ljkiwi/kiwi.lua

local kiwi = {}

local ffi = require("ffi")

local ckiwi
do
   local cpath, err = package.searchpath("ckiwi", package.cpath)
   if cpath == nil then
      error("kiwi dynamic library 'ckiwi' not found\n" .. err)
   end
   ckiwi = ffi.load(cpath)
end

ffi.cdef([[
enum KiwiErrKind {
   KiwiErrNone,
   KiwiErrUnsatisfiableConstraint = 1,
   KiwiErrUnknownConstraint,
   KiwiErrDuplicateConstraint,
   KiwiErrUnknownEditVariable,
   KiwiErrDuplicateEditVariable,
   KiwiErrBadRequiredStrength,
   KiwiErrInternalSolverError,
   KiwiErrAlloc,
   KiwiErrNullObject,
   KiwiErrUnknown,
};

enum KiwiRelOp { LE, GE, EQ };

struct KiwiVarRefType;
struct KiwiConstraintRefType;

typedef struct KiwiVarRefType* KiwiVarRef;
typedef struct KiwiConstraintRefType* KiwiConstraintRef;

struct KiwiTerm {
   KiwiVarRef var;
   double coefficient;
};

typedef struct KiwiExpression {
   double constant;
   int term_count;
   struct KiwiTerm terms_[?];
}* KiwiExpressionPtr;

typedef const struct KiwiExpression* KiwiExpressionConstPtr;

typedef struct KiwiErr {
   enum KiwiErrKind kind;
   const char* message;
   bool must_free;
} const* KiwiErrPtr;

struct KiwiSolver;
typedef struct KiwiSolver* KiwiSolverPtr;

KiwiVarRef kiwi_var_new(const char* name);
void kiwi_var_del(KiwiVarRef var);
KiwiVarRef kiwi_var_clone(KiwiVarRef var);

const char* kiwi_var_name(KiwiVarRef var);
void kiwi_var_set_name(KiwiVarRef var, const char* name);
double kiwi_var_value(KiwiVarRef var);
void kiwi_var_set_value(KiwiVarRef var, double value);
int kiwi_var_eq(KiwiVarRef var, KiwiVarRef other);

KiwiConstraintRef
kiwi_constraint_new(KiwiExpressionConstPtr expression, enum KiwiRelOp op, double strength);
void kiwi_constraint_del(KiwiConstraintRef constraint);

double kiwi_constraint_strength(KiwiConstraintRef constraint);

enum KiwiRelOp kiwi_constraint_op(KiwiConstraintRef constraint);

bool kiwi_constraint_violated(KiwiConstraintRef constraint);
int kiwi_constraint_expression(KiwiConstraintRef constraint, KiwiExpressionPtr out, int out_size);

KiwiErrPtr kiwi_solver_add_constraint(KiwiSolverPtr sp, KiwiConstraintRef constraint);
KiwiErrPtr kiwi_solver_remove_constraint(KiwiSolverPtr sp, KiwiConstraintRef constraint);
bool kiwi_solver_has_constraint(KiwiSolverPtr sp, KiwiConstraintRef constraint);
KiwiErrPtr kiwi_solver_add_edit_var(KiwiSolverPtr sp, KiwiVarRef var, double strength);
KiwiErrPtr kiwi_solver_remove_edit_var(KiwiSolverPtr sp, KiwiVarRef var);
bool kiwi_solver_has_edit_var(KiwiSolverPtr sp, KiwiVarRef var);
KiwiErrPtr kiwi_solver_suggest_value(KiwiSolverPtr sp, KiwiVarRef var, double value);
void kiwi_solver_update_vars(KiwiSolverPtr sp);
void kiwi_solver_reset(KiwiSolverPtr sp);
void kiwi_solver_dump(KiwiSolverPtr sp);
char* kiwi_solver_dumps(KiwiSolverPtr sp);

