/*
 * Copyright 2018 faddenSoft
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
using System;
using System.Collections.Generic;
using System.Diagnostics;
using System.Reflection;
using System.Text;
using System.Web.Script.Serialization;

using Asm65;
using CommonUtil;

namespace SourceGen {
    /// <summary>
    /// Data pseudo-op formatter.  Long operands, notably strings and dense hex blocks, may
    /// be broken across multiple lines.
    /// 
    /// Assembler output will use Opcode and Operand, emitting multiple lines of ASC, HEX,
    /// etc.  The display list may treat it as a single item that is split across
    /// multiple lines.
    /// </summary>
    public class PseudoOp {
        private const int MAX_OPERAND_LEN = 64;

        /// <summary>
        /// One piece of the operand.
        /// </summary>
        public struct PseudoOut {
            /// <summary>
            /// Opcode.  Same for all entries in the list.
            /// </summary>
            public string Opcode { get; set; }

            /// <summary>
            /// Formatted form of this piece of the operand.
            /// </summary>
            public string Operand { get; set; }

            /// <summary>
            /// Copy constructor.
            /// </summary>
            public PseudoOut(PseudoOut src) {
                Opcode = src.Opcode;
                Operand = src.Operand;
            }
        }

        /// <summary>
        /// Pseudo-op name collection.  Name strings may be null.
        /// </summary>
        public class PseudoOpNames {
            public string EquDirective { get; set; }
            public string OrgDirective { get; set; }
            public string RegWidthDirective { get; set; }

            public string DefineData1 { get; set; }
            public string DefineData2 { get; set; }
            public string DefineData3 { get; set; }
            public string DefineData4 { get; set; }
            public string DefineBigData2 { get; set; }
            public string DefineBigData3 { get; set; }
            public string DefineBigData4 { get; set; }
            public string Fill { get; set; }
            public string Dense { get; set; }
            public string StrGeneric { get; set; }
            public string StrGenericHi { get; set; }
            public string StrReverse { get; set; }
            public string StrReverseHi { get; set; }
            public string StrLen8 { get; set; }
            public string StrLen8Hi { get; set; }
            public string StrLen16 { get; set; }
            public string StrLen16Hi { get; set; }
            public string StrNullTerm { get; set; }
            public string StrNullTermHi { get; set; }
            public string StrDci { get; set; }
            public string StrDciHi { get; set; }
            public string StrDciReverse { get; set; }
            public string StrDciReverseHi { get; set; }

            public string GetDefineData(int width) {
                switch (width) {
                    case 1: return DefineData1;
                    case 2: return DefineData2;
                    case 3: return DefineData3;
                    case 4: return DefineData4;
                    default: Debug.Assert(false); return ".?!!";
                }
            }
            public string GetDefineBigData(int width) {
                switch (width) {
                    case 1: return DefineData1;
                    case 2: return DefineBigData2;
                    case 3: return DefineBigData3;
                    case 4: return DefineBigData4;
                    default: Debug.Assert(false); return ".!!?";
                }
            }

            public PseudoOpNames GetCopy() {
                // Do it the lazy way.
                return Deserialize(Serialize());
            }

            /// <summary>
            /// Merges the non-null, non-empty strings in "other" into this instance.
            /// </summary>
            public void Merge(PseudoOpNames other) {
                // Lots of fields, we don't do this often... use reflection.
                Type type = GetType();
                PropertyInfo[] props = type.GetProperties();
                foreach (PropertyInfo pi in props) {
                    string str = (string)pi.GetValue(other);
                    if (string.IsNullOrEmpty(str)) {
                        continue;
                    }
                    pi.SetValue(this, str);
                }
            }

            public string Serialize() {
                // This results in a JSON-encoded string being stored in a JSON-encoded file,
                // which means a lot of double-quote escaping.  We could do something here
                // that stored more nicely but it doesn't seem worth the effort.
                JavaScriptSerializer ser = new JavaScriptSerializer();
                return ser.Serialize(this);
            }

            public static PseudoOpNames Deserialize(string cereal) {
                JavaScriptSerializer ser = new JavaScriptSerializer();
                try {
                    return ser.Deserialize<PseudoOpNames>(cereal);
                } catch (Exception ex) {
                    Debug.WriteLine("PseudoOpNames deserialization failed: " + ex.Message);
                    return new PseudoOpNames();
                }
            }
        }

