package rqlite

// batch.go provides atomic multi-statement transactions over RQLite using the
// native /db/execute?transaction endpoint.
//
// Why this exists: the database/sql Begin/Commit path against the gorqlite
// stdlib driver does NOT produce real RQLite transactions (BEGIN/COMMIT are
// effectively no-ops in that driver). The only path to true atomicity is the
// native gorqlite.Connection.WriteParameterizedContext, which posts all
// statements in one HTTP request to RQLite with ?transaction set — RQLite
// then wraps them in a server-side transaction with rollback on any failure.
//
// This file exposes that path through a stable Client.Batch interface that
// works with both writes (atomic) and follow-up reads (sequenced after the
// commit). See plan: core/plans/platform/07_DB_TRANSACTION.md.

import (
	"context"
	"encoding/json"
	"fmt"
	"time"

	"github.com/rqlite/gorqlite"
)

// BatchOpKind enumerates the supported op kinds.
type BatchOpKind string

const (
	BatchOpExec  BatchOpKind = "exec"
	BatchOpQuery BatchOpKind = "query"
)

// BatchOp is a single statement in a transactional batch.
type BatchOp struct {
	Kind BatchOpKind   `json:"kind"`
	SQL  string        `json:"sql"`
	Args []interface{} `json:"args,omitempty"`
}

// OpResult holds per-op output. On rollback, OpResults for ops up to and
// including the failing one are populated; the failing op carries Error.
type OpResult struct {
	Kind         BatchOpKind              `json:"kind"`
	RowsAffected int64                    `json:"rows_affected,omitempty"`
	LastInsertID int64                    `json:"last_insert_id,omitempty"`
	Rows         []map[string]interface{} `json:"rows,omitempty"`
	Error        string                   `json:"error,omitempty"`
}

// BatchResult is the response from a transactional batch.
type BatchResult struct {
	Results     []OpResult `json:"results"`
	Committed   bool       `json:"committed"`
	FailedIndex int        `json:"failed_index,omitempty"` // valid only when !Committed
}

// MaxBatchOps caps the number of ops in a single batch to prevent abuse.
// 100 is plenty for any realistic transactional unit of work.
const MaxBatchOps = 100

// MaxBatchQueryRowsPerOp caps the row count returned per query in a
// BatchQuery result. Without this, a malicious or buggy WASM function
// could OOM the gateway by submitting `SELECT * FROM <large_table>` and
// having every row materialized into a Go map. 10000 rows fits comfortably
// in memory even when multiplied by MaxBatchOps; functions that legitimately
// need more should paginate.
const MaxBatchQueryRowsPerOp = 10000

// MaxBatchQueryTotalBytes caps the aggregate JSON-encoded size of all
// BatchQuery results across all ops. Defense in depth against the same
// OOM vector as MaxBatchQueryRowsPerOp — a single op could have 5000
// rows × 20KB each = 100MB and still be under the per-op count cap.
// 32 MiB matches the WASM module memory ceiling order-of-magnitude.
const MaxBatchQueryTotalBytes = 32 * 1024 * 1024

// BatchWithSeq executes the user's ops atomically AND, in the same atomic
// batch, increments the per-namespace publish sequence counter so the caller
// can attach the assigned seq to a follow-up wake-up message.
//
// On commit, the returned int64 is the seq assigned to this commit (and to
// any subscriber-visible side effects). On rollback (Committed=false), the
// returned int64 is 0 and the per-namespace counter is unchanged.
//
// Implementation note: the seq UPSERT runs first so that if the user's ops
// later in the batch fail, the increment also rolls back — keeping the
// counter consistent with what was actually published.
func (c *client) BatchWithSeq(ctx context.Context, namespace string, userOps []BatchOp) (*BatchResult, int64, error) {
	if namespace == "" {
		return nil, 0, fmt.Errorf("rqlite.BatchWithSeq: namespace required")
	}
	if c.conn == nil {
		return nil, 0, fmt.Errorf("rqlite.BatchWithSeq: native gorqlite connection not configured")
	}

	now := time.Now().Unix()

