package render

import (
	"fmt"
	"net/netip"
	"path/filepath"
	"slices"
	"strings"

	"jarl/internal/blocking"
	"jarl/internal/model"
	"jarl/internal/namedconf"
)

// KindPolicy is the kind of a rendered rules policy zone file.
const KindPolicy = "policy"

// PolicyZone is a response policy zone in named's configuration
// (docs/blocking.md).
type PolicyZone struct {
	Name   string // without the final dot
	ViewID int64  // 0 without views
	View   string // "" without views
	File   string
	ListID int64 // the blocklist; 0 for the rules zone and gates
	// Gate, for a gate zone: the clients it lets through (past every zone
	// after it), and the step whose lists it is in front of.
	Gate     []netip.Prefix
	GateStep string
}

// IsGate reports whether z is a gate zone.
func (z PolicyZone) IsGate() bool { return z.GateStep != "" }

// BlocklistsDir holds the zone files of downloaded blocklists, one per
// list, shared by the views that use it.
func (p Paths) BlocklistsDir() string { return filepath.Join(p.CacheDir, "blocklists") }

// BlocklistFile returns the zone file of a blocklist. It is named after
// the list's ID, so renaming the list doesn't move it.
func (p Paths) BlocklistFile(id int64) string {
	return filepath.Join(p.BlocklistsDir(), fmt.Sprintf("list-%d.rpz", id))
}

// rulesFile returns a view's rules zone file.
func (p Paths) rulesFile(view string) string {
	return filepath.Join(p.ZoneDir, ViewDir(view), blocking.RulesZone+".rpz")
}

// PolicyZones returns the policy zones named loads, per view in view
// order, each view's in the order named checks them: the rules zone first
// (rules win over lists), then for each step (normal, then the steps above
// it) a gate letting through the clients below that step, when there are
// any, and the step's enabled lists by name.
func PolicyZones(s *model.State, p Paths) []PolicyZone {
	var out []PolicyZone
	rules, lists := s.SortedBlockRules(), s.SortedBlocklists()
	scopes := []int64{0}
	if len(s.Views) > 0 {
		scopes = nil
		for _, v := range s.OrderedViews() {
			scopes = append(scopes, v.ID)
		}
	}
	for _, vid := range scopes {
		view := ""
		if v := s.Views[vid]; v != nil {
			view = v.Name
		}
		var zones []PolicyZone
		hasRules := false
		for _, r := range rules {
			if slices.Contains(s.BlockingViews(r.ViewIDs), vid) {
				hasRules = true
				break
			}
		}
		assigns := ClientAssignments(s, vid)
		for k, step := range append([]int64{model.StepNormal}, stepIDs(s)...) {
			var tier []PolicyZone
			for _, b := range lists {
				if !b.Disabled && b.StepID == step && slices.Contains(s.BlockingViews(b.ViewIDs), vid) {
					tier = append(tier, PolicyZone{Name: blocking.ListZone(b.Name), ViewID: vid, View: view, File: p.BlocklistFile(b.ID), ListID: b.ID})
				}
			}
			if len(tier) == 0 {
				continue
			}
			// The clients below this step pass, and never see its lists.
			if pass := blocking.PassBelow(assigns, k); len(pass) > 0 {
				name := "off"
				if k > 0 {
					name = s.StepName(step)
				}
				zones = append(zones, PolicyZone{Name: blocking.GateZone(name), ViewID: vid, View: view, File: p.gateFile(view, name), Gate: pass, GateStep: s.StepName(step)})
			}
			zones = append(zones, tier...)
		}
		// While paused, every view with blocking gets a rules zone: it
		// lets everything through.
		if hasRules || s.Settings.BlockingPaused() && len(zones) > 0 {
			out = append(out, PolicyZone{Name: blocking.RulesZone, ViewID: vid, View: view, File: p.rulesFile(view)})
		}
		out = append(out, zones...)
	}
	return out
}

// gateFile returns a view's gate zone file for a step.
func (p Paths) gateFile(view, name string) string {
	return filepath.Join(p.ZoneDir, ViewDir(view), blocking.GateZone(name)+".rpz")
}

// stepIDs returns the IDs of the steps above normal, lowest first.
func stepIDs(s *model.State) []int64 {
	var out []int64
	for _, st := range s.OrderedBlockSteps() {
		out = append(out, st.ID)
	}
	return out
}

