package config

import (
	"fmt"
	"strings"
)

func (c Config) Validate() error {
	if strings.TrimSpace(c.Database.URL) == "" {
		return fmt.Errorf("invalid config: database.url is required")
	}

	if len(c.Auth.Keys) == 0 && len(c.Auth.OAuth.Clients) == 0 {
		return fmt.Errorf("invalid config: at least one of auth.keys or auth.oauth.clients must be configured")
	}
	for i, key := range c.Auth.Keys {
		if strings.TrimSpace(key.ID) == "" {
			return fmt.Errorf("invalid config: auth.keys[%d].id is required", i)
		}
		if strings.TrimSpace(key.Value) == "" {
			return fmt.Errorf("invalid config: auth.keys[%d].value is required", i)
		}
	}
	for i, client := range c.Auth.OAuth.Clients {
		if strings.TrimSpace(client.ClientID) == "" {
			return fmt.Errorf("invalid config: auth.oauth.clients[%d].client_id is required", i)
		}
		if strings.TrimSpace(client.ClientSecret) == "" {
			return fmt.Errorf("invalid config: auth.oauth.clients[%d].client_secret is required", i)
		}
	}

	if strings.TrimSpace(c.MCP.Path) == "" {
		return fmt.Errorf("invalid config: mcp.path is required")
	}

	switch c.AI.Provider {
	case "litellm", "ollama", "openrouter":
	default:
		return fmt.Errorf("invalid config: unsupported ai.provider %q", c.AI.Provider)
	}

	if c.AI.Embeddings.Dimensions <= 0 {
		return fmt.Errorf("invalid config: ai.embeddings.dimensions must be greater than zero")
	}

	switch c.AI.Provider {
	case "litellm":
		if strings.TrimSpace(c.AI.LiteLLM.BaseURL) == "" {
			return fmt.Errorf("invalid config: ai.litellm.base_url is required when ai.provider=litellm")
		}
		if strings.TrimSpace(c.AI.LiteLLM.APIKey) == "" {
			return fmt.Errorf("invalid config: ai.litellm.api_key is required when ai.provider=litellm")
		}
	case "ollama":
		if strings.TrimSpace(c.AI.Ollama.BaseURL) == "" {
			return fmt.Errorf("invalid config: ai.ollama.base_url is required when ai.provider=ollama")
		}
		if strings.TrimSpace(c.AI.Ollama.APIKey) == "" {
			return fmt.Errorf("invalid config: ai.ollama.api_key is required when ai.provider=ollama")
		}
	case "openrouter":
		if strings.TrimSpace(c.AI.OpenRouter.BaseURL) == "" {
			return fmt.Errorf("invalid config: ai.openrouter.base_url is required when ai.provider=openrouter")
		}
		if strings.TrimSpace(c.AI.OpenRouter.APIKey) == "" {
			return fmt.Errorf("invalid config: ai.openrouter.api_key is required when ai.provider=openrouter")
		}
	}

	if c.Server.Port <= 0 {
		return fmt.Errorf("invalid config: server.port must be greater than zero")
	}
	if c.Search.DefaultLimit <= 0 {
		return fmt.Errorf("invalid config: search.default_limit must be greater than zero")
	}
	if c.Search.MaxLimit < c.Search.DefaultLimit {
		return fmt.Errorf("invalid config: search.max_limit must be greater than or equal to search.default_limit")
	}
	if strings.TrimSpace(c.Logging.Level) == "" {
		return fmt.Errorf("invalid config: logging.level is required")
	}

	if c.Backfill.Enabled {
		if c.Backfill.BatchSize <= 0 {
			return fmt.Errorf("invalid config: backfill.batch_size must be greater than zero when backfill is enabled")
		}
		if c.Backfill.MaxPerRun < c.Backfill.BatchSize {
			return fmt.Errorf("invalid config: backfill.max_per_run must be >= backfill.batch_size")
		}
	}
	if c.MetadataRetry.Enabled {
		if c.MetadataRetry.MaxPerRun <= 0 {
			return fmt.Errorf("invalid config: metadata_retry.max_per_run must be greater than zero when metadata_retry is enabled")
		}
	}

	return nil
}