package intent

import (
	"context"
	"fmt"
	"math"
	"sort"
	"strings"
	"time"

	"logging-system/logsys"
)

// Recognizer 是识别的公开端口（Query 语义：纯函数式、无副作用）。
// error 只表示系统级失败（nil 快照、输入超长）；BranchFallback 是正常结果。
type Recognizer interface {
	Recognize(ctx context.Context, input string, snap *Snapshot) (Result, error)
}

// FunnelRecognizer 四级漏斗实现：guard → expectation → rules → adjudicate，
// 可选注入挂起预期提供者与 Ambiguous 分支的 L2 分类器。
type FunnelRecognizer struct {
	log *logsys.Logger
	exp ExpectationProvider
	cls Classifier
}

// NewRecognizer 构建漏斗识别器。opts 仅使用 Log 字段（阈值类参数在快照内）；
// exp / cls 可为 nil（对应阶段不启用）。
func NewRecognizer(opts Options, exp ExpectationProvider, cls Classifier) *FunnelRecognizer {
	o := opts.normalized()
	return &FunnelRecognizer{log: o.Log, exp: exp, cls: cls}
}

// Recognize 识别一次输入。确定性：同输入 + 同快照 → 同结果（日志中的耗时除外）。
func (r *FunnelRecognizer) Recognize(ctx context.Context, input string, snap *Snapshot) (Result, error) {
	if snap == nil {
		err := newError(InvalidArgument, "snapshot 为 nil")
		r.log.Module("intent").WithContext(ctx).Error("intent recognize rejected", err)
		return Result{}, err
	}
	if len(input) > snap.maxInput {
		err := newError(InvalidArgument, "输入超过长度上限", "actual_len", len(input), "max_len", snap.maxInput)
		r.log.Module("intent").WithContext(ctx).Error("intent recognize rejected", err)
		return Result{}, err
	}
	start := time.Now()
	res := r.recognize(ctx, input, snap)
	res.Commands = deriveCommands(res, snap)
	topID, conf := "", 0.0
	if res.Top != nil {
		topID, conf = res.Top.ID, res.Top.Confidence
	}
	r.log.Module("intent").WithContext(ctx).Info("intent recognized",
		"branch", string(res.Branch),
		"top_id", topID,
		"confidence", conf,
		"snapshot_revision", res.SnapshotRevision,
		"duration_ms", time.Since(start).Milliseconds())
	return res, nil
}

func (r *FunnelRecognizer) recognize(ctx context.Context, input string, snap *Snapshot) Result {
	if strings.TrimSpace(input) == "" {
		return Result{Input: input, Branch: BranchFallback, SnapshotRevision: snap.rev}
	}
	// 否定只认 excludes_any 子串，不做语义否定；「不要写入」这类说法交给命令层 Cancel。
	matchInput, folded := snap.foldInput(input)

	// Stage 0：守卫命中即短路，可表达"识别即拒绝"。
	if guardHits := snap.evalGuard(matchInput, folded); len(guardHits) > 0 {
		cands := candidatesOf(trimHits(guardHits, snap.topN), input, true)
		top := cands[0]
		return Result{Input: input, Branch: BranchGuardHit, Top: &top, Candidates: cands, SnapshotRevision: snap.rev}
	}

	// Stage 1：会话挂起预期优先于一般规则（宿主可选注入）。
	if r.exp != nil {
		if pending := r.exp.Pending(ctx); pending != nil && len(pending.IntentIDs) > 0 {
			if hits := snap.evalIDs(pending.IntentIDs, matchInput, folded); len(hits) > 0 {
				cands := candidatesOf(trimHits(hits, snap.topN), input, true)
				top := cands[0]
				return Result{Input: input, Branch: BranchExpectationHit, Top: &top, Candidates: cands, SnapshotRevision: snap.rev}
			}
		}
	}

	// Stage 2 + 3：规则计分与置信度裁决。
	hits := snap.evalRules(matchInput, folded)
	switch {
	case len(hits) == 0:
		return Result{Input: input, Branch: BranchFallback, SnapshotRevision: snap.rev}
	case len(hits) == 1 || hits[0].score-hits[1].score >= snap.margin || tieBreakByPriority(hits):
		cands := candidatesOf(trimHits(hits, snap.topN), input, true)
		top := cands[0]
		return Result{Input: input, Branch: BranchMatched, Top: &top, Candidates: cands, SnapshotRevision: snap.rev}
	}

	// Ambiguous：可选 L2 分类器重排；失败或结果不合法都保持 Ambiguous。
	cands := candidatesOf(trimHits(hits, snap.topN), input, false)
	if r.cls != nil {
		refined, err := r.cls.Refine(ctx, input, cands)
		if err != nil {
			r.log.Module("intent").WithContext(ctx).Warn("intent classifier failed; keep ambiguous", "error", err.Error())
			return Result{Input: input, Branch: BranchAmbiguous, Candidates: cands, SnapshotRevision: snap.rev}
		}
		rebuilt, err := validateRefined(cands, refined)
		if err != nil {
			r.log.Module("intent").WithContext(ctx).Warn("intent classifier result rejected; keep ambiguous", "error", err.Error())
			return Result{Input: input, Branch: BranchAmbiguous, Candidates: cands, SnapshotRevision: snap.rev}
		}
		if top, ok := adjudicateRefined(rebuilt, snap); ok {
			snap.fillTopSlots(&top, input)
			top.Reason = top.Reason + "; refined_by=classifier"
			return Result{Input: input, Branch: BranchMatched, Top: &top, Candidates: rebuilt, SnapshotRevision: snap.rev}
		}
		cands = rebuilt
	}
	return Result{Input: input, Branch: BranchAmbiguous, Candidates: cands, SnapshotRevision: snap.rev}
}

