package main

// route-proxy's tools (issue 774): the web front's command line. Each answers from what the proxy keeps on the bus
// (route-proxy_routes and route-proxy_unrouted, written on change by the proxy itself), in one call, for every
// machine running a proxy: which sites are served and where they go, whether their certificates are good, what the
// last request through each got back, and which names were asked for and are served nowhere.

import (
	"encoding/json"
	"fmt"
	"sort"
	"strings"
	"time"

	stdio "git.novox.be/novox/mesh-sdk/go"

	"route-proxy/internal/routestate"
)

// The tools' names, as the manifest declares them.
const (
	RoutesTool   = "route_proxy_routes"
	RouteTool    = "route_proxy_route"
	UnroutedTool = "route_proxy_unrouted"
)

// reader is one of the module's states, as stdio.KeptState reads it.
type reader interface {
	Keys() ([]string, error)
	Get(key string) (*stdio.StateEntry, error)
}

// front is what the tools read: the routes and the refusals, and the clock a certificate's days left are counted by.
type front struct {
	routes, unrouted reader
	now              func() time.Time
}

// RouteLine is one served name in the list: where it goes, how long its certificate holds, what it last answered.
type RouteLine struct {
	Name    string   `json:"name"`
	Proxy   string   `json:"proxy"`
	Reach   string   `json:"reach"`
	Targets []string `json:"targets"`
	// Reachable is yes when the last answer upstream gave was below 500, no when it was 500 or more or none came,
	// unknown before any request.
	Reachable string `json:"reachable"`
	// Certificate is its outcome, issuer and expiry in words; ExpiresInDays is the whole days until not-after.
	Certificate   string             `json:"certificate"`
	ExpiresInDays *int               `json:"expires_in_days,omitempty"`
	LastAnswer    *routestate.Answer `json:"last_answer,omitempty"`
}

func (f front) tools() []stdio.Tool {
	node := map[string]any{"type": "string", "description": "only the proxy on this machine; every machine when left out"}
	return []stdio.Tool{
		{Name: RoutesTool,
			Description: "Every site (web name, host name) the mesh's web front serves through route-proxy, the reverse proxy " +
				"on the public machine: for each route the module and node it forwards to, its TLS certificate's issuer and " +
				"expiry (days left), and the last answer upstream gave (status, time, error), so is X reachable and is its " +
				"certificate good is answered without curl. Read from the proxy's routes state on the bus. Read-only.",
			Input: map[string]any{"type": "object", "properties": map[string]any{"node": node}},
			Run: func(args map[string]any) (any, error) {
				at, _ := args["node"].(string)
				return f.list(at)
			}},
		{Name: RouteTool,
			Description: "One site the mesh's web front (route-proxy) is asked about, in full: every rule it is served by " +
				"(path, module, node, target, refusal, redirect, authentication), its certificate (issuer, not-after, last " +
				"renewal and its outcome, or why it failed) and the last upstream answer. A name with no route says so, and " +
				"when it was last asked for. Answers is X reachable, why does this site not load. Read-only.",
			Input: map[string]any{"type": "object", "required": []string{"name"}, "properties": map[string]any{
				"name": map[string]any{"type": "string", "description": "the site's name, such as app.example.org"},
				"node": node}},
			Run: func(args map[string]any) (any, error) {
				name, _ := args["name"].(string)
				at, _ := args["node"].(string)
				return f.one(name, at)
			}},
		{Name: UnroutedTool,
			Description: "Names the mesh's web front (route-proxy) answered \"no route for\": a site asked for in a request or " +
				"a TLS handshake that no route serves, newest first, with when it was last asked and how often. Only names under a " +
				"domain the proxy serves are kept by name, a few new ones a minute; every other refusal (a scan) is counted per " +
				"proxy, the last minute's count and the total since its start. A site that should be served and is missing " +
				"its route shows here. Kept a week. Read-only.",
			Input: map[string]any{"type": "object", "properties": map[string]any{"node": node}},
			Run: func(args map[string]any) (any, error) {
				at, _ := args["node"].(string)
				return f.refusals(at)
			}},
	}
}

// read is every value of a state, of node's proxy alone when node is named, decoded into a fresh T each.
func read[T any](state reader, node string) ([]T, error) {
	keys, err := state.Keys()
	if err != nil {
		return nil, err
	}
	var out []T
	for _, key := range keys {
		at, _ := routestate.Split(key)
		if node != "" && at != node {
			continue
		}
		entry, err := state.Get(key)
		if err != nil {
			return nil, err
		}
		if entry == nil {
			continue // deleted between the list and the read
		}
		var v T
		if err := json.Unmarshal(entry.Value, &v); err != nil {
			return nil, fmt.Errorf("%s holds what is not a route-proxy record: %w", key, err)
		}
		out = append(out, v)
	}
	return out, nil
}

