package storage

import (
	"context"
	"fmt"
	"strconv"
	"strings"

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

// This file implements the CID-resolution layer that lives on top of the
// flat metadata storage in client.go. The short version:
//
//   - Roots are opaque UUIDv7s — file:<uuid>/<property> for every property.
//     The UUID is an internal implementation detail; the mental model is
//     "N CIDs → one record of keys→metadata".
//   - Every known CID for a file is registered as a reverse-index entry:
//       cid:<bareCid> → <uuid>
//     and as a member of the per-root bare-CID key-set:
//       file:<uuid>/cids/<bareCid> = "true"   (flat key, sentinel value)
//   - A CID is self-describing: its algorithm is recoverable from the CIDv1
//     multicodec (see internal/cid), so there is no per-algorithm field name
//     and no <algo>: token prefix. The canonical externally-visible CID is
//     *derived by rank* from the key-set on read (GetMetadataDocument), never
//     stored.
//
// The record write path (writeFieldsTx) catches any write of a cids/<cid>
// field and registers the reverse-index entry in the same transaction, so
// writers that just emit the key-set members don't need to know about the
// reverse index at all. The helpers here take the caller's *kv.Tx: a write
// must never open a second transaction (there is one writer connection).

// CIDIndexPrefix is the key prefix for the reverse index. Combined
// with a bare CID, it forms the full key: "cid:bafk…".
const CIDIndexPrefix = "cid:"

// CIDsKeyPrefix is the field-name prefix for the bare-CID key-set. Sibling
// CIDs live as flat keys file:<uuid>/cids/<cid> = "true"; the set IS the
// keyset, the value is the sentinel. Read by GetMetadataDocument (hoisted
// into the typed CIDs array) and by DeleteRoot/DeleteMetadata (to find the
// reverse-index entries that need cleanup).
const CIDsKeyPrefix = "cids/"

// Duplicate paths — other physical locations whose content hashes to the same
// CIDs as a root — live as dup:<rid>/<path> = "" (a key-set). The watcher
// writes one when it sees a new path for content that's already indexed.

// Mint creates a new root with filePath/sizeByte/mtimeNano and registers it
// in the root index. Returns the new UUID. The caller is expected to follow
// up with AddAlias for at least one CID — a root without any alias is
// reachable only via the index, which works but defeats the point.
func (c *Client) Mint(filePath string, size, mtimeNano int64) (string, error) {
	var uuid string
	err := c.update(func(tx *kv.Tx) error {
		var err error
		uuid, err = mintTx(tx, filePath, size, mtimeNano)
		return err
	})
	return uuid, err
}

func mintTx(tx *kv.Tx, filePath string, size, mtimeNano int64) (string, error) {
	uuid, err := NewUUID()
	if err != nil {
		return "", fmt.Errorf("uuid: %w", err)
	}
	return uuid, writeFieldsTx(tx, uuid, map[string]string{
		"filePath":  filePath,
		"sizeByte":  strconv.FormatInt(size, 10),
		"mtimeNano": strconv.FormatInt(mtimeNano, 10),
	})
}

// AddAlias registers cidStr as a sibling CID of uuid: it writes the reverse
// index cid:<cidStr> → uuid and the key-set member cids/<cidStr> = "true".
// Idempotent: registering the same CID twice is a no-op.
func (c *Client) AddAlias(uuid, cidStr string) error {
	if uuid == "" || cidStr == "" {
		return fmt.Errorf("uuid and cid are required")
	}
	return c.update(func(tx *kv.Tx) error {
		return writeFieldsTx(tx, uuid, map[string]string{CIDsKeyPrefix + cidStr: "true"})
	})
}

// addAliasTx registers the reverse-index entry for a cids/<cid> member the
// caller is writing (writeFieldsTx writes the member itself).
func addAliasTx(tx *kv.Tx, uuid, cidStr string) error {
	if uuid == "" || cidStr == "" {
		return fmt.Errorf("uuid and cid are required")
	}
	// Self-pointing alias guard. If the caller is trying to register
	// cid:<cid> → <cid> (i.e. the root IS the cid value), that's the
	// dual-root failure mode in disguise — it means somebody wrote
	// /meta/<cid> without first resolving via ResolveRoot. Refuse the alias
	// write; leave any existing alias alone. The key-set membership is still
	// recorded by the caller, so the field-level write succeeds.
	if uuid == cidStr {
		return nil
	}
	// Guard against the dual-root pattern: if cid:<cid> already points at a
	// DIFFERENT uuid, don't silently overwrite. Leave the existing alias; the
	// key-set membership keeps the CID discoverable via root → cids.
	indexKey := CIDIndexPrefix + cidStr
	existing, _, err := tx.Get(tx.Context(), indexKey)
	if err != nil {
		return fmt.Errorf("read existing alias: %w", err)
	}
	if existing != "" && existing != uuid {
		return nil
	}
	if existing == uuid {
		return nil
	}
	return tx.Put(indexKey, uuid)
}

