package locale

import (
	"bufio"
	"fmt"
	"io"
	"regexp"
	"strconv"
	"strings"
	"unicode/utf8"
)

// TODO: Is this correct? Does it handle malformed input?
var wordRegex = regexp.MustCompile(`[^\s"']+|"([^"]*)"|'([^']*)`)

// Parse transforms a text-definition of a locale into a Def
func Parse(in io.Reader) (def Def, err error) {
	s := bufio.NewScanner(in)

	commentChar := '#'
	escapeChar := '\\'
	lineNum := 0
	curCategory := ""

	// Catch any errors
	defer func() {
		if r := recover(); r != nil {
			def = Def{}
			err = fmt.Errorf("Line %d: %s", lineNum, r)
		}
	}()

	// A closure to simplify error handling
	die := func(format string, args ...interface{}) {
		panic(fmt.Errorf("line %d: %s", lineNum, fmt.Sprintf(format, args)))
	}

	// More closures to make assertions and parse input
	requireCategory := func(category, keyword string) {
		if category != curCategory {
			die("keyword %s is only applicable in category %s (current: '%s')", keyword, category, curCategory)
		}
	}
	requireString := func(val string) string {
		// TODO: Bug with escaped quote characters.
		if val[0] != '"' || val[len(val)-1] != '"' {
			die("Value '%s' needs to be a double-quoted string", val)
		}
		return val[1 : len(val)-1]
	}
	requireInt := func(val string) int {
		n, err := strconv.Atoi(val)
		if err != nil {
			die("%s is not an integer", val)
		}
		return n
	}
	requireChar := func(val string) string {
		if val[0] != '<' || val[len(val)-1] != '>' {
			die("character %s must be surrounded by angle brackets", val)
		}
		return val[1 : len(val)-1]
	}
	requireCharList := func(val string) []string {
		var out []string
		for _, s := range strings.Split(val, ";") {
			out = append(out, requireChar(s))
		}
		return out
	}
	requireCharPair := func(pair string) (first, second string) {
		if pair[0] != '(' || pair[len(pair)-1] != ')' {
			die("character pair '%s' not in parentheses", pair)
		}
		parts := strings.Split(pair[1:len(pair)-1], ",")
		if len(parts) != 2 {
			die("Need 2 elements in pair '%s'", pair)
		}
		return requireChar(parts[0]), requireChar(parts[1])
	}

	for s.Scan() {
		lineNum++
		line := s.Text()
		// Discard comment lines
		firstRune, _ := utf8.DecodeRuneInString(line)
		if firstRune == commentChar {
			continue
		}

		// Join newlines if they end with the escapeChar
		// TODO: This is very inefficient
		for {
			var lastRune rune
			for _, r := range line {
				lastRune = r
			}
			if lastRune != escapeChar {
				break
			}
			if lastRune == escapeChar {
				if !s.Scan() {
					die("Line continuation at end of file")
					return Def{}, fmt.Errorf("line continuation on line %d was not followed by another line", lineNum)
				}
				line += strings.TrimSpace(s.Text())
				lineNum++
			}
		}

		// TODO: Find more robust way to split
		words := wordRegex.FindAllString(line, -1)
		if len(words) == 0 {
			continue
		}

		if len(words) == 1 {
			// Only category declarations can have only 1 word
			switch words[0] {
			case "LC_CTYPE", "LC_COLLATE", "LC_MONETARY", "LC_NUMERIC", "LC_TIME", "LC_MESSAGES":
				curCategory = words[0]
			default:
				die("Unrecognized category name %s", words[0])
			}
			continue
		}

		// No line can have more than 2 words
		if len(words) > 2 {
			return Def{}, fmt.Errorf("line %d contains too many words: %s", lineNum, words)
		}

