package config

import (
	"flag"
	"fmt"
	"io"
	"log/slog"
	"os"
	"strconv"
	"strings"

	"github.com/BurntSushi/toml"
)

// Options is the result of parsing the server command line.
type Options struct {
	Config      Config
	ConfigPath  string
	CheckOnly   bool
	ShowVersion bool
}

// Load resolves the server configuration with precedence
//
//	flag > PAGES_* env > config file > built-in default
//
// args excludes the program name. It returns flag.ErrHelp when -h was passed.
func Load(args []string, out io.Writer) (*Options, error) {
	fs := flag.NewFlagSet("pages-server", flag.ContinueOnError)
	fs.SetOutput(out)

	// flagCfg receives whatever the user typed; we later copy across only the
	// fields whose flags were actually visited, so unset flags never shadow the
	// file or the environment.
	flagCfg := Default()
	opts := &Options{}

	fs.StringVar(&opts.ConfigPath, "config", os.Getenv("PAGES_CONFIG"), "path to the TOML config file")
	fs.BoolVar(&opts.CheckOnly, "check-config", false, "validate configuration and exit without binding ports")
	fs.BoolVar(&opts.ShowVersion, "version", false, "print version and exit")

	fs.StringVar(&flagCfg.DataDir, "data-dir", flagCfg.DataDir, "directory for the database, CAS blobs and deployment trees")
	fs.StringVar(&flagCfg.Webroot, "webroot", flagCfg.Webroot, "directory in which ~PROJECT symlinks are maintained")
	fs.StringVar(&flagCfg.Listen, "listen", flagCfg.Listen, "address for the public static-content listener")
	fs.StringVar(&flagCfg.APIListen, "api-listen", flagCfg.APIListen, "address for the management API listener")
	fs.StringVar(&flagCfg.SiteURL, "site-url", flagCfg.SiteURL, "public base URL of the static listener, e.g. https://pages.example.com (reported in API responses)")
	fs.StringVar((*string)(&flagCfg.AssembleMode), "assemble-mode", string(flagCfg.AssembleMode), "how deployment trees are built: auto|hardlink|copy|none")
	fs.StringVar(&flagCfg.LogLevel, "log-level", flagCfg.LogLevel, "debug|info|warn|error")
	fs.StringVar(&flagCfg.LogFormat, "log-format", flagCfg.LogFormat, "json|text")
	fs.Var(&flagCfg.GCInterval, "gc-interval", "how often the retention/blob sweep runs")
	fs.Var(&flagCfg.ShutdownGrace, "shutdown-grace", "how long in-flight requests may finish during shutdown")

	fs.Usage = func() {
		fmt.Fprintf(out, "Usage: pages-server [flags]\n\n"+
			"Serves static sites deployed through the pages CLI, switching each\n"+
			"project's content atomically.\n\nFlags:\n")
		fs.PrintDefaults()
	}

	if err := fs.Parse(args); err != nil {
		return nil, err
	}
	if opts.ShowVersion {
		return opts, nil
	}
	if fs.NArg() > 0 {
		return nil, fmt.Errorf("unexpected argument %q", fs.Arg(0))
	}

	set := make(map[string]bool, 16)
	fs.Visit(func(f *flag.Flag) { set[f.Name] = true })

	cfg := Default()

	if opts.ConfigPath != "" {
		if err := applyFile(&cfg, opts.ConfigPath); err != nil {
			return nil, err
		}
	}
	if err := applyEnv(&cfg); err != nil {
		return nil, err
	}