KiwiSolverPtr kiwi_solver_new();
void kiwi_solver_del(KiwiSolverPtr sp);

void free(void *);
]])

local strformat = string.format
local ffi_cast, ffi_gc, ffi_istype, ffi_new, ffi_string =
   ffi.cast, ffi.gc, ffi.istype, ffi.new, ffi.string

local concat = table.concat
local has_table_new, new_tab = pcall(require, "table.new")
if not has_table_new or type(new_tab) ~= "function" then
   new_tab = function()
      return {}
   end
end

---@alias kiwi.ErrKind
---| '"KiwiErrNone"' # No error.
---| '"KiwiErrUnsatisfiableConstraint"' # The given constraint is required and cannot be satisfied.
---| '"KiwiErrUnknownConstraint"' # The given constraint has not been added to the solver.
---| '"KiwiErrDuplicateConstraint"' # The given constraint has already been added to the solver.
---| '"KiwiErrUnknownEditVariable"' # The given edit variable has not been added to the solver.
---| '"KiwiErrDuplicateEditVariable"' # The given edit variable has already been added to the solver.
---| '"KiwiErrBadRequiredStrength"' # The given strength is >= required.
---| '"KiwiErrInternalSolverError"' # An internal solver error occurred.
---| '"KiwiErrAlloc"' # A memory allocation error occurred.
---| '"KiwiErrNullObject"' # A method was invoked on a null or empty object.
---| '"KiwiErrUnknown"' # An unknown error occurred.
kiwi.ErrKind = ffi.typeof("enum KiwiErrKind") --[[@as kiwi.ErrKind]]

---@alias kiwi.RelOp
---| '"LE"' # <= (less than or equal)
---| '"GE"' # >= (greater than or equal)
---| '"EQ"' # == (equal)
kiwi.RelOp = ffi.typeof("enum KiwiRelOp")

kiwi.Strength = {
   REQUIRED = 1001001000.0,
   STRONG = 1000000.0,
   MEDIUM = 1000.0,
   WEAK = 1.0,
}

--- Create a custom constraint strength.
---@param a number: Scale factor 1e6
---@param b number: Scale factor 1e3
---@param c number: Scale factor 1
---@param w? number: Weight
---@return number
---@nodiscard
function kiwi.Strength.create(a, b, c, w)
   local function clamp(n)
      return math.max(0, math.min(1000, n))
   end
   w = w or 1.0
   return clamp(a * w) * 1000000.0 + clamp(b * w) * 1000.0 + clamp(c * w)
end

local Var = ffi.typeof("struct KiwiVarRefType") --[[@as kiwi.Var]]
kiwi.Var = Var

local Term = ffi.typeof("struct KiwiTerm") --[[@as kiwi.Term]]
kiwi.Term = Term

local Expression = ffi.typeof("struct KiwiExpression") --[[@as kiwi.Expression]]
kiwi.Expression = Expression

local Constraint = ffi.typeof("struct KiwiConstraintRefType") --[[@as kiwi.Constraint]]
kiwi.Constraint = Constraint

--- Define a constraint with expressions as `a <= b`.
---@param a kiwi.Expression|kiwi.Term|kiwi.Var|number
---@param b kiwi.Expression|kiwi.Term|kiwi.Var|number
---@param strength? number
---@return kiwi.Constraint
function kiwi.le(a, b, strength)
   return Constraint(a - b, "LE", strength)
end

--- Define a constraint with expressions as `a >= b`.
---@param a kiwi.Expression|kiwi.Term|kiwi.Var|number
---@param b kiwi.Expression|kiwi.Term|kiwi.Var|number
---@param strength? number
---@return kiwi.Constraint
function kiwi.ge(a, b, strength)
   return Constraint(a - b, "GE", strength)
end