        /// <summary>
        /// Some reasonable defaults for on-screen display.  The object is mutable, so make
        /// a copy of it.
        /// </summary>
        public static readonly PseudoOpNames sDefaultPseudoOpNames = new PseudoOpNames() {
            EquDirective = ".eq",
            OrgDirective = ".org",
            RegWidthDirective = ".rwid",

            DefineData1 = ".dd1",
            DefineData2 = ".dd2",
            DefineData3 = ".dd3",
            DefineData4 = ".dd4",
            DefineBigData2 = ".dbd2",
            DefineBigData3 = ".dbd3",
            DefineBigData4 = ".dbd4",
            Fill = ".fill",
            Dense = ".bulk",

            StrGeneric = ".str",
            StrGenericHi = ".strh",
            StrReverse = ".rstr",
            StrReverseHi = ".rstrh",
            StrLen8 = ".l1str",
            StrLen8Hi = ".l1strh",
            StrLen16 = ".l2str",
            StrLen16Hi = ".l2strh",
            StrNullTerm = ".zstr",
            StrNullTermHi = ".zstrh",
            StrDci = ".dstr",
            StrDciHi = ".dstrh",
            StrDciReverse = ".rdstr",
            StrDciReverseHi = ".rdstrh",
        };


        /// <summary>
        /// Computes the number of lines of output required to hold the formatted output.
        /// </summary>
        /// <param name="formatter">Format definition.</param>
        /// <param name="dfd">Data format descriptor.</param>
        /// <returns>Line count.</returns>
        public static int ComputeRequiredLineCount(Formatter formatter, FormatDescriptor dfd) {
            switch (dfd.FormatType) {
                case FormatDescriptor.Type.Default:
                case FormatDescriptor.Type.NumericLE:
                case FormatDescriptor.Type.NumericBE:
                case FormatDescriptor.Type.Fill:
                    return 1;
                case FormatDescriptor.Type.Dense: {
                        // no delimiter, two output bytes per input byte
                        int maxLen = MAX_OPERAND_LEN;
                        int textLen = dfd.Length * 2;
                        return (textLen + maxLen - 1) / maxLen;
                    }
                case FormatDescriptor.Type.String: {
                        // Subtract two chars, to leave room for start/end delimiter.  We use
                        // non-ASCII delimiters on-screen, so there's nothing to escape there.
                        int maxLen = MAX_OPERAND_LEN - 2;

                        // Remove leading length or trailing null byte from string length.
                        int textLen = dfd.Length;
                        switch (dfd.FormatSubType) {
                            case FormatDescriptor.SubType.None:
                            case FormatDescriptor.SubType.Dci:
                            case FormatDescriptor.SubType.Reverse:
                            case FormatDescriptor.SubType.DciReverse:
                                break;
                            case FormatDescriptor.SubType.CString:
                            case FormatDescriptor.SubType.L8String:
                                textLen--;
                                break;
                            case FormatDescriptor.SubType.L16String:
                                textLen -= 2;
                                break;
                            default:
                                Debug.Assert(false);
                                break;
                        }
                        int strLen = (textLen + maxLen - 1) / maxLen;
                        if (strLen == 0) {
                            // Empty string, but we still need to output a line.
                            strLen = 1;
                        }
                        return strLen;
                    }
                default:
                    Debug.Assert(false);
                    return 1;
            }
        }

