Auto-generate configuration documentation in README (#26)

Auto-generate the documentation of the configuration options in
`README.md` from `config.schema.json`.

README.md

@@ -116,51 +116,81 @@ Once *Prometheus* is restarted, metrics with the `homebridge_` prefix should sta
 
 *homebridge-prometheus-exporter* offers a few advanced settings to customize its behavior.
 
-```json lines
+<!-- AUTOGENERATED CONFIG DOCS BEGIN -->
+```json5
 {
-  // …
+  // ...
   "platforms": [
     {
       "platform": "PrometheusExporter",
-      // Homebridge PIN for service authentication. String of digits, format XXX-XX-XXX. Required
-      "pin": string,
 
-      // Toggle debug mode. Run homebridge with -D if you want to see the debug output. Default: false
-      "debug": boolean,
 
-      // Prefix for all metrics. Default: "homebridge"
-      "prefix": string,
+      // Pin
+      //
+      // Homebridge PIN for service authentication
+      "pin": "<string>",
 
-      // TCP port where the Prometheus metrics server listens. Default: 36123
-      "port": number,
 
-      // Interface where the Prometheus metrics server listens. Default: "::" which means "any interface".
-      // Can be an IP, a hostname, "0.0.0.0" for all IPv4 interfaces, "::1" for all IPv6 interfaces.
-      // Default is "::" which means any interface
-      "interface": string,
+      // Debug
+      "debug": "<boolean>",
 
-      // How frequently the services should be rediscovered (in seconds). Default: 60
-      "refresh_interval": number,
 
-      // Timeout for the HTTP request that retrieves the homekit devices (in seconds). Default: 10
-      "request_timeout": number,
+      // Metrics prefix
+      "prefix": "<string>",
 
-      // Timeout for the service discovery (in seconds). Default: 20
-      "discovery_timeout": number,
 
+      // Metrics server port
+      //
+      // TCP port where the Prometheus metrics server listens
+      "port": "<integer>",
+
+
+      // Metrics server interface
+      //
+      // Interface where the Prometheus metrics server listens. Can be an IP, a
+      // hostname, "0.0.0.0" for all IPv4 interfaces, "::1" for all IPv6 interfaces.
+      // Default is "::" which means "any interface"
+      "interface": "<string>",
+
+
+      // Service refresh interval
+      //
+      // Discover new services every <interval> seconds
+      "refresh_interval": "<integer>",
+
+
+      // Request timeout
+      //
+      // Request timeout when interacting with homebridge instances
+      "request_timeout": "<integer>",
+
+
+      // Service discovery timeout
+      //
+      // Discovery timeout after which the current discovery is considered failed
+      "discovery_timeout": "<integer>",
+
+
+      // TLS cert file
+      //
       // Path to TLS certificate file (in PEM format)
-      "tls_cert_file": string,
+      "tls_cert_file": "<string>",
 
+
+      // TLS key file
+      //
       // Path to TLS key file
-      "tls_key_file": string,
+      "tls_key_file": "<string>",
 
-      // Usernames and passwords for basic auth. Key is the username, value is the password.
-      // Password must be encoded with bcrypt
-      "basic_auth": {
-        "username": "<password encoded with bcrypt>"
-      }
-    },
-    // …
+
+      // Basic auth username/password pairs
+      //
+      // Usernames and passwords for basic auth. Object key is the username, object
+      // value is the password. Password must be encoded with bcrypt. Example:
+      // {"joanna": "$2a$12$5/mmmRB28wg9yzaXhee5Iupq3UrFr/qMgAe9LvAxGoY5jLcfVGTUq"}
+      "basic_auth": "<object>"
+    }
   ]
 }
 ```
+<!-- AUTOGENERATED CONFIG DOCS END -->

code-generation/config-scheme-gen.js

@@ -5,7 +5,7 @@ const { schema } = require('../config.schema.json')
 const { format } = require('prettier')
 const { join, basename } = require('path')
 const prettierConfig = require('../prettier.config')
-const { writeFileSync } = require('fs')
+const { writeFileSync, readFileSync } = require('fs')
 
 const file = join(__dirname, '../src/generated/config_boundary.ts')
 
@@ -26,4 +26,74 @@ export const ConfigBoundary = ${zodSchema}
 
 writeFileSync(file, code)
 
+const note = 'AUTOGENERATED CONFIG DOCS'
+const comment = (...strings) => `<!-- ${strings.join(' ')} -->`
+const readmePath = join(__dirname, '../README.md')
+const readme = readFileSync(readmePath).toString()
+const regex = new RegExp(`${comment(note, 'BEGIN')}.*${comment(note, 'END')}`, 'mgs')
+if (!readme.match(regex)) {
+    console.log('Could not update README.md')
+    process.exit(1)
+}
+
+writeFileSync(
+    readmePath,
+    readme.replace(
+        regex,
+        `${comment(note, 'BEGIN')}\n\`\`\`json5\n${generateDocs(schema)}\n\`\`\`\n${comment(note, 'END')}`,
+    ),
+)
+
+function generateDocs(schema) {
+    const doc = indent(
+        Object.entries(schema.properties)
+            .map(([property, definition]) => {
+                const lines = []
+
+                if (definition.title) {
+                    lines.push(`// ${definition.title}`)
+                }
+                if (definition.description) {
+                    lines.push(`//\n// ${wordwrap(definition.description, 80, '\n// ')}`)
+                }
+
+                lines.push(`${JSON.stringify(property)}: ${JSON.stringify('<' + definition.type + '>')}`)
+
+                return lines.join('\n')
+            })
+            .join(',\n\n\n'),
+        6,
+    )
+
+    return `{
+  // ...
+  "platforms": [
+    {
+      "platform": "PrometheusExporter",
+
+
+${doc}
+    }
+  ]
+}`
+}
+
+function wordwrap(word, length, wrap = '\n') {
+    const wrapped = []
+    while (word.length > length) {
+        const cut = word.substring(0, length)
+        const pos = cut.lastIndexOf(' ')
+        wrapped.push(cut.substring(0, pos))
+        word = word.substring(pos + 1)
+    }
+
+    wrapped.push(word)
+
+    return wrapped.join(wrap)
+}
+
+function indent(string, indent) {
+    return string.replace(/^(.+)$/gm, `${' '.repeat(indent)}$1`)
+}
+
 console.log(`Finished code generation for ${file}`)