// ClientAssignments returns the step ranks the client groups of a view
// give addresses (blocking.PassBelow).
func ClientAssignments(s *model.State, viewID int64) []blocking.Assignment {
	var out []blocking.Assignment
	for _, g := range s.SortedClientGroups() {
		if !slices.Contains(s.BlockingViews(g.ViewIDs), viewID) {
			continue
		}
		rank, ok := s.StepRank(g.StepID)
		if !ok {
			continue
		}
		for _, p := range s.GroupPrefixes(g) {
			out = append(out, blocking.Assignment{Prefix: p, Rank: rank})
		}
	}
	return out
}

// ViewRules returns the rules that apply in a view (0 without views).
func ViewRules(s *model.State, viewID int64) []blocking.Rule {
	var out []blocking.Rule
	for _, r := range s.SortedBlockRules() {
		if slices.Contains(s.BlockingViews(r.ViewIDs), viewID) {
			out = append(out, blocking.Rule{Name: r.Name, Action: r.Action, Exact: r.Exact})
		}
	}
	return out
}

// writeResponsePolicy writes the response-policy statement for a view's
// policy zones (or the server's, without views). Rewrites are logged to
// Jarl's response log when statistics read it, and not at all otherwise
// (they would go to named's default log).
func writeResponsePolicy(w *confWriter, zones []PolicyZone, logRewrites bool) {
	if len(zones) == 0 {
		return
	}
	w.begin("blocking", 0, "blocking (rules and blocklists)")
	w.write("\t// Blocking (docs/blocking.md): rules first, then blocklists.\n\tresponse-policy {\n")
	for _, z := range zones {
		// Apply a new version at once: Jarl reloads a list only when it
		// changed (at most every blocking.refresh), so named's default
		// delay for batching frequent updates only adds a wait.
		opts := []string{"min-update-interval 0"}
		// A gate lets most queries through: logging that would double
		// the response log, and it blocks nothing.
		if !logRewrites || z.IsGate() {
			opts = append(opts, "log no")
		}
		w.write(fmt.Sprintf("\t\tzone %s%s;\n", namedconf.QuoteString(z.Name), prefixSpace(strings.Join(opts, " "))))
	}
	// Block without waiting for the real answer, and also for clients
	// that ask for DNSSEC data.
	w.write("\t} qname-wait-recurse no break-dnssec yes;\n")
	w.end()
}

func prefixSpace(s string) string {
	if s == "" {
		return ""
	}
	return " " + s
}

// writePolicyZones writes the zone statements of policy zones and adds
// their files to the output: rules zone files are rendered, blocklist
// files only listed (jarld downloads them; see Output.Blocklists).
func writePolicyZones(w *confWriter, s *model.State, zones []PolicyZone, out *Output, indent int) {
	tabs := strings.Repeat("\t", indent)
	for _, z := range zones {
		w.write("\n")
		label := "blocking: your rules"
		switch {
		case z.ListID != 0:
			label = "blocking: blocklist " + s.Blocklists[z.ListID].Name
		case z.IsGate():
			label = "blocking: clients below step " + z.GateStep
		}
		w.begin("blocking", z.ListID, label)
		w.write(fmt.Sprintf("%szone %s {\n%s\ttype primary;\n%s\tfile %s;\n%s\tallow-query { none; };\n%s\tallow-transfer { none; };\n%s\tnotify no;\n%s};\n",
			tabs, namedconf.QuoteString(z.Name), tabs, tabs, namedconf.QuoteString(z.File), tabs, tabs, tabs, tabs))
		w.end()
		if z.ListID != 0 {
			out.Blocklists = appendUnique(out.Blocklists, z.File)
			continue
		}
		if z.IsGate() {
			title := "Clients that skip the lists from step " + z.GateStep + " on"
			if z.View != "" {
				title += " in view " + z.View
			}
			out.Files = append(out.Files, &File{Path: z.File, Content: []byte(blocking.GateZoneFile(title, z.Gate)), Mode: 0o640, Kind: KindPolicy})
			continue
		}
		title := "Blocking rules"
		if z.View != "" {
			title += " for view " + z.View
		}
		content := blocking.RulesZoneFile(title, ViewRules(s, z.ViewID))
		if s.Settings.BlockingPaused() {
			content = blocking.PausedZoneFile(title)
		}
		out.Files = append(out.Files, &File{Path: z.File, Content: []byte(content), Mode: 0o640, Kind: KindPolicy})
	}
}

// scopeZones returns the policy zones of one view (0 without views).
func scopeZones(all []PolicyZone, viewID int64) []PolicyZone {
	var out []PolicyZone
	for _, z := range all {
		if z.ViewID == viewID {
			out = append(out, z)
		}
	}
	return out
}