v := os.Getenv("VALKEY_DB"); v != "" {
		fmt.Sscanf(v, "%d", &cfg.Cache.DB)
	}
	if v := os.Getenv("VALKEY_CACHE_TTL"); v != "" {
		cfg.Cache.DefaultTTL = v
	}
	if v := os.Getenv("CORS_ALLOWED_ORIGINS"); v != "" {
		cfg.CORS.AllowedOrigins = splitCSV(v)
	}
	if v := os.Getenv("RATE_LIMIT_REQUESTS"); v != "" {
		fmt.Sscanf(v, "%d", &cfg.RateLimit.Requests)
	}
	if v := os.Getenv("RATE_LIMIT_WINDOW"); v != "" {
		cfg.RateLimit.Window = v
	}
	if v := os.Getenv("RATE_LIMIT_CLEANUP_INTERVAL"); v != "" {
		cfg.RateLimit.CleanupInterval = v
	}
	if v := os.Getenv("BASE_URL"); v != "" {
		cfg.Server.BaseURL = v
	}
}

// HTTPTimeout parses the configured timeout string into a time.Duration.
func (c *Config) HTTPTimeout() time.Duration {
	if d, err := time.ParseDuration(c.Server.HTTPTimeout); err == nil && d > 0 {
		return d
	}
	return 10 * time.Second
}

// LocalPortedCSV returns the local ported engines as a comma-separated string.
func (c *Config) LocalPortedCSV() string {
	return strings.Join(c.Engines.LocalPorted, ",")
}

// CacheTTL parses the configured cache TTL string into a time.Duration.
func (c *Config) CacheTTL() time.Duration {
	if d, err := time.ParseDuration(c.Cache.DefaultTTL); err == nil && d > 0 {
		return d
	}
	return 5 * time.Minute
}

// RateLimitWindow parses the rate limit window into a time.Duration.
func (c *Config) RateLimitWindow() time.Duration {
	if d, err := time.ParseDuration(c.RateLimit.Window); err == nil && d > 0 {
		return d
	}
	return time.Minute
}

// RateLimitCleanupInterval parses the cleanup interval into a time.Duration.
func (c *Config) RateLimitCleanupInterval() time.Duration {
	if d, err := time.ParseDuration(c.RateLimit.CleanupInterval); err == nil && d > 0 {
		return d
	}
	return 5 * time.Minute
}

func splitCSV(s string) []string {
	if s == "" {
		return nil
	}
	parts := strings.Split(s, ",")
	out := make([]string, 0, len(parts))
	for _, p := range parts {
		p = strings.TrimSpace(p)
		if p != "" {
			out = append(out, p)
		}
	}
	return out
}