// Package quota is the z.ai coding-plan quota gate (Redmine 490) plus the
// read-only system resource monitor (Redmine 491): it tracks plan credit
// buckets (5-hour + weekly), computes per-turn credit consumption from the
// documented z.ai formula, applies TZ-aware peak-hour scheduling and
// back-pressure thresholds, and shares quota state across harness instances
// through an optional redis container. The gate NEVER hard-fails the loop:
// unknown state is permissive, exhaustion defers work with a logged reason.
//
// z.ai credit model (docs.z.ai/devpack/overview, 2026-08-29):
//
//	credits = (input*in_mult + cached_input*cache_mult + output*out_mult) / 10000
//
// GLM-5.3: 6.9/1.7/24; GLM-5.3-Flash: 2.3/0.56/8. Off-peak hours charge 50%.
// Plans: Lite 2,000/10,000, Pro 12,000/60,000, Max 28,000/140,000 credits
// (5-hour / weekly). LIVE VERIFICATION of the usage endpoint is OPEN: z.ai
// documents the buckets but no public usage REST route exists today
// (probed 2026-08-29, see REPORT-20260829-0500-quota); the parser targets
// the documented shape and runs against a fake server until z.ai ships it.
package quota

import (
	"encoding/json"
	"fmt"
	"time"
)

// Bucket IDs for the z.ai coding-plan windows.
const (
	Bucket5h     = "5h"
	BucketWeekly = "weekly"
)

// Bucket is one usage window: credits used against the plan limit and when
// the window resets. Used/Limit are in z.ai credits, not tokens or dollars.
type Bucket struct {
	ID          string    `json:"id"`
	Used        float64   `json:"used"`
	Limit       float64   `json:"limit"`
	WindowReset time.Time `json:"window_reset"`
}

// UsedPct is the bucket's consumption ratio in percent of the limit.
// A zero/negative limit reads as 0 (never blocks).
func (b Bucket) UsedPct() float64 {
	if b.Limit <= 0 {
		return 0
	}
	return b.Used / b.Limit * 100
}

// QuotaSnapshot is one account's quota state at a point in time, either
// polled from the provider (Source "usage_url") or synthesized from locally
// estimated consumption against the configured plan limits (Source
// "estimate").
type QuotaSnapshot struct {
	Account   string    `json:"account"`
	Source    string    `json:"source"`
	FetchedAt time.Time `json:"fetched_at"`
	Buckets   []Bucket  `json:"buckets"`
}

// Bucket returns the bucket with the given id, if present.
func (s *QuotaSnapshot) Bucket(id string) (Bucket, bool) {
	for _, b := range s.Buckets {
		if b.ID == id {
			return b, true
		}
	}
	return Bucket{}, false
}

// MaxUsedPct is the highest consumption ratio across all buckets — the
// number back-pressure thresholds compare against.
func (s *QuotaSnapshot) MaxUsedPct() float64 {
	if s == nil {
		return 0
	}
	max := 0.0
	for _, b := range s.Buckets {
		if p := b.UsedPct(); p > max {
			max = p
		}
	}
	return max
}

// providerUsage is the z.ai usage response shape this parser targets. z.ai
// has not published the route yet; field aliases (used_credits|credits_used,
// total_credits|limit_credits) keep the parser tolerant of either naming.
type providerUsage struct {
	Usage struct {
		FiveHour providerBucket `json:"five_hour"`
		Weekly   providerBucket `json:"weekly"`
	} `json:"usage"`
}

type providerBucket struct {
	Used       any     `json:"used_credits"`
	UsedAlias  any     `json:"credits_used"`
	Limit      any     `json:"total_credits"`
	LimitAlias any     `json:"limit_credits"`
	ResetAt    string  `json:"reset_at"`
	ResetAlias string  `json:"reset_time"`
}

// ParseUsage decodes a provider usage response into a QuotaSnapshot for the
// account. It is strict about structure (unknown shapes error so a silent
// HTML error page never reads as "quota fine") and lenient about field
// naming within the documented buckets.
func ParseUsage(account string, fetchedAt time.Time, body []byte) (*QuotaSnapshot, error) {
	var p providerUsage
	if err := json.Unmarshal(body, &p); err != nil {
		return nil, fmt.Errorf("usage decode: %w", err)
	}
	num := func(v any) (float64, bool) {
		switch n := v.(type) {
		case float64:
			return n, true
		case string:
			var f float64
			if _, err := fmt.Sscanf(n, "%g", &f); err == nil {
				return f, true
			}
		}
		return 0, false
	}
	snap := &QuotaSnapshot{Account: account, Source: "usage_url", FetchedAt: fetchedAt}
	for id, pb := range map[string]providerBucket{Bucket5h: p.Usage.FiveHour, BucketWeekly: p.Usage.Weekly} {
		used, ok := num(pb.Used)
		if !ok {
			used, ok = num(pb.UsedAlias)
		}
		if !ok {
			return nil, fmt.Errorf("usage decode: bucket %q has no used_credits", id)
		}
		limit, ok := num(pb.Limit)
		if !ok {
			limit, ok = num(pb.LimitAlias)
		}
		if !ok {
			return nil, fmt.Errorf("usage decode: bucket %q has no total_credits", id)
		}
		reset := pb.ResetAt
		if reset == "" {
			reset = pb.ResetAlias
		}
		rt := time.Time{}
		if reset != "" {
			var err error
			rt, err = time.Parse(time.RFC3339, reset)
			if err != nil {
				return nil, fmt.Errorf("usage decode: bucket %q reset_at: %w", id, err)
			}
		}
		snap.Buckets = append(snap.Buckets, Bucket{ID: id, Used: used, Limit: limit, WindowReset: rt})
	}
	if len(snap.Buckets) != 2 {
		return nil, fmt.Errorf("usage decode: want five_hour and weekly buckets, got %d", len(snap.Buckets))
	}
	return snap, nil
}