package view

import (
	"bufio"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"html/template"
	"io"
	"net"
	"net/http"
	"os"
	"path/filepath"
	"strings"
	"text/tabwriter"
	"time"
)

// ListenSocket listens on the unix socket at path, in a directory of mode 0755, with mode 0666 on the socket: the
// status it carries is no secret and the socket can change nothing.
func ListenSocket(path string) (net.Listener, error) {
	dir := filepath.Dir(path)
	if err := os.MkdirAll(dir, 0o755); err != nil {
		return nil, err
	}
	if err := os.Chmod(dir, 0o755); err != nil {
		return nil, err
	}
	if err := os.Remove(path); err != nil && !errors.Is(err, os.ErrNotExist) {
		return nil, err
	}
	l, err := net.Listen("unix", path)
	if err != nil {
		return nil, err
	}
	if err := os.Chmod(path, 0o666); err != nil {
		l.Close()
		return nil, err
	}
	return l, nil
}

type ask struct {
	Ask    string `json:"ask"`
	Key    string `json:"key,omitempty"`
	Option string `json:"option,omitempty"`
	Words  string `json:"words,omitempty"`
}

// ServeSocket answers {"ask":"rows"} on l, line-delimited JSON, until ctx ends, and {"ask":"answer","key":…,"option":…,"words":…}
// with the model's Answer (the one thing the view writes, issue 1297 B9). Any other ask is refused.
func ServeSocket(ctx context.Context, l net.Listener, m *Model) error {
	go func() { <-ctx.Done(); l.Close() }()
	for {
		c, err := l.Accept()
		if err != nil {
			if ctx.Err() != nil {
				return nil
			}
			return err
		}
		go answer(c, m)
	}
}

func answer(c net.Conn, m *Model) {
	defer c.Close()
	c.SetDeadline(time.Now().Add(10 * time.Second))
	line, err := bufio.NewReader(io.LimitReader(c, 4096)).ReadBytes('\n')
	if err != nil && len(line) == 0 {
		return
	}
	var a ask
	if json.Unmarshal(line, &a) != nil || (a.Ask != "rows" && a.Ask != "answer") {
		json.NewEncoder(c).Encode(map[string]string{"error": `refused: this socket answers {"ask":"rows"} and {"ask":"answer"} and nothing else`})
		return
	}
	if a.Ask == "answer" {
		if err := m.Answer(a.Key, a.Option, a.Words); err != nil {
			json.NewEncoder(c).Encode(map[string]string{"error": err.Error()})
			return
		}
		json.NewEncoder(c).Encode(map[string]string{"answered": a.Key})
		return
	}
	json.NewEncoder(c).Encode(m.Snapshot())
}

// AnswerAsk asks the socket at path to write the view's answer to the open ask at key. The view's refusal is the error.
func AnswerAsk(path, key, option, words string) error {
	c, err := net.DialTimeout("unix", path, 5*time.Second)
	if err != nil {
		return fmt.Errorf("cannot reach the view at %s: %w", path, err)
	}
	defer c.Close()
	c.SetDeadline(time.Now().Add(10 * time.Second))
	req, _ := json.Marshal(ask{Ask: "answer", Key: key, Option: option, Words: words})
	if _, err := c.Write(append(req, '\n')); err != nil {
		return err
	}
	var reply struct {
		Answered string `json:"answered"`
		Error    string `json:"error"`
	}
	if err := json.NewDecoder(c).Decode(&reply); err != nil {
		return fmt.Errorf("the view's reply is not an answer: %w", err)
	}
	if reply.Error != "" {
		return errors.New(reply.Error)
	}
	return nil
}

