package main

import (
	"database/sql"
	_ "embed"
	"encoding/json"
	"errors"
	"flag"
	"fmt"
	"io"
	"net/http"
	"os"
	"strings"
	"time"

	"github.com/google/uuid"
	_ "github.com/mattn/go-sqlite3"
)

//go:embed schema.sql
var schemaSQL string

type Config struct {
	Admins       []string
	Port         int
	Host         string
	InstanceName string `yaml:"instance_name"`
	AllowAnon    bool   `yaml:"allow_anon"`
	Debug        bool
	DBPath       string `yaml:"db_path"`
}

type iostreams struct {
	Err io.Writer
	Out io.Writer
}

type Opts struct {
	ConfigPath string
	IO         iostreams
	Log        func(string)
	Logf       func(string, ...interface{})
	Config     Config
	DB         *sql.DB
	Reset      bool
}

func main() {
	var configFlag = flag.String("config", "config.yml", "A path to a config file.")
	var resetFlag = flag.Bool("reset", false, "reset the database. WARNING this wipes everything.")
	flag.Parse()
	io := iostreams{
		Err: os.Stderr,
		Out: os.Stdout,
	}
	opts := &Opts{
		ConfigPath: *configFlag,
		Reset:      *resetFlag,
		IO:         io,
		// TODO use real logger
		Log: func(s string) {
			fmt.Fprintln(io.Out, s)
		},
		Logf: func(s string, args ...interface{}) {
			fmt.Fprintf(io.Out, s, args...)
			fmt.Fprintf(io.Out, "\n")
		},
	}

	err := _main(opts)
	if err != nil {
		fmt.Fprintf(os.Stderr, "failed: %s", err)
	}
}

type Teardown func()

func setupDB(opts *Opts) (Teardown, error) {
	db, err := sql.Open("sqlite3", opts.Config.DBPath)
	fmt.Printf("DBG %#v\n", db)

	opts.DB = db

	return func() { db.Close() }, err
}

func _main(opts *Opts) error {
	cfg, err := parseConfig(opts.ConfigPath)
	if err != nil {
		fmt.Fprintf(os.Stderr, "could not read config file '%s'", opts.ConfigPath)
		os.Exit(1)
	}

	opts.Config = *cfg

	teardown, err := setupDB(opts)
	if err != nil {
		return fmt.Errorf("could not initialize DB: %w", err)
	}
	defer teardown()

	err = ensureSchema(*opts)
	if err != nil {
		return err
	}

	setupAPI(*opts)

	// TODO TLS or SSL or something
	opts.Logf("starting server at %s:%d", cfg.Host, cfg.Port)
	if err := http.ListenAndServe(fmt.Sprintf("%s:%d", cfg.Host, cfg.Port), nil); err != nil {
		return fmt.Errorf("http server exited with error: %w", err)
	}

	return nil
}

func ensureSchema(opts Opts) error {
	db := opts.DB

	if opts.Reset {
		err := os.Remove(opts.Config.DBPath)
		if err != nil {
			return fmt.Errorf("failed to delete database: %w", err)
		}
	}
	rows, err := db.Query("select version from meta")
	if err == nil {
		defer rows.Close()
		rows.Next()
		var version string
		err = rows.Scan(&version)
		if err != nil {
			return fmt.Errorf("failed to check database schema version: %w", err)
		} else if version == "" {
			return errors.New("database is in unknown state")
		}
		return nil
	}

	if !strings.Contains(err.Error(), "no such table") {
		return fmt.Errorf("got error checking database state: %w", err)
	}

	_, err = db.Exec(schemaSQL)
	if err != nil {
		return fmt.Errorf("failed to initialize database schema: %w", err)
	}

	return nil
}

func handler(opts Opts, f http.HandlerFunc) http.HandlerFunc {
	// TODO make this more real
	return func(w http.ResponseWriter, req *http.Request) {
		opts.Log(req.URL.Path)
		f(w, req)
	}
}

// TODO I'm not entirely sold on this hash system; without transport
// encryption, it doesn't really help anything. I'd rather have plaintext +
// transport encryption and then, on the server side, proper salted hashing.

type User struct {
	// TODO
	ID string
}

type BBJResponse struct {
	Error   bool            `json:"error"`
	Data    interface{}     `json:"data"`
	Usermap map[string]User `json:"usermap"`
}

func writeResponse(w http.ResponseWriter, resp BBJResponse) {
	w.WriteHeader(http.StatusOK)
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(resp)
}

func writeErrorResponse(w http.ResponseWriter, code int, resp BBJResponse) {
	w.WriteHeader(code)
	w.Header().Set("Content-Type", "application/json")
	json.NewEncoder(w).Encode(resp)
}

