package main

import (
	"crypto/sha256"
	"encoding/hex"
	"encoding/json"
	"errors"
	"fmt"
	"io"
	"os"
	"path/filepath"
	"slices"
	"strings"
	"time"
)

const aiStoreVersion = 1

type AIStore struct {
	dir     string
	loadErr error
}

type aiStoredState struct {
	Version     int                        `json:"version"`
	Owner       string                     `json:"owner"`
	Repository  string                     `json:"repository"`
	Number      int                        `json:"number"`
	Threads     []ReviewThread             `json:"threads"`
	Annotations map[string][]ReviewComment `json:"annotations"`
}

func NewAIStore(dir string) *AIStore { return &AIStore{dir: dir} }

func (s *AIStore) path(pr PRDetails) string {
	sum := sha256.Sum256([]byte(fmt.Sprintf("%s/%s#%d", pr.Owner, pr.Repository, pr.Number)))
	return filepath.Join(s.dir, hex.EncodeToString(sum[:16])+".json")
}

func (s *AIStore) Load(pr PRDetails) (*aiStoredState, error) {
	state := &aiStoredState{
		Version: aiStoreVersion, Owner: pr.Owner, Repository: pr.Repository, Number: pr.Number,
		Annotations: make(map[string][]ReviewComment),
	}
	if s == nil || s.dir == "" {
		return state, nil
	}
	file, err := os.Open(s.path(pr))
	if errors.Is(err, os.ErrNotExist) {
		return state, nil
	}
	if err != nil {
		s.loadErr = err
		return nil, fmt.Errorf("read local AI state: %w", err)
	}
	defer file.Close()
	data, err := io.ReadAll(io.LimitReader(file, (16<<20)+1))
	if err != nil {
		return nil, fmt.Errorf("read local AI state: %w", err)
	}
	if len(data) > 16<<20 {
		return nil, errors.New("read local AI state: file exceeds 16 MiB safety limit")
	}
	if err := json.Unmarshal(data, state); err != nil || state.Version != aiStoreVersion ||
		state.Owner != pr.Owner || state.Repository != pr.Repository || state.Number != pr.Number {
		if err == nil {
			err = errors.New("incompatible or mismatched state")
		}
		s.loadErr = err
		return nil, fmt.Errorf("read local AI state: %w", err)
	}
	if state.Annotations == nil {
		state.Annotations = make(map[string][]ReviewComment)
	}
	return state, nil
}

func (s *AIStore) Save(pr PRDetails, state *aiStoredState) error {
	if s == nil || s.dir == "" {
		return errors.New("local AI store is unavailable")
	}
	if err := os.MkdirAll(s.dir, 0o700); err != nil {
		return fmt.Errorf("create local AI store: %w", err)
	}
	if err := os.Chmod(s.dir, 0o700); err != nil {
		return fmt.Errorf("protect local AI store: %w", err)
	}
	path := s.path(pr)
	next, err := json.MarshalIndent(state, "", "  ")
	if err != nil {
		return err
	}
	if current, err := os.ReadFile(path); err == nil && string(current) == string(next) {
		return nil
	}
	return atomicWriteJSON(path, state, 0o600)
}

func (s *aiStoredState) Merge(pr PRDetails) PRDetails {
	result := pr
	result.Threads = make([]ReviewThread, len(pr.Threads), len(pr.Threads)+len(s.Threads))
	copy(result.Threads, pr.Threads)
	for index := range result.Threads {
		result.Threads[index].Comments = slices.Clone(result.Threads[index].Comments)
	}
	for i := range s.Threads {
		thread := s.Threads[i]
		thread.Comments = slices.Clone(thread.Comments)
		thread.IsOutdated = thread.HeadOID != "" && thread.HeadOID != pr.HeadOID
		result.Threads = append(result.Threads, thread)
	}
	for i := range result.Threads {
		if comments := s.Annotations[result.Threads[i].ID]; len(comments) > 0 {
			comments = slices.Clone(comments)
			for index := range comments {
				if comments[index].Origin == reviewOriginLocalAIUser && pr.ViewerLogin != "" {
					comments[index].Author = pr.ViewerLogin
				}
			}
			result.Threads[i].Comments = append(result.Threads[i].Comments, comments...)
			slices.SortStableFunc(result.Threads[i].Comments, func(left, right ReviewComment) int {
				return left.CreatedAt.Compare(right.CreatedAt)
			})
		}
	}
	return result
}

