import Lean
import Mathlib.Tactic.Core
import Base.UtilsBase

/-
Mathlib tactics:
- rcases: https://leanprover-community.github.io/mathlib_docs/tactics.html#rcases
- split_ifs: https://leanprover-community.github.io/mathlib_docs/tactics.html#split_ifs
- norm_num: https://leanprover-community.github.io/mathlib_docs/tactics.html#norm_num
- should we use linarith or omega?
- hint: https://leanprover-community.github.io/mathlib_docs/tactics.html#hint
- classical: https://leanprover-community.github.io/mathlib_docs/tactics.html#classical
-/

/-
TODO:
- we want an easier to use cases:
  - keeps in the goal an equation of the shape: `t = case`
  - if called on Prop terms, uses Classical.em
  Actually, the cases from mathlib seems already quite powerful
  (https://leanprover-community.github.io/mathlib_docs/tactics.html#cases)
  For instance: cases h : e
  Also: **casesm**
- better split tactic
- we need conversions to operate on the head of applications.
  Actually, something like this works:
  ```
  conv at Hl =>
    apply congr_fun
    simp [fix_fuel_P]
  ```
  Maybe we need a rpt ... ; focus?
- simplifier/rewriter have a strange behavior sometimes
-/


namespace List

  -- TODO: I could not find this function??
  @[simp] def flatten {a : Type u} : List (List a) → List a
  | [] => []
  | x :: ls => x ++ flatten ls

end List

-- TODO: move?
@[simp]
theorem neq_imp {α : Type u} {x y : α} (h : ¬ x = y) : ¬ y = x := by intro; simp_all

namespace Lean

namespace LocalContext

  open Lean Lean.Elab Command Term Lean.Meta

  -- Small utility: return the list of declarations in the context, from
  -- the last to the first.
  def getAllDecls (lctx : Lean.LocalContext) : MetaM (List Lean.LocalDecl) :=
    lctx.foldrM (fun d ls => do let d ← instantiateLocalDeclMVars d; pure (d :: ls)) []

  -- Return the list of declarations in the context, but filter the
  -- declarations which are considered as implementation details
  def getDecls (lctx : Lean.LocalContext) : MetaM (List Lean.LocalDecl) := do
    let ls ← lctx.getAllDecls
    pure (ls.filter (fun d => not d.isImplementationDetail))

end LocalContext

end Lean

namespace Utils

open Lean Elab Term Meta Tactic

-- Useful helper to explore definitions and figure out the variant
-- of their sub-expressions.
def explore_term (incr : String) (e : Expr) : MetaM Unit :=
  match e with
  | .bvar _ => do logInfo m!"{incr}bvar: {e}"; return ()
  | .fvar _ => do logInfo m!"{incr}fvar: {e}"; return ()
  | .mvar _ => do logInfo m!"{incr}mvar: {e}"; return ()
  | .sort _ => do logInfo m!"{incr}sort: {e}"; return ()
  | .const _ _ => do logInfo m!"{incr}const: {e}"; return ()
  | .app fn arg => do
    logInfo m!"{incr}app: {e}"
    explore_term (incr ++ "  ") fn
    explore_term (incr ++ "  ") arg
  | .lam _bName bTy body _binfo => do
    logInfo m!"{incr}lam: {e}"
    explore_term (incr ++ "  ") bTy
    explore_term (incr ++ "  ") body
  | .forallE _bName bTy body _bInfo => do
    logInfo m!"{incr}forallE: {e}"
    explore_term (incr ++ "  ") bTy
    explore_term (incr ++ "  ") body
  | .letE _dName ty val body _nonDep => do
    logInfo m!"{incr}letE: {e}"
    explore_term (incr ++ "  ") ty
    explore_term (incr ++ "  ") val
    explore_term (incr ++ "  ") body
  | .lit _ => do logInfo m!"{incr}lit: {e}"; return ()
  | .mdata _ e => do
    logInfo m!"{incr}mdata: {e}"
    explore_term (incr ++ "  ") e
  | .proj _ _ struct => do
    logInfo m!"{incr}proj: {e}"
    explore_term (incr ++ "  ") struct

