package repositories

import (
	"fmt"
	"strings"

	"nearle/models"
)

// Sign-in for the POS terminal.
//
// Deliberately reads the same `app_users` rows the web console authenticates
// against rather than introducing a terminal-specific credential table. A shop
// manager who can sign into the back office should be able to open the till
// with the same details, and one account store means deactivating a leaver
// closes both doors at once instead of one and a half.
//
// Kept in its own file because the rest of posRepository is about moving bills
// and stock, and mixing authorisation into that made the one thing nobody
// should have to hunt for the hardest thing to find.

// posLoginRow is the credential check's raw answer.
type posLoginRow struct {
	Userid     int
	Password   string
	Status     string
	Roleid     int
	Configid   int
	Tenantid   int
	Locationid int
	Firstname  string
	Lastname   string
	Email      string
}

// PosLogin authenticates a user and returns the session they are entitled to.
//
// The outlet is resolved here, from the user's own row and the tenant's list of
// locations — never from anything the caller sent. That inversion is the whole
// point of the endpoint.
func (r *posRepository) PosLogin(req models.PosLoginRequest) (*models.PosSession, error) {
	field, value := "authname", strings.TrimSpace(req.Authname)
	if value == "" {
		field, value = "contactno", strings.TrimSpace(req.Contactno)
	}
	if value == "" {
		return nil, fmt.Errorf("an email or mobile number is required")
	}

	rows, err := r.posLoginCandidates(field, value, req.Configid)
	if err != nil {
		return nil, err
	}

	// One message for "no such account" and for "wrong password", on purpose.
	// Distinguishing them turns the login into a directory of who banks here.
	if len(rows) == 0 {
		return nil, errPosLoginRejected
	}

	// `authname` is not unique in this schema — live data has the same address
	// twice under one configid — so more than one row can come back. Resolving
	// that by taking the first would let the account a person *meant* be
	// shadowed by a stranger's, and on a POS that means billing into the wrong
	// tenant's books. Refused instead, with the fix the caller can act on.
	if len(rows) > 1 {
		return nil, fmt.Errorf(
			"more than one account uses these sign-in details; ask your administrator for the configid and send it with the login")
	}

	// Inactive accounts never reach here — posLoginCandidates excludes them, so
	// that a deactivated duplicate cannot make a live login ambiguous.
	row := rows[0]

	// Matches the web console's plaintext comparison, which is what the stored
	// column holds today. Constant-time so this endpoint at least does not add
	// a timing oracle on top.
	//
	// TODO: the password column is plaintext across the whole platform. Hashing
	// it is a migration touching every login path, not something this endpoint
	// can fix alone — but a POS token minted off a plaintext password is only
	// ever as good as that column.
	if strings.TrimSpace(row.Password) == "" {
		return nil, fmt.Errorf("this account has no password set; set one in the web console first")
	}
	if !constantTimeEqual(row.Password, req.Password) {
		return nil, errPosLoginRejected
	}

	if row.Tenantid <= 0 {
		return nil, fmt.Errorf("this account is not attached to a tenant and cannot open a till")
	}

	locations, err := r.posLoginLocations(row.Tenantid, row.Locationid)
	if err != nil {
		return nil, err
	}
	if len(locations) == 0 {
		return nil, fmt.Errorf("no active outlet is registered for this account")
	}

	// Which outlet this terminal is standing in. A request may ask for one, but
	// only from the set the account already reaches.
	chosen := locations[0]
	if req.Locationid > 0 {
		match := false
		for _, loc := range locations {
			if loc.Locationid == req.Locationid {
				chosen, match = loc, true
				break
			}
		}
		if !match {
			return nil, fmt.Errorf("this account cannot open a till at outlet %d", req.Locationid)
		}
	}

	session := &models.PosSession{
		Userid:       row.Userid,
		Fullname:     strings.TrimSpace(row.Firstname + " " + row.Lastname),
		Email:        row.Email,
		Roleid:       row.Roleid,
		Tenantid:     row.Tenantid,
		Storeid:      fmt.Sprintf("%d", chosen.Locationid),
		Locationid:   chosen.Locationid,
		Locationname: chosen.Locationname,
		Address:      chosen.Address,
		Locations:    locations,
	}

	r.decoratePosSession(session)

