// doc-map parsing and doc injection for path-scoped design document context in AI code reviews.
package review

import (
	"context"
	"fmt"
	"log/slog"
	"os"
	"path/filepath"
	"strings"
	"unicode/utf8"

	"github.com/goccy/go-yaml"
)

const (
	// DefaultDocMapMaxBytes is the default cap on total injected doc content.
	DefaultDocMapMaxBytes = 100 * 1024 // 100 KB
)

// DocMapping maps a set of path glob patterns to governing doc files/directories.
type DocMapping struct {
	Paths []string `yaml:"paths"` // glob patterns matched against changed PR files
	Docs  []string `yaml:"docs"`  // doc file paths or directories in the reviewed repo
}

// DocMapConfig is the top-level structure of a doc-map YAML file.
type DocMapConfig struct {
	Mappings []DocMapping `yaml:"mappings"`
}

// DocMapOptions configures behavior for doc loading.
type DocMapOptions struct {
	// MaxBytes caps the total size of injected doc content. Default: DefaultDocMapMaxBytes.
	MaxBytes int
}

// DocFetcher reads file and directory content from a VCS repository.
// It is a subset of vcsClient, defined here to keep the review package free
// of cmd-level dependencies.
type DocFetcher interface {
	// GetFileContent returns the content of a single file at default branch.
	GetFileContent(ctx context.Context, owner, repo, path string) (string, error)
	// GetAllFilesInPath returns all files (path → content) under a directory.
	GetAllFilesInPath(ctx context.Context, owner, repo, path string) (map[string]string, error)
}

// ParseDocMapConfig reads and parses a doc-map YAML file from a local path.
// Unknown top-level keys produce a warning but are not fatal.
func ParseDocMapConfig(localPath string) (*DocMapConfig, error) {
	data, err := readFileBytes(localPath)
	if err != nil {
		return nil, fmt.Errorf("read doc-map file %q: %w", localPath, err)
	}
	return parseDocMapBytes(data, localPath)
}

// ParseDocMapConfigContent parses a doc-map YAML config from an in-memory
// string. The source parameter is used only for error messages and log entries
// (e.g. "owner/repo@main:.review-bot/doc-map.yml").
//
// Use this when the config content has been fetched from a trusted VCS ref
// rather than read from the local workspace.
func ParseDocMapConfigContent(content, source string) (*DocMapConfig, error) {
	data := []byte(content)
	return parseDocMapBytes(data, source)
}

// parseDocMapBytes is the shared YAML parse implementation used by
// ParseDocMapConfig and ParseDocMapConfigContent.
func parseDocMapBytes(data []byte, source string) (*DocMapConfig, error) {
	var cfg DocMapConfig
	if err := yaml.UnmarshalWithOptions(data, &cfg, yaml.Strict()); err != nil {
		// Re-parse without strict mode to log which keys are unknown.
		var relaxed DocMapConfig
		if err2 := yaml.Unmarshal(data, &relaxed); err2 != nil {
			return nil, fmt.Errorf("parse doc-map YAML %q: %w", source, err)
		}
		slog.Warn("doc-map YAML contains unknown keys (ignored)", "file", source, "error", err)
		cfg = relaxed
	}
	return &cfg, nil
}

// FileCoveredByDocMap reports whether at least one paths: glob in any mapping
// of cfg matches the given file path. It is used by static validation tooling
// (e.g. the validate-docmap subcommand) to check per-file docmap coverage.
func FileCoveredByDocMap(cfg *DocMapConfig, file string) bool {
	for _, mapping := range cfg.Mappings {
		if mappingMatches(mapping.Paths, []string{file}) {
			return true
		}
	}
	return false
}

// MatchDocs returns deduplicated doc paths for the given changed file paths.
// A mapping matches if any of its path globs matches any of the changed files.
func MatchDocs(cfg *DocMapConfig, changedFiles []string) []string {
	seen := make(map[string]struct{})
	var result []string

	for _, mapping := range cfg.Mappings {
		if len(mapping.Paths) == 0 || len(mapping.Docs) == 0 {
			continue
		}
		if mappingMatches(mapping.Paths, changedFiles) {
			for _, doc := range mapping.Docs {
				if doc == "" {
					continue
				}
				if _, ok := seen[doc]; !ok {
					seen[doc] = struct{}{}
					result = append(result, doc)
				}
			}
		}
	}
	return result
}