		// Logic!
		keyword, val := words[0], words[1]
		switch keyword {
		// Header blocks
		case "comment_char":
			if curCategory != "" {
				return Def{}, fmt.Errorf("line %d: unexpected %s during category %s", lineNum, keyword, curCategory)
			}
			commentChar, _ = utf8.DecodeRuneInString(words[1])
		case "escape_char":
			if curCategory != "" {
				return Def{}, fmt.Errorf("line %d: unexpected %s during category %s", lineNum, keyword, curCategory)
			}
			escapeChar, _ = utf8.DecodeRuneInString(words[1])
		// End block
		case "END":
			if val != curCategory {
				return Def{}, fmt.Errorf("line %d: tried to end category %s during %s", lineNum, val, curCategory)
			}
			curCategory = ""
			// Ctype values
		case "charclass":
			requireCategory("LC_CTYPE", keyword)
			for _, cc := range strings.Split(val, ";") {
				if _, in := def.ctype.other[cc]; !in {
					def.ctype.other[cc] = make([]string, 0)
				}
			}
		case "upper":
			requireCategory("LC_CTYPE", keyword)
			def.ctype.upper = requireCharList(val)
		case "lower":
			requireCategory("LC_CTYPE", keyword)
			def.ctype.lower = requireCharList(val)
		case "alpha":
			requireCategory("LC_CTYPE", keyword)
			def.ctype.alpha = requireCharList(val)
		case "digit":
			requireCategory("LC_CTYPE", keyword)
			def.ctype.digit = requireCharList(val)
		case "alnum":
			requireCategory("LC_CTYPE", keyword)
			def.ctype.alnum = requireCharList(val)
		case "space":
			requireCategory("LC_CTYPE", keyword)
			def.ctype.space = requireCharList(val)
		case "cntrl":
			requireCategory("LC_CTYPE", keyword)
			def.ctype.cntrl = requireCharList(val)
		case "punct":
			requireCategory("LC_CTYPE", keyword)
			def.ctype.punct = requireCharList(val)
		case "graph":
			requireCategory("LC_CTYPE", keyword)
			def.ctype.graph = requireCharList(val)
		case "print":
			requireCategory("LC_CTYPE", keyword)
			def.ctype.print = requireCharList(val)
		case "xdigit":
			requireCategory("LC_CTYPE", keyword)
			def.ctype.xdigit = requireCharList(val)
		case "blank":
			requireCategory("LC_CTYPE", keyword)
			def.ctype.blank = requireCharList(val)
		case "toupper":
			for _, pair := range strings.Split(val, ";") {
				lower, upper := requireCharPair(pair)
				def.ctype.toupper[lower] = upper
			}
		case "tolower":
			for _, pair := range strings.Split(val, ";") {
				upper, lower := requireCharPair(pair)
				def.ctype.tolower[upper] = lower
			}

		// Monetary values
		case "int_curr_symbol":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.intCurrSymbol = requireString(val)
		case "currency_symbol":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.currencySymbol = requireString(val)
		case "mon_decimal_point":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.monDecimalPoint = requireString(val)
		case "mon_thousands_sep":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.monThousandsSep = requireString(val)
		case "mon_grouping":
			requireCategory("LC_MONETARY", keyword)
			for _, s := range strings.Split(val, ";") {
				def.monetary.monGrouping = append(def.monetary.monGrouping, requireInt(s))
			}
		case "positive_sign":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.positiveSign = val
		case "negative_sign":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.negativeSign = val
		case "int_frac_digits":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.intFracDigits = requireInt(val)
		case "frac_digits":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.fracDigits = requireInt(val)
		case "p_cs_precedes":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.pCsPrecedes = requireInt(val)
		case "p_sep_by_space":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.pSepBySpace = requireInt(val)
		case "n_cs_precedes":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.nCsPrecedes = requireInt(val)
		case "n_sep_by_space":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.nSepBySpace = requireInt(val)
		case "p_sign_posn":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.pSignPosn = requireInt(val)
		case "n_sign_posn":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.nSignPosn = requireInt(val)
		case "int_p_cs_precedes":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.intPcsPrecedes = requireInt(val)
		case "int_p_sep_by_space":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.intPsepBySpace = requireInt(val)
		case "int_n_cs_precedes":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.intNcsPrecedes = requireInt(val)
		case "int_n_sep_by_space":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.intNsepBySpace = requireInt(val)
		case "int_p_sign_posn":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.intPsignPosn = requireInt(val)
		case "int_n_sign_posn":
			requireCategory("LC_MONETARY", keyword)
			def.monetary.intNsignPosn = requireInt(val)
		default:
			// Handle more complex values
			switch {
			case curCategory == "LC_CTYPE" && def.ctype.other[keyword] != nil:
				def.ctype.other[keyword] = append(def.ctype.other[keyword], val)

			default:
				die("misc error: %s", line)
			}
		}

	}

	if curCategory != "" {
		die("Category %s never ended", curCategory)
	}

	return def, nil
}