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-- This is the main Lua file for the Interpreter package.
-- Further information in interpreter-doc.pdf or interpreter-doc.txt.
-- Paul Isambert - zappathustra AT free DOT fr - July 2011

local find, gsub, match, sub = string.find, string.gsub, string.match, string.sub
local insert, sort           = table.insert, table.sort

-- Utility function sorting patterns by length (alphabetically if they are of
-- equal length).
local function string_order (a, b)
	local a, b = a.pattern, b.pattern
	return #a == #b and a < b or #a > #b
end

interpreter = { 
-- *** interpreter.active ***
-- Following paragraphs (as defined by interpreter.paragraph) are interpreted
-- iff this is not set to false.
  active = true,
-- *** interpreter.default_class ***
-- Sets the default class for patterns which are added without specifying the
-- class. Default 1.
  default_class = 1
  }
local _classes = {}

-- *** interpreter.add_pattern (table) ***
-- Creates pattern <table>, which can contain the following entries:
-- pattern [string]   = The pattern to match. Magic characters are obeyed!
-- replace [string]   = The replacement for <pattern>. Can be a string, a
--                      table or a function. A simple string.gsub() is
--                      applied.
-- call    [function] = The function applied to <pattern>; <replace> is applied
--                      iff there is no <call>.
-- offset  [number]   = If <pattern> is used at index n, then the search on the
--                      same line for the same pattern starts again at index n
--                      + offset. Applied only when no <call> (in this case,
--                      search starts again at the beginning of the line). By
--                      default, offset = 0. This is needed to avoid infinite
--                      loops with replacements which contain the pattern;
--                      e.g. replacing "TeX" with "\TeX" will produce an
--                      infinite loop, unless offset = 2.
-- nomagic [boolean]  = Sets whether <replace> should be transformed with interpreter.nomagic.
-- class   [number]   = The pattern's <class> (classes of patterns are applied in
--                      order, e.g. all patterns in class 1 are applied, then
--                      all patterns in class 2, etc; class 0, however, is
--                      always applied last). If <class> is not given, the
--                      default_class number is used. Classes must be numbered
--                      consecutively.
function interpreter.add_pattern (tb)
	local class = tb.class or interpreter.default_class
	interpreter.set_class(class, {})
	setmetatable(tb, _classes[class].meta)
	if tb.nomagic then
    tb.pattern = interpreter.nomagic(tb.pattern)
  end
  insert(_classes[class], tb)
	sort(_classes[class], string_order)
  return tb
end

-- *** interpreter.set_class (number, table) ***
-- Sets default values (of the table normally specified in add_pattern) for
-- patterns of class <number>; patterns added to this class can still specify
-- different values, which will override defaults. In other words, this is a
-- metatable for patterns (which are tables) of that class.
function interpreter.set_class(num, tb)
	_classes[num] = _classes[num] or { meta = { __index = function (_, k) return  _classes[num].meta[k] end } }
	for a, b in pairs(tb) do
		_classes[num].meta[a] = b
	end
  return _classes[num]
end

-- Class 0 must exist since it is always used at the end of the paragraph.
interpreter.set_class(0, {})

-- *** interpreter.nomagic (string) ***
-- Turns a normal string into a string with magic characters escaped, so it
-- can be used as a pattern.
local magic_characters = {
  ["^"] = "%^",
  ["$"] = "%$",
  ["("] = "%(",
  [")"] = "%)",
  ["%"] = "%%",
  ["."] = "%.",
  ["["] = "%[",
  ["]"] = "%]",
  ["*"] = "%*",
  ["+"] = "%+",
  ["-"] = "%-",
  ["?"] = "%?",
}
--function interpreter.nomagic (str)
--  return gsub(str, ".", magic_characters)
--end
function interpreter.nomagic (str)
  local i, s = 1, ""
  while i <= #str do
    local c, c2, c3 = sub(str, i, i), sub(str, i + 1, i + 1), sub(str, i + 2, i + 2)
    i = i + 1
    if c == "%"  and magic_characters[c2] then
      s = s .. c2
      i = i + 1
    elseif c == "." and c2 == "." and c3 == "." then
      s = s .. "(.-)"
      i = i + 2
    elseif magic_characters[c] then
      s = s .. "%" .. c
    else
      s = s .. c
    end
  end
  return s
end
-- *** interpreter.protect ([spec]) ***
-- Protects a set of lines in a paragraph; a protected line won't be
-- interpreted. If <spec> is a number, this protects line <spec> in the current
-- paragraph; if <spec> is true, this protects the entire current paragraph. Of
-- course, patterns that were applied to the line(s) or paragraph before
-- protection happened aren't undone.
local _protected
function interpreter.protect (num)
  if type(num) == "number" then
    if type(_protected) ~= "boolean" then
      _protected = _protected or {}
      _protected[num] = true
    end
  else
    _protected = true
  end
end

