package process

import (
	"context"
	"fmt"
	"sort"
	"strings"
)

// GitLogResult represents the result of a git log operation.
type GitLogResult struct {
	Success bool             `json:"success"`
	Commits []*GitCommitInfo `json:"commits"`
	Error   string           `json:"error,omitempty"`
	// PerRepoErrors lists per-repo failures during a multi-repo log fan-out.
	// Empty/nil for single-repo responses or when every repo succeeded. The
	// merged response keeps Success=true as long as at least one repo
	// succeeded; callers inspect this slice to surface partial failures.
	PerRepoErrors []GitLogRepoError `json:"per_repo_errors,omitempty"`
}

// GitLogRepoError describes a single per-repo failure from a multi-repo log
// fan-out. It is omitted from the response entirely for single-repo responses.
type GitLogRepoError struct {
	RepositoryName string `json:"repository_name"`
	Error          string `json:"error"`
}

// GitCommitInfo represents a single commit in the log.
// Field names match GitCommitData and SessionCommit for frontend consistency.
type GitCommitInfo struct {
	CommitSHA     string `json:"commit_sha"`
	ParentSHA     string `json:"parent_sha"`
	CommitMessage string `json:"commit_message"`
	AuthorName    string `json:"author_name"`
	AuthorEmail   string `json:"author_email"`
	CommittedAt   string `json:"committed_at"`
	FilesChanged  int    `json:"files_changed"`
	Insertions    int    `json:"insertions"`
	Deletions     int    `json:"deletions"`
	// Pushed is true when the commit is reachable from the branch's upstream
	// tracking ref (i.e. present on the remote). Sourced from git itself —
	// not from any PR API — so it stays correct when no PR exists yet, after
	// rebases, and across multi-repo workspaces.
	Pushed bool `json:"pushed"`
	// RepositoryName tags commits returned from a multi-repo log fan-out.
	// Empty for single-repo workspaces. Set by the API layer after the call.
	RepositoryName string `json:"repository_name,omitempty"`
}

// CumulativeDiffResult represents the cumulative diff from base commit to HEAD.
type CumulativeDiffResult struct {
	Success      bool                   `json:"success"`
	BaseCommit   string                 `json:"base_commit"`
	HeadCommit   string                 `json:"head_commit"`
	TotalCommits int                    `json:"total_commits"`
	Files        map[string]interface{} `json:"files"`
	// TruncatedFilesCount is how many files were dropped from Files entirely
	// because the cumulative range exceeded maxCumulativeDiffFiles. Zero
	// (omitted) when the full file set fit. The frontend surfaces this as a
	// "N more files hidden" banner — a mid-rebase cumulative diff can otherwise
	// enumerate tens of thousands of files, one rendered row each.
	//
	// This counts only fully-dropped files. Files kept in the map but whose
	// diff was emptied by the byte budget (diff_skip_reason "budget_exceeded")
	// are NOT counted here — they remain listed and carry their own per-file
	// skip reason that the diff viewer renders, so they are visible-but-capped
	// rather than hidden.
	TruncatedFilesCount int    `json:"truncated_files_count,omitempty"`
	Error               string `json:"error,omitempty"`
}

// maxCumulativeDiffFiles bounds how many file entries GetCumulativeDiff returns.
// This is a safety valve for the rebase pathology (base→working-tree across a
// large range), not a UX limit — normal PRs stay well under it. Capping the
// count bounds the number of rendered file rows on the frontend regardless of
// the per-file/total byte budgets.
const maxCumulativeDiffFiles = 500

// Field and record separators for git log parsing.
// Using non-printable ASCII separators to avoid collision with commit message content.
const (
	fieldSep  = "\x1f" // Unit Separator (ASCII 31)
	recordSep = "\x1e" // Record Separator (ASCII 30)
)

// GetLog returns commits from baseCommit (exclusive) to HEAD (inclusive).
// If baseCommit is empty, returns recent commits (limited by limit parameter).
// Stats (files changed, insertions, deletions) are fetched in-band via --shortstat
// to avoid an N+1 git-show call per commit.
func (g *GitOperator) GetLog(ctx context.Context, baseCommit string, limit int) (*GitLogResult, error) {
	result := &GitLogResult{
		Commits: make([]*GitCommitInfo, 0),
	}