	// Prepend the seq UPSERT. RETURNING (SQLite 3.35+) gives us the new value
	// without a follow-up SELECT.
	seqOp := BatchOp{
		Kind: BatchOpExec,
		SQL: `INSERT INTO namespace_publish_seq (namespace, next_seq, updated_at)
		      VALUES (?, 2, ?)
		      ON CONFLICT(namespace) DO UPDATE SET
		          next_seq   = next_seq + 1,
		          updated_at = excluded.updated_at`,
		Args: []interface{}{namespace, now},
	}

	// We follow with a query of the just-incremented value. Sequenced after
	// commit on the same node — sees the just-applied write. The query is
	// per-namespace so under concurrent commits each call still gets its
	// own unique seq because the UPSERT itself is atomic.
	seqQuery := BatchOp{
		Kind: BatchOpQuery,
		SQL:  `SELECT next_seq - 1 AS assigned_seq FROM namespace_publish_seq WHERE namespace = ?`,
		Args: []interface{}{namespace},
	}

	combined := make([]BatchOp, 0, len(userOps)+2)
	combined = append(combined, seqOp)
	combined = append(combined, userOps...)
	combined = append(combined, seqQuery)

	res, err := c.Batch(ctx, combined)
	if err != nil || res == nil || !res.Committed {
		// Trim our seq op back out of the result so the caller sees only
		// their own ops in the response (preserve original indexing).
		trimmed := trimWrappedResults(res, len(userOps))
		return trimmed, 0, err
	}

	// Read the assigned seq from the trailing query result.
	queryResult := res.Results[len(res.Results)-1]
	if queryResult.Error != "" {
		// Writes committed but the query failed — caller still got their writes.
		// Return the trimmed result with seq=0 so the caller can detect "writes
		// landed but seq unknown."
		return trimWrappedResults(res, len(userOps)), 0, fmt.Errorf("rqlite.BatchWithSeq: seq lookup failed: %s", queryResult.Error)
	}
	if len(queryResult.Rows) == 0 {
		return trimWrappedResults(res, len(userOps)), 0, fmt.Errorf("rqlite.BatchWithSeq: seq lookup returned no rows")
	}
	rawSeq, ok := queryResult.Rows[0]["assigned_seq"]
	if !ok {
		return trimWrappedResults(res, len(userOps)), 0, fmt.Errorf("rqlite.BatchWithSeq: assigned_seq column missing")
	}
	seq, err := coerceInt64(rawSeq)
	if err != nil {
		return trimWrappedResults(res, len(userOps)), 0, fmt.Errorf("rqlite.BatchWithSeq: seq coerce: %w", err)
	}
	return trimWrappedResults(res, len(userOps)), seq, nil
}

// trimWrappedResults removes the leading seq UPSERT and trailing seq SELECT
// from a wrapped batch result so the caller sees only their original ops.
// Pass-through if res is nil.
func trimWrappedResults(res *BatchResult, userOpCount int) *BatchResult {
	if res == nil {
		return nil
	}
	if len(res.Results) < userOpCount+1 {
		// Failed before user ops ran; return as-is so caller can inspect.
		return res
	}
	out := &BatchResult{
		Committed: res.Committed,
	}
	// Drop the first (seq UPSERT) and trailing (seq SELECT) entries.
	end := len(res.Results) - 1
	if end > userOpCount+1 {
		end = userOpCount + 1
	}
	out.Results = make([]OpResult, 0, userOpCount)
	for i := 1; i < end; i++ {
		out.Results = append(out.Results, res.Results[i])
	}
	// Adjust FailedIndex if it pointed into the user's ops.
	if !res.Committed {
		switch {
		case res.FailedIndex == 0:
			// Failure was in our seq UPSERT — surface as "before user ops".
			out.FailedIndex = -1
		case res.FailedIndex > 0 && res.FailedIndex <= userOpCount:
			out.FailedIndex = res.FailedIndex - 1
		default:
			// Failure was in the trailing query (post-commit) — committed should be true; defensive.
			out.FailedIndex = userOpCount
		}
	}
	return out
}