--- Define a constraint with expressions as `a == b`.
---@param a kiwi.Expression|kiwi.Term|kiwi.Var|number
---@param b kiwi.Expression|kiwi.Term|kiwi.Var|number
---@param strength? number
---@return kiwi.Constraint
function kiwi.eq(a, b, strength)
   return Constraint(a - b, "EQ", strength)
end

local function expr_gc(expr)
   local terms_ = expr.terms_
   for i = 0, expr.term_count - 1 do
      ckiwi.kiwi_var_del(terms_[i].var)
   end
end

---@param expr kiwi.Expression
---@param var kiwi.Var
---@param coeff number?
---@nodiscard
local function add_expr_term(expr, var, coeff)
   local ret = ffi_gc(ffi_new(Expression, expr.term_count + 1), expr_gc) --[[@as kiwi.Expression]]
   for i = 0, expr.term_count - 1 do
      local st = expr.terms_[i] --[[@as kiwi.Term]]
      local dt = ret.terms_[i] --[[@as kiwi.Term]]
      dt.var = ckiwi.kiwi_var_clone(st.var)
      dt.coefficient = st.coefficient
   end
   local dt = ret.terms_[expr.term_count]
   dt.var = ckiwi.kiwi_var_clone(var)
   dt.coefficient = coeff or 1.0
   ret.constant = expr.constant
   ret.term_count = expr.term_count + 1
   return ret
end

---@param constant number
---@param var kiwi.Var
---@param coeff number?
---@nodiscard
local function new_expr_one(constant, var, coeff)
   local ret = ffi_gc(ffi_new(Expression, 1), expr_gc) --[[@as kiwi.Expression]]
   local dt = ret.terms_[0]
   dt.var = ckiwi.kiwi_var_clone(var)
   dt.coefficient = coeff or 1.0
   ret.constant = constant
   ret.term_count = 1
   return ret
end

---@param constant number
---@param var1 kiwi.Var
---@param var2 kiwi.Var
---@param coeff1 number?
---@param coeff2 number?
---@nodiscard
local function new_expr_pair(constant, var1, var2, coeff1, coeff2)
   local ret = ffi_gc(ffi_new(Expression, 2), expr_gc) --[[@as kiwi.Expression]]
   local dt = ret.terms_[0]
   dt.var = ckiwi.kiwi_var_clone(var1)
   dt.coefficient = coeff1 or 1.0
   dt = ret.terms_[1]
   dt.var = ckiwi.kiwi_var_clone(var2)
   dt.coefficient = coeff2 or 1.0
   ret.constant = constant
   ret.term_count = 2
   return ret
end

--- Variables are the values the constraint solver calculates.
---@class kiwi.Var: ffi.ctype*
---@overload fun(name: string): kiwi.Var
---@operator mul(number): kiwi.Term
---@operator div(number): kiwi.Term
---@operator unm: kiwi.Term
---@operator add(kiwi.Expression|kiwi.Term|kiwi.Var|number): kiwi.Expression
---@operator sub(kiwi.Expression|kiwi.Term|kiwi.Var|number): kiwi.Expression
local Var_cls = {
   le = kiwi.le,
   ge = kiwi.ge,
   eq = kiwi.eq,

   --- Change the name of the variable.
   ---@type fun(self: kiwi.Var, name: string)
   set_name = ckiwi.kiwi_var_set_name,

   --- Get the current value of the variable.
   ---@type fun(self: kiwi.Var): number
   value = ckiwi.kiwi_var_value,

   --- Set the value of the variable.
   ---@type fun(self: kiwi.Var, value: number)
   set = ckiwi.kiwi_var_set_value,
}

--- Get the name of the variable.
---@return string
function Var_cls:name()
   return ffi_string(ckiwi.kiwi_var_name(self))
end

--- Create a term from this variable.
---@param coefficient number?
---@return kiwi.Term
function Var_cls:toterm(coefficient)
   return Term(self, coefficient or 1.0)
end

ffi.metatype(Var, {
   __index = Var_cls,

   __new = function(_, name)
      return ffi_gc(ckiwi.kiwi_var_new(name), ckiwi.kiwi_var_del)
   end,
   __gc = ckiwi.kiwi_var_del,