	// Build the git log command with non-printable separators and --shortstat.
	// The record separator (%x1e) is placed BEFORE the fields so that --shortstat
	// output (appended after the format) stays within the same record:
	//   \x1e<fields>\n <stat summary>\n\x1e<fields>\n <stat summary>\n...
	// Splitting on recordSep groups each commit's fields + stats together.
	args := []string{"log", "--format=%x1e%H%x1f%P%x1f%an%x1f%ae%x1f%s%x1f%aI", "--shortstat"}

	switch {
	case baseCommit != "":
		// --first-parent only on the divergence-range path: when the branch
		// has merged main back in, plain `git log <base>..HEAD` walks both
		// parents of the merge and surfaces commits brought in via main as
		// if they were the branch's own work. Following only the first parent
		// keeps the branch's line plus its merge commits and excludes the
		// merged-in side. We deliberately don't apply this to the open-ended
		// "recent N commits" path so future history-view callers (activity
		// widgets, etc.) keep getting the full graph.
		args = append(args, "--first-parent", baseCommit+"..HEAD")
	case limit > 0:
		args = append(args, fmt.Sprintf("-n%d", limit))
	default:
		// Default to last 50 commits if no base and no limit
		args = append(args, "-n50")
	}

	output, err := g.runGitCommand(ctx, args...)
	if err != nil {
		result.Error = fmt.Sprintf("failed to get git log: %s", err.Error())
		return result, nil
	}

	output = strings.TrimSpace(output)
	if output == "" {
		result.Success = true
		return result, nil
	}

	// Split by record separator. The first element is empty (separator is at the start).
	records := strings.Split(output, recordSep)
	for _, record := range records {
		record = strings.TrimSpace(record)
		if record == "" {
			continue
		}

		// The record may contain a trailing shortstat line after the commit fields.
		// Split on newline: first line has the fields, remaining lines may have the stat summary.
		lines := strings.SplitN(record, "\n", 2)
		fieldLine := strings.TrimSpace(lines[0])

		parts := strings.Split(fieldLine, fieldSep)
		if len(parts) < 6 {
			continue
		}

		sha := parts[0]
		parentSHA := parts[1]
		if idx := strings.Index(parentSHA, " "); idx > 0 {
			parentSHA = parentSHA[:idx]
		}

		// Parse inline shortstat if present
		var filesChanged, insertions, deletions int
		if len(lines) > 1 {
			statLine := strings.TrimSpace(lines[1])
			if statLine != "" {
				filesChanged, insertions, deletions = parseStatSummary(statLine)
			}
		}

		result.Commits = append(result.Commits, &GitCommitInfo{
			CommitSHA:     sha,
			ParentSHA:     parentSHA,
			AuthorName:    parts[2],
			AuthorEmail:   parts[3],
			CommitMessage: parts[4],
			CommittedAt:   parts[5],
			FilesChanged:  filesChanged,
			Insertions:    insertions,
			Deletions:     deletions,
		})
	}

	g.markPushedCommits(ctx, result.Commits)

	result.Success = true
	return result, nil
}

// markPushedCommits sets Pushed on each commit by looking up which commits in
// HEAD's history are NOT reachable from the upstream tracking ref. A commit is
// pushed iff it is not in that "ahead" set. When the branch has no upstream
// (never been pushed) or the lookup fails, all commits stay Pushed=false — the
// safer default than falsely claiming a commit is on the remote.
func (g *GitOperator) markPushedCommits(ctx context.Context, commits []*GitCommitInfo) {
	if len(commits) == 0 {
		return
	}
	upstream := g.getUpstreamRef(ctx)
	if upstream == "" {
		return
	}
	// Resolve to a SHA so we can pass it to rev-list as `^<sha>`. The caret
	// prefix means the arg doesn't match LooksLikeCommitSHA; it falls through
	// to the non-branch catch-all in runGitCommand, which passes it unchanged.
	// Safe: upstreamSHA is local rev-parse output, not user input.
	upstreamSHA, err := g.runGitCommand(ctx, "rev-parse", upstream)
	if err != nil {
		return
	}
	upstreamSHA = strings.TrimSpace(upstreamSHA)
	if upstreamSHA == "" {
		return
	}
	// Cap the walk to the number of commits we're marking. Without this, a
	// branch with many local-only commits would walk unbounded history per
	// GetLog call. rev-list walks newest-first the same way GetLog does, so
	// the N most recent unpushed SHAs cover the N commits in our result.
	output, err := g.runGitCommand(ctx, "rev-list",
		fmt.Sprintf("-n%d", len(commits)), "HEAD", "^"+upstreamSHA)
	if err != nil {
		return
	}
	unpushed := make(map[string]struct{})
	for _, line := range strings.Split(strings.TrimSpace(output), "\n") {
		sha := strings.TrimSpace(line)
		if sha != "" {
			unpushed[sha] = struct{}{}
		}
	}
	for _, c := range commits {
		if _, isUnpushed := unpushed[c.CommitSHA]; !isUnpushed {
			c.Pushed = true
		}
	}
}

