package capacity

import (
	"context"
	"encoding/json"
	"fmt"
	"log/slog"
	"strings"

	"git.yeij.top/AskaEth/Cyrene_v2/internal/logger"
	"git.yeij.top/AskaEth/Cyrene_v2/internal/runtime/model"
)

// l3MaxTokens caps the classifier's reply: it is a tiny JSON object, and an
// uncapped reply would burn budget on prose the parser then rejects.
const l3MaxTokens = 128

// l3SystemPrompt instructs the model to answer with a strict JSON judgment only.
// It deliberately repeats "JSON only": a prose answer is an error, not a verdict.
const l3SystemPrompt = `你是意图分类器。判断用户这一轮是在「办事」（有明确任务动作/对象），还是在「陪伴/闲聊」。
只输出一个 JSON 对象，不要任何解释或代码块标记，格式：
{"isTask": true|false, "taskKind": "complex"|"code"|"query"|"ops", "confidence": 0.0-1.0}
taskKind 只在 isTask 为 true 时有意义；拿不准时把 confidence 给低（<0.6）。`

// l3WireJudgment is the wire shape the classifier parses. It is separate from
// Judgment so an unexpected field can never leak into the decision engine.
type l3WireJudgment struct {
	IsTask     bool    `json:"isTask"`
	TaskKind   string  `json:"taskKind"`
	Confidence float64 `json:"confidence"`
}

// LLMClassifier is the model-assisted intent classifier behind the L3 layer
// (design/14 §2.2 L3; 裁决 14.4.4). It asks the adapter for a strict JSON
// judgment and returns it; an unparsable or empty reply is an error, never a
// guess, so the caller keeps its conservative default. It is safe for concurrent
// use.
type LLMClassifier struct {
	adapter model.Adapter
	log     *slog.Logger
}

// NewLLMClassifier builds the classifier over the runtime's LLM stack. A nil
// adapter is allowed and makes Classify report ErrNotConfigured.
func NewLLMClassifier(adapter model.Adapter, log *slog.Logger) *LLMClassifier {
	if log == nil {
		log = slog.New(slog.NewTextHandler(discard{}, nil))
	}
	return &LLMClassifier{adapter: adapter, log: logger.WithSource(log, "runtime/capacity")}
}

// ErrNotConfigured is returned when the classifier has no LLM stack to ask.
var ErrNotConfigured = fmt.Errorf("capacity: L3 classifier has no model configured")

// Classify asks the model for one judgment of text. It returns the raw verdict;
// callers apply the confidence threshold (see Decider.l3).
func (c *LLMClassifier) Classify(ctx context.Context, text string) (Judgment, error) {
	if strings.TrimSpace(text) == "" {
		return Judgment{}, ErrEmptyTurn
	}
	if c.adapter == nil {
		return Judgment{}, ErrNotConfigured
	}
	resp, err := c.adapter.Chat(ctx, model.Request{
		Messages: []model.Message{
			model.TextMessage(model.RoleSystem, l3SystemPrompt),
			model.TextMessage(model.RoleUser, text),
		},
		MaxTokens: l3MaxTokens,
		Purpose:   "capacity-l3",
	}, model.Options{})
	if err != nil {
		return Judgment{}, fmt.Errorf("capacity: L3 classify: %w", err)
	}
	wire, err := parseL3Judgment(resp.Content)
	if err != nil {
		return Judgment{}, err
	}
	c.log.Debug("capacity L3 verdict",
		"is_task", wire.IsTask, "task_kind", strings.TrimSpace(wire.TaskKind),
		"confidence", wire.Confidence)
	return Judgment{
		IsTask:     wire.IsTask,
		TaskKind:   strings.TrimSpace(wire.TaskKind),
		Confidence: clampUnit(wire.Confidence),
	}, nil
}

// parseL3Judgment extracts the JSON object from a model reply. A reply wrapped in
// a ```json fence is tolerated (models add one routinely), but prose around the
// object is not: the object must be the whole answer.
func parseL3Judgment(content string) (l3WireJudgment, error) {
	raw := stripCodeFence(strings.TrimSpace(content))
	if raw == "" {
		return l3WireJudgment{}, fmt.Errorf("capacity: L3 classify: %w: empty reply", model.ErrBadRequest)
	}
	var wire l3WireJudgment
	if err := json.Unmarshal([]byte(raw), &wire); err != nil {
		return l3WireJudgment{}, fmt.Errorf("capacity: L3 classify: %w: parse reply: %v", model.ErrBadRequest, err)
	}
	return wire, nil
}

// stripCodeFence removes a single ```/```json fence around the payload when the
// whole reply is fenced.
func stripCodeFence(s string) string {
	if !strings.HasPrefix(s, "```") {
		return s
	}
	body := strings.TrimPrefix(s, "```")
	if i := strings.IndexByte(body, '\n'); i >= 0 {
		body = body[i+1:]
	}
	body = strings.TrimSuffix(body, "```")
	return strings.TrimSpace(body)
}

// clampUnit keeps a model-reported confidence inside [0,1], so a hallucinated
// 7.5 can never outrank the threshold arithmetic.
func clampUnit(v float64) float64 {
	switch {
	case v < 0:
		return 0
	case v > 1:
		return 1
	default:
		return v
	}
}