package yaml

import (

	"io"

)

// Set the reader error and return 0.

func yaml_parser_set_reader_error(parser *yaml_parser_t, problem string, offset int, value int) bool {

	parser.error = yaml_READER_ERROR

	parser.problem = problem

	parser.problem_offset = offset

	parser.problem_value = value

	return false

}

// Byte order marks.

const (

	bom_UTF8    = "\xef\xbb\xbf"

	bom_UTF16LE = "\xff\xfe"

	bom_UTF16BE = "\xfe\xff"

)

// Determine the input stream encoding by checking the BOM symbol. If no BOM is

// found, the UTF-8 encoding is assumed. Return 1 on success, 0 on failure.

func yaml_parser_determine_encoding(parser *yaml_parser_t) bool {

	// Ensure that we had enough bytes in the raw buffer.

	for !parser.eof && len(parser.raw_buffer)-parser.raw_buffer_pos < 3 {

		if !yaml_parser_update_raw_buffer(parser) {

			return false

		}

	}

	// Determine the encoding.

	buf := parser.raw_buffer

	pos := parser.raw_buffer_pos

	avail := len(buf) - pos

	if avail >= 2 && buf[pos] == bom_UTF16LE[0] && buf[pos+1] == bom_UTF16LE[1] {

		parser.encoding = yaml_UTF16LE_ENCODING

		parser.raw_buffer_pos += 2

		parser.offset += 2

	} else if avail >= 2 && buf[pos] == bom_UTF16BE[0] && buf[pos+1] == bom_UTF16BE[1] {

		parser.encoding = yaml_UTF16BE_ENCODING

		parser.raw_buffer_pos += 2

		parser.offset += 2

	} else if avail >= 3 && buf[pos] == bom_UTF8[0] && buf[pos+1] == bom_UTF8[1] && buf[pos+2] == bom_UTF8[2] {

		parser.encoding = yaml_UTF8_ENCODING

		parser.raw_buffer_pos += 3

		parser.offset += 3

	} else {

		parser.encoding = yaml_UTF8_ENCODING

	}

	return true

}

// Update the raw buffer.

func yaml_parser_update_raw_buffer(parser *yaml_parser_t) bool {

	size_read := 0

	// Return if the raw buffer is full.

	if parser.raw_buffer_pos == 0 && len(parser.raw_buffer) == cap(parser.raw_buffer) {

		return true

	}

	// Return on EOF.

	if parser.eof {

		return true

	}

	// Move the remaining bytes in the raw buffer to the beginning.

	if parser.raw_buffer_pos > 0 && parser.raw_buffer_pos < len(parser.raw_buffer) {

		copy(parser.raw_buffer, parser.raw_buffer[parser.raw_buffer_pos:])

	}

	parser.raw_buffer = parser.raw_buffer[:len(parser.raw_buffer)-parser.raw_buffer_pos]

	parser.raw_buffer_pos = 0

	// Call the read handler to fill the buffer.

	size_read, err := parser.read_handler(parser, parser.raw_buffer[len(parser.raw_buffer):cap(parser.raw_buffer)])

	parser.raw_buffer = parser.raw_buffer[:len(parser.raw_buffer)+size_read]

	if err == io.EOF {

		parser.eof = true

	} else if err != nil {

		return yaml_parser_set_reader_error(parser, "input error: "+err.Error(), parser.offset, -1)

	}

	return true

}

// Ensure that the buffer contains at least `length` characters.

// Return true on success, false on failure.

//

// The length is supposed to be significantly less that the buffer size.

func yaml_parser_update_buffer(parser *yaml_parser_t, length int) bool {

	if parser.read_handler == nil {

		panic("read handler must be set")

	}

	// [Go] This function was changed to guarantee the requested length size at EOF.

	// The fact we need to do this is pretty awful, but the description above implies

	// for that to be the case, and there are tests 

	// If the EOF flag is set and the raw buffer is empty, do nothing.

	if parser.eof && parser.raw_buffer_pos == len(parser.raw_buffer) {

		// [Go] ACTUALLY! Read the documentation of this function above.

		// This is just broken. To return true, we need to have the

		// given length in the buffer. Not doing that means every single

		// check that calls this function to make sure the buffer has a

		// given length is Go) panicking; or C) accessing invalid memory.

