[i18n] Initial i18n support.

- Add initial GetText .MO parser
- Add translation struct and helpers
- Pluralized lookup

 TODO:
- Support for more translation catalog file formats.

core/i18n/gettext.odin

@@ -0,0 +1,163 @@
+package i18n
+/*
+	A parser for GNU GetText .MO files.
+
+	Copyright 2021 Jeroen van Rijn <nom@duclavier.com>.
+	Made available under Odin's BSD-3 license.
+
+	A from-scratch implementation based after the specification found here:
+		https://www.gnu.org/software/gettext/manual/html_node/MO-Files.html
+
+	List of contributors:
+		Jeroen van Rijn: Initial implementation.
+*/
+import "core:os"
+import "core:strings"
+import "core:bytes"
+
+parse_mo_from_slice :: proc(data: []u8, pluralizer: proc(int) -> int = nil, allocator := context.allocator) -> (translation: ^Translation, err: Error) {
+	context.allocator = allocator
+	/*
+		An MO file should have at least a 4-byte magic, 2 x 2 byte version info,
+		a 4-byte number of strings value, and 2 x 4-byte offsets.
+	*/
+	if len(data) < 20 {
+		return {}, .MO_File_Invalid
+	}
+
+	/*
+		Check magic. Should be 0x950412de in native Endianness.
+	*/
+	native := true
+	magic  := read_u32(data, native) or_return
+
+	if magic != 0x950412de {
+		native = false
+		magic = read_u32(data, native) or_return
+
+		if magic != 0x950412de { return {}, .MO_File_Invalid_Signature }
+	}
+
+	/*
+		We can ignore version_minor at offset 6.
+	*/
+	version_major := read_u16(data[4:]) or_return
+	if version_major > 1 { return {}, .MO_File_Unsupported_Version }
+
+	count             := read_u32(data[ 8:]) or_return
+	original_offset   := read_u32(data[12:]) or_return
+	translated_offset := read_u32(data[16:]) or_return
+
+	if count == 0 { return {}, .Empty_Translation_Catalog }
+
+	/*
+		Initalize Translation, interner and optional pluralizer.
+	*/
+	translation = new(Translation)
+	translation.pluralize = pluralizer
+	strings.intern_init(&translation.intern, allocator, allocator)
+
+	for n := u32(0); n < count; n += 1 {
+		/*
+			Grab string's original length and offset.
+		*/
+		offset := original_offset + 8 * n
+		if len(data) < int(offset + 8) { return translation, .MO_File_Invalid }
+
+		o_length := read_u32(data[offset    :], native) or_return
+		o_offset := read_u32(data[offset + 4:], native) or_return
+
+		offset = translated_offset + 8 * n
+		if len(data) < int(offset + 8) { return translation, .MO_File_Invalid }
+
+		t_length := read_u32(data[offset    :], native) or_return
+		t_offset := read_u32(data[offset + 4:], native) or_return
+
+		max_offset := int(max(o_offset + o_length + 1, t_offset + t_length + 1))
+		if len(data) < max_offset { return translation, .Premature_EOF }
+
+		key := data[o_offset:][:o_length]
+		val := data[t_offset:][:t_length]
+
+		/*
+			Could be a pluralized string.
+		*/
+		zero := []byte{0}
+
+		keys := bytes.split(key, zero)
+		vals := bytes.split(val, zero)
+	
+		if len(keys) != len(vals) || max(len(keys), len(vals)) > MAX_PLURALS {
+			return translation, .MO_File_Incorrect_Plural_Count
+		}
+
+		for k in keys {
+			interned_key := strings.intern_get(&translation.intern, string(k))
+
+			interned_vals: [MAX_PLURALS]string = {}
+			last_val: string
+
+			i := 0
+			for v in vals {
+				interned_vals[i] = strings.intern_get(&translation.intern, string(v))
+				last_val = interned_vals[i]
+				i += 1
+			}
+			for ; i < MAX_PLURALS; i += 1 {
+				interned_vals[i] = last_val
+			}
+			translation.k_v[interned_key] = interned_vals
+		}
+		delete(vals)
+		delete(keys)
+	}
+	return
+}
+
+parse_mo_file :: proc(filename: string, pluralizer: proc(int) -> int = nil, allocator := context.allocator) -> (translation: ^Translation, err: Error) {
+	context.allocator = allocator
+
+	data, data_ok := os.read_entire_file(filename)
+	defer delete(data)
+
+	if !data_ok { return {}, .File_Error }
+
+	return parse_mo_from_slice(data, pluralizer)
+}
+
+parse_mo :: proc { parse_mo_file, parse_mo_from_slice }
+
+/*
+	Helpers.
+*/
+read_u32 :: proc(data: []u8, native_endian := true) -> (res: u32, err: Error) {
+	if len(data) < size_of(u32) { return 0, .Premature_EOF }
+
+	val := (^u32)(raw_data(data))^
+
+	if native_endian {
+		return val, .None
+	} else {
+		when ODIN_ENDIAN == .Little {
+			return u32(transmute(u32be)val), .None
+		} else {
+			return u32(transmute(u32le)val), .None
+		}
+	}
+}
+
+read_u16 :: proc(data: []u8, native_endian := true) -> (res: u16, err: Error) {
+	if len(data) < size_of(u16) { return 0, .Premature_EOF }
+
+	val := (^u16)(raw_data(data))^
+
+	if native_endian {
+		return val, .None
+	} else {
+		when ODIN_ENDIAN == .Little {
+			return u16(transmute(u16be)val), .None
+		} else {
+			return u16(transmute(u16le)val), .None
+		}
+	}
+}