package back

import (
	"context"
	"errors"
	"fmt"
	"log"
	"os"

	"crawshaw.io/sqlite"
	"crawshaw.io/sqlite/sqlitex"
	"github.com/matthewhartstonge/argon2"
	"github.com/rickb777/date"
)

var ErrNotFound = errors.New("not found")

type UnauthorizedError struct {
	EventID   string
	AdminCode string
}

func (u UnauthorizedError) Error() string {
	return fmt.Sprintf("unauthorized: EventID = %s, AdminCode = %s", u.EventID, u.AdminCode)
}

func hash(password string) (string, error) {
	hashed, err := (&argon2.Config{
		HashLength: 32,
		// We don't need a salt because our random passwords are not
		// susceptible to dictionary attacks.
		SaltLength:  0,
		TimeCost:    3,
		MemoryCost:  64 * 1024,
		Parallelism: 4,
		Mode:        argon2.ModeArgon2id,
		Version:     argon2.Version13,
	}).HashEncoded([]byte(password))
	return string(hashed), err
}

type GenString func(length int) (string, error)

type Store struct {
	pool      *sqlitex.Pool
	genString GenString
}

func NewStore(filename string, genString GenString) (*Store, error) {
	var needCreate bool
	if _, err := os.Stat(filename); os.IsNotExist(err) {
		needCreate = true
	}
	// If the file exists, then assume it was created properly.

	pool, err := sqlitex.Open(filename, 0, 10)
	if err != nil {
		return nil, err
	}
	store := &Store{
		pool:      pool,
		genString: genString,
	}
	if needCreate {
		log.Println("creating schema")
		err = store.createSchema()
		if err != nil {
			defer pool.Close()
			return nil, err
		}
	}

	return store, nil
}

func NewMemoryStore(genString GenString) (*Store, error) {
	pool, err := sqlitex.Open("file::memory:?mode=memory&cache=shared", 0, 10)
	if err != nil {
		return nil, err
	}
	store := &Store{
		pool:      pool,
		genString: genString,
	}

	err = store.createSchema()
	if err != nil {
		defer pool.Close()
		return nil, err
	}
	return store, nil
}

func (s *Store) Close() error {
	return s.pool.Close()
}

const schema = `
	CREATE TABLE event (
		id TEXT NOT NULL PRIMARY KEY,
		admin_code_hash TEXT NOT NULL,
		name TEXT NOT NULL,
		description TEXT NOT NULL,
		earliest_date DATE NOT NULL,
		latest_date DATE NOT NULL
	);

	CREATE TABLE response (
		id TEXT NOT NULL,
		event_id TEXT NOT NULL,
		guest_name TEXT NOT NULL,

		PRIMARY KEY (id, event_id),
		FOREIGN KEY (event_id) REFERENCES event(id)
	);

	CREATE TABLE response_time (
		event_id TEXT NOT NULL,
		response_id TEXT NOT NULL,
		date DATE NOT NULL,
		time INTEGER NOT NULL,

		CHECK (0 <= time < 24),
		UNIQUE (response_id, date, time),
		FOREIGN KEY(event_id, response_id) REFERENCES response(event_id, id)
	);
	
	CREATE TRIGGER enforce_valid_response_dates
	BEFORE INSERT ON response_time
	BEGIN
		SELECT
			CASE
				WHEN NEW.date NOT BETWEEN event.earliest_date AND event.latest_date
					THEN RAISE(ABORT, 'response date is out of range')
			END
		FROM response
		JOIN event ON response.event_id = event.id
		WHERE response.id = NEW.response_id;
	END;`

func (s *Store) createSchema() error {
	conn := s.pool.Get(context.Background())
	defer s.pool.Put(conn)
	return sqlitex.ExecScript(conn, schema)
}

type CreateEventCommand struct {
	Name             string
	Description      string
	Earliest, Latest date.Date
}

type CreateEventResult struct {
	EventID, AdminCode string
}

const dbDateLayout = "2006-01-02"

func (s *Store) CreateEvent(ctx context.Context, cmd CreateEventCommand) (result CreateEventResult, err error) {
	const idLength = 10
	const adminCodeLength = 10