def explore_decl (n : Name) : TermElabM Unit := do
  logInfo m!"Name: {n}"
  let env ← getEnv
  let decl := env.constants.find! n
  match decl with
  | .defnInfo val =>
     logInfo m!"About to explore defn: {decl.name}"
     logInfo m!"# Type:"
     explore_term "" val.type
     logInfo m!"# Value:"
     explore_term "" val.value
  | .axiomInfo _  => throwError m!"axiom: {n}"
  | .thmInfo _    => throwError m!"thm: {n}"
  | .opaqueInfo _ => throwError m!"opaque: {n}"
  | .quotInfo _   => throwError m!"quot: {n}"
  | .inductInfo _ => throwError m!"induct: {n}"
  | .ctorInfo _   => throwError m!"ctor: {n}"
  | .recInfo _    => throwError m!"rec: {n}"

syntax (name := printDecl) "print_decl " ident : command

open Lean.Elab.Command

@[command_elab printDecl] def elabPrintDecl : CommandElab := fun stx => do
  liftTermElabM do
    let id := stx[1]
    addCompletionInfo <| CompletionInfo.id id id.getId (danglingDot := false) {} none
    let cs ← resolveGlobalConstWithInfos id
    explore_decl cs[0]!

private def test1 : Nat := 0
private def test2 (x : Nat) : Nat := x
print_decl test1
print_decl test2

def printDecls (decls : List LocalDecl) : MetaM Unit := do
  let decls ← decls.foldrM (λ decl msg => do
    pure (m!"\n{decl.toExpr} : {← inferType decl.toExpr}" ++ msg)) m!""
  logInfo m!"# Ctx decls:{decls}"

-- Small utility: print all the declarations in the context (including the "implementation details")
elab "print_all_ctx_decls" : tactic => do
  let ctx ← Lean.MonadLCtx.getLCtx
  let decls ← ctx.getAllDecls
  printDecls decls

-- Small utility: print all declarations in the context
elab "print_ctx_decls" : tactic => do
  let ctx ← Lean.MonadLCtx.getLCtx
  let decls ← ctx.getDecls
  printDecls decls

-- A map-reduce visitor function for expressions (adapted from `AbstractNestedProofs.visit`)
-- The continuation takes as parameters:
-- - the current depth of the expression (useful for printing/debugging)
-- - the expression to explore
partial def mapreduceVisit {a : Type} (k : Nat → a → Expr → MetaM (a × Expr))
  (state : a) (e : Expr) : MetaM (a × Expr) := do
  let mapreduceVisitBinders (state : a) (xs : Array Expr) (k2 : a → MetaM (a × Expr)) :
    MetaM (a × Expr) := do
    let localInstances ← getLocalInstances
    -- Update the local declarations for the bindings in context `lctx`
    let rec visit_xs (lctx : LocalContext) (state : a) (xs : List Expr) : MetaM (LocalContext × a) := do
      match xs with
      | [] => pure (lctx, state)
      | x :: xs => do
        let xFVarId := x.fvarId!
        let localDecl ← xFVarId.getDecl
        let (state, type) ← mapreduceVisit k state localDecl.type
        let localDecl := localDecl.setType type
        let (state, localDecl) ← match localDecl.value? with
           | some value =>
             let (state, value) ← mapreduceVisit k state value
             pure (state, localDecl.setValue value)
           | none => pure (state, localDecl)
        let lctx := lctx.modifyLocalDecl xFVarId fun _ => localDecl
        -- Recursive call
        visit_xs lctx state xs
    let (lctx, state) ← visit_xs (← getLCtx) state xs.toList
    -- Call the continuation with the updated context
    withLCtx lctx localInstances (k2 state)
  -- TODO: use a cache? (Lean.checkCache)
  let rec visit (i : Nat) (state : a) (e : Expr) : MetaM (a × Expr) := do
    -- Explore
    let (state, e) ← k i state e
    match e with
    | .bvar _
    | .fvar _
    | .mvar _
    | .sort _
    | .lit _
    | .const _ _ => pure (state, e)
    | .app .. => do e.withApp fun f args => do
      let (state, args) ← args.foldlM (fun (state, args) arg => do let (state, arg) ← visit (i + 1) state arg; pure (state, arg :: args)) (state, [])
      let args := args.reverse
      let (state, f) ← visit (i + 1) state f
      let e' := mkAppN f (Array.mk args)
      return (state, e')
    | .lam .. =>
      lambdaLetTelescope e fun xs b =>
        mapreduceVisitBinders state xs fun state => do
        let (state, b) ← visit (i + 1) state b
        let e' ← mkLambdaFVars xs b (usedLetOnly := false)
        return (state, e')
    | .forallE .. => do
      forallTelescope e fun xs b =>
         mapreduceVisitBinders state xs fun state => do
         let (state, b) ← visit (i + 1) state b
         let e' ← mkForallFVars xs b
         return (state, e')
    | .letE .. => do
      lambdaLetTelescope e fun xs b =>
        mapreduceVisitBinders state xs fun state => do
        let (state, b) ← visit (i + 1) state b
        let e' ← mkLambdaFVars xs b (usedLetOnly := false)
        return (state, e')
    | .mdata _ b => do
      let (state, b) ← visit (i + 1) state b
      return (state, e.updateMData! b)
    | .proj _ _ b => do
      let (state, b) ← visit (i + 1) state b
      return (state, e.updateProj! b)
  visit 0 state e

