package main

import (
	"context"
	"encoding/json"
	"fmt"
	"html/template"
	"log"
	"net/http"
	"net/url"
	"strconv"
	"time"

	st "git.ipng.ch/ipng/nginx-logtail/internal/store"
	pb "git.ipng.ch/ipng/nginx-logtail/proto/logtailpb"
)

// Handler is the HTTP handler for the frontend.
type Handler struct {
	defaultTarget string
	defaultN      int
	refreshSecs   int
	tmpl          *template.Template
}

// Tab is a window or group-by selector link.
type Tab struct {
	Label  string
	URL    string
	Active bool
}

// Crumb is one active filter shown in the breadcrumb strip.
type Crumb struct {
	Text      string
	RemoveURL string
}

// TableRow is one row in the TopN result table.
type TableRow struct {
	Rank     int
	Label    string
	Count    int64
	Pct      float64 // 0–100, relative to rank-1 entry
	DrillURL string
}

// filterState holds the filter fields parsed from URL params.
type filterState struct {
	Website   string
	Prefix    string
	URI       string
	Status    string // expression: "200", "!=200", ">=400", etc.
	WebsiteRe string // RE2 regex against website
	URIRe     string // RE2 regex against request URI
}

// QueryParams holds all parsed URL parameters for one page request.
type QueryParams struct {
	Target   string
	Window   pb.Window
	WindowS  string // e.g. "5m"
	GroupBy  pb.GroupBy
	GroupByS string // e.g. "website"
	N        int
	Filter   filterState
}

// PageData is passed to the HTML template.
type PageData struct {
	Params         QueryParams
	Source         string
	Entries        []TableRow
	TotalCount     int64
	Sparkline      template.HTML
	Breadcrumbs    []Crumb
	Windows        []Tab
	GroupBys       []Tab
	Targets        []Tab // source/target picker; empty when only one target available
	RefreshSecs    int
	Error          string
	FilterExpr     string // current filter serialised to mini-language for the input box
	FilterErr      string // parse error from a submitted q= expression
	ClearFilterURL string // URL that removes all filter params
}

var windowSpecs = []struct{ s, label string }{
	{"1m", "1m"}, {"5m", "5m"}, {"15m", "15m"}, {"60m", "60m"}, {"6h", "6h"}, {"24h", "24h"},
}

var groupBySpecs = []struct{ s, label string }{
	{"website", "website"}, {"prefix", "prefix"}, {"uri", "uri"}, {"status", "status"},
}

func parseWindowString(s string) (pb.Window, string) {
	switch s {
	case "1m":
		return pb.Window_W1M, "1m"
	case "5m":
		return pb.Window_W5M, "5m"
	case "15m":
		return pb.Window_W15M, "15m"
	case "60m":
		return pb.Window_W60M, "60m"
	case "6h":
		return pb.Window_W6H, "6h"
	case "24h":
		return pb.Window_W24H, "24h"
	default:
		return pb.Window_W5M, "5m"
	}
}

func parseGroupByString(s string) (pb.GroupBy, string) {
	switch s {
	case "prefix":
		return pb.GroupBy_CLIENT_PREFIX, "prefix"
	case "uri":
		return pb.GroupBy_REQUEST_URI, "uri"
	case "status":
		return pb.GroupBy_HTTP_RESPONSE, "status"
	default:
		return pb.GroupBy_WEBSITE, "website"
	}
}

func (h *Handler) parseParams(r *http.Request) QueryParams {
	q := r.URL.Query()

	target := q.Get("target")
	if target == "" {
		target = h.defaultTarget
	}

	win, winS := parseWindowString(q.Get("w"))
	grp, grpS := parseGroupByString(q.Get("by"))

	n := h.defaultN
	if ns := q.Get("n"); ns != "" {
		if v, err := strconv.Atoi(ns); err == nil && v > 0 {
			n = v
		}
	}

	return QueryParams{
		Target:   target,
		Window:   win,
		WindowS:  winS,
		GroupBy:  grp,
		GroupByS: grpS,
		N:        n,
		Filter: filterState{
			Website:   q.Get("f_website"),
			Prefix:    q.Get("f_prefix"),
			URI:       q.Get("f_uri"),
			Status:    q.Get("f_status"),
			WebsiteRe: q.Get("f_website_re"),
			URIRe:     q.Get("f_uri_re"),
		},
	}
}

