// This file is part of Gopher2600.
//
// Gopher2600 is free software: you can redistribute it and/or modify
// it under the terms of the gnu general public license as published by
// the Free Software Foundation, either version 3 of the License, or
// (at your option) any later version.
//
// Gopher2600 is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with Gopher2600.  If not, see <https://www.gnu.org/licenses/>.

package cartridgeloader

import (
	"crypto/sha1"
	"fmt"
	"io"
	"io/ioutil"
	"net/http"
	"net/url"
	"os"
	"path"
	"strings"

	"github.com/jetsetilly/gopher2600/curated"
	"github.com/jetsetilly/gopher2600/hardware/memory/cartridge/mapper"
	"github.com/jetsetilly/gopher2600/logger"
)

// Loader is used to specify the cartridge to use when Attach()ing to
// the VCS. it also permits the called to specify the mapping of the cartridge
// (if necessary. fingerprinting is pretty good).
type Loader struct {
	// filename of cartridge to load.
	Filename string

	// empty string or "AUTO" indicates automatic fingerprinting
	Mapping string

	// expected hash of the loaded cartridge. empty string indicates that the
	// hash is unknown and need not be validated. after a load operation the
	// value will be the hash of the loaded data
	//
	// in the case of sound data (IsSoundData is true) then the hash is of the
	// original binary file not he decoded PCM data
	Hash string

	// copy of the loaded data. subsequenct calls to Load() will return a copy
	// of this data
	Data []byte

	// does the Data field consist of sound (PCM) data
	IsSoundData bool

	// callback function when cartridge has been successfully inserted/loaded.
	// not all cartridge formats support this
	//
	// !!TODO: all cartridge formats to support OnLoaded() callback (for completeness)
	OnLoaded func(cart mapper.CartMapper) error

	// for some file types streaming is necessary.
	//
	// note that we have a pointer to a pointer of an os.File. this is so we
	// can record a change of streamHandle even if the Loader{} struct is
	// passed by value.
	//
	// tricky to handle but it works well for our use case.
	streamHandle **os.File
}

// NewLoader is the preferred method of initialisation for the Loader type.
//
// The mapping argument will be used to set the Mapping field, unless the
// argument is either "AUTO" or the empty string. In which case the file
// extension is used to set the field.
//
// File extensions should be the same as the ID of the intended mapper, as
// defined in the cartridge package. The exception is the DPC+ format which
// requires the file extension "DP+"
//
// File extensions ".BIN" and "A26" will set the Mapping field to "AUTO".
//
// Alphabetic characters in file extensions can be in upper or lower case or a
// mixture of both.
func NewLoader(filename string, mapping string) Loader {
	cl := Loader{
		Filename:     filename,
		Mapping:      "AUTO",
		streamHandle: new(*os.File),
	}

	mapping = strings.TrimSpace(strings.ToUpper(mapping))
	if mapping != "AUTO" && mapping != "" {
		cl.Mapping = mapping
	} else {
		ext := strings.ToUpper(path.Ext(filename))
		switch ext {
		case ".BIN":
			fallthrough
		case ".ROM":
			fallthrough
		case ".A26":
			cl.Mapping = "AUTO"
		case ".2k":
			fallthrough
		case ".4k":
			fallthrough
		case ".F8":
			fallthrough
		case ".F6":
			fallthrough
		case ".F4":
			fallthrough
		case ".2k+":
			fallthrough
		case ".4k+":
			fallthrough
		case ".F8+":
			fallthrough
		case ".F6+":
			fallthrough
		case ".F4+":
			fallthrough
		case ".FA":
			fallthrough
		case ".FE":
			fallthrough
		case ".E0":
			fallthrough
		case ".E7":
			fallthrough
		case ".3F":
			fallthrough
		case ".AR":
			fallthrough
		case ".DF":
			fallthrough
		case ".3E":
			fallthrough
		case ".3E+":
			fallthrough
		case ".SB":
			fallthrough
		case ".DPC":
			cl.Mapping = ext[1:]
		case ".DP+":
			cl.Mapping = "DPC+"
		case "CDF":
			cl.Mapping = "CDF"
		case ".WAV":
			fallthrough
		case ".MP3":
			cl.Mapping = "AR"
			cl.IsSoundData = true
		case ".MVC":
			cl.Mapping = "MVC"
		}
	}

	return cl
}

// FileExtensions is the list of file extensions that are recognised by the
// cartridgeloader package.
var FileExtensions = [...]string{".BIN", ".ROM", ".A26", ".2k", ".4k", ".F8", ".F6", ".F4", ".2k+", ".4k+", ".F8+", ".F6+", ".F4+", ".FA", ".FE", ".E0", ".E7", ".3F", ".AR", ".DF", "3E", "3E+", "SB", ".DPC", ".DP+", "CDF", ".WAV", ".MP3", ".MVC"}