-- A map visitor function for expressions (adapted from `AbstractNestedProofs.visit`)
-- The continuation takes as parameters:
-- - the current depth of the expression (useful for printing/debugging)
-- - the expression to explore
partial def mapVisit (k : Nat → Expr → MetaM Expr) (e : Expr) : MetaM Expr := do
  let k' i (_ : Unit) e := do
    let e ← k i e
    pure ((), e)
  let (_, e) ← mapreduceVisit k' () e
  pure e

-- A reduce visitor
partial def reduceVisit {a : Type} (k : Nat → a → Expr → MetaM a) (s : a) (e : Expr) : MetaM a := do
  let k' i (s : a) e := do
    let s ← k i s e
    pure (s, e)
  let (s, _) ← mapreduceVisit k' s e
  pure s

-- Generate a fresh user name for an anonymous proposition to introduce in the
-- assumptions
def mkFreshAnonPropUserName := mkFreshUserName `_

section Methods
  variable [MonadLiftT MetaM m] [MonadControlT MetaM m] [Monad m] [MonadError m]
  variable {a : Type}

  /- Like `lambdaTelescopeN` but only destructs a fixed number of lambdas -/
  def lambdaTelescopeN (e : Expr) (n : Nat) (k : Array Expr → Expr → m a) : m a :=
    lambdaTelescope e fun xs body => do
    if xs.size < n then throwError "lambdaTelescopeN: not enough lambdas"
    let xs := xs.extract 0 n
    let ys := xs.extract n xs.size
    let body ← liftMetaM (mkLambdaFVars ys body)
    k xs body

  /- Like `lambdaTelescope`, but only destructs one lambda
     TODO: is there an equivalent of this function somewhere in the
     standard library? -/
  def lambdaOne (e : Expr) (k : Expr → Expr → m a) : m a :=
    lambdaTelescopeN e 1 λ xs b => k (xs.get! 0) b

  def isExists (e : Expr) : Bool := e.getAppFn.isConstOf ``Exists ∧ e.getAppNumArgs = 2