// removeAliasTx is the inverse of addAliasTx: it drops the reverse-index
// entry cid:<cid> → <uuid>. The caller deletes the cids/<cid> key-set member
// itself (DeleteProperty does both).
//
// ⚠ Why this exists. A cids/ member write touches two keys — the flat
// file:<uuid>/cids/<cid> and this reverse alias — while the delete path once
// only removed the first. A "deleted" CID therefore still resolved: GET
// /meta/<cid>, ResolveRoot and GetByCID all kept answering with the record.
// The asymmetry is not theoretical. meta-share published dag-pb roots computed
// over RAR volumes and par2 files onto six records on watch.nsl.sh; removing
// the member was expressible, removing the claim was not, so the false
// identity survived its own retraction.
//
// Guarded, not blind: the alias is removed only when it currently points at
// THIS uuid. Two records can legitimately race to claim a cid (see the
// dual-root guard in addAliasTx, which leaves the first writer's alias in
// place); deleting a member from the loser must not unpick the winner's index.
func removeAliasTx(tx *kv.Tx, uuid, cidStr string) error {
	if uuid == "" || cidStr == "" {
		return nil
	}
	indexKey := CIDIndexPrefix + cidStr
	existing, ok, err := tx.Get(tx.Context(), indexKey)
	if err != nil {
		return fmt.Errorf("read existing alias: %w", err)
	}
	if !ok || existing != uuid {
		// Absent, or somebody else owns this alias. Leave it.
		return nil
	}
	_, err = tx.Delete(indexKey)
	return err
}

// ResolveRoot maps a hash supplied by a caller (a meta-sort write, an editor
// lookup, an SSE consumer) to the actual storage root key.
//
// Callers send a bare CID (e.g. the midhash "bafk…" the watcher publishes on
// file:events, or any sibling CID). Roots are kept opaque and every CID is
// aliased into the reverse index:
//
//	cid:bafk… → 01KSBHM*
//
// Without resolution, every /meta/<cid> write creates a parallel cid-rooted
// entry that the watcher's UUID never sees.
//
// Behaviour:
//   - empty hash → empty (caller's problem)
//   - hash matches a reverse-index entry → return UUID
//   - otherwise return hash unchanged (legacy / explicit-UUID writes)
//
// Errors are converted to "no resolution" — if the store is down or the
// lookup fails we let the caller proceed with the bare hash and surface the
// failure on the actual operation.
func (c *Client) ResolveRoot(hash string) string {
	if hash == "" {
		return hash
	}
	uuid, err := c.GetByCID(hash)
	if err != nil || uuid == "" {
		return hash
	}
	return uuid
}

// GetByCID resolves a bare CID to the UUID of its root. Returns ("", nil)
// when the CID is unknown; the empty string is the "not found" signal rather
// than a typed error so callers can branch without errors.As.
func (c *Client) GetByCID(cidStr string) (string, error) {
	s, err := c.kv()
	if err != nil {
		return "", err
	}
	if cidStr == "" {
		return "", nil
	}
	ctx, cancel := opCtx()
	defer cancel()
	uuid, _, err := s.Get(ctx, CIDIndexPrefix+cidStr)
	if err != nil {
		return "", fmt.Errorf("get cid index: %w", err)
	}
	return uuid, nil
}

// AddDuplicatePath records that path is another physical location whose
// content matches uuid. Returns true if path was newly added. The watcher
// calls this when it sees a file whose midhash matches an existing root but
// at a different filePath.
func (c *Client) AddDuplicatePath(uuid, path string) (bool, error) {
	if uuid == "" || path == "" {
		return false, nil
	}
	added := false
	err := c.update(func(tx *kv.Tx) error {
		var err error
		added, err = tx.PutIfAbsent(dupPrefix(uuid)+path, "")
		return err
	})
	return added, err
}

// cidsForRoot returns a root's bare-CID key-set members (cids/ prefix
// stripped).
func cidsForRoot(ctx context.Context, r kv.Reader, uuid string) ([]string, error) {
	prefix := recordPrefix(uuid) + CIDsKeyPrefix
	rows, err := r.Range(ctx, prefix, "", 0)
	if err != nil {
		return nil, err
	}
	out := make([]string, 0, len(rows))
	for _, row := range rows {
		out = append(out, row.K[len(prefix):])
	}
	return out, nil
}

// DeleteRoot removes everything keyed off uuid: every file:<uuid>/* property
// (including the cids/<cid> key-set), every reverse-index entry for those
// CIDs, its duplicates, search row and index membership. Idempotent — a uuid
// with no remaining keys is a successful no-op.
func (c *Client) DeleteRoot(uuid string) error {
	if uuid == "" {
		return nil
	}
	return c.update(func(tx *kv.Tx) error {
		_, err := deleteRecordTx(tx, uuid)
		return err
	})
}

// cidFromKeysetField returns the bare CID encoded in a cids/<cid> field name,
// or "" if the field isn't a key-set member.
func cidFromKeysetField(field string) string {
	if !strings.HasPrefix(field, CIDsKeyPrefix) {
		return ""
	}
	return strings.TrimPrefix(field, CIDsKeyPrefix)
}

