-----------
-- Lua bindings to Harfbuzz.
-- * [Wiki](http://github.com/ufytex/luaharfbuzz/wiki)
-- * [Source on Github](https://github.com/ufytex/luaharfbuzz)
-- * [API Coverage Status](https://github.com/ufytex/luaharfbuzz/blob/master/status/done.txt)
--
-- @author Deepak Jois <<deepak.jois@gmail.com>>
-- @copyright 2016
-- @license MIT
-- @module harfbuzz

--- Wraps `hb_version`
-- @function version

--- Wraps `hb_shape`.
--  @param font `Font` to use for shaping
--
--  @param buffer `Buffer` to shape
--
--  @param[opt] options table containing one or more supported options:
--
--  * `direction`: A `Direction` object representing the object.
--  * `script`: A `Script` object representing the script.
--  * `language`: A `Language` object representing the language.
--  * `features`: features to enable, specified as either of the following.
--    - comma-separated list of features. See [feature string syntax reference](https://github.com/ufytex/luaharfbuzz/wiki/Feature-Strings)
--    - table of `Feature` objects
--  @function shape

--- Lua wrapper for `hb_blob_t` type
--  @type Blob

--- Wraps `hb_blob_create`.
--  Initializes a new `hb_blob_t`.
--  @param data lua string containing binary or character data.
--  @function Blob.new

--- Wraps `hb_blob_create_from_file`.
--  Initializes a new `hb_blob_t`.
--  @param filename lua string.
--  @function Blob.new_from_file

--- Wraps `hb_blob_get_length`.
--  @function Blob:get_length

--- Wraps `hb_blob_get_data`.
--  @function Blob:get_data

--- Lua wrapper for `hb_face_t` type
--  @type Face

--- Wraps `hb_face_create`.
--  Initializes a new `hb_face_t` from a `Blob` object.
--  @param blob `Blob` to read the font from.
--  @param[opt=0] font_index index of font to read.
--  @function Face.new_from_blob

--- Create a new `Face` from a file.
--  Makes a call to `Face:new_from_blob` after creating a `Blob` from the
--  file contents.
--  @param file path to font file.
--  @param[opt=0] font_index index of font to read.
--  @function Face.new

--- Wraps `hb_face_collect_unicodes`.
--  @return table of codepoints supported by the face.
--  @function Face:collect_unicodes

--- Wraps `hb_face_get_glyph_count`.
--  @function Face:get_glyph_count

--- Wraps `hb_face_reference_table`.
--  @param tag `Tag` object of the table.
--  @return `Blob` object for the face table of `tag`.
--  @function Face:get_table

--- Wraps `hb_face_get_table_tags`.
--  @return table of `Tag`s representing face table tags.
--  @function Face:get_table_tags

--- Wraps `hb_face_get_upem`.
--  @function Face:get_upem

--- Wraps `hb_ot_color_has_palettes`.
--  @function Face:ot_color_has_palettes

--- Wraps `hb_ot_color_palette_get_count`.
--  @function Face:ot_color_palette_get_count

--- Wraps `hb_ot_color_palette_get_colors`.
--  @function Face:ot_color_palette_get_colors

--- Wraps `hb_ot_color_has_layers`.
--  @function Face:ot_color_has_layers

--- Wraps `hb_ot_color_glyph_get_layers`.
--  @function Face:ot_color_glyph_get_layers

--- Wraps `hb_ot_color_has_png`.
--  @function Face:ot_color_has_png

--- Wraps `hb_ot_layout_table_get_script_tags`.
--  @function Face:ot_layout_get_script_tags

--- Wraps `hb_ot_layout_script_get_language_tags`.
--  @function Face:ot_layout_get_language_tags

--- Wraps `hb_ot_layout_language_get_feature_tags`.
--  @function Face:ot_layout_get_feature_tags

--- Wraps `hb_ot_layout_table_find_script`.
--  @function Face:ot_layout_find_script

--- Wraps `hb_ot_layout_script_find_language`.
--  @function Face:ot_layout_find_language

--- Wraps `hb_ot_layout_language_find_feature`.
--  @function Face:ot_layout_find_feature