// coerceInt64 normalizes a JSON-decoded number (which may arrive as float64,
// int64, or json.Number depending on the SQLite driver) to int64.
func coerceInt64(v interface{}) (int64, error) {
	switch n := v.(type) {
	case int64:
		return n, nil
	case int:
		return int64(n), nil
	case float64:
		return int64(n), nil
	case json.Number:
		return n.Int64()
	case string:
		// Some drivers return TEXT for INTEGER columns under strict mode.
		var i int64
		if _, err := fmt.Sscanf(n, "%d", &i); err != nil {
			return 0, fmt.Errorf("string %q is not an int64: %w", n, err)
		}
		return i, nil
	default:
		return 0, fmt.Errorf("unsupported type %T", v)
	}
}

// BatchQuery runs N SELECT statements in a single HTTP request to RQLite's
// /db/query endpoint via the native gorqlite Connection, returning one
// OpResult per input op in the original order.
//
// Why this exists: c.Query (sql.DB path) sends ONE statement per HTTP call,
// paying a full leader round-trip each time. For functions that gather state
// from many tables before doing work (e.g. anchat's message-create gathers
// auth + participants + devices = 7-10 reads), the per-call RTT dominates —
// 10 sequential reads on devnet's cross-region cluster take ~3.5s vs ~330ms
// for the batched form. See bugboard #270 for the workload measurement.
//
// Semantics:
//   - All ops MUST be Kind=BatchOpQuery. Exec ops error out at validation.
//   - All N statements are sent in one POST to /db/query with level=weak,
//     so they all run on the leader and see the same committed snapshot.
//   - Per-op errors are reported in OpResult.Error (one entry per input,
//     same order). The whole call only returns a Go error on transport
//     failures (network, leader unreachable, JSON malformed) or validation.
//   - Rows arrive as []map[string]interface{} just like c.Query — columns
//     are populated via the rqlite "associative" response shape.
func (c *client) BatchQuery(ctx context.Context, ops []BatchOp) ([]OpResult, error) {
	if len(ops) == 0 {
		return []OpResult{}, nil
	}
	if len(ops) > MaxBatchOps {
		return nil, fmt.Errorf("rqlite.BatchQuery: too many ops (%d > max %d)", len(ops), MaxBatchOps)
	}
	if c.conn == nil {
		return nil, fmt.Errorf("rqlite.BatchQuery: native gorqlite connection not configured (use NewClientWithDSN or NewClientWithConn)")
	}

	// Validate up-front: callers must use BatchOpQuery for every entry.
	// Mixing in an Exec would be a footgun (it'd silently be skipped or
	// trigger an unrelated error from the query endpoint), so reject loud.
	stmts := make([]gorqlite.ParameterizedStatement, len(ops))
	for i, op := range ops {
		if op.Kind != BatchOpQuery {
			return nil, fmt.Errorf("rqlite.BatchQuery: op %d has kind %q (only %q allowed; use Batch for mixed exec/query)",
				i, op.Kind, BatchOpQuery)
		}
		stmts[i] = gorqlite.ParameterizedStatement{
			Query:     op.SQL,
			Arguments: op.Args,
		}
	}

	qrs, err := c.conn.QueryParameterizedContext(ctx, stmts)
	if err != nil {
		// gorqlite returns a slice of QueryResult even on partial failure;
		// extract per-op errors if available, else surface the joined err.
		if len(qrs) == 0 {
			return nil, fmt.Errorf("rqlite.BatchQuery: %w", err)
		}
		// Fall through to map qrs → OpResults; per-op errors are in qr.Err.
	}

