Mortgage Document Types

Purpose

Work with document classification in the mortgage underwriting system.

Document Type Constants

Located in internal/model/document.go:

Income Documents

Constant	Description	Filename Patterns
`DocTypeW2`	W-2 wage statements	`w2`, `w-2`
`DocType1099`	1099 contractor income	`1099`
`DocTypePaystub`	Pay stubs/earnings	`paystub`, `pay_stub`, `pay-stub`, `earnings`
`DocTypeTaxReturn`	Tax returns (1040)	`tax`, `1040`
`DocTypeProfitLoss`	P&L statements	`profit`, `p&l`, `pnl`
`DocTypeEmploymentLetter`	Employment verification	`employment`, `verification`

Asset Documents

Constant	Description	Filename Patterns
`DocTypeBankStatement`	Bank statements	`bank`
`DocTypeAssetStatement`	General assets	`asset`
`DocTypeRetirementStmt`	401k/IRA statements	`retirement`, `401k`, `ira`
`DocTypeGiftLetter`	Gift fund letters	`gift`

Credit Documents

Constant	Description	Filename Patterns
`DocTypeCreditReport`	Credit bureau reports	`credit`
`DocTypeDebtPayoff`	Debt payoff letters	`payoff`, `debt`

Collateral Documents

Constant	Description	Filename Patterns
`DocTypeAppraisal`	Property appraisals	`appraisal`
`DocTypePurchaseContract`	Purchase agreements	`purchase`, `contract`
`DocTypeTitleReport`	Title reports	`title`
`DocTypePropertyInsurance`	Hazard insurance	`insurance`, `hazard`, `homeowner`

Type Inference Logic

Located in internal/document/store.go:

// Files are classified by checking if filename contains pattern
lower := strings.ToLower(filepath.Base(path))
for pattern, docType := range patterns {
    if strings.Contains(lower, pattern) {
        return docType
    }
}

Adding a New Document Type

Step 1: Add constant to `internal/model/document.go`

const (
    // ... existing types ...
    DocTypeNewType DocumentType = "new_type"
)

Step 2: Add pattern to `internal/document/store.go`

patterns := map[string]model.DocumentType{
    // ... existing patterns ...
    "new_pattern": model.DocTypeNewType,
}

Step 3: Add to agent's document lists

In the relevant agent (e.g., internal/agent/income/income.go):

func (a *Agent) RequiredDocuments() []model.DocumentType {
    return []model.DocumentType{
        model.DocTypeW2,
        model.DocTypeNewType,  // Add here
    }
}

Step 4: Update prompts

Update the agent's prompt to describe how to handle the new document type.

Document Structure

type Document struct {
    ID            string            // Hash-based unique ID
    ApplicationID string            // Loan application ID
    Type          DocumentType      // One of the DocType* constants
    FileName      string            // Original filename
    MimeType      string            // application/pdf, image/png, etc.
    FilePath      string            // Local filesystem path
    GeminiURI     string            // Cached Gemini File API URI
    UploadedAt    time.Time
    BorrowerID    string
    Year          int               // Tax year for tax docs
    Period        string            // Pay period for paystubs
    Metadata      map[string]string // Additional metadata
}

Supported MIME Types

From internal/document/store.go:MimeTypeFromExtension:

•.pdf -> application/pdf
•.png -> image/png
•.jpg, .jpeg -> image/jpeg
•.gif -> image/gif
•.webp -> image/webp

Related Files

•internal/model/document.go - Type definitions
•internal/document/store.go - Loading and type inference
•cmd/underwriter/main.go - CLI type inference