--- Lua wrapper for `hb_font_t` type
--  @type Font

--- Wraps `hb_font_create`, and sets up some defaults for scale and shaping functions.
--  Initializes a new `hb_font_t` from a `Face` object. Sets the default scale
--  to the face’s upem value, and sets the font shaping functions by
--  calling `hb_ot_font_set_funcs` on it.
--  @param face `Face` object.
--  @function Font.new

--- Wraps `hb_font_get_scale`.
--  @return two values for the x-scale and y-scale of the font.
--  @function Font:get_scale

--- Wraps `hb_font_set_scale`.
--  @param x_scale desired x-scale of font.
--  @param y_scale desired y-scale of font.
--  @function Font:set_scale

--- Wraps `hb_font_get_h_extents`.
--  @return font extents table for horizontal direction, contains the following
--  or `nil` if HarfBuzz fails to load font extents:
--
--  * `ascender`: typographic ascender.
--  * `descender`: typographic descender.
--  * `line_gap`: line spacing gap.
--  @function Font:get_h_extents

--- Wraps `hb_font_get_v_extents`.
--  @return font extents table for vertical direction, similar to
--  `Font:get_h_extents`, or `nil` if HarfBuzz fails to load font extents:
--  @function Font:get_v_extents

--- Wraps `hb_font_get_glyph_extents`.
--  @param glyph index inside the font.
--  @return extents table contains the following or `nil` if HarfBuzz fails to
--  load glyph extents:
--
--  * `x_bearing`: left side of glyph from origin.
--  * `y_bearing`: top side of glyph from origin.
--  * `width`: distance from left to right side.
--  * `height`: distance from top to bottom side.
--  @function Font:get_glyph_extents

--- Wraps `hb_font_get_glyph_name`.
--  @param glyph index inside the font.
--  @return name of the glyph or nil.
--  @function Font:get_glyph_name

--- Wraps `hb_font_get_glyph_from_name`.
--  @param name of the glyph.
--  @return glyph index inside the font or nil.
--  @function Font:get_glyph_from_name

--- Wraps `hb_font_get_glyph_h_advance`.
--  @param glyph index inside the font.
--  @return advance glyph advance of the glyph in horizontal direction.
--  @function Font:get_glyph_h_advance

--- Wraps `hb_font_get_glyph_v_advance`.
--  @param glyph index inside the font.
--  @return advance glyph advance of the glyph in vertical direction.
--  @function Font:get_glyph_v_advance

--- Wraps `hb_font_get_nominal_glyph`.
--  @param codepoint.
--  @return glyph index or `nil` if `codepoint` is not supported by the font.
--  @function Font:get_nominal_glyph

--- Wraps `hb_ot_color_glyph_get_png`.
--  @function Font:ot_color_glyph_get_png

--- Lua wrapper for `hb_buffer_t` type.
--  @type Buffer

--- Wraps `hb_buffer_create`.
--  @function Buffer.new

--- Wraps `hb_buffer_add_utf8`.
--  @param text UTF8 encoded string.
--  @param[opt=0] item_offset 0-indexed offset in `text`, from where to start adding.
--  @param[opt=-1] item_length length to add from `item_offset`. `-1` adds till end of `text`.
--  @function Buffer:add_utf8

--- Wraps `hb_buffer_add_codepoints`.
--  @param text table with codepoints as lua numbers.
--  @param[opt=0] item_offset 0-indexed offset in `text`, from where to start adding.
--  @param[opt=-1] item_length length to add from `item_offset`. `-1` adds till end of&nbsp;`text`.
--  @function Buffer:add_codepoints

--- Wraps `hb_buffer_set_direction`.
--  @param dir  A `Direction` object.
--  @function Buffer:set_direction

--- Wraps `hb_buffer_get_direction`.
-- @return A `Direction` object.
--  @function Buffer:get_direction

--- Wraps `hb_buffer_set_script`.
--  @param script  A `Script` object.
--  @function Buffer:set_script

--- Wraps `hb_buffer_get_script`.
-- @return A `Script` object.
--  @function Buffer:get_script

--- Wraps `hb_buffer_set_language`.
--  @param lang A `Language` object
--  @function Buffer:set_language

