local base = require("packages.base")

local package = pl.class(base)
package._name = "features"

local lpeg = require("lpeg")

local R, S, P, C = lpeg.R, lpeg.S, lpeg.P, lpeg.C
local Cf, Ct = lpeg.Cf, lpeg.Ct

local otFeatureMap = {
  Ligatures = {
    Required = "rlig",
    Common = "liga",
    Contextual = "clig",
    Rare = "dlig",
    Discretionary = "dlig",
    Historic = "hlig"
  },
  Fractions = {
    On = "frac",
    Alternate = "afrc"
  },
  StylisticSet = function (i)
    return string.format("ss%02i", tonumber(i))
  end,
  CharacterVariant = function (i)
    return string.format("cv%02i", tonumber(i))
  end,
  Letters = {
    Uppercase = "case",
    SmallCaps = "smcp",
    PetiteCaps = "pcap",
    UppercaseSmallCaps = "c2sc",
    UppercasePetiteCaps = "c2pc",
    Unicase = "unic"
  },
  Numbers = {
    Uppercase = "lnum",
    Lining = "lnum",
    LowerCase = "onum",
    OldStyle = "onum",
    Proportional = "pnum",
    monospaced = "tnum",
    SlashedZero = "zero",
    Arabic = "anum"
  },
  Contextuals = {
    Swash = "cswh",
    Alternate = "calt",
    WordInitial = "init",
    WordFinal = "fina",
    LineFinal = "falt",
    Inner = "medi"
  },
  VerticalPosition = {
    Superior = "sups",
    Inferior = "subs",
    Numerator = "numr",
    Denominator = "dnom",
    ScientificInferior = "sinf",
    Ordinal = "ordn"
  },
  Style = {
    Alternate = "salt",
    Italic = "ital",
    Ruby = "ruby",
    Swash = "swsh",
    Historic = "hist",
    TitlingCaps = "titl",
    HorizontalKana = "hkna",
    VerticalKana = "vkna"
  },
  Diacritics = {
    MarkToBase = "mark",
    MarkToMark = "mkmk",
    AboveBase = "abvm",
    BelowBase = "blwm"
  },
  Kerning = {
    Uppercase = "cpsp",
    On = "kern"
  },
  CJKShape = {
    Traditional = "trad",
    Simplified = "smpl",
    JIS1978 = "jp78",
    JIS1983 = "jp83",
    JIS1990 = "jp90",
    Expert = "expt",
    NLC = "nlck"
  },
  CharacterWidth = {
    Proportional = "pwid",
    Full = "fwid",
    Half = "hwid",
    Third = "twid",
    Quarter = "qwid",
    AlternateProportional = "palt",
    AlternateHalf = "halt"
  }
}

local function tagpos (pos, k, v)
  return k, { posneg = pos, value = v }
end

-- Parser for feature strings
local featurename = C((1 - S",;:=")^1)
local value = C(SILE.parserBits.integer)
local tag = C(S"+-") * featurename * (P"=" * value)^0 * S",;:"^-1 / tagpos
local featurestring = Cf(Ct"" * tag^0, rawset)

-- Parser for fontspec strings
-- Refer to fontspec.pdf (see doc), Chapter 3, Table 4 (p. 37)
local fontspecsafe = R("AZ", "az", "09") + P":"
local ws = SILE.parserBits.ws
local fontspecsep = P"," * ws
local fontspecname = C(fontspecsafe^1)
local fontspeclist = ws * P"{" *
                     Ct(ws * fontspecname *
                        (fontspecsep * fontspecname * ws)^0) *
                     P"}" * ws

local otFeatures = pl.class(pl.Map)

function otFeatures:_init ()
  self:super()
  local str = SILE.settings:get("font.features")
  local tbl = featurestring:match(str)
  if not tbl then
    SU.error("Unparsable Opentype feature string '"..str.."'")
  end
  for feat, flag in pairs(tbl) do
    self:set(feat, flag.posneg == "+")
  end
end

function otFeatures:__tostring ()
  local ret = {}
  for _, f in ipairs(self:items()) do
    ret[#ret+1] = (f[2] and "+" or "-") .. f[1]
  end
  return table.concat(ret, ";")
end