   __mul = function(a, b)
      if type(a) == "number" then
         return Term(b, a)
      elseif type(b) == "number" then
         return Term(a, b)
      end
      error("Invalid var *")
   end,

   __div = function(a, b)
      assert(type(b) == "number", "Invalid var /")
      return Term(a, 1.0 / b)
   end,

   __unm = function(var)
      return Term(var, -1.0)
   end,

   __add = function(a, b)
      if ffi_istype(Var, b) then
         if type(a) == "number" then
            return new_expr_one(a, b)
         else
            return new_expr_pair(0.0, a, b)
         end
      elseif ffi_istype(Term, b) then
         return new_expr_pair(0.0, b.var, a, b.coefficient)
      elseif ffi_istype(Expression, b) then
         return add_expr_term(b, a)
      elseif type(b) == "number" then
         return new_expr_one(b, a)
      end
      error("Invalid var +")
   end,

   __sub = function(a, b)
      return a + -b
   end,

   __tostring = function(var)
      return var:name() .. "(" .. var:value() .. ")"
   end,
})

--- Terms are the components of an expression.
--- Each term is a variable multiplied by a constant coefficient (default 1.0).
---@class kiwi.Term: ffi.ctype*
---@overload fun(var: kiwi.Var, coefficient: number?): kiwi.Term
---@field var kiwi.Var
---@field coefficient number
---@operator mul(number): kiwi.Term
---@operator div(number): kiwi.Term
---@operator unm: kiwi.Term
---@operator add(kiwi.Expression|kiwi.Term|kiwi.Var|number): kiwi.Expression
---@operator sub(kiwi.Expression|kiwi.Term|kiwi.Var|number): kiwi.Expression
local Term_cls = {
   le = kiwi.le,
   ge = kiwi.ge,
   eq = kiwi.eq,
}

---@return number
function Term_cls:value()
   return self.coefficient * self.var:value()
end

--- Create an expression from this term.
---@param constant number?
---@return kiwi.Expression
function Term_cls:toexpr(constant)
   return new_expr_one(constant or 0.0, self.var, self.coefficient)
end

ffi.metatype(Term, {
   __index = Term_cls,

   __new = function(_, var, coefficient)
      return ffi_gc(ffi_new(Term, ckiwi.kiwi_var_clone(var), coefficient or 1.0), function(term)
         ckiwi.kiwi_var_del(term.var)
      end)
   end,

   __mul = function(a, b)
      if type(b) == "number" then
         return Term(a.var, a.coefficient * b)
      elseif type(a) == "number" then
         return Term(b.var, b.coefficient * a)
      end
      error("Invalid term *")
   end,

   __div = function(term, denom)
      assert(type(denom) == "number", "Invalid term /")
      return Term(term.var, term.coefficient / denom)
   end,

   __unm = function(term)
      return Term(term.var, -term.coefficient)
   end,

   __add = function(a, b)
      if ffi_istype(Var, b) then
         return new_expr_pair(0.0, a.var, b, a.coefficient)
      elseif ffi_istype(Term, b) then
         if type(a) == "number" then
            return new_expr_one(a, b.var, b.coefficient)
         else
            return new_expr_pair(0.0, a.var, b.var, a.coefficient, b.coefficient)
         end
      elseif ffi_istype(Expression, b) then
         return add_expr_term(b, a.var, a.coefficient)
      elseif type(b) == "number" then
         return new_expr_one(b, a.var, a.coefficient)
      end
      error("Invalid term + op")
   end,