// MetadataDocument is the complete state of one file as the public API
// returns it: every flat string field (the cids/<cid> members included),
// plus the CIDs hoisted into a typed array, the canonical CID derived by
// rank, and the duplicates set. Distinct from GetMetadataFlat (which only
// returns the raw string keys).
type MetadataDocument struct {
	Flat       map[string]string `json:"metadata"`
	CIDs       []string          `json:"cids"`
	Canonical  string            `json:"canonical_cid,omitempty"`
	Duplicates []string          `json:"duplicates"`
}

// GetMetadataDocument returns the full document for a root: every string
// property under file:<uuid>/* (cids/<cid> members included in Flat), the
// CIDs hoisted into a typed array, the canonical CID computed by rank, and
// the duplicates SET. Returns nil if the root has no keys at all (deleted or
// never existed).
func (c *Client) GetMetadataDocument(uuid string) (*MetadataDocument, error) {
	s, err := c.kv()
	if err != nil {
		return nil, err
	}
	if uuid == "" {
		return nil, nil
	}
	ctx, cancel := opCtx()
	defer cancel()

	flat, err := readRecord(ctx, s, uuid)
	if err != nil {
		return nil, err
	}
	if flat == nil {
		flat = make(map[string]string)
	}

	// Hoist the cids/<cid> key-set members into a typed array and derive the
	// canonical CID by rank. The members remain in Flat too — that's how
	// flat-map consumers (meta-share ingest) see them.
	cids := make([]string, 0)
	canonical := ""
	for k := range flat {
		if !strings.HasPrefix(k, CIDsKeyPrefix) {
			continue
		}
		cidStr := strings.TrimPrefix(k, CIDsKeyPrefix)
		cids = append(cids, cidStr)
		if canonical == "" {
			canonical = cidStr
		} else {
			canonical = cid.Better(canonical, cidStr)
		}
	}

	dupRows, err := s.Range(ctx, dupPrefix(uuid), "", 0)
	if err != nil {
		return nil, fmt.Errorf("read duplicates: %w", err)
	}
	dups := make([]string, 0, len(dupRows))
	for _, row := range dupRows {
		dups = append(dups, row.K[len(dupPrefix(uuid)):])
	}

	if len(flat) == 0 && len(cids) == 0 && len(dups) == 0 {
		return nil, nil
	}
	return &MetadataDocument{
		Flat:       flat,
		CIDs:       cids,
		Canonical:  canonical,
		Duplicates: dups,
	}, nil
}

// RegisterFileTuple records one physical file under its midhash256 CID, the
// same way the file watcher does for every file it scans: mint a UUID root
// (filePath/sizeByte/mtimeNano) and write `cids/<midhash>`, whose hook
// registers the cid:<midhash> reverse alias. Content already known under
// another path is recorded as a duplicate; the same path just refreshes
// size/mtime.
//
// Returns the root and whether it was newly minted. Shared by the watcher and
// POST /api/files/register, which is how a box running with the watcher off
// (a meta-watch client core) still gets files it writes under /files/plugin
// resolvable by CID.
func (c *Client) RegisterFileTuple(absPath string, size, mtimeNano int64, midhash string) (string, bool, error) {
	if midhash == "" {
		return "", false, fmt.Errorf("midhash is required")
	}
	var (
		uuid   string
		minted bool
	)
	// One transaction: the lookup and the mint cannot interleave with another
	// registration of the same content, so two concurrent scans of one file
	// can no longer mint two roots for it.
	err := c.update(func(tx *kv.Tx) error {
		ctx := tx.Context()
		existing, _, err := tx.Get(ctx, CIDIndexPrefix+midhash)
		if err != nil {
			return fmt.Errorf("GetByCID(%s): %w", midhash, err)
		}
		uuid = existing
		if uuid == "" {
			if uuid, err = mintTx(tx, absPath, size, mtimeNano); err != nil {
				return fmt.Errorf("Mint(%s): %w", absPath, err)
			}
			minted = true
			if err := writeFieldsTx(tx, uuid, map[string]string{CIDsKeyPrefix + midhash: "true"}); err != nil {
				return fmt.Errorf("cids/%s for %s: %w", midhash, uuid, err)
			}
			return nil
		}
		current, _, err := tx.Get(ctx, recordPrefix(uuid)+"filePath")
		if err != nil {
			return err
		}
		if current != absPath {
			if _, err := tx.PutIfAbsent(dupPrefix(uuid)+absPath, ""); err != nil {
				return fmt.Errorf("AddDuplicatePath %s @ %s: %w", uuid, absPath, err)
			}
			return nil
		}
		if err := writeFieldsTx(tx, uuid, map[string]string{
			"sizeByte":  strconv.FormatInt(size, 10),
			"mtimeNano": strconv.FormatInt(mtimeNano, 10),
		}); err != nil {
			return fmt.Errorf("refresh tuple for %s: %w", uuid, err)
		}
		return nil
	})
	if err != nil {
		return "", false, err
	}
	return uuid, minted, nil
}