// GetCumulativeDiff returns the cumulative diff from baseCommit to the working tree
// (including uncommitted/unstaged changes).
func (g *GitOperator) GetCumulativeDiff(ctx context.Context, baseCommit string) (*CumulativeDiffResult, error) {
	result := &CumulativeDiffResult{
		Files: make(map[string]interface{}),
	}

	if baseCommit == "" {
		result.Error = "base_commit is required"
		return result, nil
	}

	result.BaseCommit = baseCommit

	// Get current HEAD
	headOutput, err := g.runGitCommand(ctx, "rev-parse", "HEAD")
	if err != nil {
		result.Error = fmt.Sprintf("failed to get HEAD: %s", err.Error())
		return result, nil
	}
	result.HeadCommit = strings.TrimSpace(headOutput)

	// Count commits between base and HEAD
	countOutput, err := g.runGitCommand(ctx, "rev-list", "--count", baseCommit+"..HEAD")
	if err == nil {
		_, _ = fmt.Sscanf(strings.TrimSpace(countOutput), "%d", &result.TotalCommits)
	}

	// Get the cumulative diff (base → working tree, includes uncommitted changes)
	diffOutput, err := g.runGitCommand(ctx, "diff", baseCommit)
	if err != nil {
		result.Error = fmt.Sprintf("failed to get diff: %s", err.Error())
		return result, nil
	}

	// Parse the diff output into files, capping per-file (256 KB) and total
	// (2 MB) diff bytes. Unlike ShowCommit (single, bounded commit) a
	// multi-commit cumulative range can produce tens of MB of patch text.
	result.Files = g.parseCommitDiffWithOptions(diffOutput, parseCommitDiffOptions{
		perFileMaxBytes: maxDiffOutputSize,
		totalMaxBytes:   maxTotalDiffBytes,
	})

	// Cap the number of file entries too — the byte budget bounds payload size
	// but not the row count, and the frontend renders one component per file.
	result.Files, result.TruncatedFilesCount = capCumulativeDiffFiles(result.Files, maxCumulativeDiffFiles)

	result.Success = true
	return result, nil
}

// capCumulativeDiffFiles keeps at most maxFiles entries (deterministically, by
// sorted path) and returns the kept map plus the number dropped.
func capCumulativeDiffFiles(files map[string]interface{}, maxFiles int) (map[string]interface{}, int) {
	if maxFiles <= 0 || len(files) <= maxFiles {
		return files, 0
	}

	paths := make([]string, 0, len(files))
	for path := range files {
		paths = append(paths, path)
	}
	sort.Strings(paths)

	capped := make(map[string]interface{}, maxFiles)
	for _, path := range paths[:maxFiles] {
		capped[path] = files[path]
	}
	return capped, len(files) - maxFiles
}

// CommitDiffResult represents the result of getting a commit's diff.
type CommitDiffResult struct {
	Success      bool                   `json:"success"`
	CommitSHA    string                 `json:"commit_sha"`
	Message      string                 `json:"message"`
	Author       string                 `json:"author"`
	Date         string                 `json:"date"`
	Files        map[string]interface{} `json:"files"` // FileInfo objects with diff content
	FilesChanged int                    `json:"files_changed"`
	Insertions   int                    `json:"insertions"`
	Deletions    int                    `json:"deletions"`
	Error        string                 `json:"error,omitempty"`
}

