package main

import (
    "fmt"
    "io/ioutil"
    "regexp"
    "time"
)

// Message Define a message structure
type Message struct {
    Name    string
    Message string
    Time    time.Time
}

// Messages Hold a slice for all the messages a user was posting at the log file
type Messages []Message

// Chats hold a map for all chats at the log based on users
type Chats map[string]Messages

func lineToMessage(line string) (Message, error) {

    re := regexp.MustCompile(`^\[([^\]]+)\] ([^:]+): (.*?)$`)
    result := re.FindStringSubmatch(line)
    if len(result) != 4 {
        return Message{}, fmt.Errorf("Invalid line format")
    }
    tm, err := time.Parse("2006-01-02 03:04:05 MST", result[1])
    if err != nil {
        return Message{}, err
    }
    msg := Message{
        Time:    tm,
        Name:    result[2],
        Message: result[3],
    }
    return msg, nil
}

func mapChats(lines []string) (chats Chats, err error) {
    chats = make(Chats)
    for _, line := range lines {
        msg, err := lineToMessage(line)
        if err != nil {
            return chats, err
        }
        chats[msg.Name] = append(chats[msg.Name], msg)
    }

    return
}

func parseFile(path string) (chats Chats, err error) {
    buff, err := ioutil.ReadFile(path)
    if err != nil {
        return chats, err
    }

    var lines []string
    line := ""
    for _, ch := range buff {
        if ch == '\n' {
            lines = append(lines, line)
            line = ""
            continue
        }
        line = line + string(ch)
    }

    chats, err = mapChats(lines)

    return chats, err
}

func main() {
    chats, err := parseFile("chat.log")
    if err != nil {
        panic(err)
    }
    for key, value := range chats {
        fmt.Printf("User: %s have #%d lines\n", key, len(value))
    }
}