-- Readers for /proc and /sys.
--
-- Every function takes the file *contents* as a string rather than reading the
-- file itself, so the parsers are testable against fixtures without mocking the
-- filesystem. The thin read-and-parse wrappers live at the bottom.

local M = {}

-- Aggregate CPU jiffies from /proc/stat. Returns total, idle.
-- iowait counts as idle: a core waiting on disk is not doing work, and
-- treating it as busy makes a disk-bound system look CPU-bound.
function M.cpu_times(stat)
  local line = stat:match('^cpu%s+([^\n]+)')
  if not line then return nil, nil end
  local v = {}
  for n in line:gmatch('%d+') do v[#v + 1] = tonumber(n) end
  if #v < 5 then return nil, nil end
  local total = 0
  for _, n in ipairs(v) do total = total + n end
  return total, v[4] + v[5]  -- idle + iowait
end

-- /proc/meminfo, values in kB as the file states them.
function M.mem_info(meminfo)
  local function field(name)
    return tonumber(meminfo:match(name .. ':%s+(%d+)'))
  end
  local total = field('MemTotal')
  local available = field('MemAvailable')
  if not (total and available) then return nil end
  return {
    total = total,
    free = field('MemFree'),
    available = available,
    -- MemAvailable already excludes reclaimable cache, so this is the figure a
    -- user recognises as "used", unlike total-free which counts cache.
    used = total - available,
  }
end

-- hwmon temp*_input is millidegrees C. Returns whole degrees, or nil.
-- nil rather than 0 on failure: 0 C is a legitimate reading.
function M.millidegrees(s)
  if not s then return nil end
  local n = tonumber(s:match('^%s*(-?%d+)'))
  if not n then return nil end
  return math.floor(n / 1000 + 0.5)
end

-- Read a whole file, returning nil if it cannot be read. Used by the wrappers
-- so a vanished sysfs path degrades to nil instead of raising.
function M.slurp(path)
  local f = io.open(path, 'r')
  if not f then return nil end
  local s = f:read('*a')
  f:close()
  return s
end

-- Find a hwmon directory by the exact contents of its `name` file.
--
-- Globbing by name, never by a fixed hwmon index: indices drift across kernel
-- and hardware reorders, and a stale index silently reports a different chip.
-- Carried over from the previous conky config, where this was the hard-won bit.
--
-- The result is memoized per chip name, hits and misses alike. A chip's hwmon
-- directory is stable for the process's life, and the draw hook calls this
-- several times per frame: without the cache every sensor read popens grep,
-- which is exactly the subprocess-per-draw the samplers exist to avoid. A miss
-- is cached too, so an absent chip is not re-globbed on every frame.
local hwmon_cache = {}

function M.hwmon_dir(name)
  if type(name) ~= 'string' then return nil end
  if hwmon_cache[name] == nil then
    local p = io.popen('grep -lx ' .. ("%q"):format(name)
      .. ' /sys/class/hwmon/hwmon*/name 2>/dev/null')
    local dir = false
    if p then
      local hit = p:read('*l')
      p:close()
      if hit then dir = hit:match('^(.*)/name$') end
    end
    hwmon_cache[name] = dir
  end
  return hwmon_cache[name] or nil
end

-- A stateful CPU-load counter.
--
-- Load is work done between two samples, so a single reading cannot produce a
-- percentage. Each counter keeps its own previous sample, which also means a
-- per-core counter is just another instance.
function M.new_cpu_counter()
  return {
    prev_total = nil,
    prev_idle = nil,
    -- Returns busy percent since the previous sample, or nil when there is no
    -- usable delta (first call, or the counters did not advance).
    sample = function(self, total, idle)
      if not (total and idle) then return nil end
      local pt, pi = self.prev_total, self.prev_idle
      self.prev_total, self.prev_idle = total, idle
      if not pt then return nil end
      local dt = total - pt
      if dt <= 0 then return nil end
      local busy = (dt - (idle - pi)) / dt * 100
      -- Clamp: a counter reset or a suspend/resume can produce a nonsense
      -- delta, and a bar drawn at -12% or 340% is worse than a clamped one.
      if busy < 0 then busy = 0 elseif busy > 100 then busy = 100 end
      return busy
    end,
  }
end