--- Wraps `hb_buffer_get_language`.
-- @return A `Language` object
--  @function Buffer:get_language

--- Wraps `hb_buffer_reverse`.
--  @function Buffer:reverse

--- Wraps `hb_buffer_get_length`.
--  @function Buffer:get_length

--- Wraps `hb_buffer_get_cluster_level`.
--  @return see [Cluster Levels](#Cluster_Levels)
--  @function Buffer:get_cluster_level

--- Wraps `hb_buffer_set_cluster_level`.
--  @param level see [Cluster Levels](#Cluster_Levels)
--  @function Buffer:set_cluster_level

--- Wraps `hb_buffer_guess_segment_properties`.
--  @function Buffer:guess_segment_properties

--- Helper method to get shaped glyph data.
--  Calls `hb_buffer_get_glyph_infos`, `hb_buffer_get_glyph_positions` and
-- `hb_glyph_info_get_glyph_flags`, and assembles the data into a Lua table.
--  @return table containing data for each glyph, in a nested table. Each nested
--  table contains the following:
--
--  * `x_advance`: horizontal advance.
--  * `y_advance`: vertical advance.
--  * `x_offset`: horizontal displacement.
--  * `y_offset`: vertical displacement.
--  * `cluster`: glyph cluster index within input.
--  * `codepoint`: glyph index inside the font _(this field name is a bit misleading, but that’s what Harfbuzz uses)_.
--  * `flags`: glyph flags
--  @function Buffer:get_glyphs

--- Cluster Levels.
-- See [Harfbuzz docs](http://behdad.github.io/harfbuzz/clusters.html) for more details
-- about what each of these levels mean.
--  @section

--- Wraps `HB_BUFFER_CLUSTER_LEVEL_MONOTONE_GRAPHEMES`.
--  @field Buffer.CLUSTER_LEVEL_MONOTONE_GRAPHEMES

--- Wraps `HB_BUFFER_CLUSTER_LEVEL_MONOTONE_CHARACTERS`.
--  @field Buffer.CLUSTER_LEVEL_MONOTONE_CHARACTERS

--- Wraps `HB_BUFFER_CLUSTER_LEVEL_CHARACTERS`.
--  @field Buffer.CLUSTER_LEVEL_CHARACTERS

--- Wraps `HB_BUFFER_CLUSTER_LEVEL_DEFAULT`.
--  @field Buffer.CLUSTER_LEVEL_DEFAULT

--- Wraps `HB_GLYPH_FLAG_UNSAFE_TO_BREAK`.
-- @field Buffer.GLYPH_FLAG_UNSAFE_TO_BREAK

--- Wraps `HB_GLYPH_FLAG_DEFINED`.
-- @field Buffer.GLYPH_FLAG_DEFINED

--- Lua wrapper for `hb_feature_t` type
--  @type Feature

--- Wraps `hb_feature_from_string`
--  @param feature_string See [feature string syntax reference](https://github.com/ufytex/luaharfbuzz/wiki/Feature-Strings)
--  @function Feature.new

--- Wraps `hb_feature_to_string`.
--  Enables nice output with `tostring(…)`.
--  @function Feature:__tostring

--- Lua wrapper for `hb_tag_t` type.
--  @type Tag

--- Wraps `hb_tag_from_string`.
-- @param string to be converted to a `Tag` object.
-- @return a `Tag` object.
-- @function Tag.new

--- Wraps `hb_tag_to_string`. Enable nice output with `tostring(…)`.
-- @return Returns a string representation for the tag object.
-- @function Tag:__to_string

--- Enables equality comparisions with `==` between two tags.
-- @return `true` or `false` depending on whether the two tags are equal.
-- @function Tag:__eq


--- Lua wrapper for `hb_script_t` type.
--  @type Script

--- Wraps `hb_script_from_string`.
-- @param script 4-letter script code according to the [ISO 15924 standard](http://www.unicode.org/iso15924/iso15924-num.html).
-- @return a `Script` object.
-- @function Script.new

--- Wraps `hb_script_from_iso15924_tag`
-- @param tag a `Tag` object representing a [ISO 15924 script](http://www.unicode.org/iso15924/iso15924-num.html).
-- @function Script.from_iso15924_tag