func (f front) list(node string) (map[string]any, error) {
	routes, err := read[routestate.Route](f.routes, node)
	if err != nil {
		return nil, err
	}
	lines := make([]RouteLine, 0, len(routes))
	unreachable, expiring := 0, 0
	for _, r := range routes {
		line := f.line(r)
		if line.Reachable == "no" {
			unreachable++
		}
		if line.ExpiresInDays != nil && *line.ExpiresInDays < 14 || r.Certificate.Outcome == routestate.Failed {
			expiring++
		}
		lines = append(lines, line)
	}
	sort.Slice(lines, func(i, j int) bool {
		if lines[i].Name != lines[j].Name {
			return lines[i].Name < lines[j].Name
		}
		return lines[i].Proxy < lines[j].Proxy
	})
	return map[string]any{"routes": lines, "served": len(lines), "unreachable": unreachable,
		"certificates_failing_or_within_14_days": expiring}, nil
}

func (f front) line(r routestate.Route) RouteLine {
	line := RouteLine{Name: r.Name, Proxy: r.Proxy, Reach: r.Reach, LastAnswer: r.LastAnswer, Reachable: "unknown",
		Targets: []string{}}
	for _, t := range r.Targets {
		line.Targets = append(line.Targets, describe(t))
	}
	if a := r.LastAnswer; a != nil {
		line.Reachable = "yes"
		if a.Error != "" || a.Status >= 500 || a.Status == 0 {
			line.Reachable = "no"
		}
	}
	c := r.Certificate
	words := []string{}
	if c.Outcome != "" {
		words = append(words, c.Outcome)
	}
	if c.Issuer != "" {
		words = append(words, "by "+c.Issuer)
	}
	if c.NotAfter != nil {
		days := int(c.NotAfter.Sub(f.now()).Hours() / 24)
		line.ExpiresInDays = &days
		words = append(words, "until "+c.NotAfter.UTC().Format("2006-01-02"))
	}
	if c.Error != "" {
		words = append(words, "("+c.Error+")")
	}
	if len(words) == 0 {
		words = append(words, "none seen yet")
	}
	line.Certificate = c.Authority + ": " + strings.Join(words, " ")
	return line
}

// describe is one rule in a few words: path → module@node at target, or what it answers with.
func describe(t routestate.Target) string {
	path := t.Path
	if path == "" {
		path = "/"
	}
	var what string
	switch {
	case t.Deny:
		what = "refused"
	case t.Redirect != "":
		what = "redirected to " + t.Redirect
	default:
		what = fmt.Sprintf("%s@%s at %s", t.Module, t.Node, t.Target)
	}
	if t.Sealed != "" {
		what += " (authentication cannot be checked: " + t.Sealed + ")"
	} else if t.Auth {
		what += " (authenticated)"
	}
	return path + " → " + what
}

func (f front) one(name, node string) (map[string]any, error) {
	name = strings.ToLower(strings.TrimSpace(name))
	if name == "" {
		return nil, fmt.Errorf("name is the site to read, such as app.example.org")
	}
	routes, err := read[routestate.Route](f.routes, node)
	if err != nil {
		return nil, err
	}
	var found []routestate.Route
	for _, r := range routes {
		if r.Name == name {
			found = append(found, r)
		}
	}
	if len(found) > 0 {
		out := map[string]any{"name": name, "routed": true, "routes": found}
		if len(found) == 1 {
			out["reachable"] = f.line(found[0]).Reachable
		}
		return out, nil
	}
	asked, _, err := f.asked(node)
	if err != nil {
		return nil, err
	}
	for _, a := range asked {
		if a.Name == name {
			return map[string]any{"name": name, "routed": false, "asked": a,
				"says": fmt.Sprintf("no proxy serves %s; the proxy on %s answered \"no route\" for it, last at %s",
					name, a.Proxy, a.AskedAt.UTC().Format(time.RFC3339))}, nil
		}
	}
	return map[string]any{"name": name, "routed": false,
		"says": fmt.Sprintf("no proxy serves %s, and none was asked for it this week", name)}, nil
}

func (f front) refusals(node string) (map[string]any, error) {
	asked, others, err := f.asked(node)
	if err != nil {
		return nil, err
	}
	sort.Slice(asked, func(i, j int) bool { return asked[i].AskedAt.After(asked[j].AskedAt) })
	if asked == nil {
		asked = []routestate.Unrouted{}
	}
	return map[string]any{"unrouted": asked, "names": len(asked), "other_refusals": others}, nil
}

// asked is the names refused and kept by name, and each proxy's count of the refusals not kept by name.
func (f front) asked(node string) ([]routestate.Unrouted, []routestate.Other, error) {
	keys, err := f.unrouted.Keys()
	if err != nil {
		return nil, nil, err
	}
	names, others := keySet{}, keySet{}
	for _, key := range keys {
		if _, name := routestate.Split(key); name == routestate.OtherName {
			others[key] = true
		} else {
			names[key] = true
		}
	}
	asked, err := read[routestate.Unrouted](only{f.unrouted, names}, node)
	if err != nil {
		return nil, nil, err
	}
	counted, err := read[routestate.Other](only{f.unrouted, others}, node)
	if counted == nil {
		counted = []routestate.Other{}
	}
	return asked, counted, err
}

// keySet is a set of keys; only is a state narrowed to them.
type keySet map[string]bool

type only struct {
	reader
	keys keySet
}

func (o only) Keys() ([]string, error) {
	out := make([]string, 0, len(o.keys))
	for k := range o.keys {
		out = append(out, k)
	}
	sort.Strings(out)
	return out, nil
}