// Ask asks the socket at path for the rows.
func Ask(path string) (Snapshot, error) {
	c, err := net.DialTimeout("unix", path, 5*time.Second)
	if err != nil {
		return Snapshot{}, fmt.Errorf("cannot reach the view at %s: %w", path, err)
	}
	defer c.Close()
	c.SetDeadline(time.Now().Add(10 * time.Second))
	if _, err := c.Write([]byte(`{"ask":"rows"}` + "\n")); err != nil {
		return Snapshot{}, err
	}
	var reply struct {
		Snapshot
		Error string `json:"error"`
	}
	if err := json.NewDecoder(c).Decode(&reply); err != nil {
		return Snapshot{}, fmt.Errorf("the view's answer is not rows: %w", err)
	}
	if reply.Error != "" {
		return Snapshot{}, errors.New(reply.Error)
	}
	return reply.Snapshot, nil
}

func since(t time.Time) string {
	if t.IsZero() {
		return ""
	}
	return t.Local().Format("2006-01-02 15:04:05")
}

func rowText(r Row) []string {
	what := r.Waits
	if r.Error != "" {
		what = "unreadable: " + r.Error
	}
	if (r.Status == StatusLeftBehind || r.Status == StatusRemoved) && what == "" {
		what = r.Status
	} else if r.Status == StatusLeftBehind || r.Status == StatusRemoved {
		what = r.Status + "; " + what
	}
	return []string{r.Node, r.Module, r.Assigned, r.Have, r.Phase, r.Health, since(r.Since), r.Detail, what}
}

// groupText is one line per pull request of a group: the branch, `<repository>#<number>`, its head, its modules.
func groupText(s Snapshot) [][]string {
	var out [][]string
	for _, g := range s.Groups {
		for i, p := range g.Pulls {
			group := ""
			if i == 0 {
				group = g.Group
			}
			out = append(out, []string{group, fmt.Sprintf("%s#%d", p.Repository, p.Number), p.Head, strings.Join(p.Modules, ", ")})
		}
	}
	return out
}

// fingerprintText is one line per module: the indexer's fingerprint beside the build's, or the reason it has none.
func fingerprintText(s Snapshot) [][]string {
	var out [][]string
	for _, f := range s.Fingerprints {
		what := f.Indexer
		switch f.State {
		case FPDiffers:
			what = "indexer " + f.Indexer + "; build " + f.Build
		case FPNone:
			what = f.Reason
		case FPNoBuild:
			what = "indexer " + f.Indexer + "; no successful trunk build recorded a fingerprint"
		case FPBuildFailed, FPBuilding:
			what = "indexer " + f.Indexer + "; builder: " + f.Reason
		case FPNoKey:
			what = "indexer " + f.Indexer + "; the builder holds no key of it"
		}
		out = append(out, []string{f.Module, f.State, what})
	}
	return out
}

// askText is one line per open ask: its key, headline, words on one line, the pull requests it covers and how to answer.
func askText(s Snapshot) [][]string {
	var out [][]string
	for _, a := range s.Asks {
		how := a.How
		switch {
		case a.Chosen != "":
			how = "answered " + a.Chosen + " in the view; the teller fills it"
		case len(a.Options) > 0:
			how += ": " + strings.Join(a.Options, " or ")
		}
		out = append(out, []string{a.Key, a.Headline, strings.Join(strings.Fields(strings.ReplaceAll(a.Words, "\n", " / ")), " "), strings.Join(a.Pulls, ", "), how})
	}
	return out
}

// differenceText is one line per difference: the node, the module, what the assigner wants, what the controller sends, the rule
// that explains it (or unexplained) and the assigner's words.
func differenceText(s Snapshot) [][]string {
	var out [][]string
	for _, d := range s.Differences {
		want, sent := d.Want, d.Sent
		switch {
		case d.WantRemoved:
			want = "removed"
		case want == "":
			want = "none"
		}
		if sent == "" {
			sent = "none"
			if d.SentBuild != "" {
				sent = "build " + d.SentBuild
			}
		}
		why := "unexplained"
		if !d.Unexplained {
			why = fmt.Sprintf("rule %d", d.Rule)
		}
		out = append(out, []string{d.Node, d.Module, want, sent, why, d.Words})
	}
	return out
}

