package config

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

	"github.com/spf13/viper"
)

type Config struct {
	Shell      ShellConfig      `mapstructure:"shell"`
	NetBox     NetBoxConfig     `mapstructure:"netbox"`
	NetBoxes   []NetBoxConfig   `mapstructure:"netboxes"`
	Resolver   ResolverConfig   `mapstructure:"resolver"`
	Cache      CacheConfig      `mapstructure:"cache"`
	SSH        SSHConfig        `mapstructure:"ssh"`
	Shortcuts  ShortcutsConfig  `mapstructure:"shortcuts"`
	Completion CompletionConfig `mapstructure:"completion"`
}

type ShellConfig struct {
	Alias string `mapstructure:"alias"`
}

type NetBoxConfig struct {
	Name         string     `mapstructure:"name"`
	URL          string     `mapstructure:"url"`
	Token        string     `mapstructure:"token"`
	TokenVersion int        `mapstructure:"token_version"`
	SSH          SSHOptions `mapstructure:"ssh"`
}

type ResolverConfig struct {
	Strategies        []string `mapstructure:"strategies"`
	ManagementSubnets []string `mapstructure:"management_subnets"`
	InterfaceName     string   `mapstructure:"interface_name"`
}

type CacheConfig struct {
	TTL  int    `mapstructure:"ttl"`
	Path string `mapstructure:"path"`
}

type SSHConfig struct {
	DefaultUser string `mapstructure:"default_user"`
	DefaultPort int    `mapstructure:"default_port"`
	SSHOptions  `mapstructure:",squash"`
	Rules       []SSHRule `mapstructure:"rules"`
}

type CompletionConfig struct {
	// MaxResults limits the number of hostnames offered per completion; 0 = unlimited.
	MaxResults int `mapstructure:"max_results"`
}

type ShortcutsConfig struct {
	Domains      []string          `mapstructure:"domains"`
	StripHyphens bool              `mapstructure:"strip_hyphens"`
	Rewrites     []ShortcutRewrite `mapstructure:"rewrites"`
}

// ShortcutRewrite replaces every match of Pattern (Go regexp syntax) with
// Replace, which may reference groups as $1. Applied after domain stripping.
type ShortcutRewrite struct {
	Pattern string `mapstructure:"pattern"`
	Replace string `mapstructure:"replace"`
}

// Enabled reports whether any shortcut normalization is configured.
func (s ShortcutsConfig) Enabled() bool {
	return len(s.Domains) > 0 || s.StripHyphens || len(s.Rewrites) > 0
}

// Validate rejects rewrite rules that cannot be compiled.
func (s ShortcutsConfig) Validate() error {
	for i, rewrite := range s.Rewrites {
		if rewrite.Pattern == "" {
			return fmt.Errorf("shortcuts.rewrites[%d]: pattern is required", i)
		}
		if _, err := regexp.Compile(rewrite.Pattern); err != nil {
			return fmt.Errorf("shortcuts.rewrites[%d]: invalid pattern %q: %v", i, rewrite.Pattern, err)
		}
	}
	return nil
}

// Path returns the canonical config file path.
func Path() string {
	configDir, err := os.UserConfigDir()
	if err != nil {
		configDir = filepath.Join(os.Getenv("HOME"), ".config")
	}
	return filepath.Join(configDir, "netssh.yaml")
}

func Load() (*Config, error) {
	v := viper.New()

	v.SetDefault("resolver.strategies", []string{"management_subnet", "primary_ip"})
	v.SetDefault("resolver.management_subnets", []string{})
	v.SetDefault("cache.ttl", 3600)

	configDir, err := os.UserConfigDir()
	if err == nil {
		v.SetConfigName("netssh")
		v.SetConfigType("yaml")
		v.AddConfigPath(filepath.Join(configDir))
		v.AddConfigPath(".")
	}

	v.SetEnvPrefix("NETSSH")
	v.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
	v.AutomaticEnv()
	for _, key := range []string{"netbox.url", "netbox.token", "netbox.token_version", "resolver.strategies", "resolver.management_subnets", "resolver.interface_name", "cache.ttl", "cache.path", "ssh.default_user", "ssh.default_port", "shortcuts.domains", "shortcuts.strip_hyphens", "shell.alias", "ssh.proxy_jump", "ssh.host_key_checking", "ssh.target", "ssh.address_family", "completion.max_results"} {
		if err := v.BindEnv(key); err != nil {
			return nil, err
		}
	}

	if err := v.ReadInConfig(); err != nil {
		if _, ok := err.(viper.ConfigFileNotFoundError); !ok {
			return nil, fmt.Errorf("reading config: %w", err)
		}
	}

	var cfg Config
	if err := v.Unmarshal(&cfg); err != nil {
		return nil, fmt.Errorf("parsing config: %w", err)
	}
	// Legacy environment variables must not invent an additional unnamed source
	// when a file explicitly configures named instances (including wizard migration).
	if len(cfg.NetBoxes) > 0 && !v.InConfig("netbox.url") {
		cfg.NetBox = NetBoxConfig{}
	}

	if err := ValidateCommandAlias(cfg.Shell.Alias); err != nil {
		return nil, err
	}

	if cfg.NetBox.TokenVersion == 0 && cfg.NetBox.Token != "" {
		if strings.HasPrefix(cfg.NetBox.Token, "nbt_") {
			cfg.NetBox.TokenVersion = 2
		} else {
			cfg.NetBox.TokenVersion = 1
		}
	}

	if err := cfg.ValidateNetBoxes(); err != nil {
		return nil, err
	}
	if err := cfg.ValidateSSH(); err != nil {
		return nil, err
	}
	if err := cfg.Shortcuts.Validate(); err != nil {
		return nil, err
	}
	for i := range cfg.NetBoxes {
		source := &cfg.NetBoxes[i]
		source.Name = strings.ToLower(source.Name)
		if source.TokenVersion == 0 && source.Token != "" {
			source.TokenVersion = 1
			if strings.HasPrefix(source.Token, "nbt_") {
				source.TokenVersion = 2
			}
		}
	}

	if cfg.Cache.Path == "" {
		cacheDir, err := os.UserCacheDir()
		if err != nil {
			cacheDir = filepath.Join(os.Getenv("HOME"), ".cache")
		}
		cfg.Cache.Path = filepath.Join(cacheDir, "netssh", "hosts.json")
	}

	return &cfg, nil
}

// ValidateCommandAlias restricts aliases to portable shell identifiers.
func ValidateCommandAlias(name string) error {
	if name == "" {
		return nil
	}
	if !regexp.MustCompile(`^[a-zA-Z_][a-zA-Z0-9_]*$`).MatchString(name) {
		return fmt.Errorf("shell.alias must be a shell identifier (e.g. j)")
	}
	switch name {
	case "netssh", "alias", "unalias", "source", "eval", "exec", "command", "builtin", "if", "then", "else", "elif", "fi", "for", "while", "until", "do", "done", "case", "esac", "in", "function", "select", "time", "coproc", "end", "begin", "switch", "set", "export", "return", "break", "continue", "not", "and", "or":
		return fmt.Errorf("shell.alias %q is reserved; choose another name", name)
	}
	return nil
}