// citrusNikOs' journal -- минималистичный сервер для веб-журнала с расписанием.
//
// Copyright (c) 2023 Nikita Osokin.
//
// Redistribution and use in source and binary forms, with or without modification, are permitted
// provided that the following conditions are met:
// 1. Redistributions of source code must retain the above copyright notice, this list of
//    conditions and the following disclaimer.
// 2. Redistributions in binary form must reproduce the above copyright notice, this list of
//    conditions and the following disclaimer in the documentation and/or other materials provided
//    with the distribution.
//
// THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND ANY EXPRESS OR
// IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY
// AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR
// CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
// CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
// SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
// THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR
// OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
// POSSIBILITY OF SUCH DAMAGE.

package main

import (
    "fmt"
    "io"
    "os"
    "sync"
    "net/http"
    "time"
    "strconv"
)

var schedFileRWMutex sync.RWMutex
var classesRWMutexes map[string]*sync.RWMutex
var classesNames []string
var error500Text []byte

func isValidClass(class string) bool {
    for i := 0; i < len(classesNames); i++ {
        if classesNames[i] == class {
            return true
        }
    }
    return false
}

func getCurrentDay() uint64 {
    return uint64(time.Now().Unix()) / 86400
}

func isValidDay(day string) bool {
    if len(day) == 0 || (day[0] == '0' && len(day) != 1) {
        return false
    }

    for i := 0; i < len(day); i++ {
        if day[i] < '0' || day[i] > '9' {
            return false
        }
    }

    return true
}

func read8BytesBE(reader io.Reader, file *os.File) (uint64, error) {
    var result uint64
    var err error
    var count int
    buffer := make([]byte, 8)
    
    count, err = reader.Read(buffer)
    if count != 8 {
        return 0, err
    }
    for i := 0; i < 8; i++ {
        result <<= 8
        result |= uint64(buffer[i])
    }

    _, err = (*file).Write(buffer)
    if err != nil {
        return 0, err
    }
    return result, nil
}

func read8BytesBENoCopy(reader io.Reader) (uint64, error) {
    var result uint64
    var err error
    var count int
    buffer := make([]byte, 8)
    
    count, err = reader.Read(buffer)
    if count != 8 {
        return 0, err
    }
    for i := 0; i < 8; i++ {
        result <<= 8
        result |= uint64(buffer[i])
    }

    return result, nil
}

func writeUint64BE(writer io.Writer, num uint64) error {
    buffer := make([]byte, 8)
    bufferI := 0
    for i := 56; i >= 0; i -= 8 {
        buffer[bufferI] = uint8((num >> i) & 0xFF)
        bufferI++
    }
    _, err := writer.Write(buffer)
    if err != nil {
        return err
    }
    return nil
}

func respondWithFile(writer http.ResponseWriter, filename string) {
    file, err := os.Open(filename)
    if err != nil {
        writer.WriteHeader(http.StatusInternalServerError)
        writer.Write(error500Text)
        return
    }

    stat, err := file.Stat()
    if err != nil {
        writer.WriteHeader(http.StatusInternalServerError)
        writer.Write(error500Text)
        file.Close()
        return
    }
    buffer := make([]byte, stat.Size())
    
    _, err = file.Read(buffer);
    if err != nil {
        writer.WriteHeader(http.StatusInternalServerError)
        writer.Write(error500Text)
        file.Close()
        return
    }

    writer.Write(buffer)
    file.Close()
}

func handleRootAnd404(writer http.ResponseWriter, request *http.Request) {
    if request.URL.Path != "/" {
        writer.WriteHeader(http.StatusNotFound)
        respondWithFile(writer, "404.html")
    } else {
        respondWithFile(writer, "index.html")
    }
}

func handleGetClassesList(writer http.ResponseWriter, request *http.Request) {
    err := writeUint64BE(writer, uint64(len(classesNames)))
    if err != nil {
        writer.WriteHeader(http.StatusInternalServerError)
    }

    for i := 0; i < len(classesNames); i++ {
        err = writeUint64BE(writer, uint64(len(classesNames[i])))
        if err != nil {
            writer.WriteHeader(http.StatusInternalServerError)
        }

