// Copyright (c) 2021 Lars Pontoppidan. All rights reserved.
// Use of this source code is governed by an MIT license
// that can be found in the LICENSE file.
module checker

import toml.ast
import toml.ast.walker
import toml.util
import toml.token
import toml.scanner
import encoding.utf8
import time
import strconv

pub const allowed_basic_escape_chars = [`u`, `U`, `b`, `t`, `n`, `f`, `r`, `"`, `\\`]

// utf8_max is the largest inclusive value of the Unicodes scalar value ranges.
const utf8_max = 0x10FFFF

// Checker checks a tree of TOML `ast.Value`'s for common errors.
pub struct Checker {
	scanner &scanner.Scanner = unsafe { nil }
}

// check checks the `ast.Value` and all it's children
// for common errors.
pub fn (c Checker) check(n &ast.Value) ! {
	walker.walk(c, n)!
}

fn (c Checker) visit(value &ast.Value) ! {
	match value {
		ast.Bool {
			c.check_boolean(value)!
		}
		ast.Number {
			c.check_number(value)!
		}
		ast.Quoted {
			c.check_quoted(value)!
		}
		ast.DateTime {
			c.check_date_time(value)!
		}
		ast.Date {
			c.check_date(value)!
		}
		ast.Time {
			c.check_time(value)!
		}
		else {}
	}
}

// excerpt returns a string of the token's surroundings
fn (c Checker) excerpt(tp token.Pos) string {
	return c.scanner.excerpt(tp.pos, 10)
}

// is_hex_bin_oct_prefixed returns true if `hbo` has either
// of: `0x`, `0o` or `0b` - as a prefix.
// Example: assert is_hex_bin_oct_prefixed('0xAF') == true
// Example: assert is_hex_bin_oct_prefixed('xAF') == false
fn is_hex_bin_oct_prefixed(hbo string) bool {
	return hbo.len > 2 && (hbo.starts_with('0x') || hbo.starts_with('0o') || hbo.starts_with('0b'))
}

// has_repeating returns true if `str` has one or more repeating
// `rune` characters provided in `repeats`.
// Example: assert has_repeating('hello__v.', [`.`,`_`]) == true
// Example: assert has_repeating('hello_v.', [`.`,`_`]) == false
fn has_repeating(str string, repeats []rune) bool {
	for i, r in str {
		if r in repeats && i + 1 < str.len {
			if r == str[i + 1] {
				return true
			}
		}
	}
	return false
}

// check_number returns an error if `num` is not a valid TOML number.
fn (c Checker) check_number(num ast.Number) ! {
	lit := num.text
	lit_lower_case := lit.to_lower()
	if lit in ['0', '0.0', '+0', '-0', '+0.0', '-0.0', '0e0', '+0e0', '-0e0', '0e00'] {
		return
	}

	if lit.contains('_') {
		if lit.starts_with('_') || lit.ends_with('_') {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' numbers like "${lit}" can not start or end with `_` in ...${c.excerpt(num.pos)}...')
		}
		if lit.contains('__') {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' numbers like "${lit}" can not have more than one underscore (`_`) in ...${c.excerpt(num.pos)}...')
		}
	}

	mut hex_bin_oct := is_hex_bin_oct_prefixed(lit)
	mut is_bin, mut is_oct, mut is_hex := false, false, false
	is_float := lit_lower_case.all_before('e').contains('.')
	has_exponent_notation := lit_lower_case.contains('e')
	float_decimal_index := lit.index('.') or { -1 }
	// mut is_first_digit := u8(lit[0]).is_digit()
	mut ascii := u8(lit[0]).ascii_str()
	is_sign_prefixed := lit[0] in [`+`, `-`]
	mut lit_sans_sign := lit
	if is_sign_prefixed { // +/- ...
		lit_sans_sign = lit[1..]
		hex_bin_oct = is_hex_bin_oct_prefixed(lit_sans_sign)
		if hex_bin_oct {
			ascii = u8(lit[0]).ascii_str()
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' numbers like "${lit}" (hex, octal and binary) can not start with `${ascii}` in ...${c.excerpt(num.pos)}...')
		}
		if lit.len > 1 && lit_sans_sign.starts_with('0') && !lit_sans_sign.starts_with('0.') {
			ascii = u8(lit_sans_sign[0]).ascii_str()
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' numbers like "${lit}" can not start with `${ascii}` in ...${c.excerpt(num.pos)}...')
		}
	} else {
		if !hex_bin_oct {
			if !is_float && lit[0] == `0` {
				if lit[1] in [`B`, `O`, `X`] {
					return error(@MOD + '.' + @STRUCT + '.' + @FN +
						' numbers like "${lit}" only lowercase notation in ...${c.excerpt(num.pos)}...')
				}
				return error(@MOD + '.' + @STRUCT + '.' + @FN +
					' numbers like "${lit}" can not start with a zero in ...${c.excerpt(num.pos)}...')
			}