        /// <summary>
        /// Generates a pseudo-op statement for the specified data operation.
        /// 
        /// For most operations, only one output line will be generated.  For larger items,
        /// like long comments, the value may be split into multiple lines.  The sub-index
        /// indicates which line should be formatted.
        /// </summary>
        /// <param name="formatter">Format definition.</param>
        /// <param name="opNames">Table of pseudo-op names.</param>
        /// <param name="symbolTable">Project symbol table.</param>
        /// <param name="labelMap">Symbol label map.  May be null.</param>
        /// <param name="dfd">Data format descriptor.</param>
        /// <param name="data">File data array.</param>
        /// <param name="offset">Start offset.</param>
        /// <param name="subIndex">For multi-line items, which line.</param>
        public static PseudoOut FormatDataOp(Formatter formatter, PseudoOpNames opNames,
                SymbolTable symbolTable, Dictionary<string, string> labelMap,
                FormatDescriptor dfd, byte[] data, int offset, int subIndex) {
            int length = dfd.Length;
            Debug.Assert(length > 0);

            // All outputs for a given offset show the same offset and length, even for
            // multi-line items.
            PseudoOut po = new PseudoOut();

            switch (dfd.FormatType) {
                case FormatDescriptor.Type.Default:
                    if (length != 1) {
                        // This shouldn't happen.
                        Debug.Assert(false);
                        length = 1;
                    }
                    po.Opcode = opNames.GetDefineData(length);
                    int operand = RawData.GetWord(data, offset, length, false);
                    po.Operand = formatter.FormatHexValue(operand, length * 2);
                    break;
                case FormatDescriptor.Type.NumericLE:
                    po.Opcode = opNames.GetDefineData(length);
                    operand = RawData.GetWord(data, offset, length, false);
                    po.Operand = FormatNumericOperand(formatter, symbolTable, labelMap, dfd,
                        operand, length, false);
                    break;
                case FormatDescriptor.Type.NumericBE:
                    po.Opcode = opNames.GetDefineBigData(length);
                    operand = RawData.GetWord(data, offset, length, true);
                    po.Operand = FormatNumericOperand(formatter, symbolTable, labelMap, dfd,
                        operand, length, false);
                    break;
                case FormatDescriptor.Type.Fill:
                    po.Opcode = opNames.Fill;
                    po.Operand = length + "," + formatter.FormatHexValue(data[offset], 2);
                    break;
                case FormatDescriptor.Type.Dense: {
                        int maxPerLine = MAX_OPERAND_LEN / 2;
                        offset += subIndex * maxPerLine;
                        length -= subIndex * maxPerLine;
                        if (length > maxPerLine) {
                            length = maxPerLine;
                        }
                        po.Opcode = opNames.Dense;
                        po.Operand = formatter.FormatDenseHex(data, offset, length);
                        //List<PseudoOut> outList = new List<PseudoOut>();
                        //GenerateTextLines(text, "", "", po, outList);
                        //po = outList[subIndex];
                    }
                    break;
                case FormatDescriptor.Type.String:
                    // It's hard to do strings in single-line pieces because of prefix lengths,
                    // terminating nulls, DCI polarity, and reverse-order strings.  We
                    // really just want to convert the whole thing to a run of chars
                    // and then pull out a chunk.  As an optimization we can handle
                    // generic strings (subtype=None) more efficiently, which should solve
                    // the problem of massive strings created by auto-analysis.
                    if (dfd.FormatSubType == FormatDescriptor.SubType.None) {
                        int maxPerLine = MAX_OPERAND_LEN - 2;
                        offset += subIndex * maxPerLine;
                        length -= subIndex * maxPerLine;
                        if (length > maxPerLine) {
                            length = maxPerLine;
                        }
                        char[] ltext = BytesToChars(formatter, opNames, dfd.FormatSubType, data,
                            offset, length, out string lpopcode, out int unused);
                        po.Opcode = lpopcode;
                        po.Operand = "\u201c" + new string(ltext) + "\u201d";
                    } else {
                        char[] text = BytesToChars(formatter, opNames, dfd.FormatSubType, data,
                            offset, length, out string popcode, out int showHexZeroes);

