Balloon sounding layers

Turn the raw telemetry of weather-balloon flights into one temperature profile per flight.

Each record is a string "flight,second,altitude,temp": the flight id, the seconds since that flight's launch, the altitude in metres, and the air temperature in tenths of a degree Celsius (so -123 means -12.3 degrees). The altitude or the temperature may be "-" when the sensor sent nothing. Records of different flights are mixed together and records of one flight may arrive in any order.

Clean and summarise the data like this:

1. Discard every record whose altitude is "-" before doing anything else.
2. If a flight still has several records with the same second, only the one listed last survives.
3. Order each flight's records by second, numerically. The flight's burst altitude is the highest altitude among its records, and the burst is the earliest record that has that altitude. Everything after the burst is the descent and is ignored; the burst itself and everything before it are the ascent.
4. A record at altitude a belongs to layer a // 1000 (layer 0 is 0-999 m, layer 1 is 1000-1999 m, and so on). Only records with a temperature are readings. A layer is reported only if the ascent has at least 2 readings in it, and its value is their mean, rounded to the nearest whole tenth, with exact halves rounded away from zero (50.5 becomes 51, -25.5 becomes -26).

A flight with no records left after step 1 does not appear in the output.

Input: records, a list of strings in the format above. Flight ids contain only letters and digits and never contain a comma.

Output: a list with one entry per remaining flight, sorted by flight id in plain string order. Each entry is [flight, burst_altitude, layers], where layers is a list of [layer, mean_temp] pairs in increasing layer order (possibly empty).