---@class vm
local vm        = require 'vm.vm'
local guide     = require 'parser.guide'

---@alias vm.runner.callback fun(src: parser.object, node?: vm.node)

---@class vm.runner
---@field _loc      parser.object
---@field _casts    parser.object[]
---@field _callback vm.runner.callback
---@field _mark     table
---@field _has      table<parser.object, true>
---@field _main     parser.object
local mt = {}
mt.__index = mt
mt._index = 1

---@return parser.object[]
function mt:_getCasts()
    local root = guide.getRoot(self._loc)
    if not root._casts then
        root._casts = {}
        local docs = root.docs
        for _, doc in ipairs(docs) do
            if doc.type == 'doc.cast' and doc.loc then
                root._casts[#root._casts+1] = doc
            end
        end
    end
    return root._casts
end

---@param obj parser.object
function mt:_markHas(obj)
    while true do
        if self._has[obj] then
            return
        end
        self._has[obj] = true
        if obj == self._main then
            return
        end
        obj = obj.parent
    end
end

function mt:_collect()
    local startPos  = self._loc.start
    local finishPos = 0

    for _, ref in ipairs(self._loc.ref) do
        if ref.type == 'getlocal'
        or ref.type == 'setlocal' then
            self:_markHas(ref)
            if ref.finish > finishPos then
                finishPos = ref.finish
            end
        end
    end

    local casts = self:_getCasts()
    for _, cast in ipairs(casts) do
        if  cast.loc[1] == self._loc[1]
        and cast.start > startPos
        and cast.finish < finishPos
        and guide.getLocal(self._loc, self._loc[1], cast.start) == self._loc then
            self._casts[#self._casts+1] = cast
        end
    end
end

---@param pos integer
---@param topNode vm.node
---@return vm.node
function mt:_fastWardCasts(pos, topNode)
    for i = self._index, #self._casts do
        local action = self._casts[i]
        if action.start > pos then
            self._index = i
            return topNode
        end
        topNode = topNode:copy()
        for _, cast in ipairs(action.casts) do
            if     cast.mode == '+' then
                if cast.optional then
                    topNode:addOptional()
                end
                if cast.extends then
                    topNode:merge(vm.compileNode(cast.extends))
                end
            elseif cast.mode == '-' then
                if cast.optional then
                    topNode:removeOptional()
                end
                if cast.extends then
                    topNode:removeNode(vm.compileNode(cast.extends))
                end
            else
                if cast.extends then
                    topNode:clear()
                    topNode:merge(vm.compileNode(cast.extends))
                end
            end
        end
    end
    return topNode
end

