package hostfunctions

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

	"github.com/DeBrosOfficial/network/pkg/rqlite"
	"github.com/DeBrosOfficial/network/pkg/serverless"
)

// dbQueryBatchTimeout caps the rqlite round-trip for a single
// `oh.DBQueryBatch` host call. Tighter than the function's invocation
// timeout (typically 15-30s) so a stalled leader doesn't burn the entire
// budget on one batched read; the WASM function still has headroom to
// do downstream work after the read returns. 10s is generous for the
// 167ms-RTT cross-region devnet cluster (one round-trip ~340ms) while
// catching genuine leader stalls quickly.
const dbQueryBatchTimeout = 10 * time.Second

// DBQuery executes a SELECT query and returns JSON-encoded results.
func (h *HostFunctions) DBQuery(ctx context.Context, query string, args []interface{}) ([]byte, error) {
	if h.db == nil {
		return nil, &serverless.HostFunctionError{Function: "db_query", Cause: serverless.ErrDatabaseUnavailable}
	}

	var results []map[string]interface{}
	if err := h.db.Query(ctx, &results, query, args...); err != nil {
		return nil, &serverless.HostFunctionError{Function: "db_query", Cause: err}
	}

	data, err := json.Marshal(results)
	if err != nil {
		return nil, &serverless.HostFunctionError{Function: "db_query", Cause: fmt.Errorf("failed to marshal results: %w", err)}
	}

	return data, nil
}

// DBExecute executes an INSERT/UPDATE/DELETE query and returns affected rows.
//
// IMPORTANT: this returns 0 for BOTH "0 rows affected" AND "SQL error"
// — callers can't distinguish. That ambiguity caused bug #218 (AnChat's
// migrate function silently dropped statements). For new code, prefer
// DBExecuteV2 which returns a typed envelope.
func (h *HostFunctions) DBExecute(ctx context.Context, query string, args []interface{}) (int64, error) {
	if h.db == nil {
		return 0, &serverless.HostFunctionError{Function: "db_execute", Cause: serverless.ErrDatabaseUnavailable}
	}

	result, err := h.db.Exec(ctx, query, args...)
	if err != nil {
		return 0, &serverless.HostFunctionError{Function: "db_execute", Cause: err}
	}

	affected, _ := result.RowsAffected()
	return affected, nil
}

// dbExecuteV2Result is the JSON wire shape returned by DBExecuteV2.
type dbExecuteV2Result struct {
	RowsAffected int64  `json:"rows_affected"`
	LastInsertID int64  `json:"last_insert_id,omitempty"`
	Error        string `json:"error,omitempty"`
}

// DBExecuteV2 is the typed equivalent of DBExecute. Returns the same shape
// regardless of success/failure so callers can distinguish "0 rows affected"
// from "SQL error" — fixing the contract gap that caused bug #218.
//
// Returns a Go error only for host-side setup failures (no DB). SQL errors
// are encoded in the JSON envelope's "error" field.
func (h *HostFunctions) DBExecuteV2(ctx context.Context, query string, args []interface{}) ([]byte, error) {
	if h.db == nil {
		return nil, &serverless.HostFunctionError{
			Function: "db_execute_v2",
			Cause:    serverless.ErrDatabaseUnavailable,
		}
	}

	out := dbExecuteV2Result{}
	result, err := h.db.Exec(ctx, query, args...)
	if err != nil {
		out.Error = err.Error()
		buf, mErr := json.Marshal(out)
		if mErr != nil {
			return nil, &serverless.HostFunctionError{Function: "db_execute_v2", Cause: mErr}
		}
		return buf, nil
	}
	if result != nil {
		out.RowsAffected, _ = result.RowsAffected()
		out.LastInsertID, _ = result.LastInsertId()
	}
	buf, mErr := json.Marshal(out)
	if mErr != nil {
		return nil, &serverless.HostFunctionError{Function: "db_execute_v2", Cause: mErr}
	}
	return buf, nil
}

// dbQueryV2Result is the JSON wire shape returned by DBQueryV2.
type dbQueryV2Result struct {
	Rows  []map[string]interface{} `json:"rows"`
	Error string                   `json:"error,omitempty"`
}

