
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Given the function $f(x)=\frac{1}{2}x^{2}-(a+2)x+2a\ln x$ $(a\in\mathbb{R})$.

$(1)$ If the tangent line to the curve $y=f(x)$ at $x=1$ is parallel to the $x$-axis, find the value of $a$.  
$(2)$ Discuss the monotonicity of the function $f(x)$.

Present the answer in LaTex format: \boxed{Your answer}
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