package api

import (
	"fmt"
	"math"
	"os"
	"path/filepath"
	"runtime"
	"time"

	"bat-api/internal/configtemplate"
	"github.com/pelletier/go-toml/v2"
)

// ConfigTOMLTemplate is the canonical template generated by bat-api. Rust
// bat consumes the same file and ignores the [api] section.
var ConfigTOMLTemplate = configtemplate.Template

// LoadConfigFromCurrentExe loads config.toml next to the running binary.
func LoadConfigFromCurrentExe(cfg *Config) error {
	exe, err := os.Executable()
	if err != nil {
		return fmt.Errorf("locate current executable: %w", err)
	}
	return LoadConfigFromBinaryDir(filepath.Dir(exe), cfg)
}

// LoadConfigFromBinaryDir loads only config.toml from binaryDir. Missing
// config.toml causes config.toml.example to be created when possible; the
// example is never parsed as the active configuration.
func LoadConfigFromBinaryDir(binaryDir string, cfg *Config) error {
	if cfg == nil {
		return fmt.Errorf("config must not be nil")
	}
	configPath := filepath.Join(binaryDir, ConfigFileName)
	examplePath := filepath.Join(binaryDir, ConfigExampleName)
	info, err := os.Lstat(configPath)
	if err != nil {
		if !os.IsNotExist(err) {
			return fmt.Errorf("stat %s: %w", configPath, err)
		}
		ensureConfigExample(examplePath)
		return nil
	}
	if info.Mode()&os.ModeSymlink != 0 || !info.Mode().IsRegular() {
		return fmt.Errorf("%s must be a regular file", configPath)
	}
	if runtime.GOOS != "windows" && info.Mode().Perm()&0o077 != 0 {
		return fmt.Errorf("%s permissions must be 0600 or stricter (current %03o)", configPath, info.Mode().Perm())
	}
	data, err := os.ReadFile(configPath)
	if err != nil {
		return fmt.Errorf("read %s: %w", configPath, err)
	}
	if err := applyAPITOML(data, cfg); err != nil {
		return fmt.Errorf("parse %s: %w", configPath, err)
	}
	return nil
}

func ensureConfigExample(path string) {
	if _, err := os.Lstat(path); err == nil || !os.IsNotExist(err) {
		return
	}
	file, err := os.OpenFile(path, os.O_WRONLY|os.O_CREATE|os.O_EXCL, 0o600)
	if err != nil {
		return
	}
	if _, err := file.WriteString(ConfigTOMLTemplate); err != nil {
		_ = file.Close()
		return
	}
	_ = file.Close()
}

func applyAPITOML(data []byte, cfg *Config) error {
	var document map[string]any
	if err := toml.Unmarshal(data, &document); err != nil {
		return err
	}
	rawAPI, exists := document["api"]
	if !exists {
		return nil
	}
	apiValues, ok := rawAPI.(map[string]any)
	if !ok {
		return fmt.Errorf("[api] must be a table")
	}
	for key, value := range apiValues {
		if err := applyAPIValue(cfg, key, value); err != nil {
			return err
		}
	}
	return nil
}

