package serv

import (
	"bytes"
	"context"
	"fmt"
	"io"

	"github.com/dosco/super-graph/qcode"
	"github.com/jackc/pgconn"
	"github.com/jackc/pgx/v4"
	"github.com/valyala/fasttemplate"
)

type preparedItem struct {
	sd      *pgconn.StatementDescription
	args    [][]byte
	st      stmt
	roleArg bool
}

var (
	_preparedList map[string]*preparedItem
)

func initPreparedList() {
	_preparedList = make(map[string]*preparedItem)

	tx, err := db.Begin(context.Background())
	if err != nil {
		errlog.Fatal().Err(err).Send()
	}
	defer tx.Rollback(context.Background()) //nolint: errcheck

	err = prepareRoleStmt(tx)
	if err != nil {
		errlog.Fatal().Err(err).Msg("failed to prepare get role statement")
	}

	if err := tx.Commit(context.Background()); err != nil {
		errlog.Fatal().Err(err).Send()
	}

	success := 0

	for _, v := range _allowList.list {
		if len(v.gql) == 0 {
			continue
		}

		err := prepareStmt(v.gql, v.vars)
		if err == nil {
			success++
			continue
		}

		if len(v.vars) == 0 {
			logger.Warn().Err(err).Msg(v.gql)
		} else {
			logger.Warn().Err(err).Msgf("%s %s", v.vars, v.gql)
		}
	}

	logger.Info().
		Msgf("Registered %d of %d queries from allow.list as prepared statements",
			success, len(_allowList.list))
}

func prepareStmt(gql string, vars []byte) error {
	qt := qcode.GetQType(gql)
	q := []byte(gql)

	if len(vars) == 0 {
		logger.Debug().Msgf("Prepared statement:\n%s\n", gql)
	} else {
		logger.Debug().Msgf("Prepared statement:\n%s\n%s\n", vars, gql)
	}

	tx, err := db.Begin(context.Background())
	if err != nil {
		return err
	}
	defer tx.Rollback(context.Background()) //nolint: errcheck

	switch qt {
	case qcode.QTQuery:
		var stmts1 []stmt
		var err error

		if conf.isABACEnabled() {
			stmts1, err = buildMultiStmt(q, vars)
		} else {
			stmts1, err = buildRoleStmt(q, vars, "user")
		}

		if err != nil {
			return err
		}

		logger.Debug().Msg("Prepared statement role: user")

		err = prepare(tx, stmts1, gqlHash(gql, vars, "user"))
		if err != nil {
			return err
		}

		if conf.isAnonRoleDefined() {
			logger.Debug().Msg("Prepared statement for role: anon")

			stmts2, err := buildRoleStmt(q, vars, "anon")
			if err != nil {
				return err
			}

			err = prepare(tx, stmts2, gqlHash(gql, vars, "anon"))
			if err != nil {
				return err
			}
		}

	case qcode.QTMutation:
		for _, role := range conf.Roles {
			logger.Debug().Msgf("Prepared statement for role: %s", role.Name)

			stmts, err := buildRoleStmt(q, vars, role.Name)
			if err != nil {
				return err
			}

			err = prepare(tx, stmts, gqlHash(gql, vars, role.Name))
			if err != nil {
				return err
			}
		}
	}

	if err := tx.Commit(context.Background()); err != nil {
		return err
	}

	return nil
}

func prepare(tx pgx.Tx, st []stmt, key string) error {
	finalSQL, am := processTemplate(st[0].sql)

	sd, err := tx.Prepare(context.Background(), "", finalSQL)
	if err != nil {
		return err
	}

	_preparedList[key] = &preparedItem{
		sd:      sd,
		args:    am,
		st:      st[0],
		roleArg: len(st) > 1,
	}
	return nil
}

// nolint: errcheck
func prepareRoleStmt(tx pgx.Tx) error {
	if !conf.isABACEnabled() {
		return nil
	}

	w := &bytes.Buffer{}

	io.WriteString(w, `SELECT (CASE WHEN EXISTS (`)
	io.WriteString(w, conf.RolesQuery)
	io.WriteString(w, `) THEN `)

	io.WriteString(w, `(SELECT (CASE`)
	for _, role := range conf.Roles {
		if len(role.Match) == 0 {
			continue
		}
		io.WriteString(w, ` WHEN `)
		io.WriteString(w, role.Match)
		io.WriteString(w, ` THEN '`)
		io.WriteString(w, role.Name)
		io.WriteString(w, `'`)
	}

	io.WriteString(w, ` ELSE {{role}} END) FROM (`)
	io.WriteString(w, conf.RolesQuery)
	io.WriteString(w, `) AS "_sg_auth_roles_query" LIMIT 1) `)
	io.WriteString(w, `ELSE 'anon' END) FROM (VALUES (1)) AS "_sg_auth_filler" LIMIT 1; `)

	roleSQL, _ := processTemplate(w.String())

	_, err := tx.Prepare(context.Background(), "_sg_get_role", roleSQL)
	if err != nil {
		return err
	}

	return nil
}

func processTemplate(tmpl string) (string, [][]byte) {
	st := struct {
		vmap map[string]int
		am   [][]byte
		i    int
	}{
		vmap: make(map[string]int),
		am:   make([][]byte, 0, 5),
		i:    0,
	}

	execFunc := func(w io.Writer, tag string) (int, error) {
		if n, ok := st.vmap[tag]; ok {
			return w.Write([]byte(fmt.Sprintf("$%d", n)))
		}
		st.am = append(st.am, []byte(tag))
		st.i++
		st.vmap[tag] = st.i
		return w.Write([]byte(fmt.Sprintf("$%d", st.i)))
	}

	t1 := fasttemplate.New(tmpl, `'{{`, `}}'`)
	ts1 := t1.ExecuteFuncString(execFunc)

	t2 := fasttemplate.New(ts1, `{{`, `}}`)
	ts2 := t2.ExecuteFuncString(execFunc)

	return ts2, st.am
}