   __sub = function(a, b)
      return a + -b
   end,

   __tostring = function(term)
      return tostring(term.coefficient) .. " " .. term.var:name()
   end,
})

do
   ---@param expr kiwi.Expression
   ---@param constant number
   ---@nodiscard
   local function mul_expr_constant(expr, constant)
      local ret = ffi_gc(ffi_new(Expression, expr.term_count), expr_gc) --[[@as kiwi.Expression]]
      for i = 0, expr.term_count - 1 do
         local st = expr.terms_[i] --[[@as kiwi.Term]]
         local dt = ret.terms_[i] --[[@as kiwi.Term]]
         dt.var = ckiwi.kiwi_var_clone(st.var)
         dt.coefficient = st.coefficient * constant
      end
      ret.constant = expr.constant * constant
      ret.term_count = expr.term_count
      return ret
   end

   ---@param a kiwi.Expression
   ---@param b kiwi.Expression
   ---@nodiscard
   local function add_expr_expr(a, b)
      local a_count = a.term_count
      local b_count = b.term_count
      local ret = ffi_gc(ffi_new(Expression, a_count + b_count), expr_gc) --[[@as kiwi.Expression]]

      for i = 0, a_count - 1 do
         local dt = ret.terms_[i] --[[@as kiwi.Term]]
         local st = a.terms_[i] --[[@as kiwi.Term]]
         dt.var = ckiwi.kiwi_var_clone(st.var)
         dt.coefficient = st.coefficient
      end
      for i = 0, b_count - 1 do
         local dt = ret.terms_[a_count + i] --[[@as kiwi.Term]]
         local st = b.terms_[i] --[[@as kiwi.Term]]
         dt.var = ckiwi.kiwi_var_clone(st.var)
         dt.coefficient = st.coefficient
      end
      ret.constant = a.constant + b.constant
      ret.term_count = a_count + b_count
      return ret
   end

   ---@param expr kiwi.Expression
   ---@param constant number
   ---@nodiscard
   local function new_expr_constant(expr, constant)
      local ret = ffi_gc(ffi_new(Expression, expr.term_count), expr_gc) --[[@as kiwi.Expression]]

      for i = 0, expr.term_count - 1 do
         local dt = ret.terms_[i] --[[@as kiwi.Term]]
         local st = expr.terms_[i] --[[@as kiwi.Term]]
         dt.var = ckiwi.kiwi_var_clone(st.var)
         dt.coefficient = st.coefficient
      end
      ret.constant = constant
      ret.term_count = expr.term_count
      return ret
   end

   --- Expressions are a sum of terms with an added constant.
   ---@class kiwi.Expression: ffi.ctype*
   ---@overload fun(terms: kiwi.Term[], constant: number?): kiwi.Expression
   ---@field constant number
   ---@field package term_count number
   ---@field package terms_ ffi.cdata*
   ---@operator mul(number): kiwi.Expression
   ---@operator div(number): kiwi.Expression
   ---@operator unm: kiwi.Expression
   ---@operator add(kiwi.Expression|kiwi.Term|kiwi.Var|number): kiwi.Expression
   ---@operator sub(kiwi.Expression|kiwi.Term|kiwi.Var|number): kiwi.Expression
   local Expression_cls = {
      le = kiwi.le,
      ge = kiwi.ge,
      eq = kiwi.eq,
   }

   ---@return number
   ---@nodiscard
   function Expression_cls:value()
      local sum = self.constant
      for i = 0, self.term_count - 1 do
         sum = sum + self.terms_[i]:value()
      end
      return sum
   end

   ---@return kiwi.Term[]
   ---@nodiscard
   function Expression_cls:terms()
      local terms = new_tab(self.term_count, 0)
      for i = 0, self.term_count - 1 do
         local t = self.terms_[i] --[[@as kiwi.Term]]
         terms[i + 1] = Term(t.var, t.coefficient)
      end
      return terms
   end