func applyAPIValue(cfg *Config, key string, raw any) error {
	field := fmt.Sprintf("[api].%s", key)
	switch key {
	case "listen":
		value, err := tomlString(raw, field)
		if err != nil {
			return err
		}
		cfg.Listen = value
	case "public_base_url":
		value, err := tomlString(raw, field)
		if err != nil {
			return err
		}
		cfg.PublicBaseURL = value
	case "state_dir":
		value, err := tomlString(raw, field)
		if err != nil {
			return err
		}
		cfg.StateDir = value
	case "socket_path":
		value, err := tomlString(raw, field)
		if err != nil {
			return err
		}
		cfg.SocketPath = value
	case "resource_root":
		value, err := tomlString(raw, field)
		if err != nil {
			return err
		}
		cfg.ResourceRoot = value
	case "server_info_file":
		value, err := tomlString(raw, field)
		if err != nil {
			return err
		}
		cfg.ServerInfoFile = value
	case "require_indexed":
		value, err := tomlBool(raw, field)
		if err != nil {
			return err
		}
		cfg.RequireIndexed = value
	case "verify_size":
		value, err := tomlBool(raw, field)
		if err != nil {
			return err
		}
		cfg.VerifySize = value
	case "rpc_timeout":
		value, err := tomlDuration(raw, field)
		if err != nil {
			return err
		}
		cfg.RPCTimeout = value
	case "refresh_interval":
		value, err := tomlDuration(raw, field)
		if err != nil {
			return err
		}
		cfg.RefreshInterval = value
	case "auth_token":
		value, err := tomlString(raw, field)
		if err != nil {
			return err
		}
		cfg.AuthToken = value
	case "auth_query_param":
		value, err := tomlString(raw, field)
		if err != nil {
			return err
		}
		cfg.AuthQueryParam = value
	case "auth_exempt_paths":
		value, err := tomlStringArray(raw, field)
		if err != nil {
			return err
		}
		cfg.AuthExemptPaths = value
	case "trust_proxy_headers":
		value, err := tomlBool(raw, field)
		if err != nil {
			return err
		}
		cfg.TrustProxyHeaders = value
	case "access_log":
		value, err := tomlBool(raw, field)
		if err != nil {
			return err
		}
		cfg.AccessLog = value
	case "rate_limit_rps":
		value, err := tomlNonNegativeNumber(raw, field)
		if err != nil {
			return err
		}
		cfg.RateLimitRPS = value
	case "rate_limit_burst":
		value, err := tomlNonNegativeInt(raw, field)
		if err != nil {
			return err
		}
		cfg.RateLimitBurst = value
	case "max_resource_page_limit":
		value, err := tomlNonNegativeInt(raw, field)
		if err != nil {
			return err
		}
		cfg.MaxResourcePageLimit = value
	case "database_url":
		value, err := tomlString(raw, field)
		if err != nil {
			return err
		}
		cfg.DatabaseURL = value
	case "database_password":
		value, err := tomlString(raw, field)
		if err != nil {
			return err
		}
		cfg.DatabasePassword = value
	case "redis_url":
		value, err := tomlString(raw, field)
		if err != nil {
			return err
		}
		cfg.RedisURL = value
	case "redis_password":
		value, err := tomlString(raw, field)
		if err != nil {
			return err
		}
		cfg.RedisPassword = value
	default:
		return fmt.Errorf("unsupported [api] key %q", key)
	}
	return nil
}

func tomlString(raw any, field string) (string, error) {
	value, ok := raw.(string)
	if !ok {
		return "", fmt.Errorf("%s must be a string (got %T)", field, raw)
	}
	return value, nil
}

func tomlBool(raw any, field string) (bool, error) {
	value, ok := raw.(bool)
	if !ok {
		return false, fmt.Errorf("%s must be a boolean (got %T)", field, raw)
	}
	return value, nil
}

func tomlDuration(raw any, field string) (time.Duration, error) {
	value, err := tomlString(raw, field)
	if err != nil {
		return 0, err
	}
	duration, err := time.ParseDuration(value)
	if err != nil || duration < 0 {
		return 0, fmt.Errorf("%s must be a non-negative duration", field)
	}
	return duration, nil
}

func tomlNonNegativeNumber(raw any, field string) (float64, error) {
	var value float64
	switch typed := raw.(type) {
	case int64:
		value = float64(typed)
	case float64:
		value = typed
	default:
		return 0, fmt.Errorf("%s must be a non-negative number (got %T)", field, raw)
	}
	if value < 0 || math.IsNaN(value) || math.IsInf(value, 0) {
		return 0, fmt.Errorf("%s must be a non-negative number", field)
	}
	return value, nil
}

func tomlNonNegativeInt(raw any, field string) (int, error) {
	value, ok := raw.(int64)
	if !ok || value < 0 || int64(int(value)) != value {
		return 0, fmt.Errorf("%s must be a non-negative integer (got %T)", field, raw)
	}
	return int(value), nil
}

func tomlStringArray(raw any, field string) ([]string, error) {
	values, ok := raw.([]any)
	if !ok {
		return nil, fmt.Errorf("%s must be an array of strings (got %T)", field, raw)
	}
	items := make([]string, len(values))
	for index, rawItem := range values {
		item, ok := rawItem.(string)
		if !ok {
			return nil, fmt.Errorf("%s[%d] must be a string (got %T)", field, index, rawItem)
		}
		items[index] = item
	}
	return items, nil
}