  -- Remark: Lean doesn't find the inhabited and nonempty instances if we don'
  -- put them explicitely in the signature
  partial def existsTelescopeProcess [Inhabited (m a)] [Nonempty (m a)]
    (fvars : Array Expr) (e : Expr) (k : Array Expr → Expr → m a) : m a := do
    -- Attempt to deconstruct an existential
    if isExists e then do
      let p := e.appArg!
      lambdaOne p fun x ne =>
      existsTelescopeProcess (fvars.push x) ne k
    else
      -- No existential: call the continuation
      k fvars e

  def existsTelescope [Inhabited (m a)] [Nonempty (m a)] (e : Expr) (k : Array Expr → Expr → m a) : m a := do
    existsTelescopeProcess #[] e k

end Methods

-- TODO: this should take a continuation
def addDeclTac (name : Name) (val : Expr) (type : Expr) (asLet : Bool) : TacticM Expr :=
  -- I don't think we need that
  withMainContext do
  -- Insert the new declaration
  let withDecl := if asLet then withLetDecl name type val else withLocalDeclD name type
  withDecl fun nval => do
    -- For debugging
    let lctx ← Lean.MonadLCtx.getLCtx
    let fid := nval.fvarId!
    let decl := lctx.get! fid
    trace[Arith] "  new decl: \"{decl.userName}\" ({nval}) : {decl.type} := {decl.value}"
    --
    -- Tranform the main goal `?m0` to `let x = nval in ?m1`
    let mvarId ← getMainGoal
    let newMVar ← mkFreshExprSyntheticOpaqueMVar (← mvarId.getType)
    let newVal ← mkLetFVars #[nval] newMVar
    -- There are two cases:
    -- - asLet is true: newVal is `let $name := $val in $newMVar`
    -- - asLet is false: ewVal is `λ $name => $newMVar`
    --   We need to apply it to `val`
    let newVal := if asLet then newVal else mkAppN newVal #[val]
    -- Assign the main goal and update the current goal
    mvarId.assign newVal
    let goals ← getUnsolvedGoals
    setGoals (newMVar.mvarId! :: goals)
    -- Return the new value - note: we are in the *new* context, created
    -- after the declaration was added, so it will persist
    pure nval

def addDeclTacSyntax (name : Name) (val : Syntax) (asLet : Bool) : TacticM Unit :=
  -- I don't think we need that
  withMainContext do
  --
  let val ← Term.elabTerm val .none
  let type ← inferType val
  -- In some situations, the type will be left as a metavariable (for instance,
  -- if the term is `3`, Lean has the choice between `Nat` and `Int` and will
  -- not choose): we force the instantiation of the meta-variable
  synthesizeSyntheticMVarsUsingDefault
  --
  let _ ← addDeclTac name val type asLet

elab "custom_let " n:ident " := " v:term : tactic => do
  addDeclTacSyntax n.getId v (asLet := true)

elab "custom_have " n:ident " := " v:term : tactic =>
  addDeclTacSyntax n.getId v (asLet := false)

example : Nat := by
  custom_let x := 4
  custom_have y := 4
  apply y

example (x : Bool) : Nat := by
  cases x <;> custom_let x := 3 <;> apply x

-- Attempt to apply a tactic
def tryTac (tac : TacticM Unit) : TacticM Unit := do
  let _ ← tryTactic tac

-- Repeatedly apply a tactic
partial def repeatTac (tac : TacticM Unit) : TacticM Unit := do
  try
    tac
    allGoals (focus (repeatTac tac))
  -- TODO: does this restore the state?
  catch _ => pure ()

def firstTac (tacl : List (TacticM Unit)) : TacticM Unit := do
  match tacl with
  | [] => pure ()
  | tac :: tacl =>
    -- Should use try ... catch or Lean.observing?
    -- Generally speaking we should use Lean.observing? to restore the state,
    -- but with tactics the try ... catch variant seems to work
    try do
      tac
      -- Check that there are no remaining goals
      let gl ← Tactic.getUnsolvedGoals
      if ¬ gl.isEmpty then throwError "tactic failed"
    catch _ => firstTac tacl
/-    let res ← Lean.observing? do
      tac
      -- Check that there are no remaining goals
      let gl ← Tactic.getUnsolvedGoals
      if ¬ gl.isEmpty then throwError "tactic failed"
    match res with
    | some _ => pure ()
    | none => firstTac tacl -/

