// Package skillexec runs saved Skill definitions via majordomo's agent
// loop (gitea.stevedudenhoeffer.com/steve/majordomo/agent).
//
// Why: a Skill is data; the executor turns data into a running agent
// (resolve model, build toolbox, start audit, run the agent loop,
// finish audit, deliver).
package budget

import (
	"context"
	"errors"
	"fmt"
	"log/slog"
	"time"
)

// BudgetTracker enforces per-user GPU budgets in v2. v1 ships
// NoOpBudget which always allows. The interface exists now so the v2
// migration is a single line in the executor.
//
// Why interface now: the executor's Check/Commit calls would need to
// be added in v2 anyway; doing it now means v2 only swaps NoOp for
// DBBudget without touching call sites.
type BudgetTracker interface {
	// Check reports whether the caller has remaining budget. Returns
	// nil for "yes" or an error describing the exhaustion.
	Check(ctx context.Context, callerID string) error

	// Commit records that the caller spent runtimeSeconds of budget on
	// this run. Called after the agent completes (success or error).
	Commit(ctx context.Context, callerID string, runtimeSeconds float64)
}

// NoOpBudget always allows and never records. v1 default.
type NoOpBudget struct{}

// NewNoOpBudget constructs the no-op tracker.
func NewNoOpBudget() BudgetTracker { return NoOpBudget{} }

// Check always returns nil.
func (NoOpBudget) Check(_ context.Context, _ string) error { return nil }

// Commit is a no-op.
func (NoOpBudget) Commit(_ context.Context, _ string, _ float64) {}

// ErrBudgetExceeded is returned by DBBudget.Check when the caller's
// 7-day rolling window has hit the convar-configured cap.
//
// Why a sentinel: callers (executor, audit writer) need to distinguish
// budget rejection from generic errors so they can record
// status="budget_exceeded" instead of "error" and skip user-visible
// delivery side-effects.
var ErrBudgetExceeded = errors.New("weekly skill budget exceeded")

// BudgetNotifier is the optional callback DBBudget invokes when a
// Check rejects a caller. Production wires a Discord-DM hook so the
// user knows why their skill failed; tests inject a recorder.
//
// nil is allowed and is silently skipped.
type BudgetNotifier func(ctx context.Context, userID string, secondsUsed, cap float64)

// DBBudget enforces per-user weekly GPU budgets via the BudgetStorage
// interface. The "weekly" cap is a rolling 7-day window — see
// SkillBudget for the rollover semantics.
//
// Why a closure for the limit instead of an int field: the cap comes
// from a runtime convar. Reading it on every Check means a `.convar
// set skills.user_budget_seconds_per_week 7200` takes effect on the
// next call without restarting the bot or rewiring the executor.
type DBBudget struct {
	storage BudgetStorage
	// weeklyLimit returns the current cap in seconds. Reads convar at
	// every Check so a runtime convar bump takes effect on the next
	// call.
	weeklyLimit func() float64

	// notify is called when a Check rejects a caller. Optional —
	// production wires a Discord-DM hook so the user knows why their
	// skill failed. nil-safe.
	notify BudgetNotifier

	// now is the time source. Test injects a fake clock; production
	// uses time.Now.
	now func() time.Time
}

// NewDBBudget constructs a DBBudget. now may be nil — defaults to
// time.Now.
//
// Why time injection: budget rollover is time-sensitive; tests need to
// fast-forward past the 7-day boundary deterministically. now=nil
// means production callers (mort.go) don't have to think about it.
//
// Test: pass a closure that returns a fixed instant; assert rollover
// only happens when (now - WindowStart) >= 7 days.
func NewDBBudget(storage BudgetStorage, weeklyLimit func() float64, notify BudgetNotifier, now func() time.Time) *DBBudget {
	if now == nil {
		now = time.Now
	}
	return &DBBudget{
		storage:     storage,
		weeklyLimit: weeklyLimit,
		notify:      notify,
		now:         now,
	}
}

// Check returns ErrBudgetExceeded if the caller has spent at least
// weeklyLimit seconds in the current rolling 7-day window.
//
// Why anonymous callerID="" is unbudgeted: scheduler-driven and
// system-initiated runs don't have a Discord user to bill; charging
// "system" would conflate them with a real user. The scheduler sets
// CallerID to the skill owner where applicable, so cron-loop
// abusiveness still consumes the owner's budget.
//
// Why cap<=0 means "disabled": operator wants a runtime kill-switch.
// Setting the convar to "0" turns enforcement off without restart.
//
// Test: Get returns nil → Check returns nil; Get returns row with
// SecondsUsed >= cap → Check returns ErrBudgetExceeded and notify is
// invoked; window expired (>=7d) → Check returns nil regardless of
// SecondsUsed.
func (b *DBBudget) Check(ctx context.Context, callerID string) error {
	if callerID == "" {
		return nil
	}
	bud, err := b.storage.Get(ctx, callerID)
	if err != nil {
		return fmt.Errorf("budget: %w", err)
	}
	if bud != nil {
		if b.now().Sub(bud.WindowStart) < 7*24*time.Hour {
			cap := b.weeklyLimit()
			if cap > 0 && bud.SecondsUsed >= cap {
				if b.notify != nil {
					b.notify(ctx, callerID, bud.SecondsUsed, cap)
				}
				return ErrBudgetExceeded
			}
		}
	}
	return nil
}

// Commit records the run's runtime against the caller's budget.
// Failures are logged but never returned — budget accounting must
// not break user-visible execution.
//
// Why callerID="" is a no-op: matches Check's anonymous-caller
// shortcut; system runs don't get billed.
//
// Why runtimeSeconds<=0 is a no-op: a run that errored before
// resolving a model has wallSecs near 0 in floating-point terms but
// can also be exactly 0 (synthetic test fixtures). Skipping avoids
// spurious 0-runs rows from short-lived failures.
//
// Test: Commit(50) → Get reports SecondsUsed=50; storage failure
// surfaces only as a slog.Warn (no panic, no return).
func (b *DBBudget) Commit(ctx context.Context, callerID string, runtimeSeconds float64) {
	if callerID == "" || runtimeSeconds <= 0 {
		return
	}
	if err := b.storage.Add(ctx, callerID, runtimeSeconds, b.now()); err != nil {
		slog.Warn("skills budget: commit failed", "user", callerID, "error", err)
	}
}