			if is_float && lit[0] == `0` && float_decimal_index > 1 {
				return error(@MOD + '.' + @STRUCT + '.' + @FN +
					' numbers like "${lit}" can not start with a zero in ...${c.excerpt(num.pos)}...')
			}
		}
	}

	if has_repeating(lit, [`_`, `.`, `b`, `o`, `x`]) {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' numbers like "${lit}" can not have ${scanner.digit_extras} as repeating characters in ...${c.excerpt(num.pos)}...')
	}

	if hex_bin_oct {
		is_bin = lit_sans_sign.starts_with('0b')
		is_oct = lit_sans_sign.starts_with('0o')
		is_hex = lit_sans_sign.starts_with('0x')

		lit_sans_sign_and_type_prefix := lit_sans_sign[2..]

		if lit_sans_sign_and_type_prefix.starts_with('_')
			|| lit_sans_sign_and_type_prefix.ends_with('_') {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' numbers like "${lit}" can not start or end with `_` in ...${c.excerpt(num.pos)}...')
		}

		if is_bin {
			if !c.is_valid_binary_literal(lit_sans_sign_and_type_prefix) {
				return error(@MOD + '.' + @STRUCT + '.' + @FN +
					' "${lit}" is not a valid binary number in ...${c.excerpt(num.pos)}...')
			}
		} else if is_oct {
			if !c.is_valid_octal_literal(lit_sans_sign_and_type_prefix) {
				return error(@MOD + '.' + @STRUCT + '.' + @FN +
					' "${lit}" is not a valid octal number in ...${c.excerpt(num.pos)}...')
			}
		} else {
			if !c.is_valid_hex_literal(lit_sans_sign_and_type_prefix) {
				return error(@MOD + '.' + @STRUCT + '.' + @FN +
					' "${lit}" is not a valid hexadecimal number in ...${c.excerpt(num.pos)}...')
			}
		}
	}

	if has_exponent_notation {
		if lit_lower_case.all_after('e').starts_with('_')
			|| lit_lower_case.all_before('e').ends_with('_') {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' the exponent in "${lit}" can not start nor end with an underscore in ...${c.excerpt(num.pos)}...')
		}
		if lit_lower_case.all_after('e').contains('.') {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' numbers like "${lit}" (with exponent) can not have a decimal point in ...${c.excerpt(num.pos)}...')
		}
		if !is_hex && lit_lower_case.count('e') > 1 {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' numbers like "${lit}" (with exponent) can only have one exponent in ...${c.excerpt(num.pos)}...')
		}
	}

	if is_float {
		if lit.count('.') > 1 {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' numbers like "${lit}" (float) can only have one decimal point in ...${c.excerpt(num.pos)}...')
		}
		last := lit[lit.len - 1]
		if last in scanner.digit_extras {
			ascii = u8(last).ascii_str()
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' numbers like "${lit}" (float) can not end with `${ascii}` in ...${c.excerpt(num.pos)}...')
		}
		if lit.contains('_.') || lit.contains('._') {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' numbers like "${lit}" (float) can not have underscores before or after the decimal point in ...${c.excerpt(num.pos)}...')
		}
		if lit_lower_case.contains('e.') || lit.contains('.e') {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' numbers like "${lit}" (float) can not have decimal points on either side of the exponent notation in ...${c.excerpt(num.pos)}...')
		}
		// Check if it contains other chars than the allowed
		for r in lit {
			if r !in [`0`, `1`, `2`, `3`, `4`, `5`, `6`, `7`, `8`, `9`, `.`, `e`, `E`, `-`, `+`,
				`_`] {
				return error(@MOD + '.' + @STRUCT + '.' + @FN +
					' numbers like "${lit}" (float) can not contain `${u8(r).ascii_str()}` in ...${c.excerpt(num.pos)}...')
			}
		}
	} else {
		if lit.len > 1 && lit.starts_with('0') && lit[1] !in [`b`, `o`, `x`] {
			ascii = u8(lit[0]).ascii_str()
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' numbers like "${lit}" can not start with `${ascii}` in ...${c.excerpt(num.pos)}...')
		}
	}
}