		//return true

	}

	// Return if the buffer contains enough characters.

	if parser.unread >= length {

		return true

	}

	// Determine the input encoding if it is not known yet.

	if parser.encoding == yaml_ANY_ENCODING {

		if !yaml_parser_determine_encoding(parser) {

			return false

		}

	}

	// Move the unread characters to the beginning of the buffer.

	buffer_len := len(parser.buffer)

	if parser.buffer_pos > 0 && parser.buffer_pos < buffer_len {

		copy(parser.buffer, parser.buffer[parser.buffer_pos:])

		buffer_len -= parser.buffer_pos

		parser.buffer_pos = 0

	} else if parser.buffer_pos == buffer_len {

		buffer_len = 0

		parser.buffer_pos = 0

	}

	// Open the whole buffer for writing, and cut it before returning.

	parser.buffer = parser.buffer[:cap(parser.buffer)]

	// Fill the buffer until it has enough characters.

	first := true

	for parser.unread < length {

		// Fill the raw buffer if necessary.

		if !first || parser.raw_buffer_pos == len(parser.raw_buffer) {

			if !yaml_parser_update_raw_buffer(parser) {

				parser.buffer = parser.buffer[:buffer_len]

				return false

			}

		}

		first = false

		// Decode the raw buffer.

	inner:

		for parser.raw_buffer_pos != len(parser.raw_buffer) {

			var value rune

			var width int

			raw_unread := len(parser.raw_buffer) - parser.raw_buffer_pos

			// Decode the next character.

			switch parser.encoding {

			case yaml_UTF8_ENCODING:

				// Decode a UTF-8 character.  Check RFC 3629

				// (http://www.ietf.org/rfc/rfc3629.txt) for more details.

				//

				// The following table (taken from the RFC) is used for

				// decoding.

				//

				//    Char. number range |        UTF-8 octet sequence

				//      (hexadecimal)    |              (binary)

				//   --------------------+------------------------------------

				//   0000 0000-0000 007F | 0xxxxxxx

				//   0000 0080-0000 07FF | 110xxxxx 10xxxxxx

				//   0000 0800-0000 FFFF | 1110xxxx 10xxxxxx 10xxxxxx

				//   0001 0000-0010 FFFF | 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

				//

				// Additionally, the characters in the range 0xD800-0xDFFF

				// are prohibited as they are reserved for use with UTF-16

				// surrogate pairs.

				// Determine the length of the UTF-8 sequence.

				octet := parser.raw_buffer[parser.raw_buffer_pos]

				switch {

				case octet&0x80 == 0x00:

					width = 1

				case octet&0xE0 == 0xC0:

					width = 2

				case octet&0xF0 == 0xE0:

					width = 3

				case octet&0xF8 == 0xF0:

					width = 4

				default:

					// The leading octet is invalid.

					return yaml_parser_set_reader_error(parser,

						"invalid leading UTF-8 octet",

						parser.offset, int(octet))

				}

				// Check if the raw buffer contains an incomplete character.

				if width > raw_unread {

					if parser.eof {

						return yaml_parser_set_reader_error(parser,

							"incomplete UTF-8 octet sequence",

							parser.offset, -1)

					}

					break inner

				}

				// Decode the leading octet.

				switch {

				case octet&0x80 == 0x00:

					value = rune(octet & 0x7F)

				case octet&0xE0 == 0xC0:

					value = rune(octet & 0x1F)

				case octet&0xF0 == 0xE0:

					value = rune(octet & 0x0F)

				case octet&0xF8 == 0xF0:

					value = rune(octet & 0x07)

				default:

					value = 0

				}

				// Check and decode the trailing octets.

				for k := 1; k < width; k++ {

					octet = parser.raw_buffer[parser.raw_buffer_pos+k]

					// Check if the octet is valid.

					if (octet & 0xC0) != 0x80 {

						return yaml_parser_set_reader_error(parser,

							"invalid trailing UTF-8 octet",

							parser.offset+k, int(octet))

					}

					// Decode the octet.

					value = (value << 6) + rune(octet&0x3F)

				}

				// Check the length of the sequence against the value.

				switch {

				case width == 1:

				case width == 2 && value >= 0x80:

				case width == 3 && value >= 0x800:

				case width == 4 && value >= 0x10000:

				default:

					return yaml_parser_set_reader_error(parser,

						"invalid length of a UTF-8 sequence",

						parser.offset, -1)

				}

				// Check the range of the value.

				if value >= 0xD800 && value <= 0xDFFF || value > 0x10FFFF {

					return yaml_parser_set_reader_error(parser,

						"invalid Unicode character",

						parser.offset, int(value))

				}

			case yaml_UTF16LE_ENCODING, yaml_UTF16BE_ENCODING:

				var low, high int

				if parser.encoding == yaml_UTF16LE_ENCODING {

					low, high = 0, 1

				} else {

					low, high = 1, 0

				}

				// The UTF-16 encoding is not as simple as one might

				// naively think.  Check RFC 2781

				// (http://www.ietf.org/rfc/rfc2781.txt).

				//

				// Normally, two subsequent bytes describe a Unicode

				// character.  However a special technique (called a

				// surrogate pair) is used for specifying character

				// values larger than 0xFFFF.

				//

				// A surrogate pair consists of two pseudo-characters:

				//      high surrogate area (0xD800-0xDBFF)

				//      low surrogate area (0xDC00-0xDFFF)

				//

				// The following formulas are used for decoding

				// and encoding characters using surrogate pairs:

				//

				//  U  = U' + 0x10000   (0x01 00 00 <= U <= 0x10 FF FF)

				//  U' = yyyyyyyyyyxxxxxxxxxx   (0 <= U' <= 0x0F FF FF)

				//  W1 = 110110yyyyyyyyyy

				//  W2 = 110111xxxxxxxxxx

				//

				// where U is the character value, W1 is the high surrogate

				// area, W2 is the low surrogate area.

