package main

import (
	"bytes"
	"context"
	"encoding/csv"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"log"
	"net"
	"net/http"
	"os/signal"
	"strconv"
	"strings"
	"syscall"
	"time"
)

func main() {
	ctx, can := signal.NotifyContext(context.Background(), syscall.SIGINT)
	defer can()

	cfg, err := newConfig(ctx)
	if err != nil {
		panic(err)
	}
	defer cfg.driver.Close()

	if err := run(ctx, cfg); err != nil && ctx.Err() == nil {
		panic(err)
	}
}

func run(ctx context.Context, cfg Config) error {
	select {
	case <-ctx.Done():
		return ctx.Err()
	case err := <-listenAndServe(ctx, cfg):
		return err
	}
}

func listenAndServe(ctx context.Context, cfg Config) chan error {
	s := http.Server{
		Addr:    fmt.Sprintf(":%d", cfg.Port),
		Handler: http.HandlerFunc(newHandler(cfg)),
		BaseContext: func(net.Listener) context.Context {
			return ctx
		},
	}

	errc := make(chan error)
	go func() {
		defer close(errc)
		log.Printf("listening on %s", s.Addr)
		errc <- s.ListenAndServe()
	}()

	return errc
}

func newHandler(cfg Config) http.HandlerFunc {
	mux := http.NewServeMux()

	mux.Handle("POST /api/v1/events/slack", http.HandlerFunc(newHandlerPostAPIV1EventsSlack(cfg)))
	mux.Handle("GET /api/v1/messages", http.HandlerFunc(newHandlerGetAPIV1Messages(cfg)))
	mux.Handle("GET /api/v1/threads", http.HandlerFunc(newHandlerGetAPIV1Threads(cfg)))
	mux.Handle("GET /api/v1/threads/{thread}", http.HandlerFunc(newHandlerGetAPIV1ThreadsThread(cfg)))

	return func(w http.ResponseWriter, r *http.Request) {
		if cfg.Debug {
			b, _ := io.ReadAll(r.Body)
			r.Body = io.NopCloser(bytes.NewReader(b))
			log.Printf("%s %s | %s", r.Method, r.URL, b)
		}

		mux.ServeHTTP(w, r)
	}
}

func newHandlerGetAPIV1Messages(cfg Config) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if !basicAuth(cfg, w, r) {
			return
		}

		since, err := parseSince(r.URL.Query().Get("since"))
		if err != nil {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		}

		messages, err := cfg.storage.MessagesSince(r.Context(), since)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}

		writeJSON(w, map[string]any{"messages": messages})
	}
}

func newHandlerGetAPIV1Threads(cfg Config) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if !basicAuth(cfg, w, r) {
			return
		}

		since, err := parseSince(r.URL.Query().Get("since"))
		if err != nil {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		}

		threads, err := cfg.storage.ThreadsSince(r.Context(), since)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}

		writeJSON(w, map[string]any{"threads": threads})
	}
}

func newHandlerGetAPIV1ThreadsThread(cfg Config) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		if !basicAuth(cfg, w, r) {
			return
		}

		thread := strings.Split(strings.Split(r.URL.Path, "/threads/")[1], "/")[0]

		messages, err := cfg.storage.Thread(r.Context(), thread)
		if err != nil {
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}

		writeJSON(w, map[string]any{"thread": map[string]any{"messages": messages}})
	}
}

func basicAuth(cfg Config, w http.ResponseWriter, r *http.Request) bool {
	if u, p, _ := r.BasicAuth(); u != cfg.BasicAuthUser || p != cfg.BasicAuthPassword {
		http.Error(w, "shoo", http.StatusForbidden)
		return false
	}
	return true
}

func newHandlerPostAPIV1EventsSlack(cfg Config) http.HandlerFunc {
	if cfg.InitializeSlack {
		return handlerPostAPIV1EventsSlackInitialize
	}
	return _newHandlerPostAPIV1EventsSlack(cfg)
}

func handlerPostAPIV1EventsSlackInitialize(w http.ResponseWriter, r *http.Request) {
	b, _ := io.ReadAll(r.Body)
	var challenge struct {
		Token     string
		Challenge string
		Type      string
	}
	if err := json.Unmarshal(b, &challenge); err != nil {
		http.Error(w, err.Error(), http.StatusBadRequest)
		return
	}

	writeJSON(w, map[string]any{"challenge": challenge.Challenge})
}

func _newHandlerPostAPIV1EventsSlack(cfg Config) http.HandlerFunc {
	return func(w http.ResponseWriter, r *http.Request) {
		b, _ := io.ReadAll(r.Body)
		r.Body = io.NopCloser(bytes.NewReader(b))

		var allowList struct {
			Token string
			Event struct {
				Channel string
			}
		}
		if err := json.Unmarshal(b, &allowList); err != nil {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		} else if allowList.Token != cfg.SlackToken {
			http.Error(w, "invalid .token", http.StatusForbidden)
			return
		} else if !func() bool {
			for _, slackChannel := range cfg.SlackChannels {
				if slackChannel == allowList.Event.Channel {
					return true
				}
			}
			return false
		}() {
			return
		}

		m, err := ParseSlack(b)
		if errors.Is(err, ErrIrrelevantMessage) {
			return
		} else if err != nil {
			http.Error(w, err.Error(), http.StatusBadRequest)
			return
		}

		if err := cfg.storage.Upsert(r.Context(), m); err != nil {
			log.Printf("failed to ingest %+v: %v", m, err)
			http.Error(w, err.Error(), http.StatusInternalServerError)
			return
		}
		log.Printf("ingested %v", m.ID)
	}
}

func parseSince(s string) (time.Time, error) {
	if s == "" {
		return time.Unix(0, 0), nil
	}

	if n, err := strconv.ParseInt(s, 10, 64); err != nil {
	} else {
		return time.Unix(n, 0), nil
	}

	if t, err := time.Parse(time.RFC3339, s); err != nil {
	} else {
		return t, nil
	}

	if t, err := time.Parse(time.RFC3339Nano, s); err != nil {
	} else {
		return t, nil
	}

	if t, err := time.ParseInLocation(time.DateOnly, s, time.Local); err != nil {
	} else {
		return t, nil
	}

	return time.Time{}, fmt.Errorf("failed to parse since=%q", s)
}

func writeJSON(w http.ResponseWriter, v interface{}) error {
	return json.NewEncoder(w).Encode(v)
}

func writeCSV(w http.ResponseWriter, fields []string, values [][]string) error {
	enc := csv.NewWriter(w)
	if err := enc.Write(fields); err != nil {
		return err
	}
	return enc.WriteAll(values)
}