package store

import (
	"context"
	"crypto/rand"
	"encoding/hex"
	"time"
)

// Forgotten is what forgetting a person did, for saying so.
type Forgotten struct {
	// Pseudonym is what their usage is counted under now: random, so it
	// links to nothing.
	Pseudonym string
	// UsageRows and RollupRows are the request records and sums moved to it.
	UsageRows  int64
	RollupRows int64
	// Requests, Files and Batches are kept requests, and personal files and
	// batches, deleted; AuditEvents the audit lines their name was taken out of.
	Requests    int64
	Files       int64
	Batches     int64
	AuditEvents int64
}

// ForgetUser erases a person: what was kept of their requests, their
// personal files and batches and their limits are deleted; their usage — the
// request records and every sum of them — is kept, for the totals stay true,
// under a random pseudonym; their name is taken out of the audit log; and the
// account goes as DeleteUser removes it. What remains cannot be tied back to
// them.
//
// Conversations and agent notes belong to projects, not people, and are not
// touched: a project forgets them by its retention, or by
// DELETE /v1/threads/{id}.
func (s *DB) ForgetUser(ctx context.Context, userID string, at time.Time) (Forgotten, error) {
	u, err := s.UserByID(ctx, userID)
	if err != nil {
		return Forgotten{}, err
	}
	b := make([]byte, 8)
	if _, err := rand.Read(b); err != nil {
		return Forgotten{}, err
	}
	f := Forgotten{Pseudonym: "forgotten-" + hex.EncodeToString(b)}
	err = s.inTx(ctx, func(c conn) error {
		n := func(q string, args ...any) (int64, error) {
			res, err := c.ExecContext(ctx, q, args...)
			if err != nil {
				return 0, err
			}
			return res.RowsAffected()
		}
		var err error
		if f.Requests, err = n(`DELETE FROM request_bodies WHERE request_id IN
			(SELECT request_id FROM usage WHERE user_id = ? AND request_id <> '')`, userID); err != nil {
			return err
		}
		session, pseudoSession := "session:"+userID, "session:"+f.Pseudonym
		if f.UsageRows, err = n(`UPDATE usage SET user_id = ? WHERE user_id = ?`, f.Pseudonym, userID); err != nil {
			return err
		}
		if _, err = n(`UPDATE usage SET key_id = ? WHERE key_id = ?`, pseudoSession, session); err != nil {
			return err
		}
		for _, t := range []string{"usage_5m", "usage_1h", "usage_1d"} {
			m, err := n(`UPDATE `+t+` SET user_id = ? WHERE user_id = ?`, f.Pseudonym, userID)
			if err != nil {
				return err
			}
			f.RollupRows += m
			if _, err := n(`UPDATE `+t+` SET key_id = ? WHERE key_id = ?`, pseudoSession, session); err != nil {
				return err
			}
		}
		owner := "user:" + userID
		if _, err = n(`DELETE FROM batch_results WHERE batch_id IN (SELECT id FROM batches WHERE owner = ?)`, owner); err != nil {
			return err
		}
		if f.Batches, err = n(`DELETE FROM batches WHERE owner = ?`, owner); err != nil {
			return err
		}
		if f.Files, err = n(`DELETE FROM files WHERE owner = ?`, owner); err != nil {
			return err
		}
		if _, err = n(`DELETE FROM limits WHERE scope_type = ? AND scope_id = ?`, string(ScopeUser), userID); err != nil {
			return err
		}
		// Who did what stays in the audit log; that it was them does not.
		for _, name := range []string{u.Email, userID} {
			if name == "" {
				continue
			}
			m, err := n(`UPDATE audit_events SET actor = REPLACE(actor, ?, ?), target = REPLACE(target, ?, ?),
				detail = REPLACE(detail, ?, ?) WHERE actor LIKE ? OR target LIKE ? OR detail LIKE ?`,
				name, f.Pseudonym, name, f.Pseudonym, name, f.Pseudonym, "%"+name+"%", "%"+name+"%", "%"+name+"%")
			if err != nil {
				return err
			}
			f.AuditEvents += m
		}
		return nil
	})
	if err != nil {
		return Forgotten{}, err
	}
	return f, s.DeleteUser(ctx, userID, at)
}