                        if (showHexZeroes == 1) {
                            po.Opcode = opNames.DefineData1;
                            po.Operand = formatter.FormatHexValue(0, 2);
                        } else if (showHexZeroes == 2) {
                            po.Opcode = opNames.DefineData2;
                            po.Operand = formatter.FormatHexValue(0, 4);
                        } else {
                            Debug.Assert(showHexZeroes == 0);
                            po.Opcode = popcode;
                            List<PseudoOut> outList = new List<PseudoOut>();
                            GenerateTextLines(text, "\u201c", "\u201d", po, outList);
                            po = outList[subIndex];
                        }
                    }
                    break;
                default:
                    Debug.Assert(false);
                    po.Opcode = ".???";
                    po.Operand = "$" + data[offset].ToString("x2");
                    break;
            }

            return po;
        }

        /// <summary>
        /// Converts a collection of bytes that represent a string into an array of characters,
        /// stripping the high bit.  Framing data, such as leading lengths and trailing nulls,
        /// are not shown.
        /// </summary>
        /// <param name="formatter">Formatter object.</param>
        /// <param name="subType">String sub-type.</param>
        /// <param name="data">File data.</param>
        /// <param name="offset">Offset, within data, of start of string.</param>
        /// <param name="length">Number of bytes to convert.</param>
        /// <param name="popcode">Pseudo-opcode string.</param>
        /// <param name="showHexZeroes">If nonzero, show 1+ zeroes (representing a leading
        ///     length or null-termination) instead of an empty string.</param>
        /// <returns>Array of characters with string data.</returns>
        private static char[] BytesToChars(Formatter formatter, PseudoOpNames opNames,
                FormatDescriptor.SubType subType, byte[] data, int offset, int length,
                out string popcode, out int showHexZeroes) {
            Debug.Assert(length > 0);

            // See also GenMerlin32.OutputString().
            int strOffset = offset;
            int strLen = length;
            bool highAscii = false;
            bool reverse = false;

            showHexZeroes = 0;

            switch (subType) {
                case FormatDescriptor.SubType.None:
                    // High or low ASCII, full width specified by formatter.
                    highAscii = (data[offset] & 0x80) != 0;
                    popcode = highAscii ? opNames.StrGenericHi : opNames.StrGeneric;
                    break;
                case FormatDescriptor.SubType.Dci:
                    // High or low ASCII, full width specified by formatter.
                    highAscii = (data[offset] & 0x80) != 0;
                    popcode = highAscii ? opNames.StrDciHi : opNames.StrDci;
                    break;
                case FormatDescriptor.SubType.Reverse:
                    // High or low ASCII, full width specified by formatter.  Show characters
                    // in reverse order.
                    highAscii = (data[offset + strLen - 1] & 0x80) != 0;
                    popcode = highAscii ? opNames.StrReverseHi : opNames.StrReverse;
                    reverse = true;
                    break;
                case FormatDescriptor.SubType.DciReverse:
                    // High or low ASCII, full width specified by formatter.  Show characters
                    // in reverse order.
                    highAscii = (data[offset + strLen - 1] & 0x80) != 0;
                    popcode = highAscii ? opNames.StrDciReverseHi : opNames.StrDciReverse;
                    reverse = true;
                    break;
                case FormatDescriptor.SubType.CString:
                    // High or low ASCII, with a terminating null.  Don't show the null.  If
                    // it's an empty string, just show the null byte as hex.
                    highAscii = (data[offset] & 0x80) != 0;
                    popcode = highAscii ? opNames.StrNullTermHi : opNames.StrNullTerm;
                    strLen--;
                    if (strLen == 0) {
                        showHexZeroes = 1;
                    }
                    break;
                case FormatDescriptor.SubType.L8String:
                    // High or low ASCII, with a leading length byte.  Don't show the null.
                    // If it's an empty string, just show the length byte as hex.
                    strOffset++;
                    strLen--;
                    if (strLen == 0) {
                        showHexZeroes = 1;
                    } else {
                        highAscii = (data[strOffset] & 0x80) != 0;
                    }
                    popcode = highAscii ? opNames.StrLen8Hi : opNames.StrLen8;
                    break;
                case FormatDescriptor.SubType.L16String:
                    // High or low ASCII, with a leading length word.  Don't show the null.
                    // If it's an empty string, just show the length word as hex.
                    Debug.Assert(strLen > 1);
                    strOffset += 2;
                    strLen -= 2;
                    if (strLen == 0) {
                        showHexZeroes = 2;
                    } else {
                        highAscii = (data[strOffset] & 0x80) != 0;
                    }
                    popcode = highAscii ? opNames.StrLen16Hi : opNames.StrLen16;
                    break;
                default:
                    Debug.Assert(false);
                    popcode = ".!!!";
                    break;
            }