-- Taken from Lean.Elab.evalAssumption
def assumptionTac : TacticM Unit :=
  liftMetaTactic fun mvarId => do mvarId.assumption; pure []

def isConj (e : Expr) : MetaM Bool :=
  e.consumeMData.withApp fun f args => pure (f.isConstOf ``And ∧ args.size = 2)

-- Return the first conjunct if the expression is a conjunction, or the
-- expression itself otherwise. Also return the second conjunct if it is a
-- conjunction.
def optSplitConj (e : Expr) : MetaM (Expr × Option Expr) := do
  e.consumeMData.withApp fun f args =>
  if f.isConstOf ``And ∧ args.size = 2 then pure (args.get! 0, some (args.get! 1))
  else pure (e, none)

-- Split the goal if it is a conjunction
def splitConjTarget : TacticM Unit := do
  withMainContext do
  let g ← getMainTarget
  trace[Utils] "splitConjTarget: goal: {g}"
  -- The tactic was initially implemened with `_root_.Lean.MVarId.apply`
  -- but it tended to mess the goal by unfolding terms, even when it failed
  let (l, r) ← optSplitConj g
  match r with
  | none => do throwError "The goal is not a conjunction"
  | some r => do
    let lmvar ← mkFreshExprSyntheticOpaqueMVar l
    let rmvar ← mkFreshExprSyntheticOpaqueMVar r
    let and_intro ← mkAppM ``And.intro #[lmvar, rmvar]
    let g ← getMainGoal
    g.assign and_intro
    let goals ← getUnsolvedGoals
    setGoals (lmvar.mvarId! :: rmvar.mvarId! :: goals)

-- Destruct an equaliy and return the two sides
def destEq (e : Expr) : MetaM (Expr × Expr) := do
  e.consumeMData.withApp fun f args =>
  if f.isConstOf ``Eq ∧ args.size = 3 then pure (args.get! 1, args.get! 2)
  else throwError "Not an equality: {e}"

-- Return the set of FVarIds in the expression
-- TODO: this collects fvars introduced in the inner bindings
partial def getFVarIds (e : Expr) (hs : HashSet FVarId := HashSet.empty) : MetaM (HashSet FVarId) := do
  reduceVisit (fun _ (hs : HashSet FVarId) e =>
    if e.isFVar then pure (hs.insert e.fvarId!) else pure hs)
    hs e

-- Return the set of MVarIds in the expression
partial def getMVarIds (e : Expr) (hs : HashSet MVarId := HashSet.empty) : MetaM (HashSet MVarId) := do
  reduceVisit (fun _ (hs : HashSet MVarId) e =>
    if e.isMVar then pure (hs.insert e.mvarId!) else pure hs)
    hs e

