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

// DBF field type conversion: raw bytes ↔ Five Value.
// Each field type (C, N, L, D, M, I, B, @, etc.) has exact byte format.
//
// Reference: /mnt/d/harbour-core/src/rdd/dbf1.c (getValue/putValue)
//            docs/dbf-engine-spec.md Section 3
package dbf

import (
	"encoding/binary"
	"five/hbrt"
	"fmt"
	"math"
	"strconv"
	"strings"
)

// GetFieldValue converts raw record bytes to a Five Value.
// Harbour: hb_dbfGetValue in dbf1.c
func GetFieldValue(recBuf []byte, offset uint16, field *FieldDesc) hbrt.Value {
	return getFieldValueImpl(recBuf, offset, field, false)
}

// getFieldValueImpl is the zero-copy-aware variant. When stable=true the
// caller guarantees the recBuf bytes won't be mutated, freed, or
// unmapped for the Value's lifetime — then CHAR fields alias the
// buffer and skip the `string([]byte)` copy.
//
// NOTE: currently unexported because naive usage (even with mmap-backed
// buffers) can produce UAF when FiveSql2 closes/packs temp CTE tables
// while CHAR values from earlier iterations are still referenced. The
// machinery is kept for a future refcounted mmap lifetime scheme.
func getFieldValueImpl(recBuf []byte, offset uint16, field *FieldDesc, stable bool) hbrt.Value {
	raw := recBuf[offset : offset+uint16(field.Len)]

	switch field.Type {
	case 'C', 'c': // Character
		if stable {
			return hbrt.MakeStringBytes(raw)
		}
		return hbrt.MakeString(string(raw))

	case 'N', 'n': // Numeric (ASCII)
		return parseNumericField(raw, field.Dec)

	case 'L', 'l': // Logical
		return parseLogicalField(raw[0])

	case 'D', 'd': // Date
		return parseDateField(raw, field.Len)

	case 'M', 'm': // Memo (block reference)
		return parseMemoRef(raw, field.Len)

	case 'I', 'i': // Integer (binary LE)
		return parseIntegerField(raw, field.Len)

	case 'B', 'b': // Double (IEEE 754 LE)
		if field.Len == 8 {
			bits := binary.LittleEndian.Uint64(raw)
			return hbrt.MakeDoubleAuto(math.Float64frombits(bits))
		}
		return hbrt.MakeNil()

	case '@': // Timestamp (4 bytes date + 4 bytes time, LE)
		if field.Len >= 8 {
			julian := int64(binary.LittleEndian.Uint32(raw[0:4]))
			timeMs := int32(binary.LittleEndian.Uint32(raw[4:8]))
			return hbrt.MakeTimestamp(julian, timeMs)
		}
		return hbrt.MakeNil()

	case '+': // Autoincrement (binary LE integer)
		return parseIntegerField(raw, field.Len)

	case '=': // Modtime (same as Timestamp)
		if field.Len >= 8 {
			julian := int64(binary.LittleEndian.Uint32(raw[0:4]))
			timeMs := int32(binary.LittleEndian.Uint32(raw[4:8]))
			return hbrt.MakeTimestamp(julian, timeMs)
		}
		return hbrt.MakeNil()

	case '^': // RowVersion (uint64 LE)
		if field.Len == 8 {
			return hbrt.MakeLong(int64(binary.LittleEndian.Uint64(raw)))
		}
		return hbrt.MakeNil()

	case 'Y', 'y': // Currency (int64 LE, implicit 4 decimal places)
		if field.Len == 8 {
			cents := int64(binary.LittleEndian.Uint64(raw))
			return hbrt.MakeDouble(float64(cents)/10000.0, 20, 4)
		}
		return hbrt.MakeNil()

	case 'T', 't': // Timestamp (Harbour extension)
		if field.Len >= 8 {
			julian := int64(binary.LittleEndian.Uint32(raw[0:4]))
			timeMs := int32(binary.LittleEndian.Uint32(raw[4:8]))
			return hbrt.MakeTimestamp(julian, timeMs)
		}
		if field.Len == 4 {
			// Time only
			timeMs := int32(binary.LittleEndian.Uint32(raw[0:4]))
			return hbrt.MakeTimestamp(0, timeMs)
		}
		return hbrt.MakeNil()

	default:
		// Unknown type: return as string
		return hbrt.MakeString(string(raw))
	}
}

