wttr/src/location/timezone_offsets.zig

// Auto-generated timezone offset table
// Generated by scripts/generate_timezone_table.py
//
// Maps longitude (0-359) to UTC offset in minutes
// Sampled at latitudes: 0°, 30°N, 30°S and uses most common offset
//
// ACCURACY NOTES:
// - This is a simplified longitude-only lookup for weather display purposes
// - Samples 3 latitudes per longitude and uses the most common offset
// - Works well for mid-latitudes (±30°) where most population lives
// - Can be off by 1-2.5 hours at extreme latitudes (e.g., Russia vs Australia)
// - Acceptable for "morning/afternoon/evening/night" weather labels
// - If higher accuracy is needed, modify getTimezoneOffset() to use latitude

const std = @import("std");

const Coordinates = @import("../Coordinates.zig");

/// Timezone offset in minutes from UTC for each degree of longitude (0-359)
/// Negative values = west of UTC, positive = east of UTC
pub const timezone_offsets: [360]i16 = .{
    720,
    -720,
    -720,
    -720,
    -720,
    -720,
    -720,
    -720,
    -660,
    -660,
    -660,
    -660,
    -660,
    -660,
    -660,
    -660,
    -660,
    -660,
    -660,
    -660,
    -660,
    -660,
    -660,
    -600,
    -600,
    -600,
    -600,
    -600,
    -600,
    -600,
    -600,
    -600,
    -600,
    -600,
    -600,
    -600,
    -600,
    -600,
    -540,
    -540,
    -540,
    -540,
    -540,
    -540,
    -540,
    -540,
    -540,
    -540,
    -540,
    -540,
    -540,
    -540,
    -540,
    -480,
    -480,
    -480,
    -480,
    -480,
    -480,
    -480,
    -480,
    -480,
    -480,
    -480,
    -480,
    -480,
    -480,
    -480,
    -420,
    -420,
    -420,
    -420,
    -420,
    -420,
    -420,
    -420,
    -420,
    -420,
    -420,
    -420,
    -420,
    -420,
    -420,
    -360,
    -360,
    -360,
    -360,
    -360,
    -360,
    -360,
    -360,
    -360,
    -360,
    -360,
    -360,
    -360,
    -360,
    -360,
    -300,
    -300,
    -300,
    -300,
    -300,
    -300,
    -300,
    -300,
    -300,
    -300,
    -300,
    -300,
    -240,
    -240,
    -240,
    -240,
    -240,
    -240,
    -240,
    -240,
    -240,
    -240,
    -240,
    -240,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -180,
    -120,
    -120,
    -120,
    -120,
    -120,
    -120,
    -120,
    -120,
    -120,
    -120,
    -120,
    -120,
    -120,
    -120,
    -120,
    -60,
    -60,
    -60,
    -60,
    -60,
    -60,
    -60,
    -60,
    -60,
    -60,
    -60,
    -60,
    -60,
    -60,
    -60,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    0,
    60,
    60,
    60,
    60,
    60,
    60,
    60,
    60,
    60,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    120,
    180,
    180,
    180,
    180,
    180,
    180,
    180,
    180,
    180,
    180,
    180,
    180,
    180,
    180,
    180,
    180,
    180,
    240,
    240,
    240,
    240,
    240,
    240,
    240,
    240,
    240,
    240,
    240,
    240,
    240,
    240,
    240,
    300,
    300,
    300,
    300,
    300,
    300,
    300,
    300,
    300,
    300,
    300,
    300,
    300,
    300,
    300,
    360,
    360,
    360,
    360,
    360,
    360,
    360,
    360,
    360,
    360,
    360,
    360,
    360,
    360,
    360,
    420,
    420,
    420,
    420,
    420,
    420,
    420,
    420,
    420,
    420,
    420,
    420,
    420,
    420,
    420,
    480,
    480,
    480,
    480,
    480,
    480,
    480,
    480,
    480,
    480,
    480,
    480,
    480,
    480,
    480,
    540,
    540,
    540,
    540,
    540,
    540,
    540,
    540,
    540,
    540,
    540,
    540,
    540,
    540,
    540,
    600,
    600,
    600,
    600,
    600,
    600,
    600,
    600,
    600,
    600,
    600,
    600,
    600,
    600,
    600,
    660,
    660,
    660,
    660,
    660,
    660,
    660,
    660,
    660,
    660,
    660,
    660,
    660,
    660,
    660,
    720,
    720,
    720,
    720,
    720,
    720,
    720,
};

/// Get timezone offset in minutes for given coordinates
/// Currently only uses longitude; latitude is available for future improvements
/// coords: Location coordinates
/// Returns: offset in minutes from UTC
pub fn getTimezoneOffset(coords: Coordinates) i16 {
    // Currently only uses longitude (see ACCURACY NOTES above)
    // Latitude could be used in future for better accuracy at extreme latitudes
    _ = coords.latitude;

    // Normalize longitude to 0-359
    const normalized = @mod(@as(i32, @intFromFloat(@round(coords.longitude))) + 180, 360);
    return timezone_offsets[@intCast(normalized)];
}

test "timezone offset lookup" {
    // London (0°) should be close to UTC
    const london_offset = getTimezoneOffset(.{ .latitude = 51.5, .longitude = 0.0 });
    try std.testing.expect(london_offset >= -60 and london_offset <= 60);

    // New York (-74°) should be around UTC-5 (-300 minutes)
    const ny_offset = getTimezoneOffset(.{ .latitude = 40.7, .longitude = -74.0 });
    try std.testing.expect(ny_offset >= -360 and ny_offset <= -240);

    // Tokyo (139°) should be around UTC+9 (540 minutes)
    const tokyo_offset = getTimezoneOffset(.{ .latitude = 35.7, .longitude = 139.0 });
    try std.testing.expect(tokyo_offset >= 480 and tokyo_offset <= 600);
}