package reforger_utils

import (
	"bytes"
	"encoding/binary"
	"fmt"
	"io"
)

func readString(r io.Reader, expected string) error {
	buf := make([]byte, 4)
	if _, err := io.ReadFull(r, buf); err != nil {
		return fmt.Errorf("failed to read identifier: %w", err)
	}
	if string(buf) != expected {
		return fmt.Errorf("expected identifier '%s', but got '%s'", expected, string(buf))
	}
	return nil
}

func parseEntry(r *bytes.Reader) (PakEntry, error) {
	var pakEntry PakEntry
	if err := binary.Read(r, binary.LittleEndian, &pakEntry.Offset); err != nil {
		return PakEntry{}, fmt.Errorf("failed to read file offset: %w", err)
	}

	if err := binary.Read(r, binary.LittleEndian, &pakEntry.Size); err != nil {
		return PakEntry{}, fmt.Errorf("failed to read file size: %w", err)
	}

	if err := binary.Read(r, binary.LittleEndian, &pakEntry.OriginalSize); err != nil {
		return PakEntry{}, fmt.Errorf("failed to read uncompressed size: %w", err)
	}

	r.Seek(4, io.SeekCurrent) // NULL

	if err := binary.Read(r, binary.BigEndian, &pakEntry.CompressType); err != nil {
		return PakEntry{}, fmt.Errorf("failed to read compression type: %w", err)
	}

	if err := binary.Read(r, binary.BigEndian, &pakEntry.UnknownData); err != nil {
		return PakEntry{}, fmt.Errorf("failed to read unknown data: %w", err)
	}

	return pakEntry, nil
}

func parseEntries(r *bytes.Reader, dataBlockLength int64) ([]PakEntry, error) {
	var entries []PakEntry
	read := 0

	for r.Len() > 0 {
		// read byte to determine entry type
		entryType, err := r.ReadByte()
		if err != nil {
			return nil, fmt.Errorf("failed to read entry type: %w", err)
		}

		nameLength, err := r.ReadByte()
		if err != nil {
			return nil, fmt.Errorf("failed to read name length: %w", err)
		}

		name := make([]byte, nameLength)
		if _, err := io.ReadFull(r, name); err != nil {
			return nil, fmt.Errorf("failed to read name: %w", err)
		}

		switch entryType {
		case 0x00: // Directory
			ent, size, err := parseDirectory(r, string(name), dataBlockLength)
			if err != nil {
				return nil, fmt.Errorf("failed to parse directory '%s': %w", string(name), err)
			}
			read += 1 + 1 + int(nameLength) + size
			entries = append(entries, ent...)
		case 0x01: // File
			pakEntry, err := parseEntry(r)
			if err != nil {
				return nil, fmt.Errorf("failed to parse entry for file '%s': %w", string(name), err)
			}

			pakEntry.Name = string(name)

			entries = append(entries, pakEntry)
			read += 1 + 1 + int(nameLength) + 4 + 4 + 4 + 4 + 4 + 4 // entryType + nameLength + name + offset + size + originalSize + NULL + compressType + unknownData

		default:
			return nil, fmt.Errorf("unknown entry type: %d", entryType)
		}
	}

	return entries, nil
}

func parseDirectory(r *bytes.Reader, path string, dataBlockOffset int64) ([]PakEntry, int, error) {
	var entries []PakEntry
	var totalSize int

	// read the number of entries in the directory
	var entryCount uint32
	if err := binary.Read(r, binary.LittleEndian, &entryCount); err != nil {
		return nil, 0, fmt.Errorf("failed to read entry count for directory '%s': %w", path, err)
	}

	totalSize += 4

	for i := 0; i < int(entryCount); i++ {
		// read byte to determine entry type
		entryType, err := r.ReadByte()
		if err != nil {
			return nil, 0, fmt.Errorf("failed to read entry type: %w", err)
		}

		nameLength, err := r.ReadByte()
		if err != nil {
			return nil, 0, fmt.Errorf("failed to read name length: %w", err)
		}

		name := make([]byte, nameLength)
		if _, err := io.ReadFull(r, name); err != nil {
			return nil, 0, fmt.Errorf("failed to read name: %w", err)
		}

		totalSize += 1 + 1 + int(nameLength)

		switch entryType {
		case 0x00: // Directory
			subEntries, size, err := parseDirectory(r, path+"/"+string(name), dataBlockOffset)
			if err != nil {
				return nil, 0, fmt.Errorf("failed to parse directory '%s': %w", path+"/"+string(name), err)
			}
			entries = append(entries, subEntries...)
			totalSize += size
		case 0x01: // File
			pakEntry, err := parseEntry(r)
			if err != nil {
				return nil, 0, fmt.Errorf("failed to parse entry for file '%s': %w", path+"/"+string(name), err)
			}
			pakEntry.Name = path + "/" + string(name)
			entries = append(entries, pakEntry)
			totalSize += 4 + 4 + 4 + 4 + 4 + 4
		}
	}

	return entries, totalSize, nil
}

func GetPakFileInfo(data []byte) ([]PakEntry, error) {
	r := bytes.NewReader(data)

	// Read FORM header
	if err := readString(r, "FORM"); err != nil {
		return nil, err
	}
	r.Seek(4, io.SeekCurrent) // Skip total file size

	// Read PAC1 header
	if err := readString(r, "PAC1"); err != nil {
		return nil, err
	}

	var dataBlockOffset int64 = -1

	// Find DATA and FILE chunks
	for {
		chunkIDBytes := make([]byte, 4)
		_, err := io.ReadFull(r, chunkIDBytes)
		if err == io.EOF {
			break
		}
		if err != nil {
			return nil, fmt.Errorf("failed to read chunk ID: %w", err)
		}
		chunkID := string(chunkIDBytes)

		var chunkSize uint32
		if err := binary.Read(r, binary.BigEndian, &chunkSize); err != nil {
			return nil, fmt.Errorf("failed to read chunk size for %s: %w", chunkID, err)
		}

		switch chunkID {
		case "HEAD":
			r.Seek(int64(chunkSize), io.SeekCurrent)
		case "DATA":
			// The file offsets are relative to the start of the data within this block.
			// So we record the start position of the data block.
			dataBlockOffset, err = r.Seek(0, io.SeekCurrent)
			if err != nil {
				return nil, fmt.Errorf("could not get DATA block offset: %w", err)
			}
			r.Seek(int64(chunkSize), io.SeekCurrent)
		case "FILE":
			if dataBlockOffset == -1 {
				return nil, fmt.Errorf("FILE chunk found before DATA chunk")
			}

			// skip unknown data
			r.Seek(6, io.SeekCurrent)

			entries, err := parseEntries(r, dataBlockOffset)

			if err != nil {
				return nil, fmt.Errorf("failed to parse FILE entries: %w", err)
			}

			return entries, nil
		default:
			// Skip unknown chunks
			r.Seek(int64(chunkSize), io.SeekCurrent)
		}
	}

	return nil, fmt.Errorf("FILE chunk not found in archive")
}