1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364 365 366 367 368 369 370 371 372 373 374 375 376 377 378 379 380 381 382 383 384 385 386 387 388 389 390 391 392 393 394 395 396 397 398 399 400 401 402 403 404 405 406 407 408 409 410 411 412 413 414 415 416 417 418 419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440 441 442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474 475 476 477 478 479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538 539 540 541 542 543 544 545 546 547 548 549 550 551 552 553 554 555 556 557 558 559 560
//! Generating timespan sets from a built Table. //! //! Once a table has been fully built, it needs to be turned into several //! *fixed timespan sets*: a series of spans of time where the local time //! offset remains the same throughout. One set is generated for each named //! time zone. These timespan sets can then be iterated over to produce //! *transitions*: when the local time changes from one offset to another. //! //! These sets are returned as `FixedTimespanSet` values, rather than //! iterators, because the generation logic does not output the timespans //! in any particular order, meaning they need to be sorted before they’re //! returned—so we may as well just return the vector, rather than an //! iterator over the vector. //! //! Similarly, there is a fixed set of years that is iterated over //! (currently 1800..2100), rather than having an iterator that produces //! timespans indefinitely. Not only do we need a complete set of timespans //! for sorting, but it is not necessarily advisable to rely on offset //! changes so far into the future! //! //! ### Example //! //! The complete definition of the `Indian/Mauritius` time zone, as //! specified in the `africa` file in my version of the tz database, has //! two Zone definitions, one of which refers to four Rule definitions: //! //! ```tz //! # Rule NAME FROM TO TYPE IN ON AT SAVE LETTER/S //! Rule Mauritius 1982 only - Oct 10 0:00 1:00 S //! Rule Mauritius 1983 only - Mar 21 0:00 0 - //! Rule Mauritius 2008 only - Oct lastSun 2:00 1:00 S //! Rule Mauritius 2009 only - Mar lastSun 2:00 0 - //! //! # Zone NAME GMTOFF RULES FORMAT [UNTIL] //! Zone Indian/Mauritius 3:50:00 - LMT 1907 # Port Louis //! 4:00 Mauritius MU%sT # Mauritius Time //! ``` //! //! To generate a fixed timespan set for this timezone, we examine each of the //! Zone definitions, generating at least one timespan for each definition. //! //! * The first timespan describes the *local mean time* (LMT) in Mauritius, //! calculated by the geographical position of Port Louis, its capital. //! Although it’s common to have a timespan set begin with a city’s local mean //! time, it is by no means necessary. This timespan has a fixed offset of //! three hours and fifty minutes ahead of UTC, and lasts until the beginning //! of 1907, at which point the second timespan kicks in. //! * The second timespan has no ‘until’ date, so it’s in effect indefinitely. //! Instead of having a fixed offset, it refers to the set of rules under the //! name “Mauritius”, which we’ll have to consult to compute the timespans. //! * The first two rules refer to a summer time transition that began on //! the 10th of October 1982, and lasted until the 21st of March 1983. But //! before we get onto that, we need to add a timespan beginning at the //! time the last one ended (1907), up until the point Summer Time kicks //! in (1982), reflecting that it was four hours ahead of UTC. //! * After this, we add another timespan for Summer Time, when Mauritius //! was an extra hour ahead, bringing the total offset for that time to //! *five* hours. //! * The next (and last) two rules refer to another summer time //! transition from the last Sunday of October 2008 to the last Sunday of //! March 2009, this time at 2am local time instead of