// PutFieldValue converts a Five Value to raw record bytes.
// Harbour: hb_dbfPutValue in dbf1.c
func PutFieldValue(recBuf []byte, offset uint16, field *FieldDesc, val hbrt.Value) {
	raw := recBuf[offset : offset+uint16(field.Len)]

	switch field.Type {
	case 'C', 'c': // Character
		s := val.AsString()
		copy(raw, s)
		// Pad with spaces
		if len(s) < int(field.Len) {
			for i := len(s); i < int(field.Len); i++ {
				raw[i] = ' '
			}
		}

	case 'N', 'n': // Numeric (ASCII, right-aligned, space-padded)
		formatNumericField(raw, field.Len, field.Dec, val)

	case 'L', 'l': // Logical
		if val.IsNil() {
			raw[0] = ' '
		} else if val.AsBool() {
			raw[0] = 'T'
		} else {
			raw[0] = 'F'
		}

	case 'D', 'd': // Date
		putDateField(raw, field.Len, val)

	case 'M', 'm': // Memo (block reference)
		// Memo writes handled by MemoHandler
		// Here just store block number
		if val.IsNumInt() {
			putMemoRef(raw, field.Len, uint32(val.AsNumInt()))
		}

	case 'I', 'i', '+': // Integer / Autoincrement
		putIntegerField(raw, field.Len, val)

	case 'B', 'b': // Double (IEEE 754 LE)
		if field.Len == 8 {
			binary.LittleEndian.PutUint64(raw, math.Float64bits(val.AsNumDouble()))
		}

	case '@', '=', 'T', 't': // Timestamp / Modtime
		if field.Len >= 8 {
			binary.LittleEndian.PutUint32(raw[0:4], uint32(val.AsJulian()))
			binary.LittleEndian.PutUint32(raw[4:8], uint32(val.AsTimeMs()))
		}

	case 'Y', 'y': // Currency
		if field.Len == 8 {
			cents := int64(val.AsNumDouble() * 10000.0)
			binary.LittleEndian.PutUint64(raw, uint64(cents))
		}

	case '^': // RowVersion
		if field.Len == 8 {
			binary.LittleEndian.PutUint64(raw, uint64(val.AsLong()))
		}

	default:
		// Unknown: write as string
		s := val.AsString()
		copy(raw, s)
	}
}

// --- Internal parsers ---

func parseNumericField(raw []byte, dec byte) hbrt.Value {
	// Byte-level fast path — avoids `string(raw)` + TrimSpace + ParseInt
	// allocations on the hot scan path. Numeric DBF fields are ASCII,
	// right-aligned, space-padded, optional leading sign, optional `.`
	// for decimals. A full 50k-row scan can hit this fn 100 k+ times,
	// so every allocation matters.
	//
	// Algorithm:
	//   1. Walk past leading spaces.
	//   2. Detect sign.
	//   3. Accumulate int64 digit-by-digit.
	//   4. If we hit `.` or the field has dec > 0, bail to float parser
	//      (that path is rare on integer-typed DBF fields like IDs /
	//      counters, which dominate WHERE predicates).
	//   5. Walk past trailing spaces.
	//
	// All operations are byte comparisons on the raw record buffer —
	// no heap allocation unless the field is genuinely fractional.

	start := 0
	end := len(raw)
	for start < end && raw[start] == ' ' {
		start++
	}
	for end > start && raw[end-1] == ' ' {
		end--
	}
	if start == end {
		return hbrt.MakeInt(0)
	}

	if dec == 0 {
		// Fast integer path
		i := start
		neg := false
		if raw[i] == '-' {
			neg = true
			i++
		} else if raw[i] == '+' {
			i++
		}
		var n int64
		ok := i < end
		for ; i < end; i++ {
			c := raw[i]
			if c == '.' {
				ok = false
				break
			}
			if c < '0' || c > '9' {
				ok = false
				break
			}
			n = n*10 + int64(c-'0')
		}
		if ok {
			if neg {
				n = -n
			}
			return hbrt.MakeNumInt(n)
		}
		// Fall through: has a `.` or unexpected char → use float path
	}

