-- Timing policy for session warming: WHEN a transient request may fire.
--
-- The semantics mirror opencode's warming feature. `interval` is the idle
-- time before a warm request fires after real activity (and again after each
-- warm attempt); `duration` is the warming window measured from the latest
-- non-warming activity. Warm attempts never extend the window:
--
--     00:00  real activity        window = [00:00, 00:30]
--     00:04  warm                 next due 00:08
--     00:08  warm                 ...
--     00:30  window expired, warming stops
--
-- A turn in flight (`turn_started` without `turn_ended`) blocks warm
-- requests: the live conversation is changing under us. With
-- `interval >= duration` the window always expires before the first warm
-- request is due, so warming never fires -- a documented consequence of the
-- opencode semantics, not a special case.
--
-- Every entry point takes `now` (monotonic milliseconds) so the policy is
-- pure and selfcheck-able; scheduling and IO live elsewhere.

local M = {}

local Policy = {}
Policy.__index = Policy

-- interval_ms and duration_ms are validated positive by config parsing.
function M.new(interval_ms, duration_ms)
    return setmetatable({
        interval = interval_ms,
        duration = duration_ms,
        last_real = nil, -- ms of the latest non-warming activity
        next_warm = nil, -- ms before which no warm request may fire
        deadline = nil, -- ms at which the warming window closes
        busy = false, -- a real turn is in flight
    }, Policy)
end

function Policy:activity(now)
    self.last_real = now
    self.next_warm = now + self.interval
    self.deadline = now + self.duration
end

function Policy:turn_started(now)
    self.busy = true
    self:activity(now)
end

function Policy:turn_ended(now)
    self.busy = false
    self:activity(now)
end

-- May a warm request start right now?
function Policy:due(now)
    return (not self.busy)
        and self.next_warm ~= nil
        and now >= self.next_warm
        and now < self.deadline
end

-- A warm attempt settled (success or failure): schedule the next one. A
-- failure waits out the same interval and the original window keeps running.
function Policy:attempted(now)
    self.next_warm = now + self.interval
end

-- Nothing left to do until real activity reopens the window. Lets the
-- caller stop its timer instead of ticking forever.
function Policy:expired(now)
    return self.deadline == nil or now >= self.deadline
end

return M