// mappingMatches returns true if any glob in patterns matches any file in files.
func mappingMatches(patterns, files []string) bool {
	for _, pat := range patterns {
		for _, f := range files {
			if globMatch(pat, f) {
				return true
			}
		}
	}
	return false
}

// globMatch matches a path against a glob pattern that may contain **.
// It supports:
//   - filepath.Match patterns (*, ?, [range])
//   - ** as a path segment that matches zero or more segments
//   - Trailing /** to match a directory and all its contents
//
// The pattern and path use forward slash as separator.
func globMatch(pattern, path string) bool {
	return globMatchParts(splitPath(pattern), splitPath(path))
}

// splitPath splits a slash-separated path into non-empty parts.
func splitPath(p string) []string {
	// Clean and split on "/"
	parts := strings.Split(p, "/")
	result := make([]string, 0, len(parts))
	for _, part := range parts {
		if part != "" {
			result = append(result, part)
		}
	}
	return result
}

// globMatchParts recursively matches pattern parts against path parts.
func globMatchParts(patParts, pathParts []string) bool {
	for len(patParts) > 0 {
		pat := patParts[0]
		if pat == "**" {
			patParts = patParts[1:]
			if len(patParts) == 0 {
				// Trailing **: matches any remaining path (including empty).
				return true
			}
			// ** in the middle: try matching the rest at every position.
			for i := 0; i <= len(pathParts); i++ {
				if globMatchParts(patParts, pathParts[i:]) {
					return true
				}
			}
			return false
		}
		// Non-** segment: path must have a segment here.
		if len(pathParts) == 0 {
			return false
		}
		matched, err := filepath.Match(pat, pathParts[0])
		if err != nil || !matched {
			return false
		}
		patParts = patParts[1:]
		pathParts = pathParts[1:]
	}
	// All pattern parts consumed; path must also be consumed.
	return len(pathParts) == 0
}

// LoadMatchingDocs fetches content for the given doc paths via VCS and returns
// a formatted string suitable for injection into the system prompt.
//
// Behavior:
//   - Paths that look like directories (end with /, or GetAllFilesInPath returns files)
//     are expanded to all .md files under them.
//   - Missing files are logged as warnings and skipped.
//   - Total content is capped at opts.MaxBytes; truncation is noted inline.
func LoadMatchingDocs(ctx context.Context, fetcher DocFetcher, owner, repo string, docPaths []string, opts DocMapOptions) (string, error) {
	if opts.MaxBytes <= 0 {
		opts.MaxBytes = DefaultDocMapMaxBytes
	}

	var sb strings.Builder
	totalBytes := 0
	limitReached := false

	for _, docPath := range docPaths {
		if ctx.Err() != nil {
			break
		}
		if limitReached {
			slog.Warn("doc-map: context size limit reached, skipping remaining docs",
				"remaining_path", docPath, "limit_bytes", opts.MaxBytes)
			break
		}

		entries, err := loadDocEntries(ctx, fetcher, owner, repo, docPath)
		if err != nil {
			slog.Warn("doc-map: could not load doc, skipping", "path", docPath, "error", err)
			continue
		}
		if len(entries) == 0 {
			slog.Debug("doc-map: no .md files found under path", "path", docPath)
			continue
		}

		for _, entry := range entries {
			if limitReached {
				break
			}
			available := opts.MaxBytes - totalBytes
			if available <= 0 {
				limitReached = true
				sb.WriteString("\n\n> ⚠️ Design document context truncated — size limit reached.\n")
				break
			}

			content := entry.content
			truncated := false
			if len(content) > available {
				content = truncateUTF8(content, available)
				truncated = true
				limitReached = true
			}

			sb.WriteString("### ")
			sb.WriteString(entry.path)
			sb.WriteString("\n\n")
			sb.WriteString(content)
			sb.WriteString("\n")
			if truncated {
				sb.WriteString("\n> ⚠️ (truncated — size limit reached)\n")
			}
			totalBytes += len(content)
			slog.Debug("doc-map: injected doc", "path", entry.path, "bytes", len(content))
		}
	}

	if sb.Len() == 0 {
		return "", nil
	}
	return sb.String(), nil
}

// docEntry holds a single doc file path and content.
type docEntry struct {
	path    string
	content string
}