            char[] text = new char[strLen];
            if (!reverse) {
                for (int i = 0; i < strLen; i++) {
                    text[i] = (char)(data[i + strOffset] & 0x7f);
                }
            } else {
                for (int i = 0; i < strLen; i++) {
                    text[i] = (char)(data[strOffset + (strLen - i - 1)] & 0x7f);
                }
            }

            return text;
        }

        /// <summary>
        /// Generate multiple operand lines from a text line, adding optional delimiters.
        /// </summary>
        /// <param name="text">Buffer of characters to output.  Must be ASCII.</param>
        /// <param name="startDelim">Delimiter character(s), or the empty string.</param>
        /// <param name="endDelim">Delimiter character(s), or the empty string.</param>
        /// <param name="template">PseudoOut with offset, length, and opcode set.  Each
        ///   returned PseudoOut will have these value plus the generated operand.</param>
        /// <param name="outList">List that receives the generated items.</param>
        private static void GenerateTextLines(char[] text, string startDelim, string endDelim,
                PseudoOut template, List<PseudoOut> outList) {
            // Could get fancy and break long strings at word boundaries.
            int textOffset = 0;

            if (text.Length == 0) {
                // empty string
                PseudoOut po = new PseudoOut(template);
                po.Operand = startDelim + endDelim;
                outList.Add(po);
                return;
            }

            int textPerLine = MAX_OPERAND_LEN - (startDelim.Length + endDelim.Length);
            StringBuilder sb = new StringBuilder(MAX_OPERAND_LEN);
            while (textOffset < text.Length) {
                int len = (text.Length - textOffset < textPerLine) ?
                           text.Length - textOffset : textPerLine;
                sb.Clear();
                sb.Append(startDelim);
                sb.Append(new string(text, textOffset, len));
                sb.Append(endDelim);

                PseudoOut po = new PseudoOut(template);
                po.Operand = sb.ToString();
                outList.Add(po);

                textOffset += len;
            }
        }

        /// <summary>
        /// Format a numeric operand value according to the specified sub-format.
        /// </summary>
        /// <param name="formatter">Text formatter.</param>
        /// <param name="symbolTable">Full table of project symbols.</param>
        /// <param name="labelMap">Symbol label remap, for local label conversion.  May be
        ///   null.</param>
        /// <param name="dfd">Operand format descriptor.</param>
        /// <param name="operandValue">Operand's value.  For most things this comes directly
        ///   out of the code, for relative branches it's a 24-bit absolute address.</param>
        /// <param name="operandLen">Length of operand, in bytes.  For an instruction, this
        ///   does not include the opcode byte.  For a relative branch, this will be 2.</param>
        /// <param name="isPcRel">Set to true if the actual operand is a PC-relative value.
        ///   These get slightly different treatment.</param>
        public static string FormatNumericOperand(Formatter formatter, SymbolTable symbolTable,
                Dictionary<string, string> labelMap, FormatDescriptor dfd,
                int operandValue, int operandLen, bool isPcRel) {
            Debug.Assert(operandLen > 0);
            int hexMinLen = operandLen * 2;

            switch (dfd.FormatSubType) {
                case FormatDescriptor.SubType.None:
                case FormatDescriptor.SubType.Hex:
                case FormatDescriptor.SubType.Address:
                    return formatter.FormatHexValue(operandValue, hexMinLen);
                case FormatDescriptor.SubType.Decimal:
                    return formatter.FormatDecimalValue(operandValue);
                case FormatDescriptor.SubType.Binary:
                    return formatter.FormatBinaryValue(operandValue, hexMinLen * 4);
                case FormatDescriptor.SubType.Ascii:
                    return formatter.FormatAsciiOrHex(operandValue);
                case FormatDescriptor.SubType.Symbol:
                    if (symbolTable.TryGetValue(dfd.SymbolRef.Label, out Symbol sym)) {
                        StringBuilder sb = new StringBuilder();