	// Track aggregate result size across all ops as a defense-in-depth
	// OOM guard. If a single op stays under MaxBatchQueryRowsPerOp but
	// the SUM across ops still grows pathologically large, this cap
	// trips and the remaining ops surface an error rather than blowing
	// the gateway's heap.
	var totalBytes int
	out := make([]OpResult, len(ops))
	for i, qr := range qrs {
		if totalBytes >= MaxBatchQueryTotalBytes {
			out[i] = OpResult{
				Kind:  BatchOpQuery,
				Error: fmt.Sprintf("rqlite.BatchQuery: aggregate result bytes exceeded cap (%d) — earlier ops consumed the budget; this op result truncated",
					MaxBatchQueryTotalBytes),
			}
			continue
		}
		opRes := queryResultToOpResult(qr)
		totalBytes += estimateOpResultBytes(opRes)
		out[i] = opRes
	}
	// If fewer results returned than ops requested (shouldn't happen per
	// gorqlite contract), pad with errors so caller indexing matches input.
	for i := len(qrs); i < len(ops); i++ {
		out[i] = OpResult{
			Kind:  BatchOpQuery,
			Error: "rqlite.BatchQuery: no result returned for op " + fmt.Sprint(i),
		}
	}
	return out, nil
}

// estimateOpResultBytes is a cheap approximation of the JSON-encoded
// size of an OpResult, used only for the aggregate-bytes cap in
// BatchQuery. Doesn't have to be exact — overestimating is safer than
// underestimating, since the cap is a DoS guard, not a billing meter.
func estimateOpResultBytes(r OpResult) int {
	// Per-row overhead: ~32 bytes for JSON braces + commas + key wrappers.
	// Per-cell: key length (assume 16) + value bytes.
	const perRowOverhead = 32
	const perCellOverhead = 16
	total := len(r.Error) + perRowOverhead
	for _, row := range r.Rows {
		total += perRowOverhead
		for k, v := range row {
			total += len(k) + perCellOverhead
			switch x := v.(type) {
			case string:
				total += len(x)
			case []byte:
				total += len(x)
			default:
				// numerics, bools, nil — bounded constants, count as 16.
				total += 16
			}
		}
	}
	return total
}

// queryResultToOpResult converts a single gorqlite.QueryResult into our
// OpResult wire shape, including row materialization via the associative
// API. Per-op errors are surfaced via OpResult.Error.
//
// Enforces MaxBatchQueryRowsPerOp as a DoS guard — a single op returning
// more rows is truncated and Error is set so the WASM caller can decide
// whether to paginate or treat it as fatal. Without this guard a malicious
// `SELECT * FROM <large_table>` could OOM the gateway.
func queryResultToOpResult(qr gorqlite.QueryResult) OpResult {
	if qr.Err != nil {
		return OpResult{
			Kind:  BatchOpQuery,
			Error: qr.Err.Error(),
		}
	}
	// Materialize all rows as map[string]interface{} via the associative
	// iterator — matches how c.Query consumers expect rows to look.
	var rows []map[string]interface{}
	for qr.Next() {
		if len(rows) >= MaxBatchQueryRowsPerOp {
			return OpResult{
				Kind:  BatchOpQuery,
				Rows:  rows,
				Error: fmt.Sprintf("rqlite.BatchQuery: row cap exceeded (%d) — paginate via LIMIT/OFFSET",
					MaxBatchQueryRowsPerOp),
			}
		}
		row, mapErr := qr.Map()
		if mapErr != nil {
			return OpResult{
				Kind:  BatchOpQuery,
				Rows:  rows,
				Error: "rqlite.BatchQuery: row map: " + mapErr.Error(),
			}
		}
		rows = append(rows, row)
	}
	return OpResult{
		Kind: BatchOpQuery,
		Rows: rows,
	}
}