	// Staff come down with the session so a till is ready to trade the moment
	// it signs in. A failure here is not a failed sign-in: a shop with no staff
	// recorded — which is almost all of them today — must still be able to open
	// its terminal.
	if staff, err := r.PosStaff(session.Tenantid, session.Locationid); err == nil {
		session.Staff = staff
	}

	return session, nil
}

// posLoginCandidates finds the accounts matching a set of sign-in details.
//
// Returns a list rather than a row because `app_users` does not constrain
// `authname` to be unique — not globally and not per configid. The caller
// decides what an ambiguous match means; silently picking one here would bury
// the decision in a LIMIT 1.
//
// The configid handling is the part worth explaining. The web console asks for
// it because the browser knows which tenant portal it is on. A till does not:
// somebody is standing at a counter typing an email and a password, and
// demanding a number they have never seen would make the login unusable. So it
// is honoured when sent and inferred when not — and inference that finds more
// than one candidate is reported, never guessed.
func (r *posRepository) posLoginCandidates(field, value string, configID int) ([]posLoginRow, error) {
	rows := make([]posLoginRow, 0, 2)

	query := fmt.Sprintf(`
		SELECT userid, COALESCE(password, '') AS password, COALESCE(status, '') AS status,
		       COALESCE(roleid, 0) AS roleid, COALESCE(configid, 0) AS configid,
		       COALESCE(tenantid, 0) AS tenantid, COALESCE(locationid, 0) AS locationid,
		       COALESCE(firstname, '') AS firstname, COALESCE(lastname, '') AS lastname,
		       COALESCE(email, '') AS email
		FROM app_users
		WHERE LOWER(TRIM(%s)) = LOWER(TRIM(?))`, field)
	params := []interface{}{value}

	if configID > 0 {
		query += ` AND configid = ?`
		params = append(params, configID)
	}

	// Inactive accounts are excluded from the match rather than matched and
	// then refused. A deactivated duplicate would otherwise make a working
	// login ambiguous, which turns "this person left" into "nobody can open
	// the till".
	query += ` AND LOWER(COALESCE(status, 'active')) <> 'inactive' ORDER BY userid`

	if err := r.db.Raw(query, params...).Scan(&rows).Error; err != nil {
		return nil, err
	}
	return rows, nil
}

// posLoginLocations lists the outlets an account may open a till at.
//
// A user pinned to one location gets that one alone; a tenant-level account
// with locationid 0 — a proprietor with several shops — gets all of the
// tenant's active outlets and picks at sign-in.
//
// Inactive outlets are excluded rather than listed and disabled: a till cannot
// usefully trade at a closed shop, and offering it is an invitation to a
// support call.
func (r *posRepository) posLoginLocations(tenantID, pinned int) ([]models.PosLoginLocation, error) {
	rows := make([]models.PosLoginLocation, 0)

	query := `
		SELECT locationid,
		       COALESCE(locationname, '') AS locationname,
		       COALESCE(address, '')      AS address,
		       COALESCE(city, '')         AS city,
		       COALESCE(status, '')       AS status
		FROM tenantlocations
		WHERE tenantid = ? AND LOWER(COALESCE(status, 'active')) <> 'inactive'`
	params := []interface{}{tenantID}

	if pinned > 0 {
		query += ` AND locationid = ?`
		params = append(params, pinned)
	}
	query += ` ORDER BY locationid`

	if err := r.db.Raw(query, params...).Scan(&rows).Error; err != nil {
		return nil, err
	}
	return rows, nil
}

// decoratePosSession fills in what a receipt needs.
//
// The store name, GSTIN and address printed on a bill are a legal requirement
// on a GST invoice, and the till had them as compile-time constants. Sending
// them down with the session means a shop that corrects its GSTIN in the back
// office sees the correction on its next receipt rather than at the next
// rebuild.
//
// Failures here are swallowed: a missing tenant name is a cosmetic problem, and
// refusing a sign-in over it would close a shop.
func (r *posRepository) decoratePosSession(session *models.PosSession) {
	var tenant struct {
		Tenantname string
		Gstin      string
		Contactno  string
		Address    string
	}

	// `registrationno` is where this schema keeps the GST number — there is no
	// `gstin` column. Aliased rather than renamed through the stack so the till
	// receives it under the name it prints on a receipt.
	err := r.db.Raw(`
		SELECT COALESCE(tenantname, '')       AS tenantname,
		       COALESCE(registrationno, '')   AS gstin,
		       COALESCE(primarycontact, '')   AS contactno,
		       COALESCE(address, '')          AS address
		FROM tenants WHERE tenantid = ? LIMIT 1`, session.Tenantid).Scan(&tenant).Error
	if err != nil {
		return
	}

	session.Tenantname = tenant.Tenantname
	session.Gstin = tenant.Gstin
	session.Phone = tenant.Contactno

