# Synopsis
# This script generates a pull request description using the OpenAI API. It takes the source branch, target branch, and OpenAI API key as parameters, and returns a generated description based on the differences between the two branches.

function Invoke-PRDescription {

    param (
        [parameter(Mandatory)]
        [string]
        $SourceBranch,
    
        [parameter(Mandatory)]
        [string]
        $TargetBranch,
    
        [parameter(Mandatory)]  
        [string]
        $OpenAIKey
    )

    $normalizedSourceBranch = $SourceBranch -replace '^refs/heads/', '' -replace '^origin/', ''
    $normalizedTargetBranch = $TargetBranch -replace '^refs/heads/', '' -replace '^origin/', ''

    # Compare the checked out source branch with the remote target branch.
    $changes = git log "origin/$normalizedTargetBranch...$normalizedSourceBranch" -p 2>&1
    write-host "Changes count: $($changes.Count)"
    if ($LASTEXITCODE -ne 0) {
        throw "Failed to collect git log for branches '$normalizedTargetBranch' and '$normalizedSourceBranch': $changes"
    }

    # Prepare the context for OpenAI API
    $content = @()
    $content += @{
        role    = 'system'
        content = 'Start with a brief summary of the changes, followed by a detailed description of the changes, and any relevant information that would help reviewers understand the context and impact of the changes.
                You will be generating a pull request description based on the following changes between branches using the git log content. A description for a pull request must not be longer than 4000 characters. Focus on the most important changes and summarize them effectively. If the changes are too many, prioritize summarizing the key changes and providing an overview rather than listing every single change.'
    }
    $content += @{
        role    = 'user'
        content = "
            Generate a pull request description based on the following changes between branches '$SourceBranch' and '$TargetBranch':`n`n$changes.
        "
    }
    $openai = @{
        api_key     = $OpenAIKey
        api_base    = "https://azuredevops-automation.openai.azure.com/"
        name        = "gpt-4o"
        api_version = "2024-06-01"
    }
    $body = [ordered]@{
        messages = $content
    } | ConvertTo-Json


    $url = "$($openai.api_base)/openai/deployments/$($openai.name)/chat/completions?api-version=$($openai.api_version)"

    # Call the OpenAI API to generate the description using the gpt-4o model.
    $response = Invoke-RestMethod -Uri $url -Method Post -Headers @{
        "api-key" = "$($openai.api_key)"
        "Content-Type" = "application/json"
    } -Body $body



    # Extract the generated description from the response
    $generatedDescription = $response.choices[0].message.content.Trim()

    return $generatedDescription
}