// NB breaking: i'm not just returning 200 always but using http status codes

func setupAPI(opts Opts) {

	http.HandleFunc("/instance_info", handler(opts, func(w http.ResponseWriter, req *http.Request) {

		type instanceInfo struct {
			InstanceName string `json:"instance_name"`
			AllowAnon    bool   `json:"allow_anon"`
			Admins       []string
		}
		writeResponse(w, BBJResponse{
			Data: instanceInfo{
				InstanceName: opts.Config.InstanceName,
				AllowAnon:    opts.Config.AllowAnon,
				Admins:       opts.Config.Admins,
			},
		})
	}))

	serverErr := func(w http.ResponseWriter, err error) {
		opts.Logf(err.Error())
		writeErrorResponse(w, 500, BBJResponse{
			Error: true,
			Data:  "server error",
		})
	}

	badMethod := func(w http.ResponseWriter) {
		writeErrorResponse(w, 400, BBJResponse{
			Error: true,
			Data:  "bad method",
		})
	}

	invalidArgs := func(w http.ResponseWriter) {
		writeErrorResponse(w, 400, BBJResponse{
			Error: true,
			Data:  "invalid args",
		})
	}

	http.HandleFunc("/user_register", handler(opts, func(w http.ResponseWriter, req *http.Request) {
		if req.Method != "POST" {
			badMethod(w)
			return
		}

		type AuthArgs struct {
			Username string `json:"user_name"`
			AuthHash string `json:"auth_hash"`
		}

		var args AuthArgs
		if err := json.NewDecoder(req.Body).Decode(&args); err != nil {
			invalidArgs(w)
			return
		}

		if args.AuthHash == "" || args.Username == "" {
			invalidArgs(w)
			return
		}

		db := opts.DB
		stmt, err := db.Prepare("select auth_hash from users where user_name = ?")
		if err != nil {
			serverErr(w, err)
			return
		}
		defer stmt.Close()

		opts.Logf("querying for %s", args.Username)

		var authHash string
		err = stmt.QueryRow(args.Username).Scan(&authHash)
		if err == nil {
			opts.Logf("found %s", args.Username)
			// code 4 apparently
			writeErrorResponse(w, 403, BBJResponse{
				Error: true,
				Data:  "user already exists",
			})
			return
		} else if err != nil && !strings.Contains(err.Error(), "no rows in result") {
			serverErr(w, err)
			return
		}

		stmt, err = db.Prepare(`INSERT INTO users VALUES (?, ?, ?, "", "", 0, 0, ?)`)
		id, err := uuid.NewRandom()
		if err != nil {
			serverErr(w, err)
			return
		}

		_, err = stmt.Exec(id, args.Username, args.AuthHash, time.Now())
		if err != nil {
			serverErr(w, err)
		}

		writeResponse(w, BBJResponse{
			Data: true, // TODO probably something else
			// TODO prob usermap
		})
	}))

	http.HandleFunc("/check_auth", handler(opts, func(w http.ResponseWriter, req *http.Request) {
		if req.Method != "POST" {
			badMethod(w)
			return
		}

		type AuthArgs struct {
			Username string `json:"target_user"`
			AuthHash string `json:"target_hash"`
		}

		var args AuthArgs
		if err := json.NewDecoder(req.Body).Decode(&args); err != nil {
			invalidArgs(w)
			return
		}

		opts.Logf("got %s %s", args.Username, args.AuthHash)

		db := opts.DB

		stmt, err := db.Prepare("select auth_hash from users where user_name = ?")
		if err != nil {
			serverErr(w, err)
			return
		}
		defer stmt.Close()

		var authHash string
		err = stmt.QueryRow(args.Username).Scan(&authHash)
		if err != nil {
			if strings.Contains(err.Error(), "no rows in result") {
				opts.Logf("user not found")
				writeErrorResponse(w, 404, BBJResponse{
					Error: true,
					Data:  "user not found",
				})
			} else {
				serverErr(w, err)
			}
			return
		}

		// TODO unique constraint on user_name

		if authHash != args.AuthHash {
			http.Error(w, "incorrect password", 403)
			writeErrorResponse(w, 403, BBJResponse{
				Error: true,
				Data:  "incorrect password",
			})
			return
		}

		// TODO include usermap?
		writeResponse(w, BBJResponse{
			Data: true,
		})
	}))
}