const BASE32 = "0123456789bcdefghjkmnpqrstuvwxyz";

export function encodeGeohash(
    coord: { latitude: number; longitude: number },
    precision = 9
): string {
    let minLat = -90;
    let maxLat = 90;
    let minLon = -180;
    let maxLon = 180;
    let hash = "";
    let bits = 0;
    let ch = 0;
    let evenBit = true;

    while (hash.length < precision) {
        if (evenBit) {
            const mid = (minLon + maxLon) / 2;
            if (coord.longitude >= mid) {
                ch = (ch << 1) | 1;
                minLon = mid;
            } else {
                ch = ch << 1;
                maxLon = mid;
            }
        } else {
            const mid = (minLat + maxLat) / 2;
            if (coord.latitude >= mid) {
                ch = (ch << 1) | 1;
                minLat = mid;
            } else {
                ch = ch << 1;
                maxLat = mid;
            }
        }
        evenBit = !evenBit;
        bits++;
        if (bits === 5) {
            hash += BASE32[ch];
            bits = 0;
            ch = 0;
        }
    }

    return hash;
}

export function decodeGeohash(hash: string): {
    latitude: number;
    longitude: number;
} {
    let minLat = -90;
    let maxLat = 90;
    let minLon = -180;
    let maxLon = 180;
    let evenBit = true;

    for (const char of hash) {
        const idx = BASE32.indexOf(char);
        for (let i = 4; i >= 0; i--) {
            const bit = (idx >> i) & 1;
            if (evenBit) {
                const mid = (minLon + maxLon) / 2;
                if (bit === 1) {
                    minLon = mid;
                } else {
                    maxLon = mid;
                }
            } else {
                const mid = (minLat + maxLat) / 2;
                if (bit === 1) {
                    minLat = mid;
                } else {
                    maxLat = mid;
                }
            }
            evenBit = !evenBit;
        }
    }

    return {
        latitude: (minLat + maxLat) / 2,
        longitude: (minLon + maxLon) / 2,
    };
}