-- Per-core jiffies from /proc/stat, in file order, so entry N is core N.
--
-- Separate from cpu_times() rather than a flag on it: the aggregate is a
-- single pair and this is a list, and a function returning one or the other
-- depending on an argument is worse than two functions.
--
-- The leading 'cpu ' aggregate is excluded by requiring a digit after 'cpu',
-- since counting it would draw an extra bar showing the average alongside the
-- real cores.
function M.per_cpu_times(stat)
  local out = {}
  if type(stat) ~= 'string' then return out end
  for line in stat:gmatch('[^\n]+') do
    local nums = line:match('^cpu%d+%s+(.+)$')
    if nums then
      local v = {}
      for n in nums:gmatch('%d+') do v[#v + 1] = tonumber(n) end
      -- Needs at least user..iowait to compute a busy fraction; a shorter line
      -- is truncated or from a kernel that reports differently, and a partial
      -- sum would look plausible while being wrong.
      if #v >= 5 then
        local total = 0
        for _, n in ipairs(v) do total = total + n end
        out[#out + 1] = { total = total, idle = v[4] + v[5] }
      end
    end
  end
  return out
end

-- A named hwmon sensor's value in whole degrees, or nil.
--
-- Wraps hwmon_dir + slurp + millidegrees so a widget names the chip and the
-- file rather than building paths. nil, never 0: zero degrees is a plausible
-- reading and must not be indistinguishable from a missing sensor.
function M.sensor(chip, file)
  if type(chip) ~= 'string' or type(file) ~= 'string' then return nil end
  local dir = M.hwmon_dir(chip)
  if not dir then return nil end
  return M.millidegrees(M.slurp(dir .. '/' .. file))
end

-- A raw hwmon integer (fan RPM, power microwatts), or nil. Same lookup as
-- sensor() without the millidegree conversion.
function M.sensor_raw(chip, file)
  if type(chip) ~= 'string' or type(file) ~= 'string' then return nil end
  local dir = M.hwmon_dir(chip)
  if not dir then return nil end
  local s = M.slurp(dir .. '/' .. file)
  if not s then return nil end
  return tonumber(s:match('^%s*(-?%d+)'))
end

-- Parse `df -P -B1` output into a list of filesystems.
--
-- The mountpoint is taken as the LAST field, not the sixth. df -P guarantees
-- one line per filesystem with the mountpoint last, and an NFS device reads
-- 'server:/export', so counting fields from the left is fragile in a way
-- counting from the right is not.
--
-- Sizes are bytes because the sampler passes -B1. Never parse `df -h` output
-- here: the user's shell aliases df to df -h, so a sampler calling bare df
-- would hand this function '1.6G' where it expects an integer.
function M.df_parse(text)
  local out = {}
  if type(text) ~= 'string' then return out end
  for line in text:gmatch('[^\n]+') do
    -- A data row ends in 'NN% /some/path'. The header ends in 'Mounted on',
    -- which fails the percent match, so it is skipped without a special case.
    local size, used, pct, mount = line:match('(%d+)%s+(%d+)%s+%d+%s+(%d+)%%%s+(%S+)%s*$')
    if size then
      -- The device is kept so a caller can tell an NFS mount from a local one
      -- and recover its server, which is how the disks card labels the two
      -- shares without hardcoding an address in the repo.
      local dev = line:match('^(%S+)')
      out[#out + 1] = {
        mount = mount,
        dev   = dev,
        host  = dev and dev:match('^([^/:]+):') or nil,
        size  = tonumber(size),
        used  = tonumber(used),
        pct   = tonumber(pct),
      }
    end
  end
  return out
end

-- Human-readable size to bytes: '1.1G' -> 1181116006.
--
-- Needed because du -sh is what the sampler runs (its output is also what the
-- card displays), and 'biggest' has to be decided numerically: sorted as
-- strings, '245M' beats '1.1G'.
local SUFFIX = { K = 1024, M = 1024^2, G = 1024^3, T = 1024^4, P = 1024^5 }

function M.human_bytes(s)
  if type(s) ~= 'string' then return nil end
  local n, suf = s:match('^%s*([%d%.]+)%s*([KMGTP]?)')
  n = tonumber(n)
  if not n then return nil end
  return n * (SUFFIX[suf] or 1)
end

-- Parse `du -sh` output: the first line is the total, the rest are children
-- already sorted largest-first by the sampler. Returns nil when there is
-- nothing usable, so the widget can draw its "no data" state.
function M.du_parse(text)
  if type(text) ~= 'string' or text == '' then return nil end
  local lines = {}
  for line in text:gmatch('[^\n]+') do lines[#lines + 1] = line end
  if #lines == 0 then return nil end

  local function entry(line)
    local label, path = line:match('^(%S+)%s+(.+)$')
    if not label then return nil end
    return { label = label, bytes = M.human_bytes(label) or 0,
             name = path:match('([^/]+)/?$') or path, path = path }
  end

  local total = entry(lines[1])
  if not total then return nil end
  local items = {}
  for i = 2, #lines do
    local e = entry(lines[i])
    if e then items[#items + 1] = e end
  end
  return { total = total, items = items }
end

return M