[plugin] Exporter: add Readwise.io support (#8548)

This extends exporter.koplugin with support for [Readwise.io](https://readwise.io), a highlight/notes aggregation service.

[Readwise API documentation](https://readwise.io/api_deets)

This additionally improves the highlight exporter's ability to get the correct title and author of a document, by checking actual metadata instead of inferring from filename. It also includes a modification to the plugin's highlight parsing logic to separate the highlight contents in `.text` from the notes in `.note`. This change actually fixes an existing bug in the HTML export template note.tpl, which has been missing notes because of the lack of the `.note` field.

plugins/exporter.koplugin/ReadwiseClient.lua

@@ -0,0 +1,70 @@
+local http = require("socket.http")
+local json = require("json")
+local logger = require("logger")
+local ltn12 = require("ltn12")
+local socket = require("socket")
+local socketutil = require("socketutil")
+
+local ReadwiseClient =  {
+    auth_token = ""
+}
+
+function ReadwiseClient:new(o)
+    o = o or {}
+    self.__index = self
+    setmetatable(o, self)
+    return o
+end
+
+function ReadwiseClient:_makeRequest(endpoint, method, request_body)
+    local sink = {}
+    local request_body_json = json.encode(request_body)
+    local source = ltn12.source.string(request_body_json)
+    socketutil:set_timeout(socketutil.LARGE_BLOCK_TIMEOUT, socketutil.LARGE_TOTAL_TIMEOUT)
+    local request = {
+        url     = "https://readwise.io/api/v2/" .. endpoint,
+        method  = method,
+        sink    = ltn12.sink.table(sink),
+        source  = source,
+        headers = {
+            ["Content-Length"] = #request_body_json,
+            ["Content-Type"] = "application/json",
+            ["Authorization"] = "Token " .. self.auth_token
+        },
+    }
+    local code, _, status = socket.skip(1, http.request(request))
+    socketutil:reset_timeout()
+
+    if code ~= 200 then
+        logger.warn("ReadwiseClient: HTTP response code <> 200. Response status: ", status)
+        error("ReadwiseClient: HTTP response code <> 200.")
+    end
+
+    local response = json.decode(sink[1])
+
+    return response
+end
+
+function ReadwiseClient:createHighlights(booknotes)
+    local highlights = {}
+    for _, chapter in ipairs(booknotes) do
+        for _, clipping in ipairs(chapter) do
+            local highlight = {
+                text = clipping.text,
+                title = booknotes.title,
+                author = booknotes.author ~= "" and booknotes.author or nil, -- optional author
+                source_type = "koreader",
+                category = "books",
+                note = clipping.note,
+                location = clipping.page,
+                location_type = "page",
+                highlighted_at = os.date("!%Y-%m-%dT%TZ", clipping.time),
+            }
+            table.insert(highlights, highlight)
+        end
+    end
+    local result = self:_makeRequest("highlights", "POST", { highlights = highlights })
+    logger.dbg("ReadwiseClient createHighlights result", result)
+end
+
+return ReadwiseClient