package rules

import (
	"regexp"
	"strings"
)

// RuleTarget is the target format for rule conversion.
type RuleTarget string

const (
	TargetMihomo RuleTarget = "mihomo"
	TargetSurge  RuleTarget = "surge"
	TargetLoon   RuleTarget = "loon"
	TargetQX     RuleTarget = "qx"
)

// Result holds the output of a rule conversion.
type Result struct {
	Content  string
	Parsed   int
	Emitted  int
	Skipped  int
	Warnings []string
}

// NormalizedRule is a parsed and normalized rule.
type NormalizedRule struct {
	Kind    string
	Value   string
	Policy  string
	Options []string
}

var kindAliases = map[string]string{
	"HOST":            "DOMAIN",
	"DOMAIN":          "DOMAIN",
	"HOST-SUFFIX":     "DOMAIN-SUFFIX",
	"DOMAIN-SUFFIX":   "DOMAIN-SUFFIX",
	"HOST-KEYWORD":    "DOMAIN-KEYWORD",
	"DOMAIN-KEYWORD":  "DOMAIN-KEYWORD",
	"IP6CIDR":         "IP-CIDR6",
	"IP-CIDR6":        "IP-CIDR6",
	"IPCIDR":          "IP-CIDR",
	"IP-CIDR":         "IP-CIDR",
	"GEOIP":           "GEOIP",
	"GEOSITE":         "GEOSITE",
	"PROCESS-NAME":    "PROCESS-NAME",
	"PROCESS":         "PROCESS-NAME",
	"DEST-PORT":       "DST-PORT",
	"DST-PORT":        "DST-PORT",
	"FINAL":           "MATCH",
	"MATCH":           "MATCH",
}

var ruleOptions = map[string]bool{
	"no-resolve":        true,
	"extended-matching": true,
	"pre-matching":      true,
}

var yamlHeaderRe = regexp.MustCompile(`(?m)^(?:payload|rules)\s*:`)

// ConvertRules converts rule content to the target format.
func ConvertRules(content string, target RuleTarget) Result {
	parsed := parseRules(content)
	var lines []string
	for _, rule := range parsed {
		line := produceRule(rule, target)
		if line != "" {
			lines = append(lines, line)
		}
	}
	return Result{
		Content:  strings.Join(lines, "\n"),
		Parsed:   len(parsed),
		Emitted:  len(lines),
		Skipped:  0,
		Warnings: []string{},
	}
}

func parseRules(content string) []NormalizedRule {
	lines := extractRuleLines(content)
	var rules []NormalizedRule
	for _, line := range lines {
		rule := parseRuleLine(line)
		if rule != nil {
			rules = append(rules, *rule)
		}
	}
	return rules
}

func extractRuleLines(content string) []string {
	text := strings.TrimSpace(content)
	if text == "" {
		return []string{}
	}
	if yamlHeaderRe.MatchString(text) {
		var lines []string
		for _, line := range strings.Split(text, "\n")[1:] {
			line = strings.TrimSpace(line)
			line = strings.TrimPrefix(line, "-")
			line = strings.TrimSpace(line)
			if line != "" && !strings.HasPrefix(line, "#") {
				lines = append(lines, line)
			}
		}
		return lines
	}
	var lines []string
	for _, line := range strings.Split(text, "\n") {
		line = strings.TrimSpace(line)
		// Strip surrounding quotes
		if len(line) >= 2 && (line[0] == '"' || line[0] == '\'') && line[len(line)-1] == line[0] {
			line = line[1 : len(line)-1]
		}
		if line != "" && !strings.HasPrefix(line, "#") && !strings.HasPrefix(line, ";") {
			lines = append(lines, line)
		}
	}
	return lines
}

func parseRuleLine(line string) *NormalizedRule {
	fields := splitCsv(line)
	if len(fields) == 0 {
		return nil
	}
	kind := kindAliases[strings.ToUpper(fields[0])]
	if kind == "" {
		return nil
	}
	if kind == "MATCH" {
		policy := ""
		if len(fields) > 1 {
			policy = fields[1]
		}
		var options []string
		for _, f := range fields[2:] {
			if f != "" {
				options = append(options, f)
			}
		}
		return &NormalizedRule{Kind: kind, Policy: policy, Options: options}
	}
	if len(fields) < 2 {
		return nil
	}
	value := strings.TrimSpace(fields[1])
	if value == "" {
		return nil
	}
	var trailing []string
	for _, f := range fields[2:] {
		if f != "" {
			trailing = append(trailing, f)
		}
	}
	policy := ""
	var options []string
	for _, f := range trailing {
		if ruleOptions[strings.ToLower(f)] {
			options = append(options, f)
		} else {
			if policy == "" {
				policy = f
			}
		}
	}
	return &NormalizedRule{Kind: kind, Value: value, Policy: policy, Options: options}
}

func produceRule(rule NormalizedRule, target RuleTarget) string {
	kind := rule.Kind
	if target == TargetQX {
		kind = qxKind(rule.Kind)
	}
	var fields []string
	if rule.Kind == "MATCH" {
		if target == TargetQX {
			fields = append(fields, "FINAL")
		} else {
			fields = append(fields, kind)
		}
		if rule.Policy != "" {
			fields = append(fields, rule.Policy)
		}
	} else {
		fields = append(fields, kind, rule.Value)
		if rule.Policy != "" {
			fields = append(fields, rule.Policy)
		}
	}
	for _, opt := range rule.Options {
		if target == TargetQX {
			if strings.ToLower(opt) == "no-resolve" {
				fields = append(fields, opt)
			}
		} else {
			fields = append(fields, opt)
		}
	}
	return strings.Join(fields, ",")
}

func qxKind(kind string) string {
	aliases := map[string]string{
		"DOMAIN":         "HOST",
		"DOMAIN-SUFFIX":  "HOST-SUFFIX",
		"DOMAIN-KEYWORD": "HOST-KEYWORD",
		"IP-CIDR":        "IP-CIDR",
		"IP-CIDR6":       "IP6-CIDR",
		"PROCESS-NAME":   "PROCESS-NAME",
		"DST-PORT":       "DEST-PORT",
		"MATCH":          "FINAL",
	}
	if a, ok := aliases[kind]; ok {
		return a
	}
	return kind
}

func splitCsv(line string) []string {
	var output []string
	current := ""
	quote := byte(0)
	for i := 0; i < len(line); i++ {
		c := line[i]
		if quote != 0 {
			if c == quote {
				quote = 0
			} else {
				current += string(c)
			}
		} else if c == '"' || c == '\'' {
			quote = c
		} else if c == ',' {
			output = append(output, strings.TrimSpace(current))
			current = ""
		} else {
			current += string(c)
		}
	}
	if strings.TrimSpace(current) != "" {
		output = append(output, strings.TrimSpace(current))
	}
	return output
}