--- Wraps `hb_script_to_iso15924_tag`.
-- @return a `Tag` object representing the script.
-- @function Script:to_iso15924_tag

--- Enable nice output with `tostring(…)`
-- @return Returns a 4-letter [ISO 15924 script code](http://www.unicode.org/iso15924/iso15924-num.html) for the script object.
-- @function Script:__to_string

--- Enables equality comparisions with `==` between two scripts.
-- @return `true` or `false` depending on whether the two scripts are equal.
-- @function Script:__eq

--- Predefined Script Codes.
-- Predefined directions that correspond to their original definitions in Harfbuzz.
-- @section

--- Wraps `HB_SCRIPT_COMMON`.
-- @field Script.COMMON

--- Wraps `HB_SCRIPT_INHERITED`.
-- @field Script.INHERITED

--- Wraps `HB_SCRIPT_UNKNOWN`.
-- @field Script.UNKNOWN

--- Wraps `HB_SCRIPT_INVALID`.
-- @field Script.INVALID

--- Lua wrapper for `hb_direction_t` type.
-- @type Direction

--- Wraps `hb_direction_from_string`.
-- @param dir can be one of `ltr`, `rtl`, `ttb`, `btt` or `invalid`.
-- @return a `Direction` object.
-- @function Direction.new

--- Wraps `hb_direction_to_string`. Enable nice output with `tostring(…)`.
-- @return Returns a string representation for direction.
-- @function Direction:__to_string

--- Enables equality comparisions with `==` between two directions.
-- @return `true` or `false` depending on whether the two tags are equal.
-- @function Direction:__eq

--- Wraps `HB_DIRECTION_IS_VALID`.
-- @return a boolean value
-- @function Direction:is_valid

--- Wraps `HB_DIRECTION_IS_HORIZONTAL`.
-- @return a boolean value
-- @function Direction:is_horizontal

--- Wraps `HB_DIRECTION_IS_VERTICAL`.
-- @return a boolean value
-- @function Direction:is_vertical

--- Wraps `HB_DIRECTION_IS_FORWARD`.
-- @return a boolean value
-- @function Direction:is_forward

--- Wraps `HB_DIRECTION_IS_BACKWARD`.
-- @return a boolean value
-- @function Direction:is_backward

--- Predefined directions.
-- Predefined directions that correspond to their original definitions in Harfbuzz.
-- @section

--- Wraps `HB_DIRECTION_LTR`.
-- @field Direction.LTR

--- Wraps `HB_DIRECTION_RTL`.
-- @field Direction.RTL

--- Wraps `HB_DIRECTION_TTB`.
-- @field Direction.TTB

--- Wraps `HB_DIRECTION_LTR`.
-- @field Direction.BTT

--- Lua wrapper for `hb_language_t` type.
--  @type Language

--- Wraps `hb_language_from_string`.
-- @param lang [three-letter language tag](http://www.microsoft.com/typography/otspec/languagetags.htm) to be converted to a `Language` object.
-- @return a `Language` object.
-- @function Language.new

--- Wraps `hb_language_to_string`. Enable nice output with `tostring(…)`.
-- @return Returns a string representation for the language object.
-- @function Language:__to_string

--- Enables equality comparisions with `==` between two languages.
-- @return `true` or `false` depending on whether the two languages are equal.
-- @function Language:__eq

--- Predefined languages.
-- Predefined languages that correspond to their original definitions in Harfbuzz.
-- @section

--- Wraps `HB_LANGUAGE_INVALID`.
-- @field Language.INVALID


--- Unicode functions.
-- @section

--- Wraps `hb_unicode_script`
-- @param char Unicode codepoint
-- @return a `Script` object.
-- @function unicode.script


--- Predefined Name IDs.
-- Predefined OpenType 'name' table name identifier.
-- @section

