package main

import (
	"bytes"
	"encoding/binary"
	"io"
	"log"
	"os"
)

// See https://gbdev.io/pandocs/The_Cartridge_Header.html#0104-0133--nintendo-logo
var expectedLogo = [48]byte{
	0xCE, 0xED, 0x66, 0x66, 0xCC, 0x0D, 0x00, 0x0B,
	0x03, 0x73, 0x00, 0x83, 0x00, 0x0C, 0x00, 0x0D,
	0x00, 0x08, 0x11, 0x1F, 0x88, 0x89, 0x00, 0x0E,
	0xDC, 0xCC, 0x6E, 0xE6, 0xDD, 0xDD, 0xD9, 0x99,
	0xBB, 0xBB, 0x67, 0x63, 0x6E, 0x0E, 0xEC, 0xCC,
	0xDD, 0xDC, 0x99, 0x9F, 0xBB, 0xB9, 0x33, 0x3E,
}

// Cartridge types
// See https://gbdev.io/pandocs/The_Cartridge_Header.html#0147--cartridge-type
var cartridgeTypes = map[byte]string{
	0x00: "ROM ONLY",
	0x01: "MBC1",
	0x02: "MBC1+RAM",
	0x03: "MBC1+RAM+BATTERY",
	0x05: "MBC2",
	0x06: "MBC2+BATTERY",
	0x08: "ROM+RAM 9",
	0x09: "ROM+RAM+BATTERY 9",
	0x0B: "MMM01",
	0x0C: "MMM01+RAM",
	0x0D: "MMM01+RAM+BATTERY",
	0x0F: "MBC3+TIMER+BATTERY",
	0x10: "MBC3+TIMER+RAM+BATTERY 10",
	0x11: "MBC3",
	0x12: "MBC3+RAM 10",
	0x13: "MBC3+RAM+BATTERY 10",
	0x19: "MBC5",
	0x1A: "MBC5+RAM",
	0x1B: "MBC5+RAM+BATTERY",
	0x1C: "MBC5+RUMBLE",
	0x1D: "MBC5+RUMBLE+RAM",
	0x1E: "MBC5+RUMBLE+RAM+BATTERY",
	0x20: "MBC6",
	0x22: "MBC7+SENSOR+RUMBLE+RAM+BATTERY",
	0xFC: "POCKET CAMERA",
	0xFD: "BANDAI TAMA5",
	0xFE: "HuC3",
	0xFF: "HuC1+RAM+BATTERY",
}

// RAM sizes
// https://gbdev.io/pandocs/The_Cartridge_Header.html#0149--ram-size
var ramSizes = map[byte]string{
	0x00: "0 - No RAM",
	0x01: "UNUSED VALUE",
	0x02: "8 KiB - 1 bank",
	0x03: "32 KiB - 4 banks of 8 KiB each",
	0x04: "128 KiB 16 banks of 8 KiB each",
	0x05: "64 KiB  8 banks of 8 KiB each",
}