// is_valid_binary_literal returns true if `num` is valid TOML binary literal.
fn (c Checker) is_valid_binary_literal(num string) bool {
	for ch in num {
		if ch == `_` {
			continue
		}
		if !(ch >= `0` && ch <= `1`) {
			return false
		}
	}
	return true
}

// is_valid_octal_literal returns true if `num` is valid TOML octal literal.
fn (c Checker) is_valid_octal_literal(num string) bool {
	for ch in num {
		if ch == `_` {
			continue
		}
		if !(ch >= `0` && ch <= `7`) {
			return false
		}
	}
	return true
}

// is_valid_hex_literal returns true if `num` is valid TOML hexadecimal literal.
fn (c Checker) is_valid_hex_literal(num string) bool {
	for ch in num {
		if ch == `_` {
			continue
		}
		if !ch.is_hex_digit() {
			return false
		}
	}
	return true
}

// check_boolean returns an error if `b` is not a valid TOML boolean.
fn (c Checker) check_boolean(b ast.Bool) ! {
	lit := b.text
	if lit in ['true', 'false'] {
		return
	}
	return error(@MOD + '.' + @STRUCT + '.' + @FN +
		' boolean values like "${lit}" can only be `true` or `false` literals, not `${lit}` in ...${c.excerpt(b.pos)}...')
}

// check_date_time returns an error if `dt` is not a valid TOML date-time string (RFC 3339).
// See also https://ijmacd.github.io/rfc3339-iso8601 for a more
// visual representation of the RFC 3339 format.
fn (c Checker) check_date_time(dt ast.DateTime) ! {
	lit := dt.text
	mut split := []string{}
	// RFC 3339 Date-Times can be split via 4 separators (` `, `_`, `T` and `t`).
	if lit.to_lower().contains_any(' _t') {
		if lit.contains(' ') {
			split = lit.split(' ')
		} else if lit.contains('_') {
			split = lit.split('_')
		} else if lit.contains('T') {
			split = lit.split('T')
		} else if lit.contains('t') {
			split = lit.split('t')
		}
		// Validate the split into date and time parts.
		if split.len != 2 {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' "${lit}" contains too many date/time separators in ...${c.excerpt(dt.pos)}...')
		}
		// Re-use date and time validation code for detailed testing of each part
		c.check_date(ast.Date{
			text: split[0]
			pos: token.Pos{
				len: split[0].len
				line_nr: dt.pos.line_nr
				pos: dt.pos.pos
				col: dt.pos.col
			}
		})!
		c.check_time(ast.Time{
			text: split[1]
			pos: token.Pos{
				len: split[1].len
				line_nr: dt.pos.line_nr
				pos: dt.pos.pos + split[0].len
				col: dt.pos.col + split[0].len
			}
		})!
		// Use V's builtin functionality to validate the string
		time.parse_rfc3339(lit) or {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' "${lit}" is not a valid RFC 3339 Date-Time format string "${err}". In ...${c.excerpt(dt.pos)}...')
		}
	} else {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' "${lit}" is not a valid RFC 3339 Date-Time format string in ...${c.excerpt(dt.pos)}...')
	}
}

// check_time returns an error if `date` is not a valid TOML date string (RFC 3339).
fn (c Checker) check_date(date ast.Date) ! {
	lit := date.text
	parts := lit.split('-')
	if parts.len != 3 {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' "${lit}" is not a valid RFC 3339 Date format string in ...${c.excerpt(date.pos)}...')
	}
	yyyy := parts[0]
	if yyyy.len != 4 {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' "${lit}" does not have a valid RFC 3339 year indication in ...${c.excerpt(date.pos)}...')
	}
	mm := parts[1]
	if mm.len != 2 {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' "${lit}" does not have a valid RFC 3339 month indication in ...${c.excerpt(date.pos)}...')
	}
	dd := parts[2]
	if dd.len != 2 {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' "${lit}" does not have a valid RFC 3339 day indication in ...${c.excerpt(date.pos)}...')
	}
	// Use V's builtin functionality to validate the string
	time.parse_rfc3339(lit) or {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' "${lit}" is not a valid RFC 3339 Date format string "${err}". In ...${c.excerpt(date.pos)}...')
	}
}