	conn := s.pool.Get(ctx)
	defer s.pool.Put(conn)

	id, err := s.genString(idLength)
	if err != nil {
		return
	}

	adminCode, err := s.genString(adminCodeLength)
	if err != nil {
		return
	}

	adminCodeHash, err := hash(adminCode)
	if err != nil {
		return
	}

	const query = `
		INSERT INTO event(id, admin_code_hash, name, description, earliest_date, latest_date)
		VALUES (?, ?, ?, ?, ?, ?);`
	err = sqlitex.Exec(conn, query, nil,
		id,
		adminCodeHash,
		cmd.Name,
		cmd.Description,
		cmd.Earliest.Format(dbDateLayout),
		cmd.Latest.Format(dbDateLayout),
	)
	if err != nil {
		return
	}

	result.AdminCode = adminCode
	result.EventID = id
	return
}

type CheckEventAdminCodeQuery struct {
	EventID   string
	AdminCode string
}

func (s *Store) AuthorizeEventAdmin(ctx context.Context, query CheckEventAdminCodeQuery) error {
	conn := s.pool.Get(ctx)
	defer s.pool.Put(conn)

	adminCodeHash, err := hash(query.AdminCode)
	if err != nil {
		return err
	}

	const dbQuery = `
		SELECT 1
		FROM event
		WHERE id = ? AND admin_code_hash = ?;`
	var doesMatch bool
	err = sqlitex.Exec(conn, dbQuery,
		func(stmt *sqlite.Stmt) error {
			doesMatch = true
			return nil
		}, query.EventID, adminCodeHash)
	if err != nil {
		return err
	}
	if !doesMatch {
		return UnauthorizedError{
			EventID:   query.EventID,
			AdminCode: query.AdminCode,
		}
	}
	return nil
}

type GetEventMetadataQuery struct {
	EventID string
}

type GetEventMetadataResult struct {
	Name             string
	Description      string
	Earliest, Latest date.Date
}

func (s *Store) GetEventMetadata(ctx context.Context, query GetEventMetadataQuery) (GetEventMetadataResult, error) {
	conn := s.pool.Get(ctx)
	defer s.pool.Put(conn)

	const dbQuery = `
		SELECT name, description, earliest_date, latest_date
		FROM event
		WHERE id = ?;`
	var result GetEventMetadataResult
	var found bool
	err := sqlitex.Exec(conn, dbQuery,
		func(stmt *sqlite.Stmt) error {
			found = true

			result.Name = stmt.ColumnText(0)
			result.Description = stmt.ColumnText(1)
			earliestDateString := stmt.ColumnText(2)
			latestDateString := stmt.ColumnText(3)

			var err error
			result.Earliest, err = date.Parse(dbDateLayout, earliestDateString)
			if err != nil {
				return err
			}
			result.Latest, err = date.Parse(dbDateLayout, latestDateString)
			return err
		}, query.EventID)
	if err != nil {
		return GetEventMetadataResult{}, err
	}
	if !found {
		return GetEventMetadataResult{}, ErrNotFound
	}
	return result, nil
}

type GetEventResponseSummaryQuery struct {
	EventID string
}

type GetEventResponseSummaryResult struct {
	RespondentNames []string
	PerHourCounts   map[date.Date]map[int]int
}

func (s *Store) GetEventResponseSummary(ctx context.Context, query GetEventResponseSummaryQuery) (GetEventResponseSummaryResult, error) {
	conn := s.pool.Get(ctx)
	defer s.pool.Put(conn)

	var found bool

	const eventIDQuery = `
		SELECT 1
		FROM event
		WHERE id = ?`
	var err = sqlitex.Exec(conn, eventIDQuery,
		func(stmt *sqlite.Stmt) error {
			found = true
			return nil
		}, query.EventID)
	if err != nil {
		return GetEventResponseSummaryResult{}, err
	}
	if !found {
		return GetEventResponseSummaryResult{}, ErrNotFound
	}