---@param action   parser.object
---@param topNode  vm.node
---@param outNode? vm.node
---@return vm.node topNode
---@return vm.node outNode
function mt:_lookIntoChild(action, topNode, outNode)
    if not self._has[action]
    or self._mark[action] then
        return topNode, topNode or outNode
    end
    self._mark[action] = true
    topNode = self:_fastWardCasts(action.start, topNode)
    if     action.type == 'getlocal' then
        if action.node == self._loc then
            self._callback(action, topNode)
            if outNode then
                topNode = topNode:copy():setTruthy()
                outNode = outNode:copy():setFalsy()
            end
        end
    elseif action.type == 'function' then
        self:_lookIntoBlock(action, topNode:copy())
    elseif action.type == 'unary' then
        if not action[1] then
            goto RETURN
        end
        if action.op.type == 'not' then
            outNode = outNode or topNode:copy()
            outNode, topNode = self:_lookIntoChild(action[1], topNode, outNode)
        end
    elseif action.type == 'binary' then
        if not action[1] or not action[2] then
            goto RETURN
        end
        if     action.op.type == 'and' then
            topNode = self:_lookIntoChild(action[1], topNode, topNode:copy())
            topNode = self:_lookIntoChild(action[2], topNode, topNode:copy())
        elseif action.op.type == 'or' then
            outNode = outNode or topNode:copy()
            local topNode1, outNode1 = self:_lookIntoChild(action[1], topNode, outNode)
            local topNode2, outNode2 = self:_lookIntoChild(action[2], outNode1, outNode1:copy())
            topNode = vm.createNode(topNode1, topNode2)
            outNode = outNode2:copy()
        elseif action.op.type == '=='
        or     action.op.type == '~=' then
            local handler, checker
            for i = 1, 2 do
                if guide.isLiteral(action[i]) then
                    checker = action[i]
                    handler = action[3-i] -- Copilot tells me use `3-i` instead of `i%2+1`
                end
            end
            if not handler then
                goto RETURN
            end
            if  handler.type == 'getlocal'
            and handler.node == self._loc then
                -- if x == y then
                topNode = self:_lookIntoChild(handler, topNode, outNode)
                local checkerNode = vm.compileNode(checker)
                if action.op.type == '==' then
                    topNode = checkerNode
                    if outNode then
                        outNode:removeNode(topNode)
                    end
                else
                    topNode:removeNode(checkerNode)
                    if outNode then
                        outNode = checkerNode
                    end
                end
            elseif handler.type == 'call'
            and    checker.type == 'string'
            and    handler.node.special == 'type'
            and    handler.args
            and    handler.args[1]
            and    handler.args[1].type == 'getlocal'
            and    handler.args[1].node == self._loc then
                -- if type(x) == 'string' then
                self:_lookIntoChild(handler, topNode:copy())
                if action.op.type == '==' then
                    topNode:narrow(checker[1])
                    if outNode then
                        outNode:remove(checker[1])
                    end
                else
                    topNode:remove(checker[1])
                    if outNode then
                        outNode:narrow(checker[1])
                    end
                end
            elseif handler.type == 'getlocal'
            and    checker.type == 'string' then
                local nodeValue = vm.getObjectValue(handler.node)
                if  nodeValue
                and nodeValue.type == 'select'
                and nodeValue.sindex == 1 then
                    local call = nodeValue.vararg
                    if  call
                    and call.type == 'call'
                    and call.node.special == 'type'
                    and call.args
                    and call.args[1]
                    and call.args[1].type == 'getlocal'
                    and call.args[1].node == self._loc then
                        -- `local tp = type(x);if tp == 'string' then`
                        if action.op.type == '==' then
                            topNode:narrow(checker[1])
                            if outNode then
                                outNode:remove(checker[1])
                            end
                        else
                            topNode:remove(checker[1])
                            if outNode then
                                outNode:narrow(checker[1])
                            end
                        end
                    end
                end
            end
        end
    elseif action.type == 'loop'
    or     action.type == 'in'
    or     action.type == 'repeat'
    or     action.type == 'for' then
        topNode = self:_lookIntoBlock(action, topNode:copy())
    elseif action.type == 'while' then
        local blockNode, mainNode
        if action.filter then
            blockNode, mainNode = self:_lookIntoChild(action.filter, topNode:copy(), topNode:copy())
        else
            blockNode = topNode:copy()
            mainNode  = topNode:copy()
        end
        blockNode = self:_lookIntoBlock(action, blockNode:copy())
        if mainNode then
            topNode = mainNode:merge(blockNode)
        end
    elseif action.type == 'if' then
        local hasElse
        local mainNode = topNode:copy()
        local blockNodes = {}
        for _, subBlock in ipairs(action) do
            local blockNode = mainNode:copy()
            if subBlock.filter then
                blockNode, mainNode = self:_lookIntoChild(subBlock.filter, blockNode, mainNode)
            else
                hasElse = true
                mainNode:clear()
            end
            blockNode = self:_lookIntoBlock(subBlock, blockNode:copy())
            local neverReturn = subBlock.hasReturn
                            or  subBlock.hasGoTo
                            or  subBlock.hasBreak
                            or  subBlock.hasError
            if not neverReturn then
                blockNodes[#blockNodes+1] = blockNode
            end
        end
        if not hasElse and not topNode:hasKnownType() then
            mainNode:merge(vm.declareGlobal('type', 'unknown'))
        end
        for _, blockNode in ipairs(blockNodes) do
            mainNode:merge(blockNode)
        end
        topNode = mainNode
    elseif action.type == 'call' then
        if action.node.special == 'assert' and action.args and action.args[1] then
            topNode = self:_lookIntoChild(action.args[1], topNode, topNode:copy())
        end
    elseif action.type == 'paren' then
        topNode, outNode = self:_lookIntoChild(action.exp, topNode, outNode)
    elseif action.type == 'setlocal' then
        if action.node == self._loc then
            if action.value then
                self:_lookIntoChild(action.value, topNode)
            end
            topNode = self._callback(action, topNode)
        end
    elseif action.type == 'local' then
        if  action.value
        and action.value.type == 'select' then
            local index = action.value.sindex
            local call  = action.value.vararg
            if  index == 1
            and call.type == 'call'
            and call.node
            and call.node.special == 'type'
            and call.args then
                local getLoc = call.args[1]
                if  getLoc
                and getLoc.type == 'getlocal'
                and getLoc.node == self._loc then
                    for _, ref in ipairs(action.ref) do
                        self:_markHas(ref)
                    end
                end
            end
        end
    end
    ::RETURN::
    guide.eachChild(action, function (src)
        if self._has[src] then
            self:_lookIntoChild(src, topNode)
        end
    end)
    return topNode, outNode or topNode
end

---@param block   parser.object
---@param topNode  vm.node
---@return vm.node topNode
function mt:_lookIntoBlock(block, topNode)
    if not self._has[block] then
        return topNode
    end
    for _, action in ipairs(block) do
        if self._has[action] then
            topNode = self:_lookIntoChild(action, topNode)
        end
    end
    topNode = self:_fastWardCasts(block.finish, topNode)
    return topNode
end

---@param loc parser.object
---@param callback vm.runner.callback
function vm.launchRunner(loc, callback)
    local main = guide.getParentBlock(loc)
    if not main then
        return
    end
    local self = setmetatable({
        _loc      = loc,
        _casts    = {},
        _mark     = {},
        _has      = {},
        _main     = main,
        _callback = callback,
    }, mt)

    self:_collect()

    self:_lookIntoBlock(main, vm.getNode(loc):copy())
end