func buildFilter(f filterState) *pb.Filter {
	if f.Website == "" && f.Prefix == "" && f.URI == "" && f.Status == "" && f.WebsiteRe == "" && f.URIRe == "" {
		return nil
	}
	out := &pb.Filter{}
	if f.Website != "" {
		out.Website = &f.Website
	}
	if f.Prefix != "" {
		out.ClientPrefix = &f.Prefix
	}
	if f.URI != "" {
		out.HttpRequestUri = &f.URI
	}
	if f.Status != "" {
		if n, op, ok := st.ParseStatusExpr(f.Status); ok {
			out.HttpResponse = &n
			out.StatusOp = op
		}
	}
	if f.WebsiteRe != "" {
		out.WebsiteRegex = &f.WebsiteRe
	}
	if f.URIRe != "" {
		out.UriRegex = &f.URIRe
	}
	return out
}

// toValues serialises QueryParams back to URL query values.
func (p QueryParams) toValues() url.Values {
	v := url.Values{}
	v.Set("target", p.Target)
	v.Set("w", p.WindowS)
	v.Set("by", p.GroupByS)
	v.Set("n", strconv.Itoa(p.N))
	if p.Filter.Website != "" {
		v.Set("f_website", p.Filter.Website)
	}
	if p.Filter.Prefix != "" {
		v.Set("f_prefix", p.Filter.Prefix)
	}
	if p.Filter.URI != "" {
		v.Set("f_uri", p.Filter.URI)
	}
	if p.Filter.Status != "" {
		v.Set("f_status", p.Filter.Status)
	}
	if p.Filter.WebsiteRe != "" {
		v.Set("f_website_re", p.Filter.WebsiteRe)
	}
	if p.Filter.URIRe != "" {
		v.Set("f_uri_re", p.Filter.URIRe)
	}
	return v
}

// buildURL returns a page URL derived from the current params with overrides applied.
// An override value of "" removes that key from the URL.
func (p QueryParams) buildURL(overrides map[string]string) string {
	v := p.toValues()
	for k, val := range overrides {
		if val == "" {
			v.Del(k)
		} else {
			v.Set(k, val)
		}
	}
	return "/?" + v.Encode()
}

// clearFilterURL returns a URL with all filter params removed.
func (p QueryParams) clearFilterURL() string {
	return p.buildURL(map[string]string{
		"f_website": "", "f_prefix": "", "f_uri": "", "f_status": "",
		"f_website_re": "", "f_uri_re": "",
	})
}

// nextGroupBy advances the drill-down dimension hierarchy (cycles at the end).
func nextGroupBy(s string) string {
	switch s {
	case "website":
		return "prefix"
	case "prefix":
		return "uri"
	case "uri":
		return "status"
	default: // status → back to website
		return "website"
	}
}

// groupByFilterKey maps a group-by name to its URL filter parameter.
func groupByFilterKey(s string) string {
	switch s {
	case "website":
		return "f_website"
	case "prefix":
		return "f_prefix"
	case "uri":
		return "f_uri"
	case "status":
		return "f_status"
	default:
		return "f_website"
	}
}

func (p QueryParams) drillURL(label string) string {
	return p.buildURL(map[string]string{
		groupByFilterKey(p.GroupByS): label,
		"by":                         nextGroupBy(p.GroupByS),
	})
}

