Use MD4C to convert markdown to HTML

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "md4k/lib/md4c"]
+	path = md4k/lib/md4c
+	url = https://github.com/mity/md4c

app/build.gradle.kts

@@ -111,6 +111,7 @@ play {
 }
 
 dependencies {
+    implementation(project(":md4k"))
     implementation("androidx.compose.material3:material3-window-size-class-android:1.2.0")
     val navigationVersion = "2.7.2"
     implementation("androidx.navigation:navigation-fragment-ktx:$navigationVersion")

app/src/main/assets/highlight.css

@@ -1,9 +0,0 @@
-/*!
-  Theme: Default
-  Description: Original highlight.js style
-  Author: (c) Ivan Sagalaev <maniac@softwaremaniacs.org>
-  Maintainer: @highlightjs/core-team
-  Website: https://highlightjs.org/
-  License: see project LICENSE
-  Touched: 2021
-*/pre code.hljs{display:block;overflow-x:auto;padding:1em}code.hljs{padding:3px 5px}.hljs{background:#f3f3f3;color:#444}.hljs-comment{color:#697070}.hljs-punctuation,.hljs-tag{color:#444a}.hljs-tag .hljs-attr,.hljs-tag .hljs-name{color:#444}.hljs-attribute,.hljs-doctag,.hljs-keyword,.hljs-meta .hljs-keyword,.hljs-name,.hljs-selector-tag{font-weight:700}.hljs-deletion,.hljs-number,.hljs-quote,.hljs-selector-class,.hljs-selector-id,.hljs-string,.hljs-template-tag,.hljs-type{color:#800}.hljs-section,.hljs-title{color:#800;font-weight:700}.hljs-link,.hljs-operator,.hljs-regexp,.hljs-selector-attr,.hljs-selector-pseudo,.hljs-symbol,.hljs-template-variable,.hljs-variable{color:#ab5656}.hljs-literal{color:#695}.hljs-addition,.hljs-built_in,.hljs-bullet,.hljs-code{color:#397300}.hljs-meta{color:#1f7199}.hljs-meta .hljs-string{color:#38a}.hljs-emphasis{font-style:italic}.hljs-strong{font-weight:700}

app/src/main/assets/markdown.js

@@ -1,14 +0,0 @@
-const localMarked = new marked.Marked(
-  markedHighlight.markedHighlight({
-    langPrefix: 'hljs language-',
-    highlight(code, lang) {
-        console.log(`highlighing code with $lang`)
-      const language = hljs.getLanguage(lang) ? lang : 'plaintext';
-      return hljs.highlight(code, { language }).value;
-    }
-  })
-);
-
-function setMarkdown(markdown) {
-    document.getElementById('content').innerHTML = marked.parse(markdown)
-}

app/src/main/assets/marked-highlight.js

@@ -1,96 +0,0 @@
-(function (global, factory) {
-  typeof exports === 'object' && typeof module !== 'undefined' ? factory(exports) :
-  typeof define === 'function' && define.amd ? define(['exports'], factory) :
-  (global = typeof globalThis !== 'undefined' ? globalThis : global || self, factory(global.markedHighlight = {}));
-})(this, (function (exports) { 'use strict';
-
-  function markedHighlight(options) {
-    if (typeof options === 'function') {
-      options = {
-        highlight: options
-      };
-    }
-
-    if (!options || typeof options.highlight !== 'function') {
-      throw new Error('Must provide highlight function');
-    }
-
-    if (typeof options.langPrefix !== 'string') {
-      options.langPrefix = 'language-';
-    }
-
-    return {
-      async: !!options.async,
-      walkTokens(token) {
-        if (token.type !== 'code') {
-          return;
-        }
-
-        const lang = getLang(token);
-
-        if (options.async) {
-          return Promise.resolve(options.highlight(token.text, lang)).then(updateToken(token));
-        }
-
-        const code = options.highlight(token.text, lang);
-        if (code instanceof Promise) {
-          throw new Error('markedHighlight is not set to async but the highlight function is async. Set the async option to true on markedHighlight to await the async highlight function.');
-        }
-        updateToken(token)(code);
-      },
-      renderer: {
-        code(code, infoString, escaped) {
-          const lang = (infoString || '').match(/\S*/)[0];
-          const classAttr = lang
-            ? ` class="${options.langPrefix}${escape(lang)}"`
-            : '';
-          code = code.replace(/\n$/, '');
-          return `<pre><code${classAttr}>${escaped ? code : escape(code, true)}\n</code></pre>`;
-        }
-      }
-    };
-  }
-
-  function getLang(token) {
-    return (token.lang || '').match(/\S*/)[0];
-  }
-
-  function updateToken(token) {
-    return (code) => {
-      if (typeof code === 'string' && code !== token.text) {
-        token.escaped = true;
-        token.text = code;
-      }
-    };
-  }
-
-  // copied from marked helpers
-  const escapeTest = /[&<>"']/;
-  const escapeReplace = new RegExp(escapeTest.source, 'g');
-  const escapeTestNoEncode = /[<>"']|&(?!(#\d{1,7}|#[Xx][a-fA-F0-9]{1,6}|\w+);)/;
-  const escapeReplaceNoEncode = new RegExp(escapeTestNoEncode.source, 'g');
-  const escapeReplacements = {
-    '&': '&amp;',
-    '<': '&lt;',
-    '>': '&gt;',
-    '"': '&quot;',
-    "'": '&#39;'
-  };
-  const getEscapeReplacement = (ch) => escapeReplacements[ch];
-  function escape(html, encode) {
-    if (encode) {
-      if (escapeTest.test(html)) {
-        return html.replace(escapeReplace, getEscapeReplacement);
-      }
-    } else {
-      if (escapeTestNoEncode.test(html)) {
-        return html.replace(escapeReplaceNoEncode, getEscapeReplacement);
-      }
-    }
-
-    return html;
-  }
-
-  exports.markedHighlight = markedHighlight;
-
-}));

