feat(health): migrate VERSION file to merkwerk integration (#83)

- Replace read_version() with merkwerk.get_health_info()
- Health endpoint now returns content_hash, vcs_info, source tracking
- Add merkwerk_integrated feature flag
- Enhanced startup logs with content-hash and VCS info
- Maintain backward compatibility with version field
- lua51 compatible integration for OpenBSD deployment

Migration from static VERSION file to dynamic merkwerk version tracking.
Health endpoint now provides rich metadata for debugging and monitoring.

Resolves DAW/furt#83

.version_history

@@ -0,0 +1,3 @@
+# merkwerk version history
+# Format: content_hash,vcs_hash,branch,timestamp,author,vcs_type,project_type
+7e82f537,7053af3,main,2025-08-19T18:14:06Z,michael,git,lua-api

integrations/lua-api.lua

@@ -0,0 +1,243 @@
+-- integrations/lua-api.lua - merkwerk Lua API integration
+-- Provides merkwerk version information for Lua applications
+
+local merkwerk = {}
+
+-- Cache for version info to avoid repeated shell calls
+local cache = {
+    data = nil,
+    timestamp = 0,
+    ttl = 300  -- 5 minutes default TTL
+}
+
+-- Execute merkwerk command and return result
+local function execute_merkwerk(args)
+    args = args or "info --json"
+    local command = "./tools/merkwerk/bin/merkwerk " .. args .. " 2>/dev/null"
+
+    local handle = io.popen(command)
+    if not handle then
+        return nil, "Failed to execute merkwerk command"
+    end
+
+    local result = handle:read("*a")
+    local success, exit_reason, exit_code = handle:close()
+
+    if not success or (exit_code and exit_code ~= 0) then
+        return nil, "merkwerk command failed with exit code " .. (exit_code or "unknown")
+    end
+
+    if result == "" then
+        return nil, "merkwerk returned empty result"
+    end
+
+    return result, nil
+end
+
+-- Parse JSON response (simple parser for basic merkwerk JSON)
+local function parse_json_response(json_str)
+    if not json_str then return nil end
+
+    -- Try to use cjson if available
+    local ok, cjson = pcall(require, "cjson")
+    if ok then
+        local success, data = pcall(cjson.decode, json_str)
+        if success then return data end
+    end
+
+    -- Fallback: simple manual parsing for merkwerk JSON structure
+    local data = {}
+
+    -- Extract basic fields using pattern matching
+    data.project_name = json_str:match('"project_name"%s*:%s*"([^"]*)"') or "unknown"
+    data.project_type = json_str:match('"project_type"%s*:%s*"([^"]*)"') or "unknown"
+    data.base_version = json_str:match('"base_version"%s*:%s*"([^"]*)"') or "?.?.?"
+    data.content_hash = json_str:match('"content_hash"%s*:%s*"([^"]*)"') or "unknown"
+    data.full_version = json_str:match('"full_version"%s*:%s*"([^"]*)"') or "?.?.?+unknown"
+    data.timestamp = json_str:match('"timestamp"%s*:%s*"([^"]*)"') or ""
+
+    -- Extract VCS info
+    local vcs_block = json_str:match('"vcs"%s*:%s*{([^}]*)}')
+    if vcs_block then
+        data.vcs = {}
+        data.vcs.type = vcs_block:match('"type"%s*:%s*"([^"]*)"') or "none"
+        data.vcs.hash = vcs_block:match('"hash"%s*:%s*"([^"]*)"') or ""
+        data.vcs.branch = vcs_block:match('"branch"%s*:%s*"([^"]*)"') or ""
+    else
+        data.vcs = { type = "none", hash = "", branch = "" }
+    end
+
+    return data
+end
+
+-- Generate fallback info when merkwerk is unavailable
+local function fallback_info()
+    return {
+        project_name = "unknown",
+        project_type = "lua-api",
+        base_version = "?.?.?",
+        content_hash = "unknown",
+        full_version = "?.?.?+unknown",
+        timestamp = os.date("%Y-%m-%dT%H:%M:%SZ"),
+        vcs = {
+            type = "none",
+            hash = "",
+            branch = ""
+        },
+        source = "fallback",
+        error = "merkwerk not available"
+    }
+end
+
+-- Check if cached data is still valid
+local function is_cache_valid(ttl)
+    ttl = ttl or cache.ttl
+    local current_time = os.time()
+    return cache.data and (current_time - cache.timestamp) < ttl
+end
+
+-- Get version information with caching
+function merkwerk.get_info(options)
+    options = options or {}
+    local use_cache = options.cache ~= false
+    local cache_ttl = options.cache_ttl or cache.ttl
+    local fallback_version = options.fallback_version
+    local include_build_info = options.include_build_info or false
+
+    -- Return cached data if valid and caching enabled
+    if use_cache and is_cache_valid(cache_ttl) then
+        local result = cache.data
+        if include_build_info then
+            result.build_info = {
+                cached = true,
+                cache_age = os.time() - cache.timestamp,
+                cache_ttl = cache_ttl
+            }
+        end
+        return result
+    end
+
+    -- Execute merkwerk command
+    local json_result, error_msg = execute_merkwerk("info --json")
+
+    if not json_result then
+        -- merkwerk failed - use fallback
+        local fallback = fallback_info()
+        if fallback_version then
+            fallback.base_version = fallback_version
+            fallback.full_version = fallback_version .. "+unknown"
+        end
+        if error_msg then
+            fallback.error = error_msg
+        end
+
+        if include_build_info then
+            fallback.build_info = {
+                cached = false,
+                error = error_msg or "merkwerk unavailable"
+            }
+        end
+
+        return fallback
+    end
+
+    -- Parse JSON response
+    local data = parse_json_response(json_result)
+    if not data then
+        -- JSON parsing failed - use fallback
+        local fallback = fallback_info()
+        fallback.error = "Failed to parse merkwerk JSON output"
+
+        if include_build_info then
+            fallback.build_info = {
+                cached = false,
+                error = "JSON parsing failed",
+                raw_output = json_result:sub(1, 100)  -- First 100 chars for debugging
+            }
+        end
+
+        return fallback
+    end
+
+    -- Add metadata
+    data.source = "merkwerk"
+
+    if include_build_info then
+        data.build_info = {
+            cached = false,
+            timestamp = os.time(),
+            cache_ttl = cache_ttl
+        }
+    end
+
+    -- Update cache
+    if use_cache then
+        cache.data = data
+        cache.timestamp = os.time()
+    end
+
+    return data
+end
+
+-- Get only the content hash (lightweight)
+function merkwerk.get_hash()
+    local hash_result, error_msg = execute_merkwerk("hash")
+
+    if not hash_result then
+        return "unknown"
+    end
+
+    -- Clean up the result (remove whitespace)
+    return hash_result:gsub("%s+", "")
+end
+
+-- Get version for HTTP health endpoints
+function merkwerk.get_health_info()
+    local info = merkwerk.get_info({ cache = true, cache_ttl = 600 })  -- 10 minute cache for health checks
+
+    return {
+        service = info.project_name,
+        version = info.full_version,
+        content_hash = info.content_hash,
+        vcs_info = info.vcs,
+        timestamp = info.timestamp,
+        source = info.source
+    }
+end
+
+-- Get minimal version string for logging
+function merkwerk.get_version_string()
+    local info = merkwerk.get_info({ cache = true })
+    return info.full_version
+end
+
+-- Clear cache (useful for testing or forced refresh)
+function merkwerk.clear_cache()
+    cache.data = nil
+    cache.timestamp = 0
+end
+
+-- Set cache TTL
+function merkwerk.set_cache_ttl(ttl)
+    cache.ttl = ttl or 300
+end
+
+-- Get cache status (for debugging)
+function merkwerk.get_cache_status()
+    return {
+        has_data = cache.data ~= nil,
+        timestamp = cache.timestamp,
+        age = cache.data and (os.time() - cache.timestamp) or 0,
+        ttl = cache.ttl,
+        valid = is_cache_valid()
+    }
+end
+
+-- Validate merkwerk availability
+function merkwerk.validate()
+    local result, error_msg = execute_merkwerk("info")
+    return result ~= nil, error_msg
+end
+
+return merkwerk
+