// backlogText is one line per language and kind: its waiting asks, the asks held by a node, the oldest waiting ask's age.
func backlogText(s Snapshot) [][]string {
	var out [][]string
	for _, b := range s.Backlog {
		age := ""
		if !b.Oldest.IsZero() {
			age = (time.Duration(b.OldestSecs) * time.Second).String() + " (since " + since(b.Oldest) + ")"
		}
		if b.Error != "" {
			age = "unreadable: " + b.Error
		}
		out = append(out, []string{b.Language, b.Kind, fmt.Sprint(b.Waiting), fmt.Sprint(b.Held), age})
	}
	return out
}

var backlogHead = []string{"LANGUAGE", "KIND", "WAITING", "HELD", "OLDEST WAITING"}

var differenceHead = []string{"NODE", "MODULE", "WANT", "SENT", "RULE", "WORDS"}

var head = []string{"NODE", "MODULE", "ASSIGNED", "HAVE", "PHASE", "HEALTH", "SINCE", "DETAIL", "WAITS"}

// Table prints the snapshot as a table.
func Table(w io.Writer, s Snapshot) {
	tw := tabwriter.NewWriter(w, 0, 4, 2, ' ', 0)
	row := func(cells []string) {
		for i, c := range cells {
			if i > 0 {
				fmt.Fprint(tw, "\t")
			}
			fmt.Fprint(tw, c)
		}
		fmt.Fprintln(tw)
	}
	row(head)
	for _, r := range s.Rows {
		row(rowText(r))
	}
	if len(s.Nodes) > 0 {
		fmt.Fprintln(tw)
		row([]string{"NODE", "WINDOWS", "BUSY", "STRAYS", "SINCE"})
		for _, n := range s.Nodes {
			row([]string{n.Node, fmt.Sprint(n.Windows), fmt.Sprint(n.Busy), fmt.Sprint(n.Strays), since(n.Since)})
		}
	}
	if g := groupText(s); len(g) > 0 {
		fmt.Fprintln(tw)
		row([]string{"CANDIDATES", "PULL REQUEST", "HEAD", "MODULES"})
		for _, cells := range g {
			row(cells)
		}
	}
	if a := askText(s); len(a) > 0 {
		fmt.Fprintln(tw)
		row([]string{"ASKS", "HEADLINE", "WORDS", "PULL REQUESTS", "ANSWER"})
		for _, cells := range a {
			row(cells)
		}
	}
	if b := backlogText(s); len(b) > 0 {
		fmt.Fprintln(tw)
		row([]string{"BACKLOG OF BUILD ASKS"})
		row(backlogHead)
		for _, cells := range b {
			row(cells)
		}
	}
	if d := differenceText(s); len(d) > 0 {
		fmt.Fprintln(tw)
		row([]string{"WANTS AGAINST SENDS"})
		row(differenceHead)
		for _, cells := range d {
			row(cells)
		}
	}
	if f := fingerprintText(s); len(f) > 0 {
		fmt.Fprintln(tw)
		row([]string{"MODULE", "FINGERPRINT", "INDEXER AGAINST BUILD"})
		for _, cells := range f {
			row(cells)
		}
	}
	if len(s.Offline) > 0 {
		fmt.Fprintln(tw)
		row([]string{"OFFLINE", "NAME", "STATE", "SINCE"})
		for _, o := range s.Offline {
			row([]string{o.Kind, o.name(), "offline", since(o.Since)})
		}
	}
	if len(s.Stuck) > 0 {
		fmt.Fprintln(tw)
		row([]string{"STUCK", "KEY", "WAITED FOR", "SINCE"})
		for _, k := range s.Stuck {
			row([]string{k.Bucket, k.Key, k.Waited, since(k.Since)})
		}
	}
	if len(s.Unreadable) > 0 {
		fmt.Fprintln(tw)
		row([]string{"UNREADABLE", "KEY", "WHY"})
		for _, u := range s.Unreadable {
			row([]string{u.Bucket, u.Key, u.Error})
		}
	}
	tw.Flush()
}

func (o OfflineRow) name() string {
	if o.Kind == "part" {
		return o.Part + "." + o.Instance
	}
	return o.Node
}