   ---@return kiwi.Expression
   ---@nodiscard
   function Expression_cls:copy()
      return new_expr_constant(self, self.constant)
   end

   ffi.metatype(Expression, {
      __index = Expression_cls,

      __new = function(_, terms, constant)
         local e = ffi_gc(ffi_new(Expression, #terms), expr_gc) --[[@as kiwi.Expression]]
         for i, t in ipairs(terms) do
            local dt = e.terms_[i - 1] --[[@as kiwi.Term]]
            dt.var = ckiwi.kiwi_var_clone(t.var)
            dt.coefficient = t.coefficient
         end
         e.constant = constant or 0.0
         e.term_count = #terms
         return e
      end,

      __mul = function(a, b)
         if type(a) == "number" then
            return mul_expr_constant(b, a)
         elseif type(b) == "number" then
            return mul_expr_constant(a, b)
         end
         error("Invalid expr *")
      end,

      __div = function(expr, denom)
         assert(type(denom) == "number", "Invalid expr /")
         return mul_expr_constant(expr, 1.0 / denom)
      end,

      __unm = function(expr)
         return mul_expr_constant(expr, -1.0)
      end,

      __add = function(a, b)
         if ffi_istype(Var, b) then
            return add_expr_term(a, b)
         elseif ffi_istype(Expression, b) then
            if type(a) == "number" then
               return new_expr_constant(b, a + b.constant)
            else
               return add_expr_expr(a, b)
            end
         elseif ffi_istype(Term, b) then
            return add_expr_term(a, b.var, b.coefficient)
         elseif type(b) == "number" then
            return new_expr_constant(a, a.constant + b)
         end
         error("Invalid expr +")
      end,

      __sub = function(a, b)
         return a + -b
      end,

      __tostring = function(expr)
         local tab = new_tab(expr.term_count + 1, 0)
         for i = 0, expr.term_count - 1 do
            tab[i + 1] = tostring(expr.terms_[i])
         end
         tab[expr.term_count + 1] = expr.constant
         return concat(tab, " + ")
      end,
   })
end

--- A constraint is a linear inequality or equality with associated strength.
--- Constraints can be built with arbitrary left and right hand expressions. But
--- ultimately they all have the form `expression [op] 0`.
---@class kiwi.Constraint: ffi.ctype*
---@overload fun(expr: kiwi.Expression, op: kiwi.RelOp?, strength: number?): kiwi.Constraint
local Constraint_cls = {
   --- The strength of the constraint.
   ---@type fun(self: kiwi.Constraint): number
   strength = ckiwi.kiwi_constraint_strength,

   --- The relational operator of the constraint.
   ---@type fun(self: kiwi.Constraint): kiwi.RelOp
   op = ckiwi.kiwi_constraint_op,

   --- Whether the constraint is violated in the current solution.
   ---@type fun(self: kiwi.Constraint): boolean
   violated = ckiwi.kiwi_constraint_violated,
}

--- The reduced expression defining the constraint.
---@return kiwi.Expression
---@nodiscard
function Constraint_cls:expression()
   local SZ = 8
   local expr = ffi_new(Expression, SZ) --[[@as kiwi.Expression]]
   local n = ckiwi.kiwi_constraint_expression(self, expr, SZ)
   if n > SZ then
      expr = ffi_new(Expression, n) --[[@as kiwi.Expression]]
      n = ckiwi.kiwi_constraint_expression(self, expr, n)
   end
   return ffi_gc(expr, expr_gc) --[[@as kiwi.Expression]] ---@diagnostic disable-line: param-type-mismatch
end

--- Create a constraint between a pair of variables with ratio.
--- The constraint is of the form `left [op|==] coeff right + [constant|0.0]`.
---@param left kiwi.Var
---@param coeff number right side term coefficient
---@param right kiwi.Var
---@param constant number? constant (default 0.0)
---@param op kiwi.RelOp? relational operator (default "EQ")
---@param strength number? strength (default REQUIRED)
---@return kiwi.Constraint
---@nodiscard
function kiwi.new_pair_ratio_constraint(left, coeff, right, constant, op, strength)
   assert(ffi_istype(Var, left) and ffi_istype(Var, right))
   return Constraint(new_expr_pair(-(constant or 0.0), right, left, -coeff), op, strength)
end