src/main.lua

@@ -13,23 +13,29 @@ local AuthRoute = require("src.routes.auth")
 -- Load configuration
 local config = require("config.server")
 
--- Read version from VERSION file
-local function read_version()
-    local file, err = io.open("VERSION", "r")
-    if not file then
-        print("WARNING: Could not read VERSION file: " .. (err or "unknown error"))
-        return "?.?.?"
+local function get_version_info()
+    -- Load merkwerk integration
+    local success, merkwerk = pcall(require, "integrations.lua-api")
+    if not success then
+        print("WARNING: merkwerk integration not available, using fallback")
+        return {
+            service = "furt-lua",
+            version = "?.?.?",
+            content_hash = "unknown",
+            vcs_info = { type = "none", hash = "", branch = "" },
+            source = "fallback-no-merkwerk"
+        }
     end
 
-    local version = file:read("*line")
-    file:close()
+    -- Get merkwerk health info
+    local health_info = merkwerk.get_health_info()
 
-    if not version or version:match("^%s*$") then
-        print("WARNING: VERSION file is empty or contains only whitespace")
-        return "?.?.?"
+    -- Ensure compatibility with old VERSION-only expectations
+    if not health_info.version then
+        health_info.version = "?.?.?"
     end
 
-    return version:match("^%s*(.-)%s*$") -- trim whitespace
+    return health_info
 end
 
 -- HTTP-Server Module
@@ -243,10 +249,12 @@ function FurtServer:start()
         error("Failed to bind to " .. self.host .. ":" .. self.port)
     end
 
-    local version = read_version()
+    local version_info = get_version_info()
 
     print(string.format("Furt HTTP-Server started on %s:%d", self.host, self.port))
-    print("Version: " .. version)
+    print("Version: " .. version_info.version .. " (merkwerk)")
+    print("Content-Hash: " .. (version_info.content_hash or "unknown"))
+    print("VCS: " .. (version_info.vcs_info and version_info.vcs_info.hash or "none"))
     print("API-Key authentication: ENABLED")
     print("Rate limiting: ENABLED (60 req/hour per API key, 100 req/hour per IP)")
     print("CORS enabled for configured origins")
@@ -267,16 +275,20 @@ local server = FurtServer:new()
 
 -- Public routes (no authentication required)
 server:add_route("GET", "/health", function(request, server)
-    local version = read_version()
+    local version_info = get_version_info()
     local response_data = {
         status = "healthy",
-        service = "furt-lua",
-        version = version,
+        service = version_info.service or "furt-lua",
+        version = version_info.version,
+        content_hash = version_info.content_hash,
+        vcs_info = version_info.vcs_info,
         timestamp = os.time(),
+        source = version_info.source,
         features = {
             smtp_configured = config.mail and config.mail.username ~= nil,
             auth_enabled = true,
-            rate_limiting = true
+            rate_limiting = true,
+            merkwerk_integrated = version_info.source == "merkwerk"
         }
     }
     return server:create_response(200, response_data, nil, nil, request)