-- Tactic to split on a disjunction.
-- The expression `h` should be an fvar.
-- TODO: there must be simpler. Use use _root_.Lean.MVarId.cases for instance
def splitDisjTac (h : Expr) (kleft kright : TacticM Unit) : TacticM Unit := do
  trace[Arith] "assumption on which to split: {h}"
  -- Retrieve the main goal
  withMainContext do
  let goalType ← getMainTarget
  let hDecl := (← getLCtx).get! h.fvarId!
  let hName := hDecl.userName
  -- Case disjunction
  let hTy ← inferType h
  hTy.withApp fun f xs => do
  trace[Arith] "as app: {f} {xs}"
  -- Sanity check
  if ¬ (f.isConstOf ``Or ∧ xs.size = 2) then throwError "Invalid argument to splitDisjTac"
  let a := xs.get! 0
  let b := xs.get! 1
  -- Introduce the new goals
  -- Returns:
  -- - the match branch
  -- - a fresh new mvar id
  let mkGoal (hTy : Expr) (nGoalName : String) : MetaM (Expr × MVarId) := do
    -- Introduce a variable for the assumption (`a` or `b`). Note that we reuse
    -- the name of the assumption we split.
    withLocalDeclD hName hTy fun var => do
    -- The new goal
    let mgoal ← mkFreshExprSyntheticOpaqueMVar goalType (tag := Name.mkSimple nGoalName)
    -- Clear the assumption that we split
    let mgoal ← mgoal.mvarId!.tryClearMany #[h.fvarId!]
    -- The branch expression
    let branch ← mkLambdaFVars #[var] (mkMVar mgoal)
    pure (branch, mgoal)
  let (inl, mleft) ← mkGoal a "left"
  let (inr, mright) ← mkGoal b "right"
  trace[Arith] "left: {inl}: {mleft}"
  trace[Arith] "right: {inr}: {mright}"
  -- Create the match expression
  withLocalDeclD (← mkFreshAnonPropUserName) hTy fun hVar => do
  let motive ← mkLambdaFVars #[hVar] goalType
  let casesExpr ← mkAppOptM ``Or.casesOn #[a, b, motive, h, inl, inr]
  let mgoal ← getMainGoal
  trace[Arith] "goals: {← getUnsolvedGoals}"
  trace[Arith] "main goal: {mgoal}"
  mgoal.assign casesExpr
  let goals ← getUnsolvedGoals
  -- Focus on the left
  setGoals [mleft]
  withMainContext kleft
  let leftGoals ← getUnsolvedGoals
  -- Focus on the right
  setGoals [mright]
  withMainContext kright
  let rightGoals ← getUnsolvedGoals
  -- Put all the goals back
  setGoals (leftGoals ++ rightGoals ++ goals)
  trace[Arith] "new goals: {← getUnsolvedGoals}"

elab "split_disj " n:ident : tactic => do
  withMainContext do
  let decl ← Lean.Meta.getLocalDeclFromUserName n.getId
  let fvar := mkFVar decl.fvarId
  splitDisjTac fvar (fun _ => pure ()) (fun _ => pure ())

example (x y : Int) (h0 : x ≤ y ∨ x ≥ y) : x ≤ y ∨ x ≥ y := by
  split_disj h0
  . apply Or.inl; assumption
  . apply Or.inr; assumption

-- Tactic to split on an exists.
-- `h` must be an FVar
def splitExistsTac (h : Expr) (optId : Option Name) (k : Expr → Expr → TacticM α) : TacticM α := do
  withMainContext do
  let goal ←  getMainGoal
  let hTy ← inferType h
  if isExists hTy then do
    -- Try to use the user-provided names
    let altVarNames ← do
      let hDecl ← h.fvarId!.getDecl
      let id ← do
        match optId with
        | none => mkFreshUserName `x
        | some id => pure id
      pure #[{ varNames := [id, hDecl.userName] }]
    let newGoals ← goal.cases h.fvarId! altVarNames
    -- There should be exactly one goal
    match newGoals.toList with
    | [ newGoal ] =>
      -- Set the new goal
      let goals ← getUnsolvedGoals
      setGoals (newGoal.mvarId :: goals)
      -- There should be exactly two fields
      let fields := newGoal.fields
      withMainContext do
      k (fields.get! 0) (fields.get! 1)
    | _ =>
      throwError "Unreachable"
  else
    throwError "Not a conjunction"

-- TODO: move
def listTryPopHead (ls : List α) : Option α × List α :=
  match ls with
  | [] => (none, ls)
  | hd :: tl => (some hd, tl)

/- Destruct all the existentials appearing in `h`, and introduce them as variables
   in the context.

   If `ids` is not empty, we use it to name the introduced variables. We
   transmit the stripped expression and the remaining ids to the continuation.
 -/
partial def splitAllExistsTac [Inhabited α] (h : Expr) (ids : List (Option Name)) (k : Expr → List (Option Name) → TacticM α) : TacticM α := do
  try
    let (optId, ids) :=
      match ids with
      | [] => (none, [])
      | x :: ids => (x, ids)
    splitExistsTac h optId (fun _ body => splitAllExistsTac body ids k)
  catch _ => k h ids