// loadDocEntries returns the doc content for a given path.
// If the path is a directory, all .md files under it are returned.
// If it's a file, a single entry is returned.
func loadDocEntries(ctx context.Context, fetcher DocFetcher, owner, repo, docPath string) ([]docEntry, error) {
	if err := ValidateDocPath(docPath); err != nil {
		return nil, fmt.Errorf("doc path %q rejected: %w", docPath, err)
	}

	// Try directory expansion first.
	files, dirErr := fetcher.GetAllFilesInPath(ctx, owner, repo, docPath)
	if dirErr == nil && len(files) > 0 {
		// Filter for .md files only.
		var entries []docEntry
		for path, content := range files {
			if isMDFile(path) {
				entries = append(entries, docEntry{path: path, content: content})
			}
		}
		// Sort for deterministic output.
		sortDocEntries(entries)
		return entries, nil
	}

	// Directory expansion returned nothing; log and fall through to single-file fetch.
	if dirErr != nil {
		slog.Debug("doc-map: directory expansion failed, trying as single file", "path", docPath, "error", dirErr)
	}

	// Try as a single file.
	content, fileErr := fetcher.GetFileContent(ctx, owner, repo, docPath)
	if fileErr != nil {
		// Return the file error (more specific than directory error).
		return nil, fmt.Errorf("fetch doc %q: %w", docPath, fileErr)
	}
	return []docEntry{{path: docPath, content: content}}, nil
}

// isMDFile returns true if the file has a .md extension.
func isMDFile(path string) bool {
	return strings.HasSuffix(strings.ToLower(path), ".md")
}

// sortDocEntries sorts entries by path for deterministic output.
func sortDocEntries(entries []docEntry) {
	// Simple insertion sort (doc lists are small).
	for i := 1; i < len(entries); i++ {
		for j := i; j > 0 && entries[j].path < entries[j-1].path; j-- {
			entries[j], entries[j-1] = entries[j-1], entries[j]
		}
	}
}

// readFileBytes reads the contents of a local file.
func readFileBytes(path string) ([]byte, error) {
	return os.ReadFile(path)
}

// ValidateDocPath rejects doc paths that could cause path traversal
// (absolute paths, any ".." segment, backslashes). Defense-in-depth: callers
// must also confine the joined path to the repo root via filepath.Rel before
// any filesystem access. Backslashes are rejected explicitly to prevent
// Windows platform edge cases.
func ValidateDocPath(p string) error {
	if strings.Contains(p, "\\") {
		return fmt.Errorf("backslashes not allowed in doc paths")
	}
	if filepath.IsAbs(p) {
		return fmt.Errorf("absolute paths not allowed")
	}
	for _, segment := range strings.Split(p, "/") {
		if segment == ".." {
			return fmt.Errorf("path traversal ('..' segment) not allowed")
		}
	}
	return nil
}

// truncateUTF8 truncates s to at most maxBytes without splitting multi-byte
// UTF-8 characters. Returns a valid UTF-8 string of at most maxBytes bytes.
//
// Note: an identical implementation exists in budget/budget.go. The two
// packages are intentionally separate (review does not import budget), so
// the duplication is accepted rather than introducing a shared internal
// package for a single small function.
func truncateUTF8(s string, maxBytes int) string {
	if len(s) <= maxBytes {
		return s
	}
	for maxBytes > 0 && !utf8.RuneStart(s[maxBytes]) {
		maxBytes--
	}
	return s[:maxBytes]
}