        _, err = writer.Write([]uint8(classesNames[i]))
        if err != nil {
            writer.WriteHeader(http.StatusInternalServerError)
        }
    }
}

func handleEditPage(writer http.ResponseWriter, request *http.Request) {
    if request.Method == http.MethodPost {
        queryValues := request.URL.Query()

        if len(queryValues["c"]) == 0 || !isValidClass(queryValues["c"][0]) {
            writer.WriteHeader(http.StatusBadRequest)
            return
        }

        var day string 
        if len(queryValues["d"]) == 0 || !isValidDay(queryValues["d"][0]) {
            day = strconv.FormatUint(getCurrentDay(), 10)
        } else {
            day = queryValues["d"][0]
        }
       
        passwordLen, err := read8BytesBENoCopy(request.Body);
        if err != nil {
            writer.WriteHeader(http.StatusBadRequest)
            return
        }

        passwordFile, err := os.Open("classes/" + queryValues["c"][0] + "/password")
        if err != nil {
            writer.WriteHeader(http.StatusInternalServerError)
            return
        }

        passwordFileInfo, err := passwordFile.Stat()
        if err != nil {
            passwordFile.Close()
            writer.WriteHeader(http.StatusInternalServerError)
            return
        }

        if uint64(passwordFileInfo.Size() - 1) != passwordLen {
            passwordFile.Close()
            writer.WriteHeader(http.StatusUnauthorized)
            return
        }

        userPassword := make([]byte, passwordLen)
        passwordCount, err := request.Body.Read(userPassword)
        if uint64(passwordCount) != passwordLen || err != nil {
            passwordFile.Close()
            writer.WriteHeader(http.StatusBadRequest)
            return
        }

        password := make([]byte, passwordLen)
        passwordCount, err = passwordFile.Read(password)
        if uint64(passwordCount) != passwordLen || err != nil {
            passwordFile.Close()
            writer.WriteHeader(http.StatusInternalServerError)
            return
        }

        for i := uint64(0); i < passwordLen; i++ {
            if password[i] != userPassword[i] {
                passwordFile.Close()
                writer.WriteHeader(http.StatusUnauthorized)
                return
            }
        }

        tmpSchedFile, err := os.CreateTemp("", "sched")
        if err != nil {
            writer.WriteHeader(http.StatusBadRequest)
            return
        }

        layoutID, err := read8BytesBE(request.Body, tmpSchedFile)
        if err != nil || layoutID != 0 {
            writer.WriteHeader(http.StatusBadRequest)
            os.Remove(tmpSchedFile.Name())
            return
        }

        lessonsCount, err := read8BytesBE(request.Body, tmpSchedFile)
        if err != nil || lessonsCount > 7 {
            writer.WriteHeader(http.StatusBadRequest)
            os.Remove((*tmpSchedFile).Name())
            return
        }

        buffer := make([]byte, 1)
        lastNumber := uint64(0)
        isFirst := true
        for i := uint64(0); i < lessonsCount; i++ {
            number, err := read8BytesBE(request.Body, tmpSchedFile)
            if err != nil {
                writer.WriteHeader(http.StatusBadRequest)
                os.Remove((*tmpSchedFile).Name())
                return
            }
            if !isFirst && number <= lastNumber {
                writer.WriteHeader(http.StatusBadRequest)
                os.Remove((*tmpSchedFile).Name())
                return
            }
            isFirst = false
            lastNumber = number

            nameLen, err := read8BytesBE(request.Body, tmpSchedFile)
            if err != nil {
                writer.WriteHeader(http.StatusBadRequest)
                os.Remove((*tmpSchedFile).Name())
                return
            }
            for j := uint64(0); j < nameLen; j++ {
                beenRead, _ := request.Body.Read(buffer)
                _, err := (*tmpSchedFile).Write(buffer)

                if beenRead == 0 || err != nil {
                    writer.WriteHeader(http.StatusBadRequest)
                    os.Remove((*tmpSchedFile).Name())
                    return
                }
            }

            descrLen, err := read8BytesBE(request.Body, tmpSchedFile)
            if err != nil {
                writer.WriteHeader(http.StatusBadRequest)
                os.Remove((*tmpSchedFile).Name())
                return
            }
            for j := uint64(0); j < descrLen; j++ {
                beenRead, _ := request.Body.Read(buffer)
                _, err := (*tmpSchedFile).Write(buffer)

