# Deep Nesting
# Detects functions with 3+ levels of control structure nesting (if/for/while/try)
id: deep-nesting
name: Deep Nesting
severity: warning
category: complexity
defect_class: safety
inline_tier: review
language: typescript

message: "Deep nesting (3+ levels) — consider early returns or extract functions"

description: |
  Deeply nested code (if/for/while/try blocks 3+ levels deep) is hard to read and test.
  Flatten by using early returns (guard clauses) or extracting nested logic.

query: |
  [
    ;; Pattern 1: if inside if inside if
    (statement_block
      (if_statement
        consequence: (statement_block
          (if_statement
            consequence: (statement_block
              (if_statement) @IF_NESTED)))))
    
    ;; Pattern 2: for inside if inside if
    (statement_block
      (if_statement
        consequence: (statement_block
          (if_statement
            consequence: (statement_block
              (for_statement) @FOR_NESTED)))))
    
    ;; Pattern 3: while inside if inside if
    (statement_block
      (if_statement
        consequence: (statement_block
          (if_statement
            consequence: (statement_block
              (while_statement) @WHILE_NESTED)))))
    
    ;; Pattern 4: try inside if inside if
    (statement_block
      (if_statement
        consequence: (statement_block
          (if_statement
            consequence: (statement_block
              (try_statement) @TRY_NESTED)))))
    
    ;; Pattern 5: if inside for inside if
    (statement_block
      (if_statement
        consequence: (statement_block
          (for_statement
            body: (statement_block
              (if_statement) @IF_IN_FOR)))))
    
    ;; Pattern 6: if inside while inside if
    (statement_block
      (if_statement
        consequence: (statement_block
          (while_statement
            body: (statement_block
              (if_statement) @IF_IN_WHILE)))))
    
    ;; Pattern 7: for inside for inside for
    (statement_block
      (for_statement
        body: (statement_block
          (for_statement
            body: (statement_block
              (for_statement) @FOR_NESTED)))))
  ]

metavars:
  - IF_NESTED
  - FOR_NESTED
  - WHILE_NESTED
  - TRY_NESTED
  - IF_IN_FOR
  - IF_IN_WHILE

tags:
  - complexity
  - readability
  - best-practice

examples:
  bad: |
    function process(user) {
      if (user) {
        if (user.active) {
          if (user.permissions) {  // 3 levels deep!
            return doSomething();
          }
        }
      }
    }
    
    function loop(items) {
      for (const item of items) {
        if (item.active) {
          for (const sub of item.subs) {  // 3 levels
            process(sub);
          }
        }
      }
    }
  
  good: |
    function process(user) {
      if (!user) return null;
      if (!user.active) return null;
      if (!user.permissions) return null;
      return doSomething();
    }

has_fix: false