	// Byte-level float parse for N(w,d) with d > 0 — avoids the
	// string(raw) + strconv.ParseFloat allocation on the hot path.
	// Profile (bench_bulk): parseNumericField was 23% of flat CPU,
	// dominated by this allocation.
	i := start
	neg := false
	if raw[i] == '-' {
		neg = true
		i++
	} else if raw[i] == '+' {
		i++
	}

	var intPart int64
	var sawDigit bool
	for ; i < end; i++ {
		c := raw[i]
		if c == '.' {
			break
		}
		if c < '0' || c > '9' {
			// Unexpected char — fall back to strconv for correctness.
			if f, err := strconv.ParseFloat(string(raw[start:end]), 64); err == nil {
				return hbrt.MakeDouble(f, uint16(len(raw)), uint16(dec))
			}
			return hbrt.MakeInt(0)
		}
		intPart = intPart*10 + int64(c-'0')
		sawDigit = true
	}

	var fracPart int64
	var fracLen int
	if i < end && raw[i] == '.' {
		i++
		for ; i < end; i++ {
			c := raw[i]
			if c < '0' || c > '9' {
				if f, err := strconv.ParseFloat(string(raw[start:end]), 64); err == nil {
					return hbrt.MakeDouble(f, uint16(len(raw)), uint16(dec))
				}
				return hbrt.MakeInt(0)
			}
			fracPart = fracPart*10 + int64(c-'0')
			fracLen++
			sawDigit = true
		}
	}

	if !sawDigit {
		return hbrt.MakeDouble(0, uint16(len(raw)), uint16(dec))
	}

	var f float64
	if fracLen == 0 {
		f = float64(intPart)
	} else {
		f = float64(intPart) + float64(fracPart)/pow10f(fracLen)
	}
	if neg {
		f = -f
	}
	return hbrt.MakeDouble(f, uint16(len(raw)), uint16(dec))
}

// pow10Table — precomputed 10^n for small n. DBF numeric fields rarely
// exceed 10 decimal places; the table covers the common range without
// calling math.Pow on the hot path.
var pow10Table = [20]float64{
	1, 10, 100, 1000, 10000, 100000, 1000000, 10000000,
	1e8, 1e9, 1e10, 1e11, 1e12, 1e13, 1e14, 1e15,
	1e16, 1e17, 1e18, 1e19,
}

func pow10f(n int) float64 {
	if n >= 0 && n < len(pow10Table) {
		return pow10Table[n]
	}
	return math.Pow(10, float64(n))
}

func parseLogicalField(b byte) hbrt.Value {
	switch b {
	case 'T', 't', 'Y', 'y':
		return hbrt.MakeBool(true)
	case 'F', 'f', 'N', 'n':
		return hbrt.MakeBool(false)
	default:
		return hbrt.MakeNil() // space = uninitialized
	}
}

func parseDateField(raw []byte, fieldLen byte) hbrt.Value {
	if fieldLen == 8 {
		// Standard: YYYYMMDD ASCII
		s := string(raw)
		if strings.TrimSpace(s) == "" {
			return hbrt.MakeDate(0) // empty date
		}
		y := parseInt(s[0:4])
		m := parseInt(s[4:6])
		d := parseInt(s[6:8])
		if y > 0 {
			return hbrt.MakeDate(dateToJulian(y, m, d))
		}
		return hbrt.MakeDate(0)
	}
	if fieldLen == 3 {
		// Short: LE uint24
		julian := int64(raw[0]) | int64(raw[1])<<8 | int64(raw[2])<<16
		return hbrt.MakeDate(julian)
	}
	if fieldLen == 4 {
		// VFP: LE uint32 Julian
		return hbrt.MakeDate(int64(binary.LittleEndian.Uint32(raw)))
	}
	return hbrt.MakeDate(0)
}

func parseMemoRef(raw []byte, fieldLen byte) hbrt.Value {
	if fieldLen == 4 {
		blockNo := binary.LittleEndian.Uint32(raw)
		return hbrt.MakeLong(int64(blockNo))
	}
	if fieldLen == 10 {
		// Inline byte-level parse: same pattern as parseNumericField.
		// Avoids string(raw) + strings.TrimSpace + strconv.ParseInt
		// — roughly 3× faster and allocation-free.
		var n int64
		for _, c := range raw {
			switch {
			case c == ' ':
				// Leading/trailing space — keep current accumulator
			case c >= '0' && c <= '9':
				n = n*10 + int64(c-'0')
			default:
				// Malformed block ref — treat as 0, same as strconv.ParseInt
				// would on the non-digit prefix.
				return hbrt.MakeLong(0)
			}
		}
		return hbrt.MakeLong(n)
	}
	return hbrt.MakeLong(0)
}