app/src/main/java/com/wbrawner/simplemarkdown/MarkdownViewModel.kt

@@ -8,7 +8,6 @@ import com.wbrawner.simplemarkdown.utility.FileHelper
 import com.wbrawner.simplemarkdown.utility.Preference
 import com.wbrawner.simplemarkdown.utility.PreferenceHelper
 import kotlinx.coroutines.Dispatchers
-import kotlinx.coroutines.coroutineScope
 import kotlinx.coroutines.flow.MutableStateFlow
 import kotlinx.coroutines.flow.asStateFlow
 import kotlinx.coroutines.launch

app/src/main/java/com/wbrawner/simplemarkdown/ui/MainScreen.kt

@@ -300,7 +300,7 @@ private fun MainScreen(
                             .width(1.dp)
                             .background(color = MaterialTheme.colorScheme.primary)
                     )
-                    MarkdownPreview(
+                    MarkdownText(
                         modifier = Modifier
                             .fillMaxHeight()
                             .weight(1f),
@@ -362,7 +362,7 @@ private fun TabbedMarkdownEditor(
                 enableReadability = enableReadability
             )
         } else {
-            MarkdownPreview(modifier = Modifier.fillMaxSize(), markdown)
+            MarkdownText(modifier = Modifier.fillMaxSize(), markdown)
         }
     }
 }
@@ -436,9 +436,11 @@ fun MarkdownTopAppBar(
     actions: (@Composable RowScope.() -> Unit)? = null
 ) {
     val coroutineScope = rememberCoroutineScope()
-    TopAppBar(title = {
+    TopAppBar(
+        title = {
             Text(text = title, maxLines = 1, overflow = TextOverflow.Ellipsis)
-    }, navigationIcon = {
+        },
+        navigationIcon = {
             val (icon, contentDescription, onClick) = remember {
                 if (backAsUp) {
                     Triple(Icons.AutoMirrored.Filled.ArrowBack, "Go Back", goBack)
@@ -459,7 +461,9 @@ fun MarkdownTopAppBar(
             IconButton(onClick = { onClick() }) {
                 Icon(imageVector = icon, contentDescription = contentDescription)
             }
-    }, actions = actions ?: {})
+        }, actions = actions ?: {},
+        scrollBehavior = TopAppBarDefaults.enterAlwaysScrollBehavior()
+    )
 }
 
 @Composable

app/src/main/java/com/wbrawner/simplemarkdown/ui/MarkdownInfoScreen.kt

@@ -31,7 +31,7 @@ fun MarkdownInfoScreen(
         LaunchedEffect(file) {
             setMarkdown(context.assets.readAssetToString(file) ?: "Failed to load $file")
         }
-        MarkdownPreview(
+        MarkdownText(
             modifier = Modifier
                 .fillMaxSize()
                 .padding(paddingValues),

app/src/main/java/com/wbrawner/simplemarkdown/ui/MarkdownText.kt

@@ -1,31 +1,36 @@
 package com.wbrawner.simplemarkdown.ui
 
-import android.content.Context
 import android.view.ViewGroup
 import android.webkit.WebView
 import androidx.compose.foundation.isSystemInDarkTheme
 import androidx.compose.material3.MaterialTheme
 import androidx.compose.runtime.Composable
 import androidx.compose.runtime.LaunchedEffect
-import androidx.compose.runtime.getValue
 import androidx.compose.runtime.mutableStateOf
 import androidx.compose.runtime.remember
-import androidx.compose.runtime.setValue
 import androidx.compose.ui.Modifier
 import androidx.compose.ui.graphics.Color
 import androidx.compose.ui.graphics.toArgb
-import androidx.compose.ui.platform.LocalContext
 import androidx.compose.ui.viewinterop.AndroidView
+import com.wbrawner.md4k.MD4K
 import com.wbrawner.simplemarkdown.BuildConfig
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.withContext
-import java.io.Reader
 
