// Package config loads the application configuration from environment variables.
package config

import (
	"errors"
	"fmt"
	"net"
	"net/url"
	"os"
	"strconv"
	"strings"
)

// DefaultReleasesURL is the Gitea endpoint used to look up the latest client release.
const DefaultReleasesURL = "https://gitea.sanplex.xyz/api/v1/repos/sansan/MusicPlayer/releases/latest"

// Config holds all settings read from the environment.
type Config struct {
	Port int
	// MetricsPort serves Prometheus metrics on a port of its own, so /metrics is never
	// reachable through the public port. 0 means metrics are not served.
	MetricsPort int

	DBHost     string
	DBPort     string
	DBUser     string
	DBPassword string
	DBName     string

	MusicPath      string
	CharactersPath string
	SoundCheckPath string
	FrontendPath   string
	// UploadMaxFileSize and UploadMaxTotalSize limit uploaded songs, in bytes: one song and
	// all songs of one uploaded soundtrack.
	UploadMaxFileSize  int64
	UploadMaxTotalSize int64

	// CoversPath is the folder for soundtrack covers. Empty turns covers off.
	CoversPath string

	// SteamGridDBAPIKey turns on the background search for covers.
	SteamGridDBAPIKey string
	// SteamGridDBURL and AniListURL replace the real cover APIs; only tests set them.
	SteamGridDBURL string
	AniListURL     string

	LogLevel string
	LogJSON  bool

	// APIPassword is required to create tokens. Empty means any password is accepted.
	APIPassword        string
	DisableSessionAuth bool

	// TrustedProxies are CIDR ranges whose X-Forwarded-For header is trusted when resolving client IPs.
	TrustedProxies []*net.IPNet

	// CORSAllowedOrigins are the browser origins, like https://music.example.com, that may call the API
	// from another site. Empty means only same-origin requests, which is enough for the bundled frontend.
	CORSAllowedOrigins []string

	ReleasesURL string
}

// Load reads the configuration from the environment and validates it.
func Load() (Config, error) {
	return load(os.Getenv)
}

func load(getenv func(string) string) (Config, error) {
	cfg := Config{
		DBHost:             getenv("DB_HOST"),
		DBPort:             getenv("DB_PORT"),
		DBUser:             getenv("DB_USERNAME"),
		DBPassword:         getenv("DB_PASSWORD"),
		DBName:             getenv("DB_NAME"),
		MusicPath:          getenv("MUSIC_PATH"),
		CharactersPath:     getenv("CHARACTERS_PATH"),
		SoundCheckPath:     withDefault(getenv("SOUND_CHECK_PATH"), "songs"),
		FrontendPath:       withDefault(getenv("FRONTEND_PATH"), "/frontend"),
		CoversPath:         getenv("COVERS_PATH"),
		SteamGridDBAPIKey:  getenv("STEAMGRIDDB_API_KEY"),
		LogLevel:           withDefault(getenv("LOG_LEVEL"), "info"),
		LogJSON:            getenv("LOG_JSON") == "true",
		APIPassword:        getenv("API_PASSWORD"),
		DisableSessionAuth: getenv("DISABLE_SESSION_AUTH") == "true",
		ReleasesURL:        withDefault(getenv("RELEASES_URL"), DefaultReleasesURL),
	}

	var errs []error

	port, err := strconv.Atoi(withDefault(getenv("PORT"), "8080"))
	if err != nil {
		errs = append(errs, fmt.Errorf("PORT: %w", err))
	}
	cfg.Port = port

	cfg.UploadMaxFileSize, err = parseMegabytes(getenv("UPLOAD_MAX_FILE_MB"), DefaultUploadMaxFileMB)
	if err != nil {
		errs = append(errs, fmt.Errorf("UPLOAD_MAX_FILE_MB: %w", err))
	}
	cfg.UploadMaxTotalSize, err = parseMegabytes(getenv("UPLOAD_MAX_TOTAL_MB"), DefaultUploadMaxTotalMB)
	if err != nil {
		errs = append(errs, fmt.Errorf("UPLOAD_MAX_TOTAL_MB: %w", err))
	}