// ShortName returns a shortened version of the CartridgeLoader filename.
func (cl Loader) ShortName() string {
	// return the empty string if filename is undefined
	if len(strings.TrimSpace(cl.Filename)) == 0 {
		return ""
	}

	sn := path.Base(cl.Filename)
	sn = strings.TrimSuffix(sn, path.Ext(cl.Filename))
	return sn
}

// HasLoaded returns true if Load() has been successfully called.
func (cl Loader) HasLoaded() bool {
	return len(cl.Data) > 0
}

// Load the cartridge data and return as a byte array. Loader filenames with a
// valid schema will use that method to load the data. Currently supported
// schemes are HTTP and local files.
func (cl *Loader) Load() error {
	if cl.Mapping == "MVC" {
		if (*cl.streamHandle) == nil {
			var err error
			*cl.streamHandle, err = os.Open(cl.Filename)
			if err != nil {
				return curated.Errorf("cartridgeloader: %v", err)
			}
			logger.Logf("cartridgeloader", "stream open (%s)", (*cl.streamHandle).Name())
		}
		return nil
	}

	if len(cl.Data) > 0 {
		// !!TODO: already-loaded error?
		return nil
	}

	scheme := "file"

	url, err := url.Parse(cl.Filename)
	if err == nil {
		scheme = url.Scheme
	}

	switch scheme {
	case "http":
		fallthrough
	case "https":
		resp, err := http.Get(cl.Filename)
		if err != nil {
			return curated.Errorf("cartridgeloader: %v", err)
		}
		defer resp.Body.Close()

		cl.Data, err = ioutil.ReadAll(resp.Body)
		if err != nil {
			return curated.Errorf("cartridgeloader: %v", err)
		}

	case "file":
		fallthrough

	case "":
		fallthrough

	default:
		f, err := os.Open(cl.Filename)
		if err != nil {
			return curated.Errorf("cartridgeloader: %v", err)
		}
		defer f.Close()

		// get file info. not using Stat() on the file handle because the
		// windows version (when running under wine) does not handle that
		cfi, err := os.Stat(cl.Filename)
		if err != nil {
			return curated.Errorf("cartridgeloader: %v", err)
		}
		size := cfi.Size()

		cl.Data = make([]byte, size)
		_, err = f.Read(cl.Data)
		if err != nil {
			return curated.Errorf("cartridgeloader: %v", err)
		}
	}

	// generate hash
	hash := fmt.Sprintf("%x", sha1.Sum(cl.Data))

	// check for hash consistency
	if cl.Hash != "" && cl.Hash != hash {
		return curated.Errorf("cartridgeloader: %v", "unexpected hash value")
	}

	// not generated hash
	cl.Hash = hash

	return nil
}

func (cl *Loader) isStreaming() bool {
	return cl.streamHandle != nil && *cl.streamHandle != nil
}

// Close ends a cartridge loader session.
func (cl *Loader) Close() error {
	if cl.isStreaming() {
		fn := (*cl.streamHandle).Name()
		err := (*cl.streamHandle).Close()
		if err != nil {
			return curated.Errorf("cartridgeloader: %v", err)
		}
		*cl.streamHandle = nil
		logger.Logf("cartridgeloader", "stream closed (%s)", fn)
	}
	return nil
}

// Streamer exposes only the Stream() function for use.
type Streamer interface {
	Stream(offset int64, buffer []byte) (int, error)
}

// Stream enough data to fill buffer from position offset.
func (cl Loader) Stream(offset int64, buffer []byte) (int, error) {
	if !cl.isStreaming() {
		return 0, curated.Errorf("cartridgeloader: stream: no stream open")
	}

	if _, err := (*cl.streamHandle).Seek(offset, io.SeekStart); err != nil {
		return 0, curated.Errorf("cartridgeloader: stream: %v", err)
	}

	n, err := (*cl.streamHandle).Read(buffer)
	if err != nil {
		if err != io.EOF {
			return 0, curated.Errorf("cartridgeloader: stream: %v", err)
		}
	}

	if n > 0 && n != len(buffer) {
		return 0, curated.Errorf("cartridgeloader: stream: buffer underrun")
	}

	return n, nil
}