func parseIntegerField(raw []byte, fieldLen byte) hbrt.Value {
	switch fieldLen {
	case 1:
		return hbrt.MakeInt(int(int8(raw[0])))
	case 2:
		return hbrt.MakeInt(int(int16(binary.LittleEndian.Uint16(raw))))
	case 3:
		v := int32(raw[0]) | int32(raw[1])<<8 | int32(raw[2])<<16
		if v&0x800000 != 0 {
			v |= ^0xFFFFFF // sign extend
		}
		return hbrt.MakeInt(int(v))
	case 4:
		return hbrt.MakeInt(int(int32(binary.LittleEndian.Uint32(raw))))
	case 8:
		return hbrt.MakeLong(int64(binary.LittleEndian.Uint64(raw)))
	default:
		return hbrt.MakeInt(0)
	}
}

// --- Internal formatters ---

func formatNumericField(raw []byte, fieldLen, dec byte, val hbrt.Value) {
	d := val.AsNumDouble()

	// NaN/Inf → asterisks (Harbour: field width overflow marker)
	if math.IsNaN(d) || math.IsInf(d, 0) {
		for i := range raw {
			raw[i] = '*'
		}
		return
	}

	// Use strconv.AppendFloat into a stack-allocated scratch buffer.
	// Skips fmt.Sprintf's format-string parsing and its temporary
	// string allocation — 3–5× faster per write, zero heap allocs on
	// the hot path. 48 bytes fits any DBF numeric field (max 20 len).
	var scratch [48]byte
	s := strconv.AppendFloat(scratch[:0], d, 'f', int(dec), 64)

	// Overflow → asterisks, same as before.
	if len(s) > int(fieldLen) {
		for i := range raw {
			raw[i] = '*'
		}
		return
	}

	// Right-align, space-pad left.
	padLen := int(fieldLen) - len(s)
	for i := 0; i < padLen; i++ {
		raw[i] = ' '
	}
	copy(raw[padLen:], s)
}

func putDateField(raw []byte, fieldLen byte, val hbrt.Value) {
	if fieldLen == 8 {
		if !val.IsDateTime() || val.AsJulian() == 0 {
			copy(raw, "        ")
			return
		}
		y, m, d := julianToDate(val.AsJulian())
		s := fmt.Sprintf("%04d%02d%02d", y, m, d)
		copy(raw, s)
	} else if fieldLen == 4 {
		binary.LittleEndian.PutUint32(raw, uint32(val.AsJulian()))
	}
}

func putMemoRef(raw []byte, fieldLen byte, blockNo uint32) {
	if fieldLen == 4 {
		binary.LittleEndian.PutUint32(raw, blockNo)
	} else if fieldLen == 10 {
		s := fmt.Sprintf("%10d", blockNo)
		copy(raw, s)
	}
}

func putIntegerField(raw []byte, fieldLen byte, val hbrt.Value) {
	n := val.AsNumInt()
	switch fieldLen {
	case 1:
		raw[0] = byte(int8(n))
	case 2:
		binary.LittleEndian.PutUint16(raw, uint16(int16(n)))
	case 4:
		binary.LittleEndian.PutUint32(raw, uint32(int32(n)))
	case 8:
		binary.LittleEndian.PutUint64(raw, uint64(n))
	}
}

// --- Julian date helpers ---

func dateToJulian(y, m, d int) int64 {
	if m <= 2 {
		y--
		m += 12
	}
	a := y / 100
	b := 2 - a + a/4
	return int64(365.25*float64(y+4716)) + int64(30.6001*float64(m+1)) + int64(d+b) - 1524
}

func julianToDate(julian int64) (y, m, d int) {
	if julian <= 0 {
		return 0, 0, 0
	}
	l := julian + 68569
	n := 4 * l / 146097
	l = l - (146097*n+3)/4
	i := 4000 * (l + 1) / 1461001
	l = l - 1461*i/4 + 31
	j := 80 * l / 2447
	d = int(l - 2447*j/80)
	l = j / 11
	m = int(j + 2 - 12*l)
	y = int(100*(n-49) + i + l)
	return
}

func parseInt(s string) int {
	n := 0
	for _, c := range s {
		if c >= '0' && c <= '9' {
			n = n*10 + int(c-'0')
		}
	}
	return n
}