	cfg.MetricsPort, err = parseMetricsPort(getenv("METRICS_PORT"))
	if err != nil {
		errs = append(errs, fmt.Errorf("METRICS_PORT: %w", err))
	}

	for name, value := range map[string]string{
		"DB_HOST":         cfg.DBHost,
		"DB_PORT":         cfg.DBPort,
		"DB_USERNAME":     cfg.DBUser,
		"DB_PASSWORD":     cfg.DBPassword,
		"DB_NAME":         cfg.DBName,
		"MUSIC_PATH":      cfg.MusicPath,
		"CHARACTERS_PATH": cfg.CharactersPath,
	} {
		if value == "" {
			errs = append(errs, fmt.Errorf("%s is required", name))
		}
	}

	cfg.TrustedProxies, err = parseCIDRs(getenv("TRUSTED_PROXIES"))
	if err != nil {
		errs = append(errs, fmt.Errorf("TRUSTED_PROXIES: %w", err))
	}

	cfg.CORSAllowedOrigins, err = parseOrigins(getenv("CORS_ALLOWED_ORIGINS"))
	if err != nil {
		errs = append(errs, fmt.Errorf("CORS_ALLOWED_ORIGINS: %w", err))
	}

	return cfg, errors.Join(errs...)
}

func parseCIDRs(value string) ([]*net.IPNet, error) {
	var nets []*net.IPNet
	for part := range strings.SplitSeq(value, ",") {
		part = strings.TrimSpace(part)
		if part == "" {
			continue
		}
		_, ipNet, err := net.ParseCIDR(part)
		if err != nil {
			return nil, err
		}
		nets = append(nets, ipNet)
	}
	return nets, nil
}

// Upload size limits in MB, used when UPLOAD_MAX_FILE_MB and UPLOAD_MAX_TOTAL_MB are not set.
const (
	DefaultUploadMaxFileMB  = 50
	DefaultUploadMaxTotalMB = 2048
)

// parseMegabytes reads a positive number of megabytes and returns it in bytes.
func parseMegabytes(value string, defaultMB int64) (int64, error) {
	if value == "" {
		return defaultMB << 20, nil
	}
	mb, err := strconv.ParseInt(value, 10, 64)
	if err != nil || mb < 1 || mb > 1<<20 {
		return 0, fmt.Errorf("%q is not a number of megabytes", value)
	}
	return mb << 20, nil
}

// DefaultMetricsPort is used when METRICS_PORT is not set.
const DefaultMetricsPort = 2112

// parseMetricsPort reads METRICS_PORT: empty for the default, "off" for no metrics, or a port.
func parseMetricsPort(value string) (int, error) {
	switch value {
	case "":
		return DefaultMetricsPort, nil
	case "off":
		return 0, nil
	}
	port, err := strconv.Atoi(value)
	if err != nil || port < 1 || port > 65535 {
		return 0, fmt.Errorf("%q is not a port or \"off\"", value)
	}
	return port, nil
}

// parseOrigins parses a comma-separated list of origins (scheme://host[:port], nothing else).
func parseOrigins(value string) ([]string, error) {
	var origins []string
	for part := range strings.SplitSeq(value, ",") {
		part = strings.TrimSpace(part)
		if part == "" {
			continue
		}
		u, err := url.Parse(part)
		if err != nil {
			return nil, err
		}
		if (u.Scheme != "http" && u.Scheme != "https") || u.Host == "" || u.Path != "" || u.RawQuery != "" ||
			u.Fragment != "" || u.User != nil || strings.Contains(u.Host, "*") {
			return nil, fmt.Errorf("%q is not an origin like https://music.example.com", part)
		}
		origins = append(origins, u.Scheme+"://"+u.Host)
	}
	return origins, nil
}

func withDefault(value, fallback string) string {
	if value == "" {
		return fallback
	}
	return value
}