// DBQueryV2 is the typed equivalent of DBQuery. Distinguishes "empty
// result set" from "query failed" via the "error" field.
func (h *HostFunctions) DBQueryV2(ctx context.Context, query string, args []interface{}) ([]byte, error) {
	if h.db == nil {
		return nil, &serverless.HostFunctionError{
			Function: "db_query_v2",
			Cause:    serverless.ErrDatabaseUnavailable,
		}
	}

	out := dbQueryV2Result{Rows: []map[string]interface{}{}}
	if err := h.db.Query(ctx, &out.Rows, query, args...); err != nil {
		out.Error = err.Error()
		// Reset rows to non-nil empty on error so callers get a stable shape.
		out.Rows = []map[string]interface{}{}
	}
	buf, mErr := json.Marshal(out)
	if mErr != nil {
		return nil, &serverless.HostFunctionError{Function: "db_query_v2", Cause: mErr}
	}
	return buf, nil
}

// dbTransactionRequest is the WASM-side shape for db_transaction input.
type dbTransactionRequest struct {
	Ops []rqlite.BatchOp `json:"ops"`
}

// DBTransaction executes ops as a single atomic batch.
// Input is JSON: {"ops": [{"kind":"exec"|"query","sql":"...","args":[...]}, ...]}
// Output is JSON: BatchResult — caller checks `committed` to know if writes landed.
//
// Returns an error only for setup/validation problems. A rolled-back batch is
// communicated via committed=false in the returned JSON; that's not a Go error.
func (h *HostFunctions) DBTransaction(ctx context.Context, opsJSON []byte) ([]byte, error) {
	if h.db == nil {
		return nil, &serverless.HostFunctionError{Function: "db_transaction", Cause: serverless.ErrDatabaseUnavailable}
	}
	var req dbTransactionRequest
	if err := json.Unmarshal(opsJSON, &req); err != nil {
		return nil, &serverless.HostFunctionError{
			Function: "db_transaction",
			Cause:    fmt.Errorf("invalid json: %w", err),
		}
	}
	if len(req.Ops) == 0 {
		return nil, &serverless.HostFunctionError{
			Function: "db_transaction",
			Cause:    fmt.Errorf("ops required"),
		}
	}
	if len(req.Ops) > rqlite.MaxBatchOps {
		return nil, &serverless.HostFunctionError{
			Function: "db_transaction",
			Cause:    fmt.Errorf("too many ops: max %d", rqlite.MaxBatchOps),
		}
	}

	res, err := h.db.Batch(ctx, req.Ops)
	// Always return the structured result, even on rollback — caller wants the
	// per-op detail to know which op failed.
	if res == nil {
		// Unrecoverable setup failure (no native conn). Surface as Go error.
		return nil, &serverless.HostFunctionError{Function: "db_transaction", Cause: err}
	}
	out, mErr := json.Marshal(res)
	if mErr != nil {
		return nil, &serverless.HostFunctionError{
			Function: "db_transaction",
			Cause:    fmt.Errorf("marshal result: %w", mErr),
		}
	}
	// Rollback errors are encoded in the JSON; do NOT propagate as Go error.
	// Only true setup/transport errors after the result was built warrant returning err.
	_ = err // intentionally swallowed — committed=false carries the signal
	return out, nil
}

// dbQueryBatchRequest is the WASM-side shape for db_query_batch input.
// Each op MUST be Kind=BatchOpQuery; mixing exec is rejected at the
// rqlite layer.
type dbQueryBatchRequest struct {
	Ops []rqlite.BatchOp `json:"ops"`
	// Consistency is the optional rqlite read level for this batch.
	// "" / "weak" (default): leader-routed, always fresh. "none": fast LOCAL
	// read (~1ms, no leader hop) — ONLY safe for reads that don't need
	// read-your-own-writes freshness (see rqlite.ReadConsistency / bug #235).
	// feat-6: lets read-heavy functions skip the cross-region weak-read hop.
	Consistency string `json:"consistency,omitempty"`
}

// batchQueryConsistencyClient is the optional capability a Client exposes when
// it can serve reads at an explicit consistency level. The production
// *rqlite.client implements it; bare test mocks don't. Kept OFF the
// rqlite.Client interface so the none-read path doesn't churn every mock.
type batchQueryConsistencyClient interface {
	BatchQueryConsistency(ctx context.Context, ops []rqlite.BatchOp, rc rqlite.ReadConsistency) ([]rqlite.OpResult, error)
}

