الترقية كانت مفاجأة حلوة في الشغل.

A natural Egyptian-style pronunciation would be:

et-tarʔeya kānet mofāgaʔa ḥelwa fi sh-shoghl

A few useful notes:

• الترقية → et-tarʔeya
  The letter ق is often pronounced like a glottal stop in Egyptian Arabic.
• كانت → kānet
• مفاجأة → mofāgaʔa
• حلوة → ḥelwa or helwa
• الشغل → esh-shoghl or, after في, often heard as fi sh-shoghl

So if you say the whole thing smoothly, it sounds something like:

et-tarʔeya kānet mofāgaʔa ḥelwa fi sh-shoghl

كانت is the past-tense form of to be / was.

Arabic often leaves out is/are in the present, but in the past you usually need a form of كان.

So:

• الترقية مفاجأة حلوة = The promotion is a nice surprise
• الترقية كانت مفاجأة حلوة = The promotion was a nice surprise

That is why كانت appears in this sentence.

Because الترقية is a feminine noun, and كان agrees with it.

• masculine: كان
• feminine: كانت

Since the subject is الترقية = the promotion, the sentence uses كانت.

This is very common in Arabic: verbs and predicate elements often show gender agreement.

Because حلوة describes مفاجأة, and مفاجأة is also feminine.

So the structure is:

• مفاجأة = surprise
• حلوة = nice / sweet

Together: مفاجأة حلوة = a nice surprise

So there are two different feminine relationships in the sentence:

• كانت is feminine because of الترقية
• حلوة is feminine because of مفاجأة

That is a detail English speakers often miss at first.

Arabic does not use a separate word for a/an.

Instead:

• الترقية with الـ means the promotion
• مفاجأة without الـ means a surprise

So:

• الترقية = the promotion
• مفاجأة حلوة = a nice surprise

This works very much like the English sentence The promotion was a nice surprise: one noun is definite, and the other is indefinite.

Because in Arabic, adjectives normally come after the noun they describe.

So:

• مفاجأة حلوة = literally surprise nice
• natural English = a nice surprise

This is one of the most basic word-order differences between English and Arabic.

Also, the adjective usually matches the noun in:

• gender
• number
• definiteness

Here both are feminine and indefinite:

• مفاجأة = feminine, indefinite
• حلوة = feminine, indefinite

Yes, حلوة literally means sweet, but in Egyptian Arabic it very often means:

• nice
• lovely
• pleasant
• great

So in this sentence, مفاجأة حلوة does not mean a surprise that tastes sweet. It means a pleasant / nice surprise.

This is a very common colloquial use in Egyptian Arabic.

في الشغل literally means in the work, but in natural English it usually means:

• at work
• on the job
• in the workplace

In Egyptian Arabic, الشغل is a very common word for:

• work
• job
• workplace
• work situation

So في الشغل here is best understood as at work.

Because the ل in الـ assimilates to certain letters, called sun letters. The letter ش is one of them.

So although it is written:

الـ + شغل

it is pronounced more like:

esh-shoghl or sh-shoghl

This happens in both Standard Arabic and Egyptian Arabic. It is a pronunciation rule, not a spelling change.

It would be widely understood, but it sounds especially natural in Egyptian Arabic.

Why it feels Egyptian or colloquial:

• حلوة is a very everyday Egyptian-style word for nice
• الشغل is the common colloquial word for work

A more formal or Standard Arabic version might be:

كانت الترقية مفاجأة سارة في العمل

That sounds more formal and less conversational.

So the given sentence is a good example of everyday Egyptian-style Arabic.

Yes, that is also possible.

Both of these are okay:

• الترقية كانت مفاجأة حلوة في الشغل
• كانت الترقية مفاجأة حلوة في الشغل

The version starting with الترقية feels a bit more like As for the promotion, it was a nice surprise at work. It puts the promotion first as the topic.

The version starting with كانت is also normal and may sound a little more neutral or narrative.

So the original order is natural, and changing it is possible without changing the basic meaning much.