				// Check for incomplete UTF-16 character.

				if raw_unread < 2 {

					if parser.eof {

						return yaml_parser_set_reader_error(parser,

							"incomplete UTF-16 character",

							parser.offset, -1)

					}

					break inner

				}

				// Get the character.

				value = rune(parser.raw_buffer[parser.raw_buffer_pos+low]) +

					(rune(parser.raw_buffer[parser.raw_buffer_pos+high]) << 8)

				// Check for unexpected low surrogate area.

				if value&0xFC00 == 0xDC00 {

					return yaml_parser_set_reader_error(parser,

						"unexpected low surrogate area",

						parser.offset, int(value))

				}

				// Check for a high surrogate area.

				if value&0xFC00 == 0xD800 {

					width = 4

					// Check for incomplete surrogate pair.

					if raw_unread < 4 {

						if parser.eof {

							return yaml_parser_set_reader_error(parser,

								"incomplete UTF-16 surrogate pair",

								parser.offset, -1)

						}

						break inner

					}

					// Get the next character.

					value2 := rune(parser.raw_buffer[parser.raw_buffer_pos+low+2]) +

						(rune(parser.raw_buffer[parser.raw_buffer_pos+high+2]) << 8)

					// Check for a low surrogate area.

					if value2&0xFC00 != 0xDC00 {

						return yaml_parser_set_reader_error(parser,

							"expected low surrogate area",

							parser.offset+2, int(value2))

					}

					// Generate the value of the surrogate pair.

					value = 0x10000 + ((value & 0x3FF) << 10) + (value2 & 0x3FF)

				} else {

					width = 2

				}

			default:

				panic("impossible")

			}

			// Check if the character is in the allowed range:

			//      #x9 | #xA | #xD | [#x20-#x7E]               (8 bit)

			//      | #x85 | [#xA0-#xD7FF] | [#xE000-#xFFFD]    (16 bit)

			//      | [#x10000-#x10FFFF]                        (32 bit)

			switch {

			case value == 0x09:

			case value == 0x0A:

			case value == 0x0D:

			case value >= 0x20 && value <= 0x7E:

			case value == 0x85:

			case value >= 0xA0 && value <= 0xD7FF:

			case value >= 0xE000 && value <= 0xFFFD:

			case value >= 0x10000 && value <= 0x10FFFF:

			default:

				return yaml_parser_set_reader_error(parser,

					"control characters are not allowed",

					parser.offset, int(value))

			}

			// Move the raw pointers.

			parser.raw_buffer_pos += width

			parser.offset += width

			// Finally put the character into the buffer.

			if value <= 0x7F {

				// 0000 0000-0000 007F . 0xxxxxxx

				parser.buffer[buffer_len+0] = byte(value)

				buffer_len += 1

			} else if value <= 0x7FF {

				// 0000 0080-0000 07FF . 110xxxxx 10xxxxxx

				parser.buffer[buffer_len+0] = byte(0xC0 + (value >> 6))

				parser.buffer[buffer_len+1] = byte(0x80 + (value & 0x3F))

				buffer_len += 2

			} else if value <= 0xFFFF {

				// 0000 0800-0000 FFFF . 1110xxxx 10xxxxxx 10xxxxxx

				parser.buffer[buffer_len+0] = byte(0xE0 + (value >> 12))

				parser.buffer[buffer_len+1] = byte(0x80 + ((value >> 6) & 0x3F))

				parser.buffer[buffer_len+2] = byte(0x80 + (value & 0x3F))

				buffer_len += 3

			} else {

				// 0001 0000-0010 FFFF . 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx

				parser.buffer[buffer_len+0] = byte(0xF0 + (value >> 18))

				parser.buffer[buffer_len+1] = byte(0x80 + ((value >> 12) & 0x3F))

				parser.buffer[buffer_len+2] = byte(0x80 + ((value >> 6) & 0x3F))

				parser.buffer[buffer_len+3] = byte(0x80 + (value & 0x3F))

				buffer_len += 4

			}

			parser.unread++

		}

		// On EOF, put NUL into the buffer and return.

		if parser.eof {

			parser.buffer[buffer_len] = 0

			buffer_len++

			parser.unread++

			break

		}

	}

	// [Go] Read the documentation of this function above. To return true,

	// we need to have the given length in the buffer. Not doing that means

	// every single check that calls this function to make sure the buffer

	// has a given length is Go) panicking; or C) accessing invalid memory.

	// This happens here due to the EOF above breaking early.

	for buffer_len < length {

		parser.buffer[buffer_len] = 0

		buffer_len++

	}

	parser.buffer = parser.buffer[:buffer_len]

	return true

}