#lang racket/base
(require racket/string)

(provide katex-convert-unicode)

(define (literal-alternatives→regexp literal-alternatives)
  (string-append "("
                 (string-join (map regexp-quote literal-alternatives) "|")
                 ")"))

(define (string-replace* str sym→*)
  (define →* (map (λ (x)
                    (cons (symbol->string (car x))
                          (cadr x)))
                  sym→*))
  (define hash→* (make-immutable-hash →*))
  (regexp-replace* (literal-alternatives→regexp (map car →*))
                   str
                   (λ (found . _)
                     (hash-ref hash→* found))))

(define (katex-convert-unicode str)
  (if (string? str)
      (string-replace*
       str
       '([₀ "_0"]
         [₁ "_1"]
         [₂ "_2"]
         [₃ "_3"]
         [₄ "_4"]
         [₅ "_5"]
         [₆ "_6"]
         [₇ "_7"]
         [₈ "_8"]
         [₉ "_9"]
         [ᵢ "_i"]
         [ⱼ "_j"]
         [ₖ "_k"]
         [ₗ "_l"]
         [ₘ "_m"]
         [ₙ "_n"]
         [ₒ "_o"]
         [⁰ "^0"]
         [¹ "^1"]
         [² "^2"]
         [³ "^3"]
         [⁴ "^4"]
         [⁵ "^5"]
         [⁶ "^6"]
         [⁷ "^7"]
         [⁸ "^8"]
         [⁹ "^9"]
         [ⁱ "^i"]
         [ʲ "^j"]
         [ᵏ "^k"]
         [ˡ "^l"]
         [ᵐ "^m"]
         [ⁿ "^n"]
         [ᵒ "^o"]
         [⊆ "\\subseteq" "\\ensuremath{\\subseteq}"]
         [⊂ "\\subset" "\\ensuremath{\\subset}"]
         [⊇ "\\supseteq" "\\ensuremath{\\supseteq}"]
         [⊃ "\\supset" "\\ensuremath{\\supset}"]
         [→ "\\rightarrow" "\\ensuremath{\\rightarrow}"]
         [⇒ "\\Rightarrow" "\\ensuremath{\\Rightarrow}"]
         [← "\\leftarrow" "\\ensuremath{\\leftarrow}"]
         [⇐ "\\Leftarrow" "\\ensuremath{\\Leftarrow}"]
         [↔ "\\leftrightarrow" "\\ensuremath{\\leftrightarrow}"]
         [⇔ "\\Leftrightarrow" "\\ensuremath{\\Leftrightarrow}"]
         ;; Partially extracted from my .XCompose generator
         [ñ "\\tilde{n}" "{\\ifmmode\\tilde{n}\\else\\~{n}\\fi}"]
         [Ñ "\\tilde{N}" "{\\ifmmode\\tilde{N}\\else\\~{N}\\fi}"]
         [⋆ "\\star" "\\ensuremath{\\star}"]
         [⍣ "\\ddot{\\star}}" "\\ensuremath{\\ddot{\\star}}"]
         [⃰ "^*" "^*"]
         [⟨ "\\langle" "\\ensuremath{\\mathsmaller{\\raisemath{.15ex}{\\langle}}}"]
         [⟩ "\\rangle" "\\ensuremath{\\mathsmaller{\\raisemath{.15ex}{\\rangle}}}"]
         [⋯ "\\cdots"]
         [⋮ "\\vdots"]
         [⋰ "\\iddots"]
         [⋱ "\\ddots"]
         [⧺ "\\mathbin{+\\mkern-6.5mu+}" "\\ensuremath{\\mathbin{+\\mkern-6.5mu+}}"]
         [∅ "\\emptyset" "\\ensuremath{\\emptyset}"]
         [ı⃗ "\\vec{\\i}}" "\\ensuremath{\\vec{\\i}"]
         [⊕ "\\oplus" "\\ensuremath{\\oplus}"]
         [⊖ "\\ominus" "\\ensuremath{\\ominus}"]
         [⋓ "\\Cup" "\\ensuremath{\\Cup}"]
         ;[ₗ "\\ensuremath{_{l}}"]
         [∷ "::"]
         [Λ "\\Lambda" "\\ensuremath{\\Lambda}"]
         [∀ "\\forall"]
         [∃ "\\exists"]
         [≡ "\\equiv"]
         [≢ "\not\\equiv"]
         [… "\\ldots"]
         [⋯ "\\cdots"]
         [⋰ "\\uddots"] ;; or \iddots from package mathdots, see http://tex.stackexchange.com/a/17650
         [⋱ "\\ddots"]
         [∌ "\\notni"]))
      str))