feat: parse the cached OWM response

Lua patterns instead of a JSON library: the current-weather response
is flat and known, so six scalars do not justify a dependency. Every
failure path (truncated write, empty file, garbage, an API error body,
nil input) returns nil rather than raising, since a Lua error here is
a blank dashboard.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

1 files changed, 41 insertions, 0 deletions

diff --git a/lib/weather.lua b/lib/weather.lua
index 84f355a..a66d79a 100644
--- a/lib/weather.lua
+++ b/lib/weather.lua
@@ -142,4 +142,45 @@ function M.is_day(now, sunrise, sunset)
   return now >= sunrise and now <= sunset
 end
 
+-- Parse the cached OWM response.
+--
+-- Lua patterns, not a JSON library: the current-weather response is flat and
+-- its shape is known, so six scalars do not justify a dependency. Returns nil
+-- on anything unreadable, never an error.
+function M.parse(src)
+  if type(src) ~= 'string' or src == '' then return nil end
+
+  -- Scalars are matched inside their own object where the key would otherwise
+  -- be ambiguous. "temp" appears as a prefix of "temp_min" and "temp_max", so
+  -- it is anchored to the character that follows it.
+  local function num(pat)
+    return tonumber(src:match(pat))
+  end
+
+  local main = src:match('"main"%s*:%s*(%b{})') or ''
+  local wind = src:match('"wind"%s*:%s*(%b{})') or ''
+  local sys  = src:match('"sys"%s*:%s*(%b{})') or ''
+  local cond = src:match('"weather"%s*:%s*%[%s*(%b{})') or ''
+
+  local w = {
+    id          = tonumber(cond:match('"id"%s*:%s*(%-?%d+)')),
+    description = cond:match('"description"%s*:%s*"([^"]*)"'),
+    temp        = tonumber(main:match('"temp"%s*:%s*(%-?[%d%.]+)')),
+    feels_like  = tonumber(main:match('"feels_like"%s*:%s*(%-?[%d%.]+)')),
+    humidity    = tonumber(main:match('"humidity"%s*:%s*(%d+)')),
+    wind_speed  = tonumber(wind:match('"speed"%s*:%s*([%d%.]+)')),
+    wind_deg    = tonumber(wind:match('"deg"%s*:%s*(%d+)')),
+    sunrise     = tonumber(sys:match('"sunrise"%s*:%s*(%d+)')),
+    sunset      = tonumber(sys:match('"sunset"%s*:%s*(%d+)')),
+    city        = src:match('"name"%s*:%s*"([^"]*)"'),
+    dt          = num('"dt"%s*:%s*(%d+)'),
+  }
+
+  -- Without these the card has nothing to draw, and a partial card is worse
+  -- than an honest "no data". An API error body fails here too: it carries a
+  -- cod and a message, no weather.
+  if not (w.id and w.temp and w.sunrise and w.sunset) then return nil end
+  return w
+end
+
 return M