/-
Copyright (c) 2021 Wojciech Nawrocki. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.

Authors: Wojciech Nawrocki, Sebastian Ullrich, Henrik Böving
-/
import Lean.Data.Json
import Lean.Parser

/-! This module defines:
- a representation of HTML trees
- together with a JSX-like DSL for writing them
- and widget support for visualizing any type as HTML. -/

namespace DocGen4

open Lean

inductive Html where
  -- TODO(WN): it's nameless for shorter JSON; re-add names when we have deriving strategies for From/ToJson
  -- element (tag : String) (flatten : Bool) (attrs : Array HtmlAttribute) (children : Array Html)
  | element : String → Bool → Array (String × String) → Array Html → Html
  | text : String → Html
  deriving Repr, BEq, Inhabited, FromJson, ToJson

instance : Coe String Html :=
  ⟨Html.text⟩

namespace Html

def attributesToString (attrs : Array (String × String)) :String :=
  attrs.foldl (λ acc (k, v) => acc ++ " " ++ k ++ "=\"" ++ v ++ "\"") ""

-- TODO: Termination proof
partial def toStringAux : Html → String
| element tag false attrs #[text s] => s!"<{tag}{attributesToString attrs}>{s}</{tag}>\n"
| element tag false attrs #[child] => s!"<{tag}{attributesToString attrs}>\n{child.toStringAux}</{tag}>\n"
| element tag false attrs children => s!"<{tag}{attributesToString attrs}>\n{children.foldl (· ++ toStringAux ·) ""}</{tag}>\n"
| element tag true attrs children => s!"<{tag}{attributesToString attrs}>{children.foldl (· ++ toStringAux ·) ""}</{tag}>"
| text s => s

def toString (html : Html) : String :=
  html.toStringAux.trimRight

instance : ToString Html :=
  ⟨toString⟩

end Html

namespace Jsx
open Parser PrettyPrinter

declare_syntax_cat jsxElement
declare_syntax_cat jsxChild

-- JSXTextCharacter : SourceCharacter but not one of {, <, > or }
def jsxText : Parser :=
  withAntiquot (mkAntiquot "jsxText" `jsxText) {
    fn := fun c s =>
      let startPos := s.pos
      let s := takeWhile1Fn (not ∘ "[{<>}]$".contains) "expected JSX text" c s
      mkNodeToken `jsxText startPos c s }

@[combinatorFormatter DocGen4.Jsx.jsxText] def jsxText.formatter : Formatter := pure ()
@[combinatorParenthesizer DocGen4.Jsx.jsxText] def jsxText.parenthesizer : Parenthesizer := pure ()

syntax jsxAttrName := ident <|> strLit
syntax jsxAttrVal := strLit <|> group("{" term "}")
syntax jsxSimpleAttr := jsxAttrName "=" jsxAttrVal
syntax jsxAttrSpread := "[" term "]"
syntax jsxAttr := jsxSimpleAttr <|> jsxAttrSpread

syntax "<" ident jsxAttr* "/>" : jsxElement
syntax "<" ident jsxAttr* ">" jsxChild* "</" ident ">" : jsxElement

syntax jsxText      : jsxChild
syntax "{" term "}" : jsxChild
syntax "[" term "]" : jsxChild
syntax jsxElement   : jsxChild

scoped syntax:max jsxElement : term

def translateAttrs (attrs : Array Syntax) : MacroM Syntax := do
  let mut as ← `(#[])
  for attr in attrs do
    as ← match attr with
    | `(jsxAttr| $n:jsxAttrName=$v:jsxAttrVal) =>
      let n ← match n with
        | `(jsxAttrName| $n:strLit) => n
        | `(jsxAttrName| $n:ident) => quote (toString n.getId)
        | _ => Macro.throwUnsupported
      let v ← match v with
        | `(jsxAttrVal| {$v}) => v
        | `(jsxAttrVal| $v:strLit) => v
        | _ => Macro.throwUnsupported
      `(($as).push ($n, $v))
    | `(jsxAttr| [$t]) => `($as ++ ($t : Array (String × String)))
    | _ => Macro.throwUnsupported
  return as

macro_rules
  | `(<$n $attrs* />) => do
    `(Html.element $(quote (toString n.getId)) true $(← translateAttrs attrs) #[])
  | `(<$n $attrs* >$children*</$m>) => do
    unless n.getId == m.getId do
      withRef m <| Macro.throwError s!"expected </{n.getId}>"
    let mut cs ← `(#[])
    for child in children do
      cs ← match child with
      | `(jsxChild|$t:jsxText)    => `(($cs).push (Html.text $(quote t[0].getAtomVal!)))
      -- TODO(WN): elab as list of children if type is `t Html` where `Foldable t`
      | `(jsxChild|{$t})          => `(($cs).push ($t : Html))
      | `(jsxChild|[$t])          => `($cs ++ ($t : Array Html))
      | `(jsxChild|$e:jsxElement) => `(($cs).push ($e:jsxElement : Html))
      | _                         => Macro.throwUnsupported
    let tag := toString n.getId
    `(Html.element $(quote tag) false $(← translateAttrs attrs) $cs)

end Jsx

/-- A type which implements `ToHtmlFormat` will be visualized
as the resulting HTML in editors which support it. -/
class ToHtmlFormat (α : Type u) where
  formatHtml : α → Html

end DocGen4