// Package config provides configuration management for the CLI Proxy API server.
// It handles loading and parsing YAML configuration files, and provides structured
// access to application settings including server port, authentication directory,
// debug settings, proxy configuration, and API keys.
package config

import (
	"fmt"
	"os"

	"gopkg.in/yaml.v3"
)

// Config represents the application's configuration, loaded from a YAML file.
type Config struct {
	// Port is the network port on which the API server will listen.
	Port int `yaml:"port"`

	// AuthDir is the directory where authentication token files are stored.
	AuthDir string `yaml:"auth-dir"`

	// Debug enables or disables debug-level logging and other debug features.
	Debug bool `yaml:"debug"`

	// ProxyURL is the URL of an optional proxy server to use for outbound requests.
	ProxyURL string `yaml:"proxy-url"`

	// APIKeys is a list of keys for authenticating clients to this proxy server.
	APIKeys []string `yaml:"api-keys"`

	// QuotaExceeded defines the behavior when a quota is exceeded.
	QuotaExceeded QuotaExceeded `yaml:"quota-exceeded"`

	// GlAPIKey is the API key for the generative language API.
	GlAPIKey []string `yaml:"generative-language-api-key"`

	// RequestLog enables or disables detailed request logging functionality.
	RequestLog bool `yaml:"request-log"`

	// RequestRetry defines the retry times when the request failed.
	RequestRetry int `yaml:"request-retry"`

	// ClaudeKey defines a list of Claude API key configurations as specified in the YAML configuration file.
	ClaudeKey []ClaudeKey `yaml:"claude-api-key"`

	// OpenAICompatibility defines OpenAI API compatibility configurations for external providers.
	OpenAICompatibility []OpenAICompatibility `yaml:"openai-compatibility"`

	// AllowLocalhostUnauthenticated allows unauthenticated requests from localhost.
	AllowLocalhostUnauthenticated bool `yaml:"allow-localhost-unauthenticated"`
}

// QuotaExceeded defines the behavior when API quota limits are exceeded.
// It provides configuration options for automatic failover mechanisms.
type QuotaExceeded struct {
	// SwitchProject indicates whether to automatically switch to another project when a quota is exceeded.
	SwitchProject bool `yaml:"switch-project"`

	// SwitchPreviewModel indicates whether to automatically switch to a preview model when a quota is exceeded.
	SwitchPreviewModel bool `yaml:"switch-preview-model"`
}

// ClaudeKey represents the configuration for a Claude API key,
// including the API key itself and an optional base URL for the API endpoint.
type ClaudeKey struct {
	// APIKey is the authentication key for accessing Claude API services.
	APIKey string `yaml:"api-key"`

	// BaseURL is the base URL for the Claude API endpoint.
	// If empty, the default Claude API URL will be used.
	BaseURL string `yaml:"base-url"`
}

// OpenAICompatibility represents the configuration for OpenAI API compatibility
// with external providers, allowing model aliases to be routed through OpenAI API format.
type OpenAICompatibility struct {
	// Name is the identifier for this OpenAI compatibility configuration.
	Name string `yaml:"name"`

	// BaseURL is the base URL for the external OpenAI-compatible API endpoint.
	BaseURL string `yaml:"base-url"`

	// APIKeys are the authentication keys for accessing the external API services.
	APIKeys []string `yaml:"api-keys"`

	// Models defines the model configurations including aliases for routing.
	Models []OpenAICompatibilityModel `yaml:"models"`
}

// OpenAICompatibilityModel represents a model configuration for OpenAI compatibility,
// including the actual model name and its alias for API routing.
type OpenAICompatibilityModel struct {
	// Name is the actual model name used by the external provider.
	Name string `yaml:"name"`

	// Alias is the model name alias that clients will use to reference this model.
	Alias string `yaml:"alias"`
}

// LoadConfig reads a YAML configuration file from the given path,
// unmarshals it into a Config struct, applies environment variable overrides,
// and returns it.
//
// Parameters:
//   - configFile: The path to the YAML configuration file
//
// Returns:
//   - *Config: The loaded configuration
//   - error: An error if the configuration could not be loaded
func LoadConfig(configFile string) (*Config, error) {
	// Read the entire configuration file into memory.
	data, err := os.ReadFile(configFile)
	if err != nil {
		return nil, fmt.Errorf("failed to read config file: %w", err)
	}

	// Unmarshal the YAML data into the Config struct.
	var config Config
	if err = yaml.Unmarshal(data, &config); err != nil {
		return nil, fmt.Errorf("failed to parse config file: %w", err)
	}

	// Return the populated configuration struct.
	return &config, nil
}