// check_time returns an error if `t` is not a valid TOML time string (RFC 3339).
fn (c Checker) check_time(t ast.Time) ! {
	lit := t.text
	// Split any offsets from the time
	mut offset_splitter := if lit.contains('+') { '+' } else { '-' }
	parts := lit.split(offset_splitter)
	mut hhmmss := parts[0].all_before('.')
	// Check for 2 digits in all fields
	mut check_length := 8
	if hhmmss.to_upper().ends_with('Z') {
		check_length++
	}
	if hhmmss.len != check_length {
		starts_with_zero := hhmmss.starts_with('0')
		if !starts_with_zero {
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' "${lit}" must be zero prefixed in ...${c.excerpt(t.pos)}...')
		}
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' "${lit}" is not a valid RFC 3339 Time format string in ...${c.excerpt(t.pos)}...')
	}
	// Use V's builtin functionality to validate the time string
	time.parse_rfc3339(parts[0]) or {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' "${lit}" is not a valid RFC 3339 Time format string "${err}". In ...${c.excerpt(t.pos)}...')
	}
}

// check_quoted returns an error if `q` is not a valid quoted TOML string.
pub fn (c Checker) check_quoted(q ast.Quoted) ! {
	lit := q.text
	quote := q.quote.ascii_str()
	triple_quote := quote + quote + quote
	if q.is_multiline && lit.ends_with(triple_quote) {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' string values like "${lit}" has unbalanced quote literals `q.quote` in ...${c.excerpt(q.pos)}...')
	}
	c.check_quoted_escapes(q)!
	c.check_utf8_validity(q)!
}

// check_quoted_escapes returns an error for any disallowed escape sequences.
// Delimiters in TOML has significant meaning:
// '/''' delimits *literal* strings (WYSIWYG / What-you-see-is-what-you-get)
// "/""" delimits *basic* strings
// Allowed escapes in *basic* strings are:
// \b         - backspace       (U+0008)
// \t         - tab             (U+0009)
// \n         - linefeed        (U+000A)
// \f         - form feed       (U+000C)
// \r         - carriage return (U+000D)
// \"         - quote           (U+0022)
// \\         - backslash       (U+005C)
// \uXXXX     - Unicode         (U+XXXX)
// \UXXXXXXXX - Unicode         (U+XXXXXXXX)
fn (c Checker) check_quoted_escapes(q ast.Quoted) ! {
	// Setup a scanner in stack memory for easier navigation.
	mut s := scanner.new_simple_text(q.text)!

	// See https://toml.io/en/v1.0.0#string for more info on string types.
	is_basic := q.quote == `\"`
	contains_newlines := q.text.contains('\n')
	for {
		ch := s.next()
		if ch == scanner.end_of_text {
			break
		}
		ch_byte := u8(ch)
		if ch == `\\` {
			next_ch := u8(s.at())

			if next_ch == `\\` {
				s.next()
				continue
			}

			escape := ch_byte.ascii_str() + next_ch.ascii_str()
			if is_basic {
				if q.is_multiline {
					if next_ch == ` ` {
						if !contains_newlines {
							st := s.state()
							return error(@MOD + '.' + @STRUCT + '.' + @FN +
								' can not escape whitespaces in multi-line strings (`\\ `) at `${escape}` (${st.line_nr},${st.col}) in ...${c.excerpt(q.pos)}...')
						}
						// Rest of line must only be space chars from this point on
						for {
							ch_ := s.next()
							if ch_ == scanner.end_of_text || ch_ == `\n` {
								break
							}
							if !(ch_ == ` ` || ch_ == `\t`) {
								st := s.state()
								return error(@MOD + '.' + @STRUCT + '.' + @FN +
									' invalid character `${u8(ch_).ascii_str()}` after `${escape}` at (${st.line_nr},${st.col}) in ...${c.excerpt(q.pos)}...')
							}
						}
					}
					if next_ch in [`\t`, `\n`, ` `] {
						s.next()
						continue
					}
				}
				if next_ch !in checker.allowed_basic_escape_chars {
					st := s.state()
					return error(@MOD + '.' + @STRUCT + '.' + @FN +
						' unknown basic string escape character `${next_ch.ascii_str()}` in `${escape}` (${st.line_nr},${st.col}) in ...${c.excerpt(q.pos)}...')
				}
			}
			// Check Unicode escapes
			if is_basic && escape.to_lower() == '\\u' {
				// Long type Unicode (\UXXXXXXXX) is a maximum of 10 chars: '\' + 'U' + 8 hex characters
				// we pass in 10 characters from the `u`/`U` which is the longest possible sequence
				// of 9 chars plus one extra.
				if s.remaining() >= 10 {
					pos := s.state().pos
					c.check_unicode_escape(s.text[pos..pos + 11]) or {
						st := s.state()
						return error(@MOD + '.' + @STRUCT + '.' + @FN +
							' escaped Unicode is invalid. ${err.msg().capitalize()} (${st.line_nr},${st.col}) in ...${c.excerpt(q.pos)}...')
					}
				} else {
					pos := s.state().pos
					c.check_unicode_escape(s.text[pos..]) or {
						st := s.state()
						return error(@MOD + '.' + @STRUCT + '.' + @FN +
							' escaped Unicode is invalid. ${err.msg().capitalize()} (${st.line_nr},${st.col}) in ...${c.excerpt(q.pos)}...')
					}
				}
			}
		}
	}
}

