CodeMirror.defineMode("gas", function(_config, parserConfig) {
  'use strict';

  // If an architecture is specified, its initialization function may
  // populate this array with custom parsing functions which will be
  // tried in the event that the standard functions do not find a match.
  var custom = [];

  // The symbol used to start a line comment changes based on the target
  // architecture.
  // If no architecture is pased in "parserConfig" then only multiline
  // comments will have syntax support.
  var lineCommentStartSymbol = "";

  // These directives are architecture independent.
  // Machine specific directives should go in their respective
  // architecture initialization function.
  // Reference:
  // http://sourceware.org/binutils/docs/as/Pseudo-Ops.html#Pseudo-Ops
  var directives = {
    ".abort" : "builtin",
    ".align" : "builtin",
    ".altmacro" : "builtin",
    ".ascii" : "builtin",
    ".asciz" : "builtin",
    ".balign" : "builtin",
    ".balignw" : "builtin",
    ".balignl" : "builtin",
    ".bundle_align_mode" : "builtin",
    ".bundle_lock" : "builtin",
    ".bundle_unlock" : "builtin",
    ".byte" : "builtin",
    ".cfi_startproc" : "builtin",
    ".comm" : "builtin",
    ".data" : "builtin",
    ".def" : "builtin",
    ".desc" : "builtin",
    ".dim" : "builtin",
    ".double" : "builtin",
    ".eject" : "builtin",
    ".else" : "builtin",
    ".elseif" : "builtin",
    ".end" : "builtin",
    ".endef" : "builtin",
    ".endfunc" : "builtin",
    ".endif" : "builtin",
    ".equ" : "builtin",
    ".equiv" : "builtin",
    ".eqv" : "builtin",
    ".err" : "builtin",
    ".error" : "builtin",
    ".exitm" : "builtin",
    ".extern" : "builtin",
    ".fail" : "builtin",
    ".file" : "builtin",
    ".fill" : "builtin",
    ".float" : "builtin",
    ".func" : "builtin",
    ".global" : "builtin",
    ".gnu_attribute" : "builtin",
    ".hidden" : "builtin",
    ".hword" : "builtin",
    ".ident" : "builtin",
    ".if" : "builtin",
    ".incbin" : "builtin",
    ".include" : "builtin",
    ".int" : "builtin",
    ".internal" : "builtin",
    ".irp" : "builtin",
    ".irpc" : "builtin",
    ".lcomm" : "builtin",
    ".lflags" : "builtin",
    ".line" : "builtin",
    ".linkonce" : "builtin",
    ".list" : "builtin",
    ".ln" : "builtin",
    ".loc" : "builtin",
    ".loc_mark_labels" : "builtin",
    ".local" : "builtin",
    ".long" : "builtin",
    ".macro" : "builtin",
    ".mri" : "builtin",
    ".noaltmacro" : "builtin",
    ".nolist" : "builtin",
    ".octa" : "builtin",
    ".offset" : "builtin",
    ".org" : "builtin",
    ".p2align" : "builtin",
    ".popsection" : "builtin",
    ".previous" : "builtin",
    ".print" : "builtin",
    ".protected" : "builtin",
    ".psize" : "builtin",
    ".purgem" : "builtin",
    ".pushsection" : "builtin",
    ".quad" : "builtin",
    ".reloc" : "builtin",
    ".rept" : "builtin",
    ".sbttl" : "builtin",
    ".scl" : "builtin",
    ".section" : "builtin",
    ".set" : "builtin",
    ".short" : "builtin",
    ".single" : "builtin",
    ".size" : "builtin",
    ".skip" : "builtin",
    ".sleb128" : "builtin",
    ".space" : "builtin",
    ".stab" : "builtin",
    ".string" : "builtin",
    ".struct" : "builtin",
    ".subsection" : "builtin",
    ".symver" : "builtin",
    ".tag" : "builtin",
    ".text" : "builtin",
    ".title" : "builtin",
    ".type" : "builtin",
    ".uleb128" : "builtin",
    ".val" : "builtin",
    ".version" : "builtin",
    ".vtable_entry" : "builtin",
    ".vtable_inherit" : "builtin",
    ".warning" : "builtin",
    ".weak" : "builtin",
    ".weakref" : "builtin",
    ".word" : "builtin"
  };

  var registers = {};

  function x86(_parserConfig) {
    lineCommentStartSymbol = "#";

    registers.ax  = "variable";
    registers.eax = "variable-2";
    registers.rax = "variable-3";

    registers.bx  = "variable";
    registers.ebx = "variable-2";
    registers.rbx = "variable-3";

