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// Package budget tracks agent spend against rolling per-provider windows so the
// dispatcher can refuse (or reroute) paid work that would breach a cap. Local
// runners are free and simply carry no configured limit.
package budget
import (
"sort"
"time"
)
// DefaultWindow is the rolling spend window when none is configured.
const DefaultWindow = 5 * time.Hour
// Limits configures per-provider spend caps within a rolling window.
type Limits struct {
// Window is the rolling lookback; DefaultWindow when zero.
Window time.Duration
// PerProvider maps a provider (claude/gemini/…) to its USD cap within the
// window. A missing or non-positive entry means "unlimited" (e.g. local).
PerProvider map[string]float64
}
// SpendSource supplies total spend per provider since a given time.
type SpendSource interface {
SpendByProviderSince(since time.Time) (map[string]float64, error)
}
// Headroom describes remaining budget for one provider in the current window.
type Headroom struct {
Provider string `json:"provider"`
Limited bool `json:"limited"`
Limit float64 `json:"limit_usd"`
Spent float64 `json:"spent_usd"`
Remaining float64 `json:"remaining_usd"`
// Fraction is the share of the cap still available, 0..1 (0 when unlimited).
Fraction float64 `json:"fraction_remaining"`
}
// Accountant answers spend questions against a SpendSource and Limits.
type Accountant struct {
src SpendSource
lim Limits
now func() time.Time
}
// New builds an Accountant. A zero Window defaults to DefaultWindow.
func New(src SpendSource, lim Limits) *Accountant {
if lim.Window <= 0 {
lim.Window = DefaultWindow
}
return &Accountant{src: src, lim: lim, now: time.Now}
}
func (a *Accountant) since() time.Time { return a.now().Add(-a.lim.Window) }
func (a *Accountant) headroomFrom(provider string, spends map[string]float64) Headroom {
limit := a.lim.PerProvider[provider]
if limit <= 0 {
return Headroom{Provider: provider, Limited: false}
}
spent := spends[provider]
remaining := limit - spent
if remaining < 0 {
remaining = 0
}
return Headroom{
Provider: provider,
Limited: true,
Limit: limit,
Spent: spent,
Remaining: remaining,
Fraction: remaining / limit,
}
}
// Headroom returns the remaining budget for one provider in the current window.
func (a *Accountant) Headroom(provider string) (Headroom, error) {
if a.lim.PerProvider[provider] <= 0 {
return Headroom{Provider: provider, Limited: false}, nil
}
spends, err := a.src.SpendByProviderSince(a.since())
if err != nil {
return Headroom{}, err
}
return a.headroomFrom(provider, spends), nil
}
// Allow reports whether starting a task on provider that may cost up to estCost
// is permitted without breaching the window cap. Unlimited providers always
// pass. estCost is typically the task's max_budget_usd (0 = unknown).
func (a *Accountant) Allow(provider string, estCost float64) (bool, error) {
h, err := a.Headroom(provider)
if err != nil {
return false, err
}
if !h.Limited {
return true, nil
}
return h.Spent+estCost <= h.Limit, nil
}
// All returns headroom for every configured provider, sorted by name, in a
// single spend query.
func (a *Accountant) All() ([]Headroom, error) {
if len(a.lim.PerProvider) == 0 {
return []Headroom{}, nil
}
spends, err := a.src.SpendByProviderSince(a.since())
if err != nil {
return nil, err
}
providers := make([]string, 0, len(a.lim.PerProvider))
for p := range a.lim.PerProvider {
providers = append(providers, p)
}
sort.Strings(providers)
out := make([]Headroom, 0, len(providers))
for _, p := range providers {
out = append(out, a.headroomFrom(p, spends))
}
return out, nil
}
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