function otFeatures:loadOption (name, val, invert)
  local posneg = not invert
  local key = otFeatureMap[name]
  if not key then
    SU.warn("Unknown OpenType feature " .. name)
  else
    local matches = lpeg.match(fontspeclist, val)
    for _, v in ipairs(matches or { val }) do
      v = v:gsub("^No", function () posneg = false; return "" end)
      local feat = type(key) == "function" and key(v) or key[v]
      if not feat then
        SU.warn("Bad OpenType value " .. v .. " for feature " .. name)
      else
        self:set(feat, posneg)
      end
    end
  end
end

-- Input like {Ligatures = Historic} or {Ligatures = "{Historic, Discretionary}"}
--
-- Most real-world use should be single value, but multiple value use is not
-- that odd.  Junicode, for example, a common font among medievalists, has many
-- Stylistic Sets and Character Variations, many of which make sense to enable
-- simultaneously.
function otFeatures:loadOptions (options, invert)
  SU.debug("features", "Features was", self)
  for k, v in pairs(options) do
    self:loadOption(k, v, invert)
  end
  SU.debug("features", "Features interpreted as", self)
end

function otFeatures:unloadOptions (options)
  self:loadOptions(options, true)
end

local fontfn = SILE.Commands.font

function package:registerCommands ()

  self:registerCommand("add-font-feature", function (options, _)
    local otfeatures = otFeatures()
    otfeatures:loadOptions(options)
    SILE.settings:set("font.features", tostring(otfeatures))
  end)

  self:registerCommand("remove-font-feature", function(options, _)
    local otfeatures = otFeatures()
    otfeatures:unloadOptions(options)
    SILE.settings:set("font.features", tostring(otfeatures))
  end)

  self:registerCommand("font", function (options, content)
    local otfeatures = otFeatures()
    -- It is guaranteed that future releases of SILE will not implement non-OT \font
    -- features with capital letters.
    -- Cf. https://github.com/sile-typesetter/sile/issues/992#issuecomment-665575353
    -- So, we reserve 'em all. ⍩⃝
    for k, v in pairs(options) do
      if k:match('^[A-Z]') then
        otfeatures:loadOption(k, v)
        options[k] = nil
      end
    end
    SU.debug("features", "Font features parsed as:", otfeatures)
    options.features = (options.features and options.features .. ";" or "") .. tostring(otfeatures)
    return fontfn(options, content)
  end, tostring(SILE.Help.font) .. " (overridden)")

end

package.documentation = [[
\begin{document}
SILE automatically applies ligatures defined by the fonts that you use.
These ligatures are defined by tables of \em{features} within the font file.
As well as ligatures (multiple glyphs displayed as a single glyph), the features tables also declare other glyph substitutions.

The standard \autodoc:command{\font} command provides an interface to selecting the features that you want SILE to apply to a font.
The features available will be specific to the font file; some fonts come with documentation explaining their supported features.
Discussion of OpenType features is beyond the scope of this manual.

These features can be turned on and off by passing “raw” feature names to the \autodoc:command{\font} command like so:

\begin[type=autodoc:codeblock]{raw}
\font[features="+dlig,+hlig"]{...} % turn on discretionary and historic ligatures
\end{raw}

However, this is unwieldy and requires memorizing the feature codes.

The \autodoc:package{features} package provides two commands, \autodoc:command{\add-font-feature} and \autodoc:command{\remove-font-feature}, which make it easier to access OpenType features.
The interface is patterned on the TeX package \code{fontspec}; for full documentation of the OpenType features supported, see the documentation for that package.\footnote{\code{http://texdoc.net/texmf-dist/doc/latex/fontspec/fontspec.pdf}}

Here is how you would turn on discretionary and historic ligatures with the \autodoc:package{features} package:

\begin[type=autodoc:codeblock]{raw}
\add-font-feature[Ligatures=Rare]\add-font-feature[Ligatures=Discretionary]
...
\remove-font-feature[Ligatures=Rare]\remove-font-feature[Ligatures=Discretionary]
\end{raw}
\end{document}
]]

return package