// Batch executes ops as a single atomic transaction.
//
// Semantics:
//   - All "exec" ops are sent in one transactional batch via RQLite's native
//     /db/execute?transaction endpoint. If any exec fails, the entire batch
//     rolls back; no exec is durable.
//   - Any "query" ops are sequenced AFTER the exec batch commits, on the same
//     node, and see the committed writes. Queries do NOT participate in the
//     rollback semantic — if a query fails after the writes commit, the writes
//     are still durable; that op's Error is set and Committed remains true.
//   - Order of OpResults preserved across the original input slice.
//
// Returns:
//   - (result, nil) when all execs commit. result.Committed is true.
//   - (result, err) when an exec fails. result.Committed is false and
//     result.FailedIndex points to the failing op. The error is nil-safe to
//     ignore if you only need the structured result.
//   - (nil, err) for setup failures (no native connection, validation, etc.).
func (c *client) Batch(ctx context.Context, ops []BatchOp) (*BatchResult, error) {
	if len(ops) == 0 {
		return &BatchResult{Committed: true, Results: []OpResult{}}, nil
	}
	if len(ops) > MaxBatchOps {
		return nil, fmt.Errorf("rqlite.Batch: too many ops (%d > max %d)", len(ops), MaxBatchOps)
	}
	if c.conn == nil {
		return nil, fmt.Errorf("rqlite.Batch: native gorqlite connection not configured (use NewClientWithDSN or NewClientWithConn)")
	}

	// Split exec vs. query, preserving original index for result ordering.
	type tagged struct {
		idx int
		op  BatchOp
	}
	var execs, queries []tagged
	for i, op := range ops {
		switch op.Kind {
		case BatchOpExec:
			execs = append(execs, tagged{i, op})
		case BatchOpQuery:
			queries = append(queries, tagged{i, op})
		default:
			return nil, fmt.Errorf("rqlite.Batch: op %d has unknown kind %q (want %q or %q)",
				i, op.Kind, BatchOpExec, BatchOpQuery)
		}
	}

	result := &BatchResult{
		Results:   make([]OpResult, len(ops)),
		Committed: false,
	}

	// Phase 1 — atomic exec batch via native API.
	if len(execs) > 0 {
		stmts := make([]gorqlite.ParameterizedStatement, len(execs))
		for i, t := range execs {
			stmts[i] = gorqlite.ParameterizedStatement{
				Query:     t.op.SQL,
				Arguments: t.op.Args,
			}
		}
		wrs, err := c.conn.WriteParameterizedContext(ctx, stmts)
		if err != nil {
			// gorqlite returns one WriteResult per statement, even on error.
			// Find the first failing one to populate FailedIndex.
			for i, wr := range wrs {
				if wr.Err != nil {
					result.FailedIndex = execs[i].idx
					result.Results[execs[i].idx] = OpResult{
						Kind:  BatchOpExec,
						Error: wr.Err.Error(),
					}
					return result, fmt.Errorf("rqlite.Batch: exec failed at op %d: %w",
						execs[i].idx, wr.Err)
				}
			}
			// No per-statement error reported, return the joined error.
			return result, fmt.Errorf("rqlite.Batch: %w", err)
		}
		// All execs succeeded; map results back into their original positions.
		for i, wr := range wrs {
			result.Results[execs[i].idx] = OpResult{
				Kind:         BatchOpExec,
				RowsAffected: wr.RowsAffected,
				LastInsertID: wr.LastInsertID,
			}
		}
	}
	result.Committed = true

	// Phase 2 — post-commit queries. Failures here do NOT trigger rollback
	// (the writes are already durable), but are surfaced per-op.
	for _, t := range queries {
		var rows []map[string]interface{}
		err := c.Query(ctx, &rows, t.op.SQL, t.op.Args...)
		if err != nil {
			result.Results[t.idx] = OpResult{
				Kind:  BatchOpQuery,
				Error: err.Error(),
			}
			continue
		}
		result.Results[t.idx] = OpResult{
			Kind: BatchOpQuery,
			Rows: rows,
		}
	}
	return result, nil
}