// tools/hako_check/rules/rule_dead_blocks.hako — HC020: Unreachable Basic Block Detection
// Block-level dead code analyzer using MIR CFG information.
// Phase 154: MIR CFG integration for fine-grained unreachable code detection.

static box DeadBlockAnalyzerBox {
  // Main entry point for unreachable block analysis
  // Input: ir (Analysis IR with CFG), path (file path), out (diagnostics array)
  // Returns: void (like other rules)
  method apply_ir(ir, path, out) {
    if ir == null { return }
    if out == null { return }

    // Phase 154: Requires CFG information from MIR
    local cfg = ir.get("cfg")
    if cfg == null {
      // CFG info not available - skip analysis
      return
    }

    local functions = cfg.get("functions")
    if functions == null || functions.size() == 0 { return }

    // Analyze each function's blocks
    local i = 0
    while i < functions.size() {
      me._analyze_function_blocks(functions.get(i), path, out)
      i = i + 1
    }

    return
  }

  // Analyze blocks within a single function
  _analyze_function_blocks(func, path, out) {
    if func == null { return }

    local func_name = func.get("name")
    local blocks = func.get("blocks")
    if blocks == null || blocks.size() == 0 { return }

    // Scan for unreachable blocks
    local bi = 0
    while bi < blocks.size() {
      local block = blocks.get(bi)
      if block == null { bi = bi + 1; continue }

      local block_id = block.get("id")
      local reachable = block.get("reachable")

      // Report unreachable blocks (HC020)
      if reachable == 0 {
        local terminator = block.get("terminator")
        local reason = me._infer_unreachable_reason(terminator)

        local msg = "[HC020] Unreachable basic block: fn=" + func_name
                  + " bb=" + me._itoa(block_id)

        if reason != null && reason != "" {
          msg = msg + " (" + reason + ")"
        }

        out.push(msg + " :: " + path)
      }

      bi = bi + 1
    }

    return
  }

  // Infer reason for unreachability based on terminator type
  _infer_unreachable_reason(terminator) {
    if terminator == null { return "no terminator" }

    // Common patterns
    if terminator == "Return" { return "after early return" }
    if terminator == "Jump" { return "unreachable branch" }
    if terminator == "Branch" { return "dead conditional" }

    return ""
  }

  // Helper: integer to string
  _itoa(n) {
    local v = 0 + n
    if v == 0 { return "0" }

    local out = ""
    local digits = "0123456789"
    local tmp = ""

    while v > 0 {
      local d = v % 10
      tmp = digits.substring(d, d+1) + tmp
      v = v / 10
    }

    out = tmp
    return out
  }
}

static box RuleDeadBlocksMain {
  method main(args) {
    return 0
  }
}