-- Utility function making a replacement in a string but only from a certain
-- position and only once. We can't let gsub unrestricted, because some
-- part(s) of the string might be protected.
local function xsub (str, num, patt, rep)
  return sub(str, 1, num-1) .. gsub(sub(str, num), patt, rep, 1)
end

-- *** interpreter.protector (left [, right]) ***
-- Sets <left> and <right> (set to <left> if missing) as protectors, i.e.
-- enclosed material won't be processed even if the line is processed
-- otherwise.  For instance: after interpreter.protector ("|"), the word
-- "little" in
--
--     Hello, |little| world!
--
-- will be left untouched; Interpreter is terribly smart (thanks to lpeg), so
-- in "|a| b |c|", "b" isn't protected, as intended, because the "|" on its
-- left doesn't match the one on its right but with the one before "a".  An
-- example with <right> specified: interpreter.protector("[", "]") and
-- then:
--
--     Hello, [little] world!
--
-- achieves the same as above. Protectors AREN'T removed when the line is
-- finally passed to TeX; and there can be several protectors. Compare with
-- interpreter.escape.
local P, Cf, Cg, Cp, Ct, V = lpeg.P, lpeg.Cf, lpeg.Cg, lpeg.Cp, lpeg.Ct, lpeg.V
local _grammar
local function _protector (str, index)
  local protections = Cf(Ct("") * Cg{ _grammar + 1 * V(1) }^1, rawset)
  protections = protections:match(str)
  if protections then
    for a, b in pairs(protections) do
      if index > a and index < b then
        return nil, b
      end
    end
  end
  return index
end
function interpreter.protector (left, right)
  right = right or left
  local gram = P(Cp() * P(left) * (1 - P(right))^0 * Cp() * P(right))
  if _grammar then
    _grammar = _grammar + gram
  else
    _grammar = gram
  end
end

-- *** interpreter.escape ***
-- A string used as an escape character: if a pattern matches, it is processed
-- iff the character immediately to its left isn't <escape>. The escape
-- character IS removed once the lines have been processed, so TeX never sees
-- it; also, only one escape character is allowed, and itself can't be escaped
-- (i.e. it doesn't mean anything to try to escape it). E.g.:
--
--     interpreter.escape = "|"
--     ... this won't be |*processed*
--
-- Assuming you have a pattern with stars, here it won't be applied. Instead
-- "this won't be *processed*" will be passed to TeX (note that the escape
-- character has disappeared).

local function get_index (str, patt, index)
  index = find(str, patt, index)
  if index then
    if sub(str, index-1, index-1) == interpreter.escape then
      return get_index(str, patt, index + 1)
    elseif _grammar then
      local right
      index, right = _protector(str, index, patt)
      return index or get_index(str, patt, right + 1)
    else
      return index
    end
  end
end

-- The main function that applies all the patterns in a <class> on a given
-- paragraph.
local function process_buffer (buffer, class)
	for _, tb in ipairs(class) do
    local num, idx = 1, 1
		while num <= #buffer do
      local line = type(buffer[num]) == "string" and buffer[num]
      if line then
        local index = get_index(line, tb.pattern, idx)
        if index then
          if tb.call then
            local l, o = tb.call(buffer, num, index, tb)
            if o then
              num, idx = l, o
            elseif l then
              idx = l
            end
          elseif tb.replace then
            buffer[num] = xsub(line, index, tb.pattern, tb.replace)
            idx = index + (tb.offset or 0)
          end
          -- If there was a function applied, protection might have been
          -- enforced. Acts accordingly.
          if _protected then
            if type(_protected) == "table" then
              for n, _ in pairs(_protected) do
                if type(buffer[n]) == "string" then
                  buffer[n] = {buffer[n]}
                end
              end
              if _protected[num] then
                num = num + 1
              end
            else
              break
            end
          end
        else
          num = num + 1
          idx = 1
        end
      else
        num = num + 1
        idx = 1
      end
		end
	end
end