func (s *aiStoredState) Apply(
	pr PRDetails, output aiOutput, provider, model, targetThread, message string,
	validLines map[string]map[int]bool,
	validDeleted map[string]map[int]bool,
	diffText map[string]string,
) (int, int) {
	existing := make(map[string]bool)
	localByFingerprint := make(map[string]int, len(s.Threads))
	for index, thread := range s.Threads {
		if thread.Fingerprint != "" {
			localByFingerprint[thread.Fingerprint] = index
		}
	}
	type priorFinding struct {
		path       string
		start, end int
		text       string
	}
	var prior []priorFinding
	for _, thread := range append(slices.Clone(pr.Threads), s.Threads...) {
		existing[thread.Fingerprint] = thread.Fingerprint != ""
		var combined strings.Builder
		for _, comment := range thread.Comments {
			existing[aiFingerprint(thread.Path, thread.StartLine, thread.Line, "", comment.Body)] = true
			existing[aiFingerprint(thread.ID, 0, 0, "", comment.Body)] = true
			if comment.Origin == reviewOriginLocalAIUser {
				existing[aiFingerprint(thread.ID, 0, 0, "user", comment.Body)] = true
			}
			combined.WriteString(" ")
			combined.WriteString(comment.Body)
		}
		prior = append(prior, priorFinding{
			path: thread.Path, start: thread.StartLine, end: thread.Line,
			text: combined.String(),
		})
	}
	findings := 0
	if targetThread != "" {
		output.Findings = nil
	}
	for _, finding := range output.Findings {
		finding.Path = safeAIText(finding.Path)
		finding.Title = safeAIText(finding.Title)
		finding.Body = safeAIText(finding.Body)
		if finding.EndLine < finding.StartLine {
			finding.EndLine = finding.StartLine
		}
		if finding.EndLine-finding.StartLine > 500 || finding.EndLine > 10_000_000 {
			continue
		}
		changed, validPath := validLines[finding.Path]
		if finding.Side == "LEFT" {
			changed, validPath = validDeleted[finding.Path]
		}
		ok := false
		for line := finding.StartLine; validPath && line <= finding.EndLine; line++ {
			ok = ok || changed[line]
		}
		if !validPath || !ok {
			continue
		}
		if finding.Path == "" || (finding.Side != "LEFT" && finding.Side != "RIGHT") ||
			finding.StartLine < 1 || finding.Body == "" || len(finding.Body) > 16_000 {
			continue
		}
		fingerprint := aiFingerprint(finding.Path, finding.StartLine, finding.EndLine, finding.Title, finding.Body)
		suggestion := validatedAISuggestion(finding, changed)
		if existing[fingerprint] {
			if index, ok := localByFingerprint[fingerprint]; ok && suggestion != "" &&
				len(s.Threads[index].Comments) > 0 &&
				len(parseCommentBody(s.Threads[index].Comments[0].Body).Suggestions) == 0 {
				s.Threads[index].Comments[0].Body +=
					"\n\n```suggestion\n" + suggestion + "\n```"
			}
			continue
		}
		nearDuplicate := false
		for _, item := range prior {
			if item.path == finding.Path &&
				rangesNear(item.start, item.end, finding.StartLine, finding.EndLine) &&
				aiTextSimilarity(item.text, finding.Title+" "+finding.Body) >= 0.68 {
				nearDuplicate = true
				break
			}
		}
		if nearDuplicate {
			continue
		}
		existing[fingerprint] = true
		id := "local-ai-" + fingerprint
		author := model
		body := "**" + finding.Severity + ": " + finding.Title + "**\n\n" + finding.Body
		if suggestion != "" {
			body += "\n\n```suggestion\n" + suggestion + "\n```"
		}
		s.Threads = append(s.Threads, ReviewThread{
			ID: id, Path: finding.Path, StartLine: finding.StartLine, Line: finding.EndLine,
			DiffSide: finding.Side, Origin: reviewOriginLocalAI, Provider: provider, Model: model,
			HeadOID: pr.HeadOID, Fingerprint: fingerprint, ViewerCanResolve: true,
			ViewerCanUnresolve: true, ViewerCanReply: true,
			Comments: []ReviewComment{{
				ID: id + "-0", Author: author, Body: body,
				CreatedAt: time.Now(), Origin: reviewOriginLocalAI, Provider: provider, Model: model,
				DiffHunk: boundedDiffHunk(diffText[finding.Path], finding.StartLine, finding.Side),
			}},
		})
		findings++
		prior = append(prior, priorFinding{
			path: finding.Path, start: finding.StartLine, end: finding.EndLine,
			text: finding.Title + " " + finding.Body,
		})
	}
	comments := 0
	validThreads := make(map[string]bool)
	for _, thread := range pr.Threads {
		validThreads[thread.ID] = !thread.IsResolved
	}
	if targetThread != "" {
		validThreads = map[string]bool{targetThread: true}
	}
	message = safeAIText(message)
	if targetThread != "" && strings.TrimSpace(message) != "" {
		fingerprint := aiFingerprint(targetThread, 0, 0, "user", message)
		if !existing[fingerprint] {
			existing[fingerprint] = true
			s.Annotations[targetThread] = append(s.Annotations[targetThread], ReviewComment{
				ID:     "local-ai-user-" + fingerprint,
				Author: firstNonEmpty(pr.ViewerLogin, "you"), Body: message,
				CreatedAt: time.Now(), Origin: reviewOriginLocalAIUser,
			})
		}
	}
	for _, annotation := range output.ThreadComments {
		if !validThreads[annotation.ThreadID] {
			continue
		}
		body := safeAIText(annotation.Body)
		if body == "" || len(body) > 16_000 {
			continue
		}
		fingerprint := aiFingerprint(annotation.ThreadID, 0, 0, "", body)
		if existing[fingerprint] {
			continue
		}
		existing[fingerprint] = true
		s.Annotations[annotation.ThreadID] = append(s.Annotations[annotation.ThreadID], ReviewComment{
			ID: "local-ai-comment-" + fingerprint, Author: model, Body: body,
			CreatedAt: time.Now(), Origin: reviewOriginLocalAI, Provider: provider, Model: model,
		})
		comments++
	}
	sortAIThreads(s.Threads)
	return findings, comments
}

