package main

import (
	"encoding/json"
	"fmt"
	"os"
)

// Config holds all tunable parameters for the ingest engine.
type Config struct {
	// WebSocket endpoint for Bybit V5 public linear trades.
	WebSocketURL string `json:"websocket_url"`

	// Symbol to subscribe to.
	Symbol string `json:"symbol"`

	// DataDir is the base directory for all database files.
	DataDir string `json:"data_dir"`

	// LogFile is the optional path to a file where logs will be written.
	LogFile string `json:"log_file"`

	// HotRetentionHours is how many hours of raw ticks to keep in the hot DB.
	HotRetentionHours int `json:"hot_retention_hours"`

	// FeatureRetentionDays is how many days of 5s features to keep.
	FeatureRetentionDays int `json:"feature_retention_days"`

	// WriterFlushIntervalMs is how often (ms) the batch writer flushes to disk.
	WriterFlushIntervalMs int `json:"writer_flush_interval_ms"`

	// WriterBatchSize is the max number of ticks before a forced flush.
	WriterBatchSize int `json:"writer_batch_size"`

	// TickChannelBuffer is the capacity of the tick channel between WS reader and DB writer.
	TickChannelBuffer int `json:"tick_channel_buffer"`

	// MaintenanceIntervalMinutes controls how often the hourly maintenance runs.
	MaintenanceIntervalMinutes int `json:"maintenance_interval_minutes"`
}

// DefaultConfig returns a Config populated with sensible defaults.
func DefaultConfig() Config {
	return Config{
		WebSocketURL:               "wss://stream.bybit.com/v5/public/linear",
		Symbol:                     "BTCUSDT",
		DataDir:                    "data",
		LogFile:                    "engine.log",
		HotRetentionHours:          12,
		FeatureRetentionDays:       30,
		WriterFlushIntervalMs:      500,
		WriterBatchSize:            100,
		TickChannelBuffer:          10000,
		MaintenanceIntervalMinutes: 60,
	}
}

// LoadConfig reads a JSON config file and merges with defaults.
func LoadConfig(path string) (Config, error) {
	cfg := DefaultConfig()

	data, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			if writeErr := writeDefaultConfig(path, cfg); writeErr != nil {
				return cfg, fmt.Errorf("failed to write default config: %w", writeErr)
			}
			fmt.Printf("No config found, wrote defaults to %s\n", path)
			return cfg, nil
		}
		return cfg, fmt.Errorf("failed to read config: %w", err)
	}

	if err := json.Unmarshal(data, &cfg); err != nil {
		return cfg, fmt.Errorf("failed to parse config: %w", err)
	}

	return cfg, nil
}

func writeDefaultConfig(path string, cfg Config) error {
	data, err := json.MarshalIndent(cfg, "", "  ")
	if err != nil {
		return err
	}
	return os.WriteFile(path, data, 0644)
}