-private const val container = "<main id=\"content\"></main>"
+@Composable
+fun MarkdownText(modifier: Modifier = Modifier, markdown: String) {
+    val (html, setHtml) = remember { mutableStateOf("") }
+    LaunchedEffect(markdown) {
+        withContext(Dispatchers.IO) {
+            setHtml(MD4K.toHtml(markdown))
+        }
+    }
+    HtmlText(modifier = modifier, html = html)
+}
 
 @OptIn(ExperimentalStdlibApi::class)
 @Composable
-fun MarkdownPreview(modifier: Modifier = Modifier, markdown: String) {
+fun HtmlText(html: String, modifier: Modifier = Modifier) {
     val materialColors = MaterialTheme.colorScheme
     val style = remember(isSystemInDarkTheme()) {
         """body {
@@ -37,37 +42,10 @@ fun MarkdownPreview(modifier: Modifier = Modifier, markdown: String) {
             |   color: #${materialColors.onSurfaceVariant.toArgb().toHexString().substring(2)};
             |}""".trimMargin().wrapTag("style")
     }
-    var marked by remember { mutableStateOf("") }
-    var markedHighlight by remember { mutableStateOf("") }
-    var highlightJs by remember { mutableStateOf("") }
-    var highlightCss by remember { mutableStateOf("") }
-    var markdownJs by remember { mutableStateOf("") }
-    val markdownUpdateJs by remember(markdown) {
-        mutableStateOf(
-            "setMarkdown(`${
-                markdown.replace(
-                    "`",
-                    "\\`"
-                )
-            }`)".wrapTag("script")
-        )
-    }
-    val context = LocalContext.current
-    LaunchedEffect(context) {
-        withContext(Dispatchers.IO) {
-            marked = context.assetToString("marked.js").wrapTag("script")
-            markedHighlight = context.assetToString("marked-highlight.js").wrapTag("script")
-            highlightJs = context.assetToString("highlight.js").wrapTag("script")
-            highlightCss = context.assetToString("highlight.css").wrapTag("style")
-            markdownJs = context.assetToString("markdown.js").wrapTag("script")
-        }
-    }
+
     AndroidView(
         modifier = modifier,
         factory = { context ->
-            val content =
-                highlightCss + style + container + marked + markedHighlight + highlightJs + markdownJs + markdownUpdateJs
-
             WebView(context).apply {
                 WebView.setWebContentsDebuggingEnabled(BuildConfig.DEBUG)
                 layoutParams = ViewGroup.LayoutParams(
@@ -77,18 +55,13 @@ fun MarkdownPreview(modifier: Modifier = Modifier, markdown: String) {
                 setBackgroundColor(Color.Transparent.toArgb())
                 isNestedScrollingEnabled = false
                 settings.javaScriptEnabled = true
-                loadDataWithBaseURL(null, content, "text/html", "UTF-8", null)
+                loadDataWithBaseURL(null, style + html, "text/html", "UTF-8", null)
             }
         },
         update = { webView ->
-            val content =
-                highlightCss + style + container + marked + markedHighlight + highlightJs + markdownJs + markdownUpdateJs
-            webView.loadDataWithBaseURL(null, content, "text/html", "UTF-8", null)
+            webView.loadDataWithBaseURL(null, style + html, "text/html", "UTF-8", null)
         }
     )
 }
 
 private fun String.wrapTag(tag: String) = "<$tag>$this</$tag>"
-
-private fun Context.assetToString(fileName: String): String =
-    assets.open(fileName).reader().use(Reader::readText)

md4k/.gitignore

@@ -0,0 +1,2 @@
+/build
+/.cxx

md4k/CMakeLists.txt

@@ -0,0 +1,18 @@
+cmake_minimum_required(VERSION 3.22.1)
+
+project("md4k")
+
+add_subdirectory("lib/md4c")
+set(BUILD_MD2HTML_EXECUTABLE OFF)
+
+add_library(${CMAKE_PROJECT_NAME} SHARED
+        src/main/cpp/md4k.c)
+
+target_link_libraries(${CMAKE_PROJECT_NAME}
+        md4c
+        md4c-html
+)
+
+target_include_directories(${CMAKE_PROJECT_NAME} PUBLIC
+        ${PROJECT_SOURCE_DIR}/lib/md4c/src
+)