// isHexChar reports whether r is a valid hexadecimal digit (0-9, a-f, A-F).
func isHexChar(r rune) bool {
	return (r >= '0' && r <= '9') || (r >= 'a' && r <= 'f') || (r >= 'A' && r <= 'F')
}

// validateCommitSHA validates a commit SHA.
// Returns an error message if invalid, empty string if valid.
func validateCommitSHA(sha string) string {
	if sha == "" {
		return "commit SHA is required"
	}

	// Must be between 4 and 40 hex characters
	if len(sha) < 4 || len(sha) > 40 {
		return "commit SHA must be between 4 and 40 characters"
	}

	for _, r := range sha {
		if !isHexChar(r) {
			return "commit SHA contains invalid characters"
		}
	}
	return ""
}

// sumFileDiffStats sums additions and deletions from a file diff map.
func sumFileDiffStats(files map[string]interface{}) (insertions, deletions int) {
	for _, f := range files {
		fi, ok := f.(map[string]interface{})
		if !ok {
			continue
		}
		if additions, ok := fi["additions"].(int); ok {
			insertions += additions
		}
		if dels, ok := fi["deletions"].(int); ok {
			deletions += dels
		}
	}
	return insertions, deletions
}

// ShowCommit gets the diff for a specific commit using git show.
func (g *GitOperator) ShowCommit(ctx context.Context, commitSHA string) (*CommitDiffResult, error) {
	result := &CommitDiffResult{
		CommitSHA: commitSHA,
	}

	// Validate commit SHA (basic validation - alphanumeric only)
	if errMsg := validateCommitSHA(commitSHA); errMsg != "" {
		result.Error = errMsg
		return result, nil
	}

	// Get commit metadata
	formatOutput, err := g.runGitCommand(ctx, "show", "--no-patch", "--format=%H%n%s%n%an <%ae>%n%aI", commitSHA)
	if err != nil {
		result.Error = fmt.Sprintf("failed to get commit info: %s", err.Error())
		return result, nil
	}

	lines := strings.Split(strings.TrimSpace(formatOutput), "\n")
	if len(lines) >= 4 {
		result.CommitSHA = lines[0]
		result.Message = lines[1]
		result.Author = lines[2]
		result.Date = lines[3]
	}

	// Get the diff with stats
	diffOutput, err := g.runGitCommand(ctx, "show", "--format=", "--stat", "--numstat", "-p", commitSHA)
	if err != nil {
		result.Error = fmt.Sprintf("failed to get commit diff: %s", err.Error())
		return result, nil
	}

	// Parse the diff output into files
	result.Files = g.parseCommitDiff(diffOutput)
	result.FilesChanged = len(result.Files)
	result.Insertions, result.Deletions = sumFileDiffStats(result.Files)

	result.Success = true
	return result, nil
}

// parseCommitDiffOptions controls per-file and cumulative budget enforcement
// while parsing a `git diff`/`git show` output into the file info map. The zero
// value applies no caps, which preserves the ShowCommit contract (single-commit
// detail views expect full diffs). The cumulative-diff path passes non-zero
// budgets because a multi-commit range can produce tens of MB of patch text
// that, JSON-encoded and shipped over the WS, grinds the browser.
type parseCommitDiffOptions struct {
	perFileMaxBytes int
	totalMaxBytes   int
}

// parseCommitDiff parses git show output into file info map. No budget caps —
// callers that need them use parseCommitDiffWithOptions.
func (g *GitOperator) parseCommitDiff(output string) map[string]interface{} {
	return g.parseCommitDiffWithOptions(output, parseCommitDiffOptions{})
}

// parseCommitDiffWithOptions parses git diff/show output into a file info map,
// applying the budgets in opts. Diffs are truncated (per-file) or dropped
// (once the cumulative budget is exceeded); additions/deletions counts are
// always computed from the full per-file content because they're cheap and
// the frontend relies on them.
func (g *GitOperator) parseCommitDiffWithOptions(output string, opts parseCommitDiffOptions) map[string]interface{} {
	files := make(map[string]interface{})

