package config

import (
	"fmt"
	"os"
	"reflect"
	"strings"
	"time"

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

type Config struct {
	Server ServerConfig `toml:"server"`
	Gitea  GiteaConfig  `toml:"gitea"`
	Log    LogConfig    `toml:"log"`
}

type ServerConfig struct {
	ListenAddr string `toml:"listen_addr"`
}

type GiteaConfig struct {
	URL            string       `toml:"url"`
	Org            string       `toml:"org"`
	WebhookSecret  string       `toml:"webhook_secret"`
	PollInterval   Duration     `toml:"poll_interval"`
	FetchTimeout   Duration     `toml:"fetch_timeout"`
	MaxConcurrency int          `toml:"max_concurrency"`
	ExcludePaths   ExcludePaths `toml:"exclude_paths"`
	ExcludeRepos   ExcludeRepos `toml:"exclude_repos"`
}

type ExcludePaths struct {
	Patterns []string `toml:"patterns"`
}

type ExcludeRepos struct {
	Names []string `toml:"names"`
}

type LogConfig struct {
	Level string `toml:"level"`
}

// Duration wraps time.Duration for TOML string parsing.
type Duration struct {
	time.Duration
}

func (d *Duration) UnmarshalText(text []byte) error {
	var err error
	d.Duration, err = time.ParseDuration(string(text))
	return err
}

func (d Duration) MarshalText() ([]byte, error) {
	return []byte(d.String()), nil
}

func Load(path string) (*Config, error) {
	data, err := os.ReadFile(path) // #nosec G304 -- config path is operator-controlled
	if err != nil {
		return nil, fmt.Errorf("read config: %w", err)
	}

	cfg := &Config{
		Server: ServerConfig{
			ListenAddr: ":8080",
		},
		Gitea: GiteaConfig{
			URL:            "https://git.wntrmute.dev",
			Org:            "mc",
			PollInterval:   Duration{15 * time.Minute},
			FetchTimeout:   Duration{30 * time.Second},
			MaxConcurrency: 4,
			ExcludePaths: ExcludePaths{
				Patterns: []string{"vendor/", ".claude/", "node_modules/", ".junie/"},
			},
		},
		Log: LogConfig{
			Level: "info",
		},
	}

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

	applyEnvOverrides(cfg)

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

	return cfg, nil
}

func (c *Config) validate() error {
	if c.Server.ListenAddr == "" {
		return fmt.Errorf("server.listen_addr is required")
	}
	if c.Gitea.URL == "" {
		return fmt.Errorf("gitea.url is required")
	}
	if c.Gitea.Org == "" {
		return fmt.Errorf("gitea.org is required")
	}
	if c.Gitea.MaxConcurrency < 1 {
		return fmt.Errorf("gitea.max_concurrency must be >= 1")
	}
	return nil
}

// applyEnvOverrides checks for MCDOC_* environment variables and applies
// them to the config. Also checks $PORT for MCP agent port assignment.
func applyEnvOverrides(cfg *Config) {
	if port := os.Getenv("PORT"); port != "" {
		cfg.Server.ListenAddr = ":" + port
	}

	applyEnvToStruct("MCDOC", reflect.ValueOf(cfg).Elem())
}

func applyEnvToStruct(prefix string, v reflect.Value) {
	t := v.Type()
	for i := range t.NumField() {
		field := t.Field(i)
		fv := v.Field(i)

		tag := field.Tag.Get("toml")
		if tag == "" || tag == "-" {
			continue
		}

		envKey := prefix + "_" + strings.ToUpper(tag)

		if fv.Kind() == reflect.Struct && field.Type != reflect.TypeOf(Duration{}) {
			applyEnvToStruct(envKey, fv)
			continue
		}

		envVal := os.Getenv(envKey)
		if envVal == "" {
			continue
		}

		switch fv.Kind() {
		case reflect.String:
			fv.SetString(envVal)
		case reflect.Int:
			var n int
			if _, err := fmt.Sscanf(envVal, "%d", &n); err == nil {
				fv.SetInt(int64(n))
			}
		}

		if field.Type == reflect.TypeOf(Duration{}) {
			if d, err := time.ParseDuration(envVal); err == nil {
				fv.Set(reflect.ValueOf(Duration{d}))
			}
		}
	}
}