// Copyright (c) 2026 Charles KWON OhJun (charleskwonohjun@gmail.com)
// All rights reserved.

// extended.go — Extended Protocol (Parse/Bind/Execute/Describe/
// Sync/Close) support for the pgserver. Without this, pgx clients
// using the default QueryExecModeCacheStatement get an "0A000
// not supported" error on every query (Phase 3 saw this — the
// integration script had to force SimpleProtocol).
//
// The implementation is deliberately minimal for v1.0:
//   * Per-session named statement cache: name → SQL + paramOIDs
//   * Per-session named portal cache: name → statement + bound params
//   * Parameter substitution happens client-side at Bind time; we
//     build a "rewrite" SQL with literals inlined so five_SQL's
//     existing template-cache pipeline (TFiveSQL.prg's
//     SqlLexAndExtractTemplate path) can re-parameterise the
//     query without us having to teach it the PG-wire param shape.
//   * Describe-statement returns NoData; pgx tolerates this and
//     issues Describe-portal after Bind, by which point we've run
//     the query and can emit a real RowDescription.
//   * Execute streams the cached result set produced at Describe-
//     portal time so we don't run the same SQL twice.
//
// Phase 4.1 will replace the literal-substitution rewrite with a
// proper `?`-param threading through five_SQL's aParams so binary
// params (timestamps, numerics) avoid round-tripping through text.

package pgserver

import (
	"encoding/binary"
	"fmt"
	"strconv"
	"strings"

	"github.com/jackc/pgx/v5/pgproto3"

	"five/hbrt"
)

// preparedStmt holds a named statement registered via Parse. It
// stores the original SQL plus the per-position param OIDs the
// client declared (or 0 = "any"). The actual parse happens lazily
// at Execute time inside five_SQL.
type preparedStmt struct {
	sql       string
	paramOIDs []uint32
}

// portal binds a prepared statement to concrete parameter values.
// We materialise the values into a fully-substituted SQL string so
// the engine sees a normal Simple-Query-shaped statement; the
// result is cached on the portal so Describe-portal can emit a
// RowDescription without a second execution.
type portal struct {
	stmt       *preparedStmt
	resolvedSQL string

	// Cached result, populated on Describe-portal so Execute can
	// stream without re-running the query. resultArr is the
	// engine's `aResult` array; once executed, used to derive
	// RowDescription + DataRow stream.
	executed bool
	resultArr *hbrt.HbArray
	resultErr *errEnvelope
}

// errEnvelope is the unpacked form of FiveSql2's error sentinel.
type errEnvelope struct {
	code int
	msg  string
	sql  string
}

// ensureExtendedState lazily allocates the per-session caches.
// Called by every extended-protocol handler; the maps stay alive
// for the whole session because pgx-style clients re-use unnamed
// statements aggressively.
func (s *session) ensureExtendedState() {
	if s.stmts == nil {
		s.stmts = make(map[string]*preparedStmt)
	}
	if s.portals == nil {
		s.portals = make(map[string]*portal)
	}
}

// handleParse stores a named prepared statement. Returns
// ParseComplete; any actual parse error from five_SQL is deferred
// until Execute so a probe-only Parse + Describe + Sync round-trip
// (which pgx does for QueryExecModeDescribeExec) stays cheap.
func (s *session) handleParse(m *pgproto3.Parse) {
	s.ensureExtendedState()
	s.stmts[m.Name] = &preparedStmt{
		sql:       m.Query,
		paramOIDs: append([]uint32(nil), m.ParameterOIDs...),
	}
	s.send(&pgproto3.ParseComplete{})
}

// handleBind materialises parameter values into the SQL text and
// stashes the portal for later Describe/Execute. Binary-format
// params are decoded for the OIDs we recognise; otherwise the raw
// bytes are passed through as a quoted text literal (good enough
// for the common SELECT/INSERT-with-int/string cases).
func (s *session) handleBind(m *pgproto3.Bind) {
	s.ensureExtendedState()
	stmt := s.stmts[m.PreparedStatement]
	if stmt == nil {
		s.send(buildErrorResponse("26000",
			fmt.Sprintf("prepared statement %q does not exist", m.PreparedStatement), ""))
		return
	}
	resolved, err := substituteParams(stmt.sql, stmt.paramOIDs, m.Parameters, m.ParameterFormatCodes)
	if err != nil {
		s.send(buildErrorResponse("42P02", err.Error(), stmt.sql))
		return
	}
	s.portals[m.DestinationPortal] = &portal{stmt: stmt, resolvedSQL: resolved}
	s.send(&pgproto3.BindComplete{})
}

