#include <stdio.h>
#include <stdbool.h>
#include <math.h>

/* Function to transfer color code from IEC 60062:2016 into an integer.
   returns 10 on error.

    Black 	BK 	0
    Brown 	BN 	1
    Blue 	BU 	6
    Gold 	GD 	-1
    Green 	GN 	5
    Gray 	GY 	8
    Orange 	OG 	3
    Pink 	PK 	-3
    Red 	RD 	2
    Silver 	SR 	-2
    Violet 	VT 	7
    Yellow 	YE 	4
*/

int colorCodeToInt(char c1, char c2)
{
    switch(c1)
    {
    case 'B':
        switch (c2)
        {
        case 'K':
            return 0;
        case 'N':
            return 1;
        case 'U':
            return 6;
        }
        break;
    case 'G':
        switch (c2)
        {
        case 'D':
            return -1;
        case 'N':
            return 5;
        case 'Y':
            return 8;
        }
        break;
    case 'O':
        if (c2 == 'G')
        {
            return 3;
        }
        break;
    case 'P':
        if (c2 == 'K')
        {
            return -3;
        }
        break;
    case 'R':
        if (c2 == 'D')
        {
            return 2;
        }
        break;
    case 'S':
        if (c2 == 'R')
        {
            return -2;
        }
        break;
    case 'V':
        if (c2 == 'T')
        {
            return 7;
        }
        break;
    case 'Y':
        if (c2 == 'E')
        {
            return 4;
        }
        break;
    }
    return 10;
}

int readBand(bool readSignificant)
{
    char c1, c2, dummy;
    int band;
    do
    {
        fflush(stdin); // clear keyboard buffer
        scanf("%c%c", &c1, &c2);
        band = colorCodeToInt(c1, c2);
        if (band == 10 || (readSignificant && band < 0))
        {
            printf("This is not a valid color code. Try again: ");
        }
    }
    while (band == 10 || (readSignificant && band < 0));
    return band;
}

// reuse printResistorValue from exercise 5.4
void printResistorValue(double value)
{
    double exponent = log10(value);
    int base1000exponent = (int) floor(exponent/3);
    char metricPrefix;
    value /= pow(10, base1000exponent * 3);

    switch (base1000exponent)
    {
        case -1 :
            metricPrefix = 'm';
            break;
        case 0 :
            metricPrefix = ' ';
            break;
        case 1 :
            metricPrefix = 'k';
            break;
        case 2 :
            metricPrefix = 'M';
            break;
        case 3 :
            metricPrefix = 'G';
            break;
    }
    if(value < 10)
    {
        printf("%3.1f%c", value, metricPrefix);
    }
    else
    {
        printf("%3.0f%c", value, metricPrefix);
    }
}

bool isE12(int value)
{
    switch(value)
    {
    case 10:
    case 12:
    case 15:
    case 18:
    case 22:
    case 27:
    case 33:
    case 39:
    case 47:
    case 56:
    case 68:
    case 82:
        return true;
    }
    return false;
}

int main(void)
{
    char answer, dummy;
    do
    {
        int band1, band2, band3;
        printf("Enter the first color code: ");
        band1 = readBand(true);
        printf("Enter the second color code: ");
        band2 = readBand(true);
        printf("Enter the third color code: ");
        band3 = readBand(false);
        printf("The value of this resistor is ");
        int significant = band1*10 + band2;
        printResistorValue(significant * pow(10, band3));
        printf("\n");
        if (isE12(significant))
        {
            printf("This value belongs to the E12 series\n");
        }
        else
        {
            printf("This value does not belong to the E12 series\n");
        }
        printf("Do you want to continue? ");
        do
        {
            fflush(stdin); // clear keyboard buffer
            scanf("%c", &answer);
            if (answer != 'Y' && answer != 'N')
            {
                printf("Not a valid answer. Try again (type Y or N): ");
            }
        }
        while (answer != 'Y' && answer != 'N');
    }
    while (answer == 'Y');
    return 0;
}