func validatedAISuggestion(finding aiFinding, changed map[int]bool) string {
	suggestion := strings.Trim(sanitizeAIControls(finding.Suggestion), "\r\n")
	if suggestion == "" || finding.Side != "RIGHT" ||
		finding.EndLine-finding.StartLine+1 > 12 ||
		len(suggestion) > 8_000 || strings.Contains(suggestion, "```") {
		return ""
	}
	for line := finding.StartLine; line <= finding.EndLine; line++ {
		if !changed[line] {
			return ""
		}
	}
	replacementLines := strings.Split(suggestion, "\n")
	if len(replacementLines) > 12 {
		return ""
	}
	for _, line := range replacementLines {
		if len(line) > 2_000 {
			return ""
		}
	}
	return suggestion
}

func rangesNear(leftStart, leftEnd, rightStart, rightEnd int) bool {
	if leftStart == 0 {
		leftStart = leftEnd
	}
	if rightStart == 0 {
		rightStart = rightEnd
	}
	return leftStart <= rightEnd+3 && rightStart <= leftEnd+3
}

func aiTextSimilarity(left, right string) float64 {
	tokenize := func(value string) map[string]bool {
		tokens := make(map[string]bool)
		stop := map[string]bool{
			"and": true, "are": true, "can": true, "for": true, "from": true,
			"that": true, "the": true, "this": true, "when": true, "with": true,
		}
		for _, token := range strings.FieldsFunc(strings.ToLower(value), func(r rune) bool {
			return !(r >= 'a' && r <= 'z' || r >= '0' && r <= '9' || r == '_')
		}) {
			if len(token) >= 3 && !stop[token] {
				tokens[token] = true
			}
		}
		return tokens
	}
	a, b := tokenize(left), tokenize(right)
	if len(a) < 3 || len(b) < 3 {
		return 0
	}
	intersection := 0
	for token := range a {
		if b[token] {
			intersection++
		}
	}
	return float64(intersection) / float64(min(len(a), len(b)))
}

