package storage

// Account-scoped UDL administration: what a uid holds, and removing all of it.
//
// Both operations enumerate the same thing — every `udl:rec:<uid>/<cid>/<key>`
// cell. Keys are ordered, so one account's cells are the key range under
// `udl:rec:<uid>/`, and every account's are the range under `udl:rec:`.
// UDLAllUserStats stays a bulk call (one walk buckets every account) because
// the accounts page needs a number for each.

import (
	"fmt"
	"strings"

	"github.com/metazla/meta-core/internal/kv"
)

// UDLUserStats counts what one account holds. Records is the number of cells,
// including tombstones — a retracted rating is still a row this account owns
// and still something a purge has to remove.
type UDLUserStats struct {
	Records int `json:"records"`
	Cids    int `json:"cids"`
	Keys    int `json:"keys"`
}

// safeUIDForPattern rejects anything that would reach across the key
// structure (a `/` would let a uid prefix-match another account's range). meta-core's uids are alphanumeric
// (identity.validUID), so this only ever fires on a hostile or malformed one —
// but it fires here, in the layer that builds the pattern, rather than relying
// on every caller having validated first.
func safeUIDForPattern(uid string) error {
	if uid == "" {
		return fmt.Errorf("empty uid")
	}
	if strings.ContainsAny(uid, "*?[]\\/:") {
		return fmt.Errorf("uid contains characters that are not valid in a uid: %q", uid)
	}
	return nil
}

// splitUDLRecSuffix splits the "<uid>/<cid>/<key>" tail of a udl:rec key.
//
// SplitN with a limit of 3 so a key containing a slash survives intact. cids
// never contain one; keys are a controlled vocabulary today, but a namespaced
// one arriving later must not silently truncate here — a truncated key would
// make the purge SREM the wrong index member and leave the real one behind.
func splitUDLRecSuffix(suffix string) (uid, cid, key string, ok bool) {
	parts := strings.SplitN(suffix, "/", 3)
	if len(parts) != 3 || parts[0] == "" || parts[1] == "" || parts[2] == "" {
		return "", "", "", false
	}
	return parts[0], parts[1], parts[2], true
}

// UDLUserCells returns every (cid, key) pair this account holds a cell for,
// keyed by the "cid/key" tail with the cid as value (the purge needs them
// grouped).
func (c *Client) UDLUserCells(uid string) (map[string]string, error) {
	if err := safeUIDForPattern(uid); err != nil {
		return nil, err
	}
	s, err := c.kv()
	if err != nil {
		return nil, err
	}
	ctx, cancel := opCtx()
	defer cancel()

	out := make(map[string]string)
	err = s.ScanPrefix(ctx, "udl:rec:"+uid+"/", readerPage, func(rows []kv.KV) error {
		for _, row := range rows {
			gotUID, cid, key, ok := splitUDLRecSuffix(strings.TrimPrefix(row.K, "udl:rec:"))
			if !ok || gotUID != uid {
				continue
			}
			out[cid+"/"+key] = cid
		}
		return nil
	})
	return out, err
}

// UDLAllUserStats counts every account's cells in one walk.
//
// Returns only accounts that actually hold records; a uid absent from the map
// holds none. Callers render a zero for those rather than treating it as an
// error — an account created a minute ago legitimately has nothing.
func (c *Client) UDLAllUserStats() (map[string]UDLUserStats, error) {
	s, err := c.kv()
	if err != nil {
		return nil, err
	}
	ctx, cancel := opCtx()
	defer cancel()

	type acc struct {
		cells int
		cids  map[string]struct{}
		keys  map[string]struct{}
	}
	byUID := make(map[string]*acc)
	err = s.ScanPrefix(ctx, "udl:rec:", readerPage, func(rows []kv.KV) error {
		for _, row := range rows {
			uid, cid, key, ok := splitUDLRecSuffix(strings.TrimPrefix(row.K, "udl:rec:"))
			if !ok {
				continue
			}
			a := byUID[uid]
			if a == nil {
				a = &acc{cids: make(map[string]struct{}), keys: make(map[string]struct{})}
				byUID[uid] = a
			}
			a.cells++
			a.cids[cid] = struct{}{}
			a.keys[key] = struct{}{}
		}
		return nil
	})
	if err != nil {
		return nil, err
	}
	out := make(map[string]UDLUserStats, len(byUID))
	for uid, a := range byUID {
		out[uid] = UDLUserStats{Records: a.cells, Cids: len(a.cids), Keys: len(a.keys)}
	}
	return out, nil
}

// UDLPurgeUser removes every trace of one account from the User Data Layer:
// its cells, its three user-scoped indexes, and its membership in the shared
// cid-scoped indexes. Returns what was removed.
//
// The shared indexes are the part that is easy to miss and expensive to leave.
// `udl:idx:cid:<cid>:key:<key>` and `udl:idx:cid:<cid>:users` are keyed by cid,
// not by uid, so a purge that only deleted `udl:rec:<uid>/*` would leave this
// uid listed as an opinion-holder on every title it ever touched.
//
// Idempotent: purging an account with nothing stored is a no-op returning
// zeroes, so a retry is safe.
func (c *Client) UDLPurgeUser(uid string) (UDLUserStats, error) {
	cells, err := c.UDLUserCells(uid)
	if err != nil {
		return UDLUserStats{}, err
	}

	stats := UDLUserStats{Records: len(cells)}
	distinctCids := make(map[string]struct{})
	distinctKeys := make(map[string]struct{})
	err = c.update(func(tx *kv.Tx) error {
		for cidKey, cid := range cells {
			key := strings.TrimPrefix(cidKey, cid+"/")
			distinctCids[cid] = struct{}{}
			distinctKeys[key] = struct{}{}
			if _, err := tx.Delete(udlRecKey(uid, cid, key)); err != nil {
				return err
			}
			if err := udlRem(tx, udlIdxCidKey(cid, key), uid); err != nil {
				return err
			}
		}
		for cid := range distinctCids {
			if err := udlRem(tx, udlIdxCidUsers(cid), uid); err != nil {
				return err
			}
		}
		// The three user-scoped indexes (`:key:*`, `:cid:*`, `:cids`) are one
		// key range, dropped whole — which also catches index entries whose
		// cell is already gone (the state a half-finished purge leaves).
		_, err := tx.DeletePrefix("udl:idx:user:"+uid+":", 0)
		return err
	})
	if err != nil {
		return UDLUserStats{}, fmt.Errorf("purge: %w", err)
	}
	stats.Cids = len(distinctCids)
	stats.Keys = len(distinctKeys)
	return stats, nil
}