var page = template.Must(template.New("p").Parse(`<!doctype html><html><head><meta charset="utf-8"><meta http-equiv="refresh" content="5">
<title>Delivery</title><style>body{font:14px sans-serif;margin:1em}table{border-collapse:collapse}td,th{padding:2px 10px;text-align:left}</style></head>
<body><h1>What each node runs</h1><table><tr>{{range .Head}}<th>{{.}}</th>{{end}}</tr>
{{range .Rows}}<tr>{{range .}}<td>{{.}}</td>{{end}}</tr>{{end}}</table>
{{if .Groups}}<h2>CANDIDATES</h2><table><tr><th>GROUP</th><th>PULL REQUEST</th><th>HEAD</th><th>MODULES</th></tr>{{range .Groups}}<tr>{{range .}}<td>{{.}}</td>{{end}}</tr>{{end}}</table>{{end}}
{{if .Asks}}<h2>ASKS</h2><table><tr><th>ASK</th><th>HEADLINE</th><th>WORDS</th><th>PULL REQUESTS</th><th>ANSWER</th></tr>{{range .Asks}}<tr>{{range .Cells}}<td>{{.}}</td>{{end}}<td>{{if .Options}}<form method="post" action="/answer"><input type="hidden" name="key" value="{{.Key}}"><input name="words" placeholder="words (optional)">{{range .Options}} <button name="option" value="{{.}}">{{.}}</button>{{end}}</form>{{end}}</td></tr>{{end}}</table>{{end}}
{{if .Backlog}}<h2>BACKLOG OF BUILD ASKS</h2><table><tr>{{range .BacklogHead}}<th>{{.}}</th>{{end}}</tr>{{range .Backlog}}<tr>{{range .}}<td>{{.}}</td>{{end}}</tr>{{end}}</table>{{end}}
{{if .Differences}}<h2>WANTS AGAINST SENDS</h2><table><tr>{{range .DifferenceHead}}<th>{{.}}</th>{{end}}</tr>{{range .Differences}}<tr>{{range .}}<td>{{.}}</td>{{end}}</tr>{{end}}</table>{{end}}
{{if .Fingerprints}}<h2>FINGERPRINTS</h2><table><tr><th>MODULE</th><th>STATE</th><th>INDEXER AGAINST BUILD</th></tr>{{range .Fingerprints}}<tr>{{range .}}<td>{{.}}</td>{{end}}</tr>{{end}}</table>{{end}}
{{if .Offline}}<h2>OFFLINE</h2><table>{{range .Offline}}<tr>{{range .}}<td>{{.}}</td>{{end}}</tr>{{end}}</table>{{end}}
{{if .Stuck}}<h2>STUCK</h2><table><tr><th>BUCKET</th><th>KEY</th><th>WAITED FOR</th><th>SINCE</th></tr>{{range .Stuck}}<tr>{{range .}}<td>{{.}}</td>{{end}}</tr>{{end}}</table>{{end}}
{{if .Unreadable}}<h2>UNREADABLE</h2><table>{{range .Unreadable}}<tr>{{range .}}<td>{{.}}</td>{{end}}</tr>{{end}}</table>{{end}}</body></html>`))

var wantsPage = template.Must(template.New("w").Parse(`<!doctype html><html><head><meta charset="utf-8"><meta http-equiv="refresh" content="5">
<title>Wants against sends</title><style>body{font:14px sans-serif;margin:1em}table{border-collapse:collapse}td,th{padding:2px 10px;text-align:left}</style></head>
<body><p><a href="/">What each node runs</a></p><h1>WANTS AGAINST SENDS</h1>
{{if .Differences}}<table><tr>{{range .Head}}<th>{{.}}</th>{{end}}</tr>{{range .Differences}}<tr>{{range .}}<td>{{.}}</td>{{end}}</tr>{{end}}</table>
{{else}}<p>no difference: every want is what the controller sends.</p>{{end}}</body></html>`))