--- Wraps `HB_OT_NAME_ID_COPYRIGHT`
-- @field ot.NAME_ID_COPYRIGHT

--- Wraps `HB_OT_NAME_ID_FONT_FAMILY`
-- @field ot.NAME_ID_FONT_FAMILY

--- Wraps `HB_OT_NAME_ID_FONT_SUBFAMILY`
-- @field ot.NAME_ID_FONT_SUBFAMILY

--- Wraps `HB_OT_NAME_ID_UNIQUE_ID`
-- @field ot.NAME_ID_UNIQUE_ID

--- Wraps `HB_OT_NAME_ID_FULL_NAME`
-- @field ot.NAME_ID_FULL_NAME

--- Wraps `HB_OT_NAME_ID_VERSION_STRING`
-- @field ot.NAME_ID_VERSION_STRING

--- Wraps `HB_OT_NAME_ID_POSTSCRIPT_NAME`
-- @field ot.NAME_ID_POSTSCRIPT_NAME

--- Wraps `HB_OT_NAME_ID_TRADEMARK`
-- @field ot.NAME_ID_TRADEMARK

--- Wraps `HB_OT_NAME_ID_MANUFACTURER`
-- @field ot.NAME_ID_MANUFACTURER

--- Wraps `HB_OT_NAME_ID_DESIGNER`
-- @field ot.NAME_ID_DESIGNER

--- Wraps `HB_OT_NAME_ID_DESCRIPTION`
-- @field ot.NAME_ID_DESCRIPTION

--- Wraps `HB_OT_NAME_ID_VENDOR_URL`
-- @field ot.NAME_ID_VENDOR_URL

--- Wraps `HB_OT_NAME_ID_DESIGNER_URL`
-- @field ot.NAME_ID_DESIGNER_URL

--- Wraps `HB_OT_NAME_ID_LICENSE`
-- @field ot.NAME_ID_LICENSE

--- Wraps `HB_OT_NAME_ID_LICENSE_URL`
-- @field ot.NAME_ID_LICENSE_URL

--- Wraps `HB_OT_NAME_ID_TYPOGRAPHIC_FAMILY`
-- @field ot.NAME_ID_TYPOGRAPHIC_FAMILY

--- Wraps `HB_OT_NAME_ID_TYPOGRAPHIC_SUBFAMILY`
-- @field ot.NAME_ID_TYPOGRAPHIC_SUBFAMILY

--- Wraps `HB_OT_NAME_ID_MAC_FULL_NAME`
-- @field ot.NAME_ID_MAC_FULL_NAME

--- Wraps `HB_OT_NAME_ID_SAMPLE_TEXT`
-- @field ot.NAME_ID_SAMPLE_TEXT

--- Wraps `HB_OT_NAME_ID_CID_FINDFONT_NAME`
-- @field ot.NAME_ID_CID_FINDFONT_NAME

--- Wraps `HB_OT_NAME_ID_WWS_FAMILY`
-- @field ot.NAME_ID_WWS_FAMILY

--- Wraps `HB_OT_NAME_ID_WWS_SUBFAMILY`
-- @field ot.NAME_ID_WWS_SUBFAMILY

--- Wraps `HB_OT_NAME_ID_LIGHT_BACKGROUND`
-- @field ot.NAME_ID_LIGHT_BACKGROUND

--- Wraps `HB_OT_NAME_ID_DARK_BACKGROUND`
-- @field ot.NAME_ID_DARK_BACKGROUND

--- Wraps `HB_OT_NAME_ID_VARIATIONS_PS_PREFIX`
-- @field ot.NAME_ID_VARIATIONS_PS_PREFIX

--- Wraps `HB_OT_NAME_ID_INVALID`
-- @field ot.NAME_ID_INVALID

--- Wraps `HB_OT_LAYOUT_NO_SCRIPT_INDEX`
-- @field ot.LAYOUT_NO_SCRIPT_INDEX

--- Wraps `HB_OT_LAYOUT_NO_FEATURE_INDEX`
-- @field ot.LAYOUT_NO_FEATURE_INDEX

--- Wraps `HB_OT_LAYOUT_DEFAULT_LANGUAGE_INDEX`
-- @field ot.LAYOUT_DEFAULT_LANGUAGE_INDEX

--- Wraps `HB_OT_LAYOUT_NO_VARIATIONS_INDEX`
-- @field ot.LAYOUT_NO_VARIATIONS_INDEX