// Package routing holds the per-user routing profile (可配置分流): the rule
// model, persistence (Store), and — in later tasks — validation and sing-box
// config rendering.
package routing

import (
	"net"
	"strings"
)

// Rule is a single user-authored routing rule (domain/IP/geosite match →
// proxy/direct action). Validation of Type/Action/Value lives in Task 2.
type Rule struct {
	Type    string `json:"type"`
	Value   string `json:"value"`
	Action  string `json:"action"`
	Note    string `json:"note,omitempty"`
	Enabled bool   `json:"enabled"`
}

// Builtin toggles the built-in routing behaviors that previously were
// hardcoded into the server's sing-box config rendering.
type Builtin struct {
	ChinaDirect bool `json:"china_direct"`
	// LanDirect is reserved/always-on: the system layer (route_exclude_address
	// + the hardcoded LAN direct rule in clientconfig.go) renders unconditionally
	// regardless of this flag's value — the renderer does not read it. Kept in
	// the wire contract for a possible future per-user opt-out; today it has no
	// effect on rendering.
	LanDirect bool `json:"lan_direct"`
	// PrivateViaTunnel is reserved/always-on: when PANGOLIN_PRIVATE_SPLIT_DOMAINS
	// is configured, those domains are always force-routed through the tunnel —
	// the renderer does not read this flag. Kept in the wire contract for a
	// possible future per-user opt-out; today it has no effect on rendering.
	PrivateViaTunnel bool `json:"private_via_tunnel"`
}

// Profile is a user's full routing configuration, persisted as JSON in
// routing_profiles.profile_json.
type Profile struct {
	Mode    string  `json:"mode"` // rule | global | direct
	Builtin Builtin `json:"builtin"`
	Rules   []Rule  `json:"rules"`
	Final   string  `json:"final"` // proxy | direct
}

// Default is the fail-safe fallback profile, equivalent to today's hardcoded
// behavior (smart routing + China direct + no user rules).
func Default() *Profile {
	return &Profile{
		Mode:    "rule",
		Builtin: Builtin{ChinaDirect: true, LanDirect: true, PrivateViaTunnel: true},
		Rules:   []Rule{},
		Final:   "proxy",
	}
}

// FieldError describes a single validation failure. Index is the offending
// rule's position in Profile.Rules, or -1 for profile-level fields
// (mode/final/rules count).
type FieldError struct {
	Index  int    `json:"index"`
	Field  string `json:"field"`
	Reason string `json:"reason"`
}

// MaxRules is the upper bound on the number of rules a profile may hold.
const MaxRules = 200

var validType = map[string]bool{"domain": true, "domain_suffix": true, "domain_keyword": true, "ip_cidr": true, "geoip": true, "geosite": true}
var validAction = map[string]bool{"direct": true, "proxy": true, "reject": true}
var geoWhitelist = map[string]bool{"cn": true} // geoip/geosite 仅自托管 cn

// reservedTunnelNet 是隧道/内部 DNS 保留段(含隧道 DNS 172.19.0.2)。direct 的
// ip_cidr 规则会并入 TUN 入站 route_exclude_address(OS/auto_route 层,位于系统
// 强制层之下),若排除此段会静默旁路 hijack-dns 与整条隧道 —— 见 Validate 里的守卫。
var reservedTunnelNet = mustCIDR("172.16.0.0/12")

func mustCIDR(s string) *net.IPNet {
	_, n, err := net.ParseCIDR(s)
	if err != nil {
		panic(err)
	}
	return n
}

// cidrsOverlap 判断两个对齐的 CIDR 块是否相交(其一的网络地址落在另一之内)。
// 家族不匹配(v4 vs v6)时 net.IPNet.Contains 返回 false,故混用安全。
func cidrsOverlap(a, b *net.IPNet) bool {
	return a.Contains(b.IP) || b.Contains(a.IP)
}

