package config

import (
	"fmt"
	"os"

	"gopkg.in/yaml.v3"
)

// Config describes the full gateway configuration file.
type Config struct {
	Server        ServerConfig             `yaml:"server"`
	Providers     map[string]ProviderEntry `yaml:"providers"`
	Models        []ModelEntry             `yaml:"models"`
	Auth          AuthConfig               `yaml:"auth"`
	Conversations ConversationConfig       `yaml:"conversations"`
}

// ConversationConfig controls conversation storage.
type ConversationConfig struct {
	// Store is the storage backend: "memory" (default) or "sql".
	Store string `yaml:"store"`
	// TTL is the conversation expiration duration (e.g. "1h", "30m"). Defaults to "1h".
	TTL string `yaml:"ttl"`
	// DSN is the database connection string, required when store is "sql".
	// Examples: "conversations.db" (SQLite), "postgres://user:pass@host/db".
	DSN string `yaml:"dsn"`
	// Driver is the SQL driver name, required when store is "sql".
	// Examples: "sqlite3", "postgres", "mysql".
	Driver string `yaml:"driver"`
}

// AuthConfig holds OIDC authentication settings.
type AuthConfig struct {
	Enabled  bool   `yaml:"enabled"`
	Issuer   string `yaml:"issuer"`
	Audience string `yaml:"audience"`
}

// ServerConfig controls HTTP server values.
type ServerConfig struct {
	Address string `yaml:"address"`
}

// ProviderEntry defines a named provider instance in the config file.
type ProviderEntry struct {
	Type       string `yaml:"type"`
	APIKey     string `yaml:"api_key"`
	Endpoint   string `yaml:"endpoint"`
	APIVersion string `yaml:"api_version"`
}

// ModelEntry maps a model name to a provider entry.
type ModelEntry struct {
	Name            string `yaml:"name"`
	Provider        string `yaml:"provider"`
	ProviderModelID string `yaml:"provider_model_id"`
}

// ProviderConfig contains shared provider configuration fields used internally by providers.
type ProviderConfig struct {
	APIKey   string `yaml:"api_key"`
	Model    string `yaml:"model"`
	Endpoint string `yaml:"endpoint"`
}

// AzureOpenAIConfig contains Azure-specific settings used internally by the OpenAI provider.
type AzureOpenAIConfig struct {
	APIKey     string `yaml:"api_key"`
	Endpoint   string `yaml:"endpoint"`
	APIVersion string `yaml:"api_version"`
}

// AzureAnthropicConfig contains Azure-specific settings for Anthropic used internally.
type AzureAnthropicConfig struct {
	APIKey   string `yaml:"api_key"`
	Endpoint string `yaml:"endpoint"`
	Model    string `yaml:"model"`
}

// Load reads and parses a YAML configuration file, expanding ${VAR} env references.
func Load(path string) (*Config, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("read config: %w", err)
	}

	expanded := os.Expand(string(data), os.Getenv)

	var cfg Config
	if err := yaml.Unmarshal([]byte(expanded), &cfg); err != nil {
		return nil, fmt.Errorf("parse config: %w", err)
	}

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

	return &cfg, nil
}

func (cfg *Config) validate() error {
	for _, m := range cfg.Models {
		if _, ok := cfg.Providers[m.Provider]; !ok {
			return fmt.Errorf("model %q references unknown provider %q", m.Name, m.Provider)
		}
	}
	return nil
}