-- Tactic to split on a conjunction.
def splitConjTac (h : Expr) (optIds : Option (Name × Name)) (k : Expr → Expr → TacticM α)  : TacticM α := do
  withMainContext do
  let goal ←  getMainGoal
  let hTy ← inferType h
  if ← isConj hTy then do
    -- Try to use the user-provided names
    let altVarNames ←
      match optIds with
      | none => do
        let id0 ← mkFreshAnonPropUserName
        let id1 ← mkFreshAnonPropUserName
        pure #[{ varNames := [id0, id1] }]
      | some (id0, id1) => do
        pure #[{ varNames := [id0, id1] }]
    let newGoals ← goal.cases h.fvarId! altVarNames
    -- There should be exactly one goal
    match newGoals.toList with
    | [ newGoal ] =>
      -- Set the new goal
      let goals ← getUnsolvedGoals
      setGoals (newGoal.mvarId :: goals)
      -- There should be exactly two fields
      let fields := newGoal.fields
      withMainContext do
      k (fields.get! 0) (fields.get! 1)
    | _ =>
      throwError "Unreachable"
  else
    throwError "Not a conjunction"

-- Tactic to fully split a conjunction
partial def splitFullConjTacAux [Inhabited α] [Nonempty α] (keepCurrentName : Bool) (l : List Expr) (h : Expr) (k : List Expr → TacticM α)  : TacticM α := do
  try
    let ids ← do
      if keepCurrentName then do
        let cur := (← h.fvarId!.getDecl).userName
        let nid ← mkFreshAnonPropUserName
        pure (some (cur, nid))
      else
        pure none
    splitConjTac h ids (λ h1 h2 =>
      splitFullConjTacAux keepCurrentName l h1 (λ l1 =>
        splitFullConjTacAux keepCurrentName l1 h2 (λ l2 =>
          k l2)))
  catch _ =>
    k (h :: l)

-- Tactic to fully split a conjunction
-- `keepCurrentName`: if `true`, then the first conjunct has the name of the original assumption
def splitFullConjTac [Inhabited α] [Nonempty α] (keepCurrentName : Bool) (h : Expr) (k : List Expr → TacticM α)  : TacticM α := do
  splitFullConjTacAux keepCurrentName [] h (λ l => k l.reverse)

syntax optAtArgs := ("at" ident)?
def elabOptAtArgs (args : TSyntax `Utils.optAtArgs) : TacticM (Option Expr) := do
  withMainContext do
  let args := (args.raw.getArgs.get! 0).getArgs
  if args.size > 0 then do
    let n := (args.get! 1).getId
    let decl ← Lean.Meta.getLocalDeclFromUserName n
    let fvar := mkFVar decl.fvarId
    pure (some fvar)
  else
    pure none

elab "split_conj" args:optAtArgs : tactic => do
  withMainContext do
  match ← elabOptAtArgs args with
  | some fvar => do
    trace[Utils] "split at {fvar}"
    splitConjTac fvar none (fun _ _ =>  pure ())
  | none => do
    trace[Utils] "split goal"
    splitConjTarget

elab "split_conjs" args:optAtArgs : tactic => do
  withMainContext do
  match ← elabOptAtArgs args with
  | some fvar =>
    trace[Utils] "split at {fvar}"
    splitFullConjTac false fvar (fun _ =>  pure ())
  | none =>
    trace[Utils] "split goal"
    repeatTac splitConjTarget

elab "split_existsl" " at " n:ident : tactic => do
  withMainContext do
  let decl ← Lean.Meta.getLocalDeclFromUserName n.getId
  let fvar := mkFVar decl.fvarId
  splitAllExistsTac fvar [] (fun _ _ => pure ())

example (h : a ∧ b) : a := by
  split_existsl at h
  split_conj at h
  assumption

example (h : ∃ x y z, x + y + z ≥ 0) : ∃ x, x ≥ 0 := by
  split_existsl at h
  rename_i x y z
  exists x + y + z

