package parser

import "git.makaay.nl/mauricem/go-parsekit"

var (
	// There are four ways to express strings: basic, multi-line basic,
	// literal, and multi-line literal. All strings must contain only valid
	// UTF-8 characters.  * Multi-line basic strings are surrounded by three
	// quotation marks on each side.  * Basic strings are surrounded by
	// quotation marks.
	doubleQuote3 = c.String(`"""`)

	// Any Unicode character may be used except those that must be escaped:
	// quotation mark, backslash, and the control characters (U+0000 to
	// U+001F, U+007F).
	charThatMustBeEscaped = c.AnyOf(c.RuneRange('\u0000', '\u001F'), c.Rune('\u007F'))

	// For convenience, some popular characters have a compact escape sequence.
	//
	// \b         - backspace       (U+0008)
	// \t         - tab             (U+0009)
	// \n         - LF        (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)
	validEscapeChar = c.AnyOf(c.Runes('b', 't', 'n', 'f', 'r'), a.DoubleQuote, a.Backslash)
	shortEscape     = c.Sequence(a.Backslash, validEscapeChar)
	shortUTF8Escape = c.Sequence(a.Backslash, c.Rune('u'), c.Repeat(4, a.HexDigit))
	longUTF8Escape  = c.Sequence(a.Backslash, c.Rune('U'), c.Repeat(8, a.HexDigit))
	validEscape     = c.AnyOf(shortEscape, shortUTF8Escape, longUTF8Escape)
)

func startString(p *parsekit.P) {
	p.Expects("a string value")
	switch {
	case p.On(doubleQuote3).RouteTo(startMultiLineBasicString).End():
	case p.On(a.DoubleQuote).RouteTo(startBasicString).End():
	}
}

func startBasicString(p *parsekit.P) {
	p.Expects("a basic string")
	p.On(a.DoubleQuote).Skip().RouteTo(parseBasicString).ThenTo(basicStringSpecifics)
}

func parseBasicString(p *parsekit.P) {
	p.Expects("string contents")
	switch {
	case p.On(charThatMustBeEscaped).End():
		p.EmitError("invalid character in basic string: %q (must be escaped)", p.LastMatch)
	case p.On(validEscape).Accept().RouteRepeat().End():
	case p.On(a.Backslash).RouteReturn().End():
	case p.On(a.DoubleQuote).RouteReturn().End():
	case p.On(a.AnyRune).Accept().RouteRepeat().End():
	}
}

// Specific handling of input for basic strings.
// * A double quote ends the string
// * No additional \escape sequences are allowed. What the spec say about this:
//   "All other escape sequences [..] are reserved and, if used, TOML should
//    produce an error.""
func basicStringSpecifics(p *parsekit.P) {
	p.Expects("string contents")
	switch {
	case p.On(a.DoubleQuote).Skip().End():
		p.EmitInterpreted(ItemString)
		p.RouteTo(startKeyValuePair)
	case p.On(a.Backslash).End():
		p.EmitError("invalid escape sequence")
	}
}

func startMultiLineBasicString(p *parsekit.P) {
	p.Expects("a multi-line basic string")
	if p.On(doubleQuote3).Skip().End() {
		p.EmitError("not yet implemented")
	}
}