package services

import (
	"database/sql"
	"fmt"
	"strings"

	"github.com/go-git/go-git/v5/plumbing"
	"github.com/go-git/go-git/v5/plumbing/object"
	goopenai "github.com/sashabaranov/go-openai"
)

// GeneratePR generates a PR description as Markdown from commit history and diff.
// It streams the LLM output via callback ("content" events) and returns the full markdown.
func GeneratePR(db *sql.DB, repoPath, base, head string, userID int64, callback StreamCallback) (string, error) {
	// Read LLM config (per-user)
	config, err := GetLLMConfig(db, userID)
	if err != nil {
		return "", err
	}

	// Open repo
	repo, err := OpenRepo(repoPath)
	if err != nil {
		return "", fmt.Errorf("open repo: %w", err)
	}

	// Get commits between base and head
	commits, err := GetCommitLog(repo, head, 100)
	if err != nil {
		return "", fmt.Errorf("get commits: %w", err)
	}

	// Filter commits to only those reachable from head but not from base
	baseHash, err := repo.ResolveRevision(plumbing.Revision(base))
	if err == nil {
		baseCommit, bcErr := repo.CommitObject(*baseHash)
		if bcErr == nil {
			baseSet := make(map[string]bool)
			baseQueue := []*object.Commit{baseCommit}
			for len(baseQueue) > 0 {
				c := baseQueue[0]
				baseQueue = baseQueue[1:]
				if baseSet[c.Hash.String()] {
					continue
				}
				baseSet[c.Hash.String()] = true
				for _, p := range c.ParentHashes {
					pc, err := repo.CommitObject(p)
					if err == nil {
						baseQueue = append(baseQueue, pc)
					}
				}
			}
			var filtered []CommitInfo
			for _, ci := range commits {
				if !baseSet[ci.Hash] {
					filtered = append(filtered, ci)
				}
			}
			if len(filtered) > 0 {
				commits = filtered
			}
		}
	}

	// Get diff
	diff, err := GetDiff(repo, base, head)
	if err != nil {
		return "", fmt.Errorf("get diff: %w", err)
	}

	// Build prompt
	var commitLines []string
	for _, c := range commits {
		commitLines = append(commitLines, fmt.Sprintf("- %s %s", c.ShortHash, c.Message))
	}

	commitStr := strings.Join(commitLines, "\n")
	if commitStr == "" {
		commitStr = "(no commits)"
	}

	// Truncate diff if too large (approx 60k chars to stay within token limits)
	if len(diff) > 60000 {
		diff = diff[:60000] + "\n\n... [diff truncated due to size]"
	}

	prompt := fmt.Sprintf(`你是一个专业的技术文档撰写助手。根据以下 Git 变更信息，生成一份 PR 描述。

## Commit 记录
%s

## 代码变更 (Diff)
%s

请直接输出 Markdown 格式的 PR 描述，包含以下部分：

# 标题

**类型**: feat|fix|refactor|docs|chore|style|test|perf

## 概述
一段话概述变更内容

## 详细说明
按模块分组的详细变更说明

## 影响范围
影响范围说明

格式要求：
- 引用文件名、函数名、变量名等代码标识时，必须用反引号包裹
- 直接写出实际的代码名称，不要用任何占位符替代
- 不要输出 JSON，直接输出 Markdown`, commitStr, diff)

	messages := []goopenai.ChatCompletionMessage{
		{Role: goopenai.ChatMessageRoleUser, Content: prompt},
	}

	// Call LLM with streaming — content events carry markdown chunks in real-time
	fullResponse, err := ChatStream(config, messages, callback)
	if err != nil {
		return "", fmt.Errorf("LLM call: %w", err)
	}

	// Signal completion
	if callback != nil {
		callback("done", map[string]interface{}{"content": ""})
	}

	return fullResponse, nil
}