// tieBreakByPriority 报告同分（分差为 0）且前两名 Priority 不同：
// 此时高 Priority 者直接胜出，不再标歧（I5）。分差小于 margin 但非零时
// 仍按 ambiguous 处理（margin 语义不变）。
func tieBreakByPriority(hits []specHit) bool {
	if len(hits) < 2 {
		return false
	}
	return hits[0].score == hits[1].score && hits[0].cs.spec.Priority > hits[1].cs.spec.Priority
}

// validateRefined 要求分类器返回与原候选完全相同的 ID 集合且无重复。
// 置信度必须是有限值并落在 [0,1]；越界判为不合法，不截断。
// 除 Confidence 外的字段一律按 ID 从原候选重建，分类器改写的 Handler 等不生效。
func validateRefined(original, refined []Candidate) ([]Candidate, error) {
	byID := make(map[string]Candidate, len(original))
	for _, c := range original {
		if _, dup := byID[c.ID]; dup {
			return nil, fmt.Errorf("duplicate original id %s", c.ID)
		}
		byID[c.ID] = c
	}
	if len(refined) != len(original) {
		return nil, fmt.Errorf("refined candidate count %d != %d", len(refined), len(original))
	}
	seen := make(map[string]struct{}, len(refined))
	out := make([]Candidate, len(refined))
	for i, got := range refined {
		if _, dup := seen[got.ID]; dup {
			return nil, fmt.Errorf("duplicate refined id %s", got.ID)
		}
		seen[got.ID] = struct{}{}
		src, ok := byID[got.ID]
		if !ok {
			return nil, fmt.Errorf("unknown refined id %s", got.ID)
		}
		if !validConfidence(got.Confidence) {
			return nil, fmt.Errorf("confidence out of range for %s", got.ID)
		}
		src.Confidence = got.Confidence
		out[i] = src
	}
	return out, nil
}

func validConfidence(v float64) bool {
	return !math.IsNaN(v) && !math.IsInf(v, 0) && v >= 0 && v <= 1
}

// adjudicateRefined 对分类器结果重排后应用同一裁决规则；分差仍贴近则返回 false。
func adjudicateRefined(refined []Candidate, snap *Snapshot) (Candidate, bool) {
	if len(refined) == 0 {
		return Candidate{}, false
	}
	sorted := append([]Candidate(nil), refined...)
	sortCandidates(sorted)
	if len(sorted) > 1 && sorted[0].Confidence-sorted[1].Confidence < snap.margin {
		return Candidate{}, false
	}
	return sorted[0], true
}

func sortCandidates(cands []Candidate) {
	sort.SliceStable(cands, func(i, j int) bool {
		a, b := cands[i], cands[j]
		if a.Confidence != b.Confidence {
			return a.Confidence > b.Confidence
		}
		if a.Priority != b.Priority {
			return a.Priority > b.Priority
		}
		return a.ID < b.ID
	})
}

func trimHits(hits []specHit, n int) []specHit {
	if len(hits) > n {
		return hits[:n]
	}
	return hits
}

// Explain 输出单条输入的裁决轨迹（guard 与 rules 全量、确定性、无识别器状态）。
// 这是配置规范要求的只读诊断；intentctl explain 在此之上构建。
func (s *Snapshot) Explain(input string) Trace {
	trace := Trace{InputLen: len(input), AmbiguityMargin: s.margin}
	if strings.TrimSpace(input) == "" {
		trace.Branch = BranchFallback
		return trace
	}
	matchInput, folded := s.foldInput(input)

	for _, idx := range s.guardIdx {
		cs := s.specs[idx]
		o := cs.evaluate(matchInput, folded)
		if o.passed {
			trace.Guard = append(trace.Guard, ScoredSpec{ID: cs.spec.ID, Score: o.score, HitTerms: o.hitTerms, HitPatterns: o.hitPat})
		} else {
			trace.GuardRejected = append(trace.GuardRejected, RejectedSpec{ID: cs.spec.ID, Reason: o.reject})
		}
	}
	sortScored(trace.Guard)
	sortRejected(trace.GuardRejected)
	if len(trace.Guard) > 0 {
		trace.Branch = BranchGuardHit
		trace.TopID = trace.Guard[0].ID
		return trace
	}

	var hits []specHit
	for _, cs := range s.specs {
		if cs.guard {
			continue
		}
		o := cs.evaluate(matchInput, folded)
		if o.passed {
			hits = append(hits, specHit{cs: cs, score: o.score, terms: o.hitTerms, pats: o.hitPat})
			trace.Rules = append(trace.Rules, ScoredSpec{ID: cs.spec.ID, Score: o.score, HitTerms: o.hitTerms, HitPatterns: o.hitPat})
		} else {
			trace.RulesRejected = append(trace.RulesRejected, RejectedSpec{ID: cs.spec.ID, Reason: o.reject})
		}
	}
	sortHits(hits)
	sortScored(trace.Rules)
	sortRejected(trace.RulesRejected)

	switch {
	case len(hits) == 0:
		trace.Branch = BranchFallback
	case len(hits) == 1 || hits[0].score-hits[1].score >= s.margin || tieBreakByPriority(hits):
		trace.Branch = BranchMatched
		trace.TopID = hits[0].cs.spec.ID
	default:
		trace.Branch = BranchAmbiguous
	}
	return trace
}

func sortScored(ss []ScoredSpec) {
	sort.SliceStable(ss, func(i, j int) bool { return ss[i].ID < ss[j].ID })
}

func sortRejected(rs []RejectedSpec) {
	sort.SliceStable(rs, func(i, j int) bool { return rs[i].ID < rs[j].ID })
}