	// Highest precedence: flags the user actually typed.
	overrides := map[string]func(){
		"data-dir":       func() { cfg.DataDir = flagCfg.DataDir },
		"webroot":        func() { cfg.Webroot = flagCfg.Webroot },
		"listen":         func() { cfg.Listen = flagCfg.Listen },
		"api-listen":     func() { cfg.APIListen = flagCfg.APIListen },
		"site-url":       func() { cfg.SiteURL = flagCfg.SiteURL },
		"assemble-mode":  func() { cfg.AssembleMode = flagCfg.AssembleMode },
		"log-level":      func() { cfg.LogLevel = flagCfg.LogLevel },
		"log-format":     func() { cfg.LogFormat = flagCfg.LogFormat },
		"gc-interval":    func() { cfg.GCInterval = flagCfg.GCInterval },
		"shutdown-grace": func() { cfg.ShutdownGrace = flagCfg.ShutdownGrace },
	}
	for name, apply := range overrides {
		if set[name] {
			apply()
		}
	}

	if err := cfg.Validate(); err != nil {
		return nil, err
	}
	opts.Config = cfg
	return opts, nil
}

// applyFile decodes the TOML file over cfg. Unknown keys are an error: a typo in
// a config file should fail loudly rather than silently leave a default in place.
func applyFile(cfg *Config, path string) error {
	md, err := toml.DecodeFile(path, cfg)
	if err != nil {
		return fmt.Errorf("config %s: %w", path, err)
	}
	if undec := md.Undecoded(); len(undec) > 0 {
		keys := make([]string, len(undec))
		for i, k := range undec {
			keys[i] = k.String()
		}
		return fmt.Errorf("config %s: unknown key(s): %s", path, strings.Join(keys, ", "))
	}
	return nil
}

func applyEnv(cfg *Config) error {
	str := func(key string, dst *string) {
		if v, ok := os.LookupEnv(key); ok {
			*dst = v
		}
	}
	str("PAGES_DATA_DIR", &cfg.DataDir)
	str("PAGES_WEBROOT", &cfg.Webroot)
	str("PAGES_LISTEN", &cfg.Listen)
	str("PAGES_API_LISTEN", &cfg.APIListen)
	str("PAGES_SITE_URL", &cfg.SiteURL)
	str("PAGES_LOG_LEVEL", &cfg.LogLevel)
	str("PAGES_LOG_FORMAT", &cfg.LogFormat)
	str("PAGES_ASSEMBLE_MODE", (*string)(&cfg.AssembleMode))

	dur := func(key string, dst *Duration) error {
		v, ok := os.LookupEnv(key)
		if !ok {
			return nil
		}
		if err := dst.UnmarshalText([]byte(v)); err != nil {
			return fmt.Errorf("%s=%q: %w", key, v, err)
		}
		return nil
	}
	if err := dur("PAGES_GC_INTERVAL", &cfg.GCInterval); err != nil {
		return err
	}
	if err := dur("PAGES_RECONCILE_INTERVAL", &cfg.ReconcileInterval); err != nil {
		return err
	}
	if err := dur("PAGES_SHUTDOWN_GRACE", &cfg.ShutdownGrace); err != nil {
		return err
	}

	if v, ok := os.LookupEnv("PAGES_TRUSTED_PROXY_CIDRS"); ok {
		parts := strings.Split(v, ",")
		out := make([]string, 0, len(parts))
		for _, p := range parts {
			if p = strings.TrimSpace(p); p != "" {
				out = append(out, p)
			}
		}
		cfg.TrustedProxyCIDRs = out
	}
	if v, ok := os.LookupEnv("PAGES_MAX_FILE_BYTES"); ok {
		n, err := strconv.ParseInt(v, 10, 64)
		if err != nil {
			return fmt.Errorf("PAGES_MAX_FILE_BYTES=%q: %w", v, err)
		}
		cfg.Limits.MaxFileBytes = n
	}
	return nil
}

// Logger builds the structured logger described by the configuration.
func (c *Config) Logger(w io.Writer) *slog.Logger {
	var level slog.Level
	switch c.LogLevel {
	case "debug":
		level = slog.LevelDebug
	case "warn":
		level = slog.LevelWarn
	case "error":
		level = slog.LevelError
	default:
		level = slog.LevelInfo
	}
	opts := &slog.HandlerOptions{Level: level}
	if c.LogFormat == "text" {
		return slog.New(slog.NewTextHandler(w, opts))
	}
	return slog.New(slog.NewJSONHandler(w, opts))
}