def mkSimpCtx (simpOnly : Bool) (declsToUnfold : List Name) (thms : List Name) (hypsToUse : List FVarId) :
  Tactic.TacticM Simp.Context := do
  -- Initialize either with the builtin simp theorems or with all the simp theorems
  let simpThms ←
    if simpOnly then Tactic.simpOnlyBuiltins.foldlM (·.addConst ·) ({} : SimpTheorems)
    else getSimpTheorems
  -- Add the equational theorem for the declarations to unfold
  let simpThms ←
    declsToUnfold.foldlM (fun thms decl => thms.addDeclToUnfold decl) simpThms
  -- Add the hypotheses and the rewriting theorems
  let simpThms ←
    hypsToUse.foldlM (fun thms fvarId =>
      -- post: TODO: don't know what that is
      -- inv: invert the equality
      thms.add (.fvar fvarId) #[] (mkFVar fvarId) (post := false) (inv := false)
      -- thms.eraseCore (.fvar fvar)
      ) simpThms
  -- Add the rewriting theorems to use
  let simpThms ←
    thms.foldlM (fun thms thmName => do
      let info ← getConstInfo thmName
      if (← isProp info.type) then
        -- post: TODO: don't know what that is
        -- inv: invert the equality
        thms.addConst thmName (post := false) (inv := false)
      else
        throwError "Not a proposition: {thmName}"
      ) simpThms
  let congrTheorems ← getSimpCongrTheorems
  pure { simpTheorems := #[simpThms], congrTheorems }


inductive Location where
  /-- Apply the tactic everywhere. Same as `Tactic.Location.wildcard` -/
  | wildcard
  /-- Apply the tactic everywhere, including in the variable types (i.e., in
      assumptions which are not propositions).  --/
  | wildcard_dep
  /-- Same as Tactic.Location -/
  | targets (hypotheses : Array Syntax) (type : Bool)

-- Comes from Tactic.simpLocation
def customSimpLocation (ctx : Simp.Context) (discharge? : Option Simp.Discharge := none)
  (loc : Location) : TacticM Simp.UsedSimps := do
  match loc with
  | Location.targets hyps simplifyTarget =>
    withMainContext do
      let fvarIds ← Lean.Elab.Tactic.getFVarIds hyps
      go fvarIds simplifyTarget
  | Location.wildcard =>
    withMainContext do
      go (← (← getMainGoal).getNondepPropHyps) (simplifyTarget := true)
  | Location.wildcard_dep =>
    withMainContext do
      let ctx ← Lean.MonadLCtx.getLCtx
      let decls ← ctx.getDecls
      let tgts := (decls.map (fun d => d.fvarId)).toArray
      go tgts (simplifyTarget := true)
where
  go (fvarIdsToSimp : Array FVarId) (simplifyTarget : Bool) : TacticM Simp.UsedSimps := do
    let mvarId ← getMainGoal
    let (result?, usedSimps) ← simpGoal mvarId ctx (simplifyTarget := simplifyTarget) (discharge? := discharge?) (fvarIdsToSimp := fvarIdsToSimp)
    match result? with
    | none => replaceMainGoal []
    | some (_, mvarId) => replaceMainGoal [mvarId]
    return usedSimps

/- Call the simp tactic.
   The initialization of the context is adapted from Tactic.elabSimpArgs.
   Something very annoying is that there is no function which allows to
   initialize a simp context without doing an elaboration - as a consequence
   we write our own here. -/
def simpAt (simpOnly : Bool) (declsToUnfold : List Name) (thms : List Name) (hypsToUse : List FVarId)
  (loc : Location) :
  Tactic.TacticM Unit := do
  -- Initialize the simp context
  let ctx ← mkSimpCtx simpOnly declsToUnfold thms hypsToUse
  -- Apply the simplifier
  let _ ← customSimpLocation ctx (discharge? := .none) loc

-- Call the simpAll tactic
def simpAll (declsToUnfold : List Name) (thms : List Name) (hypsToUse : List FVarId) :
  Tactic.TacticM Unit := do
  -- Initialize the simp context
  let ctx ← mkSimpCtx false declsToUnfold thms hypsToUse
  -- Apply the simplifier
  let _ ← Lean.Meta.simpAll (← getMainGoal) ctx

end Utils