func boundedDiffHunk(diff string, targetLine int, side string) string {
	lines := strings.Split(diff, "\n")
	for start := 0; start < len(lines); start++ {
		if !strings.HasPrefix(lines[start], "@@ ") {
			continue
		}
		fields := strings.Fields(lines[start])
		if len(fields) < 3 {
			continue
		}
		value := strings.TrimPrefix(strings.SplitN(fields[2], ",", 2)[0], "+")
		newLine := 0
		fmt.Sscanf(value, "%d", &newLine)
		oldValue := strings.TrimPrefix(strings.SplitN(fields[1], ",", 2)[0], "-")
		oldLine := 0
		fmt.Sscanf(oldValue, "%d", &oldLine)
		end := len(lines)
		for index := start + 1; index < len(lines); index++ {
			if strings.HasPrefix(lines[index], "@@ ") {
				end = index
				break
			}
		}
		for index := start + 1; index < end; index++ {
			line := lines[index]
			if line == "" {
				oldLine++
				newLine++
				continue
			}
			current := newLine
			if side == "LEFT" {
				current = oldLine
			}
			if line[0] != '+' {
				oldLine++
			}
			if line[0] != '-' {
				newLine++
			}
			targetSideLine := side == "LEFT" && line[0] != '+' ||
				side == "RIGHT" && line[0] != '-'
			if current == targetLine && targetSideLine {
				hunk := strings.Join(lines[start:end], "\n")
				if len(hunk) > 24_000 {
					hunk = compactDiffHunk(lines, start, end, index)
				}
				return sanitizeAIControls(hunk)
			}
		}
		start = end - 1
	}
	return ""
}

func compactDiffHunk(lines []string, hunkStart, hunkEnd, target int) string {
	fields := strings.Fields(lines[hunkStart])
	if len(fields) < 3 {
		return ""
	}
	oldStart, newStart := 0, 0
	fmt.Sscanf(strings.TrimPrefix(strings.SplitN(fields[1], ",", 2)[0], "-"), "%d", &oldStart)
	fmt.Sscanf(strings.TrimPrefix(strings.SplitN(fields[2], ",", 2)[0], "+"), "%d", &newStart)
	windowStart := max(hunkStart+1, target-20)
	windowEnd := min(hunkEnd, target+21)
	for index := hunkStart + 1; index < windowStart; index++ {
		line := lines[index]
		if line == "" || line[0] != '+' {
			oldStart++
		}
		if line == "" || line[0] != '-' {
			newStart++
		}
	}
	oldCount, newCount := 0, 0
	body := make([]string, 0, windowEnd-windowStart)
	for _, line := range lines[windowStart:windowEnd] {
		if line == "" || line[0] != '+' {
			oldCount++
		}
		if line == "" || line[0] != '-' {
			newCount++
		}
		if len(line) > 500 {
			prefix := ""
			if line != "" {
				prefix = line[:1]
				line = line[1:]
			}
			line = prefix + truncateAIInline(line, 480)
		}
		body = append(body, line)
	}
	header := fmt.Sprintf("@@ -%d,%d +%d,%d @@ local snapshot", oldStart, oldCount, newStart, newCount)
	return header + "\n" + strings.Join(body, "\n") + "\n… local snapshot truncated"
}

func truncateAIInline(value string, maxBytes int) string {
	if len(value) <= maxBytes {
		return value
	}
	runes := []rune(value)
	for len(runes) > 0 && len(string(runes)) > maxBytes-3 {
		runes = runes[:len(runes)-1]
	}
	return string(runes) + "…"
}

// prepareAIDiffFromDetails gives validation a conservative fallback. Thread
// hunks are the only diff material retained in PRDetails; no complete source is
// persisted in local AI state.
func prepareAIDiffFromDetails(pr PRDetails) ([]aiDiffFile, []string, int) {
	var files []aiDiffFile
	for _, thread := range pr.Threads {
		if len(thread.Comments) == 0 || strings.TrimSpace(thread.Comments[0].DiffHunk) == "" {
			continue
		}
		files = append(files, aiDiffFile{
			Path: thread.Path, Text: thread.Comments[0].DiffHunk,
			ChangedLines: map[int]bool{thread.Line: true},
			DeletedLines: map[int]bool{thread.Line: true},
		})
	}
	return files, nil, 0
}

func (s *AIStore) SetResolved(pr PRDetails, threadID string, resolved bool) (ReviewThread, error) {
	state, err := s.Load(pr)
	if err != nil {
		return ReviewThread{}, err
	}
	for i := range state.Threads {
		if state.Threads[i].ID == threadID {
			state.Threads[i].IsResolved = resolved
			if err := s.Save(pr, state); err != nil {
				return ReviewThread{}, err
			}
			result := state.Threads[i]
			result.IsOutdated = result.HeadOID != "" && result.HeadOID != pr.HeadOID
			return result, nil
		}
	}
	return ReviewThread{}, errors.New("local AI thread was not found")
}