    registers.cx  = "variable";
    registers.ecx = "variable-2";
    registers.rcx = "variable-3";

    registers.dx  = "variable";
    registers.edx = "variable-2";
    registers.rdx = "variable-3";

    registers.si  = "variable";
    registers.esi = "variable-2";
    registers.rsi = "variable-3";

    registers.di  = "variable";
    registers.edi = "variable-2";
    registers.rdi = "variable-3";

    registers.sp  = "variable";
    registers.esp = "variable-2";
    registers.rsp = "variable-3";

    registers.bp  = "variable";
    registers.ebp = "variable-2";
    registers.rbp = "variable-3";

    registers.ip  = "variable";
    registers.eip = "variable-2";
    registers.rip = "variable-3";

    registers.cs  = "keyword";
    registers.ds  = "keyword";
    registers.ss  = "keyword";
    registers.es  = "keyword";
    registers.fs  = "keyword";
    registers.gs  = "keyword";
  }

  function armv6(_parserConfig) {
    // Reference:
    // http://infocenter.arm.com/help/topic/com.arm.doc.qrc0001l/QRC0001_UAL.pdf
    // http://infocenter.arm.com/help/topic/com.arm.doc.ddi0301h/DDI0301H_arm1176jzfs_r0p7_trm.pdf
    lineCommentStartSymbol = "@";
    directives.syntax = "builtin";

    registers.r0  = "variable";
    registers.r1  = "variable";
    registers.r2  = "variable";
    registers.r3  = "variable";
    registers.r4  = "variable";
    registers.r5  = "variable";
    registers.r6  = "variable";
    registers.r7  = "variable";
    registers.r8  = "variable";
    registers.r9  = "variable";
    registers.r10 = "variable";
    registers.r11 = "variable";
    registers.r12 = "variable";

    registers.sp  = "variable-2";
    registers.lr  = "variable-2";
    registers.pc  = "variable-2";
    registers.r13 = registers.sp;
    registers.r14 = registers.lr;
    registers.r15 = registers.pc;

    custom.push(function(ch, stream) {
      if (ch === '#') {
        stream.eatWhile(/\w/);
        return "number";
      }
    });
  }

  var arch = (parserConfig.architecture || "x86").toLowerCase();
  if (arch === "x86") {
    x86(parserConfig);
  } else if (arch === "arm" || arch === "armv6") {
    armv6(parserConfig);
  }

  function nextUntilUnescaped(stream, end) {
    var escaped = false, next;
    while ((next = stream.next()) != null) {
      if (next === end && !escaped) {
        return false;
      }
      escaped = !escaped && next === "\\";
    }
    return escaped;
  }

  function clikeComment(stream, state) {
    var maybeEnd = false, ch;
    while ((ch = stream.next()) != null) {
      if (ch === "/" && maybeEnd) {
        state.tokenize = null;
        break;
      }
      maybeEnd = (ch === "*");
    }
    return "comment";
  }

  return {
    startState: function() {
      return {
        tokenize: null
      };
    },

    token: function(stream, state) {
      if (state.tokenize) {
        return state.tokenize(stream, state);
      }

      if (stream.eatSpace()) {
        return null;
      }

      var style, cur, ch = stream.next();

      if (ch === "/") {
        if (stream.eat("*")) {
          state.tokenize = clikeComment;
          return clikeComment(stream, state);
        }
      }

      if (ch === lineCommentStartSymbol) {
        stream.skipToEnd();
        return "comment";
      }

      if (ch === '"') {
        nextUntilUnescaped(stream, '"');
        return "string";
      }

      if (ch === '.') {
        stream.eatWhile(/\w/);
        cur = stream.current().toLowerCase();
        style = directives[cur];
        return style || null;
      }

      if (ch === '=') {
        stream.eatWhile(/\w/);
        return "tag";
      }

      if (ch === '{') {
        return "braket";
      }

      if (ch === '}') {
        return "braket";
      }

      if (/\d/.test(ch)) {
        if (ch === "0" && stream.eat("x")) {
          stream.eatWhile(/[0-9a-fA-F]/);
          return "number";
        }
        stream.eatWhile(/\d/);
        return "number";
      }

      if (/\w/.test(ch)) {
        stream.eatWhile(/\w/);
        if (stream.eat(":")) {
          return 'tag';
        }
        cur = stream.current().toLowerCase();
        style = registers[cur];
        return style || null;
      }

      for (var i = 0; i < custom.length; i++) {
        style = custom[i](ch, stream, state);
        if (style) {
          return style;
        }
      }
    },

    lineComment: lineCommentStartSymbol,
    blockCommentStart: "/*",
    blockCommentEnd: "*/"
  };
});