// SafeToExclude 报告一条 direct 的 ip_cidr 值是否可安全并入 TUN route_exclude_address。
// 与 Validate 的守卫同源:catch-all 或与隧道/DNS 保留段重叠一律拒绝。渲染层(clientconfig)
// 在合并 extraExclude 前调用它,作纵深防护——即便有写入闸之前存下的历史坏行,也不会
// 让它静默旁路系统强制层。
func SafeToExclude(cidr string) bool {
	_, ipnet, err := net.ParseCIDR(cidr)
	if err != nil {
		return false
	}
	if ones, _ := ipnet.Mask.Size(); ones == 0 {
		return false
	}
	return !cidrsOverlap(ipnet, reservedTunnelNet)
}

// Validate checks the profile against the type/action whitelist, CIDR
// syntax, the geo set whitelist, and the rule count cap. It returns an empty
// (non-nil) slice when the profile is valid — so JSON encoding produces `[]`
// rather than `null` — and every violation is reported independently (no
// short-circuiting) so callers can surface all errors at once.
func (p *Profile) Validate() []FieldError {
	errs := []FieldError{}
	if p.Mode != "rule" && p.Mode != "global" && p.Mode != "direct" {
		errs = append(errs, FieldError{-1, "mode", "must be rule|global|direct"})
	}
	if p.Final != "proxy" && p.Final != "direct" {
		errs = append(errs, FieldError{-1, "final", "must be proxy|direct"})
	}
	if len(p.Rules) > MaxRules {
		errs = append(errs, FieldError{-1, "rules", "exceeds max 200"})
	}
	for i, r := range p.Rules {
		if !validType[r.Type] {
			errs = append(errs, FieldError{i, "type", "invalid type"})
		}
		if !validAction[r.Action] {
			errs = append(errs, FieldError{i, "action", "invalid action"})
		}
		if r.Value == "" {
			errs = append(errs, FieldError{i, "value", "empty"})
		}
		switch r.Type {
		case "ip_cidr":
			_, ipnet, err := net.ParseCIDR(r.Value)
			if err != nil {
				errs = append(errs, FieldError{i, "value", "invalid CIDR"})
			} else if r.Action == "direct" {
				// direct 的 ip_cidr 并入 TUN route_exclude_address(系统层之下)。
				// catch-all(/0)会整条旁路隧道;与隧道/DNS 保留段重叠会破坏隧道 DNS。
				// 二者都能静默越过系统强制层,拒绝之(proxy/reject 不入排除表,不受限)。
				if ones, _ := ipnet.Mask.Size(); ones == 0 {
					errs = append(errs, FieldError{i, "value", "direct ip_cidr must not be catch-all (0.0.0.0/0 or ::/0)"})
				} else if cidrsOverlap(ipnet, reservedTunnelNet) {
					errs = append(errs, FieldError{i, "value", "direct ip_cidr must not overlap reserved tunnel range 172.16.0.0/12"})
				}
			}
		case "geoip", "geosite":
			if !geoWhitelist[strings.ToLower(r.Value)] {
				errs = append(errs, FieldError{i, "value", "geo set not in whitelist (cn only)"})
			}
		}
	}
	return errs
}

// dedupKey identifies a rule for Normalize's de-duplication. Using a struct
// (rather than string-concatenating Type+Value+Action with a separator)
// avoids false-collision when a value itself contains the separator
// character.
type dedupKey struct{ Type, Value, Action string }

// Normalize trims rule values and de-duplicates rules by (type, value,
// action), keeping the first occurrence's position (and its Note/Enabled).
func (p *Profile) Normalize() {
	seen := map[dedupKey]bool{}
	out := p.Rules[:0]
	for _, r := range p.Rules {
		r.Value = strings.TrimSpace(r.Value)
		k := dedupKey{r.Type, r.Value, r.Action}
		if seen[k] {
			continue
		}
		seen[k] = true
		out = append(out, r)
	}
	p.Rules = out
}