// handleDescribe answers Describe for either a statement or a
// portal. ObjectType 'S' = statement, 'P' = portal.
//
// Statement Describe is hard to answer fully without running the
// query (we'd need column-type inference). For v1.0 we return
// NoData + ParameterDescription with the declared OIDs; pgx
// tolerates this and re-Describes the portal after Bind.
//
// Portal Describe runs the query immediately, caches the result
// on the portal, and emits RowDescription from the actual result
// columns. Execute later just streams from the cache.
func (s *session) handleDescribe(m *pgproto3.Describe) {
	s.ensureExtendedState()
	switch m.ObjectType {
	case 'S':
		stmt := s.stmts[m.Name]
		if stmt == nil {
			s.send(buildErrorResponse("26000",
				fmt.Sprintf("prepared statement %q does not exist", m.Name), ""))
			return
		}
		// pgx-style clients send Parse without explicit OIDs and
		// expect the server to infer them from the SQL. Count the
		// `$N` placeholders and pad paramOIDs with OID 0 ("any")
		// for any that the client didn't pre-declare — otherwise
		// pgx errors with "expected 0 arguments, got N" before
		// the Bind even reaches us.
		nParams := countPgPlaceholders(stmt.sql)
		oids := stmt.paramOIDs
		for len(oids) < nParams {
			oids = append(oids, 0)
		}
		stmt.paramOIDs = oids
		s.send(&pgproto3.ParameterDescription{ParameterOIDs: oids})
		// NoData — we don't know the row shape until execution.
		// pgx tolerates this and asks again via Describe-portal.
		s.send(&pgproto3.NoData{})
	case 'P':
		p := s.portals[m.Name]
		if p == nil {
			s.send(buildErrorResponse("34000",
				fmt.Sprintf("portal %q does not exist", m.Name), ""))
			return
		}
		s.executePortal(p)
		if p.resultErr != nil {
			s.send(buildErrorResponse(sqlStateFor(p.resultErr.code), p.resultErr.msg, p.resultErr.sql))
			return
		}
		s.sendRowDescriptionFromArr(p.resultArr)
	}
}

// handleExecute streams the cached result of the portal as a
// DataRow sequence then CommandComplete. If the portal hasn't
// been executed yet (Describe-portal was skipped), execute now.
//
// pgx's default QueryExecModeCacheStatement skips Describe-portal
// and only does Describe-statement once at prepare time. Since
// Describe-statement returns NoData (we don't know the row shape
// without executing), pgx never gets a RowDescription unless we
// emit one here too. We emit it conditionally: only when the
// portal wasn't already Described (described==false) so we don't
// duplicate the descriptor for clients that *did* call Describe-P.
func (s *session) handleExecute(m *pgproto3.Execute) {
	s.ensureExtendedState()
	p := s.portals[m.Portal]
	if p == nil {
		s.send(buildErrorResponse("34000",
			fmt.Sprintf("portal %q does not exist", m.Portal), ""))
		return
	}
	wasDescribed := p.executed
	s.executePortal(p)
	if p.resultErr != nil {
		s.send(buildErrorResponse(sqlStateFor(p.resultErr.code), p.resultErr.msg, p.resultErr.sql))
		s.txStatus = currentTxStatusAfterError(s.txStatus)
		return
	}
	// If Describe-portal was never called, the client is still
	// waiting for column metadata. Emit it now from the cached
	// result so DataRow has a context the client can decode.
	if !wasDescribed {
		s.sendRowDescriptionFromArr(p.resultArr)
	}
	s.streamPortalRows(p, int(m.MaxRows))
	tag := commandTagFor(p.resolvedSQL)
	s.send(&pgproto3.CommandComplete{CommandTag: []byte(tag)})
	s.updateTxStatusForTag(tag)
}

// handleClose drops a prepared statement or portal entry.
func (s *session) handleClose(m *pgproto3.Close) {
	s.ensureExtendedState()
	switch m.ObjectType {
	case 'S':
		delete(s.stmts, m.Name)
	case 'P':
		delete(s.portals, m.Name)
	}
	s.send(&pgproto3.CloseComplete{})
}

