package server

import (
	"os"
	"time"

	"git.n1ko.dev/Niko/niko_trust/internal/tce"
	"gopkg.in/yaml.v3"
)

// Config holds every operator-tunable knob for the relay. All fields have sane
// defaults (see DefaultConfig); a YAML file overrides only the keys it sets.
type Config struct {
	ListenAddr string // HTTP listen address, e.g. ":8080"
	Audience   string // audience bound into auth assertions
	DataDir    string // directory to persist objects ("" = in-memory)
	LogLevel   string // debug | info | warn | error

	// Per-IP fixed-window rate limits.
	PutLimit        int           // POST /v1/objects requests per window
	PutWindow       time.Duration // window for PutLimit
	ChallengeLimit  int           // POST /v1/auth/challenge requests per window
	ChallengeWindow time.Duration // window for ChallengeLimit

	MaxPerSubject int // max claims stored per subject address

	ChallengeTTL time.Duration // validity of an issued auth challenge
	SessionTTL   time.Duration // validity of a verified auth session

	MaxBodyBytes int64 // hard cap on any request body
}

// configFile mirrors Config but keeps durations as strings so they can be
// written as "5m" / "1m" in YAML (yaml.v3 does not parse time.Duration).
type configFile struct {
	ListenAddr      string `yaml:"listen_addr"`
	Audience        string `yaml:"audience"`
	DataDir         string `yaml:"data_dir"`
	LogLevel        string `yaml:"log_level"`
	PutLimit        int    `yaml:"put_limit"`
	PutWindow       string `yaml:"put_window"`
	ChallengeLimit  int    `yaml:"challenge_limit"`
	ChallengeWindow string `yaml:"challenge_window"`
	MaxPerSubject   int    `yaml:"max_per_subject"`
	ChallengeTTL    string `yaml:"challenge_ttl"`
	SessionTTL      string `yaml:"session_ttl"`
	MaxBodyBytes    int64  `yaml:"max_body_bytes"`
}

// DefaultConfig returns the built-in defaults.
func DefaultConfig() Config {
	return Config{
		ListenAddr:      ":8080",
		Audience:        "trust.n1ko.dev",
		DataDir:         "data", // persist objects; "" would be in-memory only
		LogLevel:        "info",
		PutLimit:        60,
		PutWindow:       time.Minute,
		ChallengeLimit:  30,
		ChallengeWindow: time.Minute,
		MaxPerSubject:   1000,
		ChallengeTTL:    5 * time.Minute,
		SessionTTL:      30 * time.Minute,
		MaxBodyBytes:    tce.MaxClaimTCE*2 + 1024,
	}
}

// LoadConfig reads a YAML config file. A missing file yields the defaults
// (so the server can run config-less); any other read or parse error is
// returned.
func LoadConfig(path string) (Config, error) {
	cfg := DefaultConfig()
	if path == "" {
		return cfg, nil
	}
	b, err := os.ReadFile(path)
	if err != nil {
		if os.IsNotExist(err) {
			return cfg, nil
		}
		return cfg, err
	}
	return ParseConfig(b)
}

// ParseConfig decodes YAML bytes into a Config, layering overrides on top of
// the defaults.
func ParseConfig(b []byte) (Config, error) {
	cfg := DefaultConfig()
	var f configFile
	if err := yaml.Unmarshal(b, &f); err != nil {
		return cfg, err
	}
	applyConfigFile(&cfg, &f)
	return cfg, nil
}

func applyConfigFile(cfg *Config, f *configFile) {
	if f.ListenAddr != "" {
		cfg.ListenAddr = f.ListenAddr
	}
	if f.Audience != "" {
		cfg.Audience = f.Audience
	}
	if f.DataDir != "" {
		cfg.DataDir = f.DataDir
	}
	if f.LogLevel != "" {
		cfg.LogLevel = f.LogLevel
	}
	if f.PutLimit != 0 {
		cfg.PutLimit = f.PutLimit
	}
	cfg.PutWindow = parseDur(f.PutWindow, cfg.PutWindow)
	if f.ChallengeLimit != 0 {
		cfg.ChallengeLimit = f.ChallengeLimit
	}
	cfg.ChallengeWindow = parseDur(f.ChallengeWindow, cfg.ChallengeWindow)
	if f.MaxPerSubject != 0 {
		cfg.MaxPerSubject = f.MaxPerSubject
	}
	cfg.ChallengeTTL = parseDur(f.ChallengeTTL, cfg.ChallengeTTL)
	cfg.SessionTTL = parseDur(f.SessionTTL, cfg.SessionTTL)
	if f.MaxBodyBytes != 0 {
		cfg.MaxBodyBytes = f.MaxBodyBytes
	}
}

func parseDur(s string, def time.Duration) time.Duration {
	if s == "" {
		return def
	}
	if d, err := time.ParseDuration(s); err == nil {
		return d
	}
	return def
}