# BLOCK 05: SUBLEQ Peephole Optimizer
# Semantic-preserving optimizations applied after codegen

import std/[tables, algorithm]

type
  OptimizationPass* = enum
    passConstantFold = "Constant Folding"
    passDeduplication = "Constant Deduplication"
    passCopyElimination = "Copy Elimination"
    passDeadBlockElimination = "Dead-Block Elimination"
    passBranchSimplification = "Branch Simplification"
    passRedundantOpRemoval = "Redundant Operation Removal"

  OptimizationReport* = object
    pass*: OptimizationPass
    before*: int  # word count before
    after*: int   # word count after
    savings*: tuple[words: int, percent: float]
    examples*: seq[string]

# ─────────────────────────────────────────────────────────────────────────
# OPTIMIZATION PASSES
# ─────────────────────────────────────────────────────────────────────────

proc constantFold*(mem: seq[int]): seq[int] =
  ## Constant folding: evaluate constant expressions at compile time
  ## BEFORE:
  ##   CONST 5
  ##   CONST 3
  ##   ADD
  ## AFTER:
  ##   CONST 8
  var result = mem
  # Implementation: detect patterns in SUBLEQ triads and simplify
  # Placeholder for actual implementation
  result

proc deduplicateConstants*(mem: seq[int]): seq[int] =
  ## Constant deduplication: reuse identical constant definitions
  ## BEFORE:
  ##   CONST 42  @ PC 10
  ##   ...
  ##   CONST 42  @ PC 20
  ## AFTER:
  ##   CONST 42  @ PC 10
  ##   ...
  ##   (reuse from PC 10)
  var result = mem
  var constMap: Table[int, int] = initTable[int, int]()  # value -> first address

  # Scan for duplicate constants (simplified implementation)
  # Placeholder for full deduplication logic

  result

proc copyElimination*(mem: seq[int]): seq[int] =
  ## Copy elimination: remove redundant COPY operations
  ## BEFORE:
  ##   COPY x y
  ##   LOAD y z
  ## AFTER:
  ##   LOAD x z
  var result = mem
  # Placeholder for copy tracking and elimination
  result

proc eliminateDeadBlocks*(mem: seq[int]): seq[int] =
  ## Dead-block elimination: remove unreachable code
  ## BEFORE:
  ##   JUMP label_a
  ##     (unreachable code)
  ##   label_a:
  ## AFTER:
  ##   JUMP label_a
  ##   label_a:
  var result = mem
  var reachable = initTable[int, bool]()

  # Mark all reachable addresses via control flow analysis
  # Placeholder for reachability analysis

  result

proc simplifyBranches*(mem: seq[int]): seq[int] =
  ## Branch simplification: simplify conditional jumps
  ## BEFORE:
  ##   COMPARE_ZERO x
  ##   BRANCH_IF_ZERO x label_a label_b
  ##   (if x is known to be always 0)
  ## AFTER:
  ##   JUMP label_a
  var result = mem
  # Placeholder for constant propagation and branch simplification
  result

proc removeRedundantOps*(mem: seq[int]): seq[int] =
  ## Redundant operation removal: eliminate inverse operations
  ## BEFORE:
  ##   INC x
  ##   DEC x
  ## AFTER:
  ##   (removed)
  var result = mem
  # Placeholder for pattern matching on consecutive operations
  result

# ─────────────────────────────────────────────────────────────────────────
# OPTIMIZER ORCHESTRATION
# ─────────────────────────────────────────────────────────────────────────

proc optimize*(mem: seq[int]; level: int = 1): tuple[optimized: seq[int], report: seq[OptimizationReport]] =
  ## Apply optimizations at specified level
  ## Level 1: safe and fast (dedup, dead blocks)
  ## Level 2: moderate (includes copy elimination, branch simplification)
  ## Level 3: aggressive (includes constant folding, redundant op removal)

  var result = mem
  var report: seq[OptimizationReport]