                if beenRead == 0 || err != nil {
                    writer.WriteHeader(http.StatusBadRequest)
                    os.Remove((*tmpSchedFile).Name())
                    return
                }
            }
        }

        beenRead, err := request.Body.Read(buffer)
        if beenRead != 0 {
            writer.WriteHeader(http.StatusBadRequest)
            os.Remove((*tmpSchedFile).Name())
            return
        }

        classesRWMutexes[queryValues["c"][0]].Lock()
        schedFileName := "classes/" + queryValues["c"][0] + "/" + day

        os.Remove(schedFileName)
        os.Rename((*tmpSchedFile).Name(), schedFileName)

        classesRWMutexes[queryValues["c"][0]].Unlock()
    } else {
        respondWithFile(writer, "editpage.html")
    }
}

func handleSchedule(writer http.ResponseWriter, request *http.Request) {
    respondWithFile(writer, "schedule.html")
}

/* TODO: возможно стоит отправлять что-то кроме просто ошибки 500 */
func handleScheduleGet(writer http.ResponseWriter, request *http.Request) {
    queryValues := request.URL.Query()

    if len(queryValues["c"]) == 0 || !isValidClass(queryValues["c"][0]) {
        writer.WriteHeader(http.StatusBadRequest)
        return
    }

    var day string 
    if len(queryValues["d"]) == 0 || !isValidDay(queryValues["d"][0]) {
        day = strconv.FormatUint(getCurrentDay(), 10)
    } else {
        day = queryValues["d"][0]
    }

    classesRWMutexes[queryValues["c"][0]].RLock()
    defer classesRWMutexes[queryValues["c"][0]].RUnlock()
    
    i := 0
    var schedFile *os.File
    var err error
    schedFileName := "classes/" + queryValues["c"][0] + "/" + day
    for schedFile, err = os.Open(schedFileName); err != nil; schedFile, err = os.Open(schedFileName) {
        if i == 1000 {
            return
        }
        i++
    }
    
    _, err = io.Copy(writer, schedFile)
    if err != nil {
        writer.WriteHeader(http.StatusInternalServerError)
    }

    schedFile.Close()
}

// TODO: Переформатировать эту функцию.
func main() {
    var err error

    error500File, err := os.Open("500.html")
    if err != nil {
        fmt.Printf("[!!!]Не удалось открыть файл 500.html.\n")
        return
    }

    error500FileStat, err := error500File.Stat()
    if err != nil {
        error500File.Close()
        fmt.Printf("[!!!]Не удалось прочитать информацию о файле 500.html.\n")
        return
    }
    error500Text = make([]byte, error500FileStat.Size())
    
    _, err = error500File.Read(error500Text);
    if err != nil {
        error500File.Close()
        fmt.Printf("[!!!]Не удалось прочитать файл 500.html.\n")
        return
    }
    error500File.Close()

    classesRWMutexes = make(map[string]*sync.RWMutex)

    var classesDir *os.File
    var classes []os.DirEntry

    classesDir, err = os.Open("classes")
    if err != nil {
        fmt.Printf("[!!!]Не удалось открыть директорию classes.\n")
        return
    }
    
    classes, err = classesDir.ReadDir(0)
    classesDir.Close()
    if err != nil {
        fmt.Printf("[!!!]Не удалось прочитать содержимое директории classes.\n")
        return
    }
    classesNames = make([]string, len(classes))

    for i := 0; i < len(classes); i++ {
        if !classes[i].IsDir() {
            fmt.Printf("[!!!]Директория classes должна содержать только директории.\n")
            return
        }

        classesNames[i] = classes[i].Name()
        classesRWMutexes[classes[i].Name()] = new(sync.RWMutex)
    }
    
    classes = nil

    http.HandleFunc("/", handleRootAnd404)
    http.HandleFunc("/getClassesList", handleGetClassesList)
    http.HandleFunc("/schedule", handleSchedule)
    http.HandleFunc("/scheduleGet", handleScheduleGet)
    http.HandleFunc("/editpage", handleEditPage)
    http.ListenAndServe(":62314", nil)
}