                        switch (formatter.ExpressionMode) {
                            case Formatter.FormatConfig.ExpressionMode.Simple:
                                FormatNumericSymbolSimple(formatter, sym, labelMap,
                                    dfd, operandValue, operandLen, isPcRel, sb);
                                break;
                            case Formatter.FormatConfig.ExpressionMode.Merlin:
                                FormatNumericSymbolMerlin(formatter, sym, labelMap,
                                    dfd, operandValue, operandLen, isPcRel, sb);
                                break;
                            default:
                                Debug.Assert(false, "Unknown expression mode " +
                                    formatter.ExpressionMode);
                                return "???";
                        }

                        return sb.ToString();
                    } else {
                        return formatter.FormatHexValue(operandValue, hexMinLen);
                    }
                default:
                    Debug.Assert(false);
                    return "???";
            }
        }

        /// <summary>
        /// Format the symbol and adjustment using common expression syntax.
        /// </summary>
        private static void FormatNumericSymbolSimple(Formatter formatter, Symbol sym,
                Dictionary<string, string> labelMap, FormatDescriptor dfd,
                int operandValue, int operandLen, bool isPcRel, StringBuilder sb) {
            // We could have some simple code that generated correct output, shifting and
            // masking every time, but that's ugly and annoying.  For single-byte ops we can
            // just use the byte-select operators, for wider ops we get only as fancy as we
            // need to be.

            int adjustment, symbolValue;

            string symLabel = sym.Label;
            if (labelMap != null && labelMap.TryGetValue(symLabel, out string newLabel)) {
                symLabel = newLabel;
            }

            if (operandLen == 1) {
                // Use the byte-selection operator to get the right piece.
                string selOp;
                if (dfd.SymbolRef.ValuePart == WeakSymbolRef.Part.Bank) {
                    symbolValue = (sym.Value >> 16) & 0xff;
                    selOp = "^";
                } else if (dfd.SymbolRef.ValuePart == WeakSymbolRef.Part.High) {
                    symbolValue = (sym.Value >> 8) & 0xff;
                    selOp = ">";
                } else {
                    symbolValue = sym.Value & 0xff;
                    if (symbolValue == sym.Value) {
                        selOp = string.Empty;
                    } else {
                        selOp = "<";
                    }
                }
                sb.Append(selOp);
                sb.Append(symLabel);

                operandValue &= 0xff;
            } else if (operandLen <= 4) {
                // Operands and values should be 8/16/24 bit unsigned quantities.  32-bit
                // support is really there so you can have a 24-bit pointer in a 32-bit hole.
                // Might need to adjust this if 32-bit signed quantities become interesting.
                uint mask = 0xffffffff >> ((4 - operandLen) * 8);
                string shOp;
                if (dfd.SymbolRef.ValuePart == WeakSymbolRef.Part.Bank) {
                    symbolValue = (sym.Value >> 16);
                    shOp = " >> 16";
                } else if (dfd.SymbolRef.ValuePart == WeakSymbolRef.Part.High) {
                    symbolValue = (sym.Value >> 8);
                    shOp = " >> 8";
                } else {
                    symbolValue = sym.Value;
                    shOp = "";
                }

                if (isPcRel) {
                    // PC-relative operands are funny, because an 8- or 16-bit value is always
                    // expanded to 24 bits.  We output a 16-bit value that the assembler will
                    // convert back to 8-bit or 16-bit.  In any event, the bank byte is never
                    // relevant to our computations.
                    operandValue &= 0xffff;
                    symbolValue &= 0xffff;
                }

                sb.Append(symLabel);
                sb.Append(shOp);
                if (symbolValue > mask) {
                    // Post-shift value won't fit in an operand-size box.
                    symbolValue = (int) (symbolValue & mask);
                    sb.Append(" & ");
                    sb.Append(formatter.FormatHexValue((int)mask, 2));
                }

                if (sb.Length != symLabel.Length) {
                    sb.Append(' ');
                }

