pro-docs/libs/codemirror/mode/yaml-frontmatter/yaml-frontmatter.js

// CodeMirror, copyright (c) by Marijn Haverbeke and others
// Distributed under an MIT license: https://codemirror.net/LICENSE

;(function (mod) {
    if (typeof exports == 'object' && typeof module == 'object')
        // CommonJS
        mod(require('../../lib/codemirror'), require('../yaml/yaml'))
    else if (typeof define == 'function' && define.amd)
        // AMD
        define(['../../lib/codemirror', '../yaml/yaml'], mod)
    // Plain browser env
    else mod(CodeMirror)
})(function (CodeMirror) {
    var START = 0,
        FRONTMATTER = 1,
        BODY = 2

    // a mixed mode for Markdown text with an optional YAML front matter
    CodeMirror.defineMode('yaml-frontmatter', function (config, parserConfig) {
        var yamlMode = CodeMirror.getMode(config, 'yaml')
        var innerMode = CodeMirror.getMode(config, (parserConfig && parserConfig.base) || 'gfm')

        function localMode(state) {
            return state.state == FRONTMATTER ? { mode: yamlMode, state: state.yaml } : { mode: innerMode, state: state.inner }
        }

        return {
            startState: function () {
                return {
                    state: START,
                    yaml: null,
                    inner: CodeMirror.startState(innerMode),
                }
            },
            copyState: function (state) {
                return {
                    state: state.state,
                    yaml: state.yaml && CodeMirror.copyState(yamlMode, state.yaml),
                    inner: CodeMirror.copyState(innerMode, state.inner),
                }
            },
            token: function (stream, state) {
                if (state.state == START) {
                    if (stream.match('---', false)) {
                        state.state = FRONTMATTER
                        state.yaml = CodeMirror.startState(yamlMode)
                        return yamlMode.token(stream, state.yaml)
                    } else {
                        state.state = BODY
                        return innerMode.token(stream, state.inner)
                    }
                } else if (state.state == FRONTMATTER) {
                    var end = stream.sol() && stream.match(/(---|\.\.\.)/, false)
                    var style = yamlMode.token(stream, state.yaml)
                    if (end) {
                        state.state = BODY
                        state.yaml = null
                    }
                    return style
                } else {
                    return innerMode.token(stream, state.inner)
                }
            },
            innerMode: localMode,
            indent: function (state, a, b) {
                var m = localMode(state)
                return m.mode.indent ? m.mode.indent(m.state, a, b) : CodeMirror.Pass
            },
            blankLine: function (state) {
                var m = localMode(state)
                if (m.mode.blankLine) return m.mode.blankLine(m.state)
            },
        }
    })
})