// Web is the read-only web view of the same rows, refreshed by the browser.
func Web(m *Model) http.Handler {
	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
		if r.URL.Path == "/answer" && r.Method == http.MethodPost {
			answerForm(m, w, r)
			return
		}
		if r.URL.Path == "/answer" {
			w.Header().Set("Allow", "POST")
			http.Error(w, "an answer is posted from the form of the page", http.StatusMethodNotAllowed)
			return
		}
		if r.Method != http.MethodGet && r.Method != http.MethodHead {
			w.Header().Set("Allow", "GET, HEAD")
			http.Error(w, "this view is read-only", http.StatusMethodNotAllowed)
			return
		}
		if r.URL.Path == "/wants" {
			w.Header().Set("Content-Type", "text/html; charset=utf-8")
			wantsPage.Execute(w, map[string]any{"Head": differenceHead, "Differences": differenceText(m.Snapshot())})
			return
		}
		if r.URL.Path != "/" {
			http.NotFound(w, r)
			return
		}
		var rows [][]string
		for _, row := range m.Snapshot().Rows {
			rows = append(rows, rowText(row))
		}
		w.Header().Set("Content-Type", "text/html; charset=utf-8")
		snap := m.Snapshot()
		var off, stuck, bad [][]string
		for _, o := range snap.Offline {
			off = append(off, []string{o.Kind, o.name(), "offline", since(o.Since)})
		}
		for _, k := range snap.Stuck {
			stuck = append(stuck, []string{k.Bucket, k.Key, k.Waited, since(k.Since)})
		}
		for _, u := range snap.Unreadable {
			bad = append(bad, []string{u.Bucket, u.Key, u.Error})
		}
		page.Execute(w, map[string]any{"Head": head, "Rows": rows, "Groups": groupText(snap), "Asks": askPage(snap), "Fingerprints": fingerprintText(snap), "Differences": differenceText(snap), "Backlog": backlogText(snap), "BacklogHead": backlogHead, "DifferenceHead": differenceHead, "Offline": off, "Stuck": stuck, "Unreadable": bad})
	})
}

// askPageRow is an open ask on the page: its cells, and the options a form offers when the view may answer it.
type askPageRow struct {
	Cells   []string
	Key     string
	Options []string
}

func askPage(s Snapshot) []askPageRow {
	var out []askPageRow
	cells := askText(s)
	for i, a := range s.Asks {
		row := askPageRow{Cells: cells[i], Key: a.Key}
		if a.Chosen == "" {
			row.Options = a.Options
		}
		out = append(out, row)
	}
	return out
}

// loopback says whether a Host header names the machine itself, as the web view listens on 127.0.0.1 only: a page of another
// origin, or a name an attacker's DNS points here, writes nothing.
func loopback(host string) bool {
	h, _, err := net.SplitHostPort(host)
	if err != nil {
		h = host
	}
	return h == "127.0.0.1" || h == "localhost" || h == "[::1]" || h == "::1"
}

// answerForm is the one write the web view makes: POST /answer with key, option and words, from a form of this page.
func answerForm(m *Model, w http.ResponseWriter, r *http.Request) {
	if !loopback(r.Host) {
		http.Error(w, "this view answers only on its own address", http.StatusForbidden)
		return
	}
	if o := r.Header.Get("Origin"); o != "" && o != "http://"+r.Host {
		http.Error(w, "this view answers only a form of its own page", http.StatusForbidden)
		return
	}
	if r.Header.Get("Sec-Fetch-Site") == "cross-site" {
		http.Error(w, "this view answers only a form of its own page", http.StatusForbidden)
		return
	}
	r.Body = http.MaxBytesReader(w, r.Body, 8192)
	if err := r.ParseForm(); err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}
	if err := m.Answer(r.PostFormValue("key"), r.PostFormValue("option"), r.PostFormValue("words")); err != nil {
		http.Error(w, err.Error(), http.StatusUnprocessableEntity)
		return
	}
	http.Redirect(w, r, "/", http.StatusSeeOther)
}