// resolveBatchQuery runs the batched read at the requested consistency.
// Empty or "weak" → the default leader-routed read. "none" → a fast local read
// via the consistency-capable client (degrading to weak only when the client
// can't serve an explicit level — weak is always correct). Unknown values are
// rejected here at the boundary rather than silently downgraded.
func (h *HostFunctions) resolveBatchQuery(ctx context.Context, ops []rqlite.BatchOp, consistency string) ([]rqlite.OpResult, error) {
	switch consistency {
	case "", string(rqlite.ReadConsistencyWeak):
		return h.db.BatchQuery(ctx, ops)
	case string(rqlite.ReadConsistencyNone):
		if ext, ok := h.db.(batchQueryConsistencyClient); ok {
			return ext.BatchQueryConsistency(ctx, ops, rqlite.ReadConsistencyNone)
		}
		return h.db.BatchQuery(ctx, ops)
	default:
		return nil, fmt.Errorf("invalid consistency %q (allowed: \"none\", \"weak\")", consistency)
	}
}

// dbQueryBatchResult is the JSON wire shape returned to WASM callers.
// `Results` is one entry per input op, in the same order. Per-op errors
// are surfaced in `error`; transport/validation errors come back as a
// Go error from the host fn.
type dbQueryBatchResult struct {
	Results []rqlite.OpResult `json:"results"`
}

// DBQueryBatch runs N SELECTs in one round-trip via RQLite's /db/query
// bulk endpoint. Designed for read-heavy functions that gather state
// from multiple tables before doing work (e.g. anchat's message-create
// reads auth + participants + devices = 7-10 SELECTs).
//
// Wire shapes:
//
//	in:  {"ops": [{"sql":"...","args":[...]}, ...]}
//	out: {"results": [{"kind":"query","rows":[...],"error":""}, ...]}
//
// Per-query errors are reported in the per-op `error` field; the host
// fn only returns a Go error on setup/validation/transport failures.
// Kind is auto-set to "query" on input — exec ops are rejected, since
// mixing kinds in a query batch is meaningless and would silently
// drop the writes (see bugboard #270).
//
// Empirical baseline on devnet's cross-region cluster (167ms RTT to
// leader): 10 sequential DBQuery host calls = ~3.5s; one DBQueryBatch
// with 10 statements = ~340ms. 10× speedup.
func (h *HostFunctions) DBQueryBatch(ctx context.Context, opsJSON []byte) ([]byte, error) {
	if h.db == nil {
		return nil, &serverless.HostFunctionError{Function: "db_query_batch", Cause: serverless.ErrDatabaseUnavailable}
	}
	var req dbQueryBatchRequest
	if err := json.Unmarshal(opsJSON, &req); err != nil {
		return nil, &serverless.HostFunctionError{
			Function: "db_query_batch",
			Cause:    fmt.Errorf("invalid json: %w", err),
		}
	}
	if len(req.Ops) == 0 {
		return nil, &serverless.HostFunctionError{
			Function: "db_query_batch",
			Cause:    fmt.Errorf("ops required"),
		}
	}
	if len(req.Ops) > rqlite.MaxBatchOps {
		return nil, &serverless.HostFunctionError{
			Function: "db_query_batch",
			Cause:    fmt.Errorf("too many ops: max %d", rqlite.MaxBatchOps),
		}
	}
	// Force kind=query for every op. Callers can omit the field; this
	// makes the wire format more ergonomic AND prevents accidental exec
	// ops from being silently dropped by the rqlite-side validator.
	for i := range req.Ops {
		req.Ops[i].Kind = rqlite.BatchOpQuery
	}

	// Explicit batch-level deadline. The caller's ctx already carries the
	// function's invocation timeout (typically 15-30s), but we want a
	// tighter cap on the rqlite round-trip itself so a stalled leader
	// doesn't burn the entire invocation budget on one batched query.
	// Leaves headroom for downstream WASM work after the read returns.
	batchCtx, cancel := context.WithTimeout(ctx, dbQueryBatchTimeout)
	defer cancel()

	results, err := h.resolveBatchQuery(batchCtx, req.Ops, req.Consistency)
	if err != nil {
		return nil, &serverless.HostFunctionError{Function: "db_query_batch", Cause: err}
	}

	out, mErr := json.Marshal(dbQueryBatchResult{Results: results})
	if mErr != nil {
		return nil, &serverless.HostFunctionError{
			Function: "db_query_batch",
			Cause:    fmt.Errorf("marshal result: %w", mErr),
		}
	}
	return out, nil
}