--- Create a constraint between a pair of variables with ratio.
--- The constraint is of the form `left [op|==] right + [constant|0.0]`.
---@param left kiwi.Var
---@param right kiwi.Var
---@param constant number? constant (default 0.0)
---@param op kiwi.RelOp? relational operator (default "EQ")
---@param strength number? strength (default REQUIRED)
---@return kiwi.Constraint
---@nodiscard
function kiwi.new_pair_constraint(left, right, constant, op, strength)
   assert(ffi_istype(Var, left) and ffi_istype(Var, right))
   return Constraint(new_expr_pair(-(constant or 0.0), right, left, -1.0), op, strength)
end

--- Create a single term constraint
--- The constraint is of the form `var [op|==] [constant|0.0]`.
---@param var kiwi.Var
---@param constant number? constant (default 0.0)
---@param op kiwi.RelOp? relational operator (default "EQ")
---@param strength number? strength (default REQUIRED)
---@return kiwi.Constraint
---@nodiscard
function kiwi.new_single_constraint(var, constant, op, strength)
   assert(ffi_istype(Var, var))
   return Constraint(new_expr_one(-(constant or 0.0), var), op, strength)
end

local Strength = kiwi.Strength
local REQUIRED = Strength.REQUIRED

ffi.metatype(Constraint, {
   __index = Constraint_cls,

   __new = function(_, expr, op, strength)
      return ffi_gc(
         ckiwi.kiwi_constraint_new(expr, op or "EQ", strength or REQUIRED),
         ckiwi.kiwi_constraint_del
      )
   end,

   __tostring = function(self)
      local ops = {
         [0] = "<=",
         ">=",
         "==",
      }
      local strengths = {
         [Strength.REQUIRED] = "required",
         [Strength.STRONG] = "strong",
         [Strength.MEDIUM] = "medium",
         [Strength.WEAK] = "weak",
      }
      local strength = self:strength()
      return strformat(
         "%s %s 0 | %s",
         self:expression(),
         ops[tonumber(self:op())],
         strengths[strength] or tostring(strength)
      )
   end,
})

local Error_mt = {
   __tostring = function(self)
      return strformat("%s: (%s, %s)", self.message, self.solver, self.item)
   end,
}

---@param kind kiwi.ErrKind
---@param message string
---@param solver kiwi.Solver
---@param item any
local function new_error(kind, message, solver, item)
   ---@class kiwi.Error
   ---@field kind kiwi.ErrKind
   ---@field message string
   ---@field solver kiwi.Solver?
   ---@field item any?
   return setmetatable({
      kind = kind,
      message = message,
      solver = solver,
      item = item,
   }, Error_mt)
end

local C = ffi.C

---@class kiwi.KiwiErr: ffi.ctype*
---@field package kind kiwi.ErrKind
---@field package message ffi.cdata*
---@field package must_free boolean
---@overload fun(): kiwi.KiwiErr
local KiwiErr = ffi.typeof("struct KiwiErr") --[[@as kiwi.KiwiErr]]
--
---@param f fun(solver: kiwi.Solver, item: any, ...): kiwi.KiwiErr?
---@param solver kiwi.Solver
---@param item any
local function try_solver(f, solver, item, ...)
   local err = f(solver, item, ...)
   if err ~= nil then
      local kind = err.kind
      local message = err.message ~= nil and ffi_string(err.message) or ""
      if err.must_free then
         C.free(err)
      end
      error(new_error(kind, message, solver, item))
   end
end

---@class kiwi.Solver: ffi.ctype*
---@overload fun(): kiwi.Solver
local Solver_cls = {
   --- Test whether a constraint is in the solver.
   ---@type fun(self: kiwi.Solver, constraint: kiwi.Constraint): boolean
   has_constraint = ckiwi.kiwi_solver_has_constraint,

