package validator

import (
	"context"
	"errors"
	"fmt"
	"strings"

	"git.flytoex.net/yuanwei/flyto-agent/internal/transport/retry"
	"git.flytoex.net/yuanwei/flyto-agent/pkg/flyto"
)

// FlytoLLMClient wraps a flyto.ModelProvider as a minimal text-in /
// text-out client for Validator implementations that delegate verdicts
// to an LLM. It is an independent copy of the evolve package's
// adapter (same event-aggregation algorithm, different caller label)
// so validator and evolve remain siblings without a cross-package
// dependency.
//
// Direction of dependency:
// validator consumes flyto.ModelProvider; providers/ subpackages
// define concrete providers. The direction is validator -> flyto.
//
// Temperature limitation (inherited from flyto.Request contract):
// flyto.Request is the cross-provider greatest common denominator and
// deliberately omits Temperature. Per-provider knobs live in the
// provider factory Config (anthropic.Config / minimax.Config / ...).
// Callers needing per-call temperature control construct separate
// provider instances with different factory Configs.
//
// Event filtering:
//   - Aggregated:  TextEvent (authoritative), TextDeltaEvent (fallback)
//   - Error path:  ErrorEvent -> wraps ErrValidatorBackend
//   - Ignored:     ToolUse*, Thinking*, Usage, Done, Turn*, SessionInfo,
//                  Permission*, Warning, Compact, Checkpoint*
//
// Aggregation precedence (CLEVER):
// some providers emit both TextDeltaEvent (streaming increments) and
// TextEvent (the complete text block on block_stop). A naive "sum
// both" strategy double-counts. TextEvent is authoritative: on each
// TextEvent arrival we append the final text and reset the delta
// accumulator. If the stream closes without any TextEvent (providers
// that skip the complete-block emission) we fall back to the delta
// accumulator so no text is lost.
//
// FlytoLLMClient 把 flyto.ModelProvider 包装为文本进 / 文本出的最小
// 客户端, 供把审批决策委托给 LLM 的 Validator 实现使用. 本文件是
// evolve 包 adapter 的独立副本 (同事件聚合算法, 不同调用方标签), 让
// validator 与 evolve 保持平级不互相依赖.
//
// 依赖方向: validator 消费 flyto.ModelProvider; providers/ 子包定义
// 具体 provider. 方向是 validator -> flyto.
//
// Temperature 限制 (源自 flyto.Request 契约): flyto.Request 是跨
// provider 最大公约数, 刻意不含 Temperature. Provider 专有旋钮放在
// 工厂 Config (anthropic.Config / minimax.Config 等). 需要按次温度
// 控制的调用方构造不同 Config 的 provider 实例.
//
// 事件过滤:
//   - 聚合:       TextEvent (权威), TextDeltaEvent (fallback)
//   - 错误路径:    ErrorEvent -> 包装 ErrValidatorBackend
//   - 忽略:       ToolUse* / Thinking* / Usage / Done / Turn* / ...
//
// 聚合优先级 (CLEVER): 部分 provider 同时推 TextDeltaEvent 和 TextEvent,
// 简单 "都加" 会双倍计. TextEvent 为权威: 每次收到 TextEvent 追加完整
// 文本并重置 delta 累计. 流关闭时若无任何 TextEvent (跳过 block_stop
// 推送的 provider) 回退到 delta 累计器避免丢文本.
type FlytoLLMClient struct {
	provider     flyto.ModelProvider
	defaultModel string
	systemPrompt string
}

// NewFlytoLLMClient builds a FlytoLLMClient. provider is required.
// defaultModel is used when Complete's model argument is "". systemPrompt
// is injected verbatim into flyto.Request.System on every Complete call
// (pass "" to omit).
//
// NewFlytoLLMClient 构造 FlytoLLMClient. provider 必填. defaultModel 在
// Complete 的 model 参数为 "" 时使用. systemPrompt 每次 Complete 调用
// 原样注入 flyto.Request.System (传 "" 忽略).
func NewFlytoLLMClient(provider flyto.ModelProvider, defaultModel, systemPrompt string) (*FlytoLLMClient, error) {
	if provider == nil {
		return nil, errors.New("validator: NewFlytoLLMClient requires non-nil provider")
	}
	return &FlytoLLMClient{
		provider:     provider,
		defaultModel: defaultModel,
		systemPrompt: systemPrompt,
	}, nil
}

// Complete sends prompt as a single user message and drains the
// provider event stream into a response string. On backend failure
// the returned error wraps ErrValidatorBackend so callers detect the
// class via errors.Is. An empty model falls back to defaultModel.
// maxTokens = 0 leaves the field at flyto.Request default.
//
// Complete 以单条 user message 发送 prompt 并聚合 provider 事件流为
// 响应字符串. backend 失败时返回的 error 以 %w 包装 ErrValidatorBackend,
// 调用方用 errors.Is 识别. model 为 "" 回退到 defaultModel. maxTokens=0
// 使用 flyto.Request 默认.
func (c *FlytoLLMClient) Complete(ctx context.Context, prompt string, model string, maxTokens int) (string, error) {
	effectiveModel := model
	if effectiveModel == "" {
		effectiveModel = c.defaultModel
	}

	req := &flyto.Request{
		Model:     effectiveModel,
		System:    c.systemPrompt,
		Messages:  []flyto.Message{flyto.UserText(prompt)},
		MaxTokens: maxTokens,
	}

	// Validator: pre-commit gate LLM calls. Tag ctx so retry failures
	// here don't alias with main-thread user failures.
	//
	// Validator: pre-commit gate 的 LLM 调用. 标记 ctx 让此处重试失败
	// 不与主线程用户失败混淆.
	ctx = retry.WithQuerySource(ctx, "validator")

	ch, err := c.provider.Stream(ctx, req)
	if err != nil {
		return "", fmt.Errorf("%w: %v", ErrValidatorBackend, err)
	}

	var textBlocks []string
	var deltaBuf strings.Builder

	for {
		select {
		case <-ctx.Done():
			return "", ctx.Err()
		case evt, ok := <-ch:
			if !ok {
				if len(textBlocks) > 0 {
					return strings.Join(textBlocks, ""), nil
				}
				return deltaBuf.String(), nil
			}
			switch e := evt.(type) {
			case *flyto.TextEvent:
				textBlocks = append(textBlocks, e.Text)
				deltaBuf.Reset()
			case *flyto.TextDeltaEvent:
				deltaBuf.WriteString(e.Text)
			case *flyto.ErrorEvent:
				return "", fmt.Errorf("%w: %v", ErrValidatorBackend, e.Err)
			default:
				// Ignore ToolUse / Thinking / Usage / Done / Turn* / etc.
			}
		}
	}
}