func buildCrumbs(p QueryParams) []Crumb {
	var crumbs []Crumb
	if p.Filter.Website != "" {
		crumbs = append(crumbs, Crumb{
			Text:      "website=" + p.Filter.Website,
			RemoveURL: p.buildURL(map[string]string{"f_website": ""}),
		})
	}
	if p.Filter.Prefix != "" {
		crumbs = append(crumbs, Crumb{
			Text:      "prefix=" + p.Filter.Prefix,
			RemoveURL: p.buildURL(map[string]string{"f_prefix": ""}),
		})
	}
	if p.Filter.URI != "" {
		crumbs = append(crumbs, Crumb{
			Text:      "uri=" + p.Filter.URI,
			RemoveURL: p.buildURL(map[string]string{"f_uri": ""}),
		})
	}
	if p.Filter.Status != "" {
		crumbs = append(crumbs, Crumb{
			Text:      "status=" + p.Filter.Status,
			RemoveURL: p.buildURL(map[string]string{"f_status": ""}),
		})
	}
	if p.Filter.WebsiteRe != "" {
		crumbs = append(crumbs, Crumb{
			Text:      "website~=" + p.Filter.WebsiteRe,
			RemoveURL: p.buildURL(map[string]string{"f_website_re": ""}),
		})
	}
	if p.Filter.URIRe != "" {
		crumbs = append(crumbs, Crumb{
			Text:      "uri~=" + p.Filter.URIRe,
			RemoveURL: p.buildURL(map[string]string{"f_uri_re": ""}),
		})
	}
	return crumbs
}

func buildWindowTabs(p QueryParams) []Tab {
	tabs := make([]Tab, len(windowSpecs))
	for i, w := range windowSpecs {
		tabs[i] = Tab{
			Label:  w.label,
			URL:    p.buildURL(map[string]string{"w": w.s}),
			Active: p.WindowS == w.s,
		}
	}
	return tabs
}

func buildGroupByTabs(p QueryParams) []Tab {
	tabs := make([]Tab, len(groupBySpecs))
	for i, g := range groupBySpecs {
		tabs[i] = Tab{
			Label:  "by " + g.label,
			URL:    p.buildURL(map[string]string{"by": g.s}),
			Active: p.GroupByS == g.s,
		}
	}
	return tabs
}

// buildTargetTabs builds the source/target picker tabs from a ListTargets response.
// Returns nil (hide picker) when only one endpoint is reachable.
func (h *Handler) buildTargetTabs(p QueryParams, lt *pb.ListTargetsResponse) []Tab {
	// "all" always points at the configured aggregator default.
	allTab := Tab{
		Label:  "all",
		URL:    p.buildURL(map[string]string{"target": h.defaultTarget}),
		Active: p.Target == h.defaultTarget,
	}

	var collectorTabs []Tab
	if lt != nil {
		for _, t := range lt.Targets {
			addr := t.Addr
			if addr == "" {
				addr = p.Target // collector reporting itself; addr is the current target
			}
			collectorTabs = append(collectorTabs, Tab{
				Label:  t.Name,
				URL:    p.buildURL(map[string]string{"target": addr}),
				Active: p.Target == addr,
			})
		}
	}

	// Only render the picker when there is more than one choice.
	if len(collectorTabs) == 0 {
		return nil
	}
	return append([]Tab{allTab}, collectorTabs...)
}

func buildTableRows(entries []*pb.TopNEntry, p QueryParams) ([]TableRow, int64) {
	if len(entries) == 0 {
		return nil, 0
	}
	top := float64(entries[0].Count)
	var total int64
	rows := make([]TableRow, len(entries))
	for i, e := range entries {
		total += e.Count
		pct := 0.0
		if top > 0 {
			pct = float64(e.Count) / top * 100
		}
		rows[i] = TableRow{
			Rank:     i + 1,
			Label:    e.Label,
			Count:    e.Count,
			Pct:      pct,
			DrillURL: p.drillURL(e.Label),
		}
	}
	return rows, total
}

func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
	params := h.parseParams(r)

	// Handle filter expression box submission (q= param).
	var filterErr string
	filterExprInput := FilterExprString(params.Filter)
	if qVals, ok := r.URL.Query()["q"]; ok {
		q := ""
		if len(qVals) > 0 {
			q = qVals[0]
		}
		fs, err := ParseFilterExpr(q)
		if err != nil {
			filterErr = err.Error()
			filterExprInput = q // show what the user typed so they can fix it
			// fall through: render page using existing filter params
		} else {
			params.Filter = fs
			http.Redirect(w, r, params.buildURL(nil), http.StatusSeeOther)
			return
		}
	}

	filter := buildFilter(params.Filter)