	var result GetEventResponseSummaryResult
	const respondentNameQuery = `
		SELECT guest_name
		FROM response
		WHERE event_id = ?
		ORDER BY guest_name ASC;`
	err = sqlitex.Exec(conn, respondentNameQuery,
		func(stmt *sqlite.Stmt) error {
			result.RespondentNames = append(result.RespondentNames, stmt.ColumnText(0))
			return nil
		}, query.EventID)
	if err != nil {
		return GetEventResponseSummaryResult{}, err
	}

	result.PerHourCounts = make(map[date.Date]map[int]int)
	const perHourCountQuery = `
		SELECT date, time, COUNT(*)
		FROM response_time
		WHERE event_id = ?
		GROUP BY date, time;`
	err = sqlitex.Exec(conn, perHourCountQuery,
		func(stmt *sqlite.Stmt) error {
			d, err := date.Parse(dbDateLayout, stmt.ColumnText(0))
			if err != nil {
				return err
			}
			if result.PerHourCounts[d] == nil {
				result.PerHourCounts[d] = make(map[int]int)
			}
			result.PerHourCounts[d][stmt.ColumnInt(1)] = stmt.ColumnInt(2)
			return nil
		}, query.EventID)
	if err != nil {
		return GetEventResponseSummaryResult{}, err
	}
	return result, nil
}

type CreateEventResponseCommand struct {
	EventID   string
	GuestName string
	DateHours map[date.Date]map[int]struct{}
}

type CreateEventResponseResult struct {
	ResponseID string
}

func (s *Store) CreateEventResponse(ctx context.Context, cmd CreateEventResponseCommand) (result CreateEventResponseResult, err error) {
	const responseIDLength = 10

	conn := s.pool.Get(ctx)
	defer s.pool.Put(conn)

	defer sqlitex.Save(conn)(&err)
	responseID, err := s.genString(responseIDLength)
	if err != nil {
		return
	}

	const responseQuery = `
		INSERT INTO response(event_id, id, guest_name)
		VALUES (?, ?, ?);`
	err = sqlitex.Exec(conn, responseQuery, nil, cmd.EventID, responseID, cmd.GuestName)
	if err != nil {
		return
	}

	const responseTimeQuery = `
		INSERT INTO response_time(event_id, response_id, date, time)
		VALUES (?, ?, ?, ?);`
	for d, hs := range cmd.DateHours {
		for h := range hs {
			err = sqlitex.Exec(conn, responseTimeQuery, nil,
				cmd.EventID, responseID, d.Format(dbDateLayout), h)
			if err != nil {
				return
			}
		}
	}

	return CreateEventResponseResult{
		ResponseID: responseID,
	}, nil
}

type GetEventResponseQuery struct {
	EventID    string
	ResponseID string
}

type GetEventResponseResult struct {
	GuestName string
	DateHours map[date.Date]map[int]struct{}
}

func (s *Store) GetEventResponse(ctx context.Context, query GetEventResponseQuery) (GetEventResponseResult, error) {
	conn := s.pool.Get(ctx)
	defer s.pool.Put(conn)

	var found bool
	var result GetEventResponseResult

	const responseQuery = `
		SELECT guest_name
		FROM response
		WHERE id = ? AND event_id = ?;`
	var err = sqlitex.Exec(conn, responseQuery,
		func(stmt *sqlite.Stmt) error {
			found = true
			result.GuestName = stmt.ColumnText(0)
			return nil
		}, query.ResponseID, query.EventID)
	if err != nil {
		return GetEventResponseResult{}, err
	}
	if !found {
		return GetEventResponseResult{}, ErrNotFound
	}

	result.DateHours = make(map[date.Date]map[int]struct{})
	const responseTimeQuery = `
		SELECT date, time
		FROM response_time
		WHERE  event_id = ? AND response_id = ?`
	err = sqlitex.Exec(conn, responseTimeQuery,
		func(stmt *sqlite.Stmt) error {
			d, err := date.Parse(dbDateLayout, stmt.ColumnText(0))
			if err != nil {
				return err
			}
			if result.DateHours[d] == nil {
				result.DateHours[d] = make(map[int]struct{})
			}
			result.DateHours[d][stmt.ColumnInt(1)] = struct{}{}
			return nil
		}, query.EventID, query.ResponseID)
	if err != nil {
		return GetEventResponseResult{}, err
	}
	return result, nil
}