	// Split by "diff --git" to get individual file diffs
	parts := strings.Split(output, "diff --git ")
	if len(parts) <= 1 {
		return files
	}

	totalDiffBytes := 0
	for _, part := range parts[1:] {
		if part == "" {
			continue
		}

		// Re-add the "diff --git " prefix
		diffContent := "diff --git " + part

		// Extract file path from the diff header
		// Format: diff --git a/path/to/file b/path/to/file
		lines := strings.SplitN(diffContent, "\n", 2)
		if len(lines) == 0 {
			continue
		}

		header := lines[0]
		// Extract path from "diff --git a/<path> b/<path>".
		// We cannot split by space because paths may contain spaces.
		// Instead, strip the known prefix and find the " b/" separator.
		pathsPart := strings.TrimPrefix(header, "diff --git ")
		bIdx := strings.Index(pathsPart, " b/")
		if bIdx == -1 {
			continue
		}
		filePath := pathsPart[bIdx+3:]

		// Determine file status from diff content
		status := fileStatusModified
		switch {
		case strings.Contains(diffContent, "new file mode"):
			status = "added"
		case strings.Contains(diffContent, "deleted file mode"):
			status = fileStatusDeleted
		case strings.Contains(diffContent, "rename from"):
			status = "renamed"
		}

		// Count additions and deletions (always from the full content).
		additions := 0
		deletions := 0
		for _, line := range strings.Split(diffContent, "\n") {
			if strings.HasPrefix(line, "+") && !strings.HasPrefix(line, "+++") {
				additions++
			} else if strings.HasPrefix(line, "-") && !strings.HasPrefix(line, "---") {
				deletions++
			}
		}

		diffOut, skipReason := applyDiffBudget(diffContent, totalDiffBytes, opts)
		totalDiffBytes += len(diffOut)

		fileEntry := map[string]interface{}{
			"status":    status,
			"staged":    false,
			"additions": additions,
			"deletions": deletions,
			"diff":      diffOut,
		}
		if skipReason != "" {
			fileEntry["diff_skip_reason"] = skipReason
		}
		files[filePath] = fileEntry
	}

	return files
}

// applyDiffBudget enforces the per-file and cumulative byte budgets in opts and
// returns the (possibly truncated/empty) diff content plus a skip reason. A zero
// budget means "no cap" for that dimension. The cumulative budget is strict: the
// running total never exceeds totalMaxBytes — a file that would cross the
// boundary is clamped to the remaining budget rather than emitted in full.
func applyDiffBudget(diffContent string, totalSoFar int, opts parseCommitDiffOptions) (diff, skipReason string) {
	limit := len(diffContent)
	truncated := false

	if opts.totalMaxBytes > 0 {
		remaining := opts.totalMaxBytes - totalSoFar
		if remaining <= 0 {
			return "", diffSkipReasonBudgetExceeded
		}
		if remaining < limit {
			limit = remaining
			truncated = true
		}
	}

	if opts.perFileMaxBytes > 0 && opts.perFileMaxBytes < limit {
		limit = opts.perFileMaxBytes
		truncated = true
	}

	if truncated {
		return diffContent[:limit], diffSkipReasonTruncated
	}
	return diffContent, ""
}

// GetMergeBase returns the merge-base commit SHA between two refs (e.g., HEAD and origin/main).
// This is used to determine the common ancestor for filtering commits.
func (g *GitOperator) GetMergeBase(ctx context.Context, ref1, ref2 string) (string, error) {
	output, err := g.runGitCommand(ctx, "merge-base", ref1, ref2)
	if err != nil {
		return "", fmt.Errorf("failed to compute merge-base: %w", err)
	}
	return strings.TrimSpace(output), nil
}

// GetRevParse resolves a ref name to its commit SHA. Returns the empty
// string when the ref doesn't exist; used as a no-common-ancestor fallback
// for the commits panel so a base branch with unrelated history still
// produces a stable anchor for `git log <tip>..HEAD`.
func (g *GitOperator) GetRevParse(ctx context.Context, ref string) (string, error) {
	output, err := g.runGitCommand(ctx, "rev-parse", ref)
	if err != nil {
		return "", fmt.Errorf("failed to rev-parse %q: %w", ref, err)
	}
	return strings.TrimSpace(output), nil
}