// handleSync flushes any pending output and emits ReadyForQuery,
// closing one cycle of the extended-protocol exchange.
func (s *session) handleSync() {
	s.sendReadyForQuery()
}

// executePortal runs the resolved SQL through five_SQL once and
// caches the result on the portal. Idempotent — repeated calls
// short-circuit on `executed`.
func (s *session) executePortal(p *portal) {
	if p.executed {
		return
	}
	p.executed = true
	res, err := s.runSQL(p.resolvedSQL)
	if err != nil {
		p.resultErr = &errEnvelope{code: 0, msg: err.Error(), sql: p.resolvedSQL}
		return
	}
	if res.IsNil() || !res.IsArray() {
		// Non-result statement (DDL, transaction control). Synthesise
		// an empty result envelope so the streaming path emits an
		// empty RowDescription + CommandComplete cleanly.
		p.resultArr = &hbrt.HbArray{Items: []hbrt.Value{
			hbrt.MakeArrayFrom([]hbrt.Value{}),
			hbrt.MakeArrayFrom([]hbrt.Value{}),
		}}
		return
	}
	arr := res.AsArray()
	if isErrorEnvelope(arr) {
		code, msg, sql := unpackError(arr)
		p.resultErr = &errEnvelope{code: code, msg: msg, sql: sql}
		return
	}
	p.resultArr = arr
}

// sendRowDescriptionFromArr emits a RowDescription derived from
// the engine's `{aFieldNames, aRows}` envelope. Mirrors what
// emitResultSet (Simple Query) does on the field-description side
// so the wire shape is identical regardless of which protocol the
// client picks.
func (s *session) sendRowDescriptionFromArr(arr *hbrt.HbArray) {
	if arr == nil || len(arr.Items) < 1 || !arr.Items[0].IsArray() {
		s.send(&pgproto3.RowDescription{Fields: nil})
		return
	}
	fields := arr.Items[0].AsArray().Items
	var firstRow []hbrt.Value
	if len(arr.Items) >= 2 && arr.Items[1].IsArray() {
		if rows := arr.Items[1].AsArray().Items; len(rows) > 0 && rows[0].IsArray() {
			firstRow = rows[0].AsArray().Items
		}
	}
	descFields := make([]pgproto3.FieldDescription, len(fields))
	for i, f := range fields {
		name := ""
		if f.IsString() {
			name = f.AsString()
		} else {
			name = fmt.Sprintf("column%d", i+1)
		}
		var sample hbrt.Value
		if i < len(firstRow) {
			sample = firstRow[i]
		}
		oid, typeSize := pgTypeFor(sample)
		descFields[i] = pgproto3.FieldDescription{
			Name:                 []byte(name),
			DataTypeOID:          uint32(oid),
			DataTypeSize:         typeSize,
			TypeModifier:         -1,
			Format:               0,
		}
	}
	s.send(&pgproto3.RowDescription{Fields: descFields})
}

// streamPortalRows iterates the portal's cached rows and emits a
// DataRow per row, respecting maxRows (0 = unlimited).
func (s *session) streamPortalRows(p *portal, maxRows int) {
	if p.resultArr == nil || len(p.resultArr.Items) < 2 {
		return
	}
	rowsVal := p.resultArr.Items[1]
	if !rowsVal.IsArray() {
		return
	}
	rows := rowsVal.AsArray().Items
	fieldCount := 0
	if p.resultArr.Items[0].IsArray() {
		fieldCount = len(p.resultArr.Items[0].AsArray().Items)
	}
	emitted := 0
	for _, rowVal := range rows {
		if maxRows > 0 && emitted >= maxRows {
			break
		}
		if !rowVal.IsArray() {
			continue
		}
		cells := rowVal.AsArray().Items
		out := make([][]byte, fieldCount)
		for i := 0; i < fieldCount; i++ {
			if i < len(cells) {
				out[i] = encodeText(cells[i])
			}
		}
		s.send(&pgproto3.DataRow{Values: out})
		emitted++
	}
}