// Old licensees
// https://gbdev.io/pandocs/The_Cartridge_Header.html#014b--old-licensee-code
var oldLicensees = map[byte]string{
	0x00: "None",
	0x01: "Nintendo",
	0x08: "Capcom",
	0x09: "HOT-B",
	0x0A: "Jaleco",
	0x0B: "Coconuts Japan",
	0x0C: "Elite Systems",
	0x13: "EA (Electronic Arts)",
	0x18: "Hudson Soft",
	0x19: "ITC Entertainment",
	0x1A: "Yanoman",
	0x1D: "Japan Clary",
	0x1F: "Virgin Games Ltd.3",
	0x24: "PCM Complete",
	0x25: "San-X",
	0x28: "Kemco",
	0x29: "SETA Corporation",
	0x30: "Infogrames5",
	0x31: "Nintendo",
	0x32: "Bandai",
	0x33: "Indicates that the New licensee code should be used instead.",
	0x34: "Konami",
	0x35: "HectorSoft",
	0x38: "Capcom",
	0x39: "Banpresto",
	0x3C: "Entertainment Interactive (stub)",
	0x3E: "Gremlin",
	0x41: "Ubi Soft1",
	0x42: "Atlus",
	0x44: "Malibu Interactive",
	0x46: "Angel",
	0x47: "Spectrum HoloByte",
	0x49: "Irem",
	0x4A: "Virgin Games Ltd.3",
	0x4D: "Malibu Interactive",
	0x4F: "U.S. Gold",
	0x50: "Absolute",
	0x51: "Acclaim Entertainment",
	0x52: "Activision",
	0x53: "Sammy USA Corporation",
	0x54: "GameTek",
	0x55: "Park Place13",
	0x56: "LJN",
	0x57: "Matchbox",
	0x59: "Milton Bradley Company",
	0x5A: "Mindscape",
	0x5B: "Romstar",
	0x5C: "Naxat Soft14",
	0x5D: "Tradewest",
	0x60: "Titus Interactive",
	0x61: "Virgin Games Ltd.3",
	0x67: "Ocean Software",
	0x69: "EA (Electronic Arts)",
	0x6E: "Elite Systems",
	0x6F: "Electro Brain",
	0x70: "Infogrames5",
	0x71: "Interplay Entertainment",
	0x72: "Broderbund",
	0x73: "Sculptured Software6",
	0x75: "The Sales Curve Limited7",
	0x78: "THQ",
	0x79: "Accolade15",
	0x7A: "Triffix Entertainment",
	0x7C: "MicroProse",
	0x7F: "Kemco",
	0x80: "Misawa Entertainment",
	0x83: "LOZC G.",
	0x86: "Tokuma Shoten",
	0x8B: "Bullet-Proof Software2",
	0x8C: "Vic Tokai Corp.16",
	0x8E: "Ape Inc.17",
	0x8F: "I'Max18",
	0x91: "Chunsoft Co.8",
	0x92: "Video System",
	0x93: "Tsubaraya Productions",
	0x95: "Varie",
	0x96: "Yonezawa19/S'Pal",
	0x97: "Kemco",
	0x99: "Arc",
	0x9A: "Nihon Bussan",
	0x9B: "Tecmo",
	0x9C: "Imagineer",
	0x9D: "Banpresto",
	0x9F: "Nova",
	0xA1: "Hori Electric",
	0xA2: "Bandai",
	0xA4: "Konami",
	0xA6: "Kawada",
	0xA7: "Takara",
	0xA9: "Technos Japan",
	0xAA: "Broderbund",
	0xAC: "Toei Animation",
	0xAD: "Toho",
	0xAF: "Namco",
	0xB0: "Acclaim Entertainment",
	0xB1: "ASCII Corporation or Nexsoft",
	0xB2: "Bandai",
	0xB4: "Square Enix",
	0xB6: "HAL Laboratory",
	0xB7: "SNK",
	0xB9: "Pony Canyon",
	0xBA: "Culture Brain",
	0xBB: "Sunsoft",
	0xBD: "Sony Imagesoft",
	0xBF: "Sammy Corporation",
	0xC0: "Taito",
	0xC2: "Kemco",
	0xC3: "Square",
	0xC4: "Tokuma Shoten",
	0xC5: "Data East",
	0xC6: "Tonkin House",
	0xC8: "Koei",
	0xC9: "UFL",
	0xCA: "Ultra Games",
	0xCB: "VAP, Inc.",
	0xCC: "Use Corporation",
	0xCD: "Meldac",
	0xCE: "Pony Canyon",
	0xCF: "Angel",
	0xD0: "Taito",
	0xD1: "SOFEL (Software Engineering Lab)",
	0xD2: "Quest",
	0xD3: "Sigma Enterprises",
	0xD4: "ASK Kodansha Co.",
	0xD6: "Naxat Soft14",
	0xD7: "Copya System",
	0xD9: "Banpresto",
	0xDA: "Tomy",
	0xDB: "LJN",
	0xDD: "Nippon Computer Systems",
	0xDE: "Human Ent.",
	0xDF: "Altron",
	0xE0: "Jaleco",
	0xE1: "Towa Chiki",
	0xE2: "Yutaka # Needs more info",
	0xE3: "Varie",
	0xE5: "Epoch",
	0xE7: "Athena",
	0xE8: "Asmik Ace Entertainment",
	0xE9: "Natsume",
	0xEA: "King Records",
	0xEB: "Atlus",
	0xEC: "Epic/Sony Records",
	0xEE: "IGS",
	0xF0: "A Wave",
	0xF3: "Extreme Entertainment",
	0xFF: "LJN",
}

type ROMHeader struct {
	EntryPoint [4]byte
	Logo       [48]byte
	// NOTE(m): Assuming "old" cartridges here. This may cause problems with newer cartridges.
	// See https://gbdev.io/pandocs/The_Cartridge_Header.html#0134-0143--title
	Title                [16]byte
	NewLicenseeCode      [2]byte
	SGBFlag              byte
	CartridgeType        byte
	ROMSize              byte
	RAMSize              byte
	DestinationCode      byte
	OldLicenseeCode      byte
	MaskROMVersionNumber byte
	HeaderChecksum       byte
	GlobalChecksum       [2]byte
}

type Cartridge struct {
	Filename    string
	Mapper      string
	Title       string
	Licensee    string
	SGBSupport  bool
	ROMSize     int
	RAMSize     string
	Destination string
	Version     int
}

func Insert(filename string) Cartridge {
	file, err := os.Open(filename)
	if err != nil {
		log.Fatal(err)
	}
	defer file.Close()
	cartridge := Cartridge{Filename: file.Name()}

	// Jump to start of header
	_, err = file.Seek(0x0100, io.SeekStart)
	if err != nil {
		log.Fatal(err)
	}

	// Read header
	var header ROMHeader
	err = binary.Read(file, binary.LittleEndian, &header)
	if err != nil {
		log.Fatal(err)
	}

	// Validate the ROM by checking presence of the Nintendo logo
	if header.Logo != expectedLogo {
		log.Fatal("Invalid ROM file: No valid logo found!")
	}

	// Convert some header values
	cartridge.Title = string(bytes.Trim(header.Title[:], "\x00"))
	cartridge.Mapper = cartridgeTypes[header.CartridgeType]
	if header.OldLicenseeCode == 0x33 {
		// FIXME(m): Support new licensee codes
		cartridge.Licensee = "Indicates that the New licensee code should be used instead."
	} else {
		cartridge.Licensee = oldLicensees[header.OldLicenseeCode]
	}
	cartridge.SGBSupport = (header.SGBFlag == 0x03)
	cartridge.ROMSize = 32 * (1 << header.ROMSize)
	cartridge.RAMSize = ramSizes[header.RAMSize]
	switch header.DestinationCode {
	case 0x00:
		cartridge.Destination = "Japan (and possibly overseas)"
	case 0x01:
		cartridge.Destination = "Overseas only"
	default:
		cartridge.Destination = "UNKNOWN"
	}
	cartridge.Version = int(header.MaskROMVersionNumber)

	// TODO(m): Verify header checksum

	// NOTE(m): Ignoring global checksum which is not used, except by one emulator.
	// See https://gbdev.io/pandocs/The_Cartridge_Header.html#014e-014f--global-checksum

	return cartridge
}