                operandValue = (int)(operandValue & mask);
            } else {
                Debug.Assert(false, "bad numeric len");
                sb.Append("?????");
                symbolValue = 0;
            }

            adjustment = operandValue - symbolValue;

            sb.Append(formatter.FormatAdjustment(adjustment));
        }

        /// <summary>
        /// Format the symbol and adjustment using Merlin expression syntax.
        /// </summary>
        private static void FormatNumericSymbolMerlin(Formatter formatter, Symbol sym,
                Dictionary<string, string> labelMap, FormatDescriptor dfd,
                int operandValue, int operandLen, bool isPcRel, StringBuilder sb) {
            // The part-selection operators differ from "simple" in two ways:
            //  (1) They always happen last.  If FOO=$10f0, "#>FOO+$18" == $11.  (Strangely,
            //      all other operators are evaluated from left to right, with no concept
            //      of operator precedence.)
            //  (2) They select words, not bytes.  If FOO=$123456, "#>FOO" is $1234.  This is
            //      best thought of as a shift operator, rather than byte-selection.  For
            //      8-bit code this doesn't matter.
            //
            // This behavior leads to simpler expressions for simple symbol adjustments.

            string symLabel = sym.Label;
            if (labelMap != null && labelMap.TryGetValue(symLabel, out string newLabel)) {
                symLabel = newLabel;
            }

            int adjustment;

            // If we add or subtract an adjustment, it will be done on the full value, which
            // is then shifted to the appropriate part.  So we need to left-shift the operand
            // value to match.  We fill in the low bytes with the contes of the symbol, so
            // that the adjustment doesn't include unnecessary values.  (For example, let
            // FOO=$10f0, with operand "#>FOO" ($10).  We shift the operand to get $1000, then
            // OR in the low byte to get $10f0, so that when we subtract we get adjustment==0.)
            int adjOperand, keepLen;
            if (dfd.SymbolRef.ValuePart == WeakSymbolRef.Part.Bank) {
                adjOperand = operandValue << 16 | (sym.Value & 0xffff);
                keepLen = 3;
            } else if (dfd.SymbolRef.ValuePart == WeakSymbolRef.Part.High) {
                adjOperand = (operandValue << 8) | (sym.Value & 0xff);
                keepLen = 2;
            } else {
                adjOperand = operandValue;
                keepLen = 1;
            }

            keepLen = Math.Max(keepLen, operandLen);
            adjustment = adjOperand - sym.Value;
            if (keepLen == 1) {
                adjustment %= 256;
                // Adjust for aesthetics.  The assembler implicitly appiles a modulo operation,
                // so we can use the value closest to zero.
                if (adjustment > 127) {
                    adjustment = -(256 - adjustment) /*% 256*/;
                } else if (adjustment < -128) {
                    adjustment = (256 + adjustment) /*% 256*/;
                }
            } else if (keepLen == 2) {
                adjustment %= 65536;
                if (adjustment > 32767) {
                    adjustment = -(65536 - adjustment) /*% 65536*/;
                } else if (adjustment < -32768) {
                    adjustment = (65536 + adjustment) /*% 65536*/;
                }
            }

            // Use the label from sym, not dfd's weak ref; might be different if label
            // comparisons are case-insensitive.
            switch (dfd.SymbolRef.ValuePart) {
                case WeakSymbolRef.Part.Unknown:
                case WeakSymbolRef.Part.Low:
                    // For Merlin, "<" is effectively a no-op.  We can put it in for
                    // aesthetics when grabbing the low byte of a 16-bit value.
                    if ((operandLen == 1) && sym.Value > 0xff) {
                        sb.Append('<');
                    }
                    sb.Append(symLabel);
                    break;
                case WeakSymbolRef.Part.High:
                    sb.Append('>');
                    sb.Append(symLabel);
                    break;
                case WeakSymbolRef.Part.Bank:
                    sb.Append('^');
                    sb.Append(symLabel);
                    break;
                default:
                    Debug.Assert(false, "bad part");
                    sb.Append("???");
                    break;
            }

            sb.Append(formatter.FormatAdjustment(adjustment));
        }
    }
}