// Package config defines the runtime configuration for the galahad2lcd
// daemon and handles loading and saving it as a TOML file.
package config

import (
	"errors"
	"fmt"
	"os"
	"path/filepath"
	"strings"

	"github.com/BurntSushi/toml"
)

// Default paths used across the project. They mirror the historical Rust
// driver so that migration is painless.
const (
	DefaultConfigPath = "/etc/galahad2lcd.toml"
	DefaultCachePath  = "/tmp/galahad_cache.h264"
	ServiceName       = "galahad2lcd"
)

// Default hardware identifiers for the Lian Li Galahad II LCD.
const (
	DefaultVendorID  = 0x0416
	DefaultProductID = 0x7395
)

// Display holds the media-related settings.
type Display struct {
	// Input is the path to the source video or GIF file.
	Input string `toml:"input"`
	// Rotate is the clockwise rotation in degrees: 0, 90, 180 or 270.
	Rotate int `toml:"rotate"`
	// Speed scales playback: >1 plays slower, <1 plays faster. 1.0 is normal.
	Speed float64 `toml:"speed"`
}

// USB holds the device identifiers used to locate the LCD.
type USB struct {
	VendorID  int `toml:"vendor_id"`
	ProductID int `toml:"product_id"`
}

// Stream holds playback behaviour.
type Stream struct {
	// FPS forces a fixed output framerate. 0 (the default) means auto-detect
	// from the source file.
	FPS float64 `toml:"fps"`
	// CachePath is where the transcoded H.264 stream is written.
	CachePath string `toml:"cache_path"`
}

// Config is the top-level configuration model.
type Config struct {
	Display Display `toml:"display"`
	USB     USB     `toml:"usb"`
	Stream  Stream  `toml:"stream"`
}

// Default returns a configuration populated with sensible defaults.
func Default() Config {
	return Config{
		Display: Display{
			Input:  "",
			Rotate: 0,
			Speed:  1.0,
		},
		USB: USB{
			VendorID:  DefaultVendorID,
			ProductID: DefaultProductID,
		},
		Stream: Stream{
			FPS:       0,
			CachePath: DefaultCachePath,
		},
	}
}

// Load reads the configuration from path. A missing file results in a
// configuration with defaults; any other read or parse error is returned.
func Load(path string) (Config, error) {
	cfg := Default()
	if path == "" {
		path = DefaultConfigPath
	}

	data, err := os.ReadFile(path)
	if err != nil {
		if errors.Is(err, os.ErrNotExist) {
			return cfg, nil
		}
		return cfg, fmt.Errorf("read config %q: %w", path, err)
	}

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

// Save writes the configuration to path, creating parent directories.
func (c Config) Save(path string) error {
	if path == "" {
		path = DefaultConfigPath
	}
	if dir := filepath.Dir(path); dir != "" {
		if err := os.MkdirAll(dir, 0o755); err != nil {
			return fmt.Errorf("create config dir %q: %w", dir, err)
		}
	}

	var b strings.Builder
	enc := toml.NewEncoder(&b)
	if err := enc.Encode(c); err != nil {
		return fmt.Errorf("encode config: %w", err)
	}
	if err := os.WriteFile(path, []byte(b.String()), 0o644); err != nil {
		return fmt.Errorf("write config %q: %w", path, err)
	}
	return nil
}

// Validate checks the configuration for correctness and returns a
// human-readable description of the first problem found, if any.
func (c Config) Validate() error {
	if c.Display.Input == "" {
		return errors.New("display.input must not be empty")
	}
	switch c.Display.Rotate {
	case 0, 90, 180, 270:
	default:
		return fmt.Errorf("display.rotate must be 0, 90, 180 or 270, got %d", c.Display.Rotate)
	}
	if c.Display.Speed <= 0 {
		return fmt.Errorf("display.speed must be > 0, got %v", c.Display.Speed)
	}
	if c.Stream.FPS < 0 {
		return fmt.Errorf("stream.fps must be >= 0, got %v", c.Stream.FPS)
	}
	if c.Stream.CachePath == "" {
		return errors.New("stream.cache_path must not be empty")
	}
	return nil
}