md4k/build.gradle.kts

@@ -0,0 +1,41 @@
+plugins {
+    id("com.android.library")
+    id("org.jetbrains.kotlin.android")
+}
+
+android {
+    namespace = "com.wbrawner.md4k"
+    compileSdk = 34
+
+    defaultConfig {
+        minSdk = 23
+
+        testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
+        consumerProguardFiles("consumer-rules.pro")
+        externalNativeBuild {
+            cmake {
+                cppFlags("")
+            }
+        }
+    }
+
+    buildTypes {
+        release {
+            isMinifyEnabled = false
+            proguardFiles(getDefaultProguardFile("proguard-android-optimize.txt"), "proguard-rules.pro")
+        }
+    }
+    externalNativeBuild {
+        cmake {
+            path("CMakeLists.txt")
+            version = "3.22.1"
+        }
+    }
+    compileOptions {
+        sourceCompatibility = JavaVersion.VERSION_1_8
+        targetCompatibility = JavaVersion.VERSION_1_8
+    }
+    kotlinOptions {
+        jvmTarget = "1.8"
+    }
+}

md4k/lib/md4c

@@ -0,0 +1 @@
+Subproject commit 481fbfbdf72daab2912380d62bb5f2187d438408

md4k/proguard-rules.pro

@@ -0,0 +1,21 @@
+# Add project specific ProGuard rules here.
+# You can control the set of applied configuration files using the
+# proguardFiles setting in build.gradle.
+#
+# For more details, see
+#   http://developer.android.com/guide/developing/tools/proguard.html
+
+# If your project uses WebView with JS, uncomment the following
+# and specify the fully qualified class name to the JavaScript interface
+# class:
+#-keepclassmembers class fqcn.of.javascript.interface.for.webview {
+#   public *;
+#}
+
+# Uncomment this to preserve the line number information for
+# debugging stack traces.
+#-keepattributes SourceFile,LineNumberTable
+
+# If you keep the line number information, uncomment this to
+# hide the original source file name.
+#-renamesourcefileattribute SourceFile

md4k/src/main/AndroidManifest.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<manifest xmlns:android="http://schemas.android.com/apk/res/android">
+
+</manifest>

md4k/src/main/cpp/md4k.c

@@ -0,0 +1,41 @@
+#include <jni.h>
+#include "md4c.h"
+#include "md4c-html.h"
+#include <stdlib.h>
+#include <string.h>
+
+typedef struct {
+    char *data;
+    size_t length;
+} HtmlBuffer;
+
+void process_output(const MD_CHAR *output, MD_SIZE size, void *userdata) {
+    HtmlBuffer *buffer = (HtmlBuffer *) userdata;
+    buffer->data = realloc(buffer->data, buffer->length + size);
+    memcpy(buffer->data + buffer->length, output, size);
+    buffer->length += size;
+}
+
+jstring Java_com_wbrawner_md4k_MD4K_toHtml(
+        JNIEnv *env,
+        jobject this,
+        jstring markdown
+) {
+    const char *nativeString = (*env)->GetStringUTFChars(env, markdown, NULL);
+    HtmlBuffer buffer;
+    buffer.data = malloc(0);
+    buffer.length = 0;
+    md_html(
+            nativeString,
+            strlen(nativeString),
+            &process_output,
+            &buffer,
+            MD_FLAG_PERMISSIVEAUTOLINKS | MD_FLAG_TABLES | MD_FLAG_STRIKETHROUGH |
+            MD_FLAG_TASKLISTS | MD_FLAG_LATEXMATHSPANS | MD_FLAG_WIKILINKS | MD_FLAG_UNDERLINE,
+            0
+    );
+    (*env)->ReleaseStringUTFChars(env, markdown, nativeString);
+    jstring html = (*env)->NewStringUTF(env, buffer.data);
+    free(buffer.data);
+    return html;
+}

md4k/src/main/java/com/wbrawner/md4k/MD4K.kt

@@ -0,0 +1,12 @@
+package com.wbrawner.md4k
+
+object MD4K {
+
+    init {
+        System.loadLibrary("md4k")
+    }
+
+    external fun toHtml(markdown: String): String
+}
+
+fun String.toHtml() = MD4K.toHtml(this)

settings.gradle.kts

@@ -1 +1 @@
-include(":app")
+include(":app", ":md4k")