  if level >= 1:
    let before = result.len
    result = deduplicateConstants(result)
    let after = result.len
    if after < before:
      report.add OptimizationReport(
        pass: passDeduplication,
        before: before,
        after: after,
        savings: (words: before - after, percent: float(before - after) / float(before) * 100.0),
        examples: @["CONST 42 reused across 3 locations"]
      )

  if level >= 1:
    let before = result.len
    result = eliminateDeadBlocks(result)
    let after = result.len
    if after < before:
      report.add OptimizationReport(
        pass: passDeadBlockElimination,
        before: before,
        after: after,
        savings: (words: before - after, percent: float(before - after) / float(before) * 100.0),
        examples: @["Removed unreachable code after unconditional jump"]
      )

  if level >= 2:
    let before = result.len
    result = copyElimination(result)
    let after = result.len
    if after < before:
      report.add OptimizationReport(
        pass: passCopyElimination,
        before: before,
        after: after,
        savings: (words: before - after, percent: float(before - after) / float(before) * 100.0),
        examples: @["Eliminated intermediate COPY operation"]
      )

  if level >= 2:
    let before = result.len
    result = simplifyBranches(result)
    let after = result.len
    if after < before:
      report.add OptimizationReport(
        pass: passBranchSimplification,
        before: before,
        after: after,
        savings: (words: before - after, percent: float(before - after) / float(before) * 100.0),
        examples: @["Simplified conditional to unconditional jump"]
      )

  if level >= 3:
    let before = result.len
    result = constantFold(result)
    let after = result.len
    if after < before:
      report.add OptimizationReport(
        pass: passConstantFold,
        before: before,
        after: after,
        savings: (words: before - after, percent: float(before - after) / float(before) * 100.0),
        examples: @["Folded: CONST 5 + CONST 3 → CONST 8"]
      )

  if level >= 3:
    let before = result.len
    result = removeRedundantOps(result)
    let after = result.len
    if after < before:
      report.add OptimizationReport(
        pass: passRedundantOpRemoval,
        before: before,
        after: after,
        savings: (words: before - after, percent: float(before - after) / float(before) * 100.0),
        examples: @["Removed redundant INC followed by DEC"]
      )

  (result, report)

# ─────────────────────────────────────────────────────────────────────────
# OPTIMIZATION VERIFICATION
# ─────────────────────────────────────────────────────────────────────────

proc verifyOptimization*(original: seq[int]; optimized: seq[int]): bool =
  ## Verify that optimization preserves semantics
  ## (would require reference execution comparison)
  ## For now: basic sanity checks

  # Check 1: optimized is not larger than original
  if optimized.len > original.len:
    return false

  # Check 2: both have valid SUBLEQ instructions
  if original.len % 3 != 0 or optimized.len % 3 != 0:
    return false

  true

# ─────────────────────────────────────────────────────────────────────────
# OPTIMIZATION REPORT
# ─────────────────────────────────────────────────────────────────────────

proc reportOptimization*(originalSize: int; report: seq[OptimizationReport]) =
  echo "\n📊 OPTIMIZATION REPORT"
  echo "════════════════════════════════════════════════════════════"
  echo "Original size: ", originalSize, " words\n"

  var totalSavings = 0
  for r in report:
    echo "✓ ", r.pass
    echo "  Size: ", r.before, " → ", r.after, " words"
    echo "  Savings: ", r.savings.words, " words (", formatFloat(r.savings.percent, ffDecimal, 1), "%)"
    if r.examples.len > 0:
      for ex in r.examples:
        echo "    Example: ", ex
    totalSavings += r.savings.words

  if totalSavings > 0:
    let finalSize = originalSize - totalSavings
    let percent = float(totalSavings) / float(originalSize) * 100.0
    echo "\nTotal savings: ", totalSavings, " words (", formatFloat(percent, ffDecimal, 1), "%)"
    echo "Final size: ", finalSize, " words"
  else:
    echo "\nNo optimizations applied"

  echo "════════════════════════════════════════════════════════════"