// Package config loads and validates the lethe collector configuration from a
// YAML file plus LETHE_COLLECTOR_* environment overrides.
//
// Validation runs in fail-fast mode: any unknown YAML key, missing required
// field, or out-of-range value rejects the load with a culpa-wrapped error.
// The only field without a default is host — the operator must choose a stable
// identity for this machine.
package config

import (
	"errors"
	"io/fs"
	"os"
	"path/filepath"
	"strings"
	"time"

	"github.com/go-playground/validator/v10"
	"github.com/go-viper/mapstructure/v2"
	"github.com/spf13/viper"
	"go.bigb.es/auxilia/culpa"
)

// Config is the root collector configuration.
type Config struct {
	Host             string         `mapstructure:"host"       validate:"required"`
	ServerURL        string         `mapstructure:"server_url" validate:"required,url"`
	RemoteUserHeader string         `mapstructure:"remote_user_header"`
	StateDir         string         `mapstructure:"state_dir"`
	HTTP             HTTPConfig     `mapstructure:"http"`
	Outbox           OutboxConfig   `mapstructure:"outbox"`
	Sources          []SourceConfig `mapstructure:"sources"    validate:"required,min=1,dive"`
	Log              LogConfig      `mapstructure:"log"`
}

// HTTPConfig tunes the outbound POST client.
type HTTPConfig struct {
	Timeout  time.Duration `mapstructure:"timeout"    validate:"gt=0"`
	RetryMax int           `mapstructure:"retry_max"  validate:"gte=0"`
}

// OutboxConfig caps the local safety-net buffer.
type OutboxConfig struct {
	MaxBytes int64 `mapstructure:"max_bytes" validate:"gt=0"`
}

// SourceConfig describes one tool's source root and polling behaviour.
type SourceConfig struct {
	Tool          string        `mapstructure:"tool"            validate:"required"`
	Path          string        `mapstructure:"path"            validate:"required"`
	PollInterval  time.Duration `mapstructure:"poll_interval"   validate:"gt=0"`
	BatchMaxLines int           `mapstructure:"batch_max_lines" validate:"gt=0"`
	BatchMaxBytes int64         `mapstructure:"batch_max_bytes" validate:"gt=0"`
}

// LogConfig selects log level and formatter.
type LogConfig struct {
	Level  string `mapstructure:"level"  validate:"required,oneof=debug info warn error"`
	Format string `mapstructure:"format" validate:"required,oneof=tint json human"`
}

// Load reads YAML from path, applies env overrides, fills documented defaults,
// expands ~ in paths, and validates. Errors carry a culpa code.
func Load(path string) (*Config, error) {
	v := viper.New()
	v.SetConfigFile(path)
	v.SetEnvPrefix("LETHE_COLLECTOR")
	v.SetEnvKeyReplacer(strings.NewReplacer(".", "_"))
	v.AutomaticEnv()

	registerDefaults(v)

	if err := v.ReadInConfig(); err != nil {
		if _, ok := err.(viper.ConfigFileNotFoundError); ok {
			return nil, culpa.WithCode(culpa.Wrap(err, "config file not found"), "CONFIG_NOT_FOUND")
		}
		if isFileMissing(err) {
			return nil, culpa.WithCode(culpa.Wrap(err, "config file not found"), "CONFIG_NOT_FOUND")
		}
		return nil, culpa.WithCode(culpa.Wrap(err, "parse config"), "CONFIG_PARSE")
	}

	var cfg Config
	if err := v.UnmarshalExact(
		&cfg,
		viper.DecodeHook(mapstructure.ComposeDecodeHookFunc(
			mapstructure.StringToTimeDurationHookFunc(),
			mapstructure.StringToSliceHookFunc(","),
		)),
		func(c *mapstructure.DecoderConfig) {
			c.ErrorUnused = true
		},
	); err != nil {
		return nil, culpa.WithCode(culpa.Wrap(err, "decode config"), "CONFIG_PARSE")
	}

	applySourceDefaults(&cfg)
	expandTildes(&cfg)

	val := validator.New(validator.WithRequiredStructEnabled())
	if err := val.Struct(&cfg); err != nil {
		return nil, culpa.WithCode(culpa.Wrap(err, "validate config"), "CONFIG_VALIDATE")
	}
	return &cfg, nil
}

// MustLoad calls Load and panics on error.
func MustLoad(path string) *Config {
	cfg, err := Load(path)
	if err != nil {
		panic(err)
	}
	return cfg
}

func registerDefaults(v *viper.Viper) {
	home, _ := os.UserHomeDir()
	v.SetDefault("state_dir", filepath.Join(home, ".local/state/lethe"))
	v.SetDefault("http.timeout", 30*time.Second)
	v.SetDefault("http.retry_max", 5)
	v.SetDefault("outbox.max_bytes", int64(104857600)) // 100 MiB
	v.SetDefault("log.level", "info")
	v.SetDefault("log.format", "human")
}

func applySourceDefaults(cfg *Config) {
	for i := range cfg.Sources {
		if cfg.Sources[i].PollInterval == 0 {
			cfg.Sources[i].PollInterval = 30 * time.Second
		}
		if cfg.Sources[i].BatchMaxLines == 0 {
			cfg.Sources[i].BatchMaxLines = 500
		}
		if cfg.Sources[i].BatchMaxBytes == 0 {
			cfg.Sources[i].BatchMaxBytes = 8388608 // 8 MiB
		}
	}
}

func expandTildes(cfg *Config) {
	cfg.StateDir = expandTilde(cfg.StateDir)
	for i := range cfg.Sources {
		cfg.Sources[i].Path = expandTilde(cfg.Sources[i].Path)
	}
}

func expandTilde(path string) string {
	if path == "~" || strings.HasPrefix(path, "~/") {
		home, err := os.UserHomeDir()
		if err != nil {
			return path
		}
		if path == "~" {
			return home
		}
		return filepath.Join(home, path[2:])
	}
	return path
}

func isFileMissing(err error) bool {
	var pe *fs.PathError
	if errors.As(err, &pe) {
		return errors.Is(pe.Err, fs.ErrNotExist)
	}
	return errors.Is(err, fs.ErrNotExist)
}