-- The functions that iterates the previous one for each class. Note that
-- class 0 is processed last.
local function read_buffer (buffer)
	for _, class in ipairs(_classes) do
    if type(_protected) ~= "boolean" then
      process_buffer(buffer, class)
    end
	end
  if type(_protected) ~= "boolean" then
    process_buffer(buffer, _classes[0])
  end
  _protected = nil
  -- Changes protected lines (tables) back to strings.
	for n, _ in ipairs(buffer) do
    if type(buffer[n]) == "table" then
      buffer[n] = buffer[n][1]
    end
  end
  return buffer
end

local lines = { }

-- *** interpreter.paragraph ***
-- The pattern that defines a line acting as a paragraph boundary,
-- prompting Interpreter to process the lines gathered up to now. Default is a
-- line composed of spaces at most.
interpreter.paragraph = "%s*"

-- *** interpreter.direct (pattern) ***
-- Sets the pattern defining a line as direct Lua code: if a line begins with
-- <pattern> (which itself shouldn't contain the beginning-of-string character "^")
-- the code that follows is processed as Lua code, and the line is turned to
-- an empty string; note that this empty string will be seen as a paragraph
-- boundary if the line happened in the middle of a paragraph and
-- interpreter.paragraph has set paragraph boundary to empty string.  Default
-- is "%%I " (two "%" followed by one "I" followed by at least one space
-- character).
interpreter.direct = "%%%%I%s+"

-- At last, the function to be registered in open_read_file, defining the
-- function that reads a file.
function interpreter.read_file (fname)
  -- *** interpreter.unregister () ***
  -- The function used to remove read_file from the "open_read_file" callback.
  -- Uses callback.register by default, or luatexbase.remove_from_callback if
  -- detected.
  if not interpreter.unregister then
    if luatexbase and luatexbase.remove_from_callback then
      function interpreter.unregister ()
        luatexbase.remove_from_callback("open_read_file", "interpreter")
      end
    else
      function interpreter.unregister ()
        callback.register("open_read_file", nil)
      end
    end
  end
  interpreter.unregister()

	local f, line = io.open(fname), true

	local read_line = function ()
    
    -- If no lines is left in store, we gather a new paragraph.
		if #lines == 0 then
			local line = f:read ()
      while line do
        -- Checks for direct code.
        if interpreter.direct and match(line, "^" .. interpreter.direct) then
          loadstring(gsub(line, "^" .. interpreter.direct, ""))()
          line = ""
        end
        table.insert(lines, line)
        -- Checks for paragraph boundary, which breaks line gathering.
        if gsub(line, interpreter.paragraph, "") == "" then
          break
        end
        line = f:read ()
      end
      
      -- Pass the paragraph (a table of strings) to the bug functions above,
      -- if interpreter is active; then remove escape characters, if any.
			if interpreter.active then
				lines = read_buffer (lines)
        if interpreter.escape then
          for num, line in ipairs(lines) do
            lines[num] = gsub(line, interpreter.escape, "")
          end
        end
			end
		end

		return lines and table.remove (lines, 1)
	end
	return {reader = read_line}
end

-- *** interpreter.reset () ***
-- Resets to default values; mostly to be used when calling a new
-- interpretation with \interpretfile.
function interpreter.reset ()
  interpreter.active = true
  interpreter.default_class = 1
  _classes = {}
  interpreter.set_class(0, {})
  _grammar = nil
  interpreter.escape  = nil
  interpreter.paragraph = "%s*"
  interpreter.direct = "%%%%I%s+"
end

-- *** interpreter.register (function) ***
-- The function used to register the read_file function in the
-- "open_read_file" callback.  If none is given, use callback.register, or
-- luatexbase.add_to_callback if detected (with "interpreter" as the name).
-- The function is defined in \interpretfile (see interpreter.tex).