package common

import (
	"errors"
	"fmt"
	"io"
)

const (
	GitStatus_Untracked = 0
	GitStatus_Modified  = 1
	GitStatus_Ignored   = 2
	GitStatus_Unmerged  = 3 // States[0..3] -- Stage1, Stage2, Stage3 of merge objects
	GitStatus_Renamed   = 4 // orig name in States[0]
)

type GitStatusData struct {
	Path   string
	Status int
	States [3]string

	/*
	 <sub> A 4 character field describing the submodule state.
	            "N..." when the entry is not a submodule.
	            "S<c><m><u>" when the entry is a submodule.
	            <c> is "C" if the commit changed; otherwise ".".
	            <m> is "M" if it has tracked changes; otherwise ".".
	            <u> is "U" if there are untracked changes; otherwise ".".
	*/
	SubmoduleChanges string
}

func parseGit_HexString(data io.ByteReader) (string, error) {
	str := make([]byte, 0, 32)
	for {
		c, err := data.ReadByte()
		if err != nil {
			return "", err
		}
		switch {
		case c == 0 || c == ' ':
			return string(str), nil
		case c >= 'a' && c <= 'f':
		case c >= 'A' && c <= 'F':
		case c >= '0' && c <= '9':
		default:
			return "", errors.New("Invalid character in hex string:" + string(c))
		}
		str = append(str, c)
	}
}
func parseGit_String(data io.ByteReader) (string, error) {
	str := make([]byte, 0, 100)
	for {
		c, err := data.ReadByte()
		if err != nil {
			return "", errors.New("Unexpected EOF. Expected NUL string term")
		}
		if c == 0 || c == ' ' {
			return string(str), nil
		}
		str = append(str, c)
	}
}

func parseGit_StringWithSpace(data io.ByteReader) (string, error) {
	str := make([]byte, 0, 100)
	for {
		c, err := data.ReadByte()
		if err != nil {
			return "", errors.New("Unexpected EOF. Expected NUL string term")
		}
		if c == 0 {
			return string(str), nil
		}
		str = append(str, c)
	}
}

func skipGitStatusEntry(data io.ByteReader, skipSpaceLen int) error {
	for skipSpaceLen > 0 {
		c, err := data.ReadByte()
		if err != nil {
			return err
		}
		if c == ' ' {
			skipSpaceLen--
		}
	}

	return nil
}

func parseSingleStatusEntry(data io.ByteReader) (*GitStatusData, error) {
	ret := GitStatusData{}
	statusType, err := data.ReadByte()
	if err != nil {
		return nil, nil
	}
	switch statusType {
	case '1':
		var err error
		if err = skipGitStatusEntry(data, 8); err != nil {
			return nil, err
		}
		ret.Status = GitStatus_Modified
		ret.Path, err = parseGit_StringWithSpace(data)
		if err != nil {
			return nil, err
		}
	case '2':
		var err error
		if err = skipGitStatusEntry(data, 9); err != nil {
			return nil, err
		}
		ret.Status = GitStatus_Renamed
		ret.Path, err = parseGit_StringWithSpace(data)
		if err != nil {
			return nil, err
		}
		ret.States[0], err = parseGit_StringWithSpace(data)
		if err != nil {
			return nil, err
		}
	case '?':
		var err error
		if err = skipGitStatusEntry(data, 1); err != nil {
			return nil, err
		}
		ret.Status = GitStatus_Untracked
		ret.Path, err = parseGit_StringWithSpace(data)
		if err != nil {
			return nil, err
		}
	case '!':
		var err error
		if err = skipGitStatusEntry(data, 1); err != nil {
			return nil, err
		}
		ret.Status = GitStatus_Ignored
		ret.Path, err = parseGit_StringWithSpace(data)
		if err != nil {
			return nil, err
		}
	case 'u':
		var err error
		if err = skipGitStatusEntry(data, 2); err != nil {
			return nil, err
		}
		if ret.SubmoduleChanges, err = parseGit_String(data); err != nil {
			return nil, err
		}
		if err = skipGitStatusEntry(data, 4); err != nil {
			return nil, err
		}

		if ret.States[0], err = parseGit_HexString(data); err != nil {
			return nil, err
		}
		if ret.States[1], err = parseGit_HexString(data); err != nil {
			return nil, err
		}
		if ret.States[2], err = parseGit_HexString(data); err != nil {
			return nil, err
		}
		ret.Status = GitStatus_Unmerged
		ret.Path, err = parseGit_StringWithSpace(data)
		if err != nil {
			return nil, err
		}
	default:
		return nil, errors.New("Invalid status type" + string(statusType))
	}
	return &ret, nil
}

func parseGitStatusData(data io.ByteReader) (Data, error) {
	ret := make([]GitStatusData, 0, 10)
	for {
		data, err := parseSingleStatusEntry(data)
		if err != nil {
			return nil, err
		} else if data == nil {
			break
		}

		ret = append(ret, *data)
	}
	return ret, nil
}

type Data interface{}

type CommitStatus int

const (
	Add CommitStatus = iota
	Rm
	Copy
	Modify
	Rename
	TypeChange
	Unmerged
	Unknown
)

type GitDiffRawData struct {
	SrcMode, DstMode     string
	SrcCommit, DstCommit string
	Status               CommitStatus
	Src, Dst             string
}

func parseGit_DiffIndexStatus(data io.ByteReader, d *GitDiffRawData) error {
	b, err := data.ReadByte()
	if err != nil {
		return err
	}

	switch b {
	case 'A':
		d.Status = Add
	case 'C':
		d.Status = Copy
	case 'D':
		d.Status = Rm
	case 'M':
		d.Status = Modify
	case 'R':
		d.Status = Rename
	case 'T':
		d.Status = TypeChange
	case 'U':
		d.Status = Unmerged
	case 'X':
		return fmt.Errorf("Unexpected unknown change type. This is a git bug")
	}
	_, err = parseGit_StringWithSpace(data)
	if err != nil {
		return err
	}

	return nil
}

func parseSingleGitDiffIndexRawData(data io.ByteReader) (*GitDiffRawData, error) {
	var ret GitDiffRawData

	b, err := data.ReadByte()
	if err != nil {
		return nil, err
	}
	if b != ':' {
		return nil, fmt.Errorf("Expected ':' but got '%s'", string(b))
	}

	if ret.SrcMode, err = parseGit_String(data); err != nil {
		return nil, err
	}
	if ret.DstMode, err = parseGit_String(data); err != nil {
		return nil, err
	}
	if ret.Src, err = parseGit_String(data); err != nil {
		return nil, err
	}
	if ret.Dst, err = parseGit_String(data); err != nil {
		return nil, err
	}
	if err = parseGit_DiffIndexStatus(data, &ret); err != nil {
		return nil, err
	}
	ret.Dst = ret.Src
	switch ret.Status {
	case Copy, Rename:
		if ret.Src, err = parseGit_StringWithSpace(data); err != nil {
			return nil, err
		}
	}

	return &ret, nil
}

func parseGitDiffIndexRawData(data io.ByteReader) (Data, error) {
	ret := make([]GitDiffRawData, 0, 10)
	for {
		data, err := parseSingleGitDiffIndexRawData(data)
		if err != nil {
			return nil, err
		} else if data == nil {
			break
		}

		ret = append(ret, *data)
	}
	return ret, nil
}