   --- Test whether an edit variable has been added to the solver.
   ---@type fun(self: kiwi.Solver, var: kiwi.Var): boolean
   has_edit_var = ckiwi.kiwi_solver_has_edit_var,

   --- Update the values of the external solver variables.
   ---@type fun(self: kiwi.Solver)
   update_vars = ckiwi.kiwi_solver_update_vars,

   --- Reset the solver to the empty starting conditions.
   ---
   --- This method resets the internal solver state to the empty starting
   --- condition, as if no constraints or edit variables have been added.
   --- This can be faster than deleting the solver and creating a new one
   --- when the entire system must change, since it can avoid unecessary
   --- heap (de)allocations.
   ---@type fun(self: kiwi.Solver)
   reset = ckiwi.kiwi_solver_reset,

   --- Dump a representation of the solver to stdout.
   ---@type fun(self: kiwi.Solver)
   dump = ckiwi.kiwi_solver_dump,
}

--- Adds a constraint to the solver.
--- Raises
--- KiwiErrDuplicateConstraint: The given constraint has already been added to the solver.
--- KiwiErrUnsatisfiableConstraint: The given constraint is required and cannot be satisfied.
---@param constraint kiwi.Constraint
function Solver_cls:add_constraint(constraint)
   try_solver(ckiwi.kiwi_solver_add_constraint, self, constraint)
end

--- Removes a constraint from the solver.
--- Raises
--- KiwiErrUnknownConstraint: The given constraint has not been added to the solver.
---@param constraint kiwi.Constraint
function Solver_cls:remove_constraint(constraint)
   try_solver(ckiwi.kiwi_solver_remove_constraint, self, constraint)
end

--- Adds an edit variable to the solver.
---
--- This method should be called before the `suggestValue` method is
--- used to supply a suggested value for the given edit variable.
--- Raises
--- KiwiErrDuplicateEditVariable: The given edit variable has already been added to the solver.
--- KiwiErrBadRequiredStrength: The given strength is >= required.
---@param var kiwi.Var the variable to add as an edit variable
---@param strength number the strength of the edit variable (must be less than `Strength.REQUIRED`)
function Solver_cls:add_edit_var(var, strength)
   try_solver(ckiwi.kiwi_solver_add_edit_var, self, var, strength)
end

--- Remove an edit variable from the solver.
--- Raises
--- KiwiErrUnknownEditVariable: The given edit variable has not been added to the solver
---@param var kiwi.Var the edit variable to remove
function Solver_cls:remove_edit_var(var)
   try_solver(ckiwi.kiwi_solver_remove_edit_var, self, var)
end

--- Suggest a value for the given edit variable.
--- This method should be used after an edit variable has been added to the solver in order
--- to suggest the value for that variable. After all suggestions have been made,
--- the `update_vars` methods can be used to update the values of the external solver variables.
--- Raises
--- KiwiErrUnknownEditVariable: The given edit variable has not been added to the solver.
---@param var kiwi.Var the edit variable to suggest a value for
---@param value number the suggested value
function Solver_cls:suggest_value(var, value)
   try_solver(ckiwi.kiwi_solver_suggest_value, self, var, value)
end

--- Dump a representation of the solver to a string.
---@return string
---@nodiscard
function Solver_cls:dumps()
   local cs = ckiwi.kiwi_solver_dumps(self)
   local s = ffi_string(cs)
   C.free(cs)
   return s
end

kiwi.Solver = ffi.metatype("struct KiwiSolver", {
   __index = Solver_cls,
   __new = function(_)
      return ffi_gc(ckiwi.kiwi_solver_new(), ckiwi.kiwi_solver_del)
   end,

   __tostring = function(self)
      return strformat("kiwi.Solver(0x%X)", ffi_cast("intptr_t", ffi_cast("void*", self)))
   end,
}) --[[@as kiwi.Solver]]

return kiwi