// SPDX-License-Identifier: GPL-3.0-or-later

// Package config loads the flat subset of enodia-sentinel.toml needed by the
// parallel Go agent. It intentionally uses only the Go standard library.
package config

import (
	"encoding/csv"
	"fmt"
	"os"
	"strconv"
	"strings"
	"time"
)

var defaultDetectors = []string{
	"reverse_shell", "ld_preload", "deleted_exe", "input_snooper",
	"credential_access", "stealth_network", "memory_obfuscation",
	"first_seen", "new_listener", "new_suid", "persistence", "egress",
}

// Config mirrors the Phase 1 settings consumed by the Go sweep loop. More
// fields are added as their detectors are ported.
type Config struct {
	SampleInterval  time.Duration
	HeartbeatMaxAge int
	Detectors       map[string]bool
}

// Default returns Python-compatible defaults for the fields currently used.
func Default() Config {
	detectors := make(map[string]bool, len(defaultDetectors))
	for _, name := range defaultDetectors {
		detectors[name] = true
	}
	return Config{
		SampleInterval:  4 * time.Second,
		HeartbeatMaxAge: 120,
		Detectors:       detectors,
	}
}

// Enabled reports whether a detector is enabled by configuration.
func (c Config) Enabled(name string) bool {
	return c.Detectors[name]
}

// Load reads a flat Sentinel TOML file. Missing files keep defaults, matching
// Python Config.load. Unknown keys are ignored for forward compatibility.
func Load(path string) (Config, error) {
	cfg := Default()
	if path == "" {
		path = os.Getenv("ENODIA_CONFIG")
	}
	if path == "" {
		path = "/etc/enodia-sentinel.toml"
	}
	raw, err := os.ReadFile(path)
	if os.IsNotExist(err) {
		return cfg, nil
	}
	if err != nil {
		return Config{}, err
	}
	for _, assignment := range assignments(string(raw)) {
		key, value, ok := strings.Cut(assignment, "=")
		if !ok {
			continue
		}
		key, value = strings.TrimSpace(key), strings.TrimSpace(value)
		switch key {
		case "sample_interval":
			seconds, err := strconv.ParseFloat(value, 64)
			if err != nil || seconds <= 0 {
				return Config{}, fmt.Errorf("sample_interval must be positive: %q", value)
			}
			cfg.SampleInterval = time.Duration(seconds * float64(time.Second))
		case "heartbeat_max_age":
			age, err := strconv.Atoi(value)
			if err != nil || age < 0 {
				return Config{}, fmt.Errorf("heartbeat_max_age must be non-negative: %q", value)
			}
			cfg.HeartbeatMaxAge = age
		case "detectors":
			names, err := stringArray(value)
			if err != nil {
				return Config{}, fmt.Errorf("detectors: %w", err)
			}
			cfg.Detectors = make(map[string]bool, len(names))
			for _, name := range names {
				cfg.Detectors[name] = true
			}
		}
	}
	return cfg, nil
}

func assignments(text string) []string {
	var out []string
	var current strings.Builder
	depth := 0
	for _, raw := range strings.Split(text, "\n") {
		line := strings.TrimSpace(stripComment(raw))
		if line == "" {
			continue
		}
		if current.Len() > 0 {
			current.WriteByte(' ')
		}
		current.WriteString(line)
		depth += strings.Count(line, "[") - strings.Count(line, "]")
		if depth <= 0 {
			out = append(out, current.String())
			current.Reset()
			depth = 0
		}
	}
	if current.Len() > 0 {
		out = append(out, current.String())
	}
	return out
}

func stripComment(line string) string {
	inString, escaped := false, false
	for i, r := range line {
		if escaped {
			escaped = false
			continue
		}
		if r == '\\' && inString {
			escaped = true
			continue
		}
		if r == '"' {
			inString = !inString
			continue
		}
		if r == '#' && !inString {
			return line[:i]
		}
	}
	return line
}

func stringArray(value string) ([]string, error) {
	value = strings.TrimSpace(value)
	if len(value) < 2 || value[0] != '[' || value[len(value)-1] != ']' {
		return nil, fmt.Errorf("expected array, got %q", value)
	}
	body := strings.TrimSpace(value[1 : len(value)-1])
	if body == "" {
		return []string{}, nil
	}
	reader := csv.NewReader(strings.NewReader(body))
	reader.TrimLeadingSpace = true
	fields, err := reader.Read()
	if err != nil {
		return nil, err
	}
	out := make([]string, 0, len(fields))
	for _, field := range fields {
		field = strings.TrimSpace(field)
		if field != "" {
			out = append(out, field)
		}
	}
	return out, nil
}