// Package config handles loading and validating the MCIAS server configuration.
// Sensitive values (master key passphrase) are never stored in this struct
// after initial loading — they are read once and discarded.
package config

import (
	"errors"
	"fmt"
	"os"
	"time"

	"github.com/pelletier/go-toml/v2"
)

// Config is the top-level configuration structure parsed from the TOML file.
type Config struct {
	Server    ServerConfig    `toml:"server"`
	Database  DatabaseConfig  `toml:"database"`
	Tokens    TokensConfig    `toml:"tokens"`
	Argon2    Argon2Config    `toml:"argon2"`
	MasterKey MasterKeyConfig `toml:"master_key"`
}

// ServerConfig holds HTTP listener and TLS settings.
type ServerConfig struct {
	ListenAddr string `toml:"listen_addr"`
	TLSCert    string `toml:"tls_cert"`
	TLSKey     string `toml:"tls_key"`
}

// DatabaseConfig holds SQLite database settings.
type DatabaseConfig struct {
	Path string `toml:"path"`
}

// TokensConfig holds JWT issuance settings.
type TokensConfig struct {
	Issuer         string        `toml:"issuer"`
	DefaultExpiry  duration      `toml:"default_expiry"`
	AdminExpiry    duration      `toml:"admin_expiry"`
	ServiceExpiry  duration      `toml:"service_expiry"`
}

// Argon2Config holds Argon2id password hashing parameters.
// Security: OWASP 2023 minimums are time=2, memory=65536 KiB.
// We enforce these minimums to prevent accidental weakening.
type Argon2Config struct {
	Time    uint32 `toml:"time"`
	Memory  uint32 `toml:"memory"`  // KiB
	Threads uint8  `toml:"threads"`
}

// MasterKeyConfig specifies how to obtain the AES-256-GCM master key used to
// encrypt stored secrets (TOTP, Postgres passwords, signing key).
// Exactly one of PassphraseEnv or KeyFile must be set.
type MasterKeyConfig struct {
	PassphraseEnv string `toml:"passphrase_env"`
	KeyFile       string `toml:"keyfile"`
}

// duration is a wrapper around time.Duration that supports TOML string parsing
// (e.g. "720h", "8h").
type duration struct {
	time.Duration
}

func (d *duration) UnmarshalText(text []byte) error {
	var err error
	d.Duration, err = time.ParseDuration(string(text))
	if err != nil {
		return fmt.Errorf("invalid duration %q: %w", string(text), err)
	}
	return nil
}

// NewTestConfig returns a minimal valid Config for use in tests.
// It does not read a file; callers can override fields as needed.
func NewTestConfig(issuer string) *Config {
	return &Config{
		Server: ServerConfig{
			ListenAddr: "127.0.0.1:0",
			TLSCert:    "/dev/null",
			TLSKey:     "/dev/null",
		},
		Database: DatabaseConfig{Path: ":memory:"},
		Tokens: TokensConfig{
			Issuer:        issuer,
			DefaultExpiry: duration{24 * time.Hour},
			AdminExpiry:   duration{8 * time.Hour},
			ServiceExpiry: duration{8760 * time.Hour},
		},
		Argon2: Argon2Config{
			Time:    3,
			Memory:  65536,
			Threads: 4,
		},
		MasterKey: MasterKeyConfig{
			PassphraseEnv: "MCIAS_MASTER_PASSPHRASE",
		},
	}
}

// Load reads and validates a TOML config file from path.
func Load(path string) (*Config, error) {
	data, err := os.ReadFile(path)
	if err != nil {
		return nil, fmt.Errorf("config: read file: %w", err)
	}

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

	if err := cfg.validate(); err != nil {
		return nil, fmt.Errorf("config: invalid: %w", err)
	}

	return &cfg, nil
}

// validate checks that all required fields are present and values are safe.
func (c *Config) validate() error {
	var errs []error

	// Server
	if c.Server.ListenAddr == "" {
		errs = append(errs, errors.New("server.listen_addr is required"))
	}
	if c.Server.TLSCert == "" {
		errs = append(errs, errors.New("server.tls_cert is required"))
	}
	if c.Server.TLSKey == "" {
		errs = append(errs, errors.New("server.tls_key is required"))
	}

	// Database
	if c.Database.Path == "" {
		errs = append(errs, errors.New("database.path is required"))
	}

	// Tokens
	if c.Tokens.Issuer == "" {
		errs = append(errs, errors.New("tokens.issuer is required"))
	}
	if c.Tokens.DefaultExpiry.Duration <= 0 {
		errs = append(errs, errors.New("tokens.default_expiry must be positive"))
	}
	if c.Tokens.AdminExpiry.Duration <= 0 {
		errs = append(errs, errors.New("tokens.admin_expiry must be positive"))
	}
	if c.Tokens.ServiceExpiry.Duration <= 0 {
		errs = append(errs, errors.New("tokens.service_expiry must be positive"))
	}

	// Argon2 — enforce OWASP 2023 minimums (time=2, memory=65536 KiB).
	// Security: reducing these parameters weakens resistance to brute-force
	// attacks. Rejection here prevents accidental misconfiguration.
	const (
		minArgon2Time   = 2
		minArgon2Memory = 65536 // 64 MiB in KiB
		minArgon2Thread = 1
	)
	if c.Argon2.Time < minArgon2Time {
		errs = append(errs, fmt.Errorf("argon2.time must be >= %d (OWASP minimum)", minArgon2Time))
	}
	if c.Argon2.Memory < minArgon2Memory {
		errs = append(errs, fmt.Errorf("argon2.memory must be >= %d KiB (OWASP minimum)", minArgon2Memory))
	}
	if c.Argon2.Threads < minArgon2Thread {
		errs = append(errs, errors.New("argon2.threads must be >= 1"))
	}

	// Master key — exactly one source must be configured.
	hasPassEnv := c.MasterKey.PassphraseEnv != ""
	hasKeyFile := c.MasterKey.KeyFile != ""
	if !hasPassEnv && !hasKeyFile {
		errs = append(errs, errors.New("master_key: one of passphrase_env or keyfile must be set"))
	}
	if hasPassEnv && hasKeyFile {
		errs = append(errs, errors.New("master_key: only one of passphrase_env or keyfile may be set"))
	}

	return errors.Join(errs...)
}

// DefaultExpiry returns the configured default token expiry duration.
func (c *Config) DefaultExpiry() time.Duration { return c.Tokens.DefaultExpiry.Duration }

// AdminExpiry returns the configured admin token expiry duration.
func (c *Config) AdminExpiry() time.Duration { return c.Tokens.AdminExpiry.Duration }

// ServiceExpiry returns the configured service token expiry duration.
func (c *Config) ServiceExpiry() time.Duration { return c.Tokens.ServiceExpiry.Duration }