	// The outlet's own address wins — a chain's receipts must name the shop the
	// customer is standing in, not head office. The tenant address is only a
	// fallback for an outlet that has none recorded.
	if strings.TrimSpace(session.Address) == "" {
		session.Address = tenant.Address
	}
}

// PosLocationAllowed reports whether a tenant owns an outlet.
//
// The check the whole session model rests on. Everything a terminal asks for
// names a location, and this is what stops a valid token for one shop being
// replayed against another.
func (r *posRepository) PosLocationAllowed(tenantID, locationID int) (bool, error) {
	if tenantID <= 0 || locationID <= 0 {
		return false, nil
	}

	var count int64
	err := r.db.Raw(
		`SELECT COUNT(1) FROM tenantlocations WHERE tenantid = ? AND locationid = ?`,
		tenantID, locationID,
	).Scan(&count).Error
	if err != nil {
		return false, err
	}
	return count > 0, nil
}

// errPosLoginRejected is the single answer to a bad email and a bad password.
var errPosLoginRejected = fmt.Errorf("those sign-in details were not recognised")

// PosLoginRejected reports whether an error is a failed credential check, so
// the controller can answer 401 for those and 500 for a database fault without
// matching on message text.
func PosLoginRejected(err error) bool { return err == errPosLoginRejected }

// constantTimeEqual compares two secrets without leaking their contents through
// how long it took.
//
// Length is compared first and is deliberately allowed to leak — a password's
// length is not the secret, and hashing to a fixed width just to hide it would
// be more machinery than the exposure justifies.
func constantTimeEqual(a, b string) bool {
	if len(a) != len(b) {
		return false
	}
	var diff byte
	for i := 0; i < len(a); i++ {
		diff |= a[i] ^ b[i]
	}
	return diff == 0
}

// PosStaff lists the people who may ring a bill at an outlet.
//
// Two sources, unioned, because the schema has two and neither is complete.
// `tenantstaffs` is the table built for this and holds 12 rows on the entire
// platform; `app_users.locationid` is where staff actually ended up. Reading
// only the purpose-built table would return nothing for almost every shop, and
// reading only `app_users` would miss anyone assigned through the back office's
// staff screen. So both.
//
// Only people with a PIN come back. A row with `pin = 0` cannot ring anything —
// offering it to the till would put a name on screen that no one can sign in
// as, which reads as a broken terminal rather than as an unfinished setup.
func (r *posRepository) PosStaff(tenantID, locationID int) ([]models.PosStaffMember, error) {
	rows := make([]models.PosStaffMember, 0)

	query := `
		SELECT DISTINCT
		       a.userid,
		       TRIM(CONCAT(COALESCE(a.firstname,''), ' ', COALESCE(a.lastname,''))) AS fullname,
		       COALESCE(r.rolename, '')  AS role,
		       CAST(a.pin AS TEXT)       AS pin,
		       COALESCE(a.status, '')    AS status
		FROM app_users a
		LEFT JOIN app_roles r ON r.roleid = a.roleid
		WHERE a.tenantid = ?
		  AND COALESCE(a.pin, 0) > 0
		  AND LOWER(COALESCE(a.status, 'active')) <> 'inactive'
		  AND (
		        a.locationid = ?
		     OR EXISTS (SELECT 1 FROM tenantstaffs s
		                WHERE s.userid = a.userid
		                  AND s.tenantid = a.tenantid
		                  AND s.locationid = ?
		                  AND LOWER(COALESCE(s.status, 'active')) <> 'inactive')
		  )
		ORDER BY fullname`

	if err := r.db.Raw(query, tenantID, locationID, locationID).Scan(&rows).Error; err != nil {
		return nil, err
	}

	// A PIN shared by two people at one outlet would make the till attribute a
	// bill to whichever row it happened to check first — so the second one is
	// dropped rather than sent. Live data has 1234 on eleven accounts and 1111
	// on nine, so this is not hypothetical.
	seen := make(map[string]bool, len(rows))
	unique := rows[:0]
	for _, row := range rows {
		if seen[row.Pin] {
			continue
		}
		seen[row.Pin] = true
		unique = append(unique, row)
	}

	return unique, nil
}