orlowdev/gatsby-source-notion-api

const { blockToString } = require("../block-to-string")

const EOL_MD = "\n"
const DOUBLE_EOL_MD = EOL_MD.repeat(2)

// Inserts the string at the beginning of every line of the content. If the useSpaces flag is set to
// true, the lines after the first will instead be prepended with two spaces.
function prependToLines(content, string, useSpaces = true) {
    let [head, ...tail] = content.split("\n")

    return [
        `${string} ${head}`,
        ...tail.map((line) => {
            return `${useSpaces ? " " : string} ${line}`
        }),
    ].join("\n")
}

// Converts a notion block to a markdown string.
exports.notionBlockToMarkdown = (block, lowerTitleLevel) => {
    // Get the child content of the block.
    let childMarkdown = (block.children ?? [])
        .map((block) => this.notionBlockToMarkdown(block, lowerTitleLevel))
        .join("")
        .trim()

    // If the block is a page, return the child content.
    if (block.object === "page") {
        return childMarkdown
    }

    // Extract the remaining content of the block and combine it with its children.
    let blockMarkdown = block[block.type]?.text ? blockToString(block[block.type]?.text).trim() : null
    let markdown = [blockMarkdown, childMarkdown].filter((text) => text).join(DOUBLE_EOL_MD)

    // Table row
    // TODO: This should be moved to the new Notion type.
    if (block.type == "paragraph" && blockMarkdown.startsWith("|") && blockMarkdown.endsWith("|")) {
        return markdown.concat(EOL_MD)
    }

    // Paragraph
    if (block.type == "paragraph") {
        return [EOL_MD, markdown, EOL_MD].join("")
    }

    // Heading
    if (block.type.startsWith("heading_")) {
        const headingLevel = Number(block.type.split("_")[1])
        let symbol = (lowerTitleLevel ? "#" : "") + "#".repeat(headingLevel)
        return [EOL_MD, prependToLines(markdown, symbol), EOL_MD].join("")
    }

    // To do list item
    if (block.type == "to_do") {
        let symbol = `- [${block.to_do.checked ? "x" : " "}] `
        return prependToLines(markdown, symbol).concat(EOL_MD)
    }

    // Bulleted list item
    if (block.type == "bulleted_list_item") {
        return prependToLines(markdown, "*").concat(EOL_MD)
    }

    // Numbered list item
    if (block.type == "numbered_list_item") {
        return prependToLines(markdown, "1.").concat(EOL_MD)
    }

    // Toggle
    if (block.type == "toggle") {
        return [
            EOL_MD,
            "<details><summary>",
            blockMarkdown,
            "</summary>",
            childMarkdown,
            "</details>",
            EOL_MD,
        ].join("")
    }

    // Code
    if (block.type == "code") {
        return [
            EOL_MD,
            `\`\`\` ${block.code.language}${EOL_MD}`,
            blockMarkdown,
            EOL_MD,
            "```",
            EOL_MD,
            childMarkdown,
            EOL_MD,
        ].join("")
    }

    // Image
    if (block.type == "image") {
        const imageUrl = block.image.type == "external" ? block.image.external.url : block.image.file.url
        return `${EOL_MD}![${blockToString(block.image.caption)}](${imageUrl})${EOL_MD}`
    }

    // Audio
    if (block.type == "audio") {
        const audioUrl = block.audio.type == "external" ? block.audio.external.url : block.audio.file.url
        return [EOL_MD, "<audio controls>", `<source src="${audioUrl}" />`, "</audio>", EOL_MD].join("")
    }

    // Video
    if (block.type == "video" && block.video.type == "external") {
        return [EOL_MD, block.video.external.url, EOL_MD].join("")
    }

    // Embed
    if (block.type == "embed") {
        return [EOL_MD, block.embed.url, EOL_MD].join("")
    }

    // Quote
    if (block.type == "quote") {
        return [EOL_MD, prependToLines(markdown, ">", false), EOL_MD].join("")
    }

    // Bookmark
    if (block.type == "bookmark") {
        const bookmarkUrl = block.bookmark.url
        const bookmarkCaption = blockToString(block.bookmark.caption) || bookmarkUrl
        return `${EOL_MD}[${bookmarkCaption}](${bookmarkUrl})${EOL_MD}`
    }

    // Divider
    if (block.type == "divider") {
        return `${EOL_MD}---${EOL_MD}`
    }

    // Column List
    if (block.type == "column_list") {
        return [
            EOL_MD,
            "<ColumnList>",
            EOL_MD,
            markdown,
            EOL_MD,
            "</ColumnList>",
            EOL_MD
        ].join("")
    }

    // Column
    if (block.type == "column") {
        return [
            "<Column>",
            EOL_MD,
            EOL_MD,
            markdown,
            EOL_MD,
            EOL_MD,
            "</Column>",
            EOL_MD
        ].join("")
    }

    // Unsupported types.
    // TODO: Add support for callouts, internal video, and files
    return [EOL_MD, `<!-- This block type '${block.type}' is not supported yet. -->`, EOL_MD].join("")
}