package shadow

import (
	"strings"
	"unicode/utf8"
)

// Croatian digraphs — must be checked before single letters.
// Order matters: longer sequences first.
var croatianDigraphs = []struct {
	src string
	dst string
}{
	{"dž", Dzh},
	{"Dž", Dzh},
	{"DŽ", Dzh},
	{"lj", L + Y},
	{"Lj", L + Y},
	{"LJ", L + Y},
	{"nj", N + Y},
	{"Nj", N + Y},
	{"NJ", N + Y},
}

// Croatian single-letter map. Every Croatian letter that differs from
// its Shadow equivalent is listed here. Letters that map to themselves
// (A→A, B→B, etc.) are handled by the default passthrough.
var croatianSingles = map[rune]string{
	// Letters that change
	'c': T + S, 'C': T + S, // Croatian C = /ts/
	'č': Ch, 'Č': Ch,
	'ć': Ch, 'Ć': Ch, // Ć ≈ Č (palatal affricate, close enough)
	'đ': Dzh, 'Đ': Dzh, // Đ ≈ Џ (palatal stop, close enough)
	'š': Sh, 'Š': Sh,
	'ž': Zh, 'Ž': Zh,
	'j': Y, 'J': Y,

	// Passthrough — identical sound, same letter
	'a': A, 'A': A,
	'b': B, 'B': B,
	'd': D, 'D': D,
	'e': E, 'E': E,
	'f': F, 'F': F,
	'g': G, 'G': G,
	'h': H, 'H': H,
	'i': I, 'I': I,
	'k': K, 'K': K,
	'l': L, 'L': L,
	'm': M, 'M': M,
	'n': N, 'N': N,
	'o': O, 'O': O,
	'p': P, 'P': P,
	'r': R, 'R': R,
	's': S, 'S': S,
	't': T, 'T': T,
	'u': U, 'U': U,
	'v': V, 'V': V,
	'z': Z, 'Z': Z,
	'w': W, 'W': W,
	'y': Y, 'Y': Y,
}

// FromCroatian transliterates Croatian (Gaj's Latin) text into the
// Shadow Alphabet. Digits and whitespace pass through unchanged.
// Unknown characters are preserved as-is.
func FromCroatian(text string) string {
	var out strings.Builder
	out.Grow(len(text))

	i := 0
	for i < len(text) {
		// Try digraphs first (longest match)
		matched := false
		for _, dg := range croatianDigraphs {
			if strings.HasPrefix(text[i:], dg.src) {
				out.WriteString(dg.dst)
				i += len(dg.src)
				matched = true
				break
			}
		}
		if matched {
			continue
		}

		// Single character
		r, size := utf8.DecodeRuneInString(text[i:])
		if r == utf8.RuneError {
			i++
			continue
		}

		if s, ok := croatianSingles[r]; ok {
			out.WriteString(s)
		} else {
			// Digits, spaces, newlines, unknown — passthrough
			out.WriteRune(r)
		}
		i += size
	}

	return out.String()
}