	conn, client, err := dial(params.Target)
	if err != nil {
		h.render(w, http.StatusBadGateway, h.errorPage(params,
			fmt.Sprintf("cannot connect to %s: %v", params.Target, err)))
		return
	}
	defer conn.Close()

	ctx, cancel := context.WithTimeout(r.Context(), 5*time.Second)
	defer cancel()

	type topNResult struct {
		resp *pb.TopNResponse
		err  error
	}
	type trendResult struct {
		resp *pb.TrendResponse
		err  error
	}
	topNCh := make(chan topNResult, 1)
	trendCh := make(chan trendResult, 1)
	ltCh := make(chan *pb.ListTargetsResponse, 1)

	go func() {
		resp, err := client.TopN(ctx, &pb.TopNRequest{
			Filter:  filter,
			GroupBy: params.GroupBy,
			N:       int32(params.N),
			Window:  params.Window,
		})
		topNCh <- topNResult{resp, err}
	}()
	go func() {
		resp, err := client.Trend(ctx, &pb.TrendRequest{
			Filter: filter,
			Window: params.Window,
		})
		trendCh <- trendResult{resp, err}
	}()
	go func() {
		resp, err := client.ListTargets(ctx, &pb.ListTargetsRequest{})
		if err != nil {
			ltCh <- nil
		} else {
			ltCh <- resp
		}
	}()

	tn := <-topNCh
	tr := <-trendCh
	lt := <-ltCh

	if tn.err != nil {
		h.render(w, http.StatusBadGateway, h.errorPage(params,
			fmt.Sprintf("error querying %s: %v", params.Target, tn.err)))
		return
	}

	// raw=1: return JSON for scripting
	if r.URL.Query().Get("raw") == "1" {
		writeRawJSON(w, params, tn.resp)
		return
	}

	rows, total := buildTableRows(tn.resp.Entries, params)

	var sparkline template.HTML
	if tr.err == nil && tr.resp != nil {
		sparkline = renderSparkline(tr.resp.Points)
	}

	data := PageData{
		Params:         params,
		Source:         tn.resp.Source,
		Entries:        rows,
		TotalCount:     total,
		Sparkline:      sparkline,
		Breadcrumbs:    buildCrumbs(params),
		Windows:        buildWindowTabs(params),
		GroupBys:       buildGroupByTabs(params),
		Targets:        h.buildTargetTabs(params, lt),
		RefreshSecs:    h.refreshSecs,
		FilterExpr:     filterExprInput,
		FilterErr:      filterErr,
		ClearFilterURL: params.clearFilterURL(),
	}
	h.render(w, http.StatusOK, data)
}

func (h *Handler) render(w http.ResponseWriter, status int, data PageData) {
	w.Header().Set("Content-Type", "text/html; charset=utf-8")
	w.WriteHeader(status)
	if err := h.tmpl.ExecuteTemplate(w, "base", data); err != nil {
		log.Printf("frontend: template error: %v", err)
	}
}

func (h *Handler) errorPage(params QueryParams, msg string) PageData {
	return PageData{
		Params:         params,
		Windows:        buildWindowTabs(params),
		GroupBys:       buildGroupByTabs(params),
		Breadcrumbs:    buildCrumbs(params),
		RefreshSecs:    h.refreshSecs,
		Error:          msg,
		FilterExpr:     FilterExprString(params.Filter),
		ClearFilterURL: params.clearFilterURL(),
	}
}

func writeRawJSON(w http.ResponseWriter, params QueryParams, resp *pb.TopNResponse) {
	type entry struct {
		Label string `json:"label"`
		Count int64  `json:"count"`
	}
	type out struct {
		Source  string  `json:"source"`
		Window  string  `json:"window"`
		GroupBy string  `json:"group_by"`
		Entries []entry `json:"entries"`
	}
	o := out{
		Source:  resp.Source,
		Window:  params.WindowS,
		GroupBy: params.GroupByS,
		Entries: make([]entry, len(resp.Entries)),
	}
	for i, e := range resp.Entries {
		o.Entries[i] = entry{Label: e.Label, Count: e.Count}
	}
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(o)
}