package vcs

import (
	"context"
	"fmt"
	"strconv"
	"strings"
)

// GetAllFilesInPath recursively fetches all file contents under a path using the
// provided FileReader. Returns a map of filepath -> content for all files found.
// If the path points to an empty directory, returns an empty map.
func GetAllFilesInPath(ctx context.Context, client FileReader, owner, repo, path string) (map[string]string, error) {
	results := make(map[string]string)

	entries, err := client.ListContents(ctx, owner, repo, path)
	if err != nil {
		return nil, fmt.Errorf("list contents %q: %w", path, err)
	}

	for _, entry := range entries {
		switch entry.Type {
		case "file":
			content, err := client.GetFileContent(ctx, owner, repo, entry.Path, "")
			if err != nil {
				return nil, fmt.Errorf("get file %q: %w", entry.Path, err)
			}
			results[entry.Path] = content
		case "dir":
			subResults, err := GetAllFilesInPath(ctx, client, owner, repo, entry.Path)
			if err != nil {
				return nil, fmt.Errorf("recurse into %q: %w", entry.Path, err)
			}
			for k, v := range subResults {
				results[k] = v
			}
		}
	}

	return results, nil
}

// BuildLineToPositionMap parses a unified diff and returns a per-file map of
// new-file line number → diff-position.
//
// Position is a 1-indexed offset from the @@ hunk line (GitHub convention):
//   - The @@ hunk header itself counts as position 1 (for the first hunk)
//   - Every subsequent content line (context, addition, deletion) increments position
//   - A second @@ hunk in the same file continues the count; it does not reset
//   - Addition and context lines have new-file line numbers and are mapped
//   - Deletion lines have a position but no new-file line; they are not in the map
//   - "\ No newline at end of file" markers do not count as a position
//
// Returns: map[filename]map[newFileLine]diffPosition
func BuildLineToPositionMap(diff string) map[string]map[int]int {
	result := make(map[string]map[int]int)

	lines := strings.Split(diff, "\n")
	var currentFile string
	var position int
	var newLine int

	for _, line := range lines {
		// Detect new file in diff — resets position counter per file.
		if strings.HasPrefix(line, "+++ b/") {
			currentFile = strings.TrimPrefix(line, "+++ b/")
			position = 0
			newLine = 0
			if result[currentFile] == nil {
				result[currentFile] = make(map[int]int)
			}
			continue
		}

		// Skip deleted-file target (no new lines to map).
		if strings.HasPrefix(line, "+++ /dev/null") {
			currentFile = ""
			continue
		}

		// Skip metadata lines that are not part of position counting.
		if strings.HasPrefix(line, "diff --git") ||
			strings.HasPrefix(line, "--- ") ||
			strings.HasPrefix(line, "index ") ||
			strings.HasPrefix(line, "\\") {
			continue
		}

		// Parse hunk headers — the @@ line itself occupies a position.
		if strings.HasPrefix(line, "@@") && currentFile != "" {
			position++
			newLine = parseHunkNewStart(line)
			continue
		}

		if currentFile == "" {
			continue
		}

		// Content lines within a hunk.
		switch {
		case strings.HasPrefix(line, "+"):
			// Addition: maps to both a position and a new-file line.
			position++
			result[currentFile][newLine] = position
			newLine++
		case strings.HasPrefix(line, "-"):
			// Deletion: occupies a position but has no new-file line number.
			position++
		case strings.HasPrefix(line, " "):
			// Context line: maps to both a position and a new-file line.
			position++
			result[currentFile][newLine] = position
			newLine++
		}
		// Any other line (empty trailing lines from Split, etc.) is ignored.
	}

	return result
}

// parseHunkNewStart extracts the new-file starting line number from a hunk header.
// Format: @@ -old_start[,old_count] +new_start[,new_count] @@[ optional section heading]
func parseHunkNewStart(hunkLine string) int {
	// Find the +N part after the first @@
	plusIdx := strings.Index(hunkLine, "+")
	if plusIdx < 0 {
		return 1
	}
	rest := hunkLine[plusIdx+1:]

	// Read digits until comma, space, or end.
	if idx := strings.IndexAny(rest, ", @"); idx > 0 {
		rest = rest[:idx]
	}

	n, err := strconv.Atoi(rest)
	if err != nil {
		return 1
	}
	return n
}