// substituteParams produces a Simple-Query-shaped SQL by inlining
// the bound parameter values as PG-style literals. Format codes:
// 0 = text, 1 = binary. We support text for all OIDs and binary
// for INT2/INT4/INT8/FLOAT4/FLOAT8/BOOL — the rest fall back to
// hex-escaped strings, which works for VARCHAR but loses fidelity
// for binary timestamps until Phase 4.1.
//
// pgx defaults to binary for ints + text for everything else, so
// the common case is well covered.
func substituteParams(sql string, oids []uint32, params [][]byte, formats []int16) (string, error) {
	// Each `$1`/`$2`/… placeholder maps to params[i-1]. We do a
	// linear scan rather than regex to avoid quoting pitfalls
	// (strings containing literal `$1` are rare in practice but
	// the scanner respects single-quoted runs).
	var out strings.Builder
	i := 0
	inStr := byte(0)
	for i < len(sql) {
		c := sql[i]
		if inStr != 0 {
			out.WriteByte(c)
			if c == inStr {
				inStr = 0
			}
			i++
			continue
		}
		if c == '\'' || c == '"' {
			inStr = c
			out.WriteByte(c)
			i++
			continue
		}
		if c == '$' && i+1 < len(sql) && sql[i+1] >= '0' && sql[i+1] <= '9' {
			j := i + 1
			for j < len(sql) && sql[j] >= '0' && sql[j] <= '9' {
				j++
			}
			idx, err := strconv.Atoi(sql[i+1 : j])
			if err != nil || idx < 1 || idx > len(params) {
				out.WriteByte(c)
				i++
				continue
			}
			pidx := idx - 1
			oid := uint32(0)
			if pidx < len(oids) {
				oid = oids[pidx]
			}
			format := int16(0)
			if pidx < len(formats) {
				format = formats[pidx]
			} else if len(formats) == 1 {
				format = formats[0] // single format code applies to all
			}
			lit, err := paramToLiteral(params[pidx], oid, format)
			if err != nil {
				return "", err
			}
			out.WriteString(lit)
			i = j
			continue
		}
		out.WriteByte(c)
		i++
	}
	return out.String(), nil
}

// countPgPlaceholders scans SQL for the highest $N placeholder
// outside string literals and returns that count. Matches what
// substituteParams resolves at Bind time. Returns 0 for SQL with
// no placeholders. Order of placeholders doesn't matter for the
// count — repeated `$1` still counts as 1 param slot.
func countPgPlaceholders(sql string) int {
	max := 0
	inStr := byte(0)
	for i := 0; i < len(sql); i++ {
		c := sql[i]
		if inStr != 0 {
			if c == inStr {
				inStr = 0
			}
			continue
		}
		if c == '\'' || c == '"' {
			inStr = c
			continue
		}
		if c == '$' && i+1 < len(sql) && sql[i+1] >= '0' && sql[i+1] <= '9' {
			j := i + 1
			for j < len(sql) && sql[j] >= '0' && sql[j] <= '9' {
				j++
			}
			if n, err := strconv.Atoi(sql[i+1 : j]); err == nil && n > max {
				max = n
			}
			i = j - 1
		}
	}
	return max
}

func paramToLiteral(raw []byte, oid uint32, format int16) (string, error) {
	if raw == nil {
		return "NULL", nil
	}
	if format == 0 {
		// Text format — quote per type. For numerics and bools we
		// don't quote; for everything else we single-quote with
		// inline-escape.
		switch oid {
		case oidInt4, oidInt8, oidBool, oidNumeric:
			return string(raw), nil
		default:
			return "'" + strings.ReplaceAll(string(raw), "'", "''") + "'", nil
		}
	}
	// Binary format — decode the OIDs pgx uses by default.
	switch oid {
	case oidInt4:
		if len(raw) != 4 {
			return "", fmt.Errorf("int4 param: want 4 bytes, got %d", len(raw))
		}
		return strconv.FormatInt(int64(int32(binary.BigEndian.Uint32(raw))), 10), nil
	case oidInt8:
		if len(raw) != 8 {
			return "", fmt.Errorf("int8 param: want 8 bytes, got %d", len(raw))
		}
		return strconv.FormatInt(int64(binary.BigEndian.Uint64(raw)), 10), nil
	case oidBool:
		if len(raw) != 1 {
			return "", fmt.Errorf("bool param: want 1 byte, got %d", len(raw))
		}
		if raw[0] == 0 {
			return "FALSE", nil
		}
		return "TRUE", nil
	default:
		// Unknown binary OID — fall back to a quoted hex literal.
		// FiveSql2 won't accept this directly, but the resulting
		// error is at least diagnosable rather than a silent miss.
		return "'\\x" + fmt.Sprintf("%x", raw) + "'", nil
	}
}