// check_utf8_string returns an error if `str` is not valid UTF-8.
fn (c Checker) check_utf8_validity(q ast.Quoted) ! {
	lit := q.text
	if !utf8.validate_str(lit) {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' the string value "${lit}" is not valid UTF-8 in ...${c.excerpt(q.pos)}...')
	}
}

// validate_utf8_codepoint_string returns an error if `str` is not a valid Unicode code point.
// `str` is expected to be a `string` containing *only* hex values.
// Any preludes or prefixes like `0x` could pontentially yield wrong results.
fn validate_utf8_codepoint_string(str string) ! {
	int_val := strconv.parse_int(str, 16, 64) or { i64(-1) }
	if int_val > checker.utf8_max || int_val < 0 {
		return error('Unicode code point `${str}` is outside the valid Unicode scalar value ranges.')
	}
	// Check if the Unicode value is actually in the valid Unicode scalar value ranges.
	// TODO should probably be transferred / implemented in `utf8.validate(...)` also?
	if !((int_val >= 0x0000 && int_val <= 0xD7FF) || (int_val >= 0xE000 && int_val <= 0x10FFFF)) {
		return error('Unicode code point `${str}` is not a valid Unicode scalar value.')
	}
	bytes := str.bytes()
	if !utf8.validate(bytes.data, bytes.len) {
		return error('Unicode code point `${str}` is not a valid UTF-8 code point.')
	}
}

// check_unicode_escape returns an error if `esc_unicode` is not
// a valid Unicode escape sequence. `esc_unicode` is expected to be
// prefixed with either `u` or `U`.
fn (c Checker) check_unicode_escape(esc_unicode string) ! {
	if esc_unicode.len < 5 || !esc_unicode.to_lower().starts_with('u') {
		// Makes sure the input to this function is actually valid.
		return error('`${esc_unicode}` is not a valid escaped Unicode sequence.')
	}
	is_long_esc_type := esc_unicode.starts_with('U')
	mut sequence := esc_unicode[1..]
	hex_digits_len := if is_long_esc_type { 8 } else { 4 }
	if sequence.len < hex_digits_len {
		return error('Unicode escape sequence `${esc_unicode}` should be at least ${hex_digits_len} in length.')
	}
	sequence = sequence[..hex_digits_len]
	// TODO not enforced in BurnSushi testsuite??
	// if !sequence.is_upper() {
	//	return error('Unicode escape sequence `$esc_unicode` is not in all uppercase.')
	//}
	validate_utf8_codepoint_string(sequence.to_upper())!
	if is_long_esc_type {
		// Long escape type checks
	} else {
		// Short escape type checks
	}
}

// check_comment returns an error if the contents of `comment` isn't
// a valid TOML comment.
pub fn (c Checker) check_comment(comment ast.Comment) ! {
	lit := comment.text
	// Setup a scanner in stack memory for easier navigation.
	mut s := scanner.new_simple_text(lit)!
	for {
		ch := s.next()
		if ch == scanner.end_of_text {
			break
		}
		ch_byte := u8(ch)
		// Check for carrige return
		if ch_byte == 0x0D {
			st := s.state()
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' carrige return character `${ch_byte.hex()}` is not allowed in comments (${st.line_nr},${st.col}).')
		}
		// Check for control characters (allow TAB)
		if util.is_illegal_ascii_control_character(ch_byte) {
			st := s.state()
			return error(@MOD + '.' + @STRUCT + '.' + @FN +
				' control character `${ch_byte.hex()}` is not allowed (${st.line_nr},${st.col}) "${u8(s.at()).ascii_str()}" near ...${s.excerpt(st.pos, 10)}...')
		}
	}

	// Check for bad UTF-8 encoding
	if !utf8.validate_str(lit) {
		return error(@MOD + '.' + @STRUCT + '.' + @FN +
			' comment "${lit}" is not valid UTF-8 in ...${c.excerpt(comment.pos)}...')
	}
}