// execAndPublishResult is the JSON wire shape returned to WASM callers.
type execAndPublishResult struct {
	Results      []rqlite.OpResult `json:"results"`
	Committed    bool              `json:"committed"`
	FailedIndex  int               `json:"failed_index,omitempty"`
	Seq          int64             `json:"seq,omitempty"`
	Published    bool              `json:"published,omitempty"`
	PublishError string            `json:"publish_error,omitempty"`
}

// ExecAndPublish runs ops atomically (with a seq increment in the same batch)
// and, if committed, publishes data with `{{seq}}` substituted for the
// assigned per-namespace sequence number.
//
// Failure modes (each communicated in the JSON, not as Go error):
//   - Rollback: committed=false, failed_index points to the failing user op
//   - Publish failed but commit succeeded: committed=true, published=false,
//     publish_error is set. Writes are durable; caller can retry the publish.
//   - Both succeeded: committed=true, published=true.
//
// Returns a Go error only on setup failures (no DB, bad JSON, no namespace).
func (h *HostFunctions) ExecAndPublish(
	ctx context.Context, opsJSON []byte, topic string, dataTemplate []byte,
) ([]byte, error) {
	if h.db == nil {
		return nil, &serverless.HostFunctionError{
			Function: "exec_and_publish",
			Cause:    serverless.ErrDatabaseUnavailable,
		}
	}
	if h.pubsub == nil {
		return nil, &serverless.HostFunctionError{
			Function: "exec_and_publish",
			Cause:    fmt.Errorf("pubsub not available"),
		}
	}
	if topic == "" {
		return nil, &serverless.HostFunctionError{
			Function: "exec_and_publish",
			Cause:    fmt.Errorf("topic required"),
		}
	}

	// Resolve namespace from invocation context — server-trusted.
	// ctx-attached invCtx wins over singleton; see invocation_context.go.
	ns := ""
	if cur := h.currentInvocationContext(ctx); cur != nil {
		ns = cur.Namespace
	}
	if ns == "" {
		return nil, &serverless.HostFunctionError{
			Function: "exec_and_publish",
			Cause:    fmt.Errorf("no namespace in invocation context"),
		}
	}

	var req dbTransactionRequest
	if err := json.Unmarshal(opsJSON, &req); err != nil {
		return nil, &serverless.HostFunctionError{
			Function: "exec_and_publish",
			Cause:    fmt.Errorf("invalid ops json: %w", err),
		}
	}
	if len(req.Ops) > rqlite.MaxBatchOps {
		return nil, &serverless.HostFunctionError{
			Function: "exec_and_publish",
			Cause:    fmt.Errorf("too many ops: max %d", rqlite.MaxBatchOps),
		}
	}

	batchRes, seq, batchErr := h.db.BatchWithSeq(ctx, ns, req.Ops)
	out := execAndPublishResult{}
	if batchRes != nil {
		out.Results = batchRes.Results
		out.Committed = batchRes.Committed
		out.FailedIndex = batchRes.FailedIndex
	}

	// On rollback or pre-publish error, return without publishing.
	if batchErr != nil || !out.Committed {
		// On a true rollback batchErr may be non-nil; that's already encoded
		// in the result. Don't surface as Go error — caller reads `committed`.
		_ = batchErr
		buf, mErr := json.Marshal(out)
		if mErr != nil {
			return nil, &serverless.HostFunctionError{Function: "exec_and_publish", Cause: mErr}
		}
		return buf, nil
	}

	out.Seq = seq

	// Substitute {{seq}} in the data template, then publish.
	finalData := bytes.ReplaceAll(
		dataTemplate,
		[]byte("{{seq}}"),
		[]byte(strconv.FormatInt(seq, 10)),
	)
	if err := h.pubsub.Publish(ctx, topic, finalData); err != nil {
		out.PublishError = err.Error()
	} else {
		out.Published = true
	}

	buf, mErr := json.Marshal(out)
	if mErr != nil {
		return nil, &serverless.HostFunctionError{Function: "exec_and_publish", Cause: mErr}
	}
	return buf, nil
}