midnight. But, as //! before, we need to add a *standard* time timespan beginning at the //! time Summer Time ended (1983) up until the point the next span of //! Summer Time kicks in (2008), again reflecting that it was four hours //! ahead of UTC again. //! * Next, we add the Summer Time timespan, again bringing the total //! offset to five hours. We need to calculate when the last Sundays of //! the months are to get the dates correct. //! * Finally, we add one last standard time timespan, lasting from 2009 //! indefinitely, as the Mauritian authorities decided not to change to //! Summer Time again. //! //! All this calculation results in the following six timespans to be added: //! //! | Timespan start | Abbreviation | UTC offset | DST? | //! |:--------------------------|:-------------|:-------------------|:-----| //! | *no start* | LMT | 3 hours 50 minutes | No | //! | 1906-11-31 T 20:10:00 UTC | MUT | 4 hours | No | //! | 1982-09-09 T 20:00:00 UTC | MUST | 5 hours | Yes | //! | 1983-02-20 T 19:00:00 UTC | MUT | 4 hours | No | //! | 2008-09-25 T 22:00:00 UTC | MUST | 5 hours | Yes | //! | 2009-02-28 T 21:00:00 UTC | MUT | 4 hours | No | //! //! There are a few final things of note: //! //! Firstly, this library records the times that timespans *begin*, while //! the tz data files record the times that timespans *end*. Pay attention to //! this if the timestamps aren’t where you expect them to be! For example, in //! the data file, the first zone rule has an ‘until’ date and the second has //! none, whereas in the list of timespans, the last timespan has a ‘start’ //! date and the *first* has none. //! //! Secondly, although local mean time in Mauritius lasted until 1907, the //! timespan is recorded as ending in 1906! Why is this? It’s because the //! transition occurred at midnight *at the local time*, which in this case, //! was three hours fifty minutes ahead of UTC. So that time has to be //! *subtracted* from the date, resulting in twenty hours and ten minutes on //! the last day of the year. Similar things happen on the rest of the //! transitions, being either four or five hours ahead of UTC. //! //! The logic in this file is based off of `zic.c`, which comes with the //! zoneinfo files and is in the public domain. use table::{RuleInfo, Saving, Table, ZoneInfo}; /// A set of timespans, separated by the instances at which the timespans /// change over. There will always be one more timespan than transitions. /// /// This mimics the `FixedTimespanSet` struct in `datetime::cal::zone`, /// except it uses owned `Vec`s instead of slices. #[derive(PartialEq, Debug, Clone)] pub struct FixedTimespanSet { /// The first timespan, which is assumed to have been in effect up until /// the initial transition instant (if any). Each set has to have at /// least one timespan. pub first: FixedTimespan, /// The rest of the timespans, as a vector of tuples, each containing: /// /// 1. A transition instant at which the previous timespan ends and the /// next one begins, stored as a Unix timestamp; /// 2. The actual timespan to transition into. pub rest: Vec<(i64, FixedTimespan)>, } /// An individual timespan with a fixed offset. /// /// This mimics the `FixedTimespan` struct in `datetime::cal::zone`, except /// instead of “total offset” and “is DST” fields, it has separate UTC and /// DST fields. Also, the name is an owned `String` here instead of a slice. #[derive(PartialEq, Debug, Clone)] pub struct FixedTimespan { /// The number of seconds offset from UTC during this timespan. pub utc_offset: i64, /// The number of *extra* daylight-saving seconds during this timespan. pub dst_offset: i64, /// The abbreviation in use during this timespan. pub name: String, } impl FixedTimespan { /// The total offset in effect during this timespan. pub fn total_offset(&self) -> i64 { self.utc_offset + self.dst_offset } } /// Trait to put the `timespans` method on Tables. pub trait TableTransitions { /// Computes a fixed timespan set for the timezone with the given name. /// Returns `None` if the table doesn’t contain a time zone with that name. fn timespans(&self, zone_name: &str) -> Option<FixedTimespanSet>; } impl TableTransitions for Table { fn timespans(&self, zone_name: &str) -> Option<FixedTimespanSet> { let mut builder = FixedTimespanSetBuilder::default(); let zoneset = match self.get_zoneset(zone_name) { Some(zones) => zones, None => return None, }; for (i, zone_info) in zoneset.iter().enumerate() { let mut dst_offset = 0; let use_until = i != zoneset.len() - 1; let utc_offset = zone_info.offset; let mut insert_start_transition = i > 0; let mut start_zone_id = None; let mut start_utc_offset = zone_info.offset; let mut start_dst_offset = 0; match zone_info.saving { Saving::NoSaving => { builder.add_fixed_saving( zone_info, 0, &mut dst_offset, utc_offset, &mut insert_start_transition, &mut start_zone_id, ); } Saving::OneOff(amount) => { builder.add_fixed_saving( zone_info, amount, &mut dst_offset, utc_offset, &mut insert_start_transition, &mut start_zone_id, ); } Saving::Multiple(ref rules) => { let rules = &self.rulesets[&*rules]; builder.add_multiple_saving( zone_info, &*rules, &mut dst_offset, use_until, utc_offset, &mut insert_start_transition, &mut start_zone_id, &mut start_utc_offset, &mut start_dst_offset, ); } } if insert_start_transition && start_zone_id.is_some() { let t = ( builder.start_time.expect("Start time"), FixedTimespan { utc_offset: start_utc_offset, dst_offset: start_dst_offset, name: start_zone_id.clone().expect("Start zone ID"), }, ); builder.rest.push(t); } if use_until { builder.start_time = Some( zone_info.end_time.expect("End time").to_timestamp() - utc_offset - dst_offset, ); } } Some(builder.build()) } } #[derive(Debug, Default)] struct FixedTimespanSetBuilder { first: Option<FixedTimespan>, rest: Vec<(i64, FixedTimespan)>, start_time: Option<i64>, until_time: Option<i64>, } impl FixedTimespanSetBuilder { fn add_fixed_saving( &mut self, timespan: &ZoneInfo, amount: i64, dst_offset: &mut i64, utc_offset: i64, insert_start_transition: &mut bool, start_zone_id: &mut Option<String>, ) { *dst_offset = amount; *start_zone_id = Some(timespan.format.format(*dst_offset, None)); if *insert_start_transition { let time = self.start_time.unwrap(); let timespan = FixedTimespan { utc_offset: timespan.offset, dst_offset: *dst_offset, name: start_zone_id.clone().unwrap_or_else(String::new), }; self.rest.push((time, timespan)); *insert_start_transition = false; } else { self.first = Some(FixedTimespan { utc_offset: utc_offset, dst_offset: *dst_offset, name: start_zone_id.clone().unwrap_or_else(String::new), }); } } #[allow(unused_results)] fn add_multiple_saving( &mut self, timespan: &ZoneInfo, rules: &[RuleInfo], dst_offset: &mut i64, use_until: bool, utc_offset: i64, insert_start_transition: &mut bool, start_zone_id: &mut Option<String>, start_utc_offset: &mut i64, start_dst_offset: &mut i64, ) { use std::mem::replace; for year in 1800..2100 { if use_until && year > timespan.end_time.unwrap().year() { break; } let mut activated_rules = rules .iter() .filter(|r| r.applies_to_year(year)) .collect::<Vec<_>>(); loop { if use_until { self.until_time = Some(timespan.end_time.unwrap().to_timestamp() - utc_offset - *dst_offset); } // Find the minimum rule and its start time based on the current // UTC and DST offsets. let earliest = activated_rules .iter() .enumerate() .map(|(i, r)| (i, r.absolute_datetime(year, utc_offset, *dst_offset))) .min_by_key(|&(_, time)| time); let (pos, earliest_at) = match earliest { Some((pos, time)) => (pos, time), None => break, }; let earliest_rule = activated_rules.remove(pos); if use_until && earliest_at >= self.until_time.unwrap() { break; } *dst_offset = earliest_rule.time_to_add; if *insert_start_transition && earliest_at == self.start_time.unwrap() { *insert_start_transition = false; } if *insert_start_transition { if earliest_at < self.start_time.unwrap() { replace(start_utc_offset, timespan.offset); replace(start_dst_offset, *dst_offset); replace( start_zone_id, Some( timespan .format .format(*dst_offset, earliest_rule.letters.as_ref()), ), ); continue; } if start_zone_id.is_none() && *start_utc_offset + *start_dst_offset == timespan.offset + *dst_offset { replace( start_zone_id, Some( timespan .format .format(*dst_offset, earliest_rule.letters.as_ref()), ), ); } } let t = ( earliest_at, FixedTimespan { utc_offset: timespan.offset, dst_offset: earliest_rule.time_to_add, name: timespan .format .format(earliest_rule.time_to_add, earliest_rule.letters.as_ref()), }, ); self.rest.push(t); } } } fn build(mut self) -> FixedTimespanSet { self.rest.sort_by(|a, b| a.0.cmp(&b.0)); let first = match self.first { Some(ft) => ft, None => self .rest .iter() .find(|t| t.1.dst_offset == 0) .unwrap() .1 .clone(), }; let mut zoneset = FixedTimespanSet { first: first, rest: self.rest, }; optimise(&mut zoneset); zoneset } } #[allow(unused_results)] // for remove fn optimise(transitions: &mut FixedTimespanSet) { let mut from_i = 0; let mut to_i = 0; while from_i < transitions.rest.len() { if to_i > 1 { let from = transitions.rest[from_i].0; let to = transitions.rest[to_i - 1].0; if from + transitions.rest[to_i - 1].1.total_offset() <= to + transitions.rest[to_i - 2].1.total_offset() { transitions.rest[to_i - 1].1 = transitions.rest[from_i].1.clone(); from_i += 1; continue; } } if to_i == 0 || transitions.rest[to_i - 1].1 != transitions.rest[from_i].1 { transitions.rest[to_i] = transitions.rest[from_i].clone(); to_i += 1; } from_i += 1 } transitions.rest.truncate(to_i); if !transitions.rest.is_empty() && transitions.first == transitions.rest[0].1 { transitions.rest.remove(0); } } #[cfg(test)] mod test { use super::optimise; use super::*; // Allow unused results in test code, because the only ‘results’ that // we need to ignore are the ones from inserting and removing from // tables and vectors. And as we set them up ourselves, they’re bound // to be correct, otherwise the tests would fail! #[test] #[allow(unused_results)] fn optimise_macquarie() { let mut transitions = FixedTimespanSet { first: FixedTimespan { utc_offset: 0, dst_offset: 0, name: "zzz".to_owned(), }, rest: vec![ ( -2_214_259_200, FixedTimespan { utc_offset: 36000, dst_offset: 0, name: "AEST".to_owned(), }, ), ( -1_680_508_800, FixedTimespan { utc_offset: 36000, dst_offset: 3600, name: "AEDT".to_owned(), }, ), ( -1_669_892_400, FixedTimespan { utc_offset: 36000, dst_offset: 3600, name: "AEDT".to_owned(), }, ), // gets removed ( -1_665_392_400, FixedTimespan { utc_offset: 36000, dst_offset: 0, name: "AEST".to_owned(), }, ), ( -1_601_719_200, FixedTimespan { utc_offset: 0, dst_offset: 0, name: "zzz".to_owned(), }, ), ( -687_052_800, FixedTimespan { utc_offset: 36000, dst_offset: 0, name: "AEST".to_owned(), }, ), ( -94_730_400, FixedTimespan { utc_offset: 36000, dst_offset: 0, name: "AEST".to_owned(), }, ), // also gets removed ( -71_136_000, FixedTimespan { utc_offset: 36000, dst_offset: 3600, name: "AEDT".to_owned(), }, ), ( -55_411_200, FixedTimespan { utc_offset: 36000, dst_offset: 0, name: "AEST".to_owned(), }, ), ( -37_267_200, FixedTimespan { utc_offset: 36000, dst_offset: 3600, name: "AEDT".to_owned(), }, ), ( -25_776_000, FixedTimespan { utc_offset: 36000, dst_offset: 0, name: "AEST".to_owned(), }, ), ( -5_817_600, FixedTimespan { utc_offset: 36000, dst_offset: 3600, name: "AEDT".to_owned(), }, ), ], }; let mut result = transitions